Luteinising hormone-releasing and anti-fertility properties of a glucagon-selective somatostatin analogue.

The hypothalamic tetradecapeptide, somatostatin (SRIF), inhibits the secretion of growth hormone (GH) and numerous other hormones, including insulin and glucagon. Attempts to use SRIF as an adjunct in the treatment of diabetes mellitus met with limited success due to its short biological half-life and the undesirable diabetogenic activity of its insulin-lowering properties. Efforts at synthesis have yielded SRIF derivatives with prolonged GH-lowering activity which did not suppress glucagon or had equivalent insulin-inhibiting activity as well as several short-acting compounds with the appropriate glucagon specificity. A dodecapeptide analogue [des-Ala, Gly] His-D-Trp-SRIF (Wy-41, 747) has been identified that combines selective inhibition of GH and glucagon release with prolonged activity. However, in routine pharmacological tests chronic treatment of mature rats with Wy-41, 747 produced anti-reproductive effects resembling those described for luteinising hormone (LH)-releasing hormone (RH) and its agonists. We report here that Wy-41, 747, unlike SRIF and other of its analogues tested, releases LH, induces ovulation and inhibits pregnancy when administered before or after implantation; these properties are traditionally associated with the separate LH-releasing class of peptides.

Effect of a long acting glucagon selective somatostatin analogue on plasma glucose, insulin and glucagon levels in the anaesthetized rat during arginine infusion.

The effects of somatostatin and a long acting, glucagon selective somatostatin analog (des-Ala1Gly2[His4,5-D-TrP8]-somatostatin) used studied during arginine tolerance tests in normal anaesthetized rats. Arginine infusion in control animals resulted in a rapid increase in plasma insulin and glucagon, and an increase of 15 +/- 5 mg/dl in plasma glucose. Somatostatin infusion (1 mg/kg/h) resulted in suppression of basal insulin secretion and a decrease in arginine-induced insulin and glucagon release. Glucose levels increased rapidly during the combined arginine-somatostatin infusion reaching a peak of 72 +/- 10 mg/dl above basal levels. Similar results were obtained when somatostatin was injected SC (1 mg/kg) at times 0, 15, 30, and 45 minutes (arginine infused from 30-60 minutes). A single injection (1 mg/kg) of the long-acting somatostatin analogue resulted in significant inhibition of basal insulin and glucagon release; during arginine infusion glucagon levels rose only slightly, the insulin response was, however, nearly normal, and only a small arginine-induced increase in glucose levels was observed. Carbohydrate absorption was not influenced by either somatostatin or the analogue.

Agonist (ovulation induction) and post-coital contraceptive properties of [D-Ala6] and [D-Trp6]-LHRH series.

Seven derivatives of LH-RH, representing the [D-Ala6] or [D-Trp6] series, with or without a Fujino modification, were evaluated for ovulation-inducing (agonist and post-coital contraceptive activity in rats. Six of these analogues had a high degree of agonist and pregnancy-terminating potency. In general, several modifications can result in a particular series of composite molecules that possess a biologic potency greater than each of its predecessors; this correlation of structure with activity was more consistent in the [D-Ala6]-series than in the [D-Trp6]-series. The relationship between structural modifications, resistance to enzyme degradation (based on literature reports) and increased biologic potency is discussed.

The influence of glycyl residues on the flexibility of peptide hormones in solution. A 13C-nuclear-magnetic-resonance study of luteinizing hormone-releasing hormone (luliberin) and its des-glycinamide10 N-ethylamide analog.

13C nuclear magnetic resonance spectroscopy in used to gain information on the flexibility of the backbone in peptide hormones and peptide hormone analogs. 13C spin-lattice relaxation times (T1) were measured on luliberin, the luteinizing-hormone-releasing hormone and des(Gly-NH2)10-luliberin-N-ethylamide in aqueous solution at 25.2 and 67.9 MHz at temperatures of 32 degrees, 40 degrees and 55 degrees C. The 13C spin-lattice relaxation times indicate increased flexibility of the peptide backbone in the immediate environment of glycyl residues in luliberin (less than Glu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2) and the hormone analog des(Gly-NH2)10-luliberin-N-ethylamide (less than Glu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-NH-CH2CH3) in aqueous solutions. 13 C NMR spectroscopy is shown to be a sensitive technique for monitoring the time-averaged conformational flexibility of peptides in solution. Activation energies (Ea) of about 25 kJ/mol were obtained for rotational reorientation of non-terminal alpha-carbons in the peptide backbone. Rotation of methyl groups was characterized by an Ea of 9.6 kJ/mol whereas reorientation of the N-terminal pyroglutamyl residue showed an Ea value of 14.6 kJ/mol. The Ea values of individual carbons in the side-chains of prolyl, arginyl and leucyl residues in the peptides were similar to those obtained for the alpha-carbon of the same amino acid residue in the peptide backbone of the hormones.

Postcoital contraceptive effects of agonist analogs of luteinizing hormone-releasing hormone.

Various analogs of synthetic hypothalamic luteinizing hormone-releasing hormone (LH-RH) were evaluated for agonistic (ovulation-inducing), postcoital contraceptive, and direct uterotrophic activities. All analogs showing agonistic activity also possessed the ability to terminate pregnancy, as did LH-RH; there appeared to be a direct relationship between agonistic and postcoital potency and activity. The highly potent and active LH-RH agonist, D-[Ala]6-des-[Gly]10-pro9-ethylamide-LH-RH, proved to be the most potent and active postcoital preimplantational and postimplantational antifertility agent. In contrast to LH-RH, none of the analogs tested in the hypophysectomized animal produced a uterotrophic effect, revealing a selective extrapituitary effect of the parent hormone. The collective data demonstrate that peptides derived from LH-RH and bearing agonistic properties can terminate pregnancy postcoitally, via disruption of the pituitary-ovarian reproductive complex. Possible mechanisms are discussed, and the use of members of this neurohormonal class as potential profertility agents should be weighed with caution.

Structure activity studies on somatostatin.

Seven synthetic analogues of somatostatin helped clarify structural requirements for suppression of growth hormone secretion in rats. Size of the ring is not critical; deletions of serine-13, lysine-4 or asparagine-5 result in peptides which retain an appreciable fraction of the activity. The analogue des-Ala1, Gly2, Asn5-somatostatin lowers plasma growth hormone and insulin levels without affecting plasma glucagon levels significantly.

Luteinizing hormone-releasing hormone. Antiovulatory activity of analogs substituted in positions 2 and 6.

Ten analogs of luteinizing hormone-releasing hormone (LH-RH) substituted in position 2 with D-amino acids and at 6 with either a D-amino acid or a nonasymmetric amino acid were synthesized by solid-phase methodology and assayed for antiovulatory activity. [D-Phe2]-LH-RH substituted in the 6 position with D-Ala, D-Leu, D-Arg, D-(Ph)Gly, D-Phe, or 2-Me-Ala possessed varying degrees of antiovulatory activity. [D-p-F-Phe2-D-Ala6]-LH-RH was one of the most active antiovulatory compounds, while the [D-p-Cl-Phe2-D-Ala6]-LH-RH analog was devoid of activity at a comparable dose.