Background: Arginine vasopressin (AVP) activates the uterus via V1a receptors and is apparently an important factor for the myometrial hyperactivity, uterine ischemia and pain of primary dysmenorrhea. The orally active and selective, non-peptide AVP1a receptor antagonist, SR 49059, has been shown to inhibit the myometrial action of AVP, but the specific influence of this substance on the effects of AVP and other vasoactive agents on human uterine arteries is unknown.
Methods: Concentration-responses of AVP on isolated medium-sized human uterine arteries were studied after incubation with only vehicle (DMSO, 0.1%) and with SR 49059 in concentrations of 0.5, 2.5 and 10 nmol/L. Furthermore, the concentration-responses of AVP were investigated without and with SR 49059 (2 and 10 nmol/L) on small and medium-sized arteries. Finally, the influence of 2.5 nmol/L of SR 49059 on concentration-responses of endothelin-1, noradrenaline and prostaglandin F2 alpha was studied.
Results: The EC50 for AVP on medium-sized arteries was 0.53 +/- 13 nmol/L. SR 49059 caused a competitive, dose-dependent inhibition of AVP-responses, the highest concentration giving an EC50 of 460 nmol/L. The pA2 value was 9.84. The responses of the small artery preparations to AVP, both without and with the antagonist, were more pronounced than those of the medium-sized ones. The vasoconstrictive effects of endothelin-1, noradrenaline and prostaglandin F2 alpha were less pronounced than those of AVP and unaffected by pre-exposure to SR 49059.
Conclusions: The high potency of AVP on human uterine arteries, particularly those of small size, supports an involvement of the peptide in the regulation of uterine blood flow in both physiological and pathophysiological condition. SR 49059 is a potent and selective AVP V1a receptor antagonist in the smooth muscle of human uterine arteries.