Abstract:
Proc. Aust. Soc. Anim. Prod. (1978) 12: 135 THE ROLE OF GLUCOSE IN GROWTH R.A. LENG* and F.M. BALL* The relationship between glucose entry rates and growth (Kempton, Smith and Leng 1978) and also the effects of glucose infused intraduodenally or bypassing the rumen on growth and feed conversion ratio (Leng, Economides and Ball 1978; Kempton, Hill and Leng 1978) suggest an essential role for glucose in the metabolism of growing ruminants. To investigate the role of glucose in tissue synthesis a modelling approach has been developed which allows an estimate to be made of the rates of entry of glucose into pools with long retention times. This approach depends on the assumption that glucose C irreversibly lost from the glucose pool over the time of an experiment either enters pools with slow turnover (tissue synthesis) or is lost.through oxidation to carbon dioxide. In 6 growing lambs on a diet of pelleted barley and fish meal two experiments were carried out on each animal on separate days. On day 1 14C-C02 was infused intravenously over 12 or 24 h and from the specific radioactivities of plasma CO2 and glucose, the irreversible loss of CO2 and the proportion of glucose-C arising from CO2 were calculated. On day 2, 14C-glucose was infused and the irreversible loss of glucose and the proportion of CO2-C coming from glucose were calculated. From these four measurements the flow rates in the model were calculated by an algebraic approach similar to that described by Nolan, Norton and Leng (1976). . The a= b= C= d= e= f= values in brackets are the flows of carbon in g C/day where: . Glucose synthesis (without CO2 fixation) plus absorbed glucose. Glucose oxidation. CO2 produced from oxidation of substrates other than glucose. Glucose-C entering synthetic reactions (i.e. poolswith slowturnover) Glucose synthesis involving CO20 fixation reactions. CO2 irreversibly lost by all processes other than conversion into glucose. In all lambs over half the glucose-C apparently entered pools with long retention times, indicating a central role for glucose. in providing precursors for tissue synthesis in the body. KEMPTON, T.J., SMITH, G. KEMPTON, T.J., HILL, M-K. LENG, R.A., ECONOMIDES, S. NOLAN, J-V,, NORTON, B.W. * and LENG, R.A. (1978) Aust. Soc. anim. and LENG, R-A. (1978)Aust. Soc. anim. and BALL, F.M. (1978) Aust.Soc.anim. and LENG, R.A. (1976) Brit. J. Nutr. Prod. 12: Prod. v: Prod. 12: 35: 1277 S Department of Biochemistry and Nutrition, University of New England, Armidale, N.S.W. 2351, 135.