α- and β-Adrenoceptors in the detrusor muscle and bladder base of the pig and β-adrenoceptors in the detrusor muscle of man

1 The presence and type of adrenoceptors in the smooth muscle of the pig and human urinary bladder was assessed on the basis of the relative potency of α- and β-adrenoceptor agonists and antagonists.

2 In isolated, carbachol-contracted bladder strips from the pig detrusor muscle the relaxing potency of isoprenaline was four times that of salbutamol and ritodrine and thirty times that of noradrenaline.

3 Propranolol caused a parallel shift to the right of the noradrenaline dose-response curve which was not changed by phentolamine.

4 Propranolol and butoxamine showed, in contrast to practolol, a dose-dependent antagonism of the response to isoprenaline. A pA₂ value of 9.2 ± 0.2 and 6.8 ± 0.2 (mean ± s.e. mean) for the first two antagonists was calculated.

5 In the bladder base of the pig, propranolol caused a parallel shift to the right and phentolamine a shift to the left of the dose-response curve to noradrenaline.

6 In the human detrusor muscle the potency and maximum effect of isoprenaline and salbutamol were less than those in the pig detrusor muscle. The potency of isoprenaline was sixty times that of salbutamol.

7 Whereas a parallel shift to the right of the dose-response curve to isoprenaline was obtained with propranolol, no antagonism was obtained with butoxamine or practolol.

8 The results are interpreted as indicating the presence of β₂-adrenoceptors in the detrusor muscle of the pig and β-adrenoceptors with neither β₁- nor β₂-characteristics in the detrusor muscle of man. An indication of the presence of α-adrenoceptors in the bladder base but not in the detrusor muscle of the pig was obtained.