Changes in Sex Steroids, Gonadotropins, Prolactin, and Inhibin in Pregnant and Nonpregnant Japanese Black Bears (Ursus thibetanus japonicus)1

Abstract

We examined changes in the concentrations of serum progesterone (P4), estradiol-17beta (E2), FSH, LH, prolactin (PRL), and inhibin to determine their interaction and their effect on the reproductive endocrine controls of pregnant and nonpregnant female Japanese black bears. Fourteen female bears were used in this study over a 2-yr period. In the first year, six of the bears were divided into two groups; a pseudopregnant group and a nonpregnant group. In the second year, the remaining eight bears were also divided into two groups; a pregnant group and a nonpregnant group. Pregnant and pseudopregnant bears had similar P4 trends with both groups exhibiting a significant increase in December, which is the suspected time of implantation in pregnant bears. These trends correlated with an increase in PRL levels, whereas low levels of LH were maintained throughout the year. Nonpregnant bears maintained low concentrations of P4, and compared with pregnant and pseudopregnant bears, they also exhibited a delayed elevation in PRL. Luteinizing hormone activity varied among individual animals, but regardless of reproductive status, fluctuation patterns of E2, FSH, and inhibin did not differ among bears. Our results suggest that PRL may play a luteotropic role in both pregnant and pseudopregnant bears, and is possibly responsible for inducing reactivation of the dormant corpus luteum that precedes implantation in the Japanese black bear.

Annual Changes in Serum Leptin Concentration in the Adult Female Japanese Black Bear (Ursus thibetanus japonicus)

“…In the present study, the leptin concentrations of both the mated and unmated bears peaked ( Fig. 1-C) at approximately the same time, that is, at the time when the serum P 4 concentrations of the 3 mated females and one of the unmated females, which did not give birth and were possibly pseudopregnant [25], were remarkably increased ( Fig. 1-B).…”

“…In the Hokkaido brown bear, implantation occurs between late November and early December when the serum P 4 level is greatly elevated [30]. The serum P 4 concentration of the Japanese black bear also dramatically increases at the suspected time of implantation [25]. Sato et al [26] suggested that a peak in the serum P 4 concentrations in December might reflect the endocrine function of the corpus luteum at implantation.…”

Using PGFM (13,14-dihydro-15-keto-prostaglandin F2α) as a non-invasive pregnancy marker for felids

“…For example, urinary relaxin determination demands a concentration step by ultrafiltration before analysis. An additional carnivore comprehensive pregnancy marker is the prolactin concentrations in blood plasma, allowing the discrimination between pregnancy and pseudopregnancy via elevated values in cats and in other carnivores, such as the Japanese black bear [26], the dog [27] and the mink [28] making this hormone also an interesting target for pregnancy diagnosis if urine sample are available.…”

Inhibin may be involved in negative feedback in the prairie dog (Cynomys ludovicianus)

“…Low levels of plasma inhibin were found during progesterone secretion (Canpbell et al,'90). Inhibin and other hormones involved in ovulation have been measured in the plasma of blue foxes (MondainMonval et al, '93), Japanese black bears (Sato et al, 2001) and Siberian hamsters (Kenny et al, 2000), but these papers do not consider the role of the CL in inhibin secretion. The inhibin alpha subunit has been localized in the granulosa of large follicles and the CL of the bushtail opossum (Trichosurus vulpecula), which does not have implantation but secretes progesterone (Vanmontfort et al, '98).…”