Effect of chronic undernutrition on hepatocyte insulin receptors in rats

Insulin resistance during euglycemic clamp studies in chronically undernourished rats with mild streptozocin diabetes

Malnutrition has been shown to impair insulin sensitivity, but it is not known whether this effect has any impact on coexisting diabetes. Insulin sensitivity was therefore studied using the glucose clamp technique in rats with chronic nutritional deprivation superimposed on mild streptozocin (STZ) diabetes mellitus. In pair-feeding experiments, 4-week-old littermate rats were either allowed ad libitum access to food or restricted to 50% of ad libitum intake for 8 weeks, and were injected with STZ 40 mg/kg intraperitoneally halfway through the experiment. Fasting plasma glucose (FPG) was similar in both groups of rats, but fasting plasma insulin (FPI) was lower in the undernourished group (P = .016). Undernourished rats were significantly more insulin resistant during euglycemic hyperinsulinemia of the same degree, with glucose disposal rate being impaired by 50% as compared with that in ad libitum-fed diabetic littermates (24.4 +/- 2.8 v 51.5 +/- 4.4 mumol/kg/min, P = .0008). The insulin sensitivity index was significantly lower in the undernourished group (3.03 +/- 0.32 v 5.67 +/- 0.6, P = .0057). The results show that chronic undernutrition markedly reduces insulin sensitivity in rats with mild STZ diabetes. This is further evidence that chronic undernutrition is a deleterious modifying influence on coexisting diabetes mellitus. It suggests that the insulin resistance of malnutrition-related diabetes mellitus (MRDM) could potentially be an acquired defect mediated by the coexistent undernutrition, rather than a "distinctive" feature that is intrinsically unique to this diabetic syndrome.

Adaptations in glucose homeostasis during chronic nutritional deprivation in rats: hepatic resistance to both insulin and glucagon

The role of glucagon in glucose homeostasis during chronic malnutrition was studied in weanling-littermate rats either fed ad libitum or restricted to 60% of ad libitum intake for 8 weeks. Fasting glucose and insulin levels were lower in malnourished rats, and their response to glucagon (0.02 mg/kg intravenous [IV]) after a 16-hour fast was significantly less than in control littermates for both glucose (P = .039) and insulin (P = .008). During euglycemic glucose clamp studies at identical plasma glucose (PG) levels, insulin suppression of hepatic glucose production (HGP) was impaired in malnourished rats, indicating insulin resistance (mean +/- SE HGP: 48 +/- 5 v 32 +/- 10 mumol.kg-1.min-1 for controls, P = .028). Glucose disposal was not significantly different in the two groups. However, after IV glucagon, the increase in HGP was markedly impaired in malnourished rats (P = .0004), with the total amount of glucose produced by the liver over 15 minutes being 1,397 +/- 114 mumol/kg as compared with 2,031 +/- 118 in controls (P = .0047). The impaired response was not due to defective glycogenolysis, because the release of glucose from prelabeled glycogen in response to glucagon injection contributed only 6% to 8% of the overall increase in glucose output from the liver, and was not different in the two groups. Furthermore, liver glycogen stores were virtually exhausted after the 16-hour fast, without glucagon injection. Glucagon receptor affinity and number were not affected by malnutrition. It is concluded that (1) chronic malnutrition is associated with hepatic resistance to both insulin and glucagon, (2) the glucagon resistance is not due to impaired glycogenolysis, and (3) it is mediated by a postreceptor defect.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic malnutrition impairs insulin sensitivity through both receptor and postreceptor defects in rats with mild streptozocin diabetes

The effect of coexisting chronic malnutrition on insulin sensitivity in mild diabetes was studied in rats. Food intake was restricted over an 8-week period to 50% of ad libitum intake by pair-feeding 4-week-old littermate rats injected with streptozocin ([STZ] 40 mg/kg intraperitoneally) at 8 weeks. Significantly greater glucose intolerance and hypoinsulinemia were seen in response to a glucose load in the malnourished diabetic group (P < .00005), suggesting that chronic malnutrition significantly accentuated beta-cell dysfunction from STZ. Significantly greater insulin resistance was also seen, with the percentage rate constant for glucose disappearance after a bolus of insulin being markedly impaired (P < .0001) in the malnourished diabetic group (1.5% +/- 0.2% x min-1 [SE]) compared with ad libitum-fed diabetic and normal rats (3.6% +/- 0.6% x min-1 and 4.7% +/- 0.7% x min-1, respectively; P < .01). Insulin binding to receptor in liver plasma membranes was altered by malnutrition (P < .00005), with the affinity of binding being significantly reduced compared with that of ad libitum-fed diabetic controls (P < .0001) at both the high-affinity site (3.9 +/- 0.2 v 13.7 +/- 3.3 x 10(-7) x mol/L-1) and low-affinity site (2.7 +/- 0.4 v 20.1 +/- 3.8 x 10(-5) x mol/L-1). During a constant glucose and insulin infusion (1.67 mU/kg/min), glucose clearance was significantly lower in malnourished rats (5.3 +/- 0.7 v 8.6 +/- 1.7 mL/gk/min, P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)