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Injection of adrenaline in ten daily doses of 100 μg each into the chequered water-snake, Natrix piscator, stimulated glycogenolysis and lipid esterification in the liver and lipolysis in the adipose tissue of control snakes. In both thyroidectomized and control snakes plasma protein levels decreased significantly after hormone treatment, although there was no change in concentrations of muscle glycogen and plasma lactic acid. In thyroidectomized snakes, the hormone stimulated oxidation of the free fatty acids but had no significant effect on the synthesis of the triglycerides. It is suggested that in these snakes the presence of the thyroid hormones is a prerequisite for the response of most of the metabolic processes to adrenaline.
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SUMMARY
The metabolism of radioactive iodine in the adult male garden lizard, Calotes versicolor, was studied during the course of a year by examination of the following indices of thyroid function: thyroidal 131I uptake, quantitative estimation of labelled iodoamino acids in the thyroid gland and in plasma, and plasma protein-bound iodine. Labelled monoiodotyrosine, di-iodotyrosine and thyroxine were identified and seasonal variations in their proportions demonstrated. Thyroxine was not detected in winter but made its appearance in the spring and summer months. Tri-iodothyronine was not detected at any time of the year in the thyroid of Calotes.
The effects of administration of thyrotrophin (TSH), lowered temperature and dehydration were also studied. TSH augmented 131I incorporation into the thyroid gland significantly but was not effective in stimulating hormonogenesis in winter. While water withdrawal had no effect on thyroidal radioactive iodine uptake, temperature lowered artificially (15 °C) in summer reduced it by half, and altered greatly the proportions of iodoamino acids in the thyroid. The results are discussed in the light of the fragmentary information concerning thyroid function in reptiles.
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Department of Zoology, Banaras Hindu University, Varanasi 221005, India
(Received 16 September 1974)
Almost all birds investigated so far have been shown to respond to artificial illumination irrespective of their tropical or temperate distribution (see reviews Chandola, Thapliyal & Murty, 1973; Follett, 1973; Lofts & Lam, 1973) with the exception of a subtropical finch, spotted munia, Lonchura punctulata (Chandola & Thapliyal, 1973). We have now undertaken a systematic investigation of the photoresponses of this bird which is widely distributed in the Indian subcontinent (16–30° N) and report our preliminary findings here.
Adult birds were caught in the wild and, after an acclimatization period of 15 days, were weighed and the gonads inspected at laparotomy. Male birds were separated into groups of 12 and subjected to light treatments as indicated in Tables 1 and 2. In one series 3 h light: 23 h darkness (3 L: 23 D), an ahemeral light
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Daily administration of adrenaline over a 10-day period invariably induced significant increases in the metabolic rate of the whole body and of specific tissue (liver, muscle, kidney and brain) of both intact and thyroidectomized lizards except during June (breeding season) when the presence of thyroid hormones was a prerequisite for the stimulation of oxygen consumption by the whole body, muscle, kidney and brain but not by the liver. Corticosterone had no effect on whole body oxygen consumption but stimulated, inhibited or was without influence on the oxygen consumption of individual tissues, depending on the season and the presence or absence of thyroid hormones. It is suggested that adrenaline, due to its temperature-independent calorigenic effect, acts as the emergency hormone for energy release and helps the animal to survive during hibernation (winter months) when almost all the endocrine glands are inactive.
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SUMMARY
In the water-snake, Natrix piscator, the following are depressed by orchidectomy and restored to normal by testosterone treatment: glucose, free and esterified fatty acids and triglycerides in plasma, hepatic triglycerides, and total esterified fatty acids.
The increase in hepatic free fatty acids and muscle glycogen was also reduced to the level found in intact snakes. Moreover, although castration had no effect, testosterone caused a significant increase in liver weight and plasma protein, and a significant decrease in free plasma cholesterol. Except for an increase in triglyceride content by high doses of the hormone, neither castration nor the administration of 5 mg testosterone had any significant effect on the free fatty acid and triglyceride content of the adipose tissue of the snakes.
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Seasonal changes in the thyroid gland related to temperature and reproductive cycles have been observed in a number of reptiles. However, while the temperaturedependence of the thyroid has been well established, experimental studies aimed to demonstrate a direct association between reproductive events and thyroid secretions have so far been lacking (see reviews by Dodd & Matty, 1964; Lynn, 1970). We have now obtained data indicating that male hormone(s) may be of great importance in the maintenance of thyroidal function in lizards.
Indian garden lizards (Calotes versicolor) were housed in a temperature (31 ± 1 °C and photoperiod (12 h light) controlled chamber. Live maggots and water were provided ad libitum. In June, 15 adult males were castrated and 10 were sham-operated under sodium pentobarbitone anaesthesia. After 5 weeks each animal received i.p. 10 μCi carrier-free 131I in 0·2 ml 0·9% NaCl solution. Four to five animals from each group
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SUMMARY
Thyroidectomy decreased the body weight and the height of the cells lining the sex-segment of the kidney of the Chequered Water-snake, Natrix piscator maintained at 30 °C; at 40 °C the liver, kidney and gonad were also affected. At the higher temperature, thyroidectomy influenced significantly protein, carbohydrate and lipid metabolism. At 30 °C, only a decrease in the rate of esterification of the free fatty acids in the liver and of their release from the adipose tissue was observed. The difference in the effect of thyroidectomy at 30 and 40 °C is explained by suggesting that thyroid activity was low in animals maintained at the lower temperature and high in those kept at the higher temperature.
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SUMMARY
Thyroidectomy and orchidectomy led to significant reduction in the oxidative metabolism of isolated liver and skeletal muscle tissue (at 30 °C) in Calotes versicolor. Thyroxine and male hormone were shown to increase this parameter in intact and orchidectomized lizards respectively. The effects of thyroidectomy and orchidectomy on tissue oxygen uptake were not additive. It is supposed that by its effect on oxidative metabolism male hormone may be of a greater physiological importance for reptiles than for other vertebrates.
The present results show also that changes in environmental temperature can counteract the depressive effect of orchidectomy on the thyroid of this species of lizard.
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SUMMARY
Orchidectomy in Hemidactylus flaviviridis led to significant reduction of thyroidal 131I uptake, thyroidal content of thyroxine, plasma protein-bound iodine and oxygen consumption of isolated liver and skeletal muscle (at 30 °C). Administration of testosterone to orchidectomized lizards restored these parameters to normal levels. Dependence of thyroid function and oxidative metabolism on male hormone may be a general feature in reptiles. This hormone may, therefore, be of greater physiological importance in these animals than in other vertebrates. Since reptiles occupy a crucial phylogenetic position in the animal kingdom these findings are important from the point of view of evolution of the functional aspects of hormones in vertebrates.
The results also show that thyroid function is inhibited by oestrogen(s) in this lizard. This may be an adaptive compensatory measure to control (through effects of the thyroid on metabolic activities) the extra expenditure of energy usually associated with such energy-consuming functions as ovulation and egg-laying.
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Department of Zoology, Banaras Hindu University, Varanasi 221005, India
(Received 18 June 1974)
Male hormone has been classically attributed a primary role in the maintenance of reproductive function in male vertebrates. Thyroid hormone on the other hand has been shown to control oxidative metabolism in homeotherms, but its role in poikilothermous animals has not been established, except in reptiles (see reviews by Dodd & Matty, 1964; Lynn, 1970). Recently oxidative metabolism was shown to be influenced by testosterone in three species of reptiles, namely, Calotes versicolor (Chandola, Kumar & Thapliyal, 1974a), Natrix piscator (Thapliyal, Kumar & Garg, 1974) and Hemidactylus flaviviridis (Chandola et al. 1974b). Castration in all these species resulted in a significant decrease and administration of testosterone in a significant increase in the oxygen consumption of isolated liver and skeletal muscle tissues (at 30 °C). Testosterone also restored the decline in oxygen consumption in castrated animals to normal
