Tension development and associated calcium influx of control and reserpine pretreated rabbit aortae in response to norepinephrine, isoproterenol and acetylcholine.

The influence of reserpine (3mg/kg) pretreatment on phasic and tonic components of the contractile responses of rabbit aortae to maximally effective concentrations of norepinephrine, acetylcholine, and isoproterenol and on agonists-induced movements of 45Ca during these responses were studied. Four hours after reserpine administration, there were no histological changes, in extracellular space, and no change in tissue water, sodium, calcium or magnesium. Potassium contents were slightly decreased and the catecholamine content was depleted by 95%. The responses to the three agonists were enhanced in the reserpine pretreated tissues. The absence of calcium eliminated the slow tonic componenet of the responses. Reserpine induced an increase in lanthanum (La3+) resistant 45Ca uptake. The three agonists induced an increase in La3+ resitant 45Ca uptake of equal magnitude in both reserpine pretreated and control tissues. Lanthanum ion affected 45Ca efflux similarly in both reserpine pretreated and untreated tissues. The results suggest that a major portion of the enhanced responsiveness of rabbit aortic strips following reserpien administration is the result of a change in calcium retention in those tissue stores mobilized by these agonists to initiate the fast, phasic componenet, and is, therefore, a reflection of an increased agonist intrinsic activity.