Antagonism of some smooth muscle actions of prostaglandins by polyphloretin phosphate

Abstract

1 The antagonism of the smooth muscle stimulating actions of PGF_2α and PGE₂ by polyphloretin phosphate (PPP) was studied on several isolated smooth muscle preparations and on the blood pressure of the anaesthetized rabbit. 2 PPP (2·5–20 μg/ml) reversibly inhibited contractions of the jird colon produced by PGE₂ or PGF_2α; PGF_2α was more readily antagonized than PGE₂. 3 PPP (2·5–30 μg/ml) reversibly antagonized contractions produced by PGE₂ and PGF_2α on the isolated rabbit jejunum and uterus. In these preparations PPP antagonized PGE₂ as readily as PGF_2α. 4 It is concluded that PPP is a selective antagonist to the prostaglandins on these tissues, for contractions produced by other agonists, such as acetylcholine, angiotensin, 5-hydroxytryptamine and bradykinin were not reduced by concentrations of PPP which markedly antagonized responses to the prostaglandins. 5 Intravenous injections of PPP (25–200 mg/kg) resulted in a variable antagonism to the fall in blood pressure produced by intravenous injections of PGF_2α in the anaesthetized rabbit; vasodepressor responses produced by PGE₂ and acetylcholine were not antagonized. 6 The mechanism of this antagonism by PPP is not clear and must await further investigation.