IN-VITRO EVIDENCE OF TISSUE SUSCEPTIBILITY RHYTHMS - I - TEMPORAL VARIATION IN EFFECT OF POTASSIUM-CHLORIDE AND PHENYLEPHRINE ON RAT AORTA

In this study, time-dependent variations in the in vitro sensitivity o f rat thoracic aorta rings to potassium chloride (KCl) and phenylephri ne (Phe) were investigated. Animals were synchronized with a 12h light and 12h darkness.(lights on 08:00-20:00) schedule, and thoracic aorta s were obtained at six different times of the day (1, 5, 9, 13, 17, an d 21 hours after lights on). In order to avoid endothelial influence, all experiments were performed in endothelium-denuded preparations. Re sponses to KCI showed time-dependent variations in all the concentrati ons used. Phe-induced contractions also exhibited time-dependent diffe rences. The rhythmic pattern of Phe responses did not change with the presence of the alpha(1)-adrenergic antagonist prazosin. In addition, both the EC50 values of KCl and Phe, and also the K-B values of prazos in, displayed rhythmicity. In conclusion, time of obtaining tissues is an important factor for experimental standardization in, at least, va scular smooth muscle preparations.