The aim of the present study was to evaluate the role of insulin in the production of high concentrations of androstenedione in the ovary of Scotophilus heathi during the period of delayed ovulation. The concentrations of serum insulin were found to be high during November and December and declined significantly before ovulation. A significant correlation was observed between circulating insulin concentration and body weight as well as with serum androstenedione concentrations. Autoradiographic study demonstrated specific accumulation of125I-labelled insulin in the ovarian thecal and interstitial cells. Insulin increased both basal and hCG-stimulated androstenedione production by the ovary in vitro during November. These results indicate that insulin may be involved in inducing high androstenedione synthesis by the ovary and thus may be indirectly responsible for inducing delayed ovulation in S. heathi.
Abhilasha and A. Krishna
The steroid hormone profile of Scotophilus heathi, an Indian tropical vespertilionid bat, was studied, with special reference to the period of delayed ovulation. The results show unusually high concentrations of circulating androstenedione and testosterone during the first half of the period of delayed ovulation, whereas the concentrations of progesterone and oestradiol were relatively low during this period. Androstenedione, testosterone and oestradiol concentrations were high during the period of ovarian recrudescence (October–November). The oestradiol concentration increased, whereas androstenedione and testosterone declined significantly, before ovulation. Studies in vitro showed that the ovary secretes more androstenedione and testosterone than does the adrenal. A histological study showed that a major part of the ovary of S. heathi was occupied by hypertrophied interstitial cells. An immunocytochemical study showed ovarian thecal interstitial cells as the major site of high androgen synthesis in the ovary. During the period of delayed ovulation the bat ovaries thus resemble the ovaries from women with polycystic ovaries in which abnormally high androgen secretion from hypertrophied interstitial cells prevent ovulation.
A. Krishna and C. J. Dominic
Summary. Spermatozoa were observed in all parts of the genital tract in females killed in January, February, March and April although copulation occurs only until early February. The spermatozoa were arranged linearly with their heads orientated towards the epithelial lining.
A. Krishna, P. F. Terranova, R. L. Matteri, and H. Papkoff
Summary. Constant infusion of LH (400 μg NIH-S24) through an osmotic minipump inserted on Day 1 (oestrus) of the cycle in the hamster resulted in spontaneous superovulation (≃ 29 ova) at the next expected oestrus, increased blood flow (P<0·001) to the ovary on Day 3, and slight depletion (0·1 >P>0·05) of histamine in the ovary. Treatment with antihistamine (alpha-fluoromethylhistidine, an irreversible inhibitor of histidine decarboxylase, or cimetidine, an H2 blocker) by injections or by infusion using separate osmotic minipumps significantly (P<0·01) reduced the number of ova shed in the LH-treated hamsters. Infusion of LH with alpha-fluoromethylhistidine in the same osmotic minipump reduced the bioactivity of the LH. Infusion of antihistamine alone did not alter the normal number of ova shed. The results suggest that the LH-induced superovulation involves stimulation of histamine release; the histamine then may increase ovarian blood flow thus allowing more gonadotrophins to reach the ovary.
Arnab Banerjee, K J Meenakumari, S Udin, and A Krishna
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.