OBJECTIVE Perivascular adipose tissue of normotensive rats releases a transferable factor that induces relaxation by opening voltage-dependent K+ (Kv) channels. The relevance of these observations to hypertension is unknown. RESULTS We characterized mesenteric perivascular adipose tissue from 3-month-old Wistar Kyoto rats (WKY) and aged-matched spontaneously hypertensive rats (SHR). Mesenteric bed (MB) weight and MB total lipid content were lower in SHR than in WKY. Freshly isolated MB adipocytes were smaller in SHR. Plasma triglycerides, glycerol, nonesterified free-fatty acids, and cholesterol were also lower in SHR. Plasma and mesenteric leptin were correlated with the quantity of mesenteric fat. To study vascular function, the MB was cannulated and perfused at a constant 2 mL/min flow. The Kv channel blocker 4-aminopyridine (4-AP; 2 mmol/L) increased perfusion pressure less in SHR MB than WKY and was directly correlated with the mesenteric fat amount. In isolated mesenteric artery rings, 4-AP (2 mmol/L) induced a contractile effect that was attenuated in SHR compared with WKY. The anticontractile effects of perivascular fat were reduced in SHR mesenteric artery rings compared with WKY. CONCLUSIONS Differences in visceral perivascular adipose tissue mass and function may contribute to the increased vascular resistance observed in SHR.