Platelets from aged rats aggregate more, but are more sensitive to prostacyclin.

The balance between vascular eicosanoids has been explored in young (1 month of age) and aged (11 month of age) rats. PRP from mature rats was more reactive to collagen (lower threshold, greater amplitude of aggregation curve and higher TxB2 formation) than PRP from young animals. Release of 6-keto-PGF1 alpha from PRP-perfused isolated aortas (pg@ul) was higher and the inhibition of PRP aggregation after perfusion correspondingly greater, in mature rats. Platelets from aged rats were more sensitive to exogenous prostacyclin (higher inhibition of aggregation and greater accumulation of cAMP). The fatty acid compositions of plasma and platelet lipids were not different in the two age groups. Compensatory mechanisms were operating in the aged rats, counteracting the greater platelet aggregability with higher vascular prostacyclin production and greater sensitivity of platelets to this eicosanoid.