Intra- and extracellular amino acid concentrations in portacaval-shunted rabbits. Role of hyperammonemia and effects of branched-chain amino acid-enriched parenteral nutrition.

Intra- and extracellular amino acid concentrations were measured in rabbits in order to elucidate the possible role of hyperammonemia in lowering the postabsorptive plasma levels of branched-chain amino acids (BCAA) and to assess the effects of BCAA-enriched total parenteral nutrition (TPN) on the amino acid pattern of muscle. The pathophysiological part of this paper deals with portacaval anastomosis (PCA) and is aimed at substantiating or rejecting our hypothesis that excessive ammonia-by stimulating glutamine synthesis-reduces the intracellular glutamate pool which is then restored, at least in part, by an intensified BCAA degradation. Regarding infusion therapy, we were mainly interested in whether an amino acid solution adapted to the metabolism in liver cirrhosis causes an accumulation of BCAA in muscle or modifies the intracellular content of glutamate and glutamine. Eighteen rabbits did not undergo surgery and served as controls (group A), while 30 were given a portacaval end-to-side anastomosis (group B). Two weeks after creating the PCA, venous blood samples were taken and muscle biopsies (Bergström's technique) were performed postabsorptively. An 18-h TPN was then started, the regimen administered included dextrose, fat and, in addition, either a conventional (group B1, n = 15) or an adapted amino acid solution (group B2, n = 15). We obtained second blood specimens and muscle biopsies at the end of the infusion period. With the control animals, the same time schedule for blood sampling and muscle biopsies was followed. Fourteen days after the operation, the PCA rabbits displayed a mean plasma ammonia level 5.1 times higher than that measured in the controls (p less than or equal to 0.001). Conventional blood chemistry did not reveal any impairment of liver cell integrity or over-all hepatic function, whereas the nutritional state of the shunted animals worsened, as indicated by body weight and biochemical variables. Since in the PCA rabbits, the total amino acid pools of muscle and plasma were seen to be increased and decreased, respectively, the results concerning the individual amino acids are given in terms of both the absolute and percentage values, the latter more often revealing high levels of statistical significance. PCA induced a marked rise in the intra- and extracellular concentrations of glutamine, while the values of glutamate and alanine showed a decline in muscle and plasma. The extracellular levels of methionine, phenylalanine, and tyrosine were raised, while those of the BCAA were diminished.(ABSTRACT TRUNCATED AT 400 WORDS)

Stereology of myocardial hypertrophy induced by physical exercise.

Twenty young female Sprague-Dawley rats were randomly assigned to 2 groups. Ten animals served as sedentary controls, the 10 experimental animals were subjected to a training program with gradually increasing intensity of 18 weeks duration on a motor-driven treadmill. The rats were fixed by retrograde vascular perfusion via the abdominal aorta under anesthesia. Two transverse and 2 longitudinal sections per animal were selected at random from the left ventricular papillary muscles for light and electron microscopic stereological investigation. Length density and surface density of myocardial cells and capillaries were estimated with correction for partial anisotropy and curvature by means of the mathematical model of a Dimroth Watson orientation distribution. Left and right ventricular weight increased by 20% in the exercise group (P less than 0.001), whereas body weight remained unchanged. Physical training led to a significant increase of heart muscle fiber cross-sectional area by 17% (P less than 0.01). The ultrastructural volumetric composition of the myocardial cell cytoplasm by myofibrils, mitochondria, and sarcoplasmic matrix remained unchanged. Volume density, length density and surface density of capillaries, as well as capillary cross-sectional area and capillary anisotropy parameters were not significantly altered by training. From the data one concludes an increase of the 3-dimensional capillary-fiber ratio by 19% (P less than 0.001). Thus physical training induces mild absolute biventricular cardiac hypertrophy in young female rats, in which capillary proliferation compensates for the increase of mean oxygen diffusion distance resulting from fiber thickening, by supplying each unit of fiber length by more units of capillary length.