Expression and function of protease-activated receptor 4 in human myometrium

Objective: Little is known about the presence or functional effects of protease-activated receptor subtypes in human uterine tissues. The aims of this study were as follows: (1) to investigate for protease-activated receptor-4 messenger RNA and protein expression in human myometrium, (2) to evaluate the effects of a specific protease-activated receptor-4 activating peptide (AYPGKF-NH₂) on spontaneous human myometrial contractility in vitro, and (3) to examine the effects of a protease-activated receptor-4 antagonist (tcYPGKF-NH₂) on thrombin-mediated uterine contractility. Study design: Reverse transcriptase-polymerase chain reaction and Immunofluorescence studies were used to investigate for protease-activated receptor-4 messenger RNA and protein expression, respectively. Isometric tension recordings were used to examine the functional effects on contractility. Results: Reverse transcriptase-polymerase chain reaction demonstrated messenger RNA expression for protease-activated receptor-4 in pregnant and non-pregnant myometrium. Immunofluorescence confocal microscopy demonstrated the presence of protease-activated receptor-4 protein in myometrial cells. With the use of isometric recordings, protease-activated receptor 4-activating peptide elicited a stimulatory effect on spontaneous human pregnant myometrial contractility (13.1% ± 2.7 SEM; n = 6; P < .05). Protease-activated receptor-4 antagonism alone elicited a significant uterorelaxant effect (14.7% ± 2.4; n = 6; P < .05). The observed thrombin-mediated uterotonic effect was similar in the absence (46.1% ± 12.8; n = 6) and presence (48.8% ± 12.6; n = 6) of the protease-activated receptor-4 antagonist (P = .91). Conclusions: This study outlines protease-activated receptor-4 messenger RNA and protein expression in human myometrium. Protease-activated receptor-4 activation exerts a mild uterotonic effect, whereas protease-activated receptor-4 antagonism results in a mild uterorelaxant effect. The potent human uterotonic effect of thrombin is not apparently mediated to any great extent by protease-activated receptor-4.