Thermotrophic Effect of Melatonin in Adrenalectomized and Thyroidectomized Rats

Abstract

A single injection of 25 µg melatonin induced hyperthermia in rats. The mechanism(s) by which melatonin induces hyperthermia is not clear. In this study the thermotrophic effects of melatonin were studied in adrenalectomized (ADX) and thyroidectomized (TX) rats to ascertain if melatonin-induced hyperthermia is mediated through these glands, as both these glands play a significant role in mammalian thermoregulation. Melatonin (25 µg) was administered as a single subcutaneous injection at 06.00, 12.00, 18.00, and 24.00 h. Body temperatures were recorded, using an anal thermometer at hourly intervals, round the clock. In the scotophase the animals were located using dim red light and injected. Although the administration of melatonin to both intact and ADX rats resulted in a rise in body temperature, the effect was more pronounced in the former compared to the latter group. Melatonin induced hyperthemia only during the photophase of the diurnal cycle; in the scotophase the response was either poor or nil. In TX rats melatonin was ineffective in inducing hyperthermia in either the photophase or scotophase. The body temperatures of TX rats and melatonin-injected TX rats were parallel. The results indicate that in ADX rats melatonin induced minor hyperthermia, whereas in TX animals it failed to produce any hyperthermia. The findings suggest that melatonin induces hyperthermia probably through its action on thyroid activity. Other mechanisms of action cannot be ruled out, however.

Daily Melatonin Administration to Middle-Aged Male Rats Suppresses Body Weight, Intraabdominal Adiposity, and Plasma Leptin and Insulin Independent of Food Intake and Total Body Fat1

“…The increased body temperature of the melatonin-treated rats may have been a consequence of increased physical activity in this group, and although great care was taken to minimize stress during the recording of body temperatures, it is possible that temperature changes may have been mediated by physical activity and/or stress-related responses specifically associated with the handling of the animals. Treatment with melatonin or an analog has been shown to restore blunted circadian rhythms of body temperature in old rats (27) or rats exposed to continuous light (25) and to acutely increase body core temperature in intact rats (31). The effects of acute and chronic daily melatonin treatment on thermoregulation have been investigated most frequently in experiments using photoperiodic animals or pinealectomy (see Ref.…”

Significance and application of melatonin in the regulation of brown adipose tissue metabolism: relation to human obesity

“…An increase in body temperature caused by melatonin administration is mainly observed in rodents. This effect is attributed to its ability to enhance non‐shivering thermogenesis (128,129), its action on thyroid activity (130) or its ability to promote locomotor activity (89).…”

Diurnal Sensitivity in Melatonin-lnduced Hematological Changes in the Male Albino Rat

“…Melatonin, which is considered to be a chief hormonal product of the pineal gland, has a broad spectrum of physiological actions [3] which include thermoregulation [4,5], reproduction [1,6,7], intermediary metabolism [8], electrolyte metabolism [9], blood flow and evaporative water loss during heat stress in rats [10]. Melatonin is also implicated in immune response [11] and oncostatic action [12], Recent studies reveal that melatonin-induced release of opioid peptides mediate immunoenhancing effects [13], Ear lier studies from our laboratory indicated in volvement of melatonin in hemopoiesis and its rhythms [14].…”