Endocrine Abstracts

Nebivolol is a recently developed beta(1)-selective adrenergic receptor antagonist with proposed nitric oxide mediated vasodilating properties. Effect of nebivolol on vascular smooth muscle has been attributed to estrogen receptor-mediated vascular responsiveness. Although it is known that nitric oxide has relaxing effect on myometrium, there is no report whether nebivolol application affect myometrial contractility. Therefore, we have investigated the effect of nebivolol on rat uterus contractility. Myometrium strips were removed from Wistar rats following decapitation and placed in a jacked tissue bath containing Krebs solution and isometric contractions were measured by force displacement transducer. After recording the spontaneous contractions as control (n=7), various concentrations of nebivolol were added to the tissue bath cumulatively. In the other group (n=8), same doses of nebivolol applicated after oxytocin induced contractions. The amplitude and frequencies (number of contractions for 15-minute) of contractions were evaluated at 15 min interval before and after applications of nebivolol. Wilcoxon sign ranks test was used for statistical analysis. The mean peak amplitudes of contractions (mean±SEM) were 2163.6±143.9, 1845.0±134.2, 822.8±,83 mg and mean frequency of contractions were 8.0±0.3, 7.8±0.0.4 and 5.8±0.7 under control conditions and after application of 0.05mM, and 0.25mM nebivolol in spontaneous group, respectively. While there was no significant difference in peak frequency, nebivolol decreased peak amplitude levels both of doses (p<0.05). The mean peak amplitudes of contractions were 3058.4±97.8 2746.7±89.1 and 1191.8±84.7 mg and mean frequency of contractions were 10.4±0.5, 8.1±0.5 and 5.0±0.4 under control conditions and after application of 0.05mM, and 0.25mM nebivolol in oxytocin induced group, respectively. Nebivolol inhibited peak frequency and peak amplitude in 0.05 and 0.25mM doses (p<0.05 and p<0.01, respectively) both of groups. Nebivolol completely abolished the contractions in 0.5mM in both groups. Our results have shown that nebivolol inhibits spontaneous and oxytocin-induced contractions in a dose dependent manner in the rat myometrium.