Effects of chronic modification of dietary fat and carbohydrate on the insulin, corticosterone and metabolic responses of rats fed acutely with glucose, fructose or ethanol

Abstract

1. Male rats were fed for 14 days on powdered diets containing (by weight) 53% of starch, or on diets in which 20g of starch per 100g of diet was replaced by lard or corn oil. They were then fed acutely by stomach tube with a single dose of glucose, fructose or ethanol of equivalent energy contents, or with 0.15m-NaCl. The serum concentrations of corticosterone, insulin, glucose, glycerol, triacylglycerol and cholesterol were measured up to 6h after this treatment. 2. Feeding saline (0.9% NaCl) acutely to the rats maintained on the three powdered diets produced a small transient increase in circulating corticosterone that was similar to that in rats maintained on the normal 41B pelleted diet. 3. Feeding glucose acutely to the rats on the powdered diets produced peak concentrations of corticosterone that were 2-3-fold higher than those seen in rats maintained on the 41B diet. The duration of this response increased in the order starch diet<lard diet<corn-oil diet. This abnormal corticosterone response to glucose feeding appeared to be responsible for an increased activity in phosphatidate phosphohydrolase in the livers of rats fed the starch and lard diets of 2.9- and 4.9-fold respectively. The latter increase was similar to that produced by ethanol, whereas glucose did not increase the phosphohydrolase activity in the liver of rats maintained on the 41B diet. 4. Feeding fructose acutely produced even more marked increases than glucose in the concentrations of circulating corticosterone in rats given the powdered diets, but unlike glucose did not increase circulating insulin. The duration of the corticosterone response again increased in the order starch diet<lard diet<corn-oil diet. The concentrations of circulating glucose were increased by fructose feeding in rats maintained on these diets, but they were not altered in the rats maintained on the 41B pellets. A prolonged increase in serum corticosterone concentrations was also observed when fructose was fed to rats maintained on pelleted diets enriched with corn oil or beef tallow rather than with starch or sucrose. However, these effects were less marked than those seen with rats fed on the powdered diets. 5. These results are discussed in relation to the mechanism whereby high dietary fat exaggerates the effects of ethanol, fructose and sorbitol in stimulating triacylglycerol synthesis in the liver.

Glucocorticoids and cyclic AMP selectively increase hepatic lipin-1 expression, and insulin acts antagonistically

“…The GC effect is also consistent with increases in hepatic PAP1 seen after sham operations or in liver remnants after partial hepatectomy (11), in starvation (6), diabetes (12), insulin resistance (13), and hypoxia (14), and in toxic conditions (5). Increases in hepatic PAP1 also occur in response to dietary modification in rodents, for instance, when glucose or starch is replaced by fructose, sorbitol, glycerol, or ethanol (15), and these effects are exaggerated by high-fat feeding (16). These changes in PAP1 are also associated with increased GC concentrations relative to insulin.…”

Effect of Chronic Modification of Diet Fat and Cholesterol during Gestation on Plasma Hormones and Hepatic Enzyme Activities in Rat Fetus

“…This finding is in apparent con trast to the known effects of high fat diets on hepatic triacylglycerol synthesis [17], Whether or not this can be explained as a different response to diet fat of the pregnant female compared to male rat, or is due to the addition of high cholesterol to the diet is unknown. The marked decrease in total re ductase suggests that regulation of cholesterogenesis after 12 days of diet was princi pally due to reduction of enzyme quantity rather than activation state.…”

“…HMG-CoA reductase, total and active, represents enzyme activities following micro somal preparation and assay in the absence and presence, respectively, of 50 mM NaF. Statistically significant differences due to diet are: * p < 0.05; ** p < 0.01. data for male rats [17]. The reason for this is unknown although data are available to show that diet-induced hypercholesterol emia increases cholesterol uptake and stor age by the rat adrenal gland [16,32] through a mechanism not involving increased adrenocorticotropin [32].…”

“…Studies on the re lationship of early diet to adult cholesterol metabolism have employed diets rich in satu rated fat and cholesterol [2,6,7] and have been interpreted to suggest that rat HMGCoA reductase is most susceptible to long term alteration during prenatal life [6]. High fat and cholesterol diets, also appear to lead to accumulation of adrenal cholesterol [16] and increased plasma corticosterone [17] in male rats. Although data on the effects of glu cocorticoids are not consistent, glucocorti coid stimulation of rat and human fetal he patic cholesterol synthesis has been reported [18][19][20].…”

High-fat diets need not increase tryptophan availability to the brain: importance of the choice of the control diet

“…This occurred despite the fact that there were significant changes in other aspects of metabolism (Lawson et al, 198 1a,b;Brindley et al, 1981). All of these studies employed a 3 week feeding period.…”