The effects on the pituitary lh levels of norethynodrel (20 μg/rat or approximately 0·1 mg/kg daily) and mestranol (1 μg/rat or approximately 5 μg/kg daily) administered subcutaneously singly or in combination for 10 days to intact female rats have been studied. lh was assayed by the ovarian ascorbic acid depletion method of Parlow (1958). Norethynodrel caused a significant increase in hypophysial lh stores without causing ovarian atrophy or reducing compensatory hypertrophy in unilaterally ovariectomized post-pubertal rats. Mestranol administration, on the other hand, resulted in a significant ovarian atrophy without significant changes in the pituitary lh level, and also resulted in an inhibition of compensatory hypertrophy. The combined treatment resulted in effects essentially similar to those observed in the mestranoltreated group. No evidence for potentiation between the two steroids was obtained.
Data support the conclusion that when the two steroids are administered together in the dosages used, the oestrogenic component is primarily involved in the pituitary lh inhibition.
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