Insulin and gluconeogenesis

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Abstract
Two tenths to 4 units of insulin injected into fasting rats caused practically no change in the amount of liver glycogen present. (Av. liver glycogen of 2 controls 20.5, of 8 injected rats 23.6 mgm. per 100 gm. of body weight). The blood sugar was 20-69 mgm. % when the rats were killed 57 min. to 4 hours. 42 min. after the insulin injection.[long dash]In 3 fasting young rats (body weight 49-61 gm.) which received convulsive doses of insulin, the liver glycogen was of the same low value as in 1 control. In the same rats the glycogen of the carcass was on an av. 42 as compared to 64 mgm. for the control.[long dash]Four rats were given a mixture of 3 gm. flour plus 5 gm. glucose to eat. The actual amount eaten and the time needed for consumption were left undetermined. Three of these rats were given insulin injections. Four hours after presenting the food the control contained 138, the injected animals an average of 113 mgm. of liver glycogen per 100 gm. of body weight.[long dash]Five litter mate rabbits, 7 weeks old, were starved for 24 hrs. They were fed 20 cc. of a 50% glucose solution by stomach tube and killed 3 hrs. later. Four of these rabbits were injected with insulin (2-8 units). Their liver glycogen was decidedly lower than that of the control (an av. of 3% against 5%).[long dash]Speculation as to the rate of absorption of glucose from the gut led to the following experiment: 2 normal men took 4 successive doses of 50 gm. glucose at hourly intervals. The blood sugar could not be forced up by the later doses but the fall following administration of a single dose was prevented.[long dash]In one experiment a subject was injected with 10 units after a starvation period of 40 hrs. The ketone bodies in the urine increased after the injection, which is regarded as a sign of increased gluconeogenesis.[long dash]In 4 fasting young rabbits the liver glycogen was higher 2 hrs. after injection of insulin (0.25, 0.5, 0.75 and 1 unit) than in 1 control. The increases were very slight with the 3 larger, non-convulsive doses.[long dash]Finally in 5 out of 6 fasting litter mate young rabbits the liver glycogen rose after insulin injection (2 controls), whereas the muscle glycogen remained unchanged. The conclusion is reached that insulin stimulates gluconeogenesis in the liver, and that this effect is most obvious when the animal is at the stage of convulsions.

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