Extracellular and intracellular effects of polyamines on smooth muscle contractions.

The natural polyamines spermine, spermidine and putrescine, and their metabolic products N1-acetylspermine (N-AS) and 5'-deoxi-5'-methyl-thioadenosine (DMT), but not N1-acetylspermidine nor N-acetylputrescine, relax the KCl-induced contraction in rat uterus in a dose-dependent way. This relaxing effect is counteracted by CaCl2 (0.1-6 mM) but not by Bay K 8644. Spermine, N-AS and DMT also inhibit the contraction induced by methacholine and PGF2 alpha. Spermine, DMT and N-AS relax the vanadate-induced contraction in uterus incubated in calcium-free solution plus EDTA. However, in the vanadate contraction, the EC50s are higher than those obtained with other contracturants. These results suggest that polyamines inhibit smooth muscle contraction by action at plasma membrane level decreasing the influx of calcium. However, intracellular actions of polyamines could also be involved in their effects.