Effects of Methoxamine on Spontaneous Uterine Activity and Blood Flow of the Rat Uterus ‘in vivo’

Abstract

The vascular (blood pressure, heart rate and peripheral blood flow) and uterine (spontaneous motility) responses to intravenous methoxamine were studied in anaesthetized rats pre-treated with diethylstilboestrol. Methoxamine produced an increase (0.5–2 mg/kg) or did not modify (0.01 and 3 mg/kg) spontaneous uterine motility. The Α₁-agonist also induced a hypertensive effect (0.1–3 mg/kg) accompanied by bradycardia at the highest doses, and a decrease in blood flow significantly greater in intestinal than uterine tissues. These effects were abolished by prazosin. The uterine action of methoxamine in vivo appears to result from the balance between myometrial Α₁-excitatory effect and vascular Α₁-vasoconstriction which induced uterine inhibition. The oestrogens appear to protect the Α₁-mediated vasoconstriction.