Serum progesterone and estrogens in elephants.
Serum progesterone and estrogens were measured by radioimmunoassay in the serum of immature, mature, and pregnant African and Asian elephants. Progesterone was elevated from 26 to 215 pg/ml in nonpregnant animals and up to 480 pg/ml in late pregnancy animals. No relationship to reproductive state was evident for the low levels of estrogens which ranged from 9 to 37 pg/ml.