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.     

Low codon bias and high rates of synonymous substitution in Drosophila hydei and D. melanogaster histone genes

We have evaluated codon usage bias in Drosophila histone genes and have obtained the nucleotide sequence of a 5,161-bp D. hydei histone gene repeat unit. This repeat contains genes for all five histone proteins (H1, H2a, H2b, H3, and H4) and differs from the previously reported one by a second EcoRI site. These D. hydei repeats have been aligned to each other and to the 5.0-kb (i.e., long) and 4.8-kb (i.e., short) histone repeat types from D. melanogaster. In each species, base composition at synonymous sites is similar to the average genomic composition and approaches that in the small intergenic spacers of the histone gene repeats. Accumulation of synonymous changes at synonymous sites after the species diverged is quite high. Both of these features are consistent with the relatively low codon usage bias observed in these genes when compared with other Drosophila genes. Thus, the generalization that abundantly expressed genes in Drosophila have high codon bias and low rates of silent substitution does not hold for the histone genes.      

Action of vasoactive intestinal peptide (VIP) on amphibian adrenocortical function,in vitro

Vasoactive intestinal peptide (VIP) is located in chromaffin cells of the frog adrenal gland and is able to stimulate corticosteroid secretion in amphibians. In the present study we have investigated the possible involvement of prostaglandins, microfilaments and calcium in the mechanism of action of VIP on frog adrenocortical tissue. Rana ridibunda interrenal dice were perifused with amphibian culture medium for more than 10 hours. Corticosterone and aldosterone concentrations were measured in the effluent perifusate using sensitive and specific radioimmunoassay methods. In the presence of indomethacin (5 μM), a specific blocker of prostaglandin biosynthesis, the spontaneous secretion of corticosteroids was markedly reduced (80%) but the stimulatory effect of VIP was not altered. The administration of the microfilament disrupting agent cytochalasin B (50 μM) inhibited both spontaneous and VIP-induced corticosteroid secretion. In the absence of calcium, the spontaneous level of corticosteroid was reduced to about 60% but VIP was still able to stimulate corticosteroid secretion. From these data we conclude that the integrity of the cytoskeleton is required for the secretory response of adrenocortical cells to VIP, whereas neither prostaglandins nor calcium are involved in VIP-induced adrenocortical stimulation.     

Evidence for conversion of N-Tyr-MIF-1 into MIF-1 by a specific brain aminopeptidase

N-Tyr-MIF-1 (Tyr-Pro-Leu-Gly·NH₂), an immunoreactive neuropeptide exhibiting saturable high affinity binding in rat brain was found to be converted into MIF-1 (Pro-Leu-Gly·NH₂) by a specific brain aminopeptidase present in rat brain homogenates or cytosol, but with low activity associated with synaptosomal plasma membranes and microsomes. Conversion occurred at a rate of 16 μmol per g w/wt per h and was unaffected by puromycin but inhibited by bestatin (I₅₀, 5 × 10^?5 M). Aminopeptidases purified from cytosolic fractions of rat brain (arylamidase), mouse brain (Mn²⁺-activated aminopeptidase) or porcine kidney (leucine aminopeptidase) were inactive towards N-Tyr-MIF-1 but degraded MIF-1 with release of Leu-Gly·NH₂ as detected by RP-HPLC procedures. Morphiceptin (Tyr-Pro-Phe-Pro·NH₂), a μ opioid agonist, also acted as a substrate for the N-Tyr-MIF-1 converting enzyme with cleavage of the Tyr-Pro bond. These tetrapeptides, but not MIF-1 or its N-blocked analogs, were degraded in vitro by a metalloendopeptidase purified from kidney membranes. Since dipeptide products were not detected for crude extracts, a significant role for brain metalloendopeptidase on turnover can be excluded. Thus the results point to the presence of a specific (X-Pro-degrading) aminopeptidase in brain cytosol as an enzyme responsible for converting N-Tyr-MIF-1 and inactivating morphiceptin.     

Growth hormone releasing factor: comparison of two analogues and demonstration of hypothalamic defect in growth hormone release after radiotherapy.

Human pancreatic growth hormone releasing factor (hpGHRF(1-40] stimulates the release of growth hormone in normal subjects and some patients with growth hormone deficiency. A study comparing the shorter chain amidated analogue hpGHRF(1-29) with an equivalent dose of hpGHRF(1-40) in seven normal subjects showed no significant difference in growth hormone response between the two preparations. Six patients with prolactinomas were also tested; these patients had received megavoltage radiotherapy previously but had developed growth hormone deficiency as shown by insulin induced hypoglycaemia. In all six patients 200 micrograms hpGHRF(1-40) or hpGHRF(1-29)NH2 produced an increase in the serum growth hormone concentration. These data suggest that hpGHRF(1-29)NH2 may be useful for testing the readily releasable pool of growth hormone in the pituitary and that cases of hypothalamo-pituitary irradiation resulting in growth hormone deficiency may be due to failure of synthesis or delivery of endogenous GHRF from the hypothalamus to pituitary cells.     

Endogenous opiates: 1979

Since the discovery in 1971 of opiate receptors and later of the opiate-like peptides, there has been widespread interest in determining their exact localization, number and kinds, nature, and physiological and pharmacological functions. Between 1971 and 1978, vast amounts of research investigated these problem areas, but in 1979 alone the literature on the opiate peptides nearly doubled. This review is the second of an annual series and summarizes the highlights of the work published during 1979.     

Systemic injections of gastro-intestinal peptides alter behavior in rats

Twenty-four male albino rats were given daily intraperitoneal injections of vasoactive intestinal polypeptide (VIP), motilin, human gastrin I (1–17) or the diluent control vehicle at a dose of 100 μg/kg for four consecutive days and food intake, water intake, body weight, and running wheel activity were determined every 24 hours. Animals injected with motilin or human gastrin I (1–17) exhibited decreased food intake relative to those injected with VIP or diluent, which did not differ from each other, although food intake increased reliably over days. The mean water consumption followed the same pattern as that of food intake. As expected from the above results, VIP produced weight gains as compared with rats injected with motilin or gastrin but not reliably more than after diluent. A reliable effect of trials for weight gain was the greatest on day three. Running wheel activity was not affected by injections of human gastrin I (1–17), motilin, or diluent but was reliably decreased by VIP. No significant differences existed across days. Although the results indicate that GI peptides may affect behavior when injected systemically and that like other peptides they have multiple effects, caution is urged in the interpretation of behavioral results at this time.