Epidermal thermal conductivity and stratum corneum hydration in cat footpad

Epidermal thermal conductivity (k) was calculated for the cat footpad by measuringtransepidermal heat flux and temperature gradient (¿T) while changes in stratum corneum water content were produced by "internal hydration" (IH; eccrine sweat gland activity by nerve stimulation) or by "external hydration" (HH; exposure to air saturated with water vapor). In some experiments, cutaneous vasoconstriction accompanying IH was prevented by an alpha-adrenergic receptor blocking agent, phenoxybenzamine (POB), 3.52 mg/kg iv. For dry skin k=0.167 plus or minus 0.023 (SE) W.m (-1) degree C (-1). With and without POB, IH produced 49.5% and 17.2% increases in k, respectively; HH after IH did not increase k more. With POB, IH increased k more than did HH alone (49.5% and 15.5%, respectively) and at a higher rate (4.22 times 10 minus 3 and 0.63 times 10 minus 3 W.m minus 1.degree C minus 1. min minus 1, respectively.) As k increased, usually deltaT decreased. Increasing k and decreasing deltaT with skin hydration explain the phenominon that air temperature is felt to be lower the more humid a cold exposure, since the temperature of thermoreceptors at the dermoepidermal junction is closer to that of the skin surface when the corneum is hydrated than when it has a low water content.