Effects of TSH, TRH, LH and LHRH on thermoregulation and food and water intake in the rat.

The effects of administration of thyroid-stimulating hormone (TSH), thyrotropin-releasing hormone (TRH), luteinizing hormone (LH) or luteinizing hormone-releasing hormone (LHRH) into the lateral cerebral ventricle on thermoregulation and food and water intake were assessed in rats. Intracerebroventricular, but not intraperitoneal, injection of TSH, LH or LHRH produced hypothermia in rats at ambient temperatures of both 8 and 22 degrees C. The hypothermia in response to TSH injection was due to both decreased metabolic heat production and increased heat loss (cutaneous vasodilatation). The hypothermia in response to either LH or LHRH was due solely to decreased metabolic heat production. There was no change in respiratory evaporative heat loss in response to TSH, LH or LHRH injection. Furthermore, food but not water intake was greatly reduced following an intracerebroventricular injection of TSH or TRH in rats. On the other hand, intracerebroventricular administration of LH, but not LHRH, caused an increase in relative water intake (or water/food) in rats. However, intracerebroventricular administration of LH or LHRH had an insignificant effect on food intake. The data indicate that, in addition to their hormone actions, TSH, LH and their releasing hormones act through a central mechanism to influence some of the physiological or behavioral functions.