THE METABOLISM OF FRUCTOSE AND GLUCOSE BY THE SHEEP FOETUS: STUDIES ON THE ISOLATED PERFUSED PREPARATION WITH RADIOACTIVELY LABELLED SUGARS

¹ Department of Physiology, St Mary's Hospital Medical School, London, W.2

1. The metabolism of fructose and glucose in the perfused isolated sheep foetus was studied using ¹⁴C-labelled sugars.

2. At 105-135 days of conceptual age the foetus metabolized fructose at a rate equivalent to only a small fraction of the oxygen consumed. Plasma fructose showed little or no turnover, indicating a negligible endogenous formation of the sugar.

3. A substantial part of the fructose appeared as CO₂; about 3 per cent of the total CO₂ excretion could come from this sugar. This proportion was inversely related to the plasma glucose concentration and was markedly depressed when glucosewas administered.

4. [U-¹⁴C] glucose rapidly disappeared from the circulation and much of the label appeared in the CO₂ in the experimental period. The rapid turnover was compatible with glucose as the major foetal metabolite.

5. Glycogen showed only trace labelling in liver, heart muscle and skeletal muscle after giving the [U-¹⁴C] sugars. Indications were obtained that cardiac glycogen can be depleted by both hypoglycaemia and hypoxia.

6. The urine contained only small amounts of both sugars.

7. Foetal blood cells were shown to take up fructose in the absence of glucose, a fact which could account for a considerable fraction of its disappearance from the blood.

8. It is concluded that the above observations are compatible with fructose being a reserve for use when little glucose is available; the amount utilized is, however, always small. It may be that fructose is used only by tissue lacking stores of glycogen.

Note:

We wish to thank the Wellcome Trust for financial support and J. R. Hancock, R. W. Lock and Mrs E. Fenton for technical assistance.