Pittermann, W., M. Kietzmann, H.-U. Krachter, W. Holtmann, and A.H. Schoon. The Isolated Perfused Bovine Udder System (BUS): A New Natural In-Vitro Model for Mucous Membrane Compatibility. IN: The Ethics of Animal Experimentation. Ed. Philip N. O'Donoghue. Pgs. 265-266. 1998.

BUS, the isolated perfused bovine udder system (Kietzmann et al. 1993), was introduced as a natural in-vitro model for the study of percutaneous absorption. Udders from slaughtered cows are perfused in the laboratory with a cell-free, oxygenated fluid. Monitored biochemically and physically, the udder skin and the mucous membrane of the cisternae remain viable for over 8 hr. Under these conditions, barrier properties and metabolic reactions remain comparable to living skin. Additional information concerning time-dependent skin and mucous membrane irritation - modified methyl tetrazolium (MTT) assay, measurement of prostaglandin E₂ (PGE₂) concentration - after exposure to test substances can be obtained by punched biopsy (Pittermann et al. 1997).