glycogen and Alkalosis--Respiratory

The purpose of this study was to examine the effects of respiratory alkalosis on human skeletal muscle metabolism at rest and during submaximal exercise. Subjects exercised on two occasions for 15 min at 55 % of their maximal oxygen uptake while either hyperventilating (R-Alk) or breathing normally (Con). Muscle biopsies were taken at rest and after 1 and 15 min of exercise. At rest, no effects on muscle metabolism were observed in response to R-Alk. In the first minute of exercise, there was a delayed activation of pyruvate dehydrogenase (PDH) in R-Alk compared with Con, resulting in a reduced rate of pyruvate oxidation. Also, glycogenolysis was higher in R-Alk compared with Con, which was attributed to a higher availability of the monoprotonated form of inorganic phosphate (P(i)), resulting in an elevated rate of pyruvate production. The mismatch between pyruvate production and its oxidation resulted in net lactate accumulation. These effects were not seen after 15 min of exercise, with no further differences in muscle metabolism between conditions. The results from the present study suggest that respiratory alkalosis may play an important role in lactate accumulation during the transition from rest to exercise in acute hypoxic conditions, but that other factors mediate lactate accumulation during steady-state exercise.

Topics: Adenosine Triphosphate; Adult; Alkalosis, Respiratory; Blood; Exercise; Glycogen; Heart; Humans; Lactic Acid; Male; Muscle, Skeletal; Oxidation-Reduction; Pyruvates; Respiratory Physiological Phenomena; Time Factors

It has recently been demonstrated that, compared to normal conditions, ventilation (VE) was increased during exercise after glycogen depletion, in spite of a marked increase in plasma pH (pHP). It was further demonstrated that VE in patients with McArdle's syndrome was reduced when substrate availability was improved. In the present experiments, six endurance trained men performed two successive cyclo-ergometric incremental exercise tests (tests A, B) after normal nutrition (N) and after a fatty meal in conjunction with a sodium bicarbonate (NaHCO3) solution (FSB) or without NaHCO3 (F), and the relationship between VE, plasma potassium concentration ([K+]P), and pHP was checked. Plasma free fatty acid concentration ([FFA]P) was markedly increased in the F and FSB trials (P < 0.001). In FSB pHP was significantly increased, compared to N and F (P < 0.001). In all the B tests, pHP increased during moderate and intense exercise and in FSB, remained alkalotic even during maximal exercise intensity. In contrast, VE and [K+]P changes were almost equal in all the trials and in tests A and B. It was found that exercise-induced changes of VE and [K+]P in the present experiments were not markedly affected by [FFA]P or pHP values and that these changes also occurred independently of changes in pHP or plasma bicarbonate concentration. The often used glycogen depletion strategy may have slightly increased VE but apparently did not overcompensate for a possible decrease in VE due to increased pHP.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Acid-Base Equilibrium; Adult; Alkalosis, Respiratory; Bicarbonates; Exercise; Exercise Test; Fatty Acids, Nonesterified; Glycogen; Humans; Hydrogen-Ion Concentration; Male; Muscles; Nutritional Physiological Phenomena; Potassium; Respiration; Sodium; Sodium Bicarbonate