Frusemide potentiates acetylcholine and carbachol in contracting the rat urinary bladder

Abstract The interaction between acetylcholine and carbachol, and frusemide, a loop diuretic, have been studied on the rat isolated urinary bladder strip preparation. Acetylcholine (4.36 × 10−8–1.3 × 10−6 M) and carbachol (5.5 × 10−8–6.9 × 10−6 M) induced contractions and these were significantly potentiated by frusemide (3.02 × 10−6 M). The ratio of EC50 in the absence of frusemide to EC50 in the presence of frusemide was 1.58 ± 0.03 (s.e.m.) for acetylcholine and 1.86 ± 0.14 for carbachol. Potentiation of acetylcholine and carbachol contractions by frusemide was not observed in tissues treated with hexamethonium (2.5 × 10−5 M). Rhythmic contractions induced by frusemide alone were markedly reduced by hexamethonium (2.5 × 10−5 M) and tetrodotoxin (10−6 M) but they were not significantly reduced by atropine (1.7 × 10−6 M). The result suggests that frusemide increases the sensitivity of the bladder to acetylcholine and carbachol, and that it may have a nicotinic stimulant effect on the bladder. This extra-renal action may contribute to its prompt diuretic property.