Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 38-amino acid peptide that was first isolated from ovine hypothalamic extracts on the basis of its ability to stimulate cAMP formation in anterior pituitary cells. PACAP belongs to the vasoactive intestinal polypeptide (VIP)-glucagon-growth hormone releasing factor-secretin superfamily. The sequence of PACAP has been remarkably well conserved during the evolution from protochordate to mammals, suggesting that PACAP is involved in the regulation of important biological functions. PACAP is widely distributed in the brain and peripheral organs, notably in the endocrine pancreas, gonads, and respiratory and urogenital tracts. Characterization of the PACAP precursor has revealed the existence of a PACAP-related peptide whose activity remains unknown. Two types of PACAP binding sites have been characterized. Type I binding sites exhibit a high affinity for PACAP and a much lower affinity for VIP whereas type II binding sites have similar affinity for PACAP and VIP. Molecular cloning of PACAP receptors has shown the existence of three distinct receptor subtypes, the PACAP-specific PAC1 receptor, which is coupled to several transduction systems, and the two PACAP/VIP-indifferent VPAC1 and VPAC2 receptors, which are primarily coupled to adenylyl cyclase. PAC1 receptors are particularly abundant in the brain and pituitary and adrenal glands whereas VPAC receptors are expressed mainly in the lung, liver, and testis. The wide distribution of PACAP and PACAP receptors has led to an explosion of studies aimed at determining the pharmacological effects and biological functions of the peptide. This report reviews the current knowledge concerning the multiple actions of PACAP in the central nervous system and in various peripheral organs including the endocrine glands, the airways, and the cardiovascular and immune systems, as well as the different effects of PACAP on a number of tumor cell types.

Pituitary Adenylate Cyclase-Activating Polypeptide and Its Receptors: From Structure to Functions

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 38-amino acid C-terminally alpha-amidated peptide that was first isolated 20 years ago from an ovine hypothalamic extract on the basis of its ability to stimulate cAMP formation in anterior pituitary cells (Miyata et al., 1989. PACAP belongs to the vasoactive intestinal polypeptide (VIP)-secretin-growth hormone-releasing hormone-glucagon superfamily. The sequence of PACAP has been remarkably well conserved during evolution from protochordates to mammals, suggesting that PACAP is involved in the regulation of important biological functions. PACAP is widely distributed in the brain and peripheral organs, notably in the endocrine pancreas, gonads, respiratory and urogenital tracts. Characterization of the PACAP precursor has revealed the existence of a PACAP-related peptide, the activity of which remains unknown. Two types of PACAP binding sites have been characterized: type I binding sites exhibit a high affinity for PACAP and a much lower affinity for VIP, whereas type II binding sites have similar affinity for PACAP and VIP. Molecular cloning of PACAP receptors has shown the existence of three distinct receptor subtypes: the PACAP-specific PAC1-R, which is coupled to several transduction systems, and the PACAP/VIP-indifferent VPAC1-R and VPAC2-R, which are primarily coupled to adenylyl cyclase. PAC1-Rs are particularly abundant in the brain, the pituitary and the adrenal gland, whereas VPAC receptors are expressed mainly in lung, liver, and testis. The development of transgenic animal models and specific PACAP receptor ligands has strongly contributed to deciphering the various actions of PACAP. Consistent with the wide distribution of PACAP and its receptors, the peptide has now been shown to exert a large array of pharmacological effects and biological functions. The present report reviews the current knowledge concerning the pleiotropic actions of PACAP and discusses its possible use for future therapeutic applications.

Pituitary Adenylate Cyclase-Activating Polypeptide and Its Receptors: 20 Years after the Discovery

GREATER THAN 99% of ovarian follicles undergo a degenerative process called atresia during reproductive life. Extending earlier morphological analysis, recent studies have demonstrated that apoptotic cell death is the molecular mechanism underlying follicle atresia. The use of DNA 3′-end-labeling methods allows quantitation and identification of internucleosomal degradation of DNA after gel fractionation as well as in situ analysis of specific cell types undergoing DNA fragmentation in histological sections. Using rats as the experimental model, gonadotropins, epidermal growth factor (EGF)/transforming growth factor-α (TGFα), basic fibroblast growth factor (bFGF), insulin-like growth factor-I (IGF-I), and estrogens have been identified as follicle survival factors capable of suppressing apoptotic DNA fragmentation, whereas androgens, interleukin-6 (IL-6), and GnRH are potential atretogenic factors. This review summarizes the historical background of studies on follicle atresia and selection as well as rec...

Ovarian Follicle Atresia: A Hormonally Controlled Apoptotic Process*

THE TONIC and cyclic secretion of gonadotropins is mediated by the hypothalamic production of gonadotropin releasing hormone (GnRH). The direct assessment of hypothalamic function has been hampered by the absence of reliable methods for the measurement of GnRH production and secretion. Endogenous hypothalamic GnRH probably never reaches the general circulation in sufficiently high concentration to be measured by RIA (1–5), since the pituitary gland has the capacity to metabolize the majority of the peptide secreted into the hypothalamo-hypophyseal portal circulation (6–10). Attempts to determine the rate and amplitude of GnRH secretion have shown that GnRH concentrations in hypophyseal stalk plasma fluctuate between 20 and 800 pM (11–14). Such studies have revealed that GnRH is released in a pulsatile fashion, although rapid changes in secretion rate cannot be detected during the long period required for sample collection. In addition to modulating the concentration of GnRH in hypophyseal portal plasma (1...

Gonadotropin-Releasing Hormone Receptors: Characterization, Physiological Regulation, and Relationship to Reproductive Function

RESEARCH into the neuroendocrine control of reproduction by gonadotropin-releasing hormone (GnRH) has witnessed a remarkable two decades. From the isolation and chemical characterization of GnRH in 1971 through the awarding of the Nobel Prize to Drs. Serially and Guillemin for these accomplishments shortly thereafter, the translation from basic discovery to clinical usefulness has been swift. Food and Drug Administration approvals of GnRH-agonist analogues for the treatment of prostate cancer, endometriosis, and precocious puberty, as well as the use of natural GnRH to induce ovulation, are examples of the clinical usefulness of these fundamental observations. Numerous clinical therapies designed to stimulate . . .

https://www.nejm.org/doi/pdf/10.1056/NEJM199101103240205?listPDF=true

Gonadotropin-releasing hormone and its analogues.

CALCIUM fulfills the requirements of an intracellular mediator for gonadotropin-releasing hormone (GnRH; pyro-Glu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-GIU-NH2)-stimulated gonadotropin release from the pituitary (1). Evidence from our laboratory and others now suggests that GnRH action may be divided into three sequential steps: 1) interaction of GnRH with a specific plasma membrane receptor; 2) mobilization of ionic calcium (Ca2+); and 3) expulsion of the contents of the gonadotropin secretory granule to the extracellular space. At present, considerable work remains to be done regarding the mechanism of Ca2+ mobilization in response to GnRH and its precise locus of action. This review describes experiments that led to the development of this model and summarizes recent progress. A. Introduction Early studies with hemipituitaries and pituitary slices (2) suggested that the ionic makeup of the incubation medium, especially with regard to Ca2+, influenced the release of pituitary hormones. These studies relied up...

Gonadotropin-Releasing Hormone Action in the Pituitary: A Three Step Mechanism*

Binding of gonadotropin releasing hormone agonist to rat ovarian granulosa cells.

The calcium requirement in GnRH-stimulated LH release is not mediated through a specific action on receptor binding.

The subcellular localization of GnRH receptors in weanling rat anterior pituitary and ovarian tissue was determined by radioligand binding in biochemically defined fractions prepared by differential and density centrifugation. Morphological identification of membrane organelles or fragments, visualized by electron microscopy, confirmed the biochemical characterization. The greatest amount of specific ligand binding in both tissues was measured in the crude membrane fraction, while small amounts were detected in other fractions. The distribution of pituitary binding sites in sucrose gradient subfractionation of crude membranes correlated with the distribution of plasma membrane (assessed by 5′-nucleotidase activity and electron microscopy), but not that of secretory granules (identified by immunoreactive LH) or lysosomes (acid phosphatase activity). These data suggest that the GnRH-binding sites detected by radioligand binding assay in pituitaries of rats not previously exposed to GnRH are localized almost...

Jan Marian

Papers

Gonadotropin-Releasing Hormone Action in the Pituitary: A Three Step Mechanism*

Binding of gonadotropin releasing hormone agonist to rat ovarian granulosa cells.

The calcium requirement in GnRH-stimulated LH release is not mediated through a specific action on receptor binding.

Subcellular localization of the receptor for gonadotropin-releasing hormone in pituitary and ovarian tissue.

Evidence for calcium mediation of gonadotropin releasing hormone action in the pituitary