COCAINE ACUTELY INCREASES RAT MYOMETRIAL CONTRACTILE ACTIVITY BY MECHANISMS OTHER THAN POTENTIATION OF ADRENERGIC PATHWAYS

OBJECTIVE: We hypothesized that cocaine acutely increases contractile activity in isolated rat myometrium and that this effect is solely cau sed by potentiation of adrenergic pathways. STUDY DESIGN: Isometric co ntractions were measured in myometrium isolated from virgin and day-18 pregnant Sprague-Dawley rats. Frequency, duration, amplitude, and int egrated area were compared before and after the addition of cocaine (1 0(-6) to 10(-4) mol/L) by means of analysis of variance and Duncan's m ultiple-range test. The effects of alpha-adrenergic receptor antagonis ts (prazosin 10(-6) mol/L and yohimbine 10(-6) mol/L) and beta-adrener gic receptor antagonist (DL-propranolol 2 x 10(-6) mol/L) were assesse d. RESULTS: Contraction duration, expressed relative to control, incre ased acutely after cocaine (10(-5) mol/L) administration in pregnant ( 1.70 +/- 0.20) and nonpregnant (1.36 +/- 0.24) myometrium (mean +/- SE , p < 0.05), as did integrated area (pregnant 3.47 +/- 0.97, nonpregna nt 2.48 +/- 0.66) (mean +/- SE, p < 0.05). These effects were not comp letely inhibited by adrenergic blockade. CONCLUSION: Cocaine acutely i ncreases the duration and integrated area of spontaneous contractions in isolated rat myometrium by mechanisms not completely explained by i nhibition of catecholamine reuptake and potentiation of adrenergic pat hways.