Solvent drag on urea and thiourea across small intestine of Testudo hermanni and Bufo bufo urinary bladder

Exercise and forced submergence in the pond slider (Trachemys scripta) and softshell turtle (Apalone ferox): influence on bimodal gas exchange, diving behaviour and blood acid-base status

The dynamics of bimodal respiration, diving behaviour and blood acid-base status in the softshell turtle Trachemys scripta and the pond slider Apalone ferox were investigated at rest and under conditions of stress induced by exercise and forced submergence. During periods of forced submergence, only A. ferox doubled its aquatic gas exchange rate. Both A. ferox and T. scripta increased their aerial gas exchange profoundly following exercise and forced submergence, a pattern indicative of increased anaerobic respiration. Emersion duration increased significantly in A. ferox following forced submergence, and mean apnoeic time decreased significantly in A. ferox following exercise, indicating that a larger proportion of time at the surface was spent ventilating. Also, A. ferox maintained a one-breath breathing bout regardless of treatment. Submergence produced a respiratory acidosis in the plasma of approximately 0.2 pH units in magnitude in T. scripta and a mixed respiratory/metabolic acidosis of 0.4 pH units in A. ferox. Exercise induced an acidosis of 0.2 pH units of primarily metabolic origin in both species. Intra-erythrocyte pH was also reduced in both species in response to submergence and exercise. Both intracellular and extracellular acidoses were more severe and longer lasting in A. ferox after each treatment. Plasma [HCO3-] decreased by 25 % in both species following exercise, but only in A. ferox following submergence. Plasma lactate concentrations increased by equal amounts in each species following exercise; however, they returned to resting concentrations sooner in T. scripta than in A. ferox. A. ferox had significantly higher lactate levels than T. scripta following forced submergence as well as a slower recovery time. A. ferox, which is normally a good bimodal gas exchanger at rest, utilizes aerial respiration to a greater extent when under respiratory and/or metabolic stress. T. scripta, although almost entirely dependent on aerial respiration, is physiologically better able to deal with the respiratory and metabolic stresses associated with both forced submergence and exercise.

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

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.

Transfer of alanine isomers by rat small intestine

1. A study was made of the transfer of L-alanine, D-alanine and beta-alanine by sacs of everted small intestine of the rat.2. D-Alanine and beta-alanine are transported against a concentration gradient and in this respect resemble L-alanine.3. Transfer of all three isomers was stimulated in presence of glucose, but stimulation was much greater with D-alanine and beta-alanine.4. Transfer of all three isomers was inhibited by galactose.5. The effect of hexoses on amino acid transfer was relatively independent of the effect on fluid transfer.6. L-Methionine inhibited transfer of the three isomers in descending order, L-alanine, D-alanine and beta-alanine, while the magnitude of sarcosine inhibition was in the reverse order.7. At the concentration used (1 mM), L-alanine was transferred mostly by the methionine carrier, and beta-alanine mostly by the sarcosine carrier. D-Alanine occupied an intermediate position.