Cholinergic innervation and muscarinic receptors in the human prostate.

OBJECTIVE: In light of recent interest in the use of muscarinic receptor antagonists for the treatment of male lower urinary tract symptoms, understanding how such drugs work not only on the bladder but also on the prostate is important.
METHODS: A literature review was conducted to identify studies on the cholinergic innervation and presence and function of muscarinic acetylcholine receptors in the human prostate.
RESULTS: The available studies demonstrate a dense cholinergic innervation within both stromal and epithelial compartments of the prostate. Concomitantly, the human prostate expresses muscarinic receptors at densities exceeding those of alpha(1)-adrenoceptors. They mainly belong to the M(1) subtype and are found on epithelial cells, but a smaller population of M(2) receptors is found on stromal cells. Both populations have been shown to be functional in signal transduction assays. However, in line with the sparse receptor density on stromal smooth muscle cells, contractile responses of the prostate are only small. Data from prostate cancer cell lines and from botulinum toxin injections into the benign prostate raise the possibility that muscarinic receptors may promote prostatic growth. Animal data suggest that muscarinic receptors may be of primary importance in the genesis of prostatic secretions, but this needs to be confirmed in humans.
CONCLUSIONS: Taken together it appears that direct effects on the prostate need to be considered when using muscarinic receptor antagonists in men. They may primarily involve alterations of glandular secretion and prostatic growth.