Changes in Serum Progesterone, Estradiol-17β, Luteinizing Hormone and Prolactin in Lactating and Non-lactating Japanese Black Bears (Ursus thibetanus japonicus)

Abstract

The concentrations of progesterone (P4), estradiol-17β (E2), luteinizing hormone (LH) and prolactin (PRL) in serum obtained from 9 captive female Japanese black bears, Ursus thibetanus japonicus, (7 lactating and 2 non-lactating) were obtained by a heterologous radioimmunoassay to clarify hormonal profiles during the pre- and post-parturition and lactation periods. The present study provides the first evidence to validate LH and PRL radioimmunoassay in bear sera by using the canine LH and PRL and the antibody to these hormones. In 7 bears which gave birth and lactated, serum ?4 concentrations were high during prepartum phases in December and January but fell rapidly after parturition in February (p<0.05; comparison of pre- and post-parturient phases). Serum £2 and LH concentrations did not change significantly throughout pre- and post-parturition. Serum PRL concentrations increased significantly after parturition in February (p<0.05; comparison of preand post-parturient phases) and exceeded 10 ng/ml in all lactating bears from Days 41∼60 after parturition in March. On the other hand, in 2 bears which did not produce cubs, serum P4 concentrations were high in December and January and decreased after February. Serum E2 concentrations were relatively low between December and February but increased in March. Serum LH concentrations were relatively high in December and remained low throughout January to April, whereas PRL concentrations increased gradually after February, but were below 10 ng/ml. These results suggest that a rapid decline in P4 and a marked increase in PRL occurred in association with events such as parturition and lactation, but there is no clear evidence that changes in serum E2 and LH concentrations are associated with parturition and lactation.