Comparison of the effect of reversible and irreversible MAO inhibitors on renal nerve activity in the anesthetized rat.

Cardiovascular effects of the irreversible MAO-A inhibitor clorgyline and reversible MAO-inhibitors, moclobemide and brofaromine, were compared in the anesthetized rat. Electrical activity of the sympathetic renal nerve was monitored as an index of central sympathetic output. A long lasting decrease in the recorded parameters: blood pressure (BP), renal nerve activity (RNA) and heart rate (HR) was produced by acute administration of clorgyline (2 mg/Kg, IP). Acute treatment with moclobemide (10 mg/Kg, IP) or brofaromine (10 mg/Kg, IP) caused only a transient decrease in RNA. Pretreatment with the alpha 2 antagonist yohimbine, decreased significantly the inhibitory effect of clorgyline on all three parameters. The selective alpha 2 antagonist CH-38083 blocked the sympathoinhibitory effect of brofaromine. These results indicate an alpha 2 adrenoceptor involvement in the central sympathoinhibitory effect of MAO inhibitors, which may be manifested as a hypotensive effect, including orthostatic hypotension, in patients treated with irreversible selective MAO inhibitors.