[The effects of heparin on intrauterine arteries of the human non-pregnant uterus: II. The analysis of the route of action].

OBJECTIVE

Our purpose was to elucidate the mechanism of heparin action on smooth muscle of small intramyometrial arteries.

MATERIAL AND METHOD: Material was obtained, contractility and calcium concentration were measured as previously described. Calcium influx to the vascular cells was also measured.

RESULTS

Heparin did not change basal tension of the arterial strips. The strips precontracted by K(+)-depolarisation were relaxed by heparin at concentration: 200-1000 UI/mL. The maximal relaxation never exceeded 66 +/- 5.1%. Heparin (200 UI/mL) decreased the free calcium concentration in Tyrode solution to 0.8 mM. Such a lowering of the free calcium concentration diminished vascular contractile reactions. Heparin did not disturb the basal calcium influx into vascular cells but significantly decreased that which was stimulated by K+ depolarisation. 120 min treatment with heparin resulted in reducing the arterial response to 3 x 10(-8) M vasopressin recorded in Ca-free conditions.

CONCLUSIONS

1. Our results suggest that heparin, in vitro, effects the vascular smooth muscle contractions by influence on both extracellular free calcium concentration and Ca2+ influx into cytoplasm. 2. Relaxant action of heparine, on the vascular smooth muscle, is activated by additives present in commercial preparation.