CHRONIC ADRENERGIC-RECEPTOR BLOCKADE DOES NOT PREVENT HYPERINSULINEMIA-INDUCED HYPERTENSION IN RATS

Increased adrenergic activity has been suggested to mediate the hypert ension associated with hyperinsulinemia. This study tested whether com bined alpha(1)- and beta-adrenergic receptor blockade would prevent in sulin-induced hypertension when euglycemia was maintained by continuou s intravenous glucose infusion. Sprague-Dawley rats (n = 16) were inst rumented with artery and vein catheters and placed in metabolic cages. Propranolol and prazosin (10 mg/kg/day each) were infused continuousl y intravenously in 9 rats and 7 other rats received vehicle. Mean arte rial pressure (MAP) and heart rate (HR) were measured 24 h per day usi ng computerized methods. After a control period, a 7-day intravenous i nfusion of insulin (1.5 mU/kg/min) was begun and glucose was coadminis tered intravenously at 23 mg/kg/min to prevent hypoglycemia. The MAP a veraged 93 +/- 1 mm Hg in the blockade rats during the control period, which was significantly lower than the 98 +/- 1 mm Hg in the normal r ats. During insulin infusion, MAP increased similarly in both groups, with a 10 +/- 2 mm Hg and 11 +/- 1 mm Hg increase in normal and blocka de rats, respectively, by day 7. The HR also increased in both groups: from 417 +/- 8 beats/min to 426 +/- 13 beats/min (P = NS) in normal r ats and from 379 +/- 10 beats/min to 419 +/- 10 beats/min (P <.05) in blockade rats. Control sodium excretion averaged 2.5 +/- 0.1 mEq/day i n both groups and no significant change in sodium balance was measured in either group. All variables returned toward control after stopping insulin. These results suggest that increased adrenergic activity is not required for chronic hyperinsulinemia to raise blood pressure in r ats. (C) 1996 American Journal of Hypertension, Ltd.