Effect of noradrenaline on circulation in the genital tract of early and late pregnant guinea-pigs

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Abstract
Noradrenaline [norepinephrine] infusions were given to anesthetized guinea pigs in early (19-23 days) and near-term (61-66 days) pregnancy. Radioactive microspheres (15 .mu.m) were used to determine blood flow in various regions of the genital tract. In late gestation, a 10-min i.v. infusion of 1 .mu.g noradrenaline/min per kg elicited moderate increases in vascular resistance that were counteracted by the pressor response. Uterine and placental blood flow remained unchanged, although there was a 27% decrease in perfusion of the uterine cervix and a fall of 19% in vaginal blood flow. In early pregnant guinea pigs, blood pressure rose but vascular resistance was unaffected, resulting in an augmentation of placental blood flow. During infusion of 10 .mu.g noradrenaline/min per kg, the vasoconstrictor response in late pregnancy was accentuated, and a strong decrease in tissue perfusion was noted in the placenta (-36%), uterine horns (-39%), cervix (-70%) and vagina (-56%). At the higher rate of noradrenaline infusion, vascular resistance also increased in the genital tract of early pregnant animals, although to a lesser extent than in late pregnancy. An enhancement of the vasoconstrictor response to circulating catecholamines in near-term pregnancy was indicated.