Retrograde arteriography has been used to examine the effect of pregnancy on the diameters of the main uterine, internal iliac and inferior epigastric arteries in the guinea-pig. The diameters of the internal iliac and inferior epigastric arteries were not altered during gestation. By contrast, the diameter of the main uterine artery supplying a pregnant horn of the uterus increased in diameter to a mean value of 167% of its diameter in non-pregnancy. In cases of unilateral pregnancy, the uterine artery supplying the non-pregnant horn of the uterus was not increased in diameter. Administration of atropine (0·1 to 0·5 mg/kg) to animals in late pregnancy caused constriction of the enlarged uterine arteries to a mean value of 137% of their pre-pregnant diameter, but the diameters of the internal iliac and inferior epigastric arteries were not changed. In non-pregnant animals, the diameter of the uterine arteries was not affected by atropine. The results support previous evidence for an effector rôle of cholinergic vasodilator nerves in the production of uterine hyperaemia during pregnancy in the guinea-pig.
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