In Vitro Evidence of Tissue Susceptibility Rhythms. I. Temporal Variation in Effect of Potassium Chloride and Phenylephrine on Rat Aorta

Abstract

In this study, time-dependent variations in the in vitro sensitivity of rat thoracic aorta rings to potassium chloride (KC1) and phenylephrine (Phe) were investigated. Animals were synchronized with a 12h light and 12h darkness (lights on 08:00–20:00) schedule, and thoracic aortas were obtained at six different times of the day (1, 5, 9, 13, 17, and 21 hours after lights on). In order to avoid endothelial influence, all experiments were performed in endothelium-denuded preparations. Responses to KC1 showed time-dependent variations in all the concentrations used. Phe-induced contractions also exhibited time-dependent differences. The rhythmic pattern of Phe responses did not change with the presence of the a_r adrenergic antagonist prazosin. In addition, both the EC_io values of KC1 and Phe, and also the AT_B values of prazosin, displayed rhythmicity. In conclusion, time of obtaining tissues is an important factor for experimental standardization in, at least, vascular smooth muscle preparations. (Chornobio Interna-tional, 15(1)39–48, 1998)

Key Words:

• Ultradian rhythm
• Vasoactive agents
• Rat aorta