Although hyperinsulinemia and increased adrenergic activity have been postulated to be important factors in obesity-associated hypertension, a cause and effect relation between insulin, catecholamines, and hypertension has not been established. The aim of this study was to determine whether chronic hyperinsulinemia, comparable with that found in obese hypertensive patients, causes hypertension in normal dogs, increases plasma catecholamines, or potentiates the blood pressure effects of norepinephrine. In six normal dogs, insulin infusion (1.0 milliunits/kg/min) for 7 days, with euglycemia maintained, increased fasting insulin fourfold to sixfold. However, mean arterial pressure did not increase, averaging 99 +/- 2 mm Hg during the control period and 91 +/- 3 mm Hg during the 7 days of insulin infusion. Insulin did not alter plasma norepinephrine or epinephrine, which averaged 171 +/- 27 and 71 +/- 14 pg/ml, respectively, during the control period and 188 +/- 29 and 45 +/- 12 pg/ml during the 7 days of insulin infusion. In six dogs, norepinephrine was infused (0.2 microgram/kg/min) for 7 days to raise plasma norepinephrine to 2,940 +/- 103 pg/ml. Insulin infusion (1.0 milliunits/kg/min) for 7 days during simultaneous infusion of norepinephrine did not further increase mean arterial pressure, which averaged 101 +/- 3 during norepinephrine and 98 +/- 2 mm Hg during insulin plus norepinephrine infusion. Thus, chronic hyperinsulinemia did not increase mean arterial pressure or plasma catecholamines and did not potentiate the blood pressure actions of norepinephrine. These observations provide no evidence that chronic hyperinsulinemia or interactions between insulin and plasma catecholamines cause hypertension in normal dogs.