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Although the neuronal pathways within the hypothalamus critical in controlling feeding and energy expenditure and projecting to brown adipose tissue (BAT) have been identified and their peptidergic content characterized, endogenous action of such peptides in the control of BAT activity has not been elucidated. Here male Sprague Dawley rats received infusions of either melanin-concentrating hormone antagonist (SNAP-7941) (1 microg/microl x h), orexin A receptor antagonist (SB-334867-A; 1 microg/microl x h), combined SB-334867-A (1 microg/microl x h), and SNAP-7941 (1 microg/microl x h), or melanocortin-3/4 receptor antagonist (SHU9119) (1 microg/microl x h) via an indwelling cannula in the lateral ventricle attached to s.c. implanted osmotic minipump. BAT temperature, physical activity, body weight, food intake, and changes in uncoupling protein (UCP)-1 were measured. SB-334867-A and SNAP-7941 significantly increased BAT temperature and UCP1 expression and reduced food intake and body weight. Combined infusion of SB-334867-A and SNAP-7941 produced a pronounced response that was greater than the addition of the individual effects in all parameters measured. SHU9119 significantly decreased BAT temperature and UCP1 expression and increased feeding and body weight. In a second series of experiments, the effect of SB-334867-A and SNAP-7941 alone or combination on the expression of the Fos protein was determined. SB-334867-A and SNAP-7941 increased Fos expression in key hypothalamic and brainstem feeding-related regions. In combination, these antagonists produced a greater than additive elevation of Fos expression in most of the regions evaluated. These findings support a role for endogenous orexigenic and anorexigenic hypothalamic peptides acting in concert to create a thermogenic tone via BAT activity.

Two lamprey glycoprotein hormone receptors (lGpH-R I and II) highly similar with gnathostome GpH-Rs were cloned from sea lamprey testes and thyroid, respectively. Vertebrate glycoprotein protein receptors have a large extracellular domain (ED) containing a leu rich domain (LRD) linked to a rhodopsin-like transmembrane domain (TMD) through a highly divergent linker region (signal specificity domain, SSD or 'hinge' region) and a third major segment, the intracellular domain. To determine the potential roles of the different domains in the activation of the receptor following ligand-receptor binding, functional assays were performed on lGpH-R I/rat luteinizing hormone (LH)-R domain swapped chimeric receptors. These results show that the functional roles of the lamprey glycoprotein-receptor I (lGpH-R I) domains are conserved compared with its Gnathostome homologs. The ability of different glycoprotein hormones to activate chimeric lamprey/rat receptors suggests that the selectivity of the GpH-Rs in respect to their ligands is not controlled exclusively by a single domain but is the result of specific interactions between domains. We hypothesize that these interactions were refined during millions of years of co-evolution of the receptors with their cognate ligands under particular intramolecular, intermolecular and physiological constraints., (© The Author(s) 2010. Published by Oxford University Press.)

Normal hypothalamopituitary development is closely related to that of the forebrain and is dependent upon a complex genetic cascade of transcription factors and signaling molecules that may be either intrinsic or extrinsic to the developing Rathke's pouch. These factors dictate organ commitment, cell differentiation, and cell proliferation within the anterior pituitary. Abnormalities in these processes are associated with congenital hypopituitarism, a spectrum of disorders that includes syndromic disorders such as septo-optic dysplasia, combined pituitary hormone deficiencies, and isolated hormone deficiencies, of which the commonest is GH deficiency. The highly variable clinical phenotypes can now in part be explained due to research performed over the last 20 yr, based mainly on naturally occurring and transgenic animal models. Mutations in genes encoding both signaling molecules and transcription factors have been implicated in the etiology of hypopituitarism, with or without other syndromic features, in mice and humans. To date, mutations in known genes account for a small proportion of cases of hypopituitarism in humans. However, these mutations have led to a greater understanding of the genetic interactions that lead to normal pituitary development. This review attempts to describe the complexity of pituitary development in the rodent, with particular emphasis on those factors that, when mutated, are associated with hypopituitarism in humans.

Pituitary hormones are essential for normal growth and metabolic responsiveness after birth, but their role before birth remains unclear. This study examined the effects of hypophysectomizing fetal sheep on their growth and glucose metabolism during the late normal and extended periods of gestation, and on their metabolic response to maternal fasting for 48 h near term. Fetal hypophysectomy reduced crown rump length (CRL), limb lengths, and body weight but increased ponderal index relative to controls near normal term. It also lowered the daily rate of crown rump length increment uniformly from 35 d before, to 20 d after normal term. Hypophysectomized (HX) fetuses had normal weight-specific rates of umbilical uptake, utilization, and oxidation of glucose but lower rates of umbilical oxygen uptake than controls near term. All these metabolic rates were significantly less in HX fetuses during the extended period of gestation than in HX and intact fetuses near normal term. In contrast to controls, glucogenesis was negligible in HX fetuses during maternal fasting. Consequently, the rate of glucose utilization decreased significantly in fasted HX but not intact fetuses. Conversely, the rate of CO(2) production from glucose carbon decreased in fasted intact but not HX fetuses. Fetal hypophysectomy also prevented the fasting-induced increases in plasma cortisol and norepinephrine concentrations seen in controls. These findings demonstrate that the pituitary hormones are important in regulating the growth rate and adaptive responses of glucose metabolism to undernutrition in fetal sheep. They also suggest that fetal metabolism is altered when gestational length is extended.

Melanin-concentrating hormone (MCH) is a cyclic peptide originally identified as a 17-amino-acid circulating hormone in teleost fish, where it is secreted by the pituitary in response to stress and environmental stimuli. In fish, MCH lightens skin color by stimulating aggregation of melanosomes, pigment-containing granules in melanophores, cells of neuroectodermal origin found in fish scales. Although the peptide structure between fish and mammals is highly conserved, in mammals, MCH has no demonstrable effects on pigmentation; instead, based on a series of pharmacological and genetic experiments, MCH has emerged as a critical hypothalamic regulator of energy homeostasis, having effects on both feeding behavior and energy expenditure.

Because there are sex differences in feeding behavior in rats, we looked for a possible sex difference in the response to glucose of melanin-concentrating hormone (MCH) neurons in the lateral hypothalamic area using phosphorylated cAMP response element-binding protein (pCREB) as a marker of neural activity. Intact male rats and female rats at diestrus 2, proestrus, or estrus were fed normally or fasted for 48 h and injected with saline or glucose (400 mg/kg). Thereafter, preparations were subjected to immunohistochemical processing for the double staining of MCH and pCREB. Fasting increased the ratio of MCH neurons with pCREB (double-stained cells) in both male and female rats. In fasted rats, glucose injection decreased the ratio of double-stained cells more promptly in females than in males. The magnitude of decrease caused by glucose was greater at proestrus and estrus than at diestrus 2. Gonadectomy in males enhanced and in females attenuated the response of MCH neurons to glucose. Testosterone and estrogen replacement in males and females, respectively, restored the response of MCH neurons to glucose. The demonstrated sex differences in the response of MCH neurons to glucose correlated well with the gonadal steroid milieu; thus, MCH neurons may play an important role in sex differences in feeding behavior.

Melanin-concentrating hormone (MCH) receptor 1 (MCH1R) is a class A G protein-coupled receptor. The MCH system has been linked to a variety of physiological functions, including the regulation of feeding and energy metabolism. We recently reported the importance of a dibasic motif in the membrane-proximal C-terminal region for MCH1R function. Here we reveal that an Arg residue in intracellular loop 2 of MCH1R plays a critical role in receptor function. We analyzed the roles of two distinct motifs, BBXXB and BXBB (in which B is a basic residue and X is a nonbasic residue), located in the three intracellular loops of MCH1R. Triple-substitution mutants of intracellular loops 1 and 3 could still activate calcium mobilization, albeit with lower efficacy or potency. However, mutations in intracellular loop 2 led to a complete loss of induction of signal transduction without changing the high affinity constant (Kd) value. By analyzing a series of single-substitution mutants, a point mutation of Arg155 in intracellular loop 2 was found to be responsible for the signaling pathway elicited by MCH. In addition, substitution at positions corresponding to Arg155 in human MCH receptor 2 and rat somatostatin receptor 2 also markedly abolished their ligand-induced signaling capacities, indicating that this Arg is a recognition determinant in several G protein-coupled receptors.

Prohormone convertases (PCs) are thought to represent the major proteinases involved in the biosynthetic processing of peptide hormone precursors to bioactive peptide products. The maturation of PC2 requires the aid of a helper protein, 7B2, in order for the zymogen to become an active enzyme species. The 7B2 and PC2 nulls should thus be functionally equivalent with regard to deficits in precursor processing. In this article, we have examined this proposition through the study of proopiomelanocortin (POMC) biosynthesis and granule content in both null models. RIA data indicate that both PC2 and 7B2 nulls lack pituitary alpha-MSH; interestingly, 7B2 nulls are still able to generate beta-endorphin from beta-lipotropin, whereas PC2 nulls contain little if any beta-endorphin. Labeling experiments demonstrate a build-up of POMC, high molecular weight intermediates, and intact ACTH, as well as the disappearance of alpha-MSH, in both null models. Electron microscopy of neurointermediate lobe melanotrophs reveals the presence of a significantly greater number of secretory granules in both 7B2 and PC2 nulls compared with wild-type controls. However, PC2 null melanotrophs contain twice as many granules as 7B2 null melanotrophs. Another difference between the two null models is a relatively enhanced accumulation of precursors in the PC2 null compared with the 7B2 null; these include not only PC2 substrates, but also presumed PC1 substrates. These data indicate that the two nulls are not phenotypically equivalent.

Short-term cold exposure of homeothermic animals leads to higher thermogenesis and food consumption accompanied by weight loss. An analysis of cDNA-macroarray was employed to identify candidate mRNA species that encode proteins involved in thermogenic adaptation to cold. A cDNA-macroarray analysis, confirmed by RT-PCR, immunoblot, and RIA, revealed that the hypothalamic expression of melanin-concentrating hormone (MCH) is enhanced by exposure of rats to cold environment. The blockade of hypothalamic MCH expression by antisense MCH oligonucleotide in cold-exposed rats promoted no changes in feeding behavior and body temperature. However, MCH blockade led to a significant drop in body weight, which was accompanied by decreased liver glycogen, increased relative body fat, increased absolute and relative interscapular brown adipose tissue mass, increased uncoupling protein 1 expression in brown adipose tissue, and increased consumption of lean body mass. Thus, increased hypothalamic MCH expression in rats exposed to cold may participate in the process that allows for efficient use of energy for heat production during thermogenic adaptation to cold.

Peroxisome proliferator-activated receptor (PPAR) alpha is a nuclear receptor that is mainly expressed in tissues with a high degree of fatty acid oxidation such as liver, heart, and skeletal muscle. Unsaturated fatty acids, their derivatives, and fibrates activate PPARalpha. Male rats are more responsive to fibrates than female rats. We therefore wanted to investigate if there is a sex difference in PPARalpha expression. Male rats had higher levels of hepatic PPARalpha mRNA and protein than female rats. Fasting increased hepatic PPARalpha mRNA levels to a similar degree in both sexes. Gonadectomy of male rats decreased PPARalpha mRNA expression to similar levels as in intact and gonadectomized female rats. Hypophysectomy increased hepatic PPARalpha mRNA and protein levels. The increase in PPARalpha mRNA after hypophysectomy was more pronounced in females than in males. GH treatment decreased PPARalpha mRNA and protein levels, but the sex-differentiated secretory pattern of GH does not determine the sex-differentiated expression of PPARalpha. The expression of PPARalpha mRNA in heart or soleus muscle was not influenced by gender, gonadectomy, hypophysectomy, or GH treatment. In summary, pituitary-dependent hormones specifically regulate hepatic PPARalpha expression. Sex hormones regulate the sex difference in hepatic PPARalpha levels, but not via the sexually dimorphic GH secretory pattern.

We have studied male sexual differentiation of null mutant mice (-/-) for the thyroid-specific enhancer-binding protein (T/ebp or Nkx2.1) gene, a homeodomain transcription factor that plays a role in organogenesis of the thyroid, lung, ventral forebrain, and pituitary gland. Because the T/ebp/Nkx2.1 (-/-) mice do not develop the pituitary gland, their sexual differentiation, if any, must occur in the absence of action of gonadotropins and other pituitary hormones. The (-/-) mice survive only until birth (embryonic d 19-19.5 of pregnancy), and when their external and internal genitals were inspected at embryonic d 18.5, they were indistinguishable from the (+/-) and (+/+) control mice. The testis weights of (-/-) mice were 20% lower than in (+/+) and (+/-) mice. The testosterone content of the (-/-) testes (13.5 +/- 2.4 pg/gonad, mean +/- SEM, n = 11) was dramatically reduced, compared with (+/-) (165 +/- 22.5 pg, n = 14) and (+/+) (234 +/- 37.3 pg, n = 10) littermates. Light microscopy revealed no difference in seminiferous tubules, interstitial tissue, or relative proportions of the two-cell compartments between the (-/-) and (+/+) testes. However, electron microscopy confirmed that Leydig cells in the (-/-) testes were much smaller, with smaller mitochondria and proportion of smooth endoplasmic reticulum than found in the controls, which was in support of the low androgen content of the knockout testes. In conclusion, this study on T/ebp/Nkx2.1 knockout mice, devoid of the pituitary gland, demonstrates that pituitary hormone secretion is not needed for stimulation of sufficient fetal testicular androgen synthesis to induce male sexual differentiation. The endogenous testosterone level in the null mutant testes is 5-10% of the control level, which suggests that there is a considerable safety margin in the amount of testosterone that is needed for the male fetal masculinization.

The hypothalamic neuropeptide melanin-concentrating hormone (MCH) has been implicated in a variety of physiological functions including the regulation of feeding and energy homeostasis. Two MCH receptors (MCHR1 and MCHR2) have been identified so far. To decipher the functional role of the MCH receptors, we have generated and phenotypically characterized mice rendered deficient in MCHR1 expression by homologous recombination. Inactivation of MCHR1 results in mice (MCHR1-/-) that are resistant to diet-induced obesity. With a high-fat diet, body fat mass is significantly lower in both male (4.7 +/- 0.6 g vs. 9.6 +/- 1.2 g) and female (3.9 +/- 0.2 vs. 5.8 +/- 0.5 g) MCHR1-/- mice than that of the wild-type control (P < 0.01), but the lean mass remains constant. When normalized to body weight, female mice are hyperphagic, and male mice are hyperphagic and hypermetabolic, compared with wild-type mice. Consistent with the lower fat mass, both leptin and insulin levels are significantly lower in male MCHR1-/- mice than in the wild-type controls. Our data firmly establish MCHR1 as a mediator of MCH effects on energy homeostasis and suggest that inactivation of MCHR1 alone is capable to counterbalance obesity induced by a high-fat diet.

The prohormone convertase PC2 requires the aid of a helper protein, known as 7B2, for production of active enzyme. Deletion of 7B2 results in a lethal phenotype resembling Cushing's disease. In this study, we have investigated the effect of a single low dose of recombinant adenovirus vector encoding 7B2 and delivered directly to the pituitary of 7B2 nulls on pituitary ACTH, plasma ACTH, corticosterone, alpha MSH and glucose, and survival time. We show that after injection of recombinant adenovirus encoding 27-kDa 7B2 into 7B2 nulls, transgene expression, as measured by RIA for 7B2, exhibits a transient elevation in the pituitary and blood, with a slight but significant elevation of PC2 activity in pituitaries of 7B2 nulls and a drop in the level of circulating ACTH concomitant with a small increase in circulating alpha MSH. The level of circulating blood glucose was increased, and that of corticosterone was decreased. Lastly, slight but significantly prolonged survival times were observed. These data showing partial rescue of 7B2 nulls support the idea that adenoviral administration of 7B2 will represent an effective means to study the role of this interesting neuroendocrine protein on endocrine function in vivo.

The neuroendocrine-specific protein 7B2, which serves as a molecular escort for proPC2 in the secretory pathway, promotes the production of enzymatically active PC2 and may have non-PC2 related endocrine roles. Mice null for 7B2 exhibit a lethal phenotype with a complex Cushing's-like pathology, which develops from intermediate lobe ACTH hypersecretion as a consequences of interruption of PC2-mediated peptide processing as well as undefined consequences of the loss of 7B2. In this study we investigated the endocrine and metabolic alterations of 7B2 null mice from pathological and biochemical points of view. Our results show that 7B2 nulls exhibit a multisystem disorder that includes severe pathoanatomical and histopathologic alterations of vital organs, including the heart and spleen but most notably the liver, in which massive steatosis and necrosis are observed. Metabolic derangements in glucose metabolism result in glycogen and fat deposition in liver under conditions of chronic hypoglycemia. Liver failure is also likely to contribute to abnormalities in blood coagulation and blood chemistry, such as lactic acidosis. A hypoglycemic crisis coupled with respiratory distress and intensive internal thrombosis most likely results in rapid deterioration and death of the 7B2 null.

In addition to hypothalamic and feedback inputs, the secretory cells of the anterior pituitary are influenced by the activity of factors secreted within the gland. The list of putative intrapituitary factors has been expanding steadily over the past decade, although until recently much of the work was limited to descriptions of potential interactions. This took the form of evidence of production within the pituitary of factors already known to influence activity of secretory cells, or further descriptions of actions on pituitary cells by such factors when added exogenously. A new phase of discovery has been entered, with extensive efforts being made to delineate the control of the synthesis and secretion of the pituitary factors within the gland, regulation of the receptors and response mechanisms for the factors in pituitary cells, and measurements of the endogenous actions of the factors through the use of specific immunoneutralization, receptor blockade, tissue from transgenic animals, and other means. Taken together, these findings are producing blueprints of the intrapituitary interactions that influence each of the individual types of secretory cells, leading toward an understanding of the physiological significance of the interactions. The purpose of this article is to review the recent literature on many of the factors acting as intrapituitary signals and to present such finding in the context of the physiology of the secretory cells.

We have demonstrated previously that both rat and human liver microsomes contain a highly specific binding protein for the anabolic steroids stanozolol (ST) and danazol (DA). In this study we solubilized the male rat liver ST-binding protein (STBP) and investigated the following parameters: 1) pharmacological properties, 2) hydrodynamic properties, 3) peptidic composition, 4) the effects of age and hypophysectomy, and 5) inducibility by 17alpha-ethinyl estradiol. We found that STBP is an integral protein bound to the endoplasmic reticulum. 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) provided its optimal solubilization without changes in its pharmacological properties, i.e. high specificity for ST and danazol, between natural steroids and ligands of low affinity glucocorticoid-binding sites or of progesterone-binding sites. Hydrodynamic properties of the STBP showed that it has a molecular mass of at least 118 kDa. SDS-PAGE of covalently labeled STBP under nonreducing conditions showed that [3H]ST binds to a 110-kDa protein. The STBP was resolved under reducing conditions into three peptides of 55, 31, and 22 kDa, respectively. STBP increased from immature to adult rats, and it dramatically decreased after hypophysectomy. Unlike the 22-kDa peptide, both the 55- and 31-kDa peptides drastically decreased in both immature and hypophysectomized rats. 17alpha-Ethinyl estradiol administration to immature or hypophysectomized rats induced the 55- and 31-kDa [3H]STBP to a greater extent than the 22-kDa peptide. Thus, STBP appears as an oligomeric protein composed of hormone-regulated peptides. The availability of solubilized STBP and the fact that it can be induced in vivo represent major steps toward the purification and functional significance of this unique steroid-binding protein.

Melanin-concentrating hormone (MCH) is a cyclic peptide isolated first from salmon brain, then from rat and human hypothalamus. We have recently found expression of MCH messenger RNA and encoded peptides, e.g. MCH and neuropeptide-glutamic acid-isoleucine, within the rat gastrointestinal (GI) tract, but their cellular origin was unclear. Furthermore, similarities in the localization of rat atrial natriuretic factor (ANF) and rat MCH immunoreactivities within intestine suggested functional convergence. In the present study we determined first the presence and distribution of MCH messenger RNA and encoded peptides in the GI tract by combining in situ hybridization and immunohistochemical analysis. Our data revealed numerous MCH-containing cells located in the lamina propria and submucosa at both duodenal and colonic levels. Second, the localisation of MCH- and arginine vasopressin- or ANF-containing cells appears similar at the duodenal and colonic levels, respectively. Colocalization of MCH/neuropeptide-glutamic acid-isoleucine immunoreactivity (-IR) and catecholamine indicated that MCH-expressing cells are probably antigen-presenting cells forming part of the enterochromaffin cell system. Third, we performed reverse phase HPLC coupled to RIA to characterize MCH-like materials in different portions of the rat gut. Crude acidic extracts of rat intestine contained about 2-3 pmol/g tissue of MCH-IR, close to the values found in brain extracts. Reverse phase HPLC of MCH-IR in the GI tract revealed that only 10-30% of the immunoreactivity corresponded to mature MCH, whereas the rat brain contained 94% mature peptide. Finally, we compared the effect of MCH and ANF on water and electrolyte secretions at different levels of the GI tract by using the in situ ligated loop technique. Similar effects were noted for ANF and MCH; both stimulated water, Na, and K fluxes at the proximal colon level and increased Na and K fluxes in the duodenum. However, only ANF increased water and Cl fluxes in the duodenum and decreased bicarbonate secretion in the ileum, whereas MCH increased bicarbonate absorption in the jejunum. The dose required was 10 nmol/100 g.h for MCH, i.e. 10 times more than for the ANF. These studies strongly suggest that MCH produced by antigen-presenting cells of the lamina propria may have an important role, similar to that of ANF at the colonic level, in the physiology of the GI tract.

We had previously shown that homoeostatic thymus hormone (HTH), an H2A-H2B histone dimer, possesses an age-dependent adrenostimulatory activity in vivo. It was therefore of interest to investigate the adrenocorticotropin (ACTH)-releasing activity of histones and other related preparations on perifused pituitary cells from young (2-4 months) and mature (16-18 months) rats. Histones and protamines gave a positive interference with the immunoradiometric assays (IRMA) for ACTH and corticotropin releasing hormone (CRH) whereas the histone fragment MB35, as well as nucleohistone and nucleoprotamine complexes did not. The latter three substances induced a significant ACTH response in pituitary cells from young and, to a lesser extent, mature rats. Our results suggest that nucleoprotein complexes released into the extracellular milieu may act as hypophysiotropic signals. On the other hand, the responsiveness of pituitary cells to these signals seems to decrease with the age of the donor.

Experiments were conducted to determine whether continuous pituitary hormone support is required for expression of the LH and beta-adrenergic cAMP signal transduction pathways in rabbit CL during pseudopregnancy. Parameters of the LH and catecholamine cAMP signal transduction pathways in CL of estrogen-treated hypophysectomized rabbits were compared to those of pituitary-intact rabbits. Results showed that each of the parameters of the LH and beta-adrenergic cAMP signal transduction pathways was retained in CL taken from estrogen-treated pseudopregnant rabbits that had been hypophysectomized for as long as 13 days at levels not significantly different from those of estrogen-treated pituitary-intact rabbits. These included luteal basal, and LH-, epinephrine-, and fluoride-stimulated adenylyl cyclase activities; total luteal cAMP levels; the number and affinity of cAMP-dependent protein kinase regulatory subunit cAMP binding sites; binding activity of the type I and type II regulatory subunits; and the amount of catalytic subunit protein of cAMP-dependent protein kinase. We conclude that expression of the proteins of the cAMP signal pathway for LH and beta-adrenergic hormones in CL of estrogen-treated rabbits does not require pituitary hormone support.

Thirty-nine women were studied longitudinally for 3 yr, during which period 10 women passed a natural menopause. Vitamin D metabolites were determined every 3 months in these 10 women. The same variables were studied in 42 premenopausal women with endometriosis treated for 6 months with nafarelin acetate (a LHRH agonist) given alone in a dose of 200 or 400 micrograms or in a dose of 400 micrograms combined with 1.2 mg norethisterone (NET)/day and followed-up for a further 6 months. No changes were seen in 1,25-dihydroxyvitamin D [1,25-(OH)2D], vitamin D-binding protein, or the free index of 1,25-(OH)2D during the natural menopause. A small increase was found in 25-hydroxyvitamin D [25OHD] and 24,25-(OH)2D3 after correction for seasonal variation. All three nafarelin groups had a significantly decreased free index of 1,25-(OH)2D, which returned to the baseline value on withdrawal of the treatment. Serum 25OHD and 24,25-(OH)2D3 were increased at 6 months and thereafter decreased to baseline values. These changes were still visible after correction for seasonal variation. Vitamin D-binding protein showed a small transient increase in the nafarelin plus NET group, but was unchanged in the other two groups. The 24-h urinary excretion of calcium increased significantly in the groups receiving nafarelin alone, whereas it remained unchanged in the nafarelin plus NET group. We conclude that detectable changes in 1,25-(OH)2D do not occur in natural menopause. Treatment with LHRH agonists produces a significant decrease in serum 1,25-(OH)2D, which does not seem to be dependent on increased bone resorption. This suggests that LHRH agonists may induce a change in other pituitary hormones involved in vitamin D regulation.

A study was conducted with hypophysectomized hamsters to determine effects of administration of prolactin (PRL), luteinizing hormone (LH), and follicle-stimulating hormone (FSH)-alone or in combination-on testicular PRL receptors and in vitro testosterone production. Hormonal injections commenced the second day after hypophysectomy, and hamsters were killed on Day 5, approximately 13 h after the last hormonal injection. PRL receptor numbers were reduced by hypophysectomy, and PRL administration alone lessened the extent of this decrease. By themselves, neither LH nor FSH affected PRL receptors, but a combination of PRL + FSH + LH produced the greatest effect on these receptors. Receptor affinity was only modestly affected by any treatments. In vitro testosterone synthesis was measured after addition of 0, 2, 10, and 50 mIU of human chorionic gonadotropin (hCG) to incubations of testicular tissue. Neither PRL nor FSH by themselves in vivo affected basal or hCG-stimulated testosterone production. However, PRL + FSH increased (p less than 0.05) the magnitude of the in vitro testosterone response to hCG, as well as the sensitivity of that response (slope of the dose-response curve). LH alone increased both basal and hCG-stimulated testosterone production. PRL + LH provided no additional increase in the magnitude of the testosterone response, but increased (p less than 0.05) the sensitivity. PRL + FSH + LH in vivo provided for the greatest sensitivity of the testosterone response to hCG.(ABSTRACT TRUNCATED AT 250 WORDS)

Mammary carcinomas were found at autopsy 98--100 days after irradiation in 12 of 14 (86%) multiparous Fischer female rats which had been adrenalectomized and given grafts of secretory pituitary tumor strain MtT-F4 soon after exposure to gamma-rays or fission neutrons. A single carcinoma was found in 1 of 10 unirradiated, MtT-bearing, adrenalectomized animals. When adrenalectomy was not done, no tumors were found in 8 unirradiated or in 13 irradiated MtT-bearing rats rats. In view of the well-established finding that Cortisol is essential for milk production, we suggested as a working hypothesis that, in the presence of high titers of mammotropic hormone and adrenal corticoids, differentiation of a given cell for milk secretion reduced that cell's proliferative potential. When such differentiation was precluded by adrenocorticoid deficiency, more irradiation-altered mammary epithelial cells retained their high proliferative potential and contributed to carcinoma formation.

Although there are interspecies of variations in the process of follicular development, a generalized summary is presented that encompasses theories of follicular maturation from laboratory and domestic animals, nonhuman primates, and women. As there are many new substances whose actions within the follicle are unknown, it is difficult to ascribe definitive roles to these proteins in follicular development and ovulation. However, where possible, these substances are included in the summary. During early follicular development, FSH binds to granulosa cells of primary follicles to stimulate production of estradiol by the induction or enhancement of aromatase synthetase (37, 336, 337). Estradiol, in turn, induces proliferation of granulosa cells (338-344) and increases the sensitivity of the follicle to further gonadotropin stimulation (12, 339, 345-349). Estradiol can synergize with gonadotropins to increase ovarian weight, enhance proliferation of granulosa cells, and promote growth of preantral follicles and antrum formation (345, 347, 350-352). In addition, estradiol enhanced the responsiveness of granulosa cells to FSH and LH by increasing synthesis of progesterone (353, 354). The generalized enhancement of gonadotropin action by estradiol is partially mediated by FSH-induced accumulation of cAMP. However, as synthesis of estradiol increases, this steroid directly stimulated follicular growth, since estrogens have long been known to stimulate growth of ovarian cells and exert a direct antiatretic effect (355, 356). However, the exact mechanism involved in follicular growth achieving preovulatory status rather than undergoing atresia remains uncertain. Estradiol not only enhances gonadotropin stimulation of LH and FSH receptors in granulosa cells (357, 348) but is required for FSH induction of FSH receptors (359, 360). Estradiol alone can increase numbers of its own receptor in granulosa cells (350) as well as increase its own production by stimulating aromatase activity (361). Estradiol secreted by the dominant follicle has a positive feedback effect on the hypothalamus and pituitary, enhancing gonadotropin secretion and ensuring the preovulatory gonadotropin surges (362). The increased gonadotropins can further increase the production of estradiol which, in turn, enhances its own production. Therefore, estradiol is included in two positive feedback loops (one at the pituitary and one at the ovary) to maintain the dominant follicle and ensure ovulation. Progesterone and androgens also have intrafollicular effects on follicular growth and steroidogenesis.(ABSTRACT TRUNCATED AT 400 WORDS)

In recent years a variety of peptide hormones have been isolated from the mammalian hypothalamus and pituitary. Several hypothalamic hormones, including thyroliberin (thyrotropin-releasing factory), luliberin (luteinizing hormone-releasing factor), and somatostatin (somatotropin release-inhibiting factor), have been characterized and synthesized. The subsequent development of radioimmunoassays for these hormones has made possible the study of their physiology. The measurement of prolactin in serum and the release of pituitary hormones after the administration of the hypothalamic hormones has proved to be useful in clinical diagnosis. The use of hypothalamic hormones in treating various clinical disorders and the isolation and characterization of new releasing and inhibiting hormones in the hypothalamus are actively being investigated.

Ovarian development was studied in control and decapitated pig fetuses. Fetuses were decapitated at 42 days postcoitum. At 51, 61, 74, 90 and 112 days postcoitum decapitated and control females were collected. Ovarian weight gradually increased during development in control animals. Deprivation of pituitary hormones as a result of fetal decapitation did not cause a decline in ovarian weight increase. Germ cell maturation in control and decapitated fetuses proceeded in a similar fashion, with secondary follicles being the most advanced stage. Enzyme histochemical activity was present in the primary interstitial gland cells and in granulosa cells and was similar in normal and decapitated fetuses. Both NADH diaphorase activity and 3 beta-hydroxysteroid dehydrogenase activity increased from 51 to 74 days and remained relatively constant thereafter. Since fetal decapitation in the pig hardly influences ovarian development, pituitary dependency of the fetal ovary in the pig is unlikely.

Swiss Webster mice were hypophysectomized on Day 10 of pregnancy and the effect of the ablation on mammary gland development was estimated by measuring the total weight and the DNA, RNA, and alpha-lactalbumin contents and concentrations of the mammary gland on Days 14 and 18 of gestation. Although a significant increase in mammary gland weight occurred in the hypophysectomized animals between Days 10 and 18 of pregnancy, the mammary gland weight of the hypophysectomized mice was significantly reduced when compared with intact and sham-operated mice on both Days 14 and 18 of pregnancy. The total RNA content of the mammary gland was also reduced in the hypophysectomized mice, although it increased significantly from Day 10 to Day 18. The alpha-lactalbumin content of the mammary gland increased only slightly between Days 10 and 14 of gestation in the intact and sham-operated mice, but a large increase was found on Day 18 in both groups. There was, on the other hand, no increment in the alpha-lactalbumin content of the mammary gland in the hypophysectomized mice either on Day 14 or 18 of gestation. The DNA content of the mammary gland was not affected by hypophysectomy when estimated on Days 14 and 18 of pregnancy. The effects of hypophysectomy on the concentrations of mouse placental lactogen II (mPL-II), progesterone, corticosterone, and thyroxine in the maternal serum were also assessed. The concentration of mPL-II was significantly elevated in the hypophysectomized mice, whereas the circulating concentrations of both corticosterone and thyroxine were greatly reduced. The serum progesterone concentration was not significantly altered by hypophysectomy. (ABSTRACT TRUNCATED AT 250 WORDS)

The regulation of the activity of the renal enzyme ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) was examined in the rat. In the intact animal adapted to a light/dark cycle of 14 hours and 10 hours, respectively, the level of renal ornithine decarboxylase activity was rhythmical and paralleled the diurnal rhythm in plasma corticosteroid concentration. Renal ornithine decarboxylase activity and plasma corticosterone were highest during the early hours of darkness and lowest during the hours of light. Following hypophysectomy, the level of renal ornithine decarboxylase activity declined rapidly and remained low and without a demonstrable diurnal rhythm. When pituitary hormone levels were temporarily restored in the hypophysectomized rat by the injection of pituitary extract, renal ornithine decarboxylase activity increased rapidly, reached a peak within 8 hours, and returned toward pre-injection levels by 12 hours. Exogenous growth hormone, ACTH and cortisol each increased renal ornithine decarboxylase activity in the hypophysectomized rat, with the highest levels of activity being achieved with growth hormone. Other pituitary hormones (FSH, LH, TSH and prolactin) were ineffective. After bilateral adrenalectomy, renal ornithine decarboxylase activity retained a rhythmical pattern similar to that observed in the intact rat, but the levels were increased. Growth hormone and cortisol increased renal ornitine decarboxylase activity in the adrenalectomized-hypophysectomized animal to the same extent as in the hypophysectomized animal, but ACTH was almost totally ineffective. These data suggest that the pituitary plays a major role in the regulation of renal ornithine decarboxylase activity in the rat, primarily through the rhythmical secretion of growth hormone and ACTH.

To evaluate the role of the opiate-like peptidergic pathways in modulating the pituitary hormone response to stress, we measured the GH, PRL, and cortisol responses to hypoglycemia and exercise in normal subjects with and without pretreatment with naloxone, given in the centrally active dose of 0.4 mg iv. Basal serum levels of GH, PRL, and cortisol were not changed significantly by prior naloxone administration. The maximum incremental response of GH to exercise was significantly blunted (13.1 +/- 1.6 vs. 6.0 +/- 1.4; P less than 0.001) by prior naloxone administration. Pretreatment with naloxone did not affect the responses of GH, PRL, or cortisol to hypoglycemia or the PRL response to L-dopa. On the basis of these studies we conclude that the opiate-like peptidergic pathways are not important in the regulation of basal levels of GH, PRL, and cortisol and have only a modest modulating influence on the stress-induced release of the hormones, which may be obscured in the face of severe stress.