Plasma levels of progesterones (P) and estrogens (E) were monitored in captive dolphins. Females in captivity longer than one year had average plasma levels of P and E of 299 ± 27 pg/ml (n=142) and 20 ± pg/ml (n=60) respectively. Newly captured females had average levels of P and E of 412 ± 286 pg/ml (n=6) and 52 ± 3 pg/ml (n=7), respectively. Pregnant females had mean progesterone values of 369 pg/ml one week after conception to greater than 35,000 pg/ml in the 11th month of pregnancy.

Testosterone levels in males may be indicative of sexual maturity. An immature male had average testosterone levels of 261 pg/ml (n=20), two maturing males had 3752 pg/ml (n=27), and an adult male had an average of 5986 pg/ml (n=10).

Dolphins are considered to be reflex ovulators (coitus induced ovulation). Yet, artificial vaginal stimulation along and in conjunction with pregnant mare serum gonadotropin (PMSG) was not successful.

Hormonal manipulation included the use of PMSG alone and in conjunction with luteinizing releasing factor (LRF). Progesterone were not elevated. However, behavioral observations indicated that sexual activity was reduced within 48 hours after injections. PMSG experiments were then repeated with increased sampling rate (bleeding). Although progesterone was not elevated, LH (luteinizine hormone) was elevated.