OR9,50 Components of the IGF system are readily detectable in the interstitial fluid when evacuated by ‘suction blister’ technique

Abstract

week-old rats were fed a 15% casein diet as a control diet or a 5% casein diet (5C) as low protein diet for 8h per day for 14 days. On the 15th day, rats were sacrificed and plasma and epididymal WAT were collected before and after feeding. Serum glucose levels were not different between both groups after feeding, but insulin secretion in response to feeding was impaired in 5C-fed rats. In the fasted state, serum TG levels were lower in 5C-fed rats than in 15C-fed rats and serum free fatty acid levels were similar in the two groups. Hepatic TG levels were increased in 5C-fed rats compared with 15C-fed rats, while 5C-feeding did not change epididymal WAT mass. In WAT, tyrosine phosphorylation of insulin receptor and insulin receptor substrate (IRS)-1 followed by binding to a p85 regulatory subunit of PI 3-kinase after feeding were significantly reduced inWAT of 5C-fed rats than in that of 15C-fed rats. Moreover, insulin-dependent glucose uptake was suppressed in adipocytes isolated from WAT of 5C-fed rats compared to 15C-fed rats. These findings clearly indicate that protein malnutrition decreases insulin sensitivity in WAT. Furthermore, we examined TG secretion from the liver since it also determines hepatic TG levels in addition to de novo TG synthesis in the liver. However, TG secretion rate was not different between the 15C and 5C groups. Taken together with our previous results, under conditions of protein malnutrition, glucose that is not utilized is preferentially incorporated into the liver and converted to lipid. The suppression of insulin signaling in WAT may play important roles in the preferential distribution of lipid in the liver during protein malnutrition.