Facilitation of transmitter release in the urinary bladders of neonatal and adult rats via alpha(1)-adrenoceptors

Age-dependent changes in the effects of the alpha (1)-adrenoceptor agonist, phenylephrine were investigated on neurally evoked contractile responses a nd basal tone in smooth muscle strips from rat urinary bladder. Phenylephri ne facilitated the neurogenic contractions in both neonatal and 7-month-old adult rats. However, phenylephrine increased the basal tone in adult but n ot neonatal rats. In adult rats, phenylephrine-induced facilitation of neur ally evoked contractions occurred before and after the block of cholinergic contractions with 1 muM atropine. In adult rats, the phenylephrine facilit ation was reduced at stimulation parameters (20 Hz, 80 shocks and maximal v oltage) which activated muscarinic receptor mediated facilitation of acetyl choline release. The results indicate that pre-synaptic alpha (1)-adrenocep tors facilitate the release of both acetylcholine and the non-cholinergic n on-adrenergic transmitter. In summary, alpha (1)-adrenoceptor-mediated faci litation is less expressed when muscarinic M-1 receptor mediated facilitati on is functioning; pre-junctional alpha (1)-adrenoceptors are present in th e bladder of both neonatal and adult rats, whereas post-junctional alpha (1 )-adrenoceptors are expressed only in older adult rats. (C) 2001 Elsevier S cience B.V. All rights reserved.