High-carbohydrate Group Research Articles

Regulation of amylase messenger RNA concentration in rat pancreas by food content.

Regulation of the expression of pancreatic amylase genes was studied by comparing groups of rats fed diets with high (75%), intermediate (20%) and low (11%) carbohydrate content. Animals on the high carbohydrate diet had nine times as much amylase mRNA as those on low carbohydrate diet, and twice as much as the intermediate group, as determined by filter hybridization of equal amounts of total pancreatic RNA to an excess of a cloned rat amylase cDNA probe. Parallel results were obtained when levels of translatable amylase RNA were compared by means of an RNA-dependent rabbit reticulocyte cell-free system. Amylase mRNA-directed synthesis represented 35% of the total in the high carbohydrate group, 4% in the low group and 14% in the intermediate group. Relative rates of amylase synthesis, determined 30 min after [3H]phenylalanine injection, followed the same pattern. While 37% of total was incorporated into amylase in the high carbohydrate group, only 8% was incorporated in the low carbohydrate group, as compared with 22% in the intermediate group. These data indicate that modifications of diet composition alter the expression of pancreatic amylase genes as a consequence of changing the level of their transcript, and that pancreatic amylase production is mostly regulated at the pre-translational level.

Effect of dietary modification on the uptake of glucose, fatty acids, and alcohols in diabetic rats

Nutrient uptake (Jd) is enhanced in diabetes mellitus (DM) in the rat; these studies were undertaken to determine the effect of 2 wk dietary modification on the Jd of fatty acids, fatty alcohols, and glucose. In control (C) rats, fatty acid Jd was lowest with the low essential fatty acid diet, but the incremental change in free energy (∫ΔFw➙ℓ) was not affected by the other diets; in DM ∫ΔFw➙ℓ was lower with the low cholesterol or high carbohydrate diets, and higher with the high cholesterol diet. The effective resistance of the intestinal unstirred layer was assessed from the Jd of lauryl alcohol. In C intestinal unstirred layer was lowest in the high carbohydrate group and highest in the low cholesterol group; intestinal unstirred layer was less in DM than in C only in the rats fed the low cholesterol diet. In C, varying the protein content of the diet was associated with a rise in the value of the maximal transport rate and the Michaelis constant, but a decline in the passive permeability coefficient for glucose. Glucose Jd was increased in DM rats fed a high carbohydrate or a high cholesterol diet; the values of the Kms were similar in DM and C, but the maximal transport rates were higher in the DM than in the C and these values were influenced by dietary modifications. Thus short-term dietary modification influences intestinal unstirred layer, ∫ΔFw➙ℓ, and the kinetic constants for Jd of glucose in control and diabetic rats.

The effect of dexamethasone, diet control and hyperglycemia on murine hepatic T3 receptors

There exists an apparent relationship between thyroid hormones and other substrates known to influence carbohydrate homeostasis. Thyroid hormones, for example, increase lipolysis in rat adipocytes in response to glucagon, and reciprocally, T3 administration increases glucagon receptors and thus stimulates glycerol production. In order to further study these relationships we determined whether dexamethasone, streptozotocin-induced diabetes, glucose feeding and carbohydrate content of diet altered murine hepatic nuclear T3 receptors. Rats were divided into one of several protocols:(1) dexamethasone was administered i.p. at a dose of approximately 1.5 mg/kg for 6–10 days, (2) streptozotocin was administered in a dose of approximately 65 mg/kg and the rats were sacrificed and the nuclei studied approximately 7–10 days later. Mean (± SE) plasma glucose at the time of sacrifice was 539 ± 33 mg/dl (n=5) in the streptozotocin treated rats and 159 ± 8 mg/dl (n=5) in the saline injected control animals; (3) in the glucose studies, rats were divided into either a fasted group, a fasted group that was given 50% dextrose in their drinking water or into a group allowed to eat normally. These groups were given the appropriate diet for 3 days at which time they were sacrificed; (4) to assess the effect of carbohydrate content of the diet, rats were pair fed and allowed to eat either a diet containing 79% carbohydrate, 9% protein and 5% fat or a diet containing 52% carbohydrate, 36% protein and 5% fat. The diets contained adequate amounts of all other necessary nutrients. Rats were sacrificed after ingesting either of these diets for approximately 14 days. In all studies, hepatic nuclei were isolated and studied as previously reported (Endocrinology 107:1081, 1980). In dexamethasone treated rats, the maximal percentage binding of 125 I-T3 per mg DNA was 18.8 ± 2.8 (n=4) in normal non-injected rats, 21.2 ± 5.7 (n=7) in saline injected rats and 16.8 ±3.9 (n=7) in dexamethasone injected rats. The difference between the saline injected and dexamethasone injected rats was statistically significant (p<0.05). The maximal binding capacity (MBC) expressed as pmoles/mg DNA was 0.392 ± 0.079 in normal rats, 0.456 ± 0.105 in saline injected rats, and 0.317 ± 0.067 in dexamethasone treated rats. The Ka values (X10 8M −1) were 4.5 ± 0.5, 6.2 ± 1.2 and 5.1 ± 0.7 in the three groups, respectively. In the streptozotocin treated rats, the maximal percentage 125I-T3 binding per mg DNA was 18.9 ± 5.8 (n=6) and this was decreased slightly but significantly ( p<0.025) to 16.0 ± 5.8 in the diabetic rats. As expected, fasting was associated with a decreased MBC (pmoles/mg DNA) when compared to normal fed rats (0.667 ± 0.510, fast vs. 0.849 ± 0550, fed). Glucose administration in the drinking water to fasting rats, however, did not alter the MBC (0.650 ± 0.500) compared to that in fasting. Unstimulated or T3 stimulated alpha-GPD activity was also measured in these 3 groups of rats and was not different in any group studied. Lastly, several groups of studies were performed in the rats ingesting either a 79% or a 52% carbohydrate diet. The MBC (pmoles/mg DNA) was 0.39 ± 0.05 (n=10) in the high carbohydrate group and 0.31 ± 0.05 (n=10) (p<0.05) in the low carbohydrate group. Since this difference was so slight, however, we restudied a separate group of rats utilizing an identical protocol except that the MBC was determined on solubilized nuclei. In these studies, there was no significant difference in the MBC in the two groups, In conclusion, our data suggests that: (1) dexamethasone slightly decreases the T3 MBC; (2) Streptozotocin-induced diabetes decreases the 125I-T3 bound to hepatic nuclei; (3) T3 MBC decrease during fasting, and glucose feeding to fasting rats does not increase the MBC; (4) rats ingesting a 79% carbohydrates diet have a slightly higher T3 MBC than rats ingesting a 52% carbohydrate diet. This effect is very slight and not reproducible depending on the method of study of 125I-T3 binding and; (5) both unstimulated and T3 stimulated mitochondrial alpha-GPD activity are unchange in rats that are fasted, fasted plus given glucose, or normal fed.

Pressor effects of fat and salt in rats.

AbstractThe role of dietary lipids in the development of salt-induced hypertension was studied. Sprague-Dawley rats were fed a high-fat (HSAT) (5% corn oil-15% coconut oil), a high-carbohydrate (HCARB) (5% corn oil), or a commercial rat diet. Within the HSAT and HCARB groups, subgroups were randomly chosen and the level of salt was varied in the following progression: high salt (HS) (8% NaCl); medium salt (MS) (6% NaCl); and basal salt (BS) (0.15% NaCl). Rats were maintained at each level of salt for 2 weeks. Systolic blood pressure was measured from the tail artery using an electrosphygmomanometer. No significant elevation in blood pressure was demonstrated by rats maintained on the HCARB—BS or commercial laboratory diet during a 6-week experimental period. An intermediate elevation in blood pressure was seen in rats fed the HCARB—HS or HSAT—BS diets. Rats fed the HSAT—HS diet demonstrated the most significant elevation in blood pressure, becoming hypertensive within 1 week of diet introduction. Blood pr...

EFECTS OF ENERGY-CONTAINING NUTRIENTS ON BLOOD PRESSURE OF SALT-LOADED RATS

The present study was performed to investigate whether blood pressure of salt-loaded rats was influenced by the diet. Salt-loaded rats of Wistar strain were fed a high protein high fat diet or a high carbohydrate diet from the age of one month. The experiment was designed so that the intake of sodium chloride was equal in two groups. The body weight on the 14th week of the experiment was 394 +/- 15 g (Mean +/- SE) in the high protein high fat group, and 348 +/- 13 g in the high carbohydrate group. Blood pressure measured weekly by a tail plethysmographic method rose gradually and reached 176 +/- 5 mmHg (Mean +/- SE) on the 14th week in the high carbohydrate group. It was significantly higher than that (127 +/- 7 mmHg) of the high protein high fat group. The pressor responses to angiotensin and noradrenalin were also examined to investigate the mechanism through which salt hypertension was produced more easily by feeding a high carbohydrate diet. These responses to both drugs tended to be greater in the high carbohydrate group, but the differences between the two groups was not significant.

Effect of high-fat diet on thermal acclimation with special reference to thyroid activity.

In an attempt to clarify why the seasonal variation of basal metabolic rate (BMR) of Japanese is different from that of Caucasians (white American and Canadian), animal experiments were performed to clarify the effect of dietary composition on thyroid activity, metabolic adaptation to heat, and tolerance to cold, using groups of rats fed on different kinds of diets. Results obtained are as follows:1) By radioisotope techniques with 13II, it was demonstrated that the 131I uptake of thyroid gland is higher and PB131I is higher in the high-fat diet groups than in the control diet rats, while the conversion ratio and the fractional turnover rate of thyroxine are not significantly different between the two groups. Thus it is inferred that the thyroid activity is promoted by feeding rats a high-fat diet.2) The resting oxygen consumption of rats which were reared in the control temperature.(20°C) as well as kept at 30°C for 5 weeks was higher in the high-fat diet group than in the high-carbohydrate group. The resting metabolism was reduced by heat acclimation. The reduction rate of 02 consumption in heat acclimation was less in the high-fat diet group than in the high-carbohydrate group.3) Assuming that an adaptative process of the thyroid gland may be involved in the mechanism of metabolic adaptation to heat and cold and that the experimental results of metabolism in rat may be applicable to the mechanism of metabolism in man, the following explanation was presented for the difference of seasonal variations of BMR between Caucasian (white American and Canadian) and Japanese. Japanese present a seasonal variation of BMR, increasing in winter and decreasing in summer, as an outcome of metabolic adaptation to heat and cold in various seasons. In Caucasians, however, their thyroid activity is promoted by the intake of a high-fat diet. This promotion of thyroid activity may inhibit the reduction of metabolism in heat acclimatization, thus maintaining the BMR at a constant level throughout the year. Thus the appearance of climatic effect in the BMR of Japanese may be due to their habitual high-carbohydrate diet.4) In acute exposure to air of 10°C, the high-fat diet group showed superiority in maintenance of body temperature in the cold, while the high-carbohydrate group showed a most remarkable drop of rectal temperature.

Interaction of Dietary Fat and Thyroid Function with Hepatic and Renal Gluconeogenesis of Rats

The influence of thyroid function on the capacity for glucose formation in rats fed a high carbohydrate or a high fat diet was investigated with the use of propylthiouracil and L-thyroxine. The food intake, growth rate and blood glucose level of rats fed the high fat diet were depressed in hypothyroidism produced by feeding 0.01% propylthiouracil. However, rats fed the high carbohydrate diet were unaffected by feeding 0.01% or 0.05% propylthiouracil. The hepatic activity of glucose-6-phosphatase was decreased significantly by feeding propylthiouracil, while the renal activity of glucose-6-phosphatase did not show any significant change in either of these dietary groups. Moreover, percentage decline of activity due to propylthiouracil was greater in the high fat group than in the high carbohydrate group. L-Thyroxine injected intraperitoneally caused significant increases in the hepatic and renal activities of glucose-6-phosphatase of rats fed the high carbohydrate diet. The effects of thyroxine and the high fat diet were additive in the liver, whereas no change in the renal activity was observed. These findings support the hypothesis that increases in the capacity for glucose formation and glucose-6-phosphatase activity with dietary fat, which are observed in the liver only, might be related to increased thyroid activity as a consequence of feeding a high fat diet.

Experimental study on alcoholic pancreatitis.

One hundred and five Wistar rats were divided into six groups according to the compositions of diet and fed on the respective diet for four to six months, and then received orally 15% ethyl alcohol instead of drinking water for two months. The following results were obtained. 1) The serum amylase levels were above 64 units in most of the rats, except for the group of high carbohydrate diet in which 57% of rats showed a normal value. 2) Pancreatic edema was observed in almost all cases of each dietary group, but fat necrosis, ascites or pancreatic necrosis was not noted at all at laparotomy. 3) Histologic changes of the pancreas were significantly different from those of controls in groups of high protein, high fat, high protein and high fat diets, but not in the high carbohydrate group.

The influence of excess body fat on the cardiotoxicity of isoproterenol in rats

The cardiotoxicity of isoproterenol was examined in rats receiving a high-fat, a high-carbohydrate, or a normal diet for 4 months. An increased cardiotoxicity of isoproterenol was shown in all the groups where body fat was increased significantly. There appeared to be no difference in the sensitivity of the high-fat and high-carbohydrate groups.