Enhanced role for RhoA-associated kinase in adrenergic-mediated vasoconstriction in gracilis arteries from obese Zucker rats

Obesity, insulin resistance, dyslipidemia, and hypertension are components of the pathophysiological state known as metabolic syndrome. Adrenergic vasoconstriction is mediated through increases in cytosolic Ca2+ and the myofilaments' sensitivity to Ca2+. In many pathophysiological states, there is an enhanced role for Rho kinase (ROK)- mediated increases in Ca2+ sensitivity of the contractile apparatus. Thus we hypothesized that there is a greater role for ROK- mediated increases in Ca2+ sensitivity in alpha(1)-adrenergic vasoconstriction in arteries from obese Zucker (OZ) rats. Therefore, small gracilis muscle arteries from 11- to 12-wk-old and 16- to 18-wk-old lean and OZ rats were isolated, cannulated, and pressurized to 75 mmHg. For some experiments, vessels were loaded with fura 2-AM. Changes in luminal diameter and vessel wall Ca2+ concentration ([Ca2+]) were measured in response to phenylephrine ( PE), the thromboxane mimetic U-46619, and KCl. alpha(1)-Adrenergic vasoconstriction was similar between 11- to 12-wk-old lean and obese animals and greater in older obese animals compared with controls. PE- induced increases in vascular smooth muscle cell [Ca2+] were blunted in OZ animals compared with lean controls in both age groups of animals. KCl and U-46619 elicited similar vasoconstriction and vascular smooth muscle cell [Ca2+] in both groups. ROK inhibition attenuated PE vasoconstriction to a greater degree in arteries from 11 to 12-wk-old OZ rats compared with lean animals; ROK inhibition in arteries from older rats right shifted both concentration-response curves to the same point. Total RhoA and ROK alpha protein expressions were similar between groups. These results suggest an enhanced role for the ROK pathway in alpha(1)-adrenergic vasoconstriction in metabolic syndrome.