Catecholamine concentrations during exposure of resting man to the heat of a standard sweat test.

1. Normal subjects were heated for 45 min with a heat cradle under the conditions used to investigate sweating clinically. 2. Skin temperatures on the chest and in the external auditory meatus rose but concentrations of noradrenaline and adrenaline decreased during heating. 3. There was no change in adrenoceptor affinity or number as a result of the heat exposure. 4. There was little change in blood pressure and heart rate and no dysrhythmias were observed with an electrocardiogram. 5. It is concluded that heating with a heat cradle is generally not stressful and that there is a reduction in sympathetic nervous activity involving noradrenergic or adrenergic transmission during the procedure.