[Morphological and functional characteristics of pancreatic islet beta cells in natural aging SD rats]

To evaluate the effect of aging on metabolic profile and the changes in morphology and secreting function of beta-cell.

SD rats with different ages (5-6, 11-12, 20-24 Mon.) were used in this experiment to detect fasting blood glucose, lipid profile and free fatty acids (FFA) as metabolic parameters. Islet population and beta-cell shape from different age groups were assessed by immunohistochemistry and electron microscope (EM), respectively. Moreover, isolated rat islets from different ages were purified and cultured with two culture medium containing 5. 6 mmol/L and 16.7 mmol/L glucose over 24 hours, respectively. The secreted levels of insulin at 2, 4, 6, 24 hours were measured by radioimmunoassay (RIA).

(1) The significantly higher concentration of FFA was found in 11-12, 20-24 months groups (386.02+/-88.08; 349.43+/-93.47 vs. 263.93+/-68.77 mmol/L, respectively, P<0.05), with no difference in WT, FBG, lipid profile among three groups; (2) Insulin secretion by glucose (5.5 mmol/L) stimulating old rats showed lower peak value than younger counterparts did [6.40+/-2.7 vs. 13.97+/-1.23 (6 Mon.) & 12.08+/-0.76 (12 Mon.) mU/L x 30 islets] and so did another glucose (16.7 mmol/L) group [6.75+/-4.69 vs. 13.41+/-0.72 (6 Mon.) & 13.56+/-0.60 (12 Mon.)]. (3) The ratio of beta-cell mass to islet was slightly larger in old rats than in younger rats (72.99+/-29.65% vs. 67.76+/-23.48% (12 Mon.) & 61.69+/-30.12% (6 Mon.), P>0.05); The expression of insulin measured by immunohistochemistry was dramatically decreased in old rat islet compared with 5-6, 11-12 month rats [242.71+/-95.37 (24 Mon.), 309+/-83.99 (12 Mon.) vs. 558+/-69.94 (6 Mon.), P<0.05].

Older rats showed higher FFA and age-related impairment of insulin secretion with or without the glucose stimulation. These findings suggest that insulin therapy should be taken into account for elder earlier once type 2 diabetes is diagnosed.