Characterisation of excitatory and inhibitory transmitter systems in prostate glands of rats, guinea pigs, rabbits and pigs

Excitatory and inhibitory transmitter systems were investigated in strips of prostate glands from rats, guinea pigs, pigs and rabbits. In strips from all species, electrical field stimulation (1 ms pulses at 1-30 Hz for 10 s) produced frequency-dependent contractions which were abolished by tetrodotoxin (1 μM). In strips from rats, guinea pigs and rabbits, contractions were reduced by prazosin (1 μM), guanethidine (10 μM) and atropine (2 μM), indicating the presence of noradrenergic and cholinergic mechanisms. However, the smooth muscle in the pig prostate appears to have a non-(nor)adrenergic non-cholinergic (NANC) excitatory innervation for which the transmitter was not identified. When noradrenergic and cholinergic mechanisms were blocked by guanethidine and atropine, respectively, and tone was raised with noradrenaline or methoxamine, field stimulation produced relaxations only in strips of rabbit prostate, and these were greatly reduced by N(G)-nitro-L-arginine methyl ester (L-NAME, 100 μM), providing functional evidence for a nitergic relaxant innervation. In accord with this, nitric oxide (NO) synthase activity was considerably higher in rabbit than in rat or pig prostates.