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

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.

Melatonin regulates delayed embryonic development in the short-nosed fruit bat, Cynopterus sphinx

The aim of the present study was to evaluate the seasonal variation in serum melatonin levels and their relationship to the changes in the serum progesterone level, ovarian steroidogenesis, and embryonic development during two successive pregnancies of Cynopterus sphinx. Circulating melatonin concentrations showed two peaks; one coincided with the period of low progesterone synthesis and delayed embryonic development, whereas the second peak coincided with regressing corpus luteum. This finding suggests that increased serum melatonin level during November–December may be responsible for delayed embryonic development by suppressing progesterone synthesis. The study showed increased melatonin receptors (MTNR1A and MTNR1B) in the corpus luteum and in the utero–embryonic unit during the period of delayed embryonic development. The in vitro study showed that a high dose of melatonin suppressed progesterone synthesis, whereas a lower dose of melatonin increased progesterone synthesis by the ovary. The effects of melatonin on ovarian steroidogenesis are mediated through changes in the expression of peripheral-type benzodiazepine receptor, P450 side chain cleavage enzyme, and LH receptor proteins. This study further showed a suppressive impact of melatonin on the progesterone receptor (PGR) in the utero–embryonic unit; this effect might contribute to delayed embryonic development in C. sphinx. The results of the present study thus suggest that a high circulating melatonin level has a dual contribution in retarding embryonic development in C. sphinx by impairing progesterone synthesis as well as by inhibiting progesterone action by reducing expression of PGR in the utero–embryonic unit.

Superoxide dismutase, catalase, and glutathione peroxidase during epididymal maturation and prolonged storage of spermatozoa in the Mexican big-eared bat (Corynorhinus mexicanus)

We studied the activities of reactive oxygen species (ROS) scavenging enzymes during epididymal spermatozoon maturation and storage in Corynorhinus mexicanus (G.M. Allen, 1916), a vespertilionid bat that stores spermatozoa in the epididymides for several months after regression of the testes. Depending on the phase of the epididymal reproductive cycle, two different patterns of antioxidant enzyme activities were observed in C. mexicanus. Catalase activity is clearly present in both caput and cauda epididymides throughout the entire annual reproductive cycle, being particularly high during the post-testicular phase of epididymal function. Superoxide dismutase (SOD) activity, present during the testicular phase of epididymal transport and maturation of spermatozoa, is almost completely absent or inhibited in both epididymal segments during the post-testicular epididymal storage period. GPx activity is low during the testicular phase of epididymal spermatozoon maturation and is high in both epididymal segments during the storage phase of epididymal function. From our results, we postulate that (i) the pattern of epididymal antioxidant enzyme activities in C. mexicanus is significantly different from the pattern that is proposed to be unique for mammals; (ii) epididymal function in these species of bats can be clearly divided into two phases, a testicular-dependent phase that is related to the spermatozoon maturation function of the epididymides and a testicular-independent phase that is related to the long-term spermatozoon storage function observed in these mammals; (iii) the study of the regulation of the redox potential of the microenvironment, associated with mammalian spermatozoa as they transit through the epididymides, must be particularly focused on the anatomical region where ROS generation scavenging and spermatozoon maturation storage processes take place.

Changes in the thyroid gland during the reproductive cycle of the male vespertilionid bat, Scotophilus heathi

The aim of present study was to compare the changes in thyroid gland with the reproductive cycle of S. heathi. Thyroid showed marked seasonal variation in weight, quantity of colloid and follicular epithelial height, suggesting the thyroid gland to be inactive during quiescence and winter dormancy and active during the time of recrudescence and breeding similarly to the testicular cycle. Plasma thyroxin (T4) concentration showed a significant seasonal change with high concentration during breeding and post-breeding and low concentration during quiescence. However, the T4 concentration increased from breeding to post-breeding phase, when the testes weight was declining. It is suggested that in S. heathi the positive correlation between thyroid and testicular cycles occurs only during the phases of the reproductive cycle when the body weight and testicular activity are also closely correlated.

The relationship between testicular activity, accessory sex glands, and circulating steroid concentration during the reproductive cycle in a male Indian vespertilionid bat,Scotophilus heathi

The relationship between spermatogenesis, accessory sex glands, Leydig cell activity, and circulating concentrations of testosterone and androstenedione in male Scotophilus heathi, the greater yellow bat, was studied. Scotophilus heathi accumulated fat prior to winter dormancy at Varanasi, India. Spermatogenesis was seasonal and extended over the period November to March, with the testes becoming quiescent during winter. Monthly changes in testis and accessory sex gland masses showed two peaks, in November and January. Accessory gland secretory activity and fructose concentration showed only one peak, during January and February, which coincided with the mating period. The mass in the epididymides and their histological changes reflect the influence of testicular spermatogenesis. However, sperm were found in the cauda epididymidis during the spermatogenically quiescent period of winter dormancy. The Leydig cells showed intense side chain cleavage (SCC) enzyme activity from August to December. In late January and February, males had smaller Leydig cells and low SCC activity. Monthly changes in serum testosterone concentration included two peaks in November and January, coinciding with peak spermatogenic activity, whereas androstenedione showed only one peak, an unusually high concentration in November. The circulating serum androstenedione concentration may be responsible for the unique reproductive activity noted in this bat.

Seasonal changes in circulating serum concentration and in vitro testicular secretion of testosterone and androstenedione in the male vespertilionid bat (Scotophilus heathi)

Seasonal changes in the testicular activity were studied in the male Greater Yellow bat, Scotophilus heathi, in Varanasi, India (25 degrees N, 83 degrees E). The seasonal pattern of body weight of male bats was also recorded and compared with circulating androstenedione (A) and testosterone (T) concentration. There was a gradual increase in the body weight of the bat from September onward mainly due to accumulation of adipose tissue. Finally, body weight reached a peak level in November. Two periods of peak testicular weight and serum T concentration but only one peak of serum A concentration were observed. The first peak of T coincided closely with the peak A concentration and increased body weight. The first peak of T occurs several months before the time of mating and ovulation. The second peak of T correlated closely with the period of mating. In vitro study showed seasonal variation of the testicular responsiveness to LH stimulation. In vitro study also showed two peaks in the T but only one peak in the A production by testes in response to LH during different phases. Preliminary study showed that IGF-I but not insulin augmented hCG induced T production by testes in vitro. Our observation of an increase in serum A concentration during the period of overfeeding and weight gain and decline in A during the period of weight loss in S. heathi adds strength to the concept that nutritional status can influence hormonal function. This may be the reason for asynchrony between male and female gametic cycle found among vespertilionid bats.