A 96-well Nunc Maxisorb ELISA plate (ThermoFisher) was coated with 100 µg/mL anti-PAS antibody in PBS at 4 °C overnight. After washing twice with PBS/T, free binding sites were blocked with 3% w/v bovine serum albumin (BSA) in PBS/T at room temperature for 1 h. After washing 3 times with PBS/T, the rat plasma samples were applied in dilution series in PBS/T supplemented with 0.5% (v/v) plasma from an untreated animal (to maintain a constant proportion of rat plasma constituents). In the same manner, a standard curve was prepared using dilution series of purified Tα1-PAS (used for spiking rat plasma) at defined concentrations. After incubation for 1 h at RT, wells were washed 3 times with PBS/T. To detect bound Tα1-PAS, wells were incubated for 1 h with 50 µl of a 1 µg/mL PBS/T solution of the second anti-PAS antibody conjugated with alkaline phosphatase using the Lightning-Link alkaline phosphatase antibody labeling kit (BioTechne, Wiesbaden, Germany). After washing twice with PBS/T and twice with PBS, the enzymatic activity was detected using p-nitrophenyl phosphate (0.5 mg/mL). To this end, the plate was incubated for 20 min at 30 °C, the absorbance was measured at 405 nm using a SpectraMax M5e microtiter plate reader (Molecular Devices, Sunnyvale, CA, USA) and the Tα1-PAS concentrations in rat plasma samples were quantified by comparison with the standard curve.