OBJECTIVE To compare the effects of chronic glibenclamide and metformin therapy on blood pressure (BP) and cardiovascular responsiveness in patients with NIDDM.

RESEARCH DESIGN AND METHODS Fourteen patients with NIDDM received metformin or glibenclamide for 1 month in a double-blind, randomized crossover study. At the end of each treatment period, patients were tested for forearm vascular responsiveness to intrabrachial arterial infusion of diazoxide (an ATP-sensitive potassium channel opener), acetylcholine, sodium nitroprusside, and norepinephrine, BP responses to intravenous infusions of NE and angiotensin II, BP responses to cold pressor testing and isometric exercise, and 24-h ambulatory BP monitoring.

RESULTS Metformin and glibenclamide produced similar glycemic control. Mean 24-h BPs did not differ between the two groups, but mean 24-h heart rates were significantly lower (75 ± 6 bpm vs. 80 ± 6 bpm) on glibenclamide therapy than on metformin. Plasma norepinephrine levels were significantly higher on glibenclamide (6.41 ± 1.77 vs. 4.26 ± 1.54 mmol/l, P < 0.01), and systolic BP responses to intravenous norepinephrine and angiotensin II were significantly higher on glibenclamide than on metformin (P < 0.02 and P < 0.05, respectively). Systolic BP responses to cold pressor testing appeared higher on glibenclamide than on metformin, but the difference did not quite achieve statistical significance (P = 0.052). Baseline forearm vascular resistance did not differ between the two drugs, nor did forearm vascular resistance responses to diazoxide, acetylcholine, sodium nitroprusside, and norepinephrine differ.

CONCLUSIONS Glibenclamide therapy is accompanied by greater systolic BP responses to norepinephrine and angiotensin II and higher plasma norepinephrine levels than those that occur on metformin therapy. Lower heart rates on glibenclamide therapy despite evidence of greater sympathetic activity suggests that glibenclamide may have negative chronotropic effects.