Skin nerve sympathetic activity during insulin-induced hypoglycaemia.

Microelectrode recordings of skin nerve sympathetic activity, consisting of sudomotor and vasoconstrictor signals, were performed in the peroneal nerve in seven healthy subjects during insulin-induced hypoglycaemia. The nerve activity was recorded at rest and for 90 min after intravenous injection of 0.15 IU insulin/kg body weight. The net outflow of skin nerve sympathetic activity was increased during hypoglycaemia, with the exception of one subject who exhibited a high initial level of activity. In all subjects a change of the temporal pattern of the outflow was found, suggesting a shift from mixed (sudomotor and vasoconstrictor) to pure sudomotor activity. This change coincided with a sensation of warmth, sweating and varying degrees of cutaneous vasodilatation, and was followed by a fall in body temperature. It is concluded that hypoglycaemia has a differential effect on sympathetic activity in skin nerves, with a strong increase of sudomotor impulses and simultaneous inhibition of vasoconstrictor signals. Thus, neurally mediated thermoregulatory adjustment contributes to heat loss during hypoglycaemia.