Facilitatory action of adrenergic drugs on muscle twitch evoked by nerve stimulation in the curarized rat phrenic hemidiaphragm.
The facilitatory effects of alpha-adrenergic drugs on neuromuscular transmission has been studied in the curarized rat phrenic-hemidiaphragm. The reversal effect of blocking action of (+)-tubocurarine on indirectly-induced twitch by alpha-adrenergic agents was higher with noradrenaline (EC50 = 6.51 +/- 0.18 microM) compared with adrenaline (EC50 = 11.80 +/- 1.06 microM) or phenylephrine (EC50 = 17.36 +/- 1.02 microM). Methoxamine, clonidine and azepexol showed no effect. The action of noradrenaline was blocked by prazosin (IC50 = 3.96 +/- 0.76 nM) and tolazoline (IC50 = 10.30 +/- 0.5 nM) but not by yohimbine at the concentration range 0.01-0.1 microM. From these results it could be concluded that an alpha 1-adrenergic mechanism might be involved in the facilitatory action of alpha-adrenergic agents at the level of motor nerve terminals.
Departament de Farmacologia i Psiquiatria, Facultat de Medicina, Universidad Autónoma de Barcelona, Campus de Bellaterra, Spain.
J
J
Baños
A
A
Badia
F
F
Janè
D000818:Animals; D003964:Diaphragm / Q000187:drug effects; D004558:Electric Stimulation; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009638:Norepinephrine / Q000494:pharmacology; D010791:Phrenic Nerve / Q000187:drug effects; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012132:Respiratory Muscles / Q000187:drug effects* / Q000294:innervation; D013566:Sympathomimetics / Q000494:pharmacology*; D014403:Tubocurarine / Q000494:pharmacology
D013566:Sympathomimetics; D014403:Tubocurarine; D009638:Norepinephrine; D011224:Prazosin