Reduced alpha- and beta(2)-adrenergic vascular response in patients with obstructive sleep apnea

Obstructive sleep apnea (OSA) has been associated with increased sympatheti c activity. This study tested the hypothesis that the alpha- and beta(2)-re ceptor-mediated vascular response is altered in patients with OSA. Forearm vascular resistance was evaluated by venous occlusion plethysmography in 10 normotensive OSA patients and 10 normotensive controls (apnea/hypopnea ind ex [mean +/- SD] 29.4 +/- 2.3 and 1.6 +/- 0.3 per hour, respectively) rough ly matched for body mass index (BMI) and age. Forearm vascular resistance w as measured after intraarterial infusion of norepinephrine (NE) (7.4, 31, 1 20, 472 and 1421 pmol/100 ml forearm volume [FAV]/min), before and after ph entolamine infusion (2 mu g/100 ml FAV/min), and isoproterenol (ISO) (1, 2, 6, and 15 ng/100 ml FAV/min). NE-induced vasoconstriction was significantl y attenuated in OSA patients compared with controls (65.0 +/- 36.6% versus 129.4 +/- 81.8%, p = 0.049). The reduction of vascular resistance after phe ntolamine was similar in patients and control subjects (-50.8 +/- 16.7% ver sus -43.4 +/- 20.0%, p = 0.38). During ongoing phentolamine infusion NE inc reased resistance to a similar extent in both groups (0.5 +/- 4.9% versus - 0.9 +/- 10.1%, p = 0.96). Vasodilation following ISO was significantly atte nuated in OSA patients compared with control subjects (-53.3 +/- 9.0% versu s -64.7 +/- 10.3%, p = 0.049). Moreover, the vascular response to NE in OSA patients was negatively correlated with plasma NE concentration (r = -0.76 , p < 0.05). The reduced vascular response to alpha- and beta-receptor stim ulation suggests a functional downregulation of vascular sympathoadrenergic receptors in patients with sleep apnea.