The effects of lactate, acetate, glucose, insulin, starvation and alloxan-diabetes on protein synthesis in perfused rat hearts.

Compared with glucose, lactate + acetate stimulated ventricular protein synthesis in anterogradely perfused hearts from fed or 72 h-starved rats. Stimulation was greater on a percentage basis in starved rats. Atrial protein synthesis was not detectably stimulated by lactate + acetate. Insulin stimulated protein synthesis in atria and ventricles. The stimulation of protein synthesis by lactate + acetate and insulin was not additive, the percentage stimulation by insulin being less in the ventricles of lactate + acetate-perfused hearts than in glucose-perfused hearts. Perfusion of hearts from 72 h-starved or alloxan-diabetic rats with glucose + lactate + acetate + insulin did not increase protein-synthesis rates or efficiencies (protein synthesis expressed relative to total RNA) to values for fed rats, implying there is a decrease in translational activity in these hearts. In the perfused heart, inhibition of protein synthesis by starvation and its reversal by re-feeding followed a relatively prolonged time course. Synthesis was still decreasing after 3 days of starvation and did not return to normal until after 2 days of re-feeding.     

The effects of glucose, acetate, lactate and insulin on protein degradation in the perfused rat heart.

Rat hearts were perfused as working preparations by the method of Taegtmeyer, Hems & Krebs [(1980 Biochem. J. 186, 701--711]. In the presence of glucose, insulin significantly inhibited protein degradation at concentrations as low as 50 mu units/ml. Acetate or lactate, when present either as sole fuel for contraction or in combination with glucose, did not inhibit protein degradation. Insulin inhibition or protein degradation was decreased with either lactate as sole fuel. We suggest that the inhibition of protein degradation occurs over the normal range of plasma concentrations of insulin present in vivo and that the presence of glucose may be at least in part necessary for this effect of insulin.     

Lipid metabolism in the perfused chicken liver. Lipogenesis from glucose, acetate and palmitate

A procedure for the perfusion of the isolated chicken liver was developed. The preparation satisfied many of the criteria of normal physiological function, e.g. oxygen consumption and the absence in the perfusion medium of enzymes indicative of cell damage, and retained its capacity to synthesize lipids from glucose, acetate and long-chain fatty acids. Part of newly synthesized triglyceride was released into the perfusion medium as lipoprotein.     

Synthesis of stress-induced protein in isolated and perfused rat hearts

Isolated and perfused rat hearts were examined by two-dimensional gel electrophoresis and liquid scintillation counting for alterations in protein synthesis following incubation with L-[3H]leucine at 0.5-2.5, 2.5-4.5, or 4.5-6.5 h of perfusion. When 35-mL volumes of three different buffers were recycled for a 2-h period from 0.5 to 2.5 h, by fluorography little effect was seen on the normal patterns of protein synthesis and there was a moderate synthesis of a stress-induced protein (heat-shock protein) with a molecular mass of 71 X 10(3) daltons (SP71). However, hearts perfused with Krebs-improved Ringer 1 bicarbonate had the highest incorporation of L-[3H]leucine. When buffers were recycled for 30-min periods from 0.5 to 2.5 h, SP71 was synthesized in hearts perfused with Krebs-Henseleit original Ringer bicarbonate. Hearts perfused in a similar fashion with Krebs-improved Ringer 1 bicarbonate had the lowest incorporation of label into SP71 and in fact SP71 was undetectable on fluorograms. Overall protein synthesis was decreased and the ratio of SP71 to the total synthesis was increased at 4.5-6.5 h of perfusion when 35-mL volumes of Krebs-improved Ringer 1 bicarbonate was recycled for 2-h periods. A similar result was observed at 2.5-4.5 h of perfusion when this buffer was recycled for either the duration of the experiment or 30-min periods.     

Protein synthesis by perfused hearts from normal and insulin-deficient rats. Effect of insulin in the presence of glucose and after depletion of glucose, glucose 6-phosphate and glycogen

In the absence of glucose, insulin stimulated the incorporation of (14)C-labelled amino acids into protein by perfused rat hearts that had been previously substantially depleted of endogenous glucose, glucose 6-phosphate and glycogen by substrate-free perfusion. This stimulation was also demonstrated in hearts perfused with buffer containing 2-deoxy-d-glucose, an inhibitor of glucose utilization. It is concluded that insulin exerts an effect on protein synthesis independent of its action on glucose metabolism. Streptozotocin-induced diabetes was found to have no effect either on (14)C-labelled amino acid incorporation by the perfused heart or on the polyribosome profile and amino acid-incorporating activity of polyribosomes prepared from the non-perfused hearts of these insulin-deficient rats, which show marked abnormalities in glucose metabolism. Protein synthesis was not diminished in the perfused hearts from rats treated with anti-insulin antiserum. The significance of these findings is discussed in relation to the reported effects of insulin deficiency on protein synthesis in skeletal muscle.     

Myocardial lipid metabolism in cardiac hyper- and hypo-function. Studies on triiodothyronine-treated and transplanted rat hearts.

Lipid composition of the myocardium and in vitro lipid metabolism were studied in hearts from young rats after 30 days of treatment with triiodothyronine (100 microgram/kg per day) and in heterotopically isotransplanted hearts of inbred adult rats 6 days after surgery. The former served as an experimental model of cardiac hyperfunction, while the latter, empty beating hearts, served as a model of cardiac hypofunction. In hearts from hyperthyroid animals the concentration of phosphatidylcholine, phosphatidylethanolamine, cardiolipin, and the incorporation of 14C-labelled palmitic and erucic acid into these phospholipids were increased significantly as compared with controls. In contrast, the triglyceride concentration and the incorporation of palmitate into triglyceride was significantly decreased. In transplanted hearts, the phospholipid concentration and the incorporation of 14C-labelled fatty acids into phospholipids were significantly decreased as compared with the hearts of the inbred host rats of the same age. The results indicate that the mechanical performance of the heart affects the phospholipid composition, which may be a reflection of increased or decreased proliferation of subcellular membranes in sustained cardiac hyper- or hypo-function.