Key result
Papaverine demonstrated an ultradian rhythm with an 8-hour periodicity in rat aorta relaxation, whereas no time-dependent variations were found for theophylline.
The relaxation response of rat aorta to papaverine exhibits an 8-hour ultradian rhythm, whereas the response to theophylline does not.
No immediate clinical implications; leaves open whether ultradian rhythms affect vasodilator responses in humans.
The presence of temporal patterns in the responses of vascular smooth muscle to relaxing agents have been known. The aim of this study was to examine the variations in the in vitro sensitivity of rat aorta to papaverine and theophylline in both endothelium-intact and -denuded rings. The animals were synchronized with a 12-h light: 12-h dark schedule. Rat thoracic aorta rings were obtained from animals sacrificed at six different times (09:00, 13:00, 17:00, 21:00, 01:00 and 05:00) of the day. Tissues were precontracted submaximally with phenylephrine and then were relaxed by papaverine (10−8 − 10−4 M) and theophylline (10−7 − 10−3 M) applied cumulatively. The responses to most of the concentrations and EC50 values for papaverine demonstrated an ultradian rhythm with an 8 h periodicity. Time-dependent variations were not found in the responses to theophylline. The results are discussed in relation with the time-dependent differences in signal transducing mechanisms.
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Uluoğlu et al. (1998) studied this question. Papaverine and theophylline was evaluated on Responses to concentrations and EC50 values. Papaverine demonstrated an ultradian rhythm with an 8-hour periodicity in rat aorta relaxation, whereas no time-dependent variations were found for theophylline.
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