Adrenal Steroid Inhibition of the Vasopressin-Neurophysin Neurosecretory System to the Median Eminence of the Rat

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Abstract
Neurophysin and vasopressin-containing terminals in the zona externa of the median eminence (ZE) show a large increase in immunoreactive peptide following adrenalectomy which can be prevented by dexamethasone replacement therapy. The present study was undertaken to determine the effectiveness of a glucocorticoid (corticosterone; CS) and a mineralocorticoid (deoxycorticosterone; DOC) in exerting negative feedback on this system. Animals were adrenalectomized and implanted with various sized pellets of either steroid or cholesterol. The amount of neurophysin-immunoreactivity in the ZE 2 wk after adrenalectomy was estimated on a 0-4 rank scale independently by 3 observers. The data were analyzed by the X2 statistic. Low doses of CS (50 mg) reduced the amount of staining in comparison to cholesterol-replaced animals by approximately 50%. The ZE of animals receiving higher doses (100-200 mg) were identical to those of intact animals. DOC, however, at the 50 or 100 mg level produced only a slight inhibition of the response to adrenalectomy. Larger pellets (150-200 mg) did not result in a level of ZE staining as low as for intact animals. These findings suggest that the vasopressin neurosecretory system to the ZE is regulated by glucocorticoids.