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Vol. 297, Issue 3, 933-939, June 2001
Department of Pharmacology, University of Pittsburgh School of
Medicine, Pittsburgh, Pennsylvania (Y.I., M.Y., O.Y., W.C.deG.); and
Department of Urology, Kanazawa University School of Medicine,
Kanazawa, Japan (Y.I., O.Y., M.N.)
The influence of muscarinic receptor stimulation and blockade on the
central regulation of micturition was evaluated in conscious female
rats. Saline was infused into the bladder to induce repeated bladder
contractions and voiding. Increasing doses of a muscarinic agonist,
oxotremorine-M (OXO-M; 0.01 to 1 µg/rat) or antagonist, atropine (0.1 to 30 µg/rat) were administered. Intrathecal OXO-M (0.1 µg)
increased bladder capacity (BC; 85 ± 17%), but did not change
maximal voiding pressure (MVP), pressure threshold (PT), postvoiding
intravesical pressure, or voiding efficiency (VE). Intracerebroventricular OXO-M (0.1 µg) increased BC (97 ± 6%), MVP (45 ± 19%), PT (158 ± 49%), and reduced VE (
17 ± 5%). A larger dose of OXO-M (1 µg, either i.c.v. or i.t.)
produced greater changes. These effects were not reproduced by i.v.
injections of OXO-M. The effects of OXO-M were blocked by pretreatment
with atropine in a dose (1 µg i.c.v. or i.t.), which alone had no
effect on voiding parameters. A larger dose of atropine (10 µg)
reduced MP (
31 ± 7% i.c.v. and
34 ± 6% i.t.) and VE
(
21 ± 3% i.c.v. and
25 ± 5% i.t.) but increased BC
(52 ± 8% i.c.v.). These results indicate that activation of
muscarinic receptors in the brain or spinal cord can suppress voluntary
voiding, but also stimulates bladder activity during bladder filling.
The muscarinic inhibitory mechanisms do not appear to be tonically
active. The effects of atropine (i.c.v. and i.t.) indicate that
muscarinic excitatory mechanisms are tonically active. These findings
raise the possibility that voiding function is regulated by both
inhibitory and excitatory cholinergic mechanisms in the central nervous system.
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