Characterization of the adrenoceptor in the isolated cremaster muscle of the guinea-pig.

1 Contractions of the isolated cremaster muscle of the guinea-pig obtained in response to direct electrical stimulation were augmented by salbutamol, isoprenaline, adrenaline, noradrenaline and orciprenaline (in that order of potency), and by potassium chloride. Phenylephrine and xylometazoline had no effect. 2 The augmenting effect of isoprenaline on the twitch response was not altered by yohimbine or tolazoline, but was totally prevented by butoxamine, (--)-1-(4-nitrophenyl)-2-isopropylamino-ethanol (INPEA), (+/-)-INPEA, sotalol, metalol and practolol; (+)-INPEA was much less effective. The augmenting effect of potassium was not altered by beta-adrenoceptor blockade. 3 The results are consistent with the view that the augmenting effect of the sympathomimetic agents is mediated through beta2-type of adrenoceptor in the skeletal muscle fibres.