Luteinizing hormone-releasing hormone in the human fetal brain

Hypothalamic and other brain tissues were obtained after death from human fetuses aborted by hysterectomy at various conceptional ages. Immunoreactive luteinizing hormone-releasing hormone (LHRH) activity in tissue extracts was determined by a double-antibody radioimmunoassay method. Fetal hypothalamic and cortical tissue at 5 weeks after conception showed no assayable LHRH activity. At 6 weeks, immunoreactive LHRH was detectable in extracts of both the hypothalamus and the cortex, and levels appeared to fluctuate with a trend to increase until the 20th week. Two of four fetuses at 13 and 14 weeks' conceptional age had significantly higher LHRH activity in the thalamus than in the rest of the central nervous system. After 16 weeks, LHRH activity was detected in the hypothalamus, thalamus, cerebrum, and cerebellum in decreasing concentrations, respectively. As the age of the fetus progressed from 16 to 20 weeks, the LHRH concentration in the hypothalamus increased significantly, from 1.2 pg/mg to 29.3 pg/mg of wet tissue. LHRH concentrations in specimens of comparable conceptional age that could not be promptly dissected were lower than in those dissected within 30 minutes after the ligation of uterine arteries.