ALPHA(2)-ADRENOCEPTORS AND I-1-IMIDAZOLINE BINDING-SITES - RELATIONSHIP WITH CATECHOLAMINES IN WOMEN OF REPRODUCTIVE AGE

A comparison is presented between plasma catecholamine concentrations and platelet [I-125]-p-iodoclonidine binding sites in 16 healthy women . Blood samples were obtained at six regularly spaced interval; over t wo consecutive menstrual cycles from healthy women with regular menstr ual periods. Although no cycle-related changes were observed per se, t here were significant correlations between the platelet binding sites and plasma norepinephrine and epinephrine concentrations. The densitie s of platelet alpha(2)-adrenoceptors were negatively correlated in an exponential fashion (r(2) = 0.694, P=0.009) with plasma epinephrine co ncentrations, implying agonist-induced downregulation. On the other ha nd, platelet I-1-imidazoline binding sites were positively correlated with plasma concentrations of norepinephrine in a linear fashion (r(2) = 0.326, P = 0.021). This is the first indication that I. binding sit es might be upregulated by a physiological factor. Furthermore, the da ta suggest that elevations in plasma norepinephrine might explain repo rts of upregulated I, binding sites in depressed patients. (C) 1998 El sevier Science Ltd. All rights reserved.