EXTRACELLULAR AND INTRACELLULAR EFFECTS OF POLYAMINES ON SMOOTH-MUSCLE CONTRACTIONS

The natural polyamines spermine, spermidine and putrescine, and their metabolic products N-1-acetylspermine (N-AS) and 5'-deoxi-5'-methylthi oadenosine (DMT), but not N-1-acetylspermidine nor N-acetylputrescine, relax the KCl-induced contraction in rat uterus in a dose-dependent w ay. This relaxing effect is counteracted by CaCl2 (0.1-6 mM) but not b y Bay K 8644. Spermine, N-AS and DMT also inhibit the contraction indu ced by methacholine and PGF(2 alpha). Spermine, DMT and N-AS relax the vanadate-induced contraction in uterus incubated in calcium-free solu tion plus EDTA. However, in the vanadate contraction, the EC(50)s are higher than those obtained with other contracturants. These results su ggest that polyamines inhibit smooth muscle contraction by action at p lasma membrane level decreasing the influx of calcium. However, intrac ellular actions of polyamines could also be involved in their effects.