Santasri Chaudhuri-Sengupta

Ultrastructural and hormonal modulations of the thyroid gland following arecoline treatment in albino mice.

Arecoline is a plant alkaloid of betel nut Areca catechu. Arecoline has immunosuppressive, hepatotoxic, mutagenic and teratogenic effects, and disturbs some endocrine organs in rats. The objective is to investigate the untoward effects of arecoline on the thyroid gland in mice. Intraperitoneal injection of arecoline (10 mg/kg body weight only once) increased the serum T(3) and T(4) levels and decreased the serum TSH 20, 40 or 60 min after the treatment, with maximum effect at 40 min. Chronic arecoline treatment (10 mg/kg body weight daily for 15 days) caused light microscopic and ultrastructural degenerations of thyro-follicular cells with depletion of T(3) and T(4) levels followed by the elevation of the TSH level. Atropine (arecoline antagonist) injection prevented the changes (hyperactivity) induced by acute (40 min) arecline treatment. Arecoline initially stimulates thyroid activity, and eventually inhibits the activity; atropine prevents thyroid dysfunction induced by arecoline. Arecoline action is mediated probably via muscarinic cholinergic receptor-hypothalamic-pituitary-thyroid axis in mice.

Seasonal Thyroid Cycle of the Soft-shelled Turtle, Lissemys p. punctata (Bonnoterre)

The current study was undertaken to ascertain the seasonal influence of thyroid activity in female soft-shelled turtles, Lissemys p. punctata. Thyroid gland was studied month-wise throughout the year from relative gland weight, histology, epithelial height, glandular peroxidase activity, and RIA of T3 and T4 levels from blood serum and the thyroid gland. The values of all the parameters, except those of T3 and T4, were higher during March through May, decreased from June through August and began to rise thereafter (September through February). Whereas T3 and T4 levels were highest in May, lower during June to November and began to rise thereafter. The difference in the peaks between T3 and T4 levels and other parameters have been explained. The findings suggest that thyroid activity of Lissemys turtles varies seasonally and that seasonal factors like temperature play an important role in influencing thyroid activity in soft-shelled turtles.

Roles of thyroid, adrenal and pancreatic hormones on thyroid activity of the soft-shelled turtles Lissemys punctata punctata Bonnoterre.

The effects of some exogenous peripheral hormones (thyroxine, corticosterone, epinephrine, norepinephrine and insulin) on thyroid activity were investigated in juvenile female soft-shelled turtles, Lissemys punctata punctata. Each hormone was injected in three different doses (25 microg, 50 microg or 100 microg each per 100 g body weight, once daily at 9 AM) for 10 consecutive days. Thyroid activity was evaluated by gravimetry, histology (epithelial height) and thyroperoxidase assay. The findings revealed that thyroxine in low dose (25 microg) stimulated thyroid activity by increasing the relative thyroid weight, epithelial height and thyroperoxidase activity, but inhibited gland activity at a high dose (100 microg) by decreasing the values of all these parameters. The medium dose (50 microg) had no significant effect. All other hormones, in all doses, significantly decreased thyroid activity by decreasing the values of all the parameters. Thyroid responses to exogenous hormones are generally dose-dependent in turtles. The mechanisms of actions of the hormones administered are suggested.

THYROIDAL INHIBITION FOLLOWING DIVERSE STRESS IN SOFT-SHELLED TURTLE, LISSEMYS PUNCTATA PUNCTATA BONNOTERRE

The current study was undertaken to ascertain the effects of diverse stress on thyroid activity in soft-shelled turtles, Lissemys punctata punctata. The findings revealed that starvation (10 days), dehydration (10 days) or exposure to electric shock (12 volts for 15 seconds at an interval of 30 min for 3 h) caused significant decrease in the body weight (except in electric shock), relative weight, peripheral and central epithelial heights of the follicles and peroxidase activity of the thyroid gland of turtles. The degree of change in the values of these parameters was nearly same in all the stress experiments, indicating that there is not much difference in the degree of thyroid responses to diverse stress in turtles. It is suggested that these stressors might have exerted their actions on thyroid activity presumably indirectly via adrenal medulla and/or substance in metabolic stress (starvation and dehydration) and via hypothalamo-hypophysial-adrenocortical axis in non-metabolic stress (electric shock) in Lissemys turtles.

Suppression of circadian rhythms of pineal and testicular hormones following lithium treatment in normal and reversed light – dark cycles, constant light and constant dark in rats

Abstract The aim of the current investigation was to study the effect of lithium on circadian rhythms of pineal – testicular hormones by quantitations of pineal and serum serotonin, N-acetylserotonin and melatonin, and serum testosterone at four time points (06.00, 12.00, 18.00 and 24.00) of a 24-hr period under normal photoperiod (L:D), reversed photoperiod (D:L), constant light (L:L) and constant dark phase (D:D) in rats. Circadian rhythms were observed in pineal hormones in all the combinations of photoperiodic regimens, except in constant light, and in testosterone levels in all the photoperiodic combinations. Pineal and serum N-acetylserotonin and melatonin levels were higher than serotonin at night (24.00 hr), in natural L:D cycle, in reversed L:D cycle or similar to normal L:D cycle in constant dark phase, without any change in constant light. In contrast, testosterone level was higher in light phase (12.00 hr through 18.00 hr) than in the dark phase (24.00 hr through 06.00 hr) in normal L:D cycle, in reversed L:D cycle, similar to normal L:D cycle in constant dark (D:D), and reversed to that of the normal L:D cycle in constant light (L:L). Lithium treatment (2 mEq/kg body weight daily for 15 days) suppressed the magnitude of circadian rhythms of pineal and serum serotonin, N-acetylserotonin and melatonin, and testosterone levels by decreasing their levels at four time points of a 24-hr period in natural L:D or reversed D:L cycle and in constant dark (D:D). Pineal indoleamine levels were reduced after lithium treatment even in constant light (L:L). Moreover, lithium abolished the melatonin rhythms in rats exposed to normal (L:D) and reversed L:D (D:L) cycles, and sustained the rhythms in constant dark. But testosterone rhythm was abolished after lithium treatment in normal (L:D)/reversed L:D (D:L) cycle or even in constant light/dark. The findings indicate that the circadian rhythm exists in pineal hormones in alternate light – dark cycle (L:D/D:L) and in constant dark (D:D), but was absent in constant light phase (L:L) in rats. Lithium not only suppresses the circadian rhythms of pineal hormones, but abolishes the pineal melatonin rhythm only in alternate light – dark cycles, but sustains it in constant dark. The testosterone rhythm is abolished after lithium treatment in alternate light – dark cycle and constant light/dark. It is suggested that (a) normal circadian rhythms of pineal hormones are regulated by pulse dark phase in normal rats, (b) lithium abolishes pineal hormonal rhythm only in pulse light but sustains it in constant dark phase, and (c) circadian testosterone rhythm occurs in both pulse light or pulse dark phase in normal rats, and lithium abolishes the rhythm in all the combinations of the photoperiod. The differential responses of circadian rhythms of pineal and testicular hormones to pulse light or pulse dark in normal and lithium recipients are discussed.

Modulations of thyroid activity following reproductive hormonal manipulations in soft-shelled turtles, Lissemys punctata punctata

Prolactin and sex hormones are known to modulate thyroid activity in vertebrate animals, but their findings are different in different vertebrates. Prolactin inhibits thyroid activity in higher dose by decreasing 131I uptake, serum PBI and T4 levels, follicular size and epithelial height in mammals, birds, red efts Triturus viridiscens, prometamorphic tadpoles of Rana pipiens and Rana catesbeiana, but stimulates in low dose by increasing values of these parameters in mammals, birds, crested newts and eels (Decuypere and Kühn, 1985). Estradiol, estriol, estrone and progesterone also inhibit thyroid activity in intact/gonadectomized/ hypophysectomized rats, rabbits and rhesus monkeys (Boado et al., 1983), intact juvenile ducks or ovariectomized Japanese quail (Maiti and Sahu, 1982; Pethes and Peczely, 1983) and in rainbow trout Salmo gairdneri, Anabus testudineus and Chana punctatus (Leatherland, 1985; Cyr et al., 1988), but stimulate in intact/gonadectomized/hypophysectomized rats and other mammals (Bisaria and Kapoor, 1976). Thyroid activity is not altered after progesterone treatment in rabbit, or estradiol or TSH treatment in adult male rats (Kannan et al., 1980). Whereas combined treatments of progesterone and estradiol, or progesterone, estradiol and testosterone inhibit thyroid activity in adult male rats, female ducklings and ovariectomized Japanese quail, but stimulates in adult male and female rats (Maiti and Sahu, 1982; Pethes and Péczely, 1983).

Adrenomedullary and glycemic alterations following diverse stress in soft-shelled turtles Lissemys punctata punctata Bonnoterre.

The objective of the current investigation was to study adrenomedullary and glycemic responses to stress in soft-shelled turtles, Lissemys p. punctata. Dehydration (7 days) and formalin (formaldehyde 1%, 0.1 mL/100 g body wt. daily for 7 days) stress-stimulated adrenomedullary activity at histological (by increasing the nuclear diameter and degranulation of chromaffin cells) and hormonal levels (by elevations of norepinephrine and epinephrine concentrations) with hyperglycemia in turtles. But salt loading (NaCl: 1%, 1 mL/100 g body wt. daily for 7 days) had no significant effect on adrenomedullary activity or glycemia presumably owing to the nonresponsiveness of adrenocortical activity to salt stress in turtles. It is suggested that dehydration and formalin stresses might have exerted their actions through the hypothalamo (CRF)–hypophysial (ACTH)–adrenocortical axis in turtles.

Seasonal Adrenocortical Cycle of the Female Soft-shelled Turtle Lissemys p. punctata

The seasonal adrenocortical cycle in the female soft-shelled turtle Lissemys p. punctata was investigated by examining the adrenal gland once a month throughout the year from gravimetric, histological, histochemical and biochemical standpoints. The adrenal gland weight, nuclear diameter, histochemically detected 3ß-hydroxysteroid dehydrogenase activity, corticosterone and RNA concentrations, and acid phosphatase and alkaline phosphatase activities began to increase from early summer (March-June), reached a peak in late summer (July-August) and declined subsequently (September-February), but adrenal cholesterol and ascorbic acid levels together with histochemically demonstrated sudanophilic lipids were altered reversely to those of other parameters. The results indicate that adrenocortical activity varies seasonally, being higher in early summer, highest in late summer and low in winter, that coincides with the seasonal ovarian cycle in Lissemys. It is suggested that there is a correlation between ovarian and adrenocortical activity and that the seasonality in adrenocortical activity may be related to environmental (temperature) and hormonal factors in the soft-shelled turtle.