Annual Testosterone Rhythm in the Black Bear (Ursus americanus)1

Seasonal Changes in the Immunolocalization of Steroidogenic Enzymes in the Testes of the Japanese Black Bear (Ursus thibetanus japonicus).

“…Testis size and peripheral concentrations of testosterone are low in the non-mating season, increase in the pre-mating season, and reach maximum just before the mating season [12,20,24,38]. In the present study, the spermatogenic activity differed with season accompanied by differences in serum concentrations of testosterone similar to other bear species; i.e., active in May and June, reduced in November and January, and resumptive in March and April.…”

“…The facility is located in the northern part of Japan (N 40°, E 140.4°) and consists of an outdoor run where the animals can The testis of seasonal breeders including bear species exhibits morphological differences throughout the year [6,7,11,14,19]. It has been reported that spermatogenic activity exhibited seasonal changes accompanied by changes in peripheral concentrations of testosterone [11,12,14,19,20,24,38]. These findings strongly suggest the occurrence of seasonal changes in testicular steroidogenesis in seasonal breeders such as bears.…”

“…Testes of the Ursidae, including those of the brown bear Ursus arctos, and the American black bear Ursus americanus, exhibit morphological and endocrinological differences throughout the year [12,20,24,38]. Testis size and peripheral concentrations of testosterone are low in the non-mating season, increase in the pre-mating season, and reach maximum just before the mating season [12,20,24,38].…”

Sex Steroid and Prolactin Profiles in Male American Black Bears (Ursus americanus) during Denning.

“…The bear's physical condition during denning is characterized by a low (<10) serum urea to creatinine (U/C) ratio in comparison to the higher one (>10) during active seasons [15]. During denning, spermatogenic and testicular steroidogenic activity resumes in male black bears [5,11,17]. Recently, Tsubota et al [24] reported the presence of P450arom in Sertoli cells and an increase in serum estradiol-17β concentrations were coincident with the initiation of testicular recrudescence in denning black bears.…”

Localization of Five Steroidogenic Enzyme mRNAs in Japanese Black Bear (Ursus thibetanus japonicus) Testes During the Mating Season by In Situ Hybridization

“…The Japanese black bear (Ursus thibetanus japonicus), a subspecies of the Asiatic black bear living in Japan, is a typical seasonal breeder that has a mating season in early summer. The changes in the histological appearance of the testicular seminiferous tubules and the concentration of testosterone in peripheral blood have been described for some species of bears, including the Japanese black bear [1][2][3][4][5]. However, the molecular mechanisms that produce reproductive seasonality in the testis have not yet been elucidated in bears.…”