The effect of ambient temperature upon the secretion of thyroxine in the young pig.

Abstract

SUMMARY1. Fluctuations in the rate of secretion and metabolism of thyroxine in the pig were observed whilst the ambient temperature was reduced from 32 to 80 C. The quantity of food supplied was either maintained constant or doubled when the animals were exposed to the lower temperature.2. It was found that the rate of disappearance of [1251]thvroxine did not change when the animal was exposed to the cold, unless the animal's food intake was altered.3. The secretion of thyroxine increased temporarily after exposure to the cold. This was shown by a rise in the concentration of thyroxine in the plasma and a simultaneously increased loss of 1311 from the thyroid gland. The increase in secretion of thyroxine was not maintained throughout the exposure to cold when the food intake of the animal was kept constant.

Influence of different planes of energy supply prior to the breeding season on blood metabolites in female mink (Mustela vison)

“…These results were in agreement with calculations on substrate oxidation in animals exposed to a similar feeding regime [31] which showed a high level of fat oxidation during periods of restriction, whereas protein oxidation provided the major contribution to the total heat production when the food supply was ample, and with results by Fink and Tauson [17] showing negative values for retained energy [22] showing direct proportionality between insulin and level of food intake, and own previous results in mink [17]. [17], pig [16] and sheep [27] showing that [10], which probably was caused by the handling in connection with blood sampling (mink: B o rsting and Damgaard [ 10] and rat: Gdrtner et al [19]). The differences in glucose were, however, small throughout the experiment, confirming the results of Armstrong and Britt [3] showing that …”

The influence of food intake and ambient temperature on the rate of thyroxine utilization.

“…The rate of disappearance of 125I-labelled thyroxine (K) was measured as previously described (Evans & Ingram, 1977) by injecting 25 ,uc in pig plasma (25 %) and saline (75 %). A quantity (5 ml) of blood was then drawn in and out of the syringe three times, to ensure that the wall of the catheter was not contaminated with labelled hormone.…”

“…Water was always available. During the first 2 d of an experiment, each pig was given KI (8 mg/d) in the food, and subsequently KI (0-8 mg/d), in order to reduce to the minimum the recirculation of radio-iodide (Evans & Ingram, 1977). The ambient temperature and feeding conditions were kept constant for at least 4 d before a determination of the value of K was made.…”

“…When pigs were kept at 330 C, and the ambient temperature was suddenly dropped to 80 C, there was only a transitory increase in the utilization and secretion of hormone in pigs on a constant level of food intake. If food intake was doubled, however, at the same time that ambient temperature was reduced, then there was a sustained increase in the rate of utilization of hormone (Evans & Ingram, 1977).…”

Proceedings of the Physiological Society, 21‐22 July 1989, Cambridge Meeting: Poster Communications

“…Previous investigations suggest that the number of nuclear 3,5,3'-triiodothyronine (T3) receptors in skeletal muscle is dependent on environmental temperature and level of energy intake (Dauncey et al 1988). There is also an increase in thyroid thyroxine (T4) output in cold-exposed pigs, with a concomitant rise in plasma T4 concentration which increases after 1 day at 8°C but then decreases if there is no increase in food intake (Evans & Ingram, 1977). The present study investigates the time course of changes in skeletal muscle nuclear T3 receptors to a low environmental temperature, over a 14-day period during which food intake was kept constant.…”