Source of calcium for contractile responses of large and small human intramyometrial arteries.
Specimens of the human uterine artery and its branches were taken at hysterectomy. By microscopical dissection, three groups of arteries were obtained with respect to size-main stem, medium and small branches (inner diameters of greater than 1, 0.6-0.8 and less than 0.4 mm, respectively). The contractile effects of different vasoactive substances were studied and the responses expressed as percentages of that of K(+)-depolarization calculated. The most potent vasoconstrictor (the lowest EC50 concentration) was arginine vasopressin (AVP) followed in order by endothelin, oxytocin, prostaglandin (PG)F2 alpha, noradrenalin and dopamine. Angiotensin had inconsistent effects. Atrial natriuretic peptide (ANP) counteracted the contractile effects of endothelin. AVP, endothelin, oxytocin and noradrenalin were significantly more potent on the smallest branches than on the main stem of the artery. Since the former type of vessel represents resistance arteries, the present results suggest that AVP, endothelin, oxytocin and noradrenalin could be of specific importance in the regulation of uterine blood flow. PGF2 alpha, dopamine and angiotensin appear to be of minor importance from this aspect but ANP could play a role by regulating the effects of endothelin.