Active Mammary Excretion of N⁴-Acetylated Sulphanilamide

Abstract

After administration of sulphanilamide to goats and cows, sulphanilamide is excreted into milk. The concentrations of sulphanilamide in ultrafiltrate of milk (M. Ultr.) and blood plasma (P. Ultr.) are equal and the ratio M. Ultr./P. Ultr. is 1.0. The pK_a of sulphanilamide is 10.4 and thus, sulphanilamide is un-ionized in both milk and blood plasma. Therefore, sulphanilamide is excreted into milk in accordance to the theory of passive diffusion of the non-protein-bound and un-ionized fraction in blood plasma (Rasmussen 1958, 1966; Miller et al. 1967). A similar ratio was expected for acetylated sulphanilamide with a pK_a of 10.3. However, the concentration of the acetylated derivative is always found higher in milk than in plasma. This might be due to formation of acetylated sulphanilamide in the mammary tissue, as demonstrated by Rasmussen & Linzell (1967) or active excretion of the compound just as in the case of N⁴-acetylated p-aminohip-puric acid (Rasmussen 1969).