Effect Of 5-TH_1A Receptor Antagonist On Ethanol-induced Hypothermia In Old Rats And Its Relationship With Brown Adipose Tissue Thermogenesis

Alcohol beverage is one of the most widely in the world. Moderate drinking, can promote the blood circulation, has the effect of health care. However, excessive drinking can lead to dizziness, nausea, vomiting and other symptoms. The long-term excessive drinking can damage the liver cells, interference of the liver, and can cause of alcoholic hepatitis and liver cirrhosis. On the other hand, clinical and animal experiments have shown that relatively moderate doses of ethanol result in hypothermia. The mechanism appears to be via an alteration in metabolic heat production due to reduced shivering thermogenesis and an increased body heat loss via peripheral vasodilation. Although a number of studies have been conducted, but alcohol influences body temperature and thermoregulation in the elderly remain poorly understood. Since there are data on 5-HT1 A receptor involvement in the control of thermoregulation, and ambient temperature can affect the body temperature. Therefore, the present study was to assess the effect of different ambient temperatures and 5-HT1 A receptor antagonist(p-MPPI) on ethanol-induced hypothermia in old rats and its relationship with brown adipose tissue thermogenesis, and effects of ethanol on sympathetic nerve activity innervating brown adipose tissue. Its purpose is to provide experimental evidence for clinical diagnosis and treatment of alcohol intoxication.PartⅠ Effects of different ambient temperatures and 5-HT1 A receptor antagonist on ethanol-induced changes of core temperature in old ratsObjective Previous studies have demonstrated that the acute administration of ethanol induces hypothermic response in rodents and other mammals, but little is known about the effects of different ambient temperatures and 5-HT1 A receptor antagonist(p-MPPI) on ethanol-induced hypothermia in old rats. We determined if ethanol-induced hypothermia is linked to the ambient temperatures and 5-HT1 A receptor.Young(3-4 months) and old(16-18 months) male SD rats were used for all experiments(Institute of Laboratory Animal Sciences, Sichuan Academy of Medical Sciences, China). Rats were housed individually in acrylic cages lined with wood shavings, maintained at an ambient temperature of 22 °C, and exposed to a daily 12:12 light: dark photoperiod(lights on at 06:00 h). Animals were allowed free access to water and food. The core temperature and motor activity in rats at three different ambient temperatures(22°C, 10°C and 32°C) were monitored by telemetry. The animals were intraperitoneally injected with a 20%(v/v) ethanol(3 g/kg) solution(Sigma Chemical Co.) or 5-HT1 A antagonist p-MPPI(1.0 mg/kg) solution(Sigma Chemical Co.) or saline of same volume at 10:00 AM. Main methodsMain results ⑴The circadian rhythm of core temperature and motor activity was measured in undisturbed rats using telemetry at an ambient temperature of 22°C during a 12 h light:12 h dark photoperiod. Core temperature of aged rats was 0.76°C lower than that of young rats during the light phase(light on at 6:00 AM-6:00 PM). But aged rats were similar to that young rat during the dark phase(light out at 6:00 PM-6:00 AM). ⑵At ambient temperature of 22°C and 10°C, ethanol led to a rapid drop in core temperature in both young and old rats, but the amplitude of the hypothermic response is greater in old rats than that in young rats. ⑶At 32°C, ethanol caused a significant increase in core temperature in rats. However, hyperthermia in old rats was more evident than that in young rats. ⑷5-HT1 A receptor antagonist attenuated markedly the hypothermic effects of ethanol in both young and old rats. It was noted that of old rats being only half that of young rats, suggesting that young rats exhibited a higher sensitivity to the 5-HT1 A receptor antagonist than old rats.Conclusion ⑴Core temperature of old rats was lower than that of young rats during the light phase. ⑵At neutral and cold ambient temperature, old rats were more sensitive than young rats to the hypothermia effects of ethanol. Whereas this substance induced amarked hyperthermia at warm ambient temperature. The data indicated old rats were more sensitive than young rats to ethanol intoxication. ⑶ 5-HT1 A receptors were involved in the mechanisms of the ethanol-induced hypothermia, but old rats were lower sensitive than young rats to the effects of 5-HT1 A receptor.PartⅡ Ethanol-induced hypothermia in old rats and its relationship with brown adipose tissue thermogenesis and sympathetic nerve activity innervating brown adipose tissue.Objective The changes in brown adipose tissue(BAT) temperature could reflect changes in BAT metabolic thermogenesis, because the primary function of BAT is to produce heat to maintain body temperature constant. Sympathetic innervations of BAT trigger and control BAT thermogenesis. Therefore, in the present study, we determine ethanol-induced hypothermia in old rats, and its relationship with brown adipose tissue thermogenesis and sympathetic nerve activity innervating BAT.Main methods(1)The core temperature and BAT temperature were simultaneously measured by dual probe telemetric monitoring transmitters in male Sprague-Dawley rats at an ambient temperature of 22°C during a 12 h light:12 h dark photoperiod. At 10:00 AM the rats were intraperitoneally injected with a 20%(v/v) ethanol(3 g/kg) solution(Sigma Chemical Co.) or 5-HT1 A receptor antagonist p-MPPI(1.0 mg/kg) solution(Sigma Chemical Co.) or saline of same volume.(2) Stained brown adipose tissue sections were examined under a microscope by hematoxylin and eosin(H&E) staining.(3) Sympathetic nerve innervating interscapular BAT was exposed through dorsal incision. The distal end of the nerve was ligated, and then hooked up with a pair of silver wire electrodes for recording the sympathetic nerve activity innervating brownadipose tissue(BAT-SNA).The recording electrodes were immersed in a pool of liquid paraffin oil to prevent dehydration and for electrical insulation. Nerve signals were recorded by BL-420 S Data Acquisition and Analysis System Performance of Chengdu Taimeng Sorftware Co.LTD.Main results(1)BAT temperature was 1.0°C lower than core temperature in both young and old rats during the light phase. Intraperitoneal injection of ethanol could elicit rapid drop in core temperature concomitant with a marked decrease in BAT temperature. It is interesting to note that the amplitude of decrease in BAT temperature was greater in old rat than that in young rats.(2)BAT was multilocular and presented lipid droplets in young as in old rats. However, lipid droplets of old rat were larger, and cellular density of BAT was lower as compared with the young rats.(3)Intraperitoneal injection of ethanol decreased gradually the BAT-SNA in both young and old rats, with the greatest level of suppression occurring at 75 min. However, level of suppression was greater in young rats than that in old rats. In contrast, injection of saline did not cause a significant alteration in the levels of BAT-SNA. 5-HT1 A receptor antagonist p-MPPI attenuated the ethanol-induced sympathetic nerve depression in young rats.Conclusion(1)Experimental data indicate that ethanol-induced hypothermia attributed to the suppression of BAT thermogenesis, because ethanol could elicit rapid drop in core temperature concomitant with a marked decrease in BAT temperature.(2)Hypothermia in old rats attributed to the decrease cellular density of brown adipose tissue.(3)The ethanol can decrease BAT temperature and sympathetic nerve activity innervating brown adipose tissue, suggesting that the mechanism of ethanol-induced hypothermia could involve the suppression of the BAT-SNA, and decrease BAT thermogenesis.