The influence of saturable drug uptake on the drug concentration near the receptor sites was shown theoretically to depend on the geometry of the preparation; increases in the volume/surface ratio (V/S) of the preparation decrease the sensitivity of the preparation to an agonist inactivated in the tissue. 2. The positive inotropic effect of (-)-noradrenaline was found to depend on the ratio V/S of the preparation; papillary muscles with larger V/S were less sensitive to the drug and showed steeper noradrenaline concentration-effect curves. 3. An algorithm for the statistical estimation of the parameters of the saturable uptake process was derived. It was applied to the positive inotropic noradrenaline effect in relation to muscle geometry. As an analysis of variance showed, the model explained a significant proportion of the shift of (-)-noradrenaline concentration-effect curves associated with variation in size of the preparation.
The role of neuronal and extraneuronal uptake in the inactivation of 3H-(--)noradrenaline in the rabbit aorta determined by a method relating with amine diffusion in the tissue.
