Muscle sympathetic nerve activity in patients with acromegaly

Muscle sympathetic nerve activity was measured in nine acromegalic patients (age, 35 +/- 4 yr; body mass index, 28 +/- 2 kg/m(2)) and eight healthy su bjects (age, 32 +/- 3 yr; body mass index, 25 +/-: 2 kg/m2) by combining th e forearm arterial-venous difference technique with the tracer method [infu sion of tritiated norepinephrine (NE)]. Muscle NE release was quantified bo th at rest and during physiological hyperinsulinemia while maintaining eugl ycemia (similar to 90 mg/dL) by means of the euglycemic clamp. Arterial plasma NE was similar in the two groups at rest (197 +/- 28 and 20 0 +/- 27 pg/mL(-1)) and slightly increased during insulin infusion. Forearm NE release was 2.33 +/- 0.55 ng.liter(-1).min(-1) in healthy subjects and 2.67 +/- 0.61 ng liter(-1)min(-1) in acromegalic subjects in the basal stat e and increased to a similar extent during insulin infusion in both groups (3.13 +/- 0.71 and 3.32 +/- 0.75 ng.L-1 min(-1), P < 0.05 vs. basal), indic ating a normal stimulatory effect of insulin on muscle sympathetic activity . In contrast, insulin-stimulated forearm glucose uptake was markedly lower in acromegalic patients (2.3 +/- 0.4 mg.L-1 min(-1)) than in control subje cts (7.9 +/- 1.3 mg.L(-1)min(-1), P < 0.001), indicating the presence of se vere insulin resistance involving glucose metabolism. Our data demonstrate that patients with long-term acromegaly have normal sy mpathetic activity in the skeletal muscle in the basal, postabsorptive stat e and normal increments in NE spillover in response to the sympatho-excitat ory effect of insulin. Thus, the presence of severe insulin resistance in a cromegaly is not accounted for by adrenergic mechanisms.