Alterations in noradrenergic function during clorgyline treatment

The effect of four weeks treatment with the selective monoamine oxidase (MAO-A) Type A inhibitor, clorgyline, on noradrenergic function was assessed in depressed patients using steady-state intravenous tyramine pressor response tests and determinations of plasma norepinephrine (NE). During the pretreatment period: 1) resting levels of plasma NE were correlated (r = .82) with tyramine sensitivity as indicated by the dose (mg/min) of infused tyramine required to elevate and maintain systolic blood pressure 30 mmHg; 2) significant increases in plasma NE accompanied steady-state rise in blood pressure; and 3) the magnitude of tyramine stimulated NE increases were highly correlated (r = .91) with pretreatment plasma NE levels. Clorgyline administration for 3-4 weeks was accompanied by: 1) large increases in pressor sensitivity to intravenous tyramine; 2) significant decreases in resting levels of plasma NE; 3) alterations in the relationship between plasma NE and tyramine sensitivity; and 4) a trend towards a reduction in the tyramine-stimulated plasma NE release. A postulated clorgyline-induced down-regulation of presynaptic adrenergic activity is discussed with regard to the overall enhancement in tyramine pressor sensitivity produced by clorgyline.