THE BINDING CHARACTERISTICS OF [³H]‐DIHYDROERGOCRYPTINE ON INTACT HUMAN PLATELETS

Abstract

healthy, young, male subjects show a high degree of consistency both between subjects (Kd = 2.81 ± 0.27 nM; B,, = 63 ± 3 fmol/108 platelet: mean ± s.e.mean, n = 10) and between sampling occasions in a single subject (KSd= 3.28 nM± 13%; Bmax = 70 fmol/108 platelet ± 16%: mean ± coefficient of variation, n = 5). 6 There is no significant difference in the binding capacity of platelets from a group of elderly male subjects (mean age 73) compared to those from young males (mean age 27) or elderly females (mean age 77). The affinity of binding is slightly but significantly (P < 0.05) higher in the elderly male group compared to the two other groups.7 We conclude that [3H]-dihydroergocryptine binds to the a2-adrenoceptor of intact human platelets which is responsible for noradrenaline-induced platelet aggregation. The high consistency of the binding characteristics of [3H]-dihydroergocryptine indicate that this assay may be useful as a monitor of platelet o-adrenoceptor sensitivity in clinical investigation.

Role of catecholamines in platelet function: pathophysiological and clinical significance

“…The hormonal milieu influences the number of platelet -adrenoceptors: in women, it is regulated by the levels of sexual hormones and it changes during the menstrual cycle, pregnancy, post partum, the menopause and oestroprogestinic administration, as oestrogens down-regulate the number of these receptors [110,[114][115][116][117].…”

Presynaptic α-2C Adrenoceptor-mediated Control of Noradrenaline Release in Humans: Genotype- or Age-Dependent?

“…4 Data, however, are controversial with some studies finding no age-related changes in platelet a-2 AR density, other studies finding age-related decreases in a-2 AR density and at least one study finding an age-related increase in a-2 AR density. [22][23][24][25][26][27][28][29][30][31][32][33] A few studies have tested a possible age dependency of the effects of clonidine on pNA levels, but failed to show any age-related differences in decreases in pNA following oral application of clonidine (usually 1.5-5 mg/ kg). [34][35][36] We do not know the reason for the discrepancy between these and this study (age-related decline in pNA response), but it might be owing to differences in the route of clonidine application: we applied clonidine i.v., whereas in the other studies, clondine was applied orally.…”

The EFFECT OF AGING ON Α‐ADRENOCEPTORS AND THEIR RESPONSES IN RABBITS

“…Binding studies in platelets used whole platelets obtained by centrifugation of the blood at 180 g for 10 min at 20°C followed by centrifugation of the platelet rich plasma at 1700 g for 20 min at 10°C to obtain a platelet pellet (Elliott & Grahame-Smith 1982). The pellet was resuspended in 0.1% (w/v) EDTA containing 150 mmol/l NaCl @H 7.5) and platelet cell density adjusted to 100 X lo6 cells (using a Coulter counter).…”

“…Correspondence: Dr C. A. Hamilton, Department of Materia Medica, Stobhill General Hospital, There are fewer studies into the effects of age on a-adrenoceptors; of these some suggest a decrease in response (Cohen & Berkowitz 1976;Docherty & O'Malley 1983) and others no change with age (Wyse et al 1977;Buhler et al 1980;Scott & Reid 1982;Elliott & Grahame-Smith 1982). Some of the differences may relate to experimental conditions, tissues and species used and to differences in the effects of aging on a-adrenoceptor subtype.…”