NORMAL PLASMA LACTOSE CONCENTRATIONS AND KINETICS OF INTRAVENOUSLY INFUSED LACTOSE IN CATTLE

Plasma lactose concentration and its kinetics were determined in appar ently normal cattle, as a prelude to investigating its chemotherapeuti c significance in bovine trypanosomiasis. It is hoped that intravenous ly administered lactose may be able to reduce the rate of sequestratio n of desialylated erythrocytes during Trypanosoma vivax infection of c attle; thus decreasing the rate of development of trypanosomal anaemia in infected animals. A range of 0.061 to 0.55 mM with a mean of 0.208 +/- 0.128 mM standard deviation (SD), observed in adult cattle was si gnificantly lower (P<0.001) than corresponding values in recently wean ed calves; 0.429 to 1.496 mM (0.972 +/- 0.318 mM). Semi-logarithmic pl ots from calves given a single dose (0.5 g lactose per kg bodyweight a s a solution in normal saline, infused at the rate of 18 mi min(-1)) s howed a biexponential pattern of regression lines. Decrease in plasma concentrations was biphasic and lactose was rapidly distributed into t he extravascular space after administration. The biological half-life (t 1/2) of the infused lactose ranged from 4.10 to 6.00 hours (5.01 +/ - 0.81 hours); its mean elimination rate constant was 0.14 +/- 0.02 ho ur(-1), mean apparent volume of distribution was 168.09 +/- 56.65 mi k g-l while its mean total clearance was 23.54 +/- 8.31 mi kg(-1) hour(- 1). A single dose rapidly reached a peak and gradually fell below the pre-infusion level while repeated doses did not cause accumulation of the lactose in the plasma as each infusion fell back to normal relativ ely rapidly.