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Abstract

Background: Sodium nitroprusside (SNP) is a nitric oxide donor (NO) donor used as an antihypertensive agent in emergency. However, it has limited use now because of cyanide poisoning due to breakdown of SNP to NO and five cyanide radicals.

Objective: To evaluate the dose-dependent effects of SNP on active tension (inotropic response) and rate of contraction (chronotropic response) in isolated rabbit intestinal smooth muscle.

Study Design and Setting: Animal study in which experimental study design was used and study was conducted in Physiology department of Karachi University.

Methodology: The intestine was isolated from animal and mounted on organ bath assembly. Responses of varying incremental concentrations SNP (0.5mM, 1.5mM, 2.5mM, 5.5mM, 10.5mM, 12.5mM & 14.5mM) with saline used as control, were observed for two contractile parameters i.e. active tension and rate of contraction, at 40 min time point. The recordings were analyzed using one way ANOVA followed by Bonferroni post hoc test and student paired t-test.

Results: The results showed that the doses 0.5 and 1.5 mM SNP had greater while the doses 2.5, 5.5, 10.5, 12.5 and 14.5 mM caused significant decline in inotropic response compared with control. There was a decline in chronotropic response in a dose dependent manner, albeit insignificant while maximum change of relaxation noted at 1.5mM concentration when compared with saline.

Conclusion: SNP produced a dose-dependent effect on isolated rabbit intestinal smooth muscle, with higher concentrations significantly reducing active tension. This overall smooth muscle relaxation response by SNP indicates that SNP is responsible for release of NO.

Keywords

Active tension, ionotropic, nitric oxide, smooth muscle contraction, and sodium nitroprusside.