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Recent studies on mice with null mutation of the angiotensin type 2 receptor (AT(2)R) gene have implicated the involvement of AT(2)R in regulating adipocyte size and obesity, a major risk factor for metabolic syndrome. However, the outcome from these studies remains inconclusive. Therefore, current study was designed to test whether pharmacological activation of AT(2)R regulates adiposity and lipid metabolism. Male mice (5-weeks old) were pre-treated with vehicle or AT(2)R agonist (C21, 0.3 mg/kg, i.p., daily, for 4 days) and fed normal diet (ND). Then these animals were subdivided into ND and high-fat diet (HFD) regimen and concomitantly treated with vehicle or C21 through day 14. Vehicle-treated HFD-fed mice demonstrated an increase in epididymal white adipose tissue (eWAT) weight and adipocyte size, which were associated with increased eWAT expression of the lipogenic regulators, fatty acid binding protein and fatty acid synthase, decreased expression of adipose triglyceride lipase and increased expression of hormone-sensitive lipase. Interestingly, C21 pre-treatment altered HFD-induced changes in lipogenic and lipolytic regulators. C21 pre-treatment prevented decrease in expression of uncoupler protein-1 in brown adipose in HFD-fed mice, which was associated with increased core temperature. In addition, C21 pre-treatment ameliorated plasma free fatty acids, triglycerides, insulin and tumor necrosis factor-α in HFD fed mice. Ex-vivo study in isolated primary epididymal adipocytes revealed that C21 inhibits long chain fatty acid transporter, via a nitric oxide synthase/guanylate cyclase/protein kinase G-dependent pathway. Collectively, we propose pharmacological activation of AT(2)R regulates fatty acid metabolism and thermogenesis and prevents HFD-induced adiposity in mice.

Kdm3b is a JmjC domain-containing histone H3 (H3) demethylase and its physiological functions are largely unknown. In this study, we found that Kdm3b protein is highly expressed in multiple cell types in the mouse testes, including Leydig cells, Sertoli cells, spermatogonia and spermatocytes at different differentiation stages. We also observed Kdm3b protein in the epithelial cells of the caput epididymis, prostate and seminal vesicle. Breeding tests revealed that the number of pups produced by the breeding pairs with Kdm3b knockout (Kdm3bKO) males and wild type (WT) females was reduced 68% because of the decreased number of litters when compared with the breeding pairs with WT males and females. Further analysis demonstrated that Kdm3bKO male mice produced 44% fewer number of mature sperm in their cauda epididymides, displaying significantly reduced sperm motility. No significant differences in the circulating concentration of testosterone and the expression levels of androgen receptor and its representative target genes in the testis were observed. However, the circulating levels of 17β-estradiol, a modulator of sperm maturation and male sexual behaviors, was markedly reduced in Kdm3bKO male mice. Strikingly, abrogation of Kdm3b in male mice significantly increased the latencies to mount, intromit and ejaculate and decreased the number of mounts and intromissions, largely due to their loss of interest in female odors. These findings indicate that Kdm3b is required for normal spermatogenesis and sexual behaviors in male mice.

Steroid receptor coactivators (SRCs) are important transcriptional modulators that regulate nuclear receptor and transcription factor activity to adjust transcriptional output to cellular demands. Highlighting their pleiotropic effects, dysfunction of the SRCs has been found in numerous pathologies including cancer, inflammation, and metabolic disorders. The SRC family is expressed strongly in the brain including the hippocampus, cortex, and hypothalamus. Studies focusing on the effect of SRC loss using congenic SRC knockout mice (SRC(-/-)) are limited in number, yet strongly indicate that the SRCs play important roles in regulating reproductive behavior, development, and motor coordination. To better understand the unique functions of the SRCs, we performed a neurobehavioral test battery focusing on anxiety and exploratory behaviors, motor coordination, sensorimotor gating, and nociception in both male and female null mice and compared them with their wild-type (WT) littermates. Results from the test battery reveal a role for SRC1 in motor coordination. Additionally, we found that SRC1 regulates anxiety responses in SRC1(-/-) male and female mice, and nociception sensitivity in SRC1(-/-) male but not female mice. By comparison, SRC2 regulates anxiety response with SRC2(-/-) females showing decreased anxiety in novel environments, as well as increased exploratory behavior in the open field compared with WT littermates. Additionally, SRC2(-/-) males were shown to have deficits in sensorimotor gating. Loss of SRC3 also shows sex differences in anxiety and exploratory behaviors. In particular, SRC3(-/-) female mice have increased anxiety and reduced exploratory activity and impairments in prepulse inhibition, whereas SRC3(-/-) male mice show no significant behavioral differences. In both genders, ablation of SRC3 decreases nocifensive behaviors. Collectively, these resource data suggest that loss of the SRCs results in behavioral phenotypes, underscoring the importance of understanding both the general and gender-based activity of SRCs in the brain.

Steroid hormone receptors are hormone-activated transcription factors. Their activities are regulated by site specific phosphorylation. Conversely, steroids and their receptors act at many levels to regulate cell signaling and their target transcription factors in many tissues, including brain. Thus, the actions of steroids and other cellular regulators are intricately intertwined.

The hypothalamo–pituitary–adrenal (HPA) axis responds to stress by redirecting the physiology and behavior of an organism toward survival and maintenance of homeostasis using a coordinated and well-orchestrated activation of the neuroendocrine and autonomic nervous systems. A plethora of studies have demonstrated the existence of sex differences in the components of the HPA axis and its response to stress, with the females reacting more rapidly and robustly compared with males. Gonadal steroid hormones mediate these sex differences, not only by organizing the HPA axis during development, but also by modulating HPA function in adulthood, with estrogens enhancing and androgens inhibiting HPA axis activity. Part of this involves interactions with circulating glucocorticoids, which exert negative feedback actions on HPA function. Cellular and molecular evidence indicates that androgens, estrogens, and glucocorticoids can interact to affect stress responses through intracellular, membrane-associated, or extranuclear receptors in the central nervous system.

Integration of multiple hormonal and neuronal signaling pathways in the medial preoptic area (mPOA) is required for elicitation of male sexual behavior in most vertebrates. Perturbation of nitric oxide synthase (NOS) activity in the mPOA causes significant defects in male sexual behavior. Although activins and their signaling components are highly expressed throughout the brain, including the mPOA, their functional significance in the central nervous system (CNS) is unknown. Here, we demonstrate a neurophysiologic role for activin signaling in male reproductive behavior. Adult activin receptor type II null (Acvr2 � /� ) male mice display multiple reproductive behavioral deficits, including delayed initiation of copulation, reduced mount, and intromission frequencies, and increased mount, intromission, and ejaculation latencies. These behavioral defects in the adult mice are independent of gonadotropin-releasing hormone (GnRH) homeostasis or mating-induced changes in luteinizing hormone (LH) and testosterone levels. The impairment in behavior can be correlated to the nitric oxide content in the CNS because Acvr2 � /� males have decreased NOS activity in the mPOA but not the rest of the hypothalamus or cortex. Olfactory acuity tests confirmed that Acvr2 � /� mice have no defects in general odor or pheromone recognition. In addition, motor functions are not impaired and the mutants demonstrate normal neuromuscular coordination and balance. Furthermore, the penile histology in mutant mice appears normal, with no significant differences in the expression of penile differentiation marker genes compared with controls, suggesting the observed behavioral phenotypes are not due to structural defects in the penis. Our studies identify a previously unrecognized role of activin signaling in male sexual behavior and suggest that activins and/or related family members are upstream regulators of NOS activity within the mPOA of the forebrain.

Ovarian steroids, estrogen and progesterone, influence the sensitivity of certain neural processes to cannabinoid treatment by modulation of brain dopaminergic activity. We examined the effects of the active ingredient of cannabis, Delta(9)-tetrahydrocannabinol (THC), on sexual behavior in female rats and its influence on steroid hormone receptors and neurotransmitters in the facilitation of sexual receptivity. Our results revealed that the facilitatory effect of THC was inhibited by antagonists to both progesterone and dopamine D(1) receptors. To test further the idea that progesterone receptors (PR) and/or dopamine receptors (D(1)R) in the hypothalamus are required for THC-facilitated sexual behavior in rodents, antisense and sense oligonucleotides to PR and D(1)R were administered intracerebroventricularly (ICV) into the third cerebral ventricle of ovariectomized, estradiol benzoate-primed rats. Progesterone- and THC-facilitated sexual behavior was inhibited in animals treated with antisense oligonucleotides to PR or to D(1)R. Antagonists to cannabinoid receptor-1 subtype (CB(1)), but not to cannabinoid receptor-2 subtype (CB(2)) inhibited progesterone- and dopamine-facilitated sexual receptivity in female rats. Our studies indicate that THC acts on the CB(1) cannabinoid receptor to initiate a signal transduction response that requires both membrane dopamine and intracellular progesterone receptors for effective induction of sexual behavior.

Mucin-1 (Muc1), an integral membrane mucin, is expressed on the apical surface of uterine epithelial cells (UE) of various species. Loss of Muc1 is believed to be necessary for embryo attachment. Muc1 expression is markedly reduced in luminal epithelia during the receptive phase in mice, baboons, and pigs. In the present study, we examined Muc1 expression during the rat estrous cycle and at Day 5 of pregnancy, the time of embryo attachment. In contrast to findings in the mouse, indirect immunofluorescence revealed that uterine Muc1 protein expression was unaltered during the estrous cycle. However, similar to what is observed in the mouse and other species, Muc1 protein decreased at Day 5 of pregnancy in luminal UE. The decrease in Muc1 expression was specific to luminal UE and did not occur in glandular UE. A partial cDNA corresponding to the cytoplasmic tail region of rat Muc1 was generated by a reverse transcription-polymerase chain reaction (RT-PCR) strategy. This cDNA sequence is 89% and 91% identical to the corresponding region of mouse Muc1 at the nucleotide and amino acid levels, respectively. The predicted sequence of rat Muc1 protein has 70-90% identity to the Muc1 protein sequence obtained in other species. Semiquantitative RT-PCR experiments indicated that the mRNA encoding rat Muc1 decreased 57% at Day 5 as compared with the levels found at estrus. This value included mRNA from both luminal and glandular UE and so may underestimate the relative decrease in mRNA in the luminal compartment. In conclusion, we have determined that the levels of rat Muc1 protein and mRNA decrease in the luminal UE at the time of implantation, a pattern similar to that seen in the mouse, baboon, and pig. This supports the general theory that reduction of Muc1 expression is necessary for embryo implantation.

Hormonal induction of sexual receptivity in ovariectomized female mice can be effectively reinstated by sequential administration of estradiol and progesterone. In this regard, mice appear to be similar to other rodents. While it is generally accepted that hypothalamic progesterone receptors function as estradiol-induced transcription factors in the induction of sexual receptivity in rats, hamsters, and guinea pigs, relatively little is known about their role in the mouse, a species which exhibits genotypic and strain differences in the responsiveness to steroid hormones. Using a transgenic mouse carrying a null mutation for the progesterone receptor by gene targeting, we examined the role of the progesterone receptor as a coordinator of key regulatory events in the induction of sexual receptivity. A concordance between hypothalamic progesterone receptor levels and behavioral responsiveness was established by comparing the homozygous mutant, heterozygous mutant, and wild-type littermates. The behavioral and biochemical findings reveal the importance of estradiol-induced progesterone receptors for the expression of sexual behavior in female mice. The behavioral response of the two parental mouse strains from which the recombinant genotype was generated was also examined. As an extension of our earlier studies on the ligand-independent activation of progesterone receptors by neurotransmitters, the behavioral effect of dopamine in the facilitation of sexual receptivity in mice was also examined. The studies provide further evidence that steroid hormone receptors function as general transcription factors to achieve the integration of neural information in the central nervous system, and they assign a more important role for progesterone receptors than hitherto envisioned.

Although progesterone has been recognized as essential for the establishment and maintenance of pregnancy, this steroid hormone has been recently implicated to have a functional role in a number of other reproductive events. The physiological effects of progesterone are mediated by the progesterone receptor (PR), a member of the nuclear receptor superfamily of transcription factors. In most cases the PR is induced by estrogen, implying that many of the in vivo effects attributed to progesterone could also be the result of concomitantly administered estrogen. Therefore, to clearly define those physiological events that are specifically attributable to progesterone in vivo, we have generated a mouse model carrying a null mutation of the PR gene using embryonic stem cell/gene targeting techniques. Male and female embryos homozygous for the PR mutation developed normally to adulthood. However, the adult female PR mutant displayed significant defects in all reproductive tissues. These included an inability to ovulate, uterine hyperplasia and inflammation, severely limited mammary gland development, and an inability to exhibit sexual behavior. Collectively, these results provide direct support for progesterone's role as a pleiotropic coordinator of diverse reproductive events that together ensure species survival.

Although several studies have reported the localization of membrane progesterone (P(4)) receptors (mPR) in various tissues, few have attempted to describe the distribution and regulation of these receptors in the brain. In the present study, we investigated expression of two mPR subtypes, mPRα and mPRβ, within regions of the brain, known to express estradiol (E(2))-dependent [preoptic area (POA) and hypothalamus] and independent (cortex) classical progestin receptors. Saturation binding and Scatchard analyses on plasma membranes prepared from rat cortex, hypothalamus, and POA demonstrated high-affinity, specific P(4)-binding sites characteristic of mPR. Using quantitative RT-PCR, we found that mPRβ mRNA was expressed at higher levels than mPRα, indicating that mPRβ may be the primary mPR subtype in the rat brain. We also mapped the distribution of mPRβ protein using immunohistochemistry. The mPRβ-immunoreactive neurons were highly expressed in select nuclei of the hypothalamus (paraventricular nucleus, ventromedial hypothalamus, and arcuate nucleus), forebrain (medial septum and horizontal diagonal band), and midbrain (oculomotor and red nuclei) and throughout many areas of the cortex and thalamus. Treatment of ovariectomized female rats with E(2) benzoate increased mPRβ immunoreactivity within the medial septum but not the medial POA, horizontal diagonal band, or oculomotor nucleus. Together, these findings demonstrate a wide distribution of mPRβ in the rodent brain that may contribute to functions affecting behavioral, endocrine, motor, and sensory systems. Furthermore, E(2) regulation of mPRβ indicates a mechanism through which estrogens can regulate P(4) function within discrete brain regions to potentially impact behavior.

The effects of in vivo hormonal sensitization on the competence of uterine stromal (US) cells to decidualize in vitro were assessed. In vitro differentiation of uterine stroma isolated from Day 4 pregnant rats, sensitized to respond to a decidual stimulus, was compared to that in nonsensitized immature, castrated or cycling rats. The initiation of in vitro decidualization--as monitored by the expression of the decidual markers desmin and laminin in rat US cells--was independent of the hormonal status of the animal from which the cells were isolated and occurred in the absence of serum in the medium. Differentiation was accelerated in high-density cultures where contact inhibition suppressed proliferation and decreased the extent of cell growth. The extent to which in vitro decidualization imitates in vivo stromal cell differentiation was assessed by comparing decidualization in the rabbit, a species with only a limited decidual cell response, and in the rat. US cells isolated from nonpregnant rabbits differentiated in vitro by expressing laminin, but not desmin. Indirect immunofluorescence of frozen uterine sections from pregnant and nonpregnant rabbits validated in vitro differentiation as a faithful reflection of the in vivo program of decidualization. Although the program of US cell differentiation may vary between the species, initiation of differentiation in vitro appeared to be independent of hormonal preparation in vivo for both the species examined.

Characterization of glycoconjugates synthesized by polarized immature rabbit uterine epithelial (UE) cells in vitro, their vectorial patterns of secretion, and regulation by ovarian steroid hormones are reported. Large (mol wt, greater than 230 kDa) sialomucoglycoproteins and hyaluronate were primarily (86-96%) secreted from the apical cell surface domain, while heparan sulfate proteoglycans were predominantly secreted from the basal cell surface of the polarized UE cells. The polarized UE cells responded to estrogen and progesterone in vitro and exhibited distinct profiles in their synthesis and secretion of different glycoconjugates. Progesterone and/or estrogen reduced the secretion of the mucosialoglycoproteins; however, progesterone caused a 4- to 5-fold accumulation of mucosialoglycoproteins in the cell-associated fraction, suggesting regulation by the hormone at the level of secretion, rather than synthesis. Estrogen and progesterone both stimulated the synthesis and secretion of hyaluronate by the polarized UE cells. Neither hormone substantially altered the synthesis or secretory pattern of heparan sulfate proteoglycans. Collectively, these studies provide the first comprehensive characterization of the major glycoconjugates synthesized and secreted by rabbit UE cells. Furthermore, these observations demonstrate marked differential direct influences of steroid hormones on the production of distinct classes of UE cell glycoconjugates.

Integration of multiple hormonal and neuronal signaling pathways in the medial preoptic area (mPOA) is required for elicitation of male sexual behavior in most vertebrates. Perturbation of nitric oxide synthase (NOS) activity in the mPOA causes significant defects in male sexual behavior. Although activins and their signaling components are highly expressed throughout the brain, including the mPOA, their functional significance in the central nervous system (CNS) is unknown. Here, we demonstrate a neurophysiologic role for activin signaling in male reproductive behavior. Adult activin receptor type II null (Acvr2-/-) male mice display multiple reproductive behavioral deficits, including delayed initiation of copulation, reduced mount, and intromission frequencies, and increased mount, intromission, and ejaculation latencies. These behavioral defects in the adult mice are independent of gonadotropin-releasing hormone (GnRH) homeostasis or mating-induced changes in luteinizing hormone (LH) and testosterone levels. The impairment in behavior can be correlated to the nitric oxide content in the CNS because Acvr2-/- males have decreased NOS activity in the mPOA but not the rest of the hypothalamus or cortex. Olfactory acuity tests confirmed that Acvr2-/- mice have no defects in general odor or pheromone recognition. In addition, motor functions are not impaired and the mutants demonstrate normal neuromuscular coordination and balance. Furthermore, the penile histology in mutant mice appears normal, with no significant differences in the expression of penile differentiation marker genes compared with controls, suggesting the observed behavioral phenotypes are not due to structural defects in the penis. Our studies identify a previously unrecognized role of activin signaling in male sexual behavior and suggest that activins and/or related family members are upstream regulators of NOS activity within the mPOA of the forebrain.

DARPP-32, a dopamine- and adenosine 3′,5′-monophosphate (cAMP)–regulated phosphoprotein (32 kilodaltons in size), is an obligate intermediate in progesterone (P)–facilitated sexual receptivity in female rats and mice. The facilitative effect of P on sexual receptivity in female rats was blocked by antisense oligonucleotides to DARPP-32. Homozygous mice carrying a null mutation for the DARPP-32 gene exhibited minimal levels of P-facilitated sexual receptivity when compared to their wild-type littermates. P significantly increased hypothalamic cAMP levels and cAMP-dependent protein kinase activity. These increases were not inhibited by a D 1 subclass dopamine receptor antagonist. P also enhanced phosphorylation of DARPP-32 on threonine 34 in the hypothalamus of mice. DARPP-32 activation is thus an obligatory step in progestin receptor regulation of sexual receptivity in rats and mice.

Deciphering the molecular and cellular mechanisms of complex brain function and behavior is one of the major challenges of neuroscience. Recent advances in molecular biology have revolutionized the tools available for examining the neurobiological basis of brain function. The classical pharmacological approaches are being integrated with the more effective gene-targeting, antisense oligonucleotide and viral gene transfer strategies to explore fundamental issues in the field of neurobiology. Among these, antisense oligonucleotide technology has proven to be both economical and effective in exploring a variety of mechanisms underlying neuronal functions at molecular, cellular and behavioral levels.

Using the recently generated mutant mice strain (PRKO) carrying a null mutation for the progesterone receptor (PR) gene by gene targeting, we examined the critical role of PR as a coordinator of key regulatory events involved in the steroid hormone and dopamine-facilitated sexual behavior in female mice. In vitro one-point binding analyses of estradiol benzoate (EB)- induced cellular PRs and immunohistochemistry of PR in the mediobasal hypothalamus demonstrated a reduction in binding in the homozygous females, equivalent to background levels seen in EB- unresponsive tissue. The biochemical findings correlated well with the behavioral observations, with the wild type females exhibiting high levels of lordosis, while the homozygous females showed minimal lordosis in response to mating by male mice. As a critical validation of our earlier studies on ligand-independent activation of PRs by dopamine, we examined the facilitation of sexual behavior by a dopamine agonist in the null mutants. Wild type females having the full complement of PRs exhibited high levels of lordosis, while the homozygous females showed minimal lordosis in response to dopamine. To determine whether this reduced response was due to a general lack of ability to express lordosis, mice were treated with another neurotransmitter, serotonin. No significant difference in the serotonin-facilitated lordosis response was observed between the wild type and the homozygous females. We conclude that multiple signal transduction pathways coexist in the neuroendocrine system for reproductive behavior, with PR acting as a transcriptional mediator for dopamine, as well as progesterone, to achieve integration of neural communication in the central nervous system.

To test further the idea that sexual behavior in rodents is mediated via the progesterone receptor (PR) in the ventromedial nucleus of the hypothalamus, antisense and sense oligonucleotides to progesterone receptor were administered intracerebroventricularly into the third cerebral ventricle of ovariectomized estrogen-primed animals. Progesterone-facilitated sexual behavior was inhibited in animals treated with antisense oligonucleotides, with proceptive and receptive responses being minimal or completely suppressed. Sexual behavior was not altered by control sense oligonucleotides. In vitro binding assays of the cytosol progesterone receptors demonstrated a 52.2% reduction of PRs in the hypothalamus of animals that received antisense oligonucleotides, suggesting a reduction in PR synthesis. These data suggest that a threshold level of estrogen-induced hypothalamic PR is critical in the regulation of progesterone-facilitated sexual behavior in female rats.

Nitric oxide (NO), an active free radical formed during the conversion of arginine to citrulline by the enzyme NO synthase (NOS), mediates vasorelaxation, cytotoxicity, and neurotransmission. Neurons containing NOS (NOergic) are located in the hypothalamus. These NOergic neurons control the release of several hypothalamic peptides. Release of NO from these NOergic neurons stimulates pulsatile release of luteinizing hormone-releasing hormone (LHRH) in vivo and LHRH release in vitro. LHRH not only induces LH release, which induces ovulation, but also facilitates female sexual behavior. Sexual behavior can be induced reliably in estrogen-primed ovariectomized female rats by progesterone (P). This behavior consists of proceptive behavior to attract the male and the assumption of a clear characteristic posture, lordosis, when mounted by the male. To ascertain the role of NO in the control of sexual behavior in female rats, an inhibitor of NOS, NG-monomethyl-L-arginine was microinjected into the third cerebral ventricle (3V) of conscious, ovariectomized, estrogen-primed rats with indwelling cannulae. NG-Monomethyl-L-arginine (10-1000 micrograms) prevented P-facilitated lordosis when administered intracerebroventricularly into the 3V, 20 min prior to the 3V injection of P. NG-Monomethyl-D-arginine, which does not inhibit NOS, did not inhibit lordosis under the same experimental conditions. Microinjection into the 3V of sodium nitroprusside (SNP), which spontaneously releases NO, facilitated lordosis in estrogen-primed rats in the absence of P. The facilitation of lordosis induced by either P or SNP was prevented by intracerebroventricular injection of hemoglobin, which binds NO. Lordosis facilitated by P or SNP was blocked by injection of LHRH antiserum into the 3V. The results are interpreted to mean that the P-facilitated lordosis response is mediated by LHRH release. Furthermore, since NO release from SNP also facilitates lordosis in the absence of P and this response could be blocked by LHRH antiserum, we conclude that P brings about the release of NO, which stimulates LHRH release that facilitates lordosis. Thus, the results indicate that NO induces LHRH release and that LHRH then plays a crucial role in mediation of sexual behavior in the female rats.

Blastocysts are capable of attaching to a uterus only after it has been appropriately prepared by ovarian steroid hormones (receptive uterus). 1,2 They can, however, attach to extrauterine sites regardless of the hormonal environment.3 These data suggest that under certain conditions the apical surface of the uterine epithelial (UE) cell expresses molecules (ligands) which do not permit blastocyst attachment (non-receptive). It has been proposed that interactions between UE cells and various regulatory agents (hormones, growth factors) effect (induce, stimulate, repress) structural and functional changes at the apical surface of the UE cell that allow nidation.

To investigate the interaction of PRL and progesterone in regulating uterine gene expression, we have quantitated the concentration of PRL receptor and of uteroglobin (UG) mRNA in the endometrium of rabbits of different ages and after treatment with different hormones. During uterine differentiation in 2- to 4-week old rabbits, a marked increase in unoccupied uterine PRL receptor number was observed, presumably increasing uterine sensitivity to PRL. Receptor values for 4-week old rabbits were comparable to values for sexually mature, estrous females, but were lower than in 5-day pseudopregnant (PSP) animals. When total PRL receptor was determined by Scatchard analysis after in vitro desaturation with MgCl2, PSP animals again expressed the highest receptor concentration with no changes in the dissociation constant (Kd) values. To determine whether progesterone regulates uterine PRL receptor, long term ovariectomized rabbits (>12 weeks) were treated with various combinations of hormones, and unoccupied and ...