LUTZ and DUNBAR-COOPER: BLOOD CHEMISTRY OF LOGGERHEAD SEA TURTLE 



larger than any previous study on reptiles, and 

 allows some general comments on the composition 

 of sea turtle blood to be made. 



The osmotic pressure found in this study, of 321 

 mOsm, is significantly lower than that found by 

 Schoffeniels and Tercafs (1965) for the loggerhead 

 sea turtle (465 mOsm), and the value 408 mOsm 

 quoted by Dessauer (1970). It is, however, similar 

 to that found for other reptiles including crocodiles 

 and freshwater turtles (about 290 mOsm, Dessauer 

 1970). The observation, therefore, that marine 

 turtles have relatively high osmotic pressures (Min- 

 nich 1982) would appear unwarranted. Plasma sodi- 

 um and chloride concentrations are so much less 

 than those reported for the sea snake Pelamis plattis 

 caught in the wild (Na = 210 mM, CI = 167 mM, 

 Dunson and Elhart 1971) that phylogenetic con- 

 siderations may be involved. Potassium values found 

 in this study (3.8 mM) fall within the range charac- 

 teristic of other reptiles (3-6 mM, Dessauer 1970) 

 arguing against the observation that sea turtles have 

 peculiarly high potassium concentrations (Dessauer 

 1970). Magnesium values are similar to those re- 

 ported for other turtles, including sea turtles (Min- 

 nich 1982) but calcium is rather low (1.5 mM this 

 study, 3.1 mM quoted by Dessauer 1970). As men- 

 tioned above, the hematocrit, glucose, and urea data 

 agree with earlier estimations. 



The changes observed in this study are of con- 

 siderably physiological significance if internal ionic 

 concentrations are used to regulate the activity of 

 ion sensitive metabolic pathways (Lutz 1975) par- 

 ticularly if some salts, such as Na, K, and CI, have 

 highly perturbing effects on enzyme function 

 (Hochachka and Somero 1984). 



The contrast between the behaviour of sodium and 

 chloride is of interest. Sodium shows a wide excur- 

 sion in values throughout the year with several 

 peaks and troughs but tends to rise as the year pro- 

 gresses. Compared with sodium, chloride is rela- 

 tively constant and the minor changes that do occur 

 do not match in time with those of sodium. Although 

 both ions account for most of the plasma osmotic 

 pressure (78.5%), neither by themselves was sig- 

 nificantly related to osmotic pressure. Changes in 

 either sodium or chloride do not determine changes 

 in osmotic pressure. Lance (1976) found likewise 

 that plasma sodium showed a much wider excursion 

 than plasma chloride in the cobra Naja naja, but in 

 this species only a single summer sodium peak was 

 seen. It is noteworthy that the lowest sodium values 

 were found in the coldest month (February 1980, 

 Table 1). A winter decrease in plasma sodium has 

 been found for several freshwater turtle species, 



particularly those hibernating (Gilles-Baillien 1974). 



We found that plasma potassium increased as the 

 summer progressed and laboratory data suggests 

 that this may be a temperature related phenome- 

 non (Lutz and Dunbar-Cooper 1984). A rise in 

 plasma potassium during the warmer months has 

 also been observed in the lizard Trachysaurus 

 rugosus and the terrapin Malaclemys centreta 

 (Gilles-Baillien 1973). However, the pattern is not 

 constant; a fall has been seen in Varanus grisus 

 (Haggag et al. 1965) and no change seen in Pseu- 

 demys scripta (Hutton and Goodnight 1957). 



Although highly variable, calcium values are low. 

 There are several peaks per year but no consistent 

 pattern was seen. It is very likely, however, that the 

 changes in blood calcium reflect changes in physi- 

 ology. High values have been found in some reptiles 

 during vitellogenesis (as high as 34 mM, Lance 1976) 

 and calcium has also been found to rise to extra- 

 ordinary high levels in cold torpoid freshwater 

 turtles (Jackson et al. 1984). 



The seasonal changes in magnesium were much 

 smaller over this study suggesting that wide excur- 

 sions from this narrow range would be indicative 

 of exceptional circumstances. 



One of the most remarkable findings of this study 

 is the parallel sweeps in the patterns shown by blood 

 urea and osmotic pressure. As far as we are aware 

 such a phenomenon has not been reported before. 

 It is not simply a matter of changes in urea concen- 

 trations causing changes of osmotic pressure since 

 the magnitude of the urea changes are much less 

 than those of osmotic pressure. An integrated re- 

 sponse is called for; possibly the perturbing effects 

 of increasing osmotic pressure are compensated by 

 heightened urea levels (Yancey et al. 1982). In 

 loggerhead sea turtles, blood urea concentration 

 would not appear to be diet determined since we 

 observed that captured loggerhead sea turtles held 

 at RSMAS, which were all fed the same food, had 

 widely different urea values (range 3-21 mM). In- 

 terestingly, the field group with outstandingly high 

 urea levels (April 1980) were all males. 



The unchanging glucose levels demonstrate a high 

 degree of conservatism. Seasonal changes in blood 

 glucose have been observed in alligators with higher 

 levels in the summer (Coulson and Hernandez 1980). 

 In P. scripta, on the other hand, blood glucose in- 

 creases during winter (Hutton and Goodnight 1957). 



The hematocrit was also remarkable in its con- 

 stancy, contrasting with other reptiles where sea- 

 sonal changes in hematocrit have been recorded; 

 typically as an increase during winter (Duguy 1970; 

 (Jilles-Baillien 1974). In contrast, the very low values 



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