The effects of catecholamines on gluconeogenesis were studied with key gluconeogenic enzymes such as serine dehydratase and phosphoenolpyruvate carboxykinase as markers.
Phosphoenolpyruvate carboxykinase activity in liver showed a diurnal variation with the lowest value at 700h and the highest at 1800h.
When animals received an intraperitoneal injection of epinephrine or norepinephrine at 700h and were killed 2 hours later, phcsphoenolpyruvate carboxykinase in liver was significantly induced by epinephrine, whereas it was not by norepinephrine. When the animals were treated with catecholamines at 1700h and killed at 1900h, however, the enzyme responded neither to epinephrine nor to norepinephrine.
Serine dehydratase activity in liver exhibited no statistically significant 24 hour rhythm under the same condition as described above, but almost the same tendency was observed in regard to the response to the enzyme to catecholamines.
These findings suggest that epinephrine is a regulatory factor for glucose formation from amino acids, but its regulation is closely related to diurnal rhythm in gluconeogenesis.
On the other hand, diurnal variation of liver phosphoenolpyruvate carboxykinase was affected neither by the adrenergic blockers such as chloropromazine, dibenzylin (α -blocker), propranolol (β -blocker) nor by surgical operations such as adrenalectomy and thyroidectomy.
Phosphoenolpyruvate carboxykinase activity in kidney also showed diurnal variation with the highest value at 700h and the lowest at between 1500h and 2100h. This pattern is just as the mirror image with the pattern of the liver enzyme.
Daily injections of carbachol for 6 days produced a marked increase in the activity of the kidney enzyme, whereas this treatment repressed the liver enzyme. From these findings, it can be concluded that homeostasis in blood glucose was maintained through interrelationship of liver and kidney in such ways as that the liver enzyme activity is enhanced by epinephrine, a neurotransmitter of the sympathetic nervous system, while the kidney enzyme activity is enhanced by acetylcholine, a neurotransmitter of the parasympathetic nervous system.
