Influence of LH/FSH releasing hormone (LRH) on the basal secretion of gonadotrophins in relation to plasma levels of oestradiol, progesterone and prolactin during the post-partum period in lactating and in non-lactating women.

The pituitary responsiveness to LH/FSH releasing hormone (LRH) was studied in the puerperium in lactating and in non-lactating women. The response of both groups of patients to 25 mug LRH iv was tested 8-10 days, 15-17 days, and 29-32 days after a normal delivery at full term. The basal levels of FSH were low during the first 10 days after delivery. A rise was then observed, and about 4 weeks after delivery levels above or in the upper normal range of a normal follicular phase were recorded. The levels were significantly higher in the lactating group. When compared with the normal follicular phase, the relative increase in FSH basal levels was higher than the increase in LH basal levels in both groups of patients. The period of non-responsiveness of the pituitary to LRH was found to be of equal length in the two groups. In both groups the FSH response returned more rapidly than the LH response. About 2 weeks after delivery a reverse pattern of gonadotrophin response to LRH was seen with a FSH response that was greater than the LH response compared with what is generally observed in the various phases of the menstrual cycle in eumenorrhoeic women. This pattern was more pronounced in the lactating group about 4 weeks after delivery. Oestradiol levels were low and roughly equal on the three test occasions in each group, but in the non-lactating group there was a tendency to higher concentrations. Prolactin levels were highest about one week after delivery and then showed a tendency to decrease, and this was more pronounced in the non-lactating group. Progesterone levels were invariably low in both groups.