Evidence for sodium-coupled acid-base transport across the basolateral membrane of the reabsorptive duct of the human eccrine sweat gland.

Intracellular pH was measured in isolated nonperfused ducts of human eccrine sweat glands in vitro to investigate basolateral acid-base transport mechanisms. Bath sodium removal led to a bicarbonate-independent, 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid insensitive acidification. The recovery of this acidification was ethylisopropyl amiloride sensitive, suggestive of basolateral sodium:hydrogen exchange. Whereas bath chloride removal led to a small acidification this was not 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid sensitive and its causes remain unclear. Elevation of bath potassium to depolarize the basolateral membrane led to a small alkalinization but this was not mimicked by addition of barium or chloride removal. As chloride removal and barium addition would be expected to cause larger depolarizations than potassium elevation these observations do not support a major role for electrogenic acid-base transport. In conclusion, although this study does not support a major role for electrogenic acid-base transport, it has demonstrated the basolateral presence of sodium-coupled acid-base transport in the reabsorptive duct of the human eccrine sweat gland, which most likely represents a sodium:hydrogen exchanger involved in regulation of intracellular pH.

Erroneous gender differences in axillary skin surface/sweat pH.

Assessing accurately the pH of axillary eccrine sweat is of vital importance in the antiperspirant industry. Eccrine sweat pH is a critical parameter in determining the effectiveness of antiperspirants; antiperspirant salts dissolve in sweat and diffuse into the sweat glands, where the resultant acidic solution hydrolyses in more alkaline sweat forming an amorphous metal hydroxide gel, thereby restricting the flow of eccrine sweat. Comparison of the skin surface and sweat pH of males and females reported in the literature shows that, although consistent male/female differences have been observed on the forearm, determination of significant gender-based pH differences across other sites are less conclusive. Studies on the back and infra-mammary regions exhibited significant gender differences in skin surface pH, whereas those on the forehead, cheek, neck and inguinal area showed no such difference. With regard to the axilla specifically, four studies have been reported, three showing no significant difference in axillary skin surface pH and one indicating that females have an eccrine sweat pH of 7 and males have a sweat pH of 5.6. This paper describes a series of carefully controlled studies aimed at assessing potential gender differences in eccrine sweat and skin surface pH following exposure to a variety of temperature, humidity and time conditions. The results highlight the importance of controlling precisely the time of investigation, site of measurement and, most importantly, the necessity to pre-equilibrate samples in 40 mmHg carbon dioxide (equivalent to arterial CO(2) tension (pCO2)) before determining sweat pH. When these parameters are controlled no gender differences in axillary sweat or skin surface pH are observed. Large differences in eccrine sweat and skin surface pH are found, however, between the vault (hairy region) and fossa (non-hairy region) of the axilla.

Circadian rhythms in axillary skin surface pH.

Sweat and skin surface pH are critical parameters in determining the performance of antiperspirants. The mechanism of action, the so-called 'plug theory' first proposed by Reller and Luedders, involves the expression of eccrine sweat onto the surface of the skin into which the solid antiperspirant salts, typically an aluminium chlorohydrate or zirconium aluminium glycine, dissolve. The resultant acidic 'solution' then diffuses with time into the sweat glands, where it hydrolyses in more alkaline sweat and forms an amorphous metal hydroxide agglomerate that physically plugs the ducts some 20-100 mum into the glands. It is therefore important to understand whether diurnal variations in skin surface pH exist in the axilla, as these may influence strongly the time of day at which antiperspirant should be applied in order to yield maximal protection. Clinical studies demonstrate a significant fall in axillary skin surface pH between the morning (pH = 5.87 +/- 0.23) and the evening (pH = 5.49 +/- 0.23). This diurnal variation in skin surface pH suggests that antiperspirant efficacy will be optimal when products are applied in the morning. In addition, the data suggest a circadian rhythm in axillary skin barrier function, indicating that chronopharmacology, the timing of administration of medication, could be used to optimize treatment of axillary hyperhidrotics using topical administration of anticholinergic drugs.