Effect of aging and drug-induced weight reduction on rat vascular reactivity.

We determined the effects of D-fenfluramine treatment on the changes in vascular reactivity induced by aging. Nine- and 49-week-old Sprague-Dawley rats (a strain known to develop hyperinsulinemia and glucose intolerance during the aging process) were treated for 3 weeks either with D-fenfluramine 2.5 mg/kg twice daily orally or with vehicle. The rats were then exsanguinated and the abdominal aorta was carefully removed, cut into rings, and suspended in organ chambers for isometric tension recording. Control old rats (vehicle) had a significantly lower glucose infusion rate (an index of insulin resistance), and higher blood pressure (BP), glycemia, and insulinemia than young rats. The D-fenfluramine treatment in the aged animals produced a significant decrease in insulinemia and body weight. In aorta from the older treated and nontreated animals, the contraction to alpha-adrenergic stimulation and to the thromboxane analogue U46619 was significantly reduced as compared with that in young animals, but the response to KCl was unaffected. In contrast, in the old nontreated rats, the aorta was hyperresponsive to serotonin. D-Fenfluramine abolished this hyperreactivity. The response to beta-adrenergic stimulation and to forskolin was inhibited in the older animals but was not influenced by the treatment. Endothelium-dependent relaxations to acetylcholine were not statistically different in the various groups, but the endothelium-dependent relaxation to ADP was reduced in the control group of older animals. D-Fenfluramine treatment restored the response to ADP.