food or water for 10 days they lost as much as 24% of their body weight and so
can presumably withstand substantial dehydration. In their native habitat, however, the serum sodium and potassium levels of the ' D ob' are steady, indicating that
they can maintain a normal state of hydration. In order to do this they require water
equivalent to about 3 to 5% of their body weight in a day which is obtained from
the plants and occasional insects which the y eat; the y do not drink. Such a diet
contains substantial quantities of salts, particularly potassium, and these are excreted from active nasal salt glands. This secretion is rich in potassium, (the KINa
ratio is as great at SOil) and this is augmented during deh ydration. The rate of secretion also depends on the diet of the lizard. Calculations from GRENOT'S results
indicate that these lizards normally secrete 500 to 1000 .u-equiv/kg body wt of
potassium from their nasal glands in a day. The composition of the plants that the y
eat has not been reported, but if they contained 100 .u-equiv of potassium/g wet
wt the amount secreted by the salt glands would only be equivalent to that in 5
to 10 g (kg body wt) of vegetation. Presumably they eat more than this so that
urinary excretion of potassium must also be substantial. Information about the
role of the neurohypophysis and the corticosteroid hormones in the regulation of
water and salt excretion of these lizards would be most interesting, but so far has,
alas, not been described.
159
can presumably withstand substantial dehydration. In their native habitat, however, the serum sodium and potassium levels of the ' D ob' are steady, indicating that
they can maintain a normal state of hydration. In order to do this they require water
equivalent to about 3 to 5% of their body weight in a day which is obtained from
the plants and occasional insects which the y eat; the y do not drink. Such a diet
contains substantial quantities of salts, particularly potassium, and these are excreted from active nasal salt glands. This secretion is rich in potassium, (the KINa
ratio is as great at SOil) and this is augmented during deh ydration. The rate of secretion also depends on the diet of the lizard. Calculations from GRENOT'S results
indicate that these lizards normally secrete 500 to 1000 .u-equiv/kg body wt of
potassium from their nasal glands in a day. The composition of the plants that the y
eat has not been reported, but if they contained 100 .u-equiv of potassium/g wet
wt the amount secreted by the salt glands would only be equivalent to that in 5
to 10 g (kg body wt) of vegetation. Presumably they eat more than this so that
urinary excretion of potassium must also be substantial. Information about the
role of the neurohypophysis and the corticosteroid hormones in the regulation of
water and salt excretion of these lizards would be most interesting, but so far has,
alas, not been described.
159