Effects of dietary fiber and protein on rat erythrocyte insulin-receptor interaction

Abstract

The metabolic effects of cellulose on insulin receptor interaction (IRI) was studied at 10 and 20 percent protein levels in male weanling Sprague Dawley rats. One hundred and four (104) rats were divided into 8 groups of 13 each and randomly put on various dietary treatments as already reported elsewhere [Fed. Proceed. 1985; 44(5):6367]. Animals for radioreceptor studies (n=5 per group) were fed for 8 weeks. Blood samples were obtained from the rats via cardiac puncture under nembutal anesthesia. Erythrocyte IRI and serum insulin levels (IN) were measured by a standardized radioreceptor assay (10) and radioimmunoassay respectively. Fiber and protein intake had significant effect on IRI (p<0.01) and IN (p<0.05). Specific percent 125 I-insulin binding (SIB) was higher in the 20% protein group at all fiber levels while in the fiber free groups higher SIB was observed in the 10% protein group (p<0.01). At both protein levels, maximum SIB was observed at the 5% fiber level. While SIB in the absence of fiber was observed to be strictly a function of receptor site concentration (Ro) binding in the presence of fiber was a function of both Ro and empty site affinity (Ke). Fiber intake appears to interfere with the negative cooperative nature of the receptor sites by slowing down the rate of changing affinity from a high Ke to the limiting K f (filled site affinity) state as receptor occupancy [Y=Long [B]/Ro] increases. While no significant effect of calorie was observed on e and f, caloric intake (Cal) showed a positive correlation (r=0.8, p<0.001) with IN and a negative (r=0.32, p<0.02) correlation with Ro. It is concluded that: (I) diet can modulate erythrocyte IRI in growing animals, (II) the metabolic effects of dietary fiber depend on the combination with other nutrients, (III) adequate protein nutrition is essential for plasma membrane function at the cell receptor level in growing animals and (IV) the increase in IRI by dietary fiber is a function of both e, Ro and the sustenance of the average affinity of these homogeneous class of receptor sites in the high affinity states.