Effects of invariant sympathetic activity on cutaneous circulatory responses to heat stress

Abstract

This study investigated the role of sympathetic withdrawal on blood flow responses in cutaneous arteriovenous anastomoses (AVAs) and capillaries to direct and indirect heat stress. This was achieved by clamping sympathetic activity (SC) to the tail of anesthetized rats so that constrictor tone remained invariant during exposure of either the animal's tail (direct heating) or body (indirect heating) to a 35 degrees C environment. Flow through the AVAs in the tail was evaluated by laser-Doppler flowmetry (LDF), while capillary flow was investigated by videodensitometry measurements of blood cell velocity (CBV) in single capillaries within the subepidermal vascular plexus. Both direct and indirect heating significantly increased LDF and CBV. In comparison to blood flow responses in sham-operated control rats, the SC procedure resulted in significantly lower LDF responses to both direct and indirect heat stress. By contrast, the response of CBV was not significantly affected by SC during either mode of heating. These results indicate that the withdrawal of sympathetic constrictor tone plays a role in the response of cutaneous AVAs, but not precapillary arterioles, to direct as well as indirect heat stress. Additional studies on unanesthetized animals showed that superimposing body heating on a base of local heating elicited a further increase in LDF, suggesting that local heating does not deplete neural mediated dilatory reserve.

Effects of Estrogen on Thermoregulatory Responses in Freely Moving Female Rats

“…For example, Young et al 5 reported that the blood vessels in the tail of conscious female rats dilate when ambient temperature is higher than 29°C. But because their rats were confined in a small cage, augmented sympathetic nerve activity due to stress would have suppressed vasodilation 6 . Although differences in motor activities between different stages in the estrous cycle have been thought to be the reason for the differences in body temperature in female rats, 1 the high‐estrogen rats in the present study did not evidently move more than the low‐estrogen rats.…”

Effects of fasting on thermoregulatory processes and the daily oscillations in rats

“…Young and Dawson (33) reported that rats could dissipate ϳ25% of basal metabolic heat production through the tail by changing tail blood flow. In addition, tail blood flow is controlled by sympathetic nerve activity (14,19). It is known that fasting modulates sympathetic nerve activity in some organs such as the liver, adrenal gland, and adipose tissue (2,23,(34)(35)(36).…”

Effect of Urate on Nitric Oxide Microcirculatory Response in the Rat Tail to Body Heating

“…Microcirculatory blood flow measurements were made within the subepidermal vascular plexus of the rat's tail in accordance to previous methods (24,25,26,27,34). The vessels investigated in this study are referred to as capillaries, because their luminal diameters (from 3.5 to 4) are of capillary dimension.…”

“…The vessels investigated in this study are referred to as capillaries, because their luminal diameters (from 3.5 to 4) are of capillary dimension. Measurements of blood cell velocity (BCV) were obtained in individual vessels within the subepidermal vascular plexus by a videodensitometry method that was a computerized version of an analog system previously used (25,26,27,34) and described (25).…”