Cocaine and contractile responses of vascular smooth muscle from spontaneously hypertensive rats

The goal of this study was to compare the effects of cocaine on contractile responses of isolated vascular smooth muscle from spontaneously hypertensive (SHR) and normotensive rats. Helical strips of tail artery from adult SHR and normotensive rats were mounted in organ chambers between two platinum wire electrodes; isometric contractions were recorded. Vascular responsiveness was determined before and after acute denervation with 6-hydroxydopamine or before and after treatment with cocaine. Cumulative addition of cocaine (10^-10 to 10^-3 M) produced contraction of the strips. SHR was found to be less sensitive to cocaine than normotensive rats. Contractions induced by cocaine were blocked by phentolamine and reduced after acute denervation. The sensitivity to exogenous norepinephrine (3 X 10^-12 to 3 X 10^-5 M) and contractile responses to electrical stimulation (0.1 to 16 Hz) of innervated strips were similar for SHR and normotensive rats. Cocaine (10^-6 M) potentiated contractile responses to norepinephrine and electrical stimulation. The magnitude of potentiation to norepinephrine and to electrical stimulation was greater in SHR than in normotensive rats. Cocaine (10^-6 M) produced relaxation of strips contracted with tyramine (10^-4 M). The magnitude of relaxation induced by cocaine was less in SHR than in normotensive rats. The uptake of ³H-norepinephrine was greater in tail arteries isolated from SHR as compared to those from normotensive rats. Cocaine (10^-4 M) inhibited the uptake of ³H-norepinephrine in both groups of rats. The magnitude of inhibition was greater in SHR. These results suggest that the neuronal uptake pump in blood vessels from SHR is more efficient than that in normotensive rats.