RELEASE OF VASOPRESSIN DURING SUPPRESSION OF THE OESTROUS CYCLE IN THE RAT BY TAMOXIFEN AND HYPEROSMOTIC OR HYPOVOLEMIC CHALLENGES
AbstractABSTRACTPrevious studies have shown that surgical ovariectomy of the rat results in a fallin the plasma visopressin concentrations suggesting that ovarian steroids may influencehormone release and after surgical ovariectomy the response to hypertonicity wasunaffected but that to hypovolemia was attenuated. To determine whether a similar fall isobserved on suppression of the oestrous cycle, vasopressin concentrations were monitoredafter treatment with the antiestrogen preparation tamoxifen. Treatment with tamoxifen wasfound to result in a fall in circulating vasopressin concentrations, with little effect on fluidbalance.To determine whether the ovary could influence the vasopressin release in response toknown stimuli, hormone concentrations were measured in tamoxifen ovarectomized ratsduring extracellular fluid hypertonicity produced by Intra-peritoneal (i.p.) injection ofhypertonic saline and hypovolemia produced by i.p. injection of polyethylene glycol. It wasfound that after treatment with tamoxifen, the response to hypertonicity was unaffected butthat to hypovolemia was attenuated. Hence tamoxifen is a potent anti-estrogen drug, andtamoxifen ovariectomized rats behaved in the same manner as surgically ovariectomizedrats.
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