Two lines of Yucatan miniature swine have been developed by genetic selection for decreased and increased glucose clearance during an i.v. glucose tolerance test. The decreased glucose clearance is due to low peripheral insulin levels usually from a decrease in insulin secretion. In two pigs the decreased peripheral insulin resulted from increased hepatic uptake of insulin. During gestation and lactation, an increased insulin resistance and a diabetic-like state occurs in some animais. When fed a low fiber diet that contains 40% of calories from saturated fat (a typical American diet), Yucatan swine become more glucose intolerant. Seven to ten animals on the diet from the glucose intolerant line showed a glucose tolerance curve that would have been classified as diabetic if they were humans utilizing both intravenous and oral glucose tolerance tests. Miniature swine from this line are available to interested researchers.

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The intent of this study was to examine the effect of a diet nutritionally similar to that consumed by most Americans on Yucatan miniature swine that have been bred for enhanced and impaired glucose tolerance. Seventeen Yucatan miniature pigs from the glucose-intolerant line (low K) and 17 from the glucose-tolerant line (high K) were selected. The oral glucose tolerance (OGT) of both groups of pigs was determined. After the OGT test (OGTT), 13 low K pigs and 12 high K pigs were placed on the American Swine Diet (ASD). The remaining animals were left on the regular swine diet. After 5 months, the pigs were again tested with an OGTT. Mean plasma glucose levels observed during the OGTT showed significant differences between the low K and high K groups on ASD at all time intervals from 60 to 150 minutes postdosing. Serum insulin levels in the high K group were significantLy elevated over those in the low K group during the OGTT at 10, 20, and 30 minutes prediet, and at 10 minutes after 5 months on diet. Both low and high K groups showed a dietary effect with aN elevated plasma glucose response to an OGTT, although the mean increase was not significant in the high K group. In the low K group, plasma glucose levels were significantly elevated (P less than 0.05) over prediet values at 20, 30, 60, 90 and 120 minutes. In addition, 7 out of the 10 low K pigs tested at 5 months developed insulin resistance, and noninsulin-dependent diabetes.

Yucatan miniature pigs have been selectively bred for reduced and increased glucose clearance during an intravenous glucose tolerance test. Pigs with low glucose clearance rates (low K) have been selected through the F-5 generation. They have a significantly reduced rate of glucose clearance and a blunted peripheral IRI increase in response to the challenge. Through the F-5 generation, heritability of glucose tolerance is estimated at 0.26. Sporadic fasting blood glucoses in excess of 100 mg/dl are seen in later generations of this group. High glucose clearance pigs (high K) have been selected through the F-4 generation. They have significantly increased rates of glucose clearance and a greater increase in peripheral IRI than the low K animals. The estimated heritability for high K through the F-4 generation is 0.31. No evidence of fasting hypo- or hyperglycemia has been seen in the high K animals.

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