LHRH II

Stimulation of male turkey hypophyses in vitro with chicken (c)LHRH-I, cLHRH-II or porcine (p)LHRH (0.1 mumol/l) using a perifusion technique caused an increase in the release of LH. In this system, cLHRH-II was approximately 2.5-fold more potent than cLHRH-I and pLHRH which were equipotent. The difference was due to a greater amplitude of the response but not to a prolonged action. Hypophyseal desensitization to a subsequent stimulation was induced when the interval between stimulations was 30 min, but did not occur when lengthened to 60 or 120 min. Injection of a single dose of cLHRH-I or -II in vivo at doses of 10 and 0.1 nmol/kg body weight stimulated increases in the plasma concentration of LH and testosterone initiated within 1 or 10 min after injection respectively. As in vitro, cLHRH-II induced greater responses, which were dose-related, than did cLHRH-I. However, this difference could be attributed to a greater potency of cLHRH-II and to a more prolonged action. At the 10 nmol/kg dose, the shape of the LH response to cLHRH-II changed; it consisted of an initial increase during 10 min after injection, followed by a more sustained phase during which LH levels were still increasing between 20 and 60 min after injection. In contrast, after an injection of cLHRH-I at doses of 10 or 0.1 nmol/kg or cLHRH-II at a dose of 0.1 nmol/kg, LH levels were at a peak within 5 min and thereafter declined gradually.(ABSTRACT TRUNCATED AT 250 WORDS)

Modifications of the previously described LHRH antagonists, [Ac-D-Nal(2)1, D-Phe(4Cl)2, D-Trp3, D-Cit6, D-Ala10]LHRH and the corresponding D-Hci6 analogue, have been made to alter the hydrophobicity of the N-terminal acetyl-tripeptide portion. Substitution of D-Trp3 with the less hydrophobic D-Pal(3) had only marginal effects on the antagonistic activities and receptor binding potencies of the D-Cit/D-Hci6 analogues, but it appeared to further improve the toxicity lowering effect of D-Cit/D-Hci6 substitution. Antagonists containing D-Pal(3)3 and D-Cit/D-Hci6 residues, i.e. [Ac-D-Nal(2)1, D-Phe(4Cl)2, D-Pal(3)3, D-Cit6, D-Ala10]LHRH (SB-75) and [Ac-D-Nal(2)1, D-Phe(4Cl)2, D-Pal(3)3, D-Hci6, D-Ala10]LHRH (SB-88), were completely free of the toxic effects, such as cyanosis and respiratory depression leading to death, which have been observed in rats with the D-Trp3, D-Arg6 antagonist and related antagonists. Replacement of the N-acetyl group with the hydrophilic carbamoyl group caused a slight decrease in antagonistic activities, particularly in vitro. Introduction of urethane type acyl group such as methoxycarbonyl (Moc) or t-butoxycarbonyl (Boc) led to analogues that showed LHRH-potentiating effect. The increase in potency induced by these analogues, e.g. [Moc-D-Nal(2)1, D-Phe(4Cl)2, D-Trp3, D-Cit6, D-Ala10]LHRH and [Boc-D-Phe1, D-Phe(4Cl)2, D-Pal(3)3, D-Cit6, D-Ala10]LHRH, was 170-260% and persisted for more than 2 h when studied in a superfused rat pituitary system.

In vertebrate reproductive biology copper can influence peptide and protein function both in the pituitary and in the gonads. In the pituitary, copper binds to the key reproductive peptides gonadotropin-releasing hormone I (GnRH-I) and neurokinin B, to modify their structure and function, and in the male gonads, copper plays a role in testosterone production, sperm morphology and, thus, fertility. In addition to GnRH-I, most vertebrates express a second isoform, GnRH-II. GnRH-II can promote testosterone release in some species and has other non-reproductive roles. The primary sequence of GnRH-II has remained largely invariant over millennia, and it is considered the ancestral GnRH peptide in vertebrates. In this work, we use a range of spectroscopic techniques to show that, like GnRH-I, GnRH-II can bind copper. Phylogenetic analysis shows that the proposed copper-binding ligands are retained in GnRH-II peptides from all vertebrates, suggesting that copper-binding is an ancient feature of GnRH peptides.

Normal ovarian functions are regulated by a wide variety of endocrine hormones, local paracrine and autocrine factors, which functionally interact with each other in a highly coordinated fashion. Recent findings have demonstrated that both forms of gonadotropin-releasing hormone (GnRH-I and GnRH-II) are expressed in various compartments of the human ovary including the granulosa-luteal cells, ovarian surface epithelial cells and ovarian tumors, and their expressions have been shown to be tightly regulated by gonadal steroids and gonadotropins. Functionally, these neuropeptides exert diverse biological effects in the ovary via binding to their cognate receptors, supporting the notion that these peptides act as paracrine and autocrine factors in modulating local ovarian functions. In this review, we will summarize recent literatures regarding the regulation of GnRH-I and GnRH-II gene expressions in the human ovary, and discuss the possible signal transduction mechanisms by which these hormones exert their actions in the gonad. Recent cloning of the second form of the GnRH receptor (GnRH-II receptor) in primates and other vertebrates demonstrated that it was structurally, and thus, functionally distinct from the GnRH-I receptor. Cell proliferation studies showed that GnRH-II inhibited the growth of human ovarian cancer cells that express GnRH-II but not GnRH-I receptor, indicating that the GnRH-II binding sites are functional in these cells. However, it remains unknown if GnRH-II receptor is expressed as a full-length, properly processed and functional gene transcript in humans, and its potential physiological roles such as differential regulation of gonadotropin secretion, neuroendocrine modulation and female sexual behavior await further investigation.