Inhibition of the contractile response of the rat detrusor muscle by the β 2-adrenoceptor agonist clenbuterol

Abstract

The action of clenbuterol, β 2-adrenoceptor agonist, on the contractile response of isolated rat detrusor muscle strips was investigated in vitro. Clenbuterol (10 −5 M) inhibited the detrusor muscle frequency response (1–40 Hz, p<0.02) with a more pronounced effect at 1 Hz than 40 Hz. Clenbuterol (10 −6 M) significantly inhibited the contractile response to exogenous ATP (10 −4 to 10 −2 M, p<0.05) but not to carbachol (10 −9 to 10 −4 M). The presence of 10 −5 M ICI 118, 551, β 2-adrenoceptor antagonist, shifted significantly the clenbuterol dose–response to 1 Hz electrical field stimulation (EC 50 3.4×10 −6 M (±2.2×10 −6 M) for clenbuterol alone, to 4.1×10 −4 M (±8.8 ×10 −5 M), P<0.05). In conclusion, clenbuterol inhibits electrical field and ATP-stimulated contractions of detrusor muscle. Reversal of the clenbuterol inhibition of detrusor muscle contraction by ICI 118, 551 shows that clenbuterol is probably acting through postsynaptic β 2-adrenoceptors, which modulate the response to ATP released from purinergic nerves.