Abstract
5-hydroxytryptamine (5-HT, serotonin) is well-recognized to have vasodilator properties. For example, infusion of 5HT at low rates into rats decreases blood pressure acutely and chronically through reduction of total peripheral resistance. We recently showed that vasodilation in the hindquarters contributes to this fall in peripheral resistance. The hindquarter in the rat is mostly made up of skeletal muscle but also includes skin. Therefore, we hypothesized that an increase in blood flow in the skin, measured as an elevated temperature (T) in the thermoregulatory tail and paws, could contribute in part to 5-HT-induced reduction in blood pressure and hindquarters vasodilation. The temperature of thermoregulatory organs in the skin of anesthetized male, Sprague Dawley rats were measured using a Optris PI640 thermal camera. Blood pressure (from a radiotelemeter) and temperature of each paw and four locations along the tail (TL1-4) were recorded for 20 minutes before, during, and after infusion of 5-HT at a rate of 25 μg/min into the femoral vein. With this infusion protocol, the mean arterial blood pressure of rats fell over 30 mm Hg. However, the temperature of the paws (~29-32 o C) and tail (32 o at base, 25 o C at tip) were stable before and during 5-HT infusion, suggesting that flow was maintained, vs reduced, during this time. T increased during the 15-minute recovery time in all tail sections (base = from 32 o to 34 o C; tip from 23.5 o to 25.5 o C). Because the skin circulation exhibits only weak autoregulation, our results suggests that 5-HT infusion causes vasodilation of glabrous skin in the rat but without causing hyperemia. This could play a part in 5-HT induced hypotension.
Published Version
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