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

Abstract

In normal Wistar rats 10-11 wk old, the plasma vasopressin concentration (PADH) and the 24-h urinary excretion of vasopressin (UADHV) were higher in males than in females (P < 0.01). In rats that were gonadectomized when they were 3 wk old and studied when they were 10-11 wk old, PADH and UADHV were reduced in males (P < 0.01) and increased in females (P < 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 < 0.01) and lowered by estradiol plus progesterone (P < 0.01). In ovariectomized rats, PADH was unaffected by either testosterone or estradiol, but was decreased by progesterone alone (P < 0.05) or in combination with estradiol (P < 0.05). In these ovariectomized rats, UADHV was unaffected by testosterone and was decreased by estradiol and progesterone individually or in combination (P < 0.01). The gonadal steroid hormones can act either centrally to affect ADH [vasopressin] release or peripherally to affect ADH metabolism. Compared to intact male rats, the lower PADH in intact female rats were 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.