The effects of ethanol administration during a preovulatory period on both serum and pituitary gonadotrophin concentrations were studied in female rats. The animals were injected with 2 g/kg of ethanol (30v/v, in saline solution) at 18:00 hr of diestrous 2. Hormonal levels were measured by RIA at different times during the estrous cycle, especially during the proestrus day. The preovulatory LH surge was inhibited using ethanol. Serum LH levels decreased between 16.00 and 20.00 hr of proestrus (P<0.01). The levels of FSH in serum were slightly depressed by ethanol between 12.00 and 17.00 hr of proestrus (P<0.05 with respect to the control set), but the values during the proestrus surge (18.00–20.00 hr) were unaffected. Ethanol augmented pituitary hormonal content during the periods in which serum hormonal levels decreased (P<0.05 with respect to the control set) but it did not affect gonadotrophins synthesis. The increase in pituitary gonadotrophin concentrations induced by ethanol during the proestrus day is due to the accumulation of the hormone which was not released before. The preovulatory LH surge was re-established in the next cycle (5th day after treatment). These effects of ethanol on gonadotrophin levels could explain the previously observed anovulatory effects induced by ethanol administration in diestrou
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