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SUMMARYWhen compared with laboratory chow, a defined, semipurified diet prevented diabetes, reduced the frequency of insulitis, increased thymus weight and total white blood cell count, and doubled thymus T-helper/T-suppressor cell ratios in diabetes-prone BB rats. These data show that the diabetic syndrome in BB rats may be prevented or delayed by changes in diet, which may occur through alteration of pathogenic defects in the immune system. DIABETES 1985; 34:1059-62.T he fact that only up to 50% of unaffected twins of individuals with type I, insulin-dependent diabetes mellitus (IDDM) become diabetic underscores the major role of environmental factors in the expression of this genetically transmitted disease. With the exception of tropical malnutrition diabetes, a unique ketosis-resistant form of IDDM in which there is an acknowledged involvement of diet, 1 there are no data directly linking diet to incidence of type I IDDM in humans. 2 The two main obstacles have been the inability to identify prospective diabetic humans and the inherent difficulties in obtaining accurate and representative dietary information.The recent availability of the spontaneously diabetic BB rat has provided a unique model that has many of the features of human type I diabetes, permitting long-term prospective studies to be carried out. 34 BB rat diabetes appears to be an autoimmune disease resulting from the destruction of the insulin-producing beta cells of the pancreas by the animal's own immune system. Development of overt diabetes may require inheritance of at least three characteristics: mononuclear cell infiltration of the pancreas (insulitis), the pres- ence of the major histocompatibility complex haplotype (RT1 U ), and lymphopenia. 56 The protective effect of neonatal thymectomy, 78 decreased thymus (T)-derived lymphocytes in blood and lymphoid organs, 9 reduced T-helper (T h )/T-suppressor (T s ) cell ratios, 6 and decreased thymus weight in diabetes-prone BB rats all point to a key role for the thymus in the pathogenesis of this syndrome.Diet can have dramatic effects on the immune system, particularly the thymus, which seems uniquely sensitive to manipulation of nutritional variables. 10 Furthermore, it has recently been hypothesized that environment (diet) could be an important factor influencing development of diabetes in BB rats. 811 In previous studies we observed differences in incidence and age at onset, which suggested that, compared with a chow diet, a defined, semipurified AIN-76 diet 12 might modify development of the syndrome. 8 Any approach to this question must consider at least three points: (1) effect of diet on insulitis, diabetes incidence, age at onset; (2) net diet/ immune system interactions (i.e., varying susceptibility of specific T-cell subsets); and (3) presence or absence of diabetogens in the diet. MATERIALS AND METHODSExperiment 1. This experiment was designed to examine directly the effects of ad libitum feeding of a ground laboratory rat chow diet (N = 40) or a defined, semipurified AIN-76 ...

Fortified milks were saponified overnight at room temperature with 1% ethanolic pyrogallol and KOH. The digest was extracted with hexane after adding water and ethanol, and the extract was washed consecutively with 5% KOH, water, and 55% aqueous ethanol to remove polar lipids. After evaporation, the residue was first chromatographed on a column of 5 μm silica. A fraction containing vitamin D was collected, evaporated, and rechromatographed on a reverse phase column for the separation and quantitation of vitamins D2 and D3. Recovery was 96-99% and the coefficient of variation was 3% (8 replicates). Infant formula was diluted and then saponified and extracted as in the analysis of milk. Margarine was saponified by shaking overnight with 1% ethanolic pyrogallol and 80% KOH. Water and ethanol were added to the digest before extraction. Extracts from formula and margarine were chromatographed as milk except, before HPLC, the extract was dissolved in isopropanol-hexane (1 + 99) and passed through 5 cm alumina in a Pasteur pipet, and the concentration of isopropanol in the first high performance liquid chromatographic (HPLC) solvent system was halved to improve the separation of vitamin D from other absorbing lipids. Usually several peaks were obtained during the final HPLC analysis, and the identification of vitamins D2 and D3 was less certain than in the analysis of milk. The coefficients of variation for formula and margarine were 6% (5 replicates) and 9% (6 replicates), respectively.

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