In vitro study of the effect of clonidine on human umbilical artery motility.
The umbilical-placental circulation is of vital importance for fetal survival and has a dominant effect on the cardiorespiratory physiology of the fetus. The mechanisms of regulation of umbilical vessels appear to differ from those regulating other vessels. Both clonidine and alpha-methyldopa have been used in the management of hypertensive complications of pregnancy. In contrast to alpha-methyldopa, clonidine does not require previous metabolization but acts directly on the receptors. The action of the two drugs on human umbilical artery was studied in vitro. Forty-eight human umbilical artery segments were dissected and perfused as follows: 9 segments with alpha-methyldopa, 10 with clonidine, 10 with yohimbine, 9 with alpha-methyldopa in combination with yohimbine, and 10 with pure Tyrode's solution. alpha-Methyldopa had a statistically significant vasoconstrictive effect starting at 40 min (p < 0.05) and this effect was blocked by yohimbine (p < 0.05). Clonidine had no vasoconstrictive effect. The present data for clonidine do not confirm the presence of alpha 2-adrenergic receptors in the umbilico-placental circulation which had been indicated by the action of methyldopa.
Department of Gynecology and Obstetrics, Faculty of Medicine of Ribeirão Preto, University of São Paulo, Brazil.
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D003000:Clonidine / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D007231:Infant, Newborn; D008750:Methyldopa / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D014469:Umbilical Arteries / Q000187:drug effects* / Q000502:physiology; D014661:Vasoconstriction / Q000187:drug effects* / Q000502:physiology; D015016:Yohimbine / Q000494:pharmacology
D015016:Yohimbine; D008750:Methyldopa; D003000:Clonidine