RESUMO
Present study was conducted on prostaglandin F2alpha (PGF2alpha), oxytocin, (OT), potassium chloride (KCI) and barium chloride (BaCl2) pre-contracted perimetrial uterine strips of dioestrus and pregnant buffaloes to evaluate the tocolytic efficacy of selective beta2 adrenoceptor agonists-albuterol (salbutamol) and terbutaline. Cumulative concentration-response curves of both the beta2 adrenoceptor agonists were constructed and the mean effective concentration (EC50) values determined and compared statistically. Based on the comparative EC50 values in relaxing the pre-contracted uterine strips with different spasmogens, the rank order potency of albuterol was found to be--PGF2alpha > BaCl2 > OT > KCl on uterine strips from dioestrus animals, while OT> BaCl2> PGF2alpha >KCl on the uterine strips of pregnant buffaloes. The rank order potency of terbutaline on uterine strips from dioestrus stage animals was- BaCl2 > OT > KCl > PGF2alpha, while BaCl2 > PGF2alpha > KCl > OT on uterine tissues of pregnant animals. Thus, irrespective of the state of uterus, whether gravid or non-gravid, KCl-depolarized uterine tissues required comparatively higher concentrations of albuterol or terbutaline to produce tocolytic effect. High concentrations of K+ in biophase may have interfered with the beta2 adrenoceptor agonists-induced outward K+ current and hyperpolarization. From the results of present study, it was evident that selective beta2 adrenergic agonists had good tocolytic efficacy on the uterus of buffaloes. Further, indirectly the possibility of existence and activation of K(Ca) channels by selective beta2 adrenoceptor agonists in mediating tocolysis of buffalo myometrium can not be ruled out, however, detailed studies using specific K(Ca) channel blockers are required for characterizing the nature of such channels in buffalo uterus.