MECHANISMS OF HORMONE ACTIONS
195
and 3 (Fig. 8). The action of insulin seems to be independent of the
utilizability of the sugar in the tissues.
The principal lines of evidence and deduction here presented have
been confirmed and extended (though differing in detail) by several
laboratories. Thus Ross (1952) has calculated the permeability constant for glucose entry from the plasma into the aqueous humor in
"ill
1
ι
1
I
0
1
2
3 0
1
2
3
Hours
FIG. 7
The effect of insulin on the distribution of sugars in eviscerated-nephrectomized
dogs. Since D-fructose is utilized to some extent by the extrahepatic tissues, one cannot calculate a distribution volume for that sugar. Nevertheless insulin does not
change the slopes of the curves for fructose.
rabbits under varying conditions. Table 1 shows that insulin increased
the rate of entry of glucose into the eye, and that the permeability
constant is decreased in an established alloxan diabetes. In the first
paper cited he interprets his findings to mean an influence on hexokinase,
but subsequently this interpretation was modified because of results
obtained in work with rabbit lens in vitro (Ross, 1953). Using such a
tissue, insulin increased the rate of entry of glucose from 0.2 to 0.7
TABLE 1
RATE OF TRANSFER OF GLUCOSE ACROSS THE BLOOD-AQUEOUS BARRIER IN RABBITS*
Transfer constant (K, X 100)
Condition
Mean
Range
Normal
1.9
1.65-2.11
Diabetic (alloxan)
1.0
0.74-1.37
Normal, given insulin (1-2.5 units)
4.7
3.00-5.20
* From Ross (1952).