SERUM PROGESTERONE, ESTRADIOL, LUTEINIZING-HORMONE AND PROLACTIN PROFILES IN THE FEMALE BLACK BEAR (URSUS-AMERICANUS)

Identifying steroid and pituitary hormone profiles in the female black bear (Ursus americanus) throughout pregnancy may provide a greater un derstanding of the reproductive cycle and indicate which hormones are required for implantation. Our objective was to assess endocrine activ ity in black bears oestrus onset, at oestrus, during pregnancy and aft er parturition. Serum samples were obtained from 12 captive, 16 uncoll ared and five radiocollared free-ranging female black bears from March through the end of December and assayed for serum progesterone, oestr adiol, luteinizing hormone (LH) and prolactin (PRL). In captive bears, progesterone concentrations were low at days 0-10 after oestrus and i ncreased significantly days 25-35 and 45-52 after oestrus, Oestradiol concentrations were high at oestrus (day 0) and days 4-10 after oestru s and then decreased days 25-35 and 45-52 after oestrus. LH concentrat ions were not significantly different throughout the sampling period. Changes in PRL concentrations pattern were similar to those of oestrad iol, with elevated levels at oestrus and days 4-10 after oestrus, foll owed by a significant decrease 45-52 days after oestrus. In non-collar ed free-ranging bears, progesterone concentrations increased gradually after mating with a further significant increase in November-December . Oestradiol concentrations were highest in March (before mating) and in June (during mating) followed by a significant decrease in July (ea rly delay period) and November-December (peri-implantation period). LH concentrations were low until November-December and then increased si gnificantly. PRL concentrations were low in March (before mating), inc reased significantly during the mating season in June, decreased sligh tly in July, and were low in November-December (peri-implantation peri od). In radiocollared free-ranging bears, serum progesterone concentra tions were elevated in pregnant bears in December and extremely low in lactating and non-lactating bears in March. Oestradiol levels were sl ightly higher in pregnant bears in December than in non-lactating or l actating bears in March. PRL concentrations were considerably higher i n lactating bears in March than in pregnant bears in December. Our res ults suggest that: (1) serum progesterone concentrations are low, but detectable during the early delay implantation period and greatly elev ated during the peri-implantation period; (2) serum oestradiol concent rations are elevated at oestrus and decline during the delay period; ( 3) LB may be involved in luteal activation; and (4) the decline of ser um PRL concentrations during short days may be necessary for implantat ion to occur. (C) 1998 Elsevier Science B.V. All rights reserved.