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Abstract
Normal rats as well as rats with bladder hypertrophy secondary to outflow obstruction
were investigated cystometrically before and after administration of the potassium
channel openers pinacidil or cromakalim one mg./kg. orally. In normal rats cromakalim
decreased micturition pressure by 15 +/- 6%. A diminished micturition pressure was
also seen after pinacidil (by 18 +/- 8%) but this did not achieve statistical significance.
Further, no clear-cut effects on bladder capacity, residual volume, basal bladder
pressure, threshold pressure, bladder compliance or on bladder wall tension were seen
in this group of rats neither in the presence of pinacidil nor cromakalim. Rats with
bladder hypertrophy exhibited a significant bladder instability during cystometrical
investigations. The mean amplitude of the spontaneous bladder contraction exceeded
20 cm. H2O prior to micturition. Administration of pinacidil and cromakalin decreased
the spontaneous contractions to 26 +/- 12% and 22 +/- 7%, respectively, of that seen
in the absence of the drugs. Furthermore, pinacidil decreased micturition pressure
by 61 +/- 12%. Also cromakalim decreased micturition pressure (by 27 +/- 13%) but
this effect did not achieve statistical significance. After both pinacidil and cromakalim
these rats tended to develop residual urine. In accordance with the results in normal
rats pinacidil and cromakalim showed no effects on bladder capacity, basal bladder
pressure, threshold pressure, bladder compliance or on bladder wall tension in rats
with bladder hypertrophy. The findings of an almost complete disappearance of spontaneous
bladder contractions in rats with bladder instability and a remaining voiding ability
after administration of pinacidil or cromakalim suggest that potassium channel openers
may be a therapeutic alternative in the treatment of bladder instability associated
with outflow obstruction.