Multiple forms of human pancreatic growth hormone releasing factor-like immunoreactivity in teleost brain and pituitary

Ontogenetic development and neuroanatomical localization of growth hormone-releasing hormone (GHRH) in the brain and pituitary gland of pejerrey fish Odontesthes bonariensis

The presence and distribution of growth hormone-releasing hormone (GHRH) were studied by immunocytochemistry in adult and developing pejerrey fish, Odontesthes bonariensis (Atheriniformes). A few perikarya and fibers with immunoreactivity to GHRH (ir-GHRH) were identified in the olfactory bulbs at hatching. One week later, scattered ir-GHRH cell bodies were observed in the preoptic area and some fibers were detected entering the pituitary gland. Isolated ir-GHRH perikarya were revealed in the hypothalamus and in the medulla oblongata (MO) 3 weeks after hatching. Seven weeks after hatching, ir-GHRH cells were also identified in the nucleus of the lateral lemniscus and the cerebellum. Both nuclei presented strong ir-GHRH projections extending rostro-ventrally. At 11 weeks after hatching another group of ir-GHRH cells were revealed in the midbrain tegmentum. After that time the pattern of distribution of ir-GHRH structures remained unchanged. At 1 week after hatching and later, the pituitary gland consistently revealed ir-GHRH cells and fibers mainly in the proximalis pars distalis and in a minor proportion of the pars intermedia since week 1. The pineal gland showed ir-GHRH cells projecting into the pineal lumen, at week 6 after hatching and later. The pineal stalk and the subcomissural organ also presented ir-GHRH structures. Additionally, ir-GHRH material was found from week 3 to the adult stage in the following extraneural organs: gills, gut, kidney and hepatopancreas. These results represent the anatomical substrate for understanding the physiology of GHRH peptide in pejerrey, adding information on the ontogeny of neural structures expressing GHRH.

Immunocytochemical localization of growth hormone-releasing hormone-like peptide in the brain of the tiger frog, Rana tigrina

Using antisera directed against carp growth hormone-releasing hormone (cGHRH), we found more extensive brain distribution of GHRH-like immunoreactive (ir) neurons in the tiger frog, Rana tigrina, than reported in previous studies, which employed mammalian GHRH antibodies. In the telencephalon, GHRH-ir perikarya were present in the pallium dorsale, pallium laterale (pars dorsalis and pars ventralis), pallium mediale, nucleus entopeduncularis, amygdala pars medialis, and in the ventral portion of the lateral preoptic area. Most GHRH somata were present in the nucleus infundibularis ventralis located around the third ventricle, extending from the region posterior to the optic chiasma to the caudal end of infundibulum. In the thalamic region, GHRH-ir perikarya occurred in the area ventrolateralis thalami, the nuclei posterocentralis thalami, and the posterolateralis thalami. The ir cell bodies in the nucleus posteroventralis tegmenti mesencephali represented the caudal-most brain GHRH perikarya. Extensive GHRH-ir fibers occurred around the nonreactive cells in the ventral preoptic area and ventral area of the infundibulum. GHRH-ir fibers were present in the outer layers of the median eminence, but not in the neural lobe or pars distalis of the pituitary gland. This wider neuroanatomical distribution of GHRH-like peptide in the brain of R. tigrina should, provide the basis for future studies to establish the exact role of GHRH-like peptides in anuran brain.

Human pancreatic growth hormone-releasing factor (1-44) stimulates GH cells in an anuran amphibian (Rana perezi)

Subcellular responses of amphibian growth hormone (GH)-producing cells to in vivo administration of human pancreatic growth hormone-releasing factor (1-44) (hpGRF) were investigated. The volume density (Vv) of secretory granules (SG), rough endoplasmic reticulum (RER), and Golgi complex (GC) and the numerical density (Nv) of the granules were estimated by ultrastructural morphometry. Immunogold staining was applied to ultrathin sections using an antiserum to ovine GH to identify GH-producing cells. In vivo treatment with hpGRF significantly decreased the Vv of the SG and the Nv of medium SG after 6 hr. The peptide also stimulated development of the cellular biosynthetic machinery and increased the number of small SG 24 hr after stimulation. Four-day-stimulated GH cells did not recover control morphological appearances. These morphological results suggest that: (1) In vivo administered hpGRF stimulates GH cells in Rana perezi by inducing hormone release and enhances biosynthetic activity; (2) after four injections, the cellular response is more intense, indicating that GH cells remain hyperactive, probably because the exogenous hpGRF overcomes the endogenous inhibitory control of GH secretion.

Distribution and characterization of immunoreactive growth hormone (GH) in the pituitary of the frog Rana ridibunda using an antiserum against purified bullfrog GH

The presence of growth hormone (GH) in the pituitary of the frog Rana ridibunda was investigated using an antiserum raised against purified bullfrog GH. The immunofluorescence technique revealed that GH-containing cells are exclusively located in the dorsal area of the distal lobe of the pituitary. The relative abundance of these GH-positive cells, which correspond to acidophilic type 2 cells, was 18 +/- 1% of the total population of endocrine cells of the pars distalis. Frontal sections of the distal lobe indicated that GH-producing cells are distributed in an arc of a circle occupying all of the dorsal part of the lobe. At the electron microscopic level, GH-immunoreactive material was sequestered in large polymorphic granules (200-700 nm). GH was quantified in R. ridibunda pituitary extracts using a radioimmunoassay for bullfrog GH. The displacement curves obtained with serial dilutions of pars distalis extracts were not strictly parallel to the standard curve made with purified bullfrog GH. In contrast, Western blot analysis revealed that GH from R. ridibunda had a molecular weight (22 kDa) similar to that of bullfrog GH. In the pars distalis, the apparent amount of GH was 0.61 +/- 0.14 microgram per lobe, corresponding to 0.92 +/- 0.17% of total proteins in the extracts. In contrast, frog neurointermediate lobe or hypothalamus did not contain significant concentrations of immunoreactive GH (less than 0.006% of total proteins in the extracts). Taken together, these results validate the use of an antiserum to bullfrog GH to investigate the regulation of GH secretion in R. ridibunda.

Effects of serotonin on gonadotropin and growth hormone release from in vitro perifused goldfish pituitary fragments

The effects of serotonin (5-HT) on gonadotropin and growth hormone release from perifused goldfish (Carassius auratus, L.) pituitary glands were studied. Serotonin, at micromolar concentrations, caused a dose-related release of gonadotropin and an inhibition of growth hormone release in pituitaries from goldfish at different sexual stages. At lower concentrations 5-HT continued to inhibit growth hormone release, but had no effects on gonadotropin release. The stimulatory effects of 5-HT on gonadotropin release could be blocked by ketanserin and cyproheptadine; however, these two antagonists had no effects on 5-HT inhibition of growth hormone release. Perifusion with melatonin had no effect on the release of gonadotropin or growth hormone release. These results demonstrate that 5-HT has a stimulatory effect on gonadotropin secretion, probably through a 5-HT2 receptor type, and an inhibitory effect on growth hormone through an unidentified receptor type. We hypothesize that the effects on gonadotropin release are due to direct actions on gonadotrophs, whereas the effects on growth hormone release may be due to stimulation of somatostatin release from neurosecretory terminals in the pituitary.

Comparative distribution of neuropeptide-immunoreactive systems in the brain of the green molly, Poecilia latipinna

The comparative distribution of peptidergic neural systems in the brain of the euryhaline, viviparous teleost Poecilia latipinna (green molly) was examined by immunohistochemistry. Topographically distinct, but often overlapping, systems of neurons and fibres displaying immunoreactivity (ir) related to a range of neuropeptides were found in most brain areas. Neurosecretory and hypophysiotrophic hormones were localized to specific groups of neurons mostly within the preoptic and tuberal hypothalamus, giving fibre projections to the neurohypophysis, ventral telencephalon, thalamus, and brain stem. Separate vasotocin (AVT)-ir and isotocin (IST)-ir cells were located in the nucleus preopticus (nPO), but many AVT-ir nPO neurons also displayed growth hormone-releasing factor (GRF)-like-ir, and in some animals corticotrophin-releasing factor (CRF)-like-ir. The main group of CRF-ir neurons was located in the nucleus recessus anterioris, where coexistence with galanin (GAL) was observed in some cells. Enkephalin (ENK)-like-ir was occasionally present in a few IST-ir cells of the nPO and was also found in small neurons in the posterior tuberal hypothalamus and in a cluster of large cells in the dorsal midbrain tegmentum. Thyrotrophin-releasing hormone (TRH)-ir cells were found near the rostromedial tip of the nucleus recessus lateralis. Gonadotrophin-releasing hormone (GnRH)-ir cells were present in the nucleus olfactoretinalis, ventral telencephalon, preoptic area, and dorsal midbrain tegmentum. Molluscan cardioexcitatory peptide (FMRF-amide)-ir was colocalized with GnRH-ir in the ganglion cells and central projections of the nervus terminalis. Melanin-concentrating hormone (MCH)-ir neurons were restricted to the tuberal hypothalamus, mostly within the nucleus lateralis tuberis pars lateralis, and somatostatin (SRIF)-ir neurons were numerous throughout the periventricular areas of the diencephalon. A further group of SRIF-ir neurons extending from the ventral telencephalon into the dorsal telencephalon pars centralis also contained neuropeptide Y (NPY)-, peptide YY (PYY)-, and NPY flanking peptide (PSW)-like-ir. These immunoreactivities were, however, also observed in non-SRIF-ir cells and fibres, particularly in the mesencephalon. Calcitonin gene-related peptide (CGRP)-like-ir had a characteristic distribution in cells grouped in the isthmal region and fibre tracts running forward into the hypothalamus, most strikingly into the inferior lobes. Antisera to cholecystokinin (CCK) and neurokinin A (NK) or substance P (SP) stained very extensive, separate systems throughout the brain, with cells most consistently seen in the ventral telencephalon and periventricular hypothalamus. Broadly similar, but much more restricted, distributions of cells and fibres were seen with antisera to neurotensin (NT) and vasoactive intestinal peptide (VIP).(ABSTRACT TRUNCATED AT 400 WORDS)

In vitro responses of rainbow trout (Oncorhynchus mykiss) somatotrophs to carp growth hormone-releasing factor (GRF) and somatostatin

To study the hypothalamic control of growth hormone (GH) release in lower vertebrates, we employed an in vitro technique using a monolayer cell culture system of rainbow trout pituitary glands. Two newly purified carp brain growth hormone-releasing factors, carp GRF(1-45) and carp GRF(1-29), and synthetic somatostatin-14 (SST-14) were applied to the cultured pituitary cells. The results indicate that: (1) The carp GRFs had a dose-related potency in stimulating growth hormone release. The dose of half maximum effect (ED50) for carp GRF(1-45) was 0.107 nM, and an equal potency for carp GRF(1-29) was 0.388 nM. (2) SST-14 inhibited GH release having a dose-dependent potency with an ED50 of 0.186 nM. (3) Osmotic pressure did not influence SST-14 inhibited GH secretion but did affect spontaneous GH release. (4) The response of cultured cells was not affected by length of incubation period with SST-14 or carp GRF but was affected by cell density.

In vitro goldfish growth hormone responses to gonadotropin-releasing hormone: possible roles of extracellular calcium and arachidonic acid metabolism?

Two hours of incubation of primary static cultures of dispersed goldfish pituitary cells with 0.01 nM to 1 microM [Trp7,Leu8]-gonadotropin-releasing hormone (sGnRH) increased growth hormone (GH) secretion in a dose-dependent manner with an ED50 estimate of 0.13 +/- 0.04 nM. Addition of calcium ionophores, 1 to 100 microM A23187 and 5 to 100 microM ionomycin, significantly elevated GH release with ED50s of 0.84 +/- 0.38 and 4.34 +/- 1.02 microM, respectively. Replacement of normal calcium-containing media with calcium-deficient media (prepared without the addition of calcium salts) significantly depressed basal GH secretion, attenuated the A23187- and ionomycin-stimulated GH release, and completely abolished the GH response to sGnRH. Arachidonic acid (AA) at 1 to 50 microM also enhanced GH secretion with an ED50 of 4.72 +/- 1.52 microM. Coincubation with 1 and 10 microM of a lipoxygenase inhibitor, nordihydroguaiaretic acid (NDGA), 10 microM of the cyclooxygenase inhibitor, indomethacin, and 10 microM of eicosatetraynoic acid, an enzyme blocker with mixed activities on both the lipoxygenase and cyclooxygenase pathways, did not alter basal, AA-, and sGnRH-induced GH release. However, at 100 microM concentration, NDGA increased AA- and sGnRH-stimulated, as well as basal GH, responses. These results confirm the direct stimulatory action of GnRH on goldfish somatotropes and indicate the importance of extracellular calcium in mediating basal and GnRH-induced GH responses. Although AA stimulates GH secretion, its lipoxygenase and cyclooxygenase metabolites probably do not mediate sGnRH action on somatotropes.

Evidence of a growth hormone-releasing hormone-like molecule in salmon brain, Oncorhynchus keta and O. kisutch

An antiserum with conformational specificity to human growth hormone-releasing hormone (hGH-RH 1-44 NH2) was produced and used to develop a radioimmunoassay to detect immunoreactive (ir) GH-RH in brain extracts of salmon, guinea pig, and mouse. Evidence of an immunoreactive GH-RH from salmon brain extracts with a retention time on reverse-phase high-performance liquid chromatography (HPLC) distinct from hGH-RH 1-44 is presented. Salmon irGH-RH from crude extracts elutes 1-2 min earlier than hGH-RH 1-44 (NH2) in a gradient HPLC system, whereas affinity-purified salmon irGH-RH elutes 12-13 min earlier in a near-isocratic system, suggesting that the salmon molecule is more hydrophilic.

Localization of growth hormone-releasing factor-like immunoreactivity in the hypothalamo-hypophysial system of some teleost species

An antiserum to growth hormone-releasing factor (GRF) 1-44 was applied on brain and pituitary sections of nine teleost species. Immunoreactive (ir) perikarya were demonstrated in parvo- and magnocellular portions of the preoptic nucleus (PON) and occasionally in the nucleus lateralis tuberis. The two tracts originating in the PON ran ventro-laterally toward the optic chiasm and then caudally in the basal hypothalamus. In the pars distalis (PD) of the eel, carp, goldfish and salmonids, GRF-ir fibers did not enter the rostral PD and few fibers passed close to somatotropes. In Myoxocephalus and Mugil, a variable number of ir-fibers passed close to cells of the rostral and proximal PD. In the neurointermediate lobe, GRF-ir fibers were located exclusively in the neural tissue of the eel and trout. In goldfish, carp and Myoxocephalus, GRF-ir fibers entered the intermediate lobe. This antiserum also labeled corticotrops and, to a lesser extent, melanotrops in the pituitary of cyprinids. A variable number of perikarya contained both GRF and vasotocin in the PON of the eel. In all teleost species studied so far, the distribution patterns of GRF are different, and the function of the various adenohypophysial cell types appears to be differently modulated, according to the variable distribution of GRF in the pituitary.

Immunohistochemical detection of a substance resembling growth hormone-releasing factor in the brain of the rainbow trout (Salmo gairdneri)

We studied the distribution of an immunoreactive substance resembling growth hormone-releasing factor (GRF) in the hypothalamus and pituitary gland of the rainbow trout by immunofluorescence methods. The GRF-like immunoreactive perikaryon was observed in colchicine-treated fish. The majority of GRF-containing neurons were located in the nucleus lateral tuberis; others were located in the caudal part of the preoptic nucleus of the hypothalamus. The GRF-like immunoreactive neuronal processes projected into the pars distalis via the pars nervosa of the pituitary gland. The distribution of the GRF-like immunoreactive substance in the hypothalamus and pituitary gland suggests that GRF plays a physiological role in the regulation of growth hormone release from the pituitary gland of rainbow trout, as it does in mammals.

Immunocytochemical demonstration of close relationships between neuropeptidergic nerve fibers and hormone-producing cell types in the adenohypophysis of the sea bass (Dicentrarchus labrax)

Light microscopic double immunocytochemical stainings, performed on sea bass hypothalamo-hypophysial sections, revealed the projection of different neuropeptide-immunoreactive neurons innervating the hormone-producing cell populations in the pituitary gland. In the rostral pars distalis (PD) the ACTH cells were found in close proximity to fibers immunoreactive for somatostatin (SRIF), growth hormone-releasing hormone (GRF), corticotropin-releasing hormone (CRF), vasotocin (VT), isotocin (IT), substance P (SP), neurotensin, and galanin (GAL), while the PRL cell zone seemed only innervated by nerve fibers immunopositive for GAL. In the proximal PD, fibers immunoreactive for SRIF, GRF, VT, IT, cholecystokinin, SP, neuropeptide Y, and GAL formed a close relationship with the growth hormone cells. The gonadotrophs were observed near nerve fibers immunostained for gonadotropin-releasing hormone, IT, and less obviously GRF and VT, while fibers positive for GRF, CRF, VT, IT, SP, and GAL penetrated between and formed a close association with the thyrotrophs. In the pars intermedia the MSH cells and the PAS-positive (PAS+) cells seemed both innervated by separate nerve fibers immunoreactive for GRF, CRF, melanin concentrating hormone, VT, IT, and SP. All these results suggest a functional role of the neuropeptides in the adenohypophysis of the sea bass, possibly in the synthesis and/or release of hypophysial hormones from the different cell types.

Partial purification and characterization of a novel growth hormone-releasing factor (GRF) from teleost brain related to the rat hypothalamic peptide

A growth hormone-releasing factor (GRF)-like molecule has been partially purified and characterized from acid extracts of codfish (Gadhus morhua) brain using immunoaffinity and gel chromatography, followed by HPLC. This material has a mol.wt. which is similar to known mammalian forms of GRF but is immunologically and/or chromatographically distinct from previously described GRF peptides. However, it is related to rat(r) GRF(1-43) since it causes marked displacement in the rGRF RIA. Codfish GRF is a highly specific and potent hypophysiotropic factor as shown by its ability to stimulate the release of GH, but no other hormone, from rat anterior pituitary cells in vitro. These findings suggest that, phylogenetically, GRF is an ancient molecule with its biologic activity and certain immunoreactive domain(s) conserved, at least, from teleost to mammal.

Localization of growth hormone releasing factor-like immunoreactivity in the hypothalamo-hypophyseal system of the frog (Rana temporaria) and the sea bass (Dicentrarchus labrax)

Using two different antisera, one raised against total human pancreatic growth hormone releasing factor (hpGRF) coupled through a two-step glutaraldehyde method and the other one raised against rat hypothalamic growth hormone releasing factor 1-10 (rGRF1-10), GRF-like immunoreactivity was localized in the hypothalamo-hypophyseal system of the frog (Rana temporaria) and the sea bass (Dicentrarchus labrax). In the frog immunoreactive neurons were found in the nucleus preopticus, pars magnocellularis. The immunopositive fibers were localized in the lateral wall of the preoptic recess, the pars ventralis of the tuber cinereum, the internal and external zone of the median eminence, and the neural lobe. Positive-stained neurons in the sea bass were located in the preoptic nucleus, in the pars magnocellularis as well as in the pars parvocellularis, and in the nucleus lateralis tuberis, pars rostralis. GRF-ir nerve fibers, originating in the hypothalamus, projected to the rostral and proximal pars distalis, the posterior neurohypophysis, and the pars intermedia (PI). Double stainings with anti-GRF and anti-ACTH or anti-trout GH showed some close relationship between GRF immunoreactive nerve fibers and adenohypophyseal cell types. In the PI both the MSH and the PI "PAS" positive cells seemed to be directly innervated by the GRF-ir axons. These results show that a GRF-like system is present in the hypothalamo-hypophyseal system of amphibians and teleosts and that in these lower vertebrates GRF-like material may be secreted directly in the systemic circulation. The function of this GRF, however, is not yet clear.