This study characterised the inhibitory actions of prostaglandins on smooth muscle contractility in the rat prostate gland. Immunohistochemical studies were carried out to identify and localise the two isoforms of cyclooxygenase (COX) enzyme and the subtypes of prostanoid receptors present in the rat prostate. Isolated organ bath studies were carried out to pharmacologically characterise the subtype of prostanoid receptor mediating the inhibitory effects of prostanoids on the rat prostate. Immunohistochemical studies confirmed the presence of mainly COX-2 within the prostatic stroma. Isolated organ bath studies showed that prostaglandin E(2) (PGE(2); 10 nM-10 microM) but not prostaglandin D(2) (10 nM-10 microM), PGF2alpha (10 nM-10 microM), prostacyclin (10 nM-10 microM) or U46619 (10 nM-10 microM) inhibited nerve-mediated contractile responses to electrical field stimulation. Similarly, sulprostone (10 nM-10 microM) had no affect on the magnitude of the electrically evoked contractions. PGE(2) (0.1-10 microM) did not affect contractions elicited by noradrenaline or adenosine 5'-triphosphate. PGE(2)-mediated inhibition of electrical field stimulation induced contractions was attenuated by AH 6809 (10 microM) but not SC 19220 (10 microM) or AH 23848 (10 microM). It is concluded that prostaglandins can inhibit contractions of the rat prostate gland through a prostanoid receptor of the EP(2) subtype.