In vivo quantification of renal sulfate and glucuronide conjugation in the chicken

A Specific Activity Difference Ratio (SADR) technique was developed to quantify simultaneously the in vivo sulfate and glucuronide conjugation in the kidneys. In man and the chicken, p-nitrophenol (PNP) is excreted almost entirely in the urine, where it is present as the sulfate and glucuronide conjugates. Measurements of the SADR's for p-nitro[14C]phenyl sulfate (14C-PNPS) and p-nitro[14C] phenyl glucuronide (14C-PNPG) in the fasted, unanesthetized chicken during the infusion of 14C-PNP at a rate of 100 nmol/min/kg, revealed that a minimum of 38% of the conjugation of PNP occurred in the kidneys. 14C-PNPS accounted for virtually all of the nephrogenic conjugates. Catechol, which is known to compete with PNP for renal conjugation, was used to test the validity of the SADR technique. During catechol infusion into the renal portal circulation of one kidney, the renal tubular conjugation and excretory transport of 14C-PNP decreased essentially to zero, as did the SADR for 14C-PNP conjugates, suggesting that the SADR technique is a valid indicator of in vivo renal conjugation.