Normal plasma lactose concentrations and kinetics of intravenously infused lactose in cattle

Plasma lactose concentration and its kinetics were determined in apparently normal cattle, as a prelude to investigating its chemotherapeutic significance in bovine trypanosomiasis. It is hoped that intravenously administered lactose may be able to reduce the rate of sequestration of desialylated erythrocytes during Trypanosoma vivax infection of cattle; 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 significantly lower (P<0.001) than corresponding values in recently weaned calves; 0.429 to 1.496 mM (0.972 +/- 0.318 mM). Semi-logarithmic plots from calves given a single dose (0.5 g lactose per kg bodyweight as a solution in normal saline, infused at the rate of 18 ml min(-1)) showed a biexponential pattern of regression lines. Decrease in plasma concentrations was biphasic and lactose was rapidly distributed into the extravascular space after administration. The biological half-life (t1/2) 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 hour(-1), mean apparent volume of distribution was 168.09 +/- 56.65 ml kg(-1) while its mean total clearance was 23.54 +/- 8.31 ml 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 relatively rapidly.