Contractions of the Mouse Prostate Elicited by Acetylcholine Are Mediated by M₃ Muscarinic Receptors

Abstract

Increased smooth muscle tone in the human prostate contributes to the symptoms associated with benign prostatic hyperplasia. In the mouse prostate gland, cholinergic innervation is responsible for a component of the nerve-mediated contractile response. This study investigates the muscarinic receptor subtype responsible for the cholinergic contractile response in the mouse prostate gland. To characterize the muscarinic receptor subtype, mouse prostates taken from wild-type or M 3 muscarinic receptor knockout mice were mounted in organ baths. The isometric force that tissues developed in response to electricalfield stimulation or exogenously applied cholinergic agonists in the presence or absence of a range of muscarinic receptor antagonists was evaluated. Carbachol elicited reproducible and concentration-dependent contractions of the isolated mouse prostate, which were antagonized by the presence of muscarinic receptor antagonists. Calculation of antagonist affinities (pA 2 values) indicated a rank order of antagonist potencies in the mouse prostate of: darifenacin (9.08) ϭ atropine (9.07) ϭ 1,1-dimethyl-4-diphenylacetoxypiperidinium iodide (9.02) Ͼ cyclohexyl-hydroxy-phenyl-(3-piperidin-1-ylpropyl)silane (7.85) Ͼ cyclohexyl-(4-fluorophenyl)-hydroxy-(3-piperidin-1-ylpropyl)silane (7.39) Ͼ himbacine (7.19) Ͼ pirenzipine (6.88) Ͼ methoctramine (6.20). Furthermore, genetic deletion of the M 3 muscarinic receptor inhibited prostatic contractions to electrical-field stimulation or exogenous administration of acetylcholine. In this study we identified that the cholinergic component of contraction in the mouse prostate is mediated by the M 3 muscarinic receptor subtype. Pharmacological antagonism of the M 3 muscarinic receptor may be a beneficial additional target for the treatment of benign prostatic hyperplasia in the human prostate gland.

Age-related changes in the innervation of the prostate gland

“…Despite muscarinic receptors being located primarily in the glandular epithelium, they play a direct role in post-junctional contraction in the prostate, as in vitro contraction of isolated prostates elicited by electrical field stimulation or exogenous agonists can be inhibited by muscarinic receptor antagonists in the human, 12 , 31 , 55 canine, 41 , 56 rabbit, 57 , 58 guinea pig, 38 , 58 , 59 rat 58 , 59 and mouse 60 , 61 prostates. However, the magnitude of cholinergic contractions in the prostate is less than that observed for α 1 -adrenoceptor stimulation 62 .…”

“…M 2 muscarinic receptors mediate contraction in the canine prostate 56 and are also the predominant subtype in human stromal cells where they inhibit the accumulation of cAMP 64 . In the guinea pig prostate, M 1 muscarinic receptors facilitate nerve mediated contraction, 63 whereas contraction of the rat and mouse prostates is mediated by M 3 muscarinic receptors, 61 , 65 which are localized on the prostatic smooth muscle 51 …”

The Non-Neuronal Cholinergic System in Health and Disease

“…ChAT was also shown to be expressed in spermatozoa [159], and release of non-neuronal ACh was measured in the germinal epithelium [158]. For the prostate gland, activation of mAChR results in secretion of prostate fluids [160] as well as in contractile response which is being mediated via M3 mAChR in the mouse [161]. Further, prostate cells were shown to express the ACh-degrading enzymes AChE and butyrylcholinesterase [162].…”

Increased Rho-kinase-mediated prostate contractions associated with impairment of β-adrenergic-cAMP-signaling pathway by chronic nitric oxide deficiency

“…In the lower urinary tract, including prostate (Christ and Andersson, 2007), both α 1 -adrenoceptor and muscarinic receptor-mediated PSM contractile responses are regulated by RhoA/ Rho-kinase Ca 2 þ -senitization pathway, as demonstrated in animal (Lam et al, 2013;Saito et al, 2011;White et al, 2011White et al, , 2013 and human tissues (Rees et al, 2003;Strittmatter et al, 2011;Takahashi et al, 2007). Elevated RhoA/Rho-kinase signaling has also been shown to play a role in BPH (Adam, 2003;Gur et al, 2011).…”