The following points highlight the seven major endocrine influences on metabolism of carbohydrates. The endocrine influences are: 1. Insulin 2. Adrenocortical Hormones 3. Anterior Pituitary Factors 4. Epinephrine 5. Thyroid Hormone 6. Glucagon 10. Sex Hormones.
a. Causes glucose transport across cell membrane by increasing the permeability of the cells.
b. Increases glycogen formation in liver and muscle by stimulating hexokinase and glycogen synthetase.
c. Accelerates the conversion of glucose to fat.
d. Stimulates protein synthesis.
e. Inhibits ketogenesis.
f. Inhibits gluconeogenesis.
g. Increases glycolysis by stimulating hexokinase and phosphofructokinase in liver and muscle.
h. Has effect on muscle ion balance.
i. Causes initial phosphorylation (hexokinase reaction) of glucose for further oxidation.
The sulfonylureas e.g., tolbutamides are the stimulators of insulin release.
Insulin is destroyed by insulinase which separates the A and B chain of it. Peptidases also play a part in the destruction of insulin.
2. Adrenocortical Hormones:
The adrenalectomized animal exhibits the following changes in carbohydrate metabolism:
a. Decrease in liver glycogen.
b. Less marked decrease in muscle glycogen.
d. Decreased intestinal absorption of glucose.
The changes are prevented by glucocorticoids. The glucocorticoid hormones release gluconeogenic precursors, such as amino acids, from muscle. The hormones also release FFA from adipose tissue, resulting in inhibition of hepatic glycolysis. The increase in FFA in the liver results in an increase of acetyl-CoA which activates pyruvate carboxylase and so stimulates gluconeogenesis.
3.Anterior Pituitary Factors:
Growth hormone produces the following changes in carbohydrate metabolism:
a. Hyperglycemia and aggravation of diabetes in depancreatized animals.
b. Inhibition of insulin action with decreased utilization of carbohydrate and lowering of the respiratory quotient.
c. Diminution of the breakdown of muscle protein.
d. Increase in the mobilization of fat in the form of FFA from adipose tissue with the increase in lipase activity. The increase in FFA, and its use as the source of energy results in the excessive production of ketone bodies.
e. ACTH enhances the release of free fatty acids from adipose tissue and inhibits glucose utilization. It causes increase in blood sugar level by stimulating the secretion of adrenal cortex hormones.
a. Causes an increase in blood sugar and in blood lactate due to the acceleration of glycogenolysis in the liver and muscles.
b. Diminishes the uptake of glucose by tissue cells, thus interfering with its utilization.
c. Causes diminution in the amount of insulin released from the pancreas.
a. Thyroxine accelerates hepatic glycogenolysis with consequent rise in blood sugar. This is due to increased sensitivity to epinephrine.
b. Thyroxine also increases the rate of absorption of hexoses from the intestine and accelerates gluconeogenesis.
c. It has diabetogenic action.
a. Promotes glycogenolysis in liver stimulating phosphorylase via cyclic AMP.
b. Causes breakdown of glycogen to lactic acid in muscle. The lactic acid is again converted to glucose by “Cori Cycle”.
c. Stimulates gluconeogenesis in liver.
Estrogens stimulate increased insulin secretion and thus reduce blood sugar level. Testosterone also decreases blood sugar level.