Selective blockade of the vasodepressor response to prostaglandin F 2 in the anaesthetized rabbit.

1. The prostaglandin-blocking activity of meclofenamic acid, N-(2,6-dichloro-m-tolyl)anthranilic acid (CI-583), was analysed in the anaesthetized rabbit. PGF(2alpha), PGE(1) and isoprenaline were injected before and after meclofenamic acid infusion.2. Isoprenaline produced a fall in blood pressure, a reduction in oviduct motility and a reduction in uterine motility if the uterus showed marked spontaneous motility. PGF(2alpha) uniformly produced a fall in blood pressure and an increase in both uterine and oviduct contractility. PGE(1) produced a fall in blood pressure, a reduction in oviduct motility and no consistent effect on uterine motility.3. Meclofenamic acid selectively blocked the vasodepressor response to PGF(2alpha). The vasodepressor responses to PGE(1) and isoprenaline as well as the effects of all three agonists on uterine and oviduct contractility were not reduced by treatment with meclofenamic acid.4. Polyphloretin phosphate (PPP) administered to two rabbits in a cumulative dose of 94 mg/kg showed no significant blocking action on the vasodepressor or uterine and oviduct contractor responses to PGE(1) or PGF(2alpha) though this compound, like meclofenamic acid, has been reported to antagonize the actions of PGE(1) and PGF(2alpha) on isolated smooth muscle preparations.