Antagonism of some smooth muscle actions of prostaglandins by polyphloretin phosphate

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Abstract
1 The antagonism of the smooth muscle stimulating actions of PGF2α 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 PGF2α; PGF2α was more readily antagonized than PGE2. 3 PPP (2·5–30 μg/ml) reversibly antagonized contractions produced by PGE2 and PGF2α on the isolated rabbit jejunum and uterus. In these preparations PPP antagonized PGE2 as readily as PGF2α. 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 PGF2α 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.