Abstract
To clarify the relationship between kinetics of alpha-2 adrenergic receptors and aging or arteriosclerosis, the density (Bmax) and affinity (Kd) of alpha-2 adrenergic receptors, plasma levels of norepinephrine, platelet aggregation induced by epinephrine, adenosine diphosphate or collagen, and platelet releasing substance were simultaneously analyzed by radioreceptor binding assay, radioenzymatic assay, an aggregometer and radioimmunoasssay, respectively. Plasma norepinephrine levels revealed a positive correlation with age in healthy control group (p<0.001), where as Bmax showed a negative correlation (p<0.001). In addition, a negative correlation (p<0.001) was noted between Bmax and plasma levels of norepinephrine, suggesting that the reduced Bmax can be depending on elevated catecholamine levels showing down regulation with aging in healthy control group. In the group of patients with effort angina, aggregatory responses to epinephrine were significantly higher than age-matched healthy donors in the healthy control group. Although there was no significant difference of plasma norepinephrine levels between the patient group and age-matched healthy group, Bmax was significantly lower in the patient group with effort angina compared to age-matched healthy group. The increase in aggregation in patients group, with alpha-2 adrenergic receptor reduction, which is independent of plasma norepinephrine levels, were more prominent in patients with effort angina. These results suggest that platelet alpha-2 adrenergic receptor kinetics could be an important tool to study the pathogenesis of arteriosclerosis.
