Vasopressin Release in Male and Female Rats: Effects of Gonadectomy and Treatment with Gonadal Steroid Hormones*

We have found, in normal Wistar rats 10-11 weeks old, that the plasma vasopressin concentration (PADH) and the 24-h urinary excretion of vasopressin (UADHV) were higher in males than in females (P less than 0.01). In rats that were gonadectomized when they were 3 weeks old and studied when they were 10-11 weeks old, PADH and UADHV were reduced in males (P less than 0.01) and increased in females (P less than 0.01 for UADHV; PADH not significant) compared to those in intact males and females, respectively. Treatment of castrated male rats with testosterone tended to increase PADH, but estradiol, progesterone, or a combination of estradiol and progesterone were without effect; UADHV was increased by testosterone (P less than 0.01) and lowered by estradiol plus progesterone (P less than 0.01). In ovariectomized rats, PADH was unaffected by either testosterone or estradiol, but was decreased by progesterone alone (P less than 0.05) or in combination with estradiol (P less than 0.05). In these ovariectomized rats, UADHV was unaffected by testosterone and was decreased by estradiol and progesterone individually or in combination (P less than 0.01). These findings suggest that the gonadal steroid hormones can act either centrally to affect ADH release or peripherally to affect ADH metabolism. Compared to intact male rats, the lower PADH in intact female rats was accompanied by lower urine osmolality and greater urine volume, but further study will be required to appreciate fully the physiological significance of the differing PADH in males and females.