Sweating and skin temperature responses of normal and anhidrotic horses to intravenous adrenaline

Summary Anhidrosis has been recognised for over half a century, but despite some excellent epidemiological studies, there has been little progress in understanding the aetiology of the condition. Using a modified ventilated capsule, we obtained dynamic, quantitative data on sweating responses in anhidrotic horses and normal sweating controls from the same environment. Ten horses with current seasonal anhidrosis and 10 matched normal sweating controls were selected. Each horse was given two 10 min infusions of 1 and 2 μg/kg/min adrenaline, separated by at least 6 h. Sweating responses and skin temperatures on the neck and gluteal region were measured. Plasma and sweat for analysis of total protein and electrolytes and plasma for analysis of adrenaline were collected. Anhidrotic horses produced significantly less sweat, had lower initial and peak sweat rates and a greater neck:gluteal ratio for sweat production. Plasma adrenaline at rest or at the time of peak sweating rate was not different between groups. In nearly three‐quarters of the anhidrotic horses, the shape of the sweat rate against time curve was different compared to controls. Volume of sweat produced was significantly correlated with skin temperature on the neck of controls and anhidrotic horses and on the gluteal region of controls, but not anhidrotic horses. Plasma total protein and electrolyte concentrations were not different between groups. There were significant differences in sweat electrolyte concentrations between controls and anhidrotic horses. These differences were reduced when sweat electrolytes were expressed per g of total protein, and no differences existed when expressed as g/m 2 . This study has provided insight into the response of anhidrotic horses to β2 adrenergic stimulation and may be a useful technique to investigate this condition.