The purinoceptor agonist ATP has been shown to induce sweating in isolated glands (Sato et al. 1991) and to increase intracellular calcium in primary cultures of human glands (Bovell et al. 2000). These findings have indicated the presence of a P2Y receptor and recently we have localised three receptor subtypes in normal human glands (Lindsay et al. 2002). Although the function of purinoceptors is still elusive, their presence in normal glands suggests they have a role in sweat secretion. Hyperhidrosis, a condition characterised by the production of an inappropriately large volume of sweat, may have purinoceptor involvement. The presence of such receptors in hyperhidrotic glands has, to our knowledge, not been investigated and therefore immunohistochemistry was employed to investigate the localisation and possible differing distribution of the P2Y₁, P2Y₂ and P2Y₄ subtypes, in human hyperhidrotic eccrine sweat glands.

Skin biopsies were obtained by informed consent and with local medical ethical committee approval, from both male and female patients, with the condition hyperhidrosis. Samples were fixed (10 % buffered formalin) and processed using standard techniques. Immunohistochemical staining was performed using rabbit antibodies raised against P2Y₁, P2Y₂ and P2Y₄ (Alomone Labs, Israel), employing the avidin-biotin complex (ABC) procedure (Vector Labs, UK). Sections were counterstained with haematoxylin, dehydrated, cleared, mounted and viewed using light microscopy.

In all samples analysed, the eccrine reabsorptive duct of hyperhidrotic glands was shown to contain dark P2Y₁-, P2Y₂-and P2Y₄-like immunoreactivity localised to the apical membrane (n = 6, n = 8 and n = 5, respectively), which was similar to that found in normal glands. However, hyperhidrotic glands exhibited staining throughout the basolateral membranes with all three antibodies, which was not seen in normal glands. The secretory coil of hyperhidrotic sweat glands was shown to have staining localised to what looks to be the light cells of the coil with P2Y₁, P2Y₂ and P2Y₄ (n = 4). This pattern of staining was only seen in normal glands with P2Y₄ antibody and not with the other two subtypes. Immunoreactivity was localised to the outer myoepithelial cells with P2Y₁ and P2Y₂ (n = 4 and n = 7) in both normal and hyperhidrotic glands. Preabsorption of the antibodies with the appropriate control peptide abolished all specific staining.

The presence of apical purinoceptors in the duct of hyperhidrotic glands is similar to that of normal glands and is suggestive of apical regulation of absorption. Hyperhidrotic sweat glands showed an increased distribution of the P2Y receptor subtypes compared to normal glands. These receptors may be present to help reabsorb as much fluid as possible and prevent drastic salt loss. The clear cells of the secretory coil are the ones predominantly involved in sweat secretion and the localisation of all three subtypes in these cells of hyperhidrotic glands suggests that these receptors are implicated in sweat secretion and could play a role in the condition hyperhidrosis. The myoepithelial cells of the sweat gland are not regarded as cells involved in either secretion or reabsorption of sweat and the presence of purinoceptors requires further investigation.

S.L.L is supported by a GCU studentship.