INTRINSIC TONE AS POTENTIAL VASCULAR RESERVE IN CONDUCTANCE AND RESISTANCE VESSELS

Background The purpose of this study was to define the degree of intri nsic tone in conductance and resistance vessels, to define the calcium dependency of intrinsic tone in these vascular preparations, and to i nvestigate the efficacy of vasodilatory agents on the level of intrins ic tone in these vascular preparations. Methods and Results All vessel s were deendothelialized. Isometric force was recorded from strips of ferret aorta, ferret pulmonary artery, and human coronary artery. Vess el diameter was recorded from the ferret epicardial coronary artery an d from ferret coronary microvessel in a pressurized no-flow state. Int rinsic tone was defined as the active increase in force or decrease in diameter with warming from 6 degrees C to 37 degrees C. Changes in fo rce or diameter with various pharmacological agents were expressed as a percentage of intrinsic tone. Our results indicate that intrinsic to ne accounts for approximate to 35% to 40% of total tone in all vascula r preparations studied and is not dependent on extracellular calcium. Agents that increased cAMP levels leg, forskolin, milrinone) and agent s that decreased protein kinase C activity leg, staurosporine) were pa rtially effective in decreasing intrinsic tone. Nitroprusside, adenosi ne, hydralazine, and nifedipine had no significant effect Conclusions Our results indicate that intrinsic tone represents a significant comp onent of vascular tone that has not been previously recognized and rem ains largely unexploited by current pharmacological therapies.