Different responses to prostaglandin F2 alpha and E2 in human extra- and intramyometrial arteries

Tubal segments of the ascending uterine arteries and of intramyometrial arteries were obtained from 18 women who underwent hysterectomy at various phases of the menstrual cycle. Ring preparations of the vessels were mounted in organ baths and isometric tension was recorded. In extramyometrial arteries (outer diameter 2-3 mm) prostaglandin (PG) F2 alpha most potently, but also PGE2 caused concentration-related contractions. In contrast, the contractant effects of both PGs on intramyometrial arteries (outer diameter 0.5-0.6 mm) were negligible. Both extra- and intramyometrial vessels were relaxed to a moderate degree (10-25%) by low concentrations of PGF2 alpha and PGE2. No significant differences between the responses to vasopressin and noradrenaline were found between the vessel preparations. Thus human uterine arteries seem to change their responses to PGF2 alpha and PGE2 as they enter the myometrium and decrease in diameter, and the results raise doubt about the view that direct vasoconstrictor effects of these PGs contribute to the regulation of myometrial blood flow. Such effects of vasopressin and noradrenaline cannot be excluded.