Synergistic Effect of Thyrotropin Releasing
نویسنده
چکیده
There have been suggestions that the genetically obese rat has abnormal thyroid function [1,2]. It is also known that while the obese rat shows various physiological and metabolic abnormalities normally associated with hypothyroidism, it also has other defects that are not generally found in hypothyroid animals. Like the hypothyroid rat, which shows decreased oxygen consumption in adipose tissue in vitro [3], the obese Zucker rat has decreased oxygen consumption in vivo [4] and a β-oxidation of lipids [5]. Obese Zucker rats also show cold intolerance [6-8] that is unresponsive to catecholamine infusion [8]. Preliminary study of our own showed that norepinephrine enhanced food intake and resting metabolic rate in lean rats [9]. It has been demonstrated that peripheral administration of thyrotropin releasing hormone (TRH) has both an inhibitory effect on food intake and acts, probably through the thyroid axis, to stimulate whole body metabolism [10], TRH administration causes an increased release of thyroid stimulating hormone (TSH) [11] which in turn causes the release of triiodothyronin [12] which causes weight loss in the obese Zucker rat [1]. Thyroid hormone administration is known to potentiate the metabolic response to noradrenaline in lean and obese rats [13]. Cold acclimation is known to cause increased thermogenic activity of brown adipose tissue [14]. We therefore treated warm-acclimated, obese Zucker and lean Wistar rats with a combined and separate infusions of TRH and NE to investigate the influence of TRH on the whole-body metabolic effect of NE.
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