Bioactivity of growth hormone releasing hormone (1-29) analogues after SC injection in man

The bioactivity of growth hormone releasing hormone 1-29 [GHRH(1-29)NH2] has been compared with that of an agonist analogue [Ac-D-Tyr1,D-Ala2]-GHRH(1-29)NH2, in normal male volunteers. Using a submaximal dose of 3 micrograms/kg administered subcutaneously, peak growth hormone (GH) response and area under the GH curve were similar for the native and agonist analogue. In addition, no significant differences were found in peak GHRH(1-29) immunoreactivity, area under the GHRH(1-29) curves or plasma disappearance rates of the two peptides. The results suggest that, in keeping with the relative activities of other "superactive" analogues tested so far, the greatly enhanced activity of [Ac-D-Tyr1,D-Ala2]-GHRH(1-29)NH2 observed in the rat is not found in humans. It is possible that this species difference is due to differences in the interaction of GHRH peptides with the rat and the human somatotroph GHRH receptor.     

In vitro and in vivo inhibition of human small cell lung carcinoma (NCI-H69) growth by a somatostatin analogue

An endocrinologically-potent octapeptide analogue of somatostatin (SRIF), 3-(2-naphthyl)-D-Ala-Cys-Tyr-D-Trp-Lys-Val-Cys-Thr-NH2 (BIM-23014 C), was examined for its ability to inhibit the in vitro and in vivo growth of the human small cell lung carcinoma (SCLC) line, NCI-H69. When cultured cells were implanted into athymic nude mice, treatment (500 micrograms/injection, twice daily) resulted in a prolongation of lag time for the appearance of measurable tumors, and there was a marked inhibition of the growth rate. Indeed, peptide injection in the region of the tumor resulted in a complete regression of the NCI-H69 tumors. Withdrawal of BIM-23014 C treatment resulted in an acceleration of tumor growth indicating an antiproliferative rather the oncolytic action. A similar inhibition of tumor growth was also observed when solid tumors obtained from the first implantation were used as the donor tissues. In cell culture, the proliferation in the presence of a low concentration (10nM) of BIM-23104 C was also significantly retarded suggesting a direct mechanism of action.     

Octapeptide analogs of somatostatin exhibiting greatly enhanced in vivo and in vitro inhibition of growth hormone secretion in the rat

Analogs of a superactive somatostatin (SRIF) octapeptide (code named SMS 201-995 (1)) were synthesized using solid-phase synthetic methodology and assayed for their ability to inhibit growth hormone release from cultured rat anterior pituitary cells and in sodium pentobarbital-anesthetized rats. One analog: (Formula: see text) exhibited greatly enhanced in vitro inhibitory activity (greater than 1,000x) relative to both the parent octapeptide molecule and to the 14 amino acid SRIF molecule. This analog which was also very potent in vivo contains a tyrosine residue and, given its high in vitro activity, may be of investigative importance as a radioiodinated ligand in receptor assays. An octapeptide retro-inverso analog also exhibited significant SRIF-like activity. Several very low activity octapeptide analogs were synthesized and were found to be devoid of SRIF-antagonist activity. A dodecapeptide analog previously shown to be superactive in vivo also demonstrated high in vitro activity.     

Administration of human pancreatic growth hormone-releasing factor (GRF) analogs enhances responsiveness of cultured rat pituitary cells to GRF

The aim of this study was to investigate whether anterior pituitary responsiveness to human pancreatic growth hormone-releasing factor containing 29 amino acids (GRF-29) can be modulated by GRF-29 itself. Male rats were injected (sc) daily for 3 days with 50 ug of GRF-29, or were treated twice daily for 14 days with 5 ug of [D-Ala-2]-GRF-29 (a potent GRF agonist). Control animals were injected with saline. After the last injection, pituitaries were removed, dispersed, cultured for 96 h and then challenged with either GRF-29 or [D-Trp-6]-LHRH (a LHRH agonist). Cultured cells from analog-treated rats were more responsive to GRF-29 stimulation than were cells obtained from controls. In contrast, neither treatment altered the response to [D-Trp-6]-LHRH. These studies indicate that periodic administration of GRF analogs can increase hypophyseal GRF responsiveness. Such control may be an important component in the physiological regulation of GH secretion and has important implications for potential therapeutic uses of GRF analogs.     

Effects of secretin and gastric inhibitory polypeptide on human pancreatic growth hormone-releasing factor(1-40)-stimulated growth hormone levels in the rat

Synthetic human pancreatic growth hormone-releasing factor containing 40 amino acids ([hpGRF (1-40)]-OH) significantly stimulated plasma growth hormone (GH) levels in both sodium pentobarbital and urethane anesthetized rats. Synthetic secretin, gastric inhibitory polypeptide (GIP), and glucagon significantly decreased plasma GH levels while synthetic vasoactive intestinal peptide (VIP) had no effect. Secretin and GIP also altered the in vivo plasma GH response to [hpGRF(1-40)]-OH. Whether this effect is the result of an interaction at the pituitary level or is due to an extra-pituitary effect of secretin and GIP awaits further study.     

Solid phase synthesis of growth hormone-release inhibiting factor

The growth hormone-release inhibiting factor (GH-RIF) tetradecapeptide

, was prepared by the cyclization of a linear, disulfhydryl peptide intermediate by treatment with potassium ferricyanide. The linear peptide was synthesized by an automated solid-phase technique. The cyclic material inhibited the secretion of radioimmunoassayable growth hormone $\text{in vitro}$ at doses as low as 0.1 μg. A high molecular weight compound formed during the cyclization reaction and believed to be predominantly dimer also possessed considerable inhibitory activity.     

Characterization of somatostatin receptor subtypes controlling rat gastric acid and pancreatic amylase release

An examination of the binding characteristics of a large number of somatostatin analogues with respect to the five known somatostatin receptor subtypes has recently resulted in the discovery of several peptides with some selectivity for types 2, 3, and 4 and little affinity for type 1 or 5 receptor. A panel of these peptides has thus far implicated type 2 receptors in the inhibition of release of pituitary growth hormone and type 4 receptors in inhibiting pancreatic insulin release. In the present article, we have examined the inhibitory effects of the same group of peptides on in vivo rat gastric acid and pancreatic amylase release and binding to rat pancreatic acinar cells. The type 2-selective ligand NC-8–12 was a potent inhibitor of gastric acid release (EC₅₀s in the 1.5 nM region) whereas the type 4-selective ligand, DC-23–99, elicited little response. However, some involvement of type 3 receptors could not be ruled out because the type 3-selective analoueg, DC-25–20, exhibited inhibitory effects at higher dose levels (EC₅₀ > 10 nM). Conversely, the type 4 analogue was a potent inhibitor of amylase release (EC₅₀ 1.1 nM) whereas the type 3 analogue had no significant effects at doses tested. DC-23–99 also bound with high affinity to rat acinar cells (EC₅₀ 3.8 nM), whereas DC-25-20 exhibited more than 10-fold less affinity. Thus, these two major biological functions of somatostatin appear to be controlled by different receptors and, furthermore, effects on both endocrine and exocrine pancreas appear to be type 4 receptor mediated.     

Sperm concentration influences fertilization and male pronuclear formation in vitro in pigs

To study the effect of sperm concentration on the results of pig in vitro fertilization (IVF), 313 oocytes recovered from oviducts of prepubertal gilts after induction of ovulation were used. After capacitation, the number of live spermatozoa in the fertilization dishes was adjusted to 3 x 10(5), 6 x 10(5) and 12 x 10(5) cell/ml. After 4 hours of co-culture in TCM-199, the oocytes were pippeted to remove cumulus cells and the excess spermatozoa around the zona pellucida, and were transferred to fresh TCM-199 for another 12 14 hours . The results showed that 6 x 10(5) spermatozoa/ml is the optimum concentration for this system; the percentage of fertilized ova (71.6%) was not different from the best (76.8%), that was obtained with the highest concentration, and the percentage of monospermy (62.3%) was not different from the best (68.1%), that was obtained with the lowest concentration. The percentage of spermatozoa that reached the pronuclear stage increased while sperm concentration was decreased. The percentage of spermatozoa at the decondensed stage was decreased when the sperm concentration increased.