Influence of age on norepinephrine-induced vascular contractions as a function of extracellular calcium.

: Age has been shown to produce various morphological and biochemical changes within the vasculature as well as changes in the responsiveness of the vasculature to various drugs. In the present study, the influences of age and extracellular calcium on norephinephrine-induced aortic contractions in male rats were examined. The aging process resulted in a decrease in sensitivity and responsiveness of rat aorta to norepinephrine-induced contractions. The progressive decrease in maximum contractile force (mg force/mg tissue) in response to norepinephrine as the result of aging occurred in all the different extracellular calcium concentrations used. In addition, the EC50 for norepinephrine in aortae from younger animals was directly related to the extracellular calcium concentration. As the animals, however, became progressively older (49-63 weeks) the aortic tissues became less sensitive and the calculated EC50 for norepinephrine was not altered by changes in the extracellular calcium concentration.