Pharmacology of neurotransmission to the smooth muscle of the rat and the guinea-pig prostate glands

1 Histochemical studies carried out on sections of rat and guinea-pig prost ate glands revealed the presence of acetylcholinesterase- and noradrenaline -containing nerve fibres in the fibromuscular stroma. Positive staining for acetylcholinesterase but not for noradrenaline was also seen in the epithe lium. 2 Electrical field stimulation with trains of 0.5 ms pulses, dial setting o f 60 V, delivered at 1-30 Hz for 10 s at 5 min intervals, was applied to ne rve terminals within the rat and guinea-pig isolated prostate glands, The e voked contractions were frequency-dependent Tetrodotoxin (1 mu M) abolished contractions evoked by short pulse repetitive stimulation (trains of 20 0. 5 ms pulses at 10 Hz every 100 s) in tissues from both species. 3 The field stimulation-induced contractions of the prostatic smooth muscle were markedly attenuated by guanethidine (10 mu M) and prazosin (0.1 and 1 mu M) indicating that neurotransmission to the prostatic smooth muscle in both species is predominantly sympathetic and noradrenergic, and that norad renaline released during field stimulation acts at postjunctional alpha(1)- adrenoceptors. 4 Atropine (0.1 and 1 mu M) caused a slight bur significant reduction of th e field stimulation-induced contractions of prostate smooth muscle from bot h the rat and the guinea-pig. In the guinea-pig, cholinesterase inhibition by physostigmine and neostigmine, both at 10 mu M, enhanced the field stimu lation-induced contractions of the prostatic smooth muscle. This enhancemen t was reversed by atropine (0.1 mu M) but not by hexamethonium (0.1 mM). Th ese data are compatible with some participation of acetylcholine, acting at muscarinic receptors, in neurotransmission to prostatic smooth muscle.