The Effects of Adrenalectomy and Glucocorticoid Replacement on Vasopressin and Vasopressin-Neurophysin in the Zona Externa of the Median Eminence of the Rat

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Abstract
Adrenal regulation of the vasopressin-containing fibers to the portal capillary system in the zona externa of the median eminence was studied in the rat. Tissue sections of the hypothalamus were examined by immunoperoxidase technique and light microscopy using antisera to oxytocin and arginine vasopressin, and an antiserum which reacts with all rat neurophysins. These peptides were localized in the intact normal rat and after adrenalectomy, glucocorticoid replacement with dexamethasone, and after dehydration. The effect of adrenalectomy was also examined in the homozygous Brattleboro rat with diabetes insipidus (DI rat) which lacks arginine vasopressin and, arginine vasopressin-neurophysin. In the zona externa of the normal rat a small number of arginine vasopressin and neurophysin-containing fibers, and an occasional one containing oxytocin were traced to the portal capillary bed. The zona externa of the unoperated DI rat contained only an occasional neurophysin- and oxytocin-reactive fiber. In the normal rat, 5 and 21 days after adrenalectomy there was a marked increase in the immunostaining of neurophysin and vasopressin fibers of the zona externa and no change in oxytocin. In the DI rat there was no difference in oxytocin or neurophysin in the zona externa after adrenalectomy. Dexamethasone treatment suppressed the increase in neurophysin or vasopressin seen after adrenalectomy in the normal rat. Dehydration for 5 days had no effect on immunostaining in the zona externa. The data suggest that vasopressin and its associated neurophysin are stimulated by adrenalectomy, and that their content in pathways to the portal capillaries is regulated by glucocorticoids.