Effect of melatonin administration and long day-length on endocrine cycles in the hedgehog Erinaceus europaeus

Melatonin affects steroidogenesis and delayed ovulation during winter in vespertilionid bat, Scotophilus heathi

The aim of this study was to evaluate the role of melatonin in ovarian activity of Scotophilus heathi particularly in reference to changes in steroidogenesis and steroid receptor expression during the anovulatory period of delayed ovulation. Female S. heathi showed an increased circulating melatonin level during the period of delayed ovulation in winter coinciding with the increased androstenedione (A(4)) levels, body fat and ovarian androgen receptor expression. The circulating melatonin level decreased to a low level after winter during the period of ovulation in March which also coincided with the decreased circulating A(4) levels and body fat. The circulating estrogen (E(2)) showed two peaks corresponding with the two waves of follicular development in November and February. Both the isoforms of progesterone receptor (PR), PR-A and PR-B, remained high throughout the follicular development, but expression of PR-A declined significantly during the ovulation. The treatment with melatonin, both in vitro and in vivo, significantly increased progesterone and A(4), but not the estradiol synthesis by the ovaries of S. heathi. The study further suggested that the increased androgens during winter may be primarily due to the stimulatory effect of melatonin on steroidogenic enzyme 3beta-hydroxysteroid dehydrogenase (3beta-HSD) activity. Therefore the increased circulating melatonin level in S. heathi during winter delay (inhibits) ovulation through increased androgen synthesis, but suppression of estradiol synthesis.

Inhibitory effects of melatonin on testosterone but not on androstenedione production during winter in the vespertilionid bat, Scotophilus heathi

The possible effects of melatonin on testosterone and androstenedione production in vitro by testes of wild-caught bats, Scotophilus heathi, during different reproductive phases were investigated. Bats were captured during reproductive quiescent (April-August), recrudescent (September-October), breeding (November-February), and winter dormancy (late December-January) phases. Testes were incubated in media-199 for 2 h at 37 degrees C with luteinizing hormone (LH) and with or without melatonin. Melatonin had no effect on LH-induced testosterone (T) or androstenedione (A) production during the quiescent, recrudescent, and breeding phases. However, it significantly (P < 0.05) suppressed LH-induced T production but had no effect on A during winter dormancy. Testicular 17 beta-hydroxy steroid dehydrogenase (17 beta-HSD) activity was then measured in the testes from bats trapped during quiescence, breeding, and winter dormancy. Interestingly, melatonin along with LH caused suppression of 17 beta-HSD activities (3.56 +/- 0.03 unit/min/mg protein) when compared with levels of LH treated testes (7.10 +/- 1.15 unit/min/mg protein) during winter dormancy, while it had no significant effect on 17 beta-HSD activity during quiescence and breeding phases. These results suggest that in S. heathi, melatonin during winter dormancy suppresses LH-induced T production by the testes via the suppression of 17 beta-HSD activity. This may be the reason for the decline in testicular activity during winter dormancy.

Effects of bilateral superior cervical ganglionectomy on thyroid and gonadal functions in the edible dormouse Glis glis

1. The annual profiles of plasma thyroid-stimulating hormone (TSH), thyroxine (T4), luteinizing hormone (LH) and testosterone (T) concentrations in control and ganglionectomized (SCGx) dormice were analyzed to determine whether the pineal gland affects thyroid-gonadal interactions in response to the seasonal influence of environmental factors. 2. Dormice ganglionectomized in September, around the time of prehibernation when hormonal activity is minimal had significantly disturbed annual cycles of plasma T4, LH and T, while the TSH cycle was unchanged. 3. SCGx performed after breeding season (June), only affected the T4 variations, while the T and LH titers were similar to those of controls. 4. We conclude that the annual cycles of T4 and testosterone are controlled by the sympathetic nervous system via the superior cervical ganglion which innervates both the pineal gland and the thyroid. 5. During the start of seasonal gonadal activity, which is strongly dependent on thyroid-gonadal interactions, the inhibitory action of the pineal gland on the neuroendocrine thyroid axis, or most probably a direct inhibition of the thyroid by the sympathetic innervation from SCG, might influence the timing of the reproduction cycle. 6. The lack of thyroid-gonadal interaction at the end of the breeding season suggests that the thyroid disturbance caused by ganglionectomy in June does not cause gonadal perturbation at this time.