The role of the autonomic innervation in the control of glucagon release during hypoglycaemia in the calf

Abstract

1. The extent to which the autonomic innervation to the pancreas is implicated in the control of glucagon release during hypoglycaemia has been investigated in calves 3–6 weeks after birth. 2. A pronounced rise in plasma glucagon concentration occurred in normal conscious calves in response to hypoglycaemia following administration of insulin (0·1 u./kg). Prior treatment with atropine caused no significant change in the hypoglycaemic response to insulin in these animals but the rise in plasma glucagon concentration was delayed. 3. Section of both splanchnic nerves produced no significant change in the tolerance of conscious calves to this small dose of insulin and the changes in plasma glucagon concentration in these animals were within the normal range. 4. In contrast, the same dose of insulin produced severe hypoglycaemia, accompanied by convulsions, in atropinized calves with cut splanchnic nerves. In spite of the intensity of the hypoglycaemic stimulus the rise in plasma glucagon concentration was both delayed and diminished in these animals. 5. Administration of atropine alone (0·2 mg/kg) to normal fasting calves produced a significant fall in the mean plasma concentrations of both glucose and glucagon (P < 0·01) within 30 min, without affecting that of insulin. 6. A significant increase in plasma glucagon concentration also occurred in response to stimulation of the peripheral ends of the thoracic vagi in adrenalectomized calves with cut splanchnic nerves under barbiturate anaesthesia. A rise in mean plasma glucose concentration was also observed in these experiments and found to be significantly correlated with the glucagon response. 7. It is concluded that changes in either sympathetic or parasympathetic efferent activity may modify plasma glucagon concentration in the conscious calf, but that only the latter mechanism is likely to be implicated in the response to changes in plasma glucose concentration within the physiological range.