1. The sensitivity of the hepatic glycogenolytic mechanism to splanchnic nerve stimulation at relatively low frequencies has been investigated in adrenalectomized calves, dogs and cats.2. In young calves the hyperglycaemic response to splanchnic nerve stimulation at 1.0 c/s for 5 min increased steadily during the first 2 weeks after birth.3. The hyperglycaemic response to splanchnic nerve stimulation for 5 min was directly related to frequency of stimulation within the range 0.5-4.0 c/s in calves tested 2-5 weeks after birth. Pronounced rises in plasma glucose concentration also occurred in calves of this age in response to maximal stimulation (20 c/s) for shorter periods (30 sec) whereas occlusion of the portal vein for the same period produced no comparable effect.4. The effects of splanchnic nerve stimulation for prolonged periods were also investigated in 2- to 5-week-old calves. Under these conditions increased concentrations of glucose in the plasma were maintained for periods of up to 90 min and fell towards the initial values when stimulation was discontinued.5. Prolonged stimulation of the peripheral ends of both splanchnic nerves at either 2.0 or 4.0 c/s produced a transient reversal of hypoglycaemia in calves pretreated with large doses of insulin; both the extent and duration of these responses were related to frequency of stimulation.6. The hyperglycaemic response to bilateral splanchnic nerve stimulation was directly related to frequency of stimulation within the range 0.5-4.0 c/s in adrenalectomized dogs. Comparable responses were obtained in adrenalectomized cats in response to stimulation at 2.0 c/s, but stimulation at 1.0 c/s produced no rise in mean plasma glucose concentration in these animals.7. The sensitivity of the hepatic glycogenolytic mechanism has been assessed in relation to the associated changes in haematocrit and mean aortic blood pressure under the same conditions.8. The results of these experiments support the contention that tonic changes in sympathetic efferent activity are associated with variations in the rate at which glucose is released from the liver under physiological conditions.
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