The response of fetal sheep bladder tissue to partial outlet obstruction

Purpose: We characterized the response of fetal ovine bladder strips to sti mulated contraction and relaxation, and compared this response to that of s trips from the pregnant mother and those obtained after a short duration of fetal bladder outlet obstruction. Materials and Methods: Sham surgery or bladder obstruction was performed in fetal sheep at 90 days of gestation (term 147 days). Bladder tissue was ob tained 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 stimulat ion. Alternate strips were stimulated by adding carbachol, adenosine tripho sphate and KCl. Each strip stimulated by carbachol also underwent field sti mulation in the presence of carbachol. Relaxation was also tested using iso proterenol and nitroprusside. Results: 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 en d of stimulation. In fetal bladder strips field stimulation at all frequenc ies after carbachol stimulation produced phasic relaxation or a biphasic re sponse with an initial relaxation phase followed by phasic contraction. Thi s field stimulated relaxant response was not present in adult female bladde r strips. In addition, field stimulation stimulated relaxation was complete ly eliminated by pretreatment with N-nitro-L-arginine-methyl ester, indicat ing that relaxation was nitric oxide mediated. The fetal responses to all f orms 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 si gnificant differences in contractile responses to adenosine triphosphate, c arbachol or KCl, or the relaxant response to field stimulation after obstru ction. However, there was a significant reduction in relaxant responses to isoproterenol and nitroprusside. Conclusions: In mid gestation sheep fetus contractile responses to field st imulation, adenosine triphosphate, carbachol and isoproterenol are well dev eloped. The fetal ovine bladder shows a strong neuronal nitric oxide respon se that is not present in the pregnant mother and is maintained after short -term obstruction.