α1 -Blocker inhibits non-voiding contractions and decreases the level of intravesical prostaglandin E2 in rats with partial bladder outlet obstruction

Long-term administration of alpha-1 blocker can reverse the micturition pattern in a bladder outlet obstruction murine model

OBJECTIVE

To investigate the effect of chronic administration of an alpha-1 blocker on micturition patterns in long-term partial bladder outlet obstruction.

METHODS

Mice were divided into three groups: a normal group, in which animals were fed a standard diet; a partial bladder outlet obstruction group, in which the proximal urethra was tied and animals were fed a standard diet; and a partial bladder outlet obstruction + naftopidil group, in which the proximal urethra was tied and animals were fed a standard diet containing naftopidil. Micturition behavior was evaluated in all groups for 6 months after partial bladder outlet obstruction surgery. The parameters evaluated included voided volume, time per void, urination frequency and total urine volume. Quantitative assessment of gene expression was also carried out.

RESULTS

Total urine volume, as well as total and average voided volume during night, was significantly decreased in partial bladder outlet obstruction + naftopidil mice compared with partial bladder outlet obstruction animals. The levels of transcripts encoding 5-hydroxytryptamine 2A and tissue inhibitor of metalloproteinase 2 were significantly decreased in the partial bladder outlet obstruction + naftopidil group compared with the partial bladder outlet obstruction group.

CONCLUSIONS

Long-term administration of an alpha-1 blocker seems to reverse the disturbance of the micturition pattern caused by partial bladder outlet obstruction. Mechanistically, this effect might be mediated by changes in the expression of a serotonin receptor and/or in the activity of the fibrogenesis pathway.

In Vitro Effects of Plasma Collected From Rats Administered Naftopidil on Whole Urinary Bladder Preparation Isolated From Rats

Purpose

Alpha-1-adrenoceptor blockers (e.g., naftopidil) are prescribed for the treatment of male lower urinary tract symptoms. Although the mechanism of action of naftopidil has been studied in various organs, that in the urinary bladder remains unknown. To clarify the direct effects of naftopidil on this organ, activities were assessed in the isolated rat whole urinary bladder.

Methods

A total of 30 female rats were used. In Experiment 1, bladder activity was measured during a cumulative administration of 2.5–75μM naftopidil (n=7). In Experiment 2, rats were divided into 2 groups: control (n=10) and naftopidil (5 mg/animal/day, oral gavage, once-daily for 2 weeks) (n=13). After the treatment period, plasma was obtained from each rat. The urinary bladders were harvested from the control rats. Isovolumetric rhythmic bladder contractions were induced at above the threshold volume, and intravesical pressure was recorded. Control plasma was added to the organ bath; after subsequent wash-out, plasma collected from rats administered naftopidil was added. In Experiment 3, the plasma levels of monoamines and amino acids were quantified using the individual plasma prepared in the Experiment 2.

Results

Cumulative dosing with naftopidil did not change the interval between spontaneous contractions compared to the interval at baseline. After adding control plasma, the interval was shortened compared to the baseline (P=0.008). The plasma collected from rats administered naftopidil suppressed the shortening of the interval compared to the control plasma (P=0.041). Naftopidil resulted in a decrease in the level of noradrenaline (P=0.009) and an increase in that of glycine (P=0.014).

Conclusions

Although naftopidil did not directly act on the interval between spontaneous contractions of the urinary bladder, the plasma collected from rats administered naftopidil, with changing levels of monoamines and amino acids, may suppressed shortening the interval.