Pre- and Postnatal Developmental Changes in Hypothalamic and Pituitary Content of α-Melanocyte-Stimulating Hormone and Somatostatin in the Rat

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Abstract
The developmental pattern of hypothalamic and pituitary somatostatin and α-melanocyte-stimulating hormone (α-MSH) was studied in the rat by radioimmunoassay (RIA). Prenatally hypothalamic somatostatin was low and the first increase in content occurred on day 5 of the postnatal period. Pituitary somatostatin was undetectable prenatally and was first detected on day 6 postnatally. Pituitary somatostatin showed the same development pattern as hypothalamic somatostatin. Whole pituitaries were analyzed from the fetuses and neonates. Analysis of anterior and posterior lobes from adults revealed that all the somatostatin was in the posterior lobe. Therefore, it is believed that the somatostatin found in the glands of the younger animals was in the neural lobe. α-MSH was detected in the fetal hypothalamus as early as day 16, with a marked increase occurring on day 19 prenatally and a further increase on day 10 postnatally. Pituitary α-MSH content, readily detectable on the first day examined, i.e. day 16 of the fetal period, increased throughout development. The effect of α-MSH on the release of growth hormone in vitro from pituitaries of rats of various ages was tested. α-MSH had no effect on growth hormone release.

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