Glucose Utilization of Cardiac and Skeletal Muscle Homogenates from Fetal and Adult Rhesus Monkesy

Abstract

ExtractThe oxygen consumptions and CO 2 productions were similar for the homogenates of adult and 113-day fetal muscle from rhesus monkeys but higher in the 155-day fetal series (Table I). The percentages of total CO 2 and the micromoles of CO 2 arising from glucose plus glycogen (carbohydrate) were the same in homogenates of fetal and adult skeletal muscle. No difference was observed between the metabolism of homogenates of adult and neonatal muscle.In homogenates of cardiac muscle, the oxygen consumption and CO 2 production in fetal muscle were higher at 113 days than in adult muscle; by 155 days, values in the fetal and adult muscle were similar ( Table I). The percentage of total CO 2 arising from carbohydrate and the micromoles of CO 2 produced from the oxidation of carbohydrate were higher in both fetal series than in the adult. The oxygen consumption, CO 2 production, and micromoles of CO 2 arising from carbohydrate per gram protein per 30 min were two-to sevenfold higher in cardiac than in skeletal muscle, the greatest difference occurring in the 113-day fetal series. However, the percentages of total CO 2 arising from carbohydrate were remarkably similar; the only difference was seen in the adult series where skeletal muscle was relatively more dependent on carbohydrate as a substrate than cardiac muscle. All these parameters were also measured in homogenates of cardiac muscle from neonates, and no difference in metablism was observed between the neonatal and adult series.In the fetal homogenates from both types of muscle, a major portion, 65 to 73%, of the total CO 2 produced originated from a source or sources other than glucose and glycogen. Thus, both skeletal and cardiac homogenates of fetal, neonatal, and adult muscle are potentially able to obtain a large portion of their energy from the oxidation of substrates other than glucose and glycogen. SpeculationIn vitro experiments from our laboratory demonstrate that 65% or more of the total CO 2 produced by skeletal and cardiac muscle homogenates originated from the oxidation of substrates other than glucose and glycogen in the fetal as well as in the adult series; the data from broken cell preparations (homogenate) and previous data from intact cell preparations (muscle fiber groups) are similar. The possibility that other tissues and organs of the fetus utilize noncarbohydrates as an energy 813 814 BEATTY, YOUNG, DWYER, AND BOCEK source should be investigated. Tsoulos et al. have reported that fetal lambs obtain a maximum of 50% of their metabolic requirements from glucose utilization under presumably normal conditions.

Propriétés des fibres musculaires squelettiques. 1. Influence de l'innervation motrice

“…Les Stetten, 1960 ;Cohen, 1983). Toutefois, des études plus récentes montrent que la glycogénolyse n'aurait un rôle important qu'au début de l'activité physique en produisant un surplus d'ATP, ou lorsque l'énergie néces-saire à l'accomplissement de travaux musculaires intenses excède celle produite par l'utilisation des acides gras et autres substrats circulants (Rowell etal., 1966 ;Bergstrôm et al, 1967 ;Havel, 1970 ;Beatty et al, 1972 ;Newsholme et al, 1978).…”

Human Placental Transfer of Glucagon

“…Glucose is generally considered to be the major energy substrate in the mammalian fetus, but recent experiments (Beatty, Young, Dwyer & Bocek, 1972) suggest the possibility that the fetus utilizes non-carbohydrates as a major energy source. The work of Tsoulos, Schneider, Colwill, Meschia, Makowski & Battaglia (1972) suggests that the amount of glucose acquired by the fetal lamb via the umbilical circulation can satisfy, at most, one-half of the total fetal aerobic needs.…”