Exploring the mechanisms underpinning sweating: The development of a specialized ventilated capsule for use with intradermal microdialysis

Abstract

Many studies have aimed to identify the controllers of sweating using ventilated capsules with intradermal microdialysis. It is unclear, however, if the surface area covered by the capsule influences the observed response as a result of differences in the number of sweat glands affected by the infused pharmacological agent relative to the total glands captured by the capsule. We evaluated the area of skin perfused with agents delivered via microdialysis. Thereafter, we developed a specialized sweat capsule (1.1 cm2) and compared the sweating response with a classic capsule (2.8 cm2). In Protocol 1 (n = 6), methacholine was delivered to forearm skin in a dose-dependent manner (1-2000 mmol L-1). The area of activated sweat glands was assessed via the modified iodine-paper technique. In Protocol 2 (n = 6), the area of inhibited sweat glands induced by ouabain and atropine was assessed during moderate-intensity cycling. Marked variability in the affected skin area was observed (0.9 ± 0.4 to 5.2 ± 1.1 cm2). In Protocol 3 (n = 6), we compared the attenuation in local sweat rate (LSR) induced by atropine between the new and classic capsule during moderate-intensity cycling. Atropine attenuated sweating as assessed using the new (control: 0.87 ± 0.23 mg min-1 cm-2 vs. atropine: 0.54 ± 0.22 mg min-1 cm-2; P < 0.01) and classic (control: 0.85 ± 0.33 mg min-1 cm-2 vs. atropine: 0.60 ± 0.26 mg min-1 cm-2; P = 0.05) capsule designs. Importantly, responses did not differ between capsule designs (P = 0.23). These findings provide critical information regarding the skin surface area perfused by microdialysis and suggest that use of a larger capsule does not alter the mechanistic insight into the sweating response gained when using microdialysis. This study addresses the important question related to interpretability of sweating data based on the size (surface area coverage) of the sweat capsule when employed in conjunction with intradermal microdialysis. We showed marked variability in the area of skin perfused by the microdialysis fiber, which was strongly dose dependent. From these findings, a new ventilated capsule was designed specifically for use with intradermal microdialysis. Contrary to our hypothesis, we showed that the new capsule performed similarly to the classic capsule design suggesting that capsule surface is not a factor when determining the mechanisms of local sweating using microdialysis.