Effects of exogenous glucose on glucose metabolism in the lactating goat in vivo.

1. Glucose turnover in fed and 48 h-starved lactating goats was determined during a glucose load of 500 mumol/min using a continuous infusion of [U-14C]- and [3-3H]glucose. 2. Endogenous rates of irreversible glucose turnover (i.e. total rates of irreversible glucose turnover minus the rate of exogenous glucose supply) were depressed during glucose loading by 14 and 62% in the fed and starved animals respectively. 3. Plasma glucose concentrations increased significantly by 57 and 88% in the fed and starved goats respectively. Plasma insulin concentrations increased by 108 and 128% in the fed and starved animals respectively. 4. Milk yields increased significantly (41%) in the starved animals during glucose loading, but were unaffected in fed animals. 5. In both the fed and 48 h-starved goats, mammary glucose metabolism via glycolysis and the pentose phosphate pathway appeared to be stimulated by glucose loading.