Variations in thyroid activity and respiratory rate during a 24-hr period and role of testosterone and thyroxine on the oxidative metabolism of the water snake, Natrix piscator

Abstract In intact adult male Natrix piscator testosterone and l -thyroxine stimulate oxygen uptake of skeletal muscle and liver homogenates to the same extent. The effects of the hormones are additive on skeletal muscle but not on liver. Testosterone and l -thyroxine are also able to restore the decline in respiratory rate of liver and skeletal muscle caused by surgical thyroidectomy. Variations in thyroid activity and oxidative metabolism during a 24-hr period were also studied. Compared with animals examined during the day, thyroidal uptake of 131 I and intrathyroidal thyroxine were significantly lower and protein-bound iodine was higher than in snakes examined at night. Further, while no significant change was observed in the respiratory rates of liver homogenates, muscle samples of day animals (30°) had significantly lower respiratory rates when measured at the night temperature of 15°.