A NEW METHOD FOR COMBINED ISOMETRIC AND ISOBARIC PHARMACODYNAMIC STUDIES ON PORCINE CORONARY-ARTERIES

1. The principal aim of the present study was to explore the isometric and isobaric capacity of a new intravascular technique, impedance pla nimetry, in basic pharmacodynamic investigations on porcine isolated e picardial coronary arteries, 2, The balloon-based catheter technique p rovides simultaneous measurements of luminal cross-sectional area and pressure, Sources of errors that may influence the accuracy of measure ments were evaluated in detail, 3, Under isometric conditions, the str etch ratio-tension diagram showed typical developments of resting and active tensions of the smooth muscle when exposed to alternating maxim al K+ depolarization and mechanical stretching. The mean (+/-SEM) maxi mum active tension was 28.43+/-1.72 mN/mm, which was reached at a stre tch ratio of 1.26+/-0.02, corresponding to a resting tension of 10.50/-0.53 mN/mm (n = 7), The concentratian-response relationship to Kt at optimal basal tension was characterized by a mean (+/-SEM) pot value of 1.67+/-0.01 (n = 7) 4, Under isobaric conditions in the pressure ra nge 40-140 mmHg, the method allowed the investigation of active vascul ar responses to partial Kf depolarization. The maximal active response to 25 mmol/L K+ was found at the transmural. pressure of 60 mmHg (n = 7), To obtain full K+ concentration-response curves, a basal tension corresponding to a transmural pressure of 120 mmHg was required, The m ean (+/-SEM) pot value for the concentration-response relationship to Kf was 1.53+/-0.01 (n = 10). 5, The vascular sensitivities to cumulati vely added K+ and various agonists, such as acetylcholine, 5-hydroxytr yptamine and noradrenaline, obtained from the same vessel segment at t he same initial conditions corresponding to 120 mmHg were significantl y higher with the isometric than,vith the isobaric approach. 6, The re sults of the present study suggest that impedance planimetry could be a useful tool in pharmacological and physiological investigations of m edium-sized arteries, both under isometric and isobaric conditions.