Calorigenic effect of thyroid hormones and noradrenaline in warm- and cold-acclimated mice.
|Title:||Calorigenic effect of thyroid hormones and noradrenaline in warm- and cold-acclimated mice.|
|Abstract:||The effect of diacetyl-2,6-diiodohydroquinone (DDIH) on the calorigenic action of exogenous L-thyroxine and L-triiodothyronine was studied in normal and thyroidectomized male mice acclimated to 30° or 10°C. Two methods for determining the oxygen consumption rates (OCRs) were used: one was a modified Maclagan system in which the OCRs were determined on groups of eight mice; the other a system using single animals. The animals were pretreated with thyroxine or triiodothyronine in conjunction with DDIH, and their OCRs were determined using both methods. A comparison of the results showed that grouping had an effect, on the measured response in both treated and untreated animals. A series of experiments in which 131I-labled hormones were administered did not reveal any correlation between the amount of 131I excreted and the magnitude of increase in OCR in warm- and cold-acclimated mice. The calorigenic response of untreated and pretreated mice to noradrenaline was measured under two sets of environmental conditions. In one, untreated and pretreated mice were tested with noradrenaline, their OCRs being determined at the temperature of acclimation. In the other, the noradrenaline test was conducted after the animals had been exposed to 10° or 30°C for one hour. When noradrenaline was tested the temperature of acclimation, the results showed that pretreatment had an effect on the sensitivity to noradrenaline; DDIH generally inhibited the sensitivity of thyroxine pretreated mice and enhanced the sensitivity of triiodothyronine pretreated ones. Thyroidoctomy reduced the sensitivity to noradrenaline. When cold-acclimated, mice sensitive to the higher dosage of noradrenaline were placed at 30°C for one hour, they lost this sensitivity. This lack of sensitivity of cold-acclimated mice was contrary to the sensitivity seen in cold acclimated rats tested With a lower dosage of noradrenaline at 30°C and indicated a definate species difference. The difference in the response of mice to noradrenaline under the two environmental conditions indicated the importance of the temperature at which the test was conducted. The rapidity with which cold-acclimated mice lost their sensitivity to noradrenaline indicates a larger role for the nervous system in thermogenesis than is seen in the rat, and perhaps different means of nonshivering thermogenesis are to be found in these two species.|
|Collection||Thèses, 1910 - 2010 // Theses, 1910 - 2010|