The influence of reproductive status on vasopressin release in the rat

It has been shown that surgical ovariectomy of the rat results in a fall in plasma vasopressin concentrations suggesting that ovarian steroids may influence hormone release. To determine whether a similar fall is found on suppression of the oestrous cycle, vasopressin concentrations were monitored after treatment with the antioestrogen preparation tamoxifen or a long-acting analogue of LH-releasing hormone (LHRH) which suppresses ovarian function. Treatment with either agent was found to result in a fall in circulating vasopressin concentrations, with little effect on fluid balance. To determine whether the ovary could influence the vasopressin release in response to known stimuli, hormone concentrations were measured in ovariectomized animals during extracellular fluid hypertonicity produced by an i.p. injection of hypertonic saline and hypovolaemia produced by an i.p. injection of polyethylene glycol. It was found that after ovariectomy or treatment with tamoxifen, the response to hypertonicity was unaffected but that to hypovolaemia was attenuated. Treatment with LHRH affected the response to both hypovolaemia and hypertonicity.