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changes in ion, urea concentrations and blood plasma osmolarity of Pelobates syriacus juveniles under varying conditions
Camp. Biochrm. Phvsiol. Vol. 75A. No. 4, pp. 619 to 623, 1983 Printed in Great B&in
0300-9629/83 $3.00+ 0.00 Q 1983 Pergamon Press Ltd
CHANGES IN ION, UREA CONCENTRATIONS AND BLOOD PLASMA OSMOLARITY OF PELOBATES SYRIACUS JUVENILES UNDER VARYING CONDITIONS G. DEGANI, S. GOLDENBERG and M. R. WARBURG* Department of Biology,
Technion-Israel
Institute
(Receiced 30 Nocemher
of Technology,
Haifa 32000, Israel
1982)
Blood plasma osmolarity and ion concentration, and intra-cellular fluids (muscle) were determined in juvenile toadlets in tap water, in wet soil and after dehydration of 18% body weight or following acclimatization to 400 mM/l urea. 2. Plasma concentration increased during dehydration (375 mOsm/kg), after three months in soil (415 mOsm/kg), and after acclimatization to 400 mM/l urea (540 mOsm/kg). 3. In hydrated toadlets Na+ and Cl- accounted for 81% and urea for 27,, the latter increased to 22:” when in soil. 4. Urea concentration was higher in muscle of toadlets burrowed in soil or following acclimatization to 400 mM/l urea. 5. Sodium concentration increased in both plasma and muscle after dehydration or following acclimatization to 400 mM/l urea. In both situations the animals lost weight. 6. Potassium increased in muscle fluid when acclimated to urea, but was very low in all other experimental groups. 7. Both plasma and muscle Cl- concentrations were found to be higher in animals after dehydration Abstract-l.
or following acclimatization to 400 mM/l urea.
INTRODUCTION
Terrestrial Amphibia of xeric habitats are known to spend a large part of the year in hiding places to prevent dehydration (Warburg, 1972). Pelobates syriacus is found in Israel (its southern limit distribution), along the coastal plain and in the Galilee Mountains. Breeding takes place in temporary ponds containing water for at least a few months (Warburg, 1972; Degani, 1982). When the pond dries the juveniles burrow into the soil until winter. McClanahan (1972) has shown that as the soil dries, plasma concentration of Scaphiopus couchi rises mainly due to urea concentration. Urea accumulation was found in other terrestrial amphibians: Bufi riridis (Katz, 1973; Rick et al., 1980; Degani, 1981b). ,hbJ’stoma tigrinum (Delson & Whitford, 1973), and SuIumandra suhandra (Degani, 1981a). These studies have shown that plasma Na+ and Cl- concentrations increased during prolonged dehydration. During rapid dehydration or when exposed to saline conditions, plasma concentration of S. salumandru rose mainly because of increased ion concentration (Degani, 1981a). Only euryhaline amphibians (Rana cancriuora, B. uiridis) can accumulate urea during adaptation to saline conditions but not such high values as were found in other terrestrial species during prolonged periods in the soil, (Gordon et al., 1961; Gordon, 1962; Katz, 1973). There is little information on the concentration of Na+, K+, Cl- and urea in the plasma and tissues during dehydration,
* Author
to whom
correspondence
should
be addressed. 619
acclimation to urea solutions or during long periods in the soil. The purpose of this study is to compare between concentration of Na+, K+, Cl- and urea in the plasma and muscle of P. syiacus under the following conditions: (a) dehydration, (b) long periods inside the soil and (c) during acclimation to urea concentrations. MATERIALS
AND
METHODS
Tadpoles of P. syriaas were collected at the beginning of summer from a pond in Sasa (Galilee Mountains). Animals were kept inside plastic containers measuring 40 x 20 x 10 cm at room temperature until metamorphosing. One group of juveniles (N = 5) was kept for one week in tap water. A second group of juveniles (N = 5) was kept one week in 2OOmM/l urea and then transferred to 400 mM/l urea for another week. A third group (N = 5) was dehydrated in 0 5”,, R.H. over Silica Gel at 20-C up to 18”,, of initial body weight using methods described pl-eviously (Warburg & Degani. 1979). A further group of juveniles (N = 5) was kept for 3 months in soil at 60”,, soil moisture. The percentage of water in the soil was determined as described previously (Warburg & Degani. 1979). Blood samples were taken from acclimated animals by heart puncture, using I ml syringe previously washed with lithium heparin. The blood sample was immediately centrifuged for 10 min at 252 9. and the plasma either analyzed immediately or frozen for later analysis. Muscle tissue from the hind leg was taken and used for both urea and electrolytes (Na+, K+ and Cl-) determination. Sodium potassium and chloride in plasma and in muscle tissue were determined using methods described by Briihman & Hanke (1980). Urea was determined by Foster & Hochholzer’s (1971) method. Urea in muscle was determined after homogenization with TCA (55”) and immediate centrifugation
G. DEGANI et d.
620
for 15 min at 3009. Water contents in muscle tissue was determined by desiccating the muscle tissue at 60°C until it reached a constant dry weight when it could be calculated. Tbe muscle concentration of Na+, K*, Cl- and urea were related to the water content of the muscle. Five animals were studied in each experiment, both means and standard deviations are given. t-Test was used io compare the means. RESULTS Juvenile P. s_v&ctrs that stayed in either soil or in tap water did not lose weight. Dehydration at 5% R.H. and 20°C caused a decrease in weight that was greater than when toads were kept in urea solution (Figs l-4). Plasma concentration of juveniles in tap water was found to be about 280 mOsm/kg. After dehydration of 187; body weight plasma concentration rose to 375 mOsm~kg, and after three months of burrowing inside the soil it rose to 415 m&m/kg. Acclimation to ~rnM~1 urea caused an increase in plasma concentration to 540 m&m/kg (Fig. 5). The various components in plasma responsible for its osmotic values varied under different conditions (dehydration, burrowing and urea acclimation). Both Na+ and CI- concentrations in the plasma in fully
In Soil
a
1
1 t
I
,
I
I
0
I
2
3
Time Fig. 1.
l months)
0
2
I
Time (days)
Fig. 3. Weight loss of juvenile P. spimxs in dry air at 2o’C.
after dehydration
hydrated juveniles were responsible for 81% of the total osmolarity, whereas urea was responsible for only 2nd. After dehydration the percentage of urea increased to 6%, the remaining osmolarity of the plasma was mainly due to Na’ and Cl-. During burrowing in so& urea concentration increased and reached 22%; of the plasma concentration. A similar situation was found in plasma of juveniles that were acclimated to 400mM/I of urea. Concentration of Na+ was higher in juveniles after dehydration and following acclimation to urea (Fig. 6). Under both situations the animals lost about 18% of their initial body weight (Fig. 1). but Na’ concentration in the muscle increased. Concentration of Cl- in both plasma and muscle followed changes in a similar way as Na+ concentrations. The difference between concentrations of Cl- in plasma and Cl- in muscle was less remarkable than the difference between concentration of Naf in plasma and Na’ in muscle (Figs 6,X). Concentration of KS in muscle was higher foilowing dehydration, or after acclimation to 400 mM/t urea, than when the animals were kept in tap water or dry soil (Fig. 7). However, no significant difference was found between the different experimental groups in Kf concentration in plasma (P > 0.05; t-test),
Weight loss of juvenile P. S.LY%Z~I~S in soil.
Urea
I Time Fig. 2.
3
f Doysl
Weight loss of juvenile P. s.viucus in water.
L
0
t
100 External
7
Acciimat~af~n
1
200
Osmotarity
I
3cm
t
400
mOsm/Kg
Fig. 4. Weight loss of juvenile P. s~ritxxs when acclimated to different urea concentrations.
Water balance in P&bates
ts!lphJtQ
El muack
201
P :: ” .
t
f ._s f E
tot
I + Y
100 -
80-
60-
40
I
..
Fig. 7. Muscle and plasma K+ concentrations
I
,‘.
-.LL 1
)
:’ -:
~
.
,’ : ; : : .. :.
.._
.’
TOP water
400 m/t Urea
3
months I”
WI1
oohY4rPtron
Ii%
BW
Fig. 5. Blood plasma osmolarity, electrolyte concentrations
of juvenile
P. syriacus under different conditions.
and urea of juvenile P. svriacus under different conditions:
SimiIarly, no significant difference was found between the urea concentration in plasma and muscles of animals kept in tap water or dehydrated by up to 18% of initial body weight (Fig. 9). However, urea concentration in muscle was found to be higher than the urea con~ntration in plasma in both groups, those in the soil and thorn acclimated to 400 mMit urea.
!islplasma #
TOP
Fig. 6. Mu&e and plasma Naf concentrations of juvenile P. syriacus under different conditions.
muacls
wotrr
Fig. 8. Muscle and plasma Cl- concentrations of juvenile P. sriacus under different conditions.
622
G. DEGANI et al.
20
400
mM/I
Fig. 9. Urea concentration of muscle and plasma in juvenile P. spriucus under different conditions.
DISCUSSION
The burrowing toad, P. syriacus, spends 8-10 months of the year burrowed in soil (Warburg 1971, 1972). During summer the soil dries and the osmotic relationship between the toad and the surrounding soil changes. Thus, water passes from the toad to the soil (or to the air), and the toad dehydrates. This situation takes place only in dry air or in dry soil. Plasma concentration increased under these conditions. Both Nat and Cll are the most important ions in the plasma during dehydration, as was shown in the urodele S. .sa/atmndro (Degani, 1981a), and again here. Similar situations (increased plasma Na+ and Cll concentration) occur during saline adaptation (Katz. 1973; Degani, 1981 b). In some amphibians, (K. cancriuoru, B. ciridis) a prolonged exposure to saline environment caused increased urea concentration (Gordon et (I/., 1961; Katz, 1973; Balinsky, 1981). It is possible that dehydration affects accumulation of urea. About 6’?,, of the total plasma concentration of P. .sp+tcus was due to urea compared with 32’:;, found in S. salatnundra after dehydration (Degani, 1981a). The adult salamander is larger than the juvenile P. dehydration was syriacus studied here, therefore slower there. We assume that during long dehydration urea accumulates in the blood plasma. The soil surrounding the animal dries slowly. thus plasma concentration of the burrowed animal increased mostly through accumulation of urea. The same situation was described previously in several other amphibians: S. couch (McClanahan. 1972) B. riridis (Degdni rf (I/., 1981), A. tigrinurtl (Delson & Whitford, 1973) and S. .saktttutndrct (Degani, 1981a). Urea ac-
cumulation during the period when burrowed inside the soil may be explained by increased production (Jones. 1980) or by the reduction in the excretion of urea when glomerular filtration rate is low (SchmidtNielsen & Lee, 1962). The ability to accumulate urea and the ability to tolerate urea in the plasma are more important to terrestrial amphibians than to aquatic ones. In this situation the animals do not excrete urine and can absorb water from the soil. Urea accumulation during burrowing in P. .syriucus was found to be lower (26”,, of total plasma concentration) than in B. ciridis (689,, of total plasma concentration) after 3 months in soil (Degani et [I/., 1981). In S. couchi concentration of urea in the plasma was 73”,, (McClanahan, 1972). The ability to accumulate urea is possibly an adaptation to terrestrial mode of life. The differences between B. riridis, S. cowhi and P. .s)Ctcus in accumulating urea are correlated to the different habitats which they inhabit. There is information in literature concerning changes in muscle Na+, K+, Cl- and urea. Balinsky (1981) summarized the information about amphibians adapted to increasing salinities. Level of potassium in muscle in red blood cells and in skin cells increased. A similar situation is described here for P. syriacu.s following dehydration and acclimation to 400 mM/l urea. Urea concentration of both muscle and plasma did not differ in either R. cancricoru, B. ciridis (Balinsky, 1981). or P. sq’riucus kept in fresh water. In B. uiridis adapted to 380 mOsm/kg NaCl, urea concentration in muscle (90 mM/l) was higher than urea in plasma (69 mM/l). This was found here also for P. s~riacus. In Bt& horem adapted to 380 mOsm/kg NaCl the urea concentration in muscle was found to be lower (64 mM/l) than the urea concentration in plasma (81 mM/‘I). A~rCtlo~rlrt~~emc,nt.~~;-This study was carried out while the senior author was supported by a research fellowship at the Technion, for which he would like to express his gratitude. The technical assistance of Mrs Mira Rosenberg is gratefully acknowledged.
REFERENCES
BALINSKY J. B. (1981) Adaptation of nitrogen metabolism to hypersomatic environment in Amphibia. J. rxp. Zoo/. 215, 3355350. BR~~HMANNM. & HANU W. (1980) Cell volume regulation in juveniles of Xrnnpus Ittrris in hypertonic urea solution. Conrp. Biochrttt. Physiol. 67A, 361 366. DEGANI G. (1981a) The adaptation of Sttlunzundrtr ,stt/tttttctttdrrt (L.) from different habitats to terrestrial life. BY. J. Ht~per. 6. 169-l 72. DEGANI G. (1981b) Salinity tolerance and osmoregulation in Sulatnandra sahtandra (L.) from different populations J. wmp. PhJxiol. 145, 133. 137. DEC~ANIG. (1982) Amphibian tadpole interaction in wsinter ponds. Hydrohioloyiu (in press). DEGANI G., SILANIKOVE N. & SHKOLNIK A. (1981) Osmotic and urea concentration of blood plasma in burrowing green toads. Isruel J. Zoo!. 30, 96. DELSON J. & WHITFORD W. C. (1973) Adaptation of the tiger salamander Amh_rstorna tiyrinnnz to arid habitats. Camp. Biockem. Phrsiol. 46A, 631-638. FOSTER L. B. & HOC.HHOLZEK J. M. (1971) A single reagent manual method for directly determining urea nitrogen in serum. C/in. Chttt. 17, 921.
Water balance in Peiobntes GURUoN M. S. (1962) Osmotic regulation in the green toad (&&I &‘dis). .I. exp. Bid/. 39, 261-270. GUR~XINM. S., SCHMIDT-NIELSENK. & KEUY H. M. (1961) Osmotic regulation in the crab-eating frog Rana cancrirora.
J. exp. Biol. 38, 659-678.
JDNE~R. M. (1980) Metabolic consequences of accelerated urea synthesis during seasonal dormancy of spadefoot toads. ~~~~~~~~~~~~.~ coatltrhiand ~~~~~iu~z~.~ ~~l~~~f~p~i~~~~~s. 3. eq.
Zooi. tf 2, 255-267.
(1973) Studies on the adaptation of the toad Bufi plasma concentration and water content of the tissues. J. CV+
KATZ U.
iiidb BiCJi.
to high salinities: Oxygen consumption.
.%,
785.-796.
L. (1972) Changes in body fluids of burrowed spadefoot toads as a function OFwater potential. Co/>&a 1972, 209-2 16.
MC.CLANAI-IAN
623
RICK R., DORCE
A., RATZ LJ., BAUER R. & THURAU K. (1980) The osmotic behaviour of toad skin epithelium (Bufo viridis), an electron microprobe analysis, Q%iyers Arch. 385, l-10. SCHMIDT-NIELSEN K. & LEE P. (1962) Kidney function in the crab-eating frog (Ram cancrimv). f. exp. Biol. 39, 167-177. W~R~URG M. R. (1971) On the water economy of Israel a~phjbjans: the anurans. fomp. ~i~c~7~~?3.Ph_siof. 40.4, 9L t-924. kf. R. (1972) Water economy and thermal bafance oE fsraeh and Australian Alnph~bia from x&c habitats. Qmp. zoo1. Sac. to&. 31, 79-i Il. WARBURGM. R. & DEGANL G. (1979) Evaporative water loss and uptake in juvenile and adult S&numilr~ XI/~rnun&a (L.) (Amphibia, Urodela). Contp. Bioc~h~,m. Plrysiol. 62A, 1071-1075.
WARBURG
0300-9629/83 $3.00+ 0.00 Q 1983 Pergamon Press Ltd
CHANGES IN ION, UREA CONCENTRATIONS AND BLOOD PLASMA OSMOLARITY OF PELOBATES SYRIACUS JUVENILES UNDER VARYING CONDITIONS G. DEGANI, S. GOLDENBERG and M. R. WARBURG* Department of Biology,
Technion-Israel
Institute
(Receiced 30 Nocemher
of Technology,
Haifa 32000, Israel
1982)
Blood plasma osmolarity and ion concentration, and intra-cellular fluids (muscle) were determined in juvenile toadlets in tap water, in wet soil and after dehydration of 18% body weight or following acclimatization to 400 mM/l urea. 2. Plasma concentration increased during dehydration (375 mOsm/kg), after three months in soil (415 mOsm/kg), and after acclimatization to 400 mM/l urea (540 mOsm/kg). 3. In hydrated toadlets Na+ and Cl- accounted for 81% and urea for 27,, the latter increased to 22:” when in soil. 4. Urea concentration was higher in muscle of toadlets burrowed in soil or following acclimatization to 400 mM/l urea. 5. Sodium concentration increased in both plasma and muscle after dehydration or following acclimatization to 400 mM/l urea. In both situations the animals lost weight. 6. Potassium increased in muscle fluid when acclimated to urea, but was very low in all other experimental groups. 7. Both plasma and muscle Cl- concentrations were found to be higher in animals after dehydration Abstract-l.
or following acclimatization to 400 mM/l urea.
INTRODUCTION
Terrestrial Amphibia of xeric habitats are known to spend a large part of the year in hiding places to prevent dehydration (Warburg, 1972). Pelobates syriacus is found in Israel (its southern limit distribution), along the coastal plain and in the Galilee Mountains. Breeding takes place in temporary ponds containing water for at least a few months (Warburg, 1972; Degani, 1982). When the pond dries the juveniles burrow into the soil until winter. McClanahan (1972) has shown that as the soil dries, plasma concentration of Scaphiopus couchi rises mainly due to urea concentration. Urea accumulation was found in other terrestrial amphibians: Bufi riridis (Katz, 1973; Rick et al., 1980; Degani, 1981b). ,hbJ’stoma tigrinum (Delson & Whitford, 1973), and SuIumandra suhandra (Degani, 1981a). These studies have shown that plasma Na+ and Cl- concentrations increased during prolonged dehydration. During rapid dehydration or when exposed to saline conditions, plasma concentration of S. salumandru rose mainly because of increased ion concentration (Degani, 1981a). Only euryhaline amphibians (Rana cancriuora, B. uiridis) can accumulate urea during adaptation to saline conditions but not such high values as were found in other terrestrial species during prolonged periods in the soil, (Gordon et al., 1961; Gordon, 1962; Katz, 1973). There is little information on the concentration of Na+, K+, Cl- and urea in the plasma and tissues during dehydration,
* Author
to whom
correspondence
should
be addressed. 619
acclimation to urea solutions or during long periods in the soil. The purpose of this study is to compare between concentration of Na+, K+, Cl- and urea in the plasma and muscle of P. syiacus under the following conditions: (a) dehydration, (b) long periods inside the soil and (c) during acclimation to urea concentrations. MATERIALS
AND
METHODS
Tadpoles of P. syriaas were collected at the beginning of summer from a pond in Sasa (Galilee Mountains). Animals were kept inside plastic containers measuring 40 x 20 x 10 cm at room temperature until metamorphosing. One group of juveniles (N = 5) was kept for one week in tap water. A second group of juveniles (N = 5) was kept one week in 2OOmM/l urea and then transferred to 400 mM/l urea for another week. A third group (N = 5) was dehydrated in 0 5”,, R.H. over Silica Gel at 20-C up to 18”,, of initial body weight using methods described pl-eviously (Warburg & Degani. 1979). A further group of juveniles (N = 5) was kept for 3 months in soil at 60”,, soil moisture. The percentage of water in the soil was determined as described previously (Warburg & Degani. 1979). Blood samples were taken from acclimated animals by heart puncture, using I ml syringe previously washed with lithium heparin. The blood sample was immediately centrifuged for 10 min at 252 9. and the plasma either analyzed immediately or frozen for later analysis. Muscle tissue from the hind leg was taken and used for both urea and electrolytes (Na+, K+ and Cl-) determination. Sodium potassium and chloride in plasma and in muscle tissue were determined using methods described by Briihman & Hanke (1980). Urea was determined by Foster & Hochholzer’s (1971) method. Urea in muscle was determined after homogenization with TCA (55”) and immediate centrifugation
G. DEGANI et d.
620
for 15 min at 3009. Water contents in muscle tissue was determined by desiccating the muscle tissue at 60°C until it reached a constant dry weight when it could be calculated. Tbe muscle concentration of Na+, K*, Cl- and urea were related to the water content of the muscle. Five animals were studied in each experiment, both means and standard deviations are given. t-Test was used io compare the means. RESULTS Juvenile P. s_v&ctrs that stayed in either soil or in tap water did not lose weight. Dehydration at 5% R.H. and 20°C caused a decrease in weight that was greater than when toads were kept in urea solution (Figs l-4). Plasma concentration of juveniles in tap water was found to be about 280 mOsm/kg. After dehydration of 187; body weight plasma concentration rose to 375 mOsm~kg, and after three months of burrowing inside the soil it rose to 415 m&m/kg. Acclimation to ~rnM~1 urea caused an increase in plasma concentration to 540 m&m/kg (Fig. 5). The various components in plasma responsible for its osmotic values varied under different conditions (dehydration, burrowing and urea acclimation). Both Na+ and CI- concentrations in the plasma in fully
In Soil
a
1
1 t
I
,
I
I
0
I
2
3
Time Fig. 1.
l months)
0
2
I
Time (days)
Fig. 3. Weight loss of juvenile P. spimxs in dry air at 2o’C.
after dehydration
hydrated juveniles were responsible for 81% of the total osmolarity, whereas urea was responsible for only 2nd. After dehydration the percentage of urea increased to 6%, the remaining osmolarity of the plasma was mainly due to Na’ and Cl-. During burrowing in so& urea concentration increased and reached 22%; of the plasma concentration. A similar situation was found in plasma of juveniles that were acclimated to 400mM/I of urea. Concentration of Na+ was higher in juveniles after dehydration and following acclimation to urea (Fig. 6). Under both situations the animals lost about 18% of their initial body weight (Fig. 1). but Na’ concentration in the muscle increased. Concentration of Cl- in both plasma and muscle followed changes in a similar way as Na+ concentrations. The difference between concentrations of Cl- in plasma and Cl- in muscle was less remarkable than the difference between concentration of Naf in plasma and Na’ in muscle (Figs 6,X). Concentration of KS in muscle was higher foilowing dehydration, or after acclimation to 400 mM/t urea, than when the animals were kept in tap water or dry soil (Fig. 7). However, no significant difference was found between the different experimental groups in Kf concentration in plasma (P > 0.05; t-test),
Weight loss of juvenile P. S.LY%Z~I~S in soil.
Urea
I Time Fig. 2.
3
f Doysl
Weight loss of juvenile P. s.viucus in water.
L
0
t
100 External
7
Acciimat~af~n
1
200
Osmotarity
I
3cm
t
400
mOsm/Kg
Fig. 4. Weight loss of juvenile P. s~ritxxs when acclimated to different urea concentrations.
Water balance in P&bates
ts!lphJtQ
El muack
201
P :: ” .
t
f ._s f E
tot
I + Y
100 -
80-
60-
40
I
..
Fig. 7. Muscle and plasma K+ concentrations
I
,‘.
-.LL 1
)
:’ -:
~
.
,’ : ; : : .. :.
.._
.’
TOP water
400 m/t Urea
3
months I”
WI1
oohY4rPtron
Ii%
BW
Fig. 5. Blood plasma osmolarity, electrolyte concentrations
of juvenile
P. syriacus under different conditions.
and urea of juvenile P. svriacus under different conditions:
SimiIarly, no significant difference was found between the urea concentration in plasma and muscles of animals kept in tap water or dehydrated by up to 18% of initial body weight (Fig. 9). However, urea concentration in muscle was found to be higher than the urea con~ntration in plasma in both groups, those in the soil and thorn acclimated to 400 mMit urea.
!islplasma #
TOP
Fig. 6. Mu&e and plasma Naf concentrations of juvenile P. syriacus under different conditions.
muacls
wotrr
Fig. 8. Muscle and plasma Cl- concentrations of juvenile P. sriacus under different conditions.
622
G. DEGANI et al.
20
400
mM/I
Fig. 9. Urea concentration of muscle and plasma in juvenile P. spriucus under different conditions.
DISCUSSION
The burrowing toad, P. syriacus, spends 8-10 months of the year burrowed in soil (Warburg 1971, 1972). During summer the soil dries and the osmotic relationship between the toad and the surrounding soil changes. Thus, water passes from the toad to the soil (or to the air), and the toad dehydrates. This situation takes place only in dry air or in dry soil. Plasma concentration increased under these conditions. Both Nat and Cll are the most important ions in the plasma during dehydration, as was shown in the urodele S. .sa/atmndro (Degani, 1981a), and again here. Similar situations (increased plasma Na+ and Cll concentration) occur during saline adaptation (Katz. 1973; Degani, 1981 b). In some amphibians, (K. cancriuoru, B. ciridis) a prolonged exposure to saline environment caused increased urea concentration (Gordon et (I/., 1961; Katz, 1973; Balinsky, 1981). It is possible that dehydration affects accumulation of urea. About 6’?,, of the total plasma concentration of P. .sp+tcus was due to urea compared with 32’:;, found in S. salatnundra after dehydration (Degani, 1981a). The adult salamander is larger than the juvenile P. dehydration was syriacus studied here, therefore slower there. We assume that during long dehydration urea accumulates in the blood plasma. The soil surrounding the animal dries slowly. thus plasma concentration of the burrowed animal increased mostly through accumulation of urea. The same situation was described previously in several other amphibians: S. couch (McClanahan. 1972) B. riridis (Degdni rf (I/., 1981), A. tigrinurtl (Delson & Whitford, 1973) and S. .saktttutndrct (Degani, 1981a). Urea ac-
cumulation during the period when burrowed inside the soil may be explained by increased production (Jones. 1980) or by the reduction in the excretion of urea when glomerular filtration rate is low (SchmidtNielsen & Lee, 1962). The ability to accumulate urea and the ability to tolerate urea in the plasma are more important to terrestrial amphibians than to aquatic ones. In this situation the animals do not excrete urine and can absorb water from the soil. Urea accumulation during burrowing in P. .syriucus was found to be lower (26”,, of total plasma concentration) than in B. ciridis (689,, of total plasma concentration) after 3 months in soil (Degani et [I/., 1981). In S. couchi concentration of urea in the plasma was 73”,, (McClanahan, 1972). The ability to accumulate urea is possibly an adaptation to terrestrial mode of life. The differences between B. riridis, S. cowhi and P. .s)Ctcus in accumulating urea are correlated to the different habitats which they inhabit. There is information in literature concerning changes in muscle Na+, K+, Cl- and urea. Balinsky (1981) summarized the information about amphibians adapted to increasing salinities. Level of potassium in muscle in red blood cells and in skin cells increased. A similar situation is described here for P. syriacu.s following dehydration and acclimation to 400 mM/l urea. Urea concentration of both muscle and plasma did not differ in either R. cancricoru, B. ciridis (Balinsky, 1981). or P. sq’riucus kept in fresh water. In B. uiridis adapted to 380 mOsm/kg NaCl, urea concentration in muscle (90 mM/l) was higher than urea in plasma (69 mM/l). This was found here also for P. s~riacus. In Bt& horem adapted to 380 mOsm/kg NaCl the urea concentration in muscle was found to be lower (64 mM/l) than the urea concentration in plasma (81 mM/‘I). A~rCtlo~rlrt~~emc,nt.~~;-This study was carried out while the senior author was supported by a research fellowship at the Technion, for which he would like to express his gratitude. The technical assistance of Mrs Mira Rosenberg is gratefully acknowledged.
REFERENCES
BALINSKY J. B. (1981) Adaptation of nitrogen metabolism to hypersomatic environment in Amphibia. J. rxp. Zoo/. 215, 3355350. BR~~HMANNM. & HANU W. (1980) Cell volume regulation in juveniles of Xrnnpus Ittrris in hypertonic urea solution. Conrp. Biochrttt. Physiol. 67A, 361 366. DEGANI G. (1981a) The adaptation of Sttlunzundrtr ,stt/tttttctttdrrt (L.) from different habitats to terrestrial life. BY. J. Ht~per. 6. 169-l 72. DEGANI G. (1981b) Salinity tolerance and osmoregulation in Sulatnandra sahtandra (L.) from different populations J. wmp. PhJxiol. 145, 133. 137. DEC~ANIG. (1982) Amphibian tadpole interaction in wsinter ponds. Hydrohioloyiu (in press). DEGANI G., SILANIKOVE N. & SHKOLNIK A. (1981) Osmotic and urea concentration of blood plasma in burrowing green toads. Isruel J. Zoo!. 30, 96. DELSON J. & WHITFORD W. C. (1973) Adaptation of the tiger salamander Amh_rstorna tiyrinnnz to arid habitats. Camp. Biockem. Phrsiol. 46A, 631-638. FOSTER L. B. & HOC.HHOLZEK J. M. (1971) A single reagent manual method for directly determining urea nitrogen in serum. C/in. Chttt. 17, 921.
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WARBURG