Reduced preprosomatostatin messenger ribonucleic acid in the periventricular nucleus of hypophysectomized rats determined by quantitative in situ hybridization.

Physiological evidence suggests that somatostatin (SS) inhibits the release of GH and TSH from the anterior pituitary and that elements of these two systems may feed back to regulate hypothalamic SS release or synthesis. Hypophysectomy reduces hypothalamic SS content in rats, an effect that may be attributable to a change in SS synthesis, storage, or release. We tested the hypothesis that hypophysectomy would reduce hypothalamic SS synthetic capacity, as reflected by a reduction in SS mRNA levels. Using in situ hybridization and a computerized image analysis system, we measured SS mRNA signal levels over individual cells in the periventricular nucleus of hypophysectomized and intact male rats. SS mRNA signal levels were 45.1% lower in hypophysectomized rats compared to those in intact controls (P less than 0.05). These results demonstrate that SS synthetic capacity in the periventricular nucleus is influenced by the presence of the pituitary, and this system may represent one example of the regulation of central nervous system neuropeptide gene expression by a circulating pituitary hormone.