Regional Differences in the Na+ Reabsorption of Sweat Glands.

Abstract

Sweat glands with a higher capacity for both sweat secretion and sodium reabsorption would contribute more effectively to thermoregulation, with less tendency to cause sodium depletion. The rate at which sweat glands reabsorb sodium and chloride does not increase proportionally as the rate of sweating increases, so that [Na + ] and [Cl -] in sweat sampled on the skin surface increase with sweating. It has been reported that there is a significant positive correlation between sweat secretory capacity and the capacity of sweat to reabsorb Na + (Sato and Dobson, 1970) and between sweat gland size and sweat secretory capacity (Sato and Sato, 1983). It has also been suggested that the sweat glands on the trunk may be larger than those on the limbs (Inoue and Shibasaki, 1996). Based on these findings, it is expected that the sweat glands on the trunk have a superior Na + reabsorptive capacity than those on the limbs. We know little about the slope of the relation of sweat [Na + ] to sweating rate at different body sites. Obtaining such information may be valuable to a better understanding of regional differences in sweat glands capacity for Na + reabsorption. Therefore, we compared the relationship between sweating rate and [Na + ] on the chest, back, forearm and thigh. MethodsThe subjects for this study were seven healthy male volunteers. The mean ± SD age, height, weight, . percentage body fat and maximal oxygen uptake (VO2max) of the subjects were 23.9 ± 4.7 years, 172 ± 3 cm, 69.35 ± 3.65 kg, 13.7 ± 1.7 % and 50.7 ± 4.2 mL · kg -1 · min -1 , respectively. Six of the men were college students who occasionally played various sports (rugby, soccer, golf and handball) and the remaining man was a laboratory researcher. All of the subjects were informed of the potential risks involved in participating in the study and gave their written consent.All of the experiments were conducted in August and September. The subjects refrained from food and water for at least two hours prior to each exercise session, to better control their state of hydration. There were no other dietary restrictions. The subjects, wearing only swimming trunks, pedaled a cycle ergometer for 60 min at different workloads (165-908 kpm · min -1 ) on separate days. Each subject carried out the 60-min exercise 4 to 7 times. Each 60-min exercise was performed in a climatic chamber, controlled at an air temperature of 30 ± 0.5°C and a relative humidity of 60 ± 5%. During the exercise, local sweat samples (12.6 cm 2 ) were collected successively on the chest (mid-pectoral), back (sub-scapular), forearm (mid-anterior), and thigh (mid-anterior) at 20 min intervals by the filter paper method (Inoue et al., 1991). . The local sweating rate (msw) on the chest, back, forearm, and thigh was then determined from the change in the weight of the filter paper, using an electronic balance accurate to ± 0.1 mg and expressed in mg · cm -2 · min -1 . The sodium concentration ([Na + ]) in the sweat was determined after eluting the Na + from the paper, and analyzing for Na + b...

Changes in the index of sweat ion concentration with increasing sweat during passive heat stress in humans

“…On the other hand, the threshold of sweat rate at which sweat ion concentration increases rapidly may reflect a threshold for imbalance between production and reabsorption of ion in the sweat secretion system (a process of secretion from sweat gland to sweat duct). Thus, this threshold might reflect the capacity for ion reabsorption in the sweat duct, as it has been previously reported (Cage and Dobson 1965;Inoue et al 1998;Schwarz and Simpson 1985;Slegers 1967).…”

“…3). These relationships have not been identified in earlier studies, due to the methodological deficiencies of the previous techniques of sweat ion concentration measurement at low levels of sweating (Allan and Wilson 1971;Elizondo et al 1972;Inoue et al 1998;Tanaka et al 1992). …”

“…Since sweat sodium and chloride concentrations are lower than those in plasma, it has been suggested that these electrolytes are reabsorbed as they pass through the sweat duct (Inoue et al 1998;Sato 1977;Sato et al 1989). To determine ductal sodium reabsorption indirectly, a practical method of using the relationship between SR and SR · sweat ion concentration has been proposed by the earlier reports (Schwartz and Thaysen 1956;Cage and Dobson 1965).…”

Sodium ion concentration vs. sweat rate relationship in humans

“…The exact mechanism responsible for this is unknown; however, it has been suggested that above a certain sweat rate threshold there is insufficient time for complete sodium ion reabsorption from the duct (28). It is believed that this threshold reflects the capacity for ion reabsorption of the sweat duct (11,28). In light of the above, it is clear that changes in sweat [Na ϩ ] following heat acclimation can be misleading if they are not presented in relation to sweat rate.…”

Determination of the maximum rate of eccrine sweat glands’ ion reabsorption using the galvanic skin conductance to local sweat rate relationship

“…Conventionally, filter paper, gauze pads, or commercial sweat collectors have been used to collect sweat for measurement of electrolyte concentrations (Buono et al 2007;Inoue et al 1998;Allan and Wilson 1971;Verde et al 1982;Araki et al 1981;Hamouti et al 2011). …”