Gastrin releasing peptide (GRP) is present in a GRP(1-27) form in anterior pituitary cells of the guinea pig

Localization and expression of gastrin-releasing peptide (GRP) in the bovine cervix

Gastrin-releasing peptide (GRP) has been suggested as a novel regulatory peptide in the female reproductive tract but the presence of GRP and GRP mRNA in the non-neurogenic tissue of the cervix has not yet been clarified. In the present study, immunohistochemistry and in situ hybridization were used to reveal the distribution of GRP immunoreactivity and expression of GRP mRNA in the bovine cervix. The cervixes from 21 non-pregnant and 20 pregnant cows, and 6 fetuses were used in the study. In the fetus, adult non-pregnant and pregnant specimens, GRP and GRP mRNA were predominantly detected in the luminal epithelial cells of basal areas of peripheral regions of the cervix. Positive staining of GRP in the epithelial cells of the cervix was first detected in the CRL 37 cm of the fetus. During the estrous cycles, the staining intensity of GRP in the epithelial cells was stronger in the follicular phase than in the luteal phase. During the early gestational period, GRP immunoreactivity was detected at relatively similar intensity to the follicular phase. In situ hybridization results ascertained the expression of GRP mRNA in the superficial epithelial cells of the cervix of non-pregnant and pregnant cows. The results suggest that GRP may be important both in the development of the fetal cervix and secretory activity of the epithelial cells of the cervix.

Central bombesin activates the hypothalamic-pituitary-adrenal axis. Effects on regional levels and release of corticotropin-releasing hormone and arginine-vasopressin

While corticotropin-releasing hormone (CRH) is a primary regulator of the hypothalamic-pituitary-adrenal (HPA) axis, the mechanism(s) triggering the release of this corticotropin (ACTH) secretagogue remains unknown. Stressful and appetitive events evoke the release of not only CRH but also of bombesin (BN)-like peptides. Furthermore, CRH antagonists attenuate the endocrine and behavioral effects of BN, suggesting that BN-like peptides may mediate their effects via CRH release. An initial (mapping) study revealed that centrally administered BN (0.25 or 0.5 microg i.c.v.) increased circulating corticosterone and ACTH levels and decreased immunoreactive (ir)-CRH at the nucleus of the solitary tract, ventromedial (VMH) and anterior hypothalamic nuclei, and the central amygdaloid nucleus. Whereas BN treatment decreased ir-vasopressin (AVP) at the VMH, it elevated levels of this peptide in the hypothalamic paraventricular and median eminence/arcuate (Me/Arc) regions. Dynamic, in vivo release experiments (using push-pull perfusion) revealed that BN evoked the release of ir-CRH and ir-AVP from the Me/Arc and increased interstitial levels of these secretagogues at the anterior pituitary. These results suggest that BN-like peptides may regulate certain hypothalamic and extrahypothalamic circuits, including the HPA axis, by affecting regional utilization of ir-CRH and ir-AVP, and/or by provoking the release of these peptides at the Me/Arc, thus increasing their availability downstream at the anterior pituitary and increasing circulating ACTH and corticosterone levels.

Bioactive peptides in anterior pituitary cells

The anterior pituitary (AP) has been shown to contain a wide variety of bioactive peptides: brain-gut peptides, growth factors, hypothalamic releasing factors, posterior lobe peptides, opioids, and various other peptides. The localization of most of these peptides was first established by immunocytochemical methods and some of the peptides were localized in identified cell types. Although intracellular localization of a peptide may be the consequence of internalization from the plasma compartment, there is evidence for local synthesis of most of these peptides in the AP based on the identification of their messenger-RNA (mRNA). In several cases the release of the peptide from the AP cell has been shown and regulation of synthesis, storage and release have also been described. Because the amount of most of the AP peptides is very low (except for POMC peptides and galanin), endocrine functions are not expected. There is more evidence for paracrine, autocrine, or intracrine roles in growth, differentiation, and regeneration, or in the control of hormone release. To demonstrate such functions, in vitro AP experiments have been designed to avoid the interference of hypothalamic or peripheral hormones. The strategy is first to show a direct effect of the peptide after adding it to the in vitro system and, secondly, to explore if the endogenous AP peptide has a similar action by using blockers of peptide receptors or antisera immunoneutralizing the peptide.

Expression of the genes encoding bombesin-related peptides and their receptors in anterior pituitary tissue

The bombesin-related peptides gastrin-releasing peptide (GRP) and neuromedin B (NMB) have been demonstrated in the anterior pituitary (AP) on an immunological basis. We studied the presence of mRNAs for these peptides and for their receptors by RNAse protection assay using fresh adult male rat AP, AP cell reaggregates cultured in the presence of estradiol and the rat AP derived GH3 cell line. In total RNA from fresh AP we detected high amounts of NMB mRNA and much smaller amounts of GRP mRNA, while finding a weak signal for GRP-receptor (GRP-R) and NMB-receptor (NMB-R) mRNAs. In total RNA from the reaggregate cell cultures we detected high levels of NMB mRNA as well as a strong signal for GRP-R mRNA. Finally, in GH3 cells, high levels of NMB mRNA and GRP-R mRNA were found, while GRP mRNA and NMB-R mRNA remained undetectable even in high amounts (200 micrograms) of total RNA. We conclude that mRNAs encoding both bombesin-related peptides and each of the mRNAs encoding their receptors are expressed in rat AP tissue. NMB mRNA is more prominent than GRP mRNA in all AP-like tissues examined (fresh AP, estradiol-treated reaggregate AP cell cultures and GH3 cells). NMB-R mRNA and GRP-R mRNA are both present in low levels in fresh AP whereas the GRP-R mRNA is predominant in GH3 cells and estradiol treated AP reaggregate cell cultures. Compared to fresh AP tissue, NMB mRNA and GRP-R mRNA expression is enhanced in estradiol-treated reaggregate cell cultures.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of the bombesin receptor blockers [Leu13, psi CH2NH-Leu14]bombesin and N-pivaloyl GRP(20-25) alkylamide (L 686,095-001C002) on basal and neuromedin C-stimulated PRL and GH release in pituitary cell aggregates

Perifusion of rat anterior pituitary cell aggregates, cultured in estrogen-supplemented serum-free medium with 1 nM of the bombesin (BBN)-like peptide, neuromedin C (NMC), significantly stimulates GH and PRL release. This effect is dose-dependently inhibited by the BBN receptor blocker L 686,095-001C002 [an N-pivaloyl-gastrin-releasing-peptide(20-25) alkylamide]. The IC50 was 0.20 nM in the case of the GH response and 0.16 nM in the case of the PRL response. The antagonist has no effect on basal PRL or GH release. [Leu13, psi CH2NH-Leu14]BBN (psi BBN) displays an IC50 of 0.41 microM for inhibiting the GH response and 0.36 microM for inhibiting the PRL response to NMC. At a concentration of 0.5 microM or 5 microM, however, the latter antagonist stimulates PRL and GH release when perifused alone. This stimulatory effect is dose dependent, augments when aggregates are cultured in 1 nM E2 (as is the case for NMC) and is abolished by 2 nM L 686,095-001C002. It is concluded that L 686,095-001C002 is a potent and pure antagonist of pituitary BBN receptors mediating PRL and GH release, whereas psi BBN is a relatively weak antagonist with considerable partial agonist activity.

Gastrin releasing peptide in the rat suprachiasmatic nucleus: an immunohistochemical, chromatographic and radioimmunological study

The localization of gastrin releasing peptide-immunoreactive neurons within the rat suprachiasmatic nucleus was investigated with the indirect peroxidase-antiperoxidase and avidin-biotin techniques. Gastrin releasing peptide-immunoreactive perikarya were found in the ventral part of the suprachiasmatic nucleus, which suggests a direct afferent innervation from the retina or the lateral geniculate, placing the gastrin releasing peptide neurons centrally in the regulation of circadian rhythmicity. Gastrin releasing peptide neurons gave rise to fibers and terminals within the suprachiasmatic nucleus, especially in the ventral part among the immunoreactive and non-immunoreactive neurons. The largest number of gastrin releasing peptide-immunoreactive axons leaving the suprachiasmatic nucleus could be followed in a caudodorsal direction to the subparaventricular zone and the dorsal hypothalamic area. Moreover, minor projections could be traced from the suprachiasmatic nucleus rostrally along the dorsal surface of the optic chiasm to the prechiasmatic area, rostrodorsally into the periventricular area and laterally along the dorsal surface of the optic chiasm and tract. Gel filtration and high performance liquid chromatography profiles of the tissue extracts from the suprachiasmatic area revealed the presence of two GRP-immunoreactive peptides, co-eluting with synthetic gastrin releasing peptide18-27 and gastrin releasing peptide1-27 in almost equivalent concentrations. Gastrin releasing peptide18-27 or gastrin releasing peptide1-27 might therefore play a role in regulation of circadian rhythms in hypothalamic nuclei generated by the suprachiasmatic nucleus.

Regulatory peptides produced in the anterior pituitary

Several peptide families have been detected in the anterior pituitary of several species, including man, and for many of them evidence for local synthesis has been found. Although a paracrine action seems evident for a few, the precise function of most of these peptides remains unknown.