Prajna Paramita Ray

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.

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 hormonal and glycemic modulation following gonadotropin and sex hormone administration in the soft-shelled turtle Lissemys punctata punctata.

The aim of the current investigation was to ascertain whether gonadotropins and sex hormones can modulate adrenomedullary and glycemic functions in turtles. Exogenous FSH (3.0 µg/100 gm body wt daily for 10 days) stimulated adrenomedullary activity by increasing nuclear diameter and cytoplasmic degranulation, and elevating adrenal norepinephrine and epinephrine, and blood glycemic levels in turtles. LH (3.0 µg/100 gm body wt daily for 10 days) had no significant effect and the combined treatment of FSH and LH (3.0 µg each/100 gm body wt daily for 10 days) failed to show further adrenomedullary stimulation and hyperglycemia beyond that of FSH alone. Estrogen treatment in low dose (25 µg/100 gm body wt daily for 10 days) had no significant effect on adrenomedullary activity or glycemia, but at higher doses (50 µg or 100 µg/100 gm body wt daily for 10 days) showed dose-dependent adrenomedullary stimulation by inducing the same manifestations as those of FSH. Progesterone in low dose (25 µg/100 gm body wt daily for 10 days) had no perceptible effect, but in other doses (50 µg/100 µg per 100 gm body wt daily for 10 days), suppressed dose-dependent adrenomedullary activity by reversing the changes to those of estrogen. Simultaneous treatment with estrogen and progesterone (50 µg each/100 gm body wt daily for 10 days) failed to show further changes beyond that of estrogen alone.

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.

Seasonal Patterns of Adrenomedullary Hormones and Glycemia in the Soft-Shelled Turtle Lissemys punctata punctata

The aim of the present study was to acertain the seasonal pattern of adrenomedullary hormones and of glycemia in Lissemys turtles. Both the norepinephrine and epinephrine concentrations as well as blood glucose levels varied seasonally which began to rise from February, became maximum during April–May (early summer), declined during June–September (late summer) and were extremely low subsequently (October–January). The seasonal adrenomedullary hormonal and glycemic cycles however do not coincide with the annual ovarian cycle, thereby indicating that the adrenomedullary and glycemic cycles are out of phase with the ovarian cycle in turtles. The possible mechanisms of seasonality of the adrenal medulla and glycemia are discussed.