Effects of p38 mitogen-activated protein kinase inhibition on blood pressure, renal hemodynamics, and renal vascular reactivity in normal and diabetic rats.

p38 mitogen-activated protein kinase (p38) has been implicated in mediating vascular smooth muscle and mesangial cell contraction in response to several vasoactive factors, including angiotensin II. Early stages of diabetic nephropathy are associated with renal hemodynamic changes that are, at least in part, attributable to the dysbalance of vasoactive factors that control afferent and efferent arteriolar tone resulting in increased glomerular capillary pressure. Vascular and renal p38 have been found to be activated in diabetes. Therefore, p38 may be involved in the control of systemic and renal hemodynamics in diabetes. To address this issue, mean arterial blood pressure (MAP), glomerular filtration rate (GFR, inulin clearance), renal plasma flow (RPF, PAH clearance), metabolic parameters, and plasma renin concentrations (PRC) were determined in streptozotocin-diabetic rats (DM), and in age-matched non-diabetic controls (C), administered with the p38 inhibitor SB 239063 (SB, 50 mg/bwt, p.o.) or with vehicle. Furthermore, renal vascular responses to p38 inhibition (SB 202190, 25 microM) before and after stimulation with the endothelium-dependent vasodilator acetylcholine (ACh) were studied in vitro in tertiary branches of the renal artery from separate groups of DM and C rats, using a fixed support and a force transducer in a myograph system. SB treatment was associated with marked reductions in MAP and GFR in both C and DM rats, whereas RPF remained unchanged, as compared with vehicle-treated animals. Observed differences in MAP and renal hemodynamics were not associated with changes in urinary sodium excretion or PRC. Incubation of KCl-contracted renal arteries from both C and DM rats with the p38 inhibitor resulted in progressive and significant vasorelaxation. Also, vessels from control and diabetic rats treated with the p38 inhibitor exhibited enhancement of ACh-induced vasorelaxation. These data indicate the role of p38 in the control of systemic and renal hemodynamics both in normal and in diabetic rats. The observed effects of p38 inhibition could be mediated at least in part by enhancement of endothelium-dependent vasodilation.