Observations on the 2,4-dichlorophenoxyacetic acid (2,4-D) excretion in the goat.

The protein binding of 2,4-D in goat plasma was studied by means of equilibrium dialysis and the renal excretion of 2,4-D in three female goats by means of clearance methods. At low plasma levels of 2,4-D (less than 20 microgram/ml) about 97% of 2,4-D is bound to plasma proteins. The fraction of 2,4-D bound to plasma proteins decreases with rising plasma 2,4-D concentrations. A tubular secretion mechanism for 2,4-D, with a Tm value of about 9 mg (40 mumol)/min., is demonstrated. The contribution from the tubules to the 2,4-D excreted per minute is greater than 97% at a plasma 2,4-D level of 10 microgram/ml. At moderate and high plasma 2,4-D concentrations (greater than 40 microgram/ml) the inulin clearance decreases with rising plasma 2,4-D concentrations.