Nitroprusside enhances isoprenaline-induced increases in cAMP in rat aortic smooth muscle.

Low concentrations of sodium nitroprusside (SNP) and of isoprenaline acted synergistically to inhibit the phenylephrine-induced contraction of rat aortic smooth muscle. In experiments with these concentrations, SNP enhanced the increases in smooth muscle cAMP caused by isoprenaline by 4- to 5-fold, whereas the SNP-induced increases in tissue cGMP were unaffected by isoprenaline. We conclude that cAMP is likely to mediate the synergistic inhibition of the contraction of rat aortic smooth muscle by these compounds.