Elevated insulin, norepinephrine, and neuropeptide Y in hypertension. To investigate the relationship between insulin and sympathetic activity, plasma norepinephrine, neuropeptide Y, serum glucose and insulin concentrations were measured in ten age-, weight-, and sex-matched normotensive and untreated hypertensive subjects at fasting and 2 h following ingestion of a 75 g oral glucose dose. Hypertensives had higher fasting serum insulin (27 +/- 6 v 12 +/- 2 microU/mL; P = .02) and plasma norepinephrine (356 +/- 38 v 235 +/- 35 pg/mL; P = .03) concentrations than normotensives. Glucose load increased serum insulin (P less than .001) and plasma norepinephrine concentrations (P = .001) in both groups and hypertensives had still higher postglucose insulin (P = .003) and norepinephrine levels (P = .003) than normotensives. Fasting neuropeptide Y was higher in hypertensives than in normotensives (P = .03) and correlated with age in both groups (r = 0.7; r = 0.77). Postglucose serum insulin correlated positively with plasma norepinephrine (r = 0.75; P = .013) in normotensives, but these parameters correlated negatively in hypertensives (r = -0.7; P = .036). We hypothesize that elevated plasma norepinephrine and neuropeptide Y levels reflect an increased level of sympathetic nervous activity in hypertensives, which in turn may be responsible for the abnormal relationship between plasma NE and insulin levels. 