Effect of phentolamine on the insulin, glucagon, and glucose responses to exercise in adrenal-denervated sheep

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Abstract
Hyperglycemia and increased hepatic glucose output are characteristic responses to exercise in sheep. They appear to be due in part to α-adrenergic stimulation. To delineate the contributions of sympathetic innervation and adrenal catecholamines to the hormonal and metabolic responses to exercise, adrenal-denervated sheep were exercised with and without α-blockade (phentolamine treatment). Alpha blockade exaggerated the hyperinsulinemia during exercise (increment of 61 ± 8 vs. 34 ± 7 μU/mL for the control). This was associated with a reduction in glucose appearance (increments of 63 ± 8 vs. 236 ± 23 μmol/min, respectively). The metabolic clearance rates were not altered by α-blockade. It appears that both the adrenal catecholamines and adrenergic innervation to the pancreas contribute to the prevention of a rise in insulin concentrations during exercise in sheep. While this may not be essential for glucose appearance to rise during exercise, it appears necessary for an optimal response.

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