On the inotropic effects of leukotrienes in the isolated urinary bladder of guinea pigs and rats.

Leukotrienes (LTs) B4, C4 and D4 were tested on the motility of rings isolated from the urinary bladder of guinea pigs and rats. LTB4 did not evoke inotropic influences in any of the preparations, whereas LTC4 and LTD4 augmented the magnitudes of tonic and phasic contractions in the guinea pig but not in the rat detrusor muscle, LTC4 evoking a greater enhancement than LTD4. On molar bases, acetylcholine induced smaller positive inotropic effects. In the presence of 10(-4) acetylsalicylic acid (ASA), cumulative dose-response curves of phasic and tonic contractions for LTC4 were shifted to the right of controls, whereas curves of the phasic motility for LTD4 remained unaltered. However, ASA shifted to the left the dose-response curve of tonic contractions for LTD4 and in addition evoked an augmentation of the absolute developed tension. The initial (postequilibrium) contractile levels of basal phasic contractions did not differ between controls and preparations incubated with ASA (10(-4) M), nordihydroguaiaretic acid (10(-7) M) or FPL-55712 (3 X 10(-6) M). The findings suggest that some musculo-active prostanoid(s) could be modulating, in opposite directions, the smooth muscle contractile reactivity of the guinea pig urinary bladder when challenged in vitro with LTC4 and LTD4. Our data reported hereing also suggest that the role, if any, of endogenous prostanoids and leukotrienes for the normal basal contractile functioning of the guinea pig urinary bladder, remains obscure.