[Platelet alpha 2 adrenergic receptors, plasma catecholamines and orthostatic hypotension in insulin-dependent...

Plasma catecholamine levels, total platelet alpha 2-adrenoceptor number and affinity state (using [3H]-yohimbine binding) have been investigated in insulin-dependent diabetic patients with (n = 12) or without (n = 10) orthostatic hypotension as well as in normal control subjects (n = 6). Mean resting basal catecholamine values were similar in the three groups. One min standing elicited an increase in norepinephrine plasma level (but not in epinephrine plasma levels) in control group but not in diabetic patients (with or without orthostatic hypotension). The maximal number of platelet alpha 2-adrenoceptors (and Kd) calculated by [3H]-yohimbine saturation experiments was similar in the three groups. The percentage of platelet alpha 2-adrenoceptors in high affinity state determined by inhibition experiments of [3H]-yohimbine binding by UK14,304 (a specific alpha 2-adrenergic full agonist) was significantly lower in diabetic patients with orthostatic hypotension (29.2 +/- 5.3%) than in the other two groups. No significant difference was found between the control group (60.0 +/- 2.0%) and diabetic patients without orthostatic hypotension (64.3 +/- 3.1%). These results indicate that orthostatic hypotension in insulin-dependent diabetic patients is marked by a lack of noradrenaline increase in standing position and by a decrease in platelet alpha 2-adrenoceptors in high affinity state. Thus we suggest that orthostatic hypotension of diabetes mellitus is the result of sympathetic nerves injuries and of abnormalities in alpha 2-adrenoceptors coupling.