Effect of labetalol on the uptake of [3H]-(-)-noradrenaline into the isolated vas deferens of the rat.
1 The effects of the combined alpha- and beta-adrenoceptor blocking drug, labetalol, on the uptake of [3H]-(-)-noradrenaline into the isolated vas deferens of the rat have been determined and compared with those of some other alpha-adrenoceptor blocking drugs and cocaine. 2 Labetalol, like cocaine, produced a simple competitive inhibition of [3H]-(-)-noradrenaline uptake and was about 4 times less potent than cocaine. It is concluded that labetalol is a potent inhibitor of uptake1. Phentolamine and thymoxamine also inhibited [3H]-(-)-noradrenaline uptake, and were respectively 8 and 14 times less potent than cocaine. Tolazoline, piperoxan and yohimbine were inactive in concentrations up to 30 microgram/ml. 3 The uptake1 blocking action of labetalol could explain, at least in part, the previously reported difference in its ability to block noradrenaline and phenylephrine vasopressor responses in the anaesthetized dog. 4 The possibility that uptake1 inhibitory concentrations of labetalol could be present in the blood of subjects receiving normal antihypertensive doses of the drug is discussed.
D000818:Animals; D003864:Depression, Chemical; D004347:Drug Interactions; D004983:Ethanolamines / Q000494:pharmacology*; D066298:In Vitro Techniques; D007700:Kinetics; D007741:Labetalol / Q000494:pharmacology*; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism*; D051381:Rats; D014649:Vas Deferens / Q000378:metabolism
D004983:Ethanolamines; D007741:Labetalol; D009638:Norepinephrine