Pituitary response to LHRH in midtrimester pregnancy

The effects of lutenizing hormone releasing hormone (LHRH) on serum luteinizing hormone (LH), follicle stimulating hormone (FSH), prolactin (PRL), thyroid stimulating hormone (TSH), and growth hormone (GH) were studied in 10 women in the second trimester of pregnancy. Serum LH was measured using the LHbeta-RIA, with the anti-betaLH serum being preabsorbed with purified hCG. This assay was unaffected by hCG levels up to 500 IU/ml. Basal serum levels of LH was undetectable and basal FSH levels were low in these 10 women. No release of LH or FSH was observed after administration of 100 microgram of LHRH. However, there was a statistically significant rise in PRL from mean basal levels of 139.9 ng/ml to a mean peak level of 159.0 ng/ml at 30 minutes after LHRH administration. Both TSH and GH displayed small elevations at 15 minutes after LHRH administration; however, these elevations were not significant because of the wide range in responses. The results of this study indicate that gonadotropin release is inhibited during the second trimester of pregnancy. Finally, it appears that pregnancy is a condition in which LHRH administration results in a nonspecific release of several hormones.