Albert B. Eisenstein

Increased Hepatic Gluconeogenesis without a Rise of Glucagon Secretion in Rats Fed a High Fat Diet

We have recently demonstrated that in rats fed a high protein, carbohydrate-free (HP) diet plasma glucagon and liver cyclic AMP are increased and as a result hepatic gluconeogenesis is stimulated. To determine whether increased protein intake or lack of dietary carbohydrate was responsible for these changes, the effects of a high fat, carbohydrate-free (HF) diet on plasma glucagon and insulin, liver cyclic AMP and hepatic gluconeogenesis were determined. Perfused livers of HF-fed rats showed greater conversion of alanine and pyruvate into carbohydrate than did control liver, although the rates were less than in HP-liver. Despite elevated gluconeogenesis in liver of HF-rats, plasma glucagon and insulin and liver cyclic AMP were normal. These findings demonstrate that some mechanism other than a rise in the level of glucagon is responsible for stimulating carbohydrate synthesis. We have postulated that acetyl CoA, which is formed in large amounts as a result of accelerated fatty acid oxidation, promotes gluconeogenesis in HF-fed rats. The observation that plasma glucagon is elevated in HP-fed but not in HF-fed rats demonstrates that protein intake and not carbohydrate restriction stimulates glucagon secretion since both diets are carbohydrate-free. Despite the lack of dietary carbohydrate, plasma glucose of HF-fed rats was normal and liver glycogen was about half that of controls. When HF animals were starved for twenty-four hours, mobilization of carbohydrate stores was diminished indicating that glucose utilization is reduced as a result of fat feeding.

Effect of High Protein Feeding on Gluconeogenesis in Rat Liver

Although alanine (A) is the major substrate for hepatic gluconeogenesis, it is utilized less effectively than pyruvate or lactate, thus suggesting that glutamic alanine transaminase (GAT) regulates A conversion to glucose. To test this hypothesis incorporation of A and pyruvate into glucose, glycogen and protein by isolated livers of rats fed a high protein (HP) diet was determined and compared with that by liver of normally fed animals. Effect of HP feeding on transport of α-aminoisobutyric acid (AIB), a nonutiliz-able amino acid, into liver was investigated. Liver GAT and phosphoenolpyruvate carboxykinase (PEPCK) activities were determined. HP feeding produced a twofold increase in conversion of A to glucose when perfusate A-concentration was physiological (0.5 mM) and when excess A was present. Liver glycogen synthesis from A was less than that of glucose and was unaffected by HP feeding. Incorporation of A into protein by control and HP livers was negligible. Hepatic conversion of pyruvate to glucose was markedly enhanced by the HP diet whereas glycogen synthesis from pyruvate was limited and not affected by HP feeding. AIB transport by liver of HP fed rats was double that of control liver. Liver GAT and PEPCK activities were greatly increased by HP feeding. Increased gluconeogenesis in HP liver at physiological and excess perfusate A concentrations indicates that amino acid transport and transamination are stimulated since other investigations have demonstrated that at low A levels transport is rate limiting and at high A concentrations, transamination controls gluconeogenesis. Furthermore, we observed increased AIB transport and elevated GAT activity in HP liver, thus it is clear that the GAT does not alone control conversion of A to glucose. Increased gluconeogenesis from pyruvate and elevated PEPCK activity were found suggesting that HP feeding stimulates conversion of pyruvate to phosphoenolpyruvate. The effects produced by the HP diet also occur after glucagon administration thus HP feeding probably influences gluconeogenesis by stimulating glucagon secretion.

The effect of pyridoxine deficiency on liver and muscle phosphorylase

Abstract The effects of pyridoxine deficiency on phosphorylase activity of rat liver and skeletal muscle have been investigated. It was shown that phosphorylase a and total phosphorylase activity of muscle were decreased with the greater reduction occurring in total enzyme activity. Liver phosphorylase activity was also diminished in pyridoxine depleted animals although the decline in activity was less marked than that which occurred in muscle tissue.

Relationship of ascorbic acid to secretion of adrenocortical hormones in guinea pigs.

Summary and Conclusions (1) The weight of the adrenal glands of guinea pigs on graded levels of intake of ascorbic acid varied inversely with daily intake of this vitamin. (2) A progressive decrease in the number of circulating eosinophiles occurred in guinea pigs maintained on a scorbutigenie diet. (3) There was a delay in onset of severe symptoms of scurvy and an increase of the mean survival period in scorbutic animals treated with ACTH. (4) The administration of a large close of ACTH to guinea pigs with severe scurvy was promptly followed by a decline of more than 50% in the level of circulating eosinophiles. (5) These observations are interpreted as indicating that ascorbic acid deficiency functions as a non-specific stress and that this vitamin is not directly involved in mechanisms of elaboration of adrenal cortical hormones with an oxygen atom at the C-ll position.

Amino Acid Stimulation of Glucagon Secretion by Perifused Islets of High-protein-fed Rats

Feeding of a high-protein, carbohydrate-free (HP) diet to rats results in elevated plasma glucagon and increased glucagon secretion by isolated islets of Langerhans. Since amino acids liberated during protein digestion may cause increased pancreatic glucagon release, the effects of 21 amino acids on glucagon secretion by perifused islets of HP-fed and control rats were examined. Arginine caused a marked rise of glucagon secretion, which consisted of an initial burst followed by a sustained phase of elevated hormone release. Total glucagon secretion by HP islets in response to arginine was 69.8 ± 5.3 pg./islet/30 minutes and by control islets was 30.0 ± 2.6, P = <0.001. Perifused islets responded physiologically to suppression as well as stimulation, since the arginine effect was abolished by raising the medium glucose level to 16.7 mM or by addition of small amounts of somatostatin (10 ng./ml). Of the 10 essential amino acids, only arginine had a major effect on hormone release by the alpha cell. Glutamine and α-aminobutyrate caused increases of glucagon secretion that were similar in pattern and magnitude to that induced by arginine. Total glucagon secretion by HP islets in response to glutamine was 65.6 ±4.6 pg./islet/30 minutes and by control islets was 39.1 ±8.1. Glucagon release by HP islets in response to α-aminobutyrate was 63.4 ± 4.6 pg./islet/30 minutes. Ornithine caused a sharp rise of glucagon release that was not sustained. Total hormone secretion induced by ornithine amounted to 27.3 ±6.9 pg./islet/30 minutes. None of the other nonessential amino acids, including alanine, had a major effect on pancreatic alpha cell function.

Effect of Cortisol on Liver Phosphorylase Activity.

Summary The effects of single and multiple doses of Cortisol on liver phosphorylase activity have been determined and correlated with alterations in blood glucose and liver glycogen. Phosphorylase activity was increased 12 hours after a single injection of Cortisol and continued to rise for 48 hours. Multiple injections of the hormone produced a much greater increase in enzyme activity than did a single dose. Elevation of blood sugar and liver glycogen which followed Cortisol occurred several hours before a change in phosphorylase activity could be demonstrated.

Effect of Triparanol (MER/29) on Gorticosterone Secretion by Rat Adrenals.

Summary Triparanol feeding produces a significant reduction in the amount of corticosterone secreted by the adrenals of rats subjected to surgery and bleeding. It is postulated that this reduction is secondary to the marked decrease in adrenal cholesterol which results from triparanol therapy.

Effect of spinal cord transection on adrenocortical function.

Summary Adrenocortical hormone secretion of patients with spinal cord transection has been studied by determining urinary and plasma 17-hydroxycorticosteroid concentrations before and after ACTH and by measuring diurnal variation in plasma adrenal steroid levels. These values were compared with those obtained from control subjects and no difference in adrenal hormone secretion was evident. Metabolic inactivation of Cortisol was determined by infusing the steroid intravenously and measuring rate of disappearance from plasma. The rate of steroid degradation in cord-sectioned patients was not different from that of controls.

Effect of sodium chloride feeding on adrenocortical hormone secretion of salt deprived rats.

Summary Effect of salt replacement on secretion of adrenocortical hormones by rats which had been deprived of sodium for 1 month was investigated. Results demonstrated that total cortical hormone production, which had been depressed, increased to equal that of control animals; that elevated aldosterone synthesis declined to previous levels; and that cortisterone secretion, which had been undetectable, increased rapidly. Thus, within 48 hours after resumption of salt feeding secretion of adrenocortical hormones returned to normal.

Steroid Compounds Resulting from Incubation of Cortisone with Surviving Liver Slices.

Summary 1. Liver slices were incubated in a physiologic, buffered medium containing cortisone. Following incubation, the steroid fraction was recovered and the individual steroids isolated by paper chromatography. 2. Under the conditions of this experiment, 3 steroids were isolated on the paper chromatogram. The compound of greatest mobility and obtained in largest amount was cortisone, unaltered by incubation. The product of intermediate mobility was identified as Compound F. The least mobile compound was not identified. 3. On the basis of observations in the literature and the experimental data reported here, it is suggested that the metabolic activity of cortisone may actually be dependent on its conversion to Compound