Epinephrine-induced aggregation and α-adrenergic receptors on human platelets

Abstract

1) Types of epinephrine-induced aggregation in chronic myeloproliferative disorders were classified into three types according to a concentration of epinephrine added in the PRP. The first type of aggregation curve revealed normal responsiveness in response to a usual concentration of l-epinephrine (5μM). The second type revealed defective or decreased responsiveness to 5μM l-epinephrine, but a normal responsiveness appeared at a higher concentration of l-epinephrine. The third type showed no responsiveness to any concentration of l-epinephrine (10μM, 100M and 1mM). We called above those types of aggregation curves Type I, Type II and Type III, respectively.
2) ³H-DHEC (³H-Dihydroergocryptine) binding assay in washed intact platelets was studied according to the method of Newman et al. with a minor modification. Platelets in Type I revealed normal values in ³H-DHEC binding sites. In Type II, ³H-DHEC binding sites were slightly fewer than in normal controls or reduced to half numbers of normal controls. In Type III, ³H-DHEC binding sites revealed half numbers of normal controls.
3) The cAMP level in the PRP in Type I showed normal enhancement by PGE₁ and a sufficient decrease in response to epinephrine. In Type III, the cAMP level in the PRP demonstrated only 10 to 20% of normal enhancement by PGE₁ and no responsiveness to epinephrine. Whereas, in Type II, various attitudes were observed in response to PGE₁ and epinephrine.
4) Platelets in Type III revealed sufficient potentiation of ADP aggregation due to a low-dose epinephrine. Therefore, the mechanism of epinephrine aggregation might be different from that of potentiation of ADP aggregation due to a low-dose epinephrine.