The role of rho-kinase in phenylephrine and 5-HT-induced smooth muscle contractions in the porcine ureter

[Speaker] Iris Lim:1
[Co-author] Russ Chess-Williams:1, Donna Sellers:1
1:Centre for Urology Researh, Bond University, Australia

Background. Urolithiasis is frequently accompanied by colic¸ which is understood to be caused by contractions of the ureteral smooth muscle. Since calcium sensitisation via the rho-kinase pathway plays a significant role in smooth muscle contraction¸ our aim was to investigate the role of Rho-kinase in phenylephrine and 5-HT-induced contractile activity in isolated ureters from young and older animals.

Methods. Contractile responses of isolated smooth muscle strips to EC50 (low) and maximal (high) doses of phenylephrine and 5-HT were examined in distal ureter from young (6 months) and old (3 years) pigs¸ in the absence and presence of Rho-kinase inhibitors, fasudil (30&muM) or Y-27632 (10&muM). Tissues developed phasic contractions and were expressed as area under the ¸ normalized to tissue weight. Additionally¸ isolated ureteral smooth muscle strips were homogenized¸ and rho-kinase activity assay kit was utilised to measure rho-kinase activity at basal, phenylephrine- and 5-HT-induced states.

Results. Fasudil significantly attenuated ureteral contractions to low and high doses of phenylephrine by 81.9±3.0% and 89.8±9.2% vs control response in tissues from young animals. In response to 5-HT¸ fasudil reduced contractions by 83.7±6.2% and 77.7±3.2 vs control response at low and high doses respectively. In tissues from older animals, similar effects were observed¸ where contractions to low and high doses of phenylephrine were reduced by 84.0±3.9% and 78.7±3.0% vs control response. Contractions to 5-HT were also reduced by 80.1±6.9% and 79.3±3.2% vs control response at low and high doses respectively. Y-27632 produced similar effects with both agonists in tissues from young and old animals. Active rho-kinase activity was similar in both age groups at basal and agonists-induced states.

Conclusions. Our results show that rho-kinase mediates contractile responses to phenylephrine and 5-HT in isolated ureteral tissues of the pig and may be a potential target for development of treatments aimed at relaxing ureteral smooth muscle.

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