Glycogen depletion in exercising rats infused with glucose, lactate, or pyruvate

Abstract

The influence of an intravenous infusion of glucose, lactate, or pyruvate on the work capacity and rates of glycogen depletion in the liver and hindlimb skeletal muscles of rats has been studied. Running time to exhaustion at a speed of 21 m/min on a treadmill at a +10 degrees incline was prolonged by glucose infusion but shortened by lactate or pyruvate infusions. Blood glucose concentrations were only lowered in the terminal stages of the exercise, whereas at this point lactate was elevated. Declines in liver and muscle glycogen concentrations were retarded by glucose infusion but accelerated by either lactate or pyruvate infusions. In all cases a marked depletion of both muscle and liver glycogen existed at the point of exhaustion. It is concluded from the lack of any major elevation of glucose, lactate, or pyruvate in the blood of the rats during running that these materials were taken up and oxidized, presumably by the working muscles. These observations suggest that skeletal muscle can take up large amounts of glucose and when it is supplied from an external source this can exert a glycogen sparing effect on the liver and working skeletal muscles.

Fuel kinetics during intense running and cycling when fed carbohydrate

“…These authors concluded that net glycogen degradation during intermittent exercise could be reduced by up to 20% with CHO ingestion. This view was also supported by later workers (Ehrenstein et al 1970;Bagby et al 1978;Coyle et al 1983) However, some scientists in the 1980's, showed that CHO ingestion during exercise had no effect on rates of muscle glycogen utilisation (Fielding et al 1985;Coyle et al 1986;Flynn et al 1987;Hargreaves & Briggs 1988;Noakes et al 1988b;Mitchell et al 1989), while others demonstrated a sparing of muscle glycogen when CHO's were ingested during exercise (Bjorkman et al 1984;Hargreaves et al 1984;Erickson et al 1987;Simard et al 1988;Brouns et al 1989). The question of whether water or CHO replacement should be emphasised during prolonged exercise received a large amount of attention in the mid to late 1980s when commercial interests sponsored this type of research.…”

“…Over the past 30 years there has been evidence both for and against muscle glycogen sparing when ingesting CHO while exercising (Ahlberg et al 1967b;Bergstrom and Hultman 1967;Hultman 1967;Ehrenstein et al 1970;Bagby et al 1978;Bjorkman et al 1984;Hargreaves et al 1984;Fielding et al 1985;Coyle et al 1986;Flynn et al 1987;Erickson et al 1987;Hargreaves & Briggs 1988;Simard et al 1988;Brouns et al 1989;Noakes et al 1988;Mitchell et al 1989). However, Coggan and Coyle (1991) concluded that CHO ingestion while cycling at moderate-intensity (70-75% of V02max) does not reduce the rate of muscle glycogen utilisation.…”

Glycogen storage and muscle glucose transporters (GLUT-4) of mice selectively bred for high voluntary wheel running

“…Hepatic gluconeogenesis (John-Alder et al, 1986) and especially increased rates of glycogenolysis (Bagby et al, 1978) are essential to sustain prolonged submaximal locomotor activity in rats. Even when faced with an exogenous glucose infusion [final concentration 25% (w/w)], both trained and untrained rats experience significant hepatic glycogenolysis during exercise (Azevedo et al, 1998).…”

Maltodextrin's Effect on the Performance of Elite Mountain Biking Athletes During Simulated Competition and on Power Output at the Ventilatory Threshold

“…In other studies, carbohydrate supplementation has been shown to increase the amount of work that can be performed [3][4][5] as well as increase the duration of aerobic exercises [6,7]. The elevation of blood glucose, found in the laboratory test, can be associated with improved aerobic performance through the reduction of muscle glycogen use [7,27,28] or through the use of blood glucose as a predominant fuel source as glycogen becomes depleted [4,9,11].…”