Pressure-diameter curves of mesometrial arteries of guinea pigs demonstrate a non-muscular, oestrogen-inducible mechanism of lumen regulation.

Pressure-diameter curves were determined on mesometrial (uterine radial) arteries obtained from guinea pigs during different stages of ovarian cycle and pregnancy. In order to investigate changes in arterial diameter that are not caused by the vascular musculature, we studied excised arteries that were relaxed by papaverine (40 mg/l). The pressure-diameter curves were found to be shifted toward wider diameters when the arteries studied were obtained from pregnant, oestrous or oestrogen treated animals (oestradiol benzoate, 10 micrograms s.c.): the external diameter at 60 mm Hg transmural pressure on the 14th day of pregnancy exceeded the one during dioestrus by 50%. At term, there was a 7-fold increase. During oestrus and 24 h after oestrogen treatment the diameter was 30-40% wider than during dioestrus. Moreover, we found that the diameter measured on excised vessels in the presence of papaverine is the same as the one observed in situ. We conclude that the mesometrial arteries of guinea pigs possess a muscle-independent mechanism of lumen regulation. The mechanism operates in non-pregnant and pregnant animals. It may be induced by oestrogen and seems to be qualified for long-term lumen regulation during pregnancy. In contrast, dilation by smooth muscle relaxation appears to be of minor importance in mesometrial arteries.