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Somatolactin (SL) and SL receptor (SLR) belong to the growth hormone and cytokine type I receptor superfamilies, respectively. However, further research is required to define the duplications and functions of SL and its receptors in basal vertebrates including environmental background color adaptation in fish. In the present study, we cloned and sequenced SL and its putative receptor (SLR), classified and compared the sequences phylogenetically, and determined SL and SLR mRNA expression levels during long-term background color exposure in Cichlasoma dimerus, a freshwater South American cichlid. Our results show that C. dimerus SL and SLR share high sequence similarity with homologous from other perciform fish. Phylogenetic analysis indicates that C. dimerus SL belongs to the SLα clade sub-group. C. dimerus SLR is clearly a member of the GHR1 receptor subgroup, which includes the experimentally validated SLR from salmonids. Higher transcript levels of SLα in the pituitary and SLR in the epidermis and dermis cells of fish scales were observed in fish following long-term black background color exposure compared to those exposed to a white background. A higher number of melanophores was also observed in fish exposed for 10days to a black background compared to those exposed to a white background. These changes were concomitant to differences in SL or SLR transcript levels found in fish exposed to these two different background colors. Our results suggest, for the first time, that SLR is expressed in fish scales, and that there is an increase in SL in the pituitary and the putative SLR in likely target cells, i.e., melanophores, in long-term black background exposure in C. dimerus., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Numerous small potentially bioactive peptides are derived from the selective processing of the ~600 amino acid secretogranin II (SgII) precursor, but only the 31-42 amino acid segment termed secretoneurin (SN) is well-conserved from sharks to mammals. Both SNa and SNb paralogs have been identified in some teleosts, likely arising as a result of the specific genome duplication event in this lineage. Only one copy of the putative lamprey SgII (188 amino acids) could be identified which gives rise to a divergent agnathan SN that contains the signature YTPQ-X-LA-X(7)-EL sequence typical of the central core of all known SN peptides. In rodent models, SN has regulatory effects on neuroinflammation and neurotransmitter release, and possesses therapeutic potential for the induction of angiogenesis. The wide distribution of SN in neuroendocrine neurons and pituitary cells suggests important endocrine roles. The clearest example of the endocrine action of SN is the stimulatory effects on pituitary luteinizing hormone release from goldfish pituitary and mouse LβT2 gonadotroph cells, indicative of an important role in reproduction. Several lines of evidence suggest that the SN receptor is most likely a G-protein coupled protein. Microarray analysis of SN effects on dispersed goldfish pituitary cells in vitro reveals novel SN actions that include effects on genes involved in notch signaling and the guanylate cyclase pathway. Intracerebroventricular injection of SN increases feeding and locomotory behaviors in goldfish. Given that SgII appeared early in vertebrate evolution, SN is an old peptide with emerging implications as a new multifunctional hormone., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Endogenous and environmental estrogens have been proved to affect male reproduction in vertebrates. Both positive and negative effects in the regulation of the reproductive tract have been described. Since it is well known that amphibians represent a useful model to study several aspects concerning reproductive activity, we have taken advantage of the frog, Rana esculenta, to study the involvement of estrogens in sperm release. We show here that pituitary hormones increased the number of peritubular myoid cells (PMCs) expressing Fra-1 and induced testicular morphological changes related to sperm release. The estrogen antagonist ICI182-780 counteracted the hypophysis driven effects. In vivo and in vitro experiments demonstrated that 17beta-Estradiol acted directly on the testis to switch-on Fra-1 in PMCs. Furthermore, impairment of estrogen activity significantly reduced sperm release mainly affecting the detachment of spermatozoa from Sertoli cells (spermiation). Therefore, estrogens can be considered a new entry in the list of substances involved in spermiation.

Melanin-concentrating hormone (MCH) is a neuropeptide generated in neurons originating in the hypothalamus, from which axons project to the entire brain and neurohypophysis in fish. MCH has both central and peripheral roles such as food intake and body color change. Here we cloned two MCH receptors (MCH-R) from the barfin flounder, Verasper moseri, Pleuronectiformes. The phylogenetic analysis shows that these are orthologues to the mammalian MCH-R1 and MCH-R2 showing 49 and 30% amino acid sequence identity to the corresponding human receptors while they have 31% amino acid sequence identify between them. Essential amino acid residues for ligand binding, signal transduction and receptor conformation, which have been shown in mammalian MCH-R, are well conserved in the flounder MCH-Rs. MCH-R1 has one intron in the extracellular N-terminal region and MCH-R2 has one intron in the DRY motif, which is a homologous position to one of the five introns of human MCH-R2. Orthologues of MCH-R1 and MCH-R2 may have appeared by gene duplication of the ancestry of MCH-Rs having at least two introns, and then MCH-R1 and MCH-R2 inherited different introns in flounder strains. We also determined their tissue distribution and functional role in rearing condition. Reverse transcription PCR revealed that the expression of MCH-R1 is confined to the brain of the barfin flounder, while transcripts of MCH-R2 were detected in the brain, pituitary, eyeball, gill, atrium, ventricle, head kidney, body kidney, spleen, intestine, inclinator, skeletal muscle testis, ovary, eyed-side skin, and non-eyed-side skin. The expression of MCH-R2 in eyed-side skin was higher in fish reared in a black tank (121 days) than in a white tank while the expression levels of MCH in the brain were significantly greater in the group reared with the white background suggesting down-regulation of this receptor gene with increased levels of MCH. The results suggest that the MCH-R2 mediates the effect of MCH to control body color for background adaptation in the eyed-side skin of the barfin flounder.

The endocrine system mediates many of the physiological responses to the homeostatic and acclimation demands of salt and water transport. Many of the hormones involved in the control of salt and water transport are common to all vertebrates, although their precise function and target tissues have changed during evolution. Arginine vasopressin (vasotocin), angiotensin II, natriuretic peptides, vasoactive intestinal peptide, urotensin II, insulin and non-genomic actions of corticosteroids are involved in acute (minutes and hours) alterations in ion and water transport. This rapid alteration in transport is primarily the result changes in behavior, blood flow to osmoregulatory organs, and membrane insertion or activation (e.g., phosphorylation) of existing transport proteins, ion and water channels, contransporters and pumps. Corticosteroids (through genomic actions), prolactin, growth hormone, and insulin-like growth factor I primarily control long-term (several hours to days) changes in transport capacity that are the result of synthesis of new transport proteins, cell proliferation, and differentiation. In addition to the important task of establishing broad evolutionary patterns in hormones involved in ion regulation, comparative endocrinology can determine species and population level differences in signaling pathways that may be critical for adaptation to extreme or rapidly changing environments.

Using specific antibody for chum salmon somatolactin (SL), immunocytochemical studies were employed to determine the distribution of this hormone in the pituitary gland and the brain of Orechromis niloticus. The results indicated that the SL-immunoreactive (ir) cells are found in the pars intermedia (PI) of the pituitary gland. The SL-ir cells showed strong and specific immunoreactivity to anti-chum salmon SL. Moreover, SL-ir cells were found to be widely distributed in most brain regions. Most of the SL-ir cell bodies were scattered along a nearly continuous line extending posteriorly from the olfactory bulb to the medulla oblongata through the nucleus preopticus periventricularis, habenula, and midbrain tegmentum and ventral to the nucleus lateralis tuberis pars posterior through the nucleus preopticus basalis lateralis and organum vasculosum luminae terminalis. Also SL-ir cells were observed in the cerebellum. The synthetic and secretory activity of the SL-ir cells, in the pituitary and the brain, showed an increase during sexual maturation and spawning. The highly organized SL-containing system and the gradual stimulation of SL synthesis and release during sexual maturation and spawning of O. nilotcus suggest that SL may be involved in the control of some steps of reproductive processes., (Copyright 1999 Academic Press.)

Chemical identification of neurohypophysial hormones from about 80 vertebrate species reveals that two evolutionary lineages can be traced in bony vertebrates, a vasopressin-like hormone line and an oxytocin-like hormone line, which were derived from the duplication of an ancestral gene that may have been present in agnathans. All of the 13 neurohypophysial hormones are built in the same structural pattern, namely, a nonapeptide with a disulfide bridge linking half-cystines in positions 1 and 6. There is a striking evolutionary stability in bony vertebrates since virtually all species belonging to a given class are endowed with the same peptides. In contrast, in cartilaginous fishes, the oxytocin-like hormone displays a great diversity. Six distinct peptides are characterized in this group. The proposed hypothesis is that the stability in primary structure in bony vertebrates is due to selective pressure. This selective pressure is associated with an ion-based osmoregulation, whereas in Chondrichthyes the occurrence of an urea-based osmoregulation has relieved the hormones from the control of ionic homeostasis. Variations in primary structures in cartilaginous fishes are regarded as relevant to the neutral evolution as defined by Kimura. According to this concept, oxytocin of placental mammals results from selective evolution, whereas the same molecule found in ratfish proceeds from random genetic drift.

The actions of hormones on growth, cellular proliferation, and on synthetic rates of the major surfactant phospholipids, phosphatidylcholine (PC) and disaturated PC (DSPC), were studied in the lung of the chick embryo. Particular emphasis was placed on the effects of hypophysectomy, pituitary transplantation, and treatment with corticosterone (CORT). One study was concerned with hydrocortisone (HYCORT), estrogen (E2), thyroxine (T4), ovine prolactin (oPRL), and insulin. Hypophysectomy interfered with the normal gain in protein, the progressive dehydration of the embryonic lung, and also caused a reduction in the number of pulmonary cells on Days 16 and 18 of incubation. Absence of the pituitary gland diminished pulmonary PC by Day 16. Transplantation of one pituitary gland or exogenous CORT partially restored pulmonary phospholipid and PC (normalized per wet weight) in hypophysectomized (hypox) embryos. Transplantation also restored relative protein content in lungs of hypox individuals. Beyond this, transplantation was generally ineffective in reversing deficits of hypox individuals. All concentrations of CORT administered (30-100-300 micrograms) reduced the rate of pulmonary cell division. The highest dose was toxic as judged by its capacity to cause cellular death. Treatment of intact chicken embryos with CORT or E2 for two days stimulated incorporation of [14C]choline into PC and DSPC (the most surface-active component of PC) in the lungs of Day 17 embryos. CORT, but not E2, stimulated DSPC synthesis when treatment was increased to 3 days. Other hormones tested (T4, oPRL, insulin, and HYCORT) had no effect upon the rate of incorporation of [14C]choline into PC or DSPC. These results indicate that during ontogeny the avian lung becomes sensitive to CORT, and possibly E2, prior to 16 days of incubation. CORT, in particular, acts both to trigger the prehatching stimulation of surfactant phospholipid synthesis, especially the vital DSPC fraction, and to slow the rate of pulmonary cellular division coincident with biochemical differentiation of the surfactant system.

A radioimmunoassay was developed for salmonid melanin concentrating hormone (MCH) and used to measure immunoreactive (ir)MCH in the hypothalamus and pituitary of trout (Salmo gairdneri) and eels, (Anguilla anguilla) maintained under different regimes of background color. In trout, 95% of the total irMCH was located in the pituitary gland. The amount of MCH in both pituitary and hypothalamus was increased when white-adapted trout were transferred to a black background. In eels, a similar change of background led to an accumulation of MCH in the pituitary but not in the hypothalamus. The results suggest that MCH is released from the neurohypophysis in association with physiological color change. Neurointermediate lobes of trout and eels released both ir alpha MSH and irMCH when they were cultured in vitro. The release of alpha MSH was significantly enhanced when endogenous MCH was immunoabsorbed by MCH antiserum added to the culture medium. The results indicate that MCH can induce pallor in fish not only by its peripheral effect on the melanophores but also by an inhibitory action on the release of alpha MSH from the pituitary.

The existence of melanocyte-stimulating hormone (MSH) in fish brains was investigated by a range of techniques: radioimmunoassay, HPLC, bioassay, and immunocytochemistry. Immunoreactive alpha MSH (ir alpha MSH) was detected by radioimmunoassay in all regions of carp and trout brains, with the highest concentration in the basal hypothalamus. In trout, ir alpha MSH cell bodies were located by immunocytochemistry only periventricularly, in the medial basal hypothalamus near the third ventricle, whereas in the carp ir alpha MSH staining was seen both in periventricular cells and also in some of the magnocellular neurones in the lateral hypothalamus. When white-adapted fish were transferred to a black tank for 6 days, the melanin-concentrating hormone (MCH) content of the basal hypothalamus of both carp and trout increased 2- and 4.6-fold, respectively, but the alpha MSH content did not change in either species. Analysis by HPLC of pituitary gland, hypothalamic, and optic tectal extracts revealed that the pituitary contains desacetyl, monoacetyl, and diacetyl alpha MSH, although the ratio of these forms differed in the two species. The hypothalamus and optic tectum, however, contained predominantly the desacetyl form of alpha MSH. Bioassays for MSH in the HPLC fractions revealed the existence of presumptive beta MSH in both the pituitary and hypothalamus. An argument is advanced that the periventricular ir alpha MSH neurones are homologous with the proopiomelanocortin cells of the arcuate nucleus in mammals, and that the immunocytochemical alpha MSH-like activity in the MCH neurones may not be authentic alpha MSH.

A gonadotropin-receptor preparation from trout during full spermatogenesis known to bind 125I-hCG was used to test the ability of trout pituitary proteins to dislocate hCG from the receptors. From the proteins of male trout pituitaries chromatographed on immobilized concanavalin A, only the glycoprotein fraction was able to compete with hCG for the receptors. Unabsorbed proteins eluting in three fractions were radioiodinated and used as ligands. The fact that they were not taken up specifically by the receptor preparation, and the competition of the glycoproteins with 125I-hCG, is discussed in the context of the vertebrate's gonadotropic hormone system.