Acetylpolyamines decrease blood pressure, [Ca++]i and isometric force of vascular smooth muscle.

Abstract

Polyamines are polycations in cells and acetylation is the first step in their intracellular metabolism. We investigated the effects of the acetylated polyamines on arterial blood pressure and vascular reactivities in rats. Acetylspermine and acetylspermidine, administered at concentrations ranging from 12.5 to 50 mmol/kg b.wt., both induced a transient decrease in mean arterial blood pressure. The magnitudes of the hypotensive effects of these acetylpolyamines and polyamines were in the order of spermine > acetylspermine > acetylspermidine = spermidine. Pretreatment of rats with calcium diminished polyamine-induced hypotensive effects. The effects of spermine and acetylspermine on isolated vascular smooth muscle were examined in rat aortic rings and tail artery strips. Both compounds relaxed precontracted arterial preparations, and this relaxation could be counteracted by increasing extracellular calcium concentration. Tail artery strips were more sensitive to acetylspermine when compared to aortic rings. In tail artery strips preloaded with the bioluminescent protein aequorin, both spermine and acetylspermine caused a concomitant decrease in intracellular calcium and isometric force activated by 36 mM of KCl. These results demonstrate clearly that acetylspermine and spermine alike decrease intracellular calcium concentration of vascular smooth muscle, which is likely to account for the relaxation of vasculature. The relaxation of smooth muscle in the vascular wall in turn might lead to decreased arterial blood pressure.