Immediate and Late Effects of Premature Weaning and of Feeding a High Fat or High Carbohydrate Diet to Weanling Rats

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Abstract
Male infant rats were weaned to a normal laboratory diet or to a high fat (HF) or high carbohydrate (HC) diet when aged 15 days (premature weaning, PW) or to a normal diet when aged 30 days (normal weaning, NW). They were killed when aged 30, 57, 215 or 254 days, having all been fed the laboratory diet from day 30. The immediate effects of the HF and HC diets were also determined. Within 24 hours, the activity of phosphoenolpyruvate carboxykinase was elevated by more than 400% in brown adipose tissue after feeding a HF diet. The rise in activity in the liver was less pronounced and slower. In liver a HF diet resulted in an elevation of carnitine acetyltransferase activity. Other enzymes related to glycolysis and lipogenesis reacted in the expected manner. In rats aged 30 and 57 days premature weaning, particularly to a HF diet, caused a significant decrease in the length of the large intestine, but this effect was no longer apparent in older animals. The blood cholesterol level was found to be elevated in rats aged 215 or 254 days weaned prematurely to a HC diet or to laboratory stock diet. Feeding a HF diet to PW rats, however, prevented this elevation. In younger animals this was not observed. It is concluded that the early nutritional regime has long lasting effects that may appear only much later in life.