Permeability of urinary bladder of Rana cancrivora to urea in the presence of oxytocin

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Abstract
1. When Rana cancrivora collected from fresh water had been exposed for 3 days to saline solutions having osmolalities from 280 to 690 m-osmole/kg, urea concentrations in plasma and urine appeared to come into equilibrium, and were from 70 to 200 m-mole/l.2. Plasma urea level of fresh water R. cancrivora (48 m-mole/l.) was doubled (82 m-mole/l.) after 8 hr of exposure to 270 m-osmolal saline. It continued the same after 24 hr of exposure.3. When isolated urinary bladders of R. cancrivora were exposed to Ringer on the serosal aspect and one-fifth Ringer on the mucosal aspect, then in response to this osmotic difference of 190 m-osmole/kg, the rate of fluid movement (mucosa to serosa), which was 10.3(+/-2) mul./cm(2).hr, was not significantly altered when up to 60% of the NaCl of the Ringer solution was substituted by urea.4. Under the same circumstances, when oxytocin (50 m-u./ml.) was present in the serosal solution, the rate of fluid movement (mucosa to serosa) was 133.2(+/-7.9) mul./cm(2).hr in the absence of urea; it was progressively decreased by the presence of urea until, when 80% of the NaCl had been substituted by urea, the rate of fluid movement was reduced to 14.5(+/-4.0) mul./cm(2).hr.5. The diminished rate of fluid movement under the above circumstances could not be correlated with serosal urea concentration, with serosal availability of Na(+), nor with Na(+) concentration difference across the bladder wall. It appeared to be directly related to the ;non-urea osmotic difference' across the bladder wall provided by solutes other than urea.6. When isolated bladders were exposed to an osmotic difference of 190 m-osmole/kg, but having 25 mM urea present in the mucosal solution, then fluid moved from mucosa to serosa at a rate of 10.4(+/-1.3) mul./cm(2).hr in the absence of oxytocin and 124(+/-9) mul./cm(2).hr when oxytocin (50 m-u./ml.) was present. In the former case no urea passed across the bladder wall, but in the latter case urea passed from mucosa to serosa at a rate of 3.16(+/-0.3) mumole/cm(2).hr. The fluid moving from mucosa to serosa thus contained urea 25.5 m-mole/l.7. Vasotocin (10(-9)M), which is equipotent with oxytocin (50 m-u./ml.) in affecting permeability of the isolated urinary bladder to water, was also equipotent in producing a reduced rate of water fluid movement in the presence of 40% urea (vasotocin, 63 mul./cm(2).hr; oxytocin, 59 mul./cm(2).hr).8. When groups of frogs were cystectomized, and other groups of frogs were sham-operated, then after 48 hr of exposure to fresh water or to 300 m-osmolal saline the sham-operated frogs had plasma urea level raised from 20 m-mole/l. (fresh water) to 42 m-mole/l. (saline), while the cystectomized frogs had 20 m-mole/l. (fresh water) and 26 m-mole/l. (saline).9. The hypothesis is presented that hormone-induced permeability of the urinary bladder to urea contributes to the immediate adjustment of plasma urea level by which R. cancrivora survives when exposed to high environmental salinity.