The response of fetal sheep bladder tissue to partial outlet obstruction

We characterized the response of fetal ovine bladder strips to stimulated contraction and relaxation, and compared this response to that of strips from the pregnant mother and those obtained after a short duration of fetal bladder outlet obstruction.

Sham surgery or bladder obstruction was performed in fetal sheep at 90 days of gestation (term 147 days). Bladder tissue was obtained 3 and 5 days later. Isolated strips of full-thickness bladders from fetuses and pregnant females were mounted individually in Tyrode's solution containing glucose. The strips were subjected to electrical field stimulation. Alternate strips were stimulated by adding carbachol, adenosine triphosphate and KCl. Each strip stimulated by carbachol also underwent field stimulation in the presence of carbachol. Relaxation was also tested using isoproterenol and nitroprusside.

The response of isolated strips to field stimulation showed phasic contraction or biphasic response, consisting of initial phasic contraction followed by phasic relaxation and a return to control tension after the end of stimulation. In fetal bladder strips field stimulation at all frequencies after carbachol stimulation produced phasic relaxation or a biphasic response with an initial relaxation phase followed by phasic contraction. This field stimulated relaxant response was not present in adult female bladder strips. In addition, field stimulation stimulated relaxation was completely eliminated by pretreatment with N-nitro-L-arginine-methyl ester, indicating that relaxation was nitric oxide mediated. The fetal responses to all forms of stimulation and relaxation were significantly greater than those of pregnant females. After 5 days or greater of obstruction the responses to field stimulation were reduced significantly. In contrast, there were no significant differences in contractile responses to adenosine triphosphate, carbachol or KCl, or the relaxant response to field stimulation after obstruction. However, there was a significant reduction in relaxant responses to isoproterenol and nitroprusside.

In mid gestation sheep fetus contractile responses to field stimulation, adenosine triphosphate, carbachol and isoproterenol are well developed. The fetal ovine bladder shows a strong neuronal nitric oxide response that is not present in the pregnant mother and is maintained after short-term obstruction.