Luteinizing hormone and gonadal steroid levels during the menstrual cycle of orangutans.

Serum luteinizing hormone (LH), progesterone, 17 beta-estradiol, and testosterone were measured during a single cycle each of five female orangutans, and urinary LH was measured in four of those cycles. Midcycle peaks in LH and luteal phase elevations in progesterone (5.7-13.8 ng/ml) suggested that the cycles were ovulatory. 17 beta-Estradiol was elevated at midcycle (163-318 pg/ml) and during the luteal phase (56-136 pg/ml) and testosterone was also elevated at midcycle (143-580 pg/ml). These hormone patterns in the orangutans closely resemble those for chimpanzees, gorillas, and human females.