Losartan was administered orally in the above studies, but in our study, was continuously administered subcutaneously using an osmotic pump. In the rat, the concentrations
of losartan in the blood and tissue vary widely among individuals after oral administration, because the absorption of losartan is visibly affected by the timing of administration, such as before or after eating feed.31 In addition, oral treatment is also affected by first-pass metabolism, and bioavailability is low. Therefore, the concentration of losartan in bladder tissue stabilizes after 14-day repeated oral administration.32 The continuous subcutaneous infusion is assumed to produce stable concentrations of the drug in the blood and tissue at an early stage of treatment. Losartan blood concentrations were not monitored in the two studies PLX4032 cited above, or in our study. However, the dose and method of administration of losartan that we used in our study was reported to prevent injury progression after myocardial infarction in rats.30 In addition, because the contractile response of bladder strips to 0.1 µM AngII disappeared in the losartan group, it is believed that the signaling from the AT1s that were expressed in the bladder was sufficiently blocked. The histological characteristics of the hypertrophic bladder growth in BOO rats, as revealed
by Elastica-Masson staining, included a marked increase in collagen fibers in the bladder smooth muscle layer and resulting muscle division. C59 wnt ic50 out Losartan treatment decreased these hypertrophic characteristics, and the collagen-to-muscle ratio also decreased
to sham levels. Consistent with these results, HB-EGF mRNA levels that were increased in obstructed bladders were reduced by losartan treatment. In a previous study, HB-EGF mRNA and protein levels were reported to increase in murine bladder tissue in response to urethral ligation, and these increases in HB-EGF mRNA were mainly confined to the bladder muscle layer.33 In cardiovascular studies, locally overexpressed HB-EGF after myocardial infarction increased the level of fibrosis through a mitogenic effect on fibroblasts and exacerbated remodeling at the subacute and chronic stages post-myocardial infarction.34 The combined observations suggest that AT1s are activated by BOO, at least partially, and this activation upregulates HB-EGF and induces fibrosis through induction of the proliferation of fibroblasts in the bladder muscle layer. The urodynamic findings of our study; a shortened micturition interval, a decrease in urine volume per void volume and development of residual urine, indicated that BOO decreased bladder function. However, bladder capacity is greater in the losartan group than in the sham group. The reason for this may be due to bladder hypertrophy induced as a compensatory response to obstruction before treatment with losartan.