Radioenzymatic assay measurement of yohimbine's influence on adrenergic neurotransmission of rat vas deferens: unique consequence of using normetanephrine as an uptake2-blocking agent.
The effect of the alpha 2-receptor antagonist, yohimbine on norepinephrine overflow was studied in the transmural-stimulated isolated rat vas deferens. A radioenzymatic assay was used to measure the endogenous norepinephrine overflow. In initial studies conducted in the presence of uptake1 blocker desipramine (10(-6) M) and uptake 2 blocker, normetanephrine (10(-5) M) there was an apparent uncoupling of the influence of yohimbine on nerve-stimulated contractile response from norepinephrine overflow. These results were found to be due to the electrolytic O-demethylation of normetanephrine with the resultant generation of large quantities of norepinephrine obscuring the influence of yohimbine on nerve-stimulated norepinephrine overflow from the vas deferens. These findings serve as a warming to the use of normetanephrine as an uptake1 blocker when radioenzymatic assay is used to measure norepinephrine overflow from transmural-stimulated isolated tissue preparations. Yohimbine (10(-6) M), in the absence of uptake blockade, causes a 3-fold enhancement of nerve-stimulated norepinephrine overflow at 1 Hz and a 2-fold enhancement at 10 Hz. This report demonstrates utilization of a radioenzymatic assay to study endogenous norepinephrine overflow from rat vas deferens. Results for yohimbine are complementary to others using measurement of 3H-label overflow from [3H]norepinephrine prelabeled isolated tissue.
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects; D009647:Normetanephrine / Q000494:pharmacology*; D010625:Phenylethanolamine N-Methyltransferase; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013564:Sympathetic Nervous System / Q000187:drug effects*; D009435:Synaptic Transmission / Q000187:drug effects*; D014316:Tritium; D014649:Vas Deferens / Q000294:innervation; D015016:Yohimbine / Q000494:pharmacology*
D009647:Normetanephrine; D014316:Tritium; D015016:Yohimbine; D010625:Phenylethanolamine N-Methyltransferase; D011188:Potassium