It is known that the oxytocin (vasotocin) response in the domestic hen varies during the period of a single egg cycle with a significant increase in sensitivity as the time of spontaneous oviposition approaches (Gilbert, 1971). In this respect, the avian shell gland is similar to the mammalian uterus.We have reported previously that intrauterine injection of prostaglandins (PG) or essential fatty acids (which may serve as prostaglandin precursors) can induce premature oviposition in the domestic fowl (Hertelendy et al., 1974) and the japanese quail (Hertelendy, 1972(Hertelendy, , 1974. In these studies premature oviposition was induced when there was a hard egg in the uterus, but several hours before the anticipated spontaneous oviposition. The present report is of the response of the domestic fowl to PGE1 at two different stages of the egg cycle, and the effect of route of administration on the efficacy of PGE1 and PGF2\g=a\ in the Japanese quail (Coturnix coturnix japonica) .In addition, we measured plasma progesterone levels in two groups of hens when there was either a soft or hard egg in the uterus in view of the well known inhibitory action of this steroid on the uterus of certain mammals (Reynolds & Allen, 1932;Csapo, 1961). White Leghorn hens were caged singly under a photoperiod of 14 hr light/ 10 hr dark. The time of oviposition was accurately determined by means of an electronic scanning device which recorded the presence of an egg in the cage every 15 min. The presence of a hard or soft egg in the uterus was verified manually. Prostaglandins (Upjohn Co., Kalamazoo, Michigan) were freshly diluted with saline from ethanolic stock solutions ( 1 to 5 mg/ml) and administered as indicated in the tables. Blood was collected from a wing vein into a heparinized syringe just before the injection of PGEj for the induction of oviposition. After centrifugation, the plasma was removed and stored at -20°C until analysis. Plasma progesterone was determined by radioimmunoassay developed for the estimation of progesterone in fowl plasma (Furr, 1973). Our results using this procedure are in good agreement with values reported by Furr (1973) and Furr et al. (1973).Japanese quail were maintained and the stage of egg formation at the time of premature oviposition was estimated as previously described (Hertelendy, 579
To determine whether synthetic somatostatin originally isolated from sheep hypothalamus can inhibit hormone secretion in the same species, we measured plasma levels of GH, insulin, glucagon, and glucose of normal sheep under a variety of experimental conditions in the presence and absence of somatostatin infusion. An oral dose of 2.5 mg./kg. 3,5-dimethypyrazole increase plasma GH from 10.9 to 376.9 ng. per milliliter, which was suppressed by 50 per cent and 80 per cent with 0.5 and 1 mg. synthetic cyclic somatostatin, respectively. Linear somatostatin (0.5 mg.) was without effect in two animals tested. Propionate (0.5 mmole per kilogram) and arginine (10 gm.) induced a rise in plasma insulin and GH, and glucagon was effectively blocked by cyclic somatostatin (0.5 mg.). Similarly, somatostatin inhibited glucose, and glucagon provoked GH and insulin secretory responses without affecting glucose or FFA levels. Somatostatin had no effect on the disappearance of injected glucagon. Finally, addition of somatostatin to incubation media prevented PGE promoted GH release, and suppressed cyclic AMP accumulation, although to a lesser extent, in sheep anterior pituitary pieces. In view of the large amounts required to suppress stimulated hormone release and the general lack of specificity of somatostatin, it is suggested that this peptide may have a functional role only in the release of hormones of the pituitary, where it could occur in relatively high local concentrations. Its inhibition of extrapituitary hormone secretion may be purely a pharmacologic effect that, nevertheless, suggests an interference with a step common to the secretory process of hormones.
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