The influence of exogenous oestradiol benzoate on the pituitary responsiveness to LHRH during the puerperium in women.

The FSH and LH compared to 25 micrograms LHRH was measured in lactating women and the results compared to a similar group in whom lactation was suppressed by administration of bromocriptine shortly after delivery. The response was also measured in both groups after "challenge" with oestradiol benzoate. In lactating women the FSH response to LHRH was diminished following the oestradiol challenge, as compared with that in unchallenged women. At the same time the LH responses were low in both circumstances, indicating a negative feedback effect of oestradiol. However, the oestradiol challenge resulted in a significantly increased response of FSH and LH to LHRH in bromocriptine-treated puerperal women, i.e. a positive feedback effect of oestradiol. We concluded that this and previous experiments favour the hypothesis that the lactational amenorrhoea during hyperprolactinaemia is caused by hypothalamic changes due to a predominance of the negative feedback system.