Elevation in Plasma Catecholamines in Response to Insulin Stress Is under Both Neuronal and Nonneuronal Control*

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Abstract
We have examined the contribution of neurogenic and nonneurogenic influences to the secretion of adrenal catecholamines (CA) in adult rats after iv administration of insulin. Plasma CA levels were measured in control rats and in rats after surgical or pharmacological adrenal denervation or adrenalectomy. Insulin-induced CA secretion was biphasic and proportional to the insulin dose used. The first phase was neurogenic in origin and produced a moderate increase in plasma adrenaline (A) levels, with little or no change in noradrenaline (NA) levels. This neurogenic increase in plasma A was reduced by partial denervation and abolished by surgical complete adrenal denervation, adrenalectomy, or administration of hexamethonium and atropine. The second phase occurred later and produced a dramatic increase in both plasma A and NA. This phase was initiated when the plasma glucose level fell below 75 mg/100 ml. This late release of A and NA was not altered by surgical or pharmacological adrenal denervation, showing that it was nonneuronal in origin. However, both the early and late phases were abolished by adrenalectomy, showing that adrenal secretion of CA was the origin of the increased plasma levels of NA and A. The late rise in plasma CA was also abolished by iv administration of glucose. These data suggest that the mechanism responsible for the nonneurogenic secretion of adrenal CA in response to insulin stress was sensitive to the level of hypoglycemia.