RELEASE OF VASOPRESSIN DURING SUPPRESSION OF THE OESTROUS CYCLE IN THE RAT BY TAMOXIFEN AND HYPEROSMOTIC OR HYPOVOLEMIC CHALLENGES
Abstract
ABSTRACTPrevious studies have shown that surgical ovariectomy of the rat results in a fall
in the plasma visopressin concentrations suggesting that ovarian steroids may influence
hormone release and after surgical ovariectomy the response to hypertonicity was
unaffected but that to hypovolemia was attenuated. To determine whether a similar fall is
observed on suppression of the oestrous cycle, vasopressin concentrations were monitored
after treatment with the antiestrogen preparation tamoxifen. Treatment with tamoxifen 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 tamoxifen ovarectomized rats
during extracellular fluid hypertonicity produced by Intra-peritoneal (i.p.) injection of
hypertonic saline and hypovolemia produced by i.p. injection of polyethylene glycol. It was
found that after treatment with tamoxifen, the response to hypertonicity was unaffected but
that to hypovolemia was attenuated. Hence tamoxifen is a potent anti-estrogen drug, and
tamoxifen ovariectomized rats behaved in the same manner as surgically ovariectomized
rats.
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