Localized β-adrenergic receptor blockade does not affect sweating during exercise

The purpose of the current study was to determine the effect of a locally administered nonselective β-adrenergic antagonist on sweat gland function during exercise. Systemically administered propranolol has been reported to increase, decrease, or not alter sweat production during exercise. To eliminate the confounding systemic effects associated with orally administered propranolol, we used iontophoresis to deliver it to the eccrine sweat glands within a localized area on one forearm prior to exercise. This allowed for determination of the direct effect of β-adrenergic receptor blockade on sweating during exercise. Subjects ( n = 14) reported to the laboratory (23 ± 1°C, 35 ± 3% relative humidity) after having refrained from exercise for ≥12 h. Propranolol (1% solution) was administered to a 5-cm2 area of the flexor surface of one forearm via iontophoresis (1.5 mA) for 5 min. A saline solution was administered to the opposing arm via iontophoresis. Each subject then exercised on a motor-driven treadmill at 75% of their age-predicted maximal heart rate for 20 min, while sweat rate was measured simultaneously in both forearms. Immediately after cessation of exercise, the number of active sweat glands was measured by application of iodine-impregnated paper to each forearm. The sweat rate for the control and propranolol-treated forearm was 0.62 ± 41 and 0.60 ± 0.44 (SD) mg·cm−2·min−1, respectively ( P = 0.86). The density of active sweat glands for the control and propranolol-treated forearm was 130 ± 6 and 134 ± 5 (SD) glands/cm2, respectively, ( P = 0.33). End-exercise skin temperature was 32.9 ± 0.2 and 33.1 ± 0.3°C for the control and propranolol-treated forearm, respectively ( P = 0.51). Results of the current study show that when propranolol is administered locally, thus eliminating the potential confounding systemic effects of the drug, it does not directly affect sweating during the initial stages of high-intensity exercise in young, healthy subjects.

Locomotory energetics in a marsupial, Setonix Brachyurus

The gait patterns, rates of oxygen consumption, body temperature and sweat gland activity were examined in S. brachyurus during locomotion on a treadmill. At speeds up to 12.6 km h-1 the animal moved in a quadrupedal bound occasionally punctuated by six or seven hops. At the higher speeds within this range, stride frequency became relatively constant and increases in stride length were the primary determinants of increased speed. Rates of oxygen consumption increased linearly with speed of locomotion up to 7.6 km h-1; above this range the animals would not run for prolonged periods when wearing a gas collection mask. The gradient of this line was similar to that predicted for a eutherian of similar body mass, but the extrapolation to zero speed was much higher than found in other mammals. As the quokka increased speed, a greater proportion of the heat produced while running was stored. At 7.6 km h-1, this was 60% of the total production. Active sweat glands were demonstrated on the limbs and feet during locomotion.

HISTOCHEMICAL DIFFERENTIATION OF TWO FORMS OF GLYCOGEN SYNTHETASE

Glycogen synthetase exists in two forms; one form is dependent on glucose 6-phosphate while the other is not. Variations in the levels of activities of the two forms of the enzyme were observed histochemically in active and inactive eccrine sweat glands from eight rhesus monkeys. The clear cells of active sweat glands showed less glucose 6-phosphate-independent glycogen synthetase activity than the clear cells of inactive sweat glands.