Responses of the myometrial and maternal placental circulations to adrenergic stimulation and blockade have been studied in the rabbit by serial angiography after selective catheterization of the urogenital artery. Changes in myometrial activity and arterial blood pressure have been registered and taken into account. Myometrial and placental blood flow was reduced by a few nanograms of noradrenaline or adrenaline, but increased after blockade of \g=a\adrenoceptors with phenoxybenzamine or thymoxamine. The main effect of phentolamine was to evoke a long series of myometrial contractions, which counteracted the tendency of this drug to improve placental perfusion. The \ g = b \ b l o c k i n g blocking agent, propranolol, had no effect at all on the parameters studied. Isoprenaline did not clearly affect myometrial and placental blood flow. Isoxsuprine, however, caused a slight increase by dilating the uterine arteries, possibly due to its papaverine-like properties. Both isoprenaline and isoxsuprine tended to depress myometrial activity. None of the drugs tested markedly affected distribution of uterine blood flow between the uterine wall and the placentae.

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