Alpha1 -adrenergic receptors mediate bladder overactivity induced by cold stress in rats with bladder outlet obstruction.

Purpose: To determine if alpha1 -adrenergic receptors (AR) mediate bladder overactivity induced by cold stress in rats with bladder outlet obstruction (BOO).

Materials And Methods: The urethras of 10-week-old female Sprague-Dawley rats were ligated to create BOO. After 4 weeks, cystometric investigations were performed at room temperature (RT, 27 ± 2°C) for 20 min. The rats were then given 0.3 mg/kg naftopidil (n = 6) or vehicle (n = 5) intravenously. Five minutes later, they were transferred to low temperature (LT, 4 ± 2°C), and the cystometric patterns were again recorded for 40 min. In BOO rats and in sham-operated rats (n = 8) the expression levels of alpha1A - and alpha1D -AR mRNAs and the presence of alpha1A - and alpha1D -AR immunoreactivity on calcitonin gene-related peptide (CGRP)-positive nerve cells were investigated.

Results: During LT exposure, the vehicle-treated BOO rats exhibited cold stress-induced bladder overactivity. In the naftopidil-treated rats, the increase of basal pressure and decreases of both voiding interval and bladder capacity induced by LT were significantly reduced compared to the vehicle-treated animals. In the bladders of BOO rats exposed to LT, the expression of alpha1D -AR mRNA was significantly higher than in sham-operated rats, and the immunoreactivity for alpha1D -ARs on the CGRP-positive nerve cells tended to be more pronounced.

Conclusions: Alpha1 -ARs mediate part of the bladder overactivity induced by cold stress in rats with BOO. Cold stress increases the expression of alpha1D -AR mRNA and the immunoreactivity for alpha1D -ARs on the CGRP-positive nerve cells in BOO rats. Naftopidil partially inhibits the cold stress overactivity, suggesting that it is mediated, at least partially, through alpha1D/1A -ARs.