Seasonal changes in testicular size and serum LH, prolactin and testosterone concentrations in male polar bears (Ursus maritimus)
Howell-Skalla, L.A.; Cattet, M.R.L.; Ramsay, M.A.; Bahr, J.M.
Reproduction 123(5): 729-733
ISSN/ISBN: 1470-1626 PMID: 12006101 DOI: 10.1530/rep.0.1230729
Little is known about the reproductive endocrinology of the male polar bear, Ursus maritimus, except that serum testosterone concentrations are high in April and May during the mating season and are low from August to November during the non-mating season. The objective of this study was to describe the relationship between seasonal changes in testicular size and serum concentrations of testosterone, LH and prolactin. Blood samples and testicular measurements were obtained from free-ranging male polar bears in Canada in April (n=5) and May (n=15) near Resolute Bay, Northwest Territories and near Churchill, Manitoba in July (n=15) and October (n=22). Testis size was greater in May (39.4[plus or minus]3.5 cm2) than in October (27.3[plus or minus]2.0 cm2) (P=0.002). Serum testosterone concentrations were approximately threefold higher in April (5.8[plus or minus]0.8 ng ml-1) than in May (1.7[plus or minus]0.5 ng ml-1), July (0.6[plus or minus]0.2 ng ml-1) and October (1.1[plus or minus]0.2 ng ml-1). Similarly, serum LH concentrations were high in April (0.14[plus or minus]0.04 ng ml-1) and low in May (0.09[plus or minus]0.01 ng ml-1), July (0.10[plus or minus]0.02 ng ml-1) and October (0.08[plus or minus]0.00 ng ml-1). Serum prolactin concentrations were high in April (1.9[plus or minus]0.3 ng ml-1), highest in May (2.5[plus or minus]0.2 ng ml-1), lower in July (1.3[plus or minus]0.1 ng ml-1) and lowest in October (0.8[plus or minus]0.07 ng ml-1). The present study demonstrates a positive relationship between testicular size and serum concentrations of LH, prolactin and testosterone in the male polar bear and confirms the previously reported seasonal changes in serum testosterone concentrations. Data from the present study provide important baseline and comparative endocrine information, that can be used to aid captive breeding programmes in zoos and to further ecological-behavioural studies of polar bears.