Role of thyroid in tissue respiration of birds

Circadian time dependence of erythropoietic and respiratory responses of Indian garden lizard, Calotes versicolor, to mammalian urinary erythropoietin and thyroxine

The circadian stage-dependent effects of mammalian urinary erythropoietin (Ep) and thyroxine (T4) on tissue energy metabolism (in vivo and in vitro) and erythropoiesis were examined in the Indian garden lizard. Both T4 and Ep increased erythropoiesis and also affected hepatic and muscle energy metabolism. Although both treatments increased circulating RBC count, irrespective of the timing of the treatment, the maximum erythropoietic stimulation was achieved only in the late photophase (9 hr after light onset, HALO). Hepatic oxygen uptake was significantly elevated at 3 and 9 HALO following in vivo Ep administration and 3, 9, and 15 HALO following in vivo T4 injection. In contrast, in vitro addition of either Ep or T4 to hepatic homogenates of untreated lizards significantly elevated respiratory rate, irrespective of the time of tissue collection. The rate of muscle tissue respiration was statistically elevated when Ep was administered in vivo at 9 and 15 HALO. The oxygen uptake was stimulated by T4 only at 15 HALO. While in vitro addition of Ep to tissue homogenates significantly depressed the respiratory rate of muscle collected at 3 HALO, addition of T4 stimulated oxygen uptake by the muscle tissue collected at 9 and 15 HALO. It is concluded that the effectiveness of Ep or T4 largely depends upon the phase of the organism's circadian system(s).

Effect of gonadal steroid hormones on the metabolic rate of the cold-acclimated gonadectomized male and female Chalcides ocellatus (Forskal)

Male and female Chalcides ocellatus were gonadectomized and cold acclimated at 15 degrees for 1 week. Lizards were injected with testosterone and estradiol, and their oxygen consumption was determined at 15 degrees. Testosterone and estradiol caused a significant increase in the whole body rate of oxygen consumption in male and female lizards, respectively.

Intermediary metabolism in a lizard, Calotes versicolor: role of thyroid hormones

In Calotes versicolor, thyroidectomy did not alter the blood glucose level, lactate dehydrogenase (LDH liver and heart), acid phosphatase (Ac.Pase liver and kidney), and alkaline phosphatase (Alk.Pase liver and kidney) activities; significantly decreased the activities of glucose-6-phosphatase (G-6-Pase liver and kidney), glutamic oxaloacetic transaminase (GOT liver and heart), glutamic pyruvic transaminase (GPT liver), and urea concentration (liver and kidney); and increased liver cholesterol when compared to sham-operated controls. Administration of L-thyroxine (L-T4) or triiodo-L-thyronine (L-T3) to thyroidectomized lizards significantly stimulated the activities of G-6-Pase, Ac.Pase, GOT and GPT, concentration of glucose and urea, and decreased the cholesterol level. While the activities of all the enzymes studied and cholesterol level remain unchanged, glucose and urea levels decreased and increased, respectively, in thyroidectomized animals treated with actinomycin D. Chloramphenicol treatment did not affect any of the parameters studied. Simultaneous injections of actinomycin D or chloramphenicol with L-T4 prevented the hormone-stimulated activities of Ac.Pase, GOT, and GPT while the activities of LDH, G-6-Pase, Alk.Pase, glucose, urea, and cholesterol levels remain unchanged.

The effect of thyroxine on the oxygen consumption of the ocellated skink, Chalcides ocellatus (Forskal)

Acutely administered thyroxine caused significant increase in the whole body rate of oxygen consumption of C. ocellatus at temperatures between 4 and 25 degrees C. No significant increase in the oxygen consumption was observed over the voluntary body temperature range of 30-40 degrees C.

Role of thyroid and testicular hormones in the oxidative metabolism of the Indian garden lizard, Calotes versicolor

L-Thyroxine (L-T4) and testosterone were administered separately to intact, thyroidectomized, and castrated male Indian garden lizards, Calotes versicolor (maintained under natural climatic conditions) throughout the year to study their effects on the whole-body oxygen consumption and on tissue (liver, muscle, kidney, and brain) respiration. The findings indicate that the calorigenic actions of L-T4 and testosterone are independent of ambient temperature, and different tissues have different, temperature-independent, annual rhythms of sensitivity to L-T4 and testosterone. Internal factors seem to play a major role in the determination of these annual tissue sensitivity rhythms. Effects of thyroidectomy and castration are brought about by decreased levels of both thyroidal and testicular hormones. It is suggested that gonadal hormones are directly involved in the oxidative metabolism of Calotes which is regulated jointly by thyroid and gonadal steroids, and the degree of involvement of the glands depends upon the energy demand and sensitivity of tissues during different months of the year.

Role of thyroid and testicular hormones in the regulation of basal metabolic rate, gonad development, and body weight of spotted munia, Lonchura punctulata

Normal saline, L-thyroxine (L-T4, 0.5 micrograms/bird/day), and testosterone (100 micrograms/bird/day) were administered separately to intact, thyroidectomized, and castrated spotted munia over a 30-day period and the effects on basal metabolic rate (BMR), gonads, and body weight were recorded. Thyroidectomy and castration decreased the BMR. L-Thyroxine increased the BMR of intact and thyroidectomized but not of the castrated birds. Testosterone had no effect on BMR of either the intact or of the operated birds. L-Thyroxine and testosterone both had no effect on regressing gonads but inhibited thyroidectomy-induced testicular development. Body weight increased in intact, testosterone-treated birds, and in thyroidectomized and castrated spotted munia. L-Thyroxine inhibited body weight gain only in thyroidectomized birds. It is suggested that the physiological actions of L-T4 and testosterone depend on the gonadal status, thyroid activity, and nature of the thyroid-gonad relationship.

Thyroid and gonad in the oxidative metabolism, erythropoiesis, and light response of the migratory redheaded bunting, Emberiza bruniceps

In the thyroidectomized, adult male redheaded bunting exposed to a L/D cycle of 15/09, there were no significant changes in body weight, gonad size, respiratory rates of whole body, liver, muscle, red blood cell number, hemoglobin concentration, or hematocrit, unlike in intact birds. Further, while testosterone appeared as effective as L-T4 in determining body weight, gonadal size, and activity and oxygen uptake by skeletal muscle, it was of greater significance for kidney respiration and of secondary importance in its influence on blood morphology and respiratory rates of the liver and of the whole body of the bird.