CONTRACTILITY PARAMETERS OF THE GUINEA-PIG BLADDER IN-SITU - SIMILARITY TO HUMAN BLADDER CONTRACTILITY

The parameters P-isv (active isovolumetric detrusor pressure) and v(max) (maximum shortening velocity), which characterize the contractility of the detrusor muscle, were determined in guinea pigs. To this end it was necessary to develop a method of measuring flow rates in these small animals. The values found were used to calculate the contractility parameter W-max. Thirteen animals were used. The results found for P-isv and v(max) were 43.0 +/- 3.7 cm. H2O and 20.2 +/- 3.7 mm. per second, respectively. The latter corresponded to about 0.38 muscle lengths per second, which is similar to values reported for bladder strips from other species. Previous work showed that in vitro P-isv decreased with increasing bladder volume over a wide range of volumes. In vivo P-isv seemed to be independent of bladder volume. This suggests that neurogenic stimulation intensifies as volume increases. v(max) also was independent of volume. W-max appeared to be suitable for detecting differences in the contractility of the bladders of different animals. Values were not significantly different in isovolumetric and nonisovolumetric contractions. Normalized to the size of the bladder, the W-max values indicated that the power generated by the guinea pig bladder is similar to the power generated by the human bladder.