Endocrinologie et syndrome métabolique
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Sex Differences in Some Physiological Effects of Cold Season or Short-Term Cold Exposure in Adult Albino Rat

Adel Shalaby, Khaled A Abdel-Sater Eliwa, Ahmed M Hassan and Mohamed El-Fiky

Background: Cold exposure is a permanent part of human life. Response to cold varies according to different factors and individual differences. The main factors potentially differentiating thermoregulation in men and women are the properties of female physiology, anthropometric characteristics, body composition, social behavior and physical working capacity.

Aim of the study: Detecting the effect of short term cold exposure or cold season on body weight, food consumption, and levels of TSH, T3 , T4 , insulin, glucagon, adrenaline, cortisol, testosterone, progesterone and estrogen.

Material and methods: This study was carried out on 96 adult albino rats of local strain, half of them were males and the other half were females. The animals were divided equally into two control groups (males and females), and four experimental groups (two males and two females). Each group was divided into two equal sub-groups (one for morning experiment where blood samples were collected at 7:00 a.m to 8:00 a.m., and one for night experiment where blood samples were collected at 700 p.m to 8:00 p.m.). Blood samples were taken at the end of experimental period (7 days) for determination of TSH, T3 , T4 , insulin, glucagon, adrenaline, cortisol, testosterone, and progesterone and estrogen levels.

Results: Exposure of the body to cold produced the physiological responses according to the degree of cooling. The more severe the exposure to cold, the more marked were the effects that can be observed in body heat balance. Thyroid hormones increased through release of hypothalamus to TRH which led to release of TSH from the pituitary gland. Cortisol increased through stimulation of HPA axis. Adrenaline increased through stimulation of sympathetic nervous system and led to vasoconstriction and increased the release of fatty acids from adipose tissue to be used as energy substrates for heat production. Increased activity of the sympathetic nervous system during cold exposure led to decreased insulin secretion to increase blood glucose level which was used as a fuel for heat production. Activation of HPA was associated with increased progesterone hormone which has a role in thermogenesis. The increased needs for heat production in cold situations to keep body temperature constant led to increased food consumption, and the body weight showed no changes. This was because energy intake was used for heat production. Conclusion: Exposure to 4°C for 60 minutes for seven days cause significant increase in cortisol, adrenaline, estrogen, progesterone, insulin, T3 and TSH, while testosterone significantly decreased. Also, exposure to 15-17°C for seven days caused significant increase in cortisol, adrenaline, estrogen and progesterone, while testosterone hormone significantly decreased. No significant changes occurred in T4 and glucagon.