Inhibitory Effect Of Fasting Research Articles

Inhibitory effect of fasting on the activation of liver glycogen phosphorylase of rats by arginine-vasopressin.

The i.v. bolus of 50 ng kg-1 Arginine-vasopressin administered to adult male rats anaesthetized with Pentobarbital (50 mg kg-1 i.p.) increases the activity of liver glycogen phosphorylase in fed and 24 h fasted rats to the same extent; after 25 ng kg-1 of the drug the enzyme response after fasting is barely detectable, whereas in the fed animals a response similar to that after 50 ng kg-1 persists.

Impairment of liver GH receptor signaling by fasting.

Fasting causes a state of GH resistance responsible for low circulating IGF-I levels. To investigate whether this resistance may result from alterations in the GH signaling pathway, we determined the effects of fasting on the GH transduction pathway in rat liver. Forty-eight-hour fasted or fed male rats were injected with recombinant rat GH via the portal vein. Liver was removed 0 and 15 min after injection. Although GH stimulated Janus kinase 2 (JAK2) phosphorylation in all animals, this was severely blunted in fasted animals. Similarly, the phosphorylation of the GH receptor, although observed in both fasted and fed rats after GH injection, was markedly reduced in fasted rats. A rapid signal transducer and activator of transcription 5 (STAT5) tyrosine phosphorylation was also induced in the liver of fed animals in response to GH. In contrast, in fasted rats only a slight phosphorylated STAT5 signal was observed. The inhibitory effect of fasting on these GH signaling molecules occurred without changes in their protein content. Furthermore, the impairment of the JAK-STAT pathway in fasted animals was associated with increased liver suppressor of cytokine signaling 3 mRNA levels. Although glucocorticoids, which are increased by fasting, may cause GH resistance, adrenalectomy failed to prevent alterations in the JAK-STAT pathway caused by fasting. In conclusion, the GH resistance induced by fasting is associated with impairment of the JAK-STAT signaling pathway. This might contribute to the decrease in liver IGF-I production observed in fasting.

Inhibitory effect of fasting on the glucagon-induced increase of liver phosphorylase A activity in rats

The increase of liver phosphorylase A activity observed 1, 2 and 3 min after i.v. administration of 0.1 μg kg−1 glucagon to fed rats was found to be completely absent in 24 h fasted animals, although there is even an exaggerated liver cAMP response to glucagon after fasting.