Palmer S S, Nelson R A, Ramsay M A, Stirling I, Bahr J M
Department of Animal Sciences, University of Illinois, Urbana 61801.
Biol Reprod. 1988 Jun;38(5):1044-50. doi: 10.1095/biolreprod38.5.1044.
The adaptation of black and polar bears to their environments is proportional to the severity of climate and food restriction. Both black and polar bears mate during the spring, despite differences in their recent metabolic state. Reproductive activity in black bears follows 4 mo of torpor, whereas reproduction in polar bears occurs prior to torpor. The goals of this study were to measure the annual changes in serum sex steroids in male and female black and polar bears, and to determine if changes in serum levels of these steroids were associated with metabolic condition or photoperiod. Serum testosterone (T) concentrations were elevated during spring in black and polar bears. Moreover, this increase in serum T in polar bears during spring was correlated with age and testis size. Serum progesterone (P4) concentrations increased in pregnant polar bears in fall coincident with the time of expected implantation. No increases in serum P4 were observed in nonpregnant black and polar bears. Serum estradiol (E2) was elevated in nonpregnant and pregnant polar bears 2 mo prior to the time of expected implantation. We found that serum sex steroids measured in black and polar bears change independent of torpor. Therefore, our results suggest that photoperiod may be a more important regulator of serum steroid levels and reproduction than metabolic condition.
黑熊和北极熊对环境的适应与气候和食物限制的严重程度成正比。尽管它们近期的代谢状态有所不同，但黑熊和北极熊均在春季交配。黑熊的生殖活动在蛰伏4个月后进行，而北极熊的繁殖则在蛰伏之前发生。本研究的目的是测量雄性和雌性黑熊及北极熊血清性类固醇的年度变化，并确定这些类固醇血清水平的变化是否与代谢状况或光周期有关。春季时，黑熊和北极熊的血清睾酮（T）浓度均升高。此外，春季北极熊血清T的这种升高与年龄和睾丸大小相关。秋季时，怀孕北极熊的血清孕酮（P4）浓度升高，与预期着床时间一致。未怀孕的黑熊和北极熊血清P4未见升高。在预期着床前2个月，未怀孕和怀孕的北极熊血清雌二醇（E2）均升高。我们发现，在黑熊和北极熊中测得的血清性类固醇变化与蛰伏无关。因此，我们的结果表明，光周期可能比代谢状况更重要地调节血清类固醇水平和繁殖。
