Steroid hormones in multiple tissues of East Greenland polar bears (Ursus maritimus)

Abstract

The polar bear (Ursus maritimus) is threatened by climate changes and also from persistent organic pollutants affecting polar bear endocrinology governing growth and reproduction. To provide further insight into basic polar bear endocrinology, we determined the levels of steroids in multiple tissues and plasma from East Greenland polar bears. Tissue samples from 10 polar bears, 5 males (2 adults, 3 juveniles) and 5 females (all juveniles) were obtained from the Inuit hunt in Scoresby Sound during springtime. Eleven steroids: pregnenolone, 17-hydroxypregnenolone, progesterone, 17-hydroxyprogesterone, dehydroepiandrosterone, androstenedione, testosterone, dihydrotestosterone, estrone, 17α-estradiol and 17β-estradiol were determined in brain, adrenal cortex, testis, testicular vein, plasma, and ovary using GC–MS/MS. In brain tissue, the neuroactive progestagen pregnenolone (11.9 ± 4.4 ng/g ww) and dehydroepiandrosterone (2.26 ± 0.43 ng/g ww) were found in high concentrations. Very high levels of testosterone and androstenedione were observed in testes (>100 ng/g ww) and plasma from testicular vein (testosterone: 108 ± 41 ng/ml; androstenedione: 35.2 ± 11.1 ng/ml). Additionally, a strong correlation was found between the levels of steroids in testes and testicular vein plasma. Progestagens were found in very high levels in ovaries from juvenile females (>100 ng/g ww). Finally, our study indicates that polar bears synthesize androstenedione via the ∆-4 pathway. The present study adds new insight to our knowledge on polar bear endocrinology, which may be used in future studies on polar bear ecology and studies on some of the threats from pollution and climate changes that these animals are facing.