Effects of an Oral Glucose Load on Serum Immunoreactive Insulin, Free Fatty Acid, Growth Hormone and Blood Sugar Levels in Young and Elderly Subjects*

Abstract

In 29 healthy young adults and 22 ambulatory elderly subjects, a study was made of the effects of an oral glucose load on the levels of serum immunoreactive insulin (IRI), free fatty acids (FFA), growth hormone (HGH) and blood glucose. In the elderly, the pre‐load blood glucose and serum IRI levels were higher than in the younger group, reached the peak more gradually, and took longer to return to the baseline values. There was no significant difference in the serum FFA levels between the two groups until 3 hours after the glucose load, at which time the FFA values had returned to the fasting level in the young subjects but remained depressed in the elderly subjects. Serum HGH fasting levels in the elderly males were significantly higher than in the younger males and remained so at 1–2 hours after the glucose load. For the females, the numbers were too small and the intragroup variability too great to permit drawing conclusions. The total findings lend support to Dilman's hypothesis of a genetically programmed elevation of the hypothalamic threshold to feedback suppression, with age.

Mechanisms of Insulin Resistance in Aging

“…Most studies have demonstrated normal or increased insulin secretion as a function of aging following an oral or intravenous glucose load (3)(4)(5)(6)(7) Subjects. The study group consisted of 44 nonobese subjects.…”

“…These subjects also have greater elevations of serum insulin levels, normal insulin binding, and marked insulin resistance manifested as both a decrease in insulin action at submaximal and maximal levels. 6 of the 17 elderly subjects fell into this group and they had a 53, 58, and 42% decrease in glucose disposal rates compared with the nonelderly group at insulin infusion rates of 15, 40, and 1,200 mU/M2 per min, respectively (Fig. 6 A).…”

Role of insulin in age-related changes in macronutrient metabolism

“…Body protein content Table 1 Insulin effectiveness on glucose metabolism in aging humans (vs young controls) (cf. Davidson, 1979;Borkan et al, 1983;Gumbiner et al, 1989;Chen et al, 1985;Pacini et al, 1988;Jackson, 1990;DeFronzo, 1979;Meneilly et al, 1987;Fink et al, 1983;Rowe et al, 1983;Broughton et al, 1991;Bonadonna et al, 1994;Ferrannini et al, 1996;Sandberg et al 1973;Fraze et al, 1987) 1994;Sandberg et al, 1973;Fraze et al, 1987;Groop et al, 1991;Shulman et al, 1980) Production normal or decreased suppression Oxidation normal or increased stimulation…”

“…One way to approach this issue is to look at free-fatty acid (FFA) metabolism. FFA concentrations may be normal, increased or decreased in elderly individuals (Sandberg et al, 1973;Fraze et al, 1987), and this variability may depend on the subjects' insulin levels. Indeed, hyperinsulinemic older subjects may also have normal or decreased FFA (Sandberg et al, 1973;Fraze et al, 1987).…”

“…FFA concentrations may be normal, increased or decreased in elderly individuals (Sandberg et al, 1973;Fraze et al, 1987), and this variability may depend on the subjects' insulin levels. Indeed, hyperinsulinemic older subjects may also have normal or decreased FFA (Sandberg et al, 1973;Fraze et al, 1987). According to some authors, the parameters of lipid and free fatty acid kinetics should be better expressed per kg of body fat mass, ie the metabolically-active body compartment of fat.…”