1. T.l.c. of the 24-48 h urine of rats dosed with 4-aminobiphenyl (ABP) showed that 4-acetylaminobiphenyl (AABP), 4'-hydroxy-4-aminobiphenyl(4'-hydroxy-ABP), 2'-hydroxy-4-acetylaminobiphenyl(2'-hydroxy-AABP), 4'-hydroxy-4-acetylaminobiphenyl(4'-hydroxy-AABP), 3'-hydroxy, 4'-methoxy-4-acetylaminobiphenyl (3'-hydroxy-4'methoxy-AABP), 4'-hydroxy, 3'-methoxy-4-acetylaminobiphenyl (4'-hydroxy-3'-methoxy-AABP), and 3',4'-dihydroxy-4-acetylaminobiphenyl(3',4'-dihydroxy-AABP) are urinary metabolites. Neither 4-nitrosobiphenyl(nitroso-BP) nor N-hydroxy-4-acetylaminobiphenyl(N-hydroxy-AABP) were detected. 2. Radiochromatography of the 48-h urine of rats dosed with 14C-ABP gave three fractions, U1, U2 and U3 containing 34.6%, 38.8% and 20.4%, respectively, of the total 14C. The conjugated metabolites of ABP were found in U1 and U2, and the unconjugated metabolites in U3, indicating that 80% of the 14C activity in urine was in conjugated, and only 20% in unconjugated metabolites. 3. Rechromatography of U3 gave six radioactive bands from which the following metabolites were isolated and identified as being 4'-hydroxy-AABP, 3'-hydroxy-4'-methoxy-AABP, 4'-hydroxy-3'-methoxy-AABP, 3',4'-dihydroxy-AABP, AABP, ABP, 4,4'-bisazoxybiphenyl (BABP) and 4-(4-aminophenyl)-1,2-benzoquinone. Neither nitroso-BP nor N-hydroxy-AABP were detected.

1. Rats dosed with nitrosobenzene (56 mumol/kg), 4-chloronitrosobenzene (53 mumol/kg), 3,4-dichloronitrosobenzene (53 mumol/kg), 4-ethoxynitrosobenzene (86 mumol/kg), 4-nitrosobiphenyl(nitroso-BP, 55 mumol/kg) or 2-nitrosofluorene (256 mumol/kg) had maximal ferrihaemoglobin (HbFe3+) concn of 69, 68, 69, 67, 55 and 42% after 15, 25, 48, 35, 80 and 115 min, respectively, indicating differences in solubility of the nitrosoarenes in body fluids. 2. Nitroso-BP and 3-hydroxy-4-aminobiphenyl (3-hydroxy-ABP) catalytically oxidized HbFe2+ in bovine erythrocytes in vitro; nitroso-BP was three times as active as 3-hydroxy-ABP. 3',4'-Dihydroxy-4-aminobiphenyl (3',4'dihydroxy-ABP) showed only low catalytic activity, and seven other ABP metabolites exhibited only marginal activity. 3. Nitroso-BP was inactive in solutions of purified human Hb, but 3-hydroxy-ABP catalytically oxidized HbFe2+, indicating that nitrosoarenes oxidize HbFe2+ in erythrocytes in vitro and in vivo by a mechanism different from that of o-aminophenols. The second-order rate constant for HbFe2+ oxidation by 3-hydroxy-ABP at 37 degrees C was k2 = 19.1 +/- 1.31/mol per s.

1. N-Hydroxy-4-aminobiphenyl (N-hydroxy-ABP) reacts with HbFe2+ of rat blood in vitro at a molar ratio of 1:47 to produce 20% HbFe3+ within 1 min; N-hydroxy-ABP oxidized 9.4 equiv. of HbFe2+. N-hydroxy-ABP rapidly disappeared and HbFe3+ was reduced at a rate of 44 microM/min. 2. On titration of rat blood in vitro with N-hydroxy-ABP up to 0.81 mM, 4-nitrosobiphenyl (nitroso-BP) disappeared within 5 min; with concn of N-hydroxy-ABP greater than 0.81 mM, N-hydroxy-ABP was present also as nitroso-BP, indicating saturation of reactive binding sites. When N-hydroxy-ABP reacted with HbFe2+ at a molar ratio of 1:103 to 1:1.9, 13 to 1.3 equiv. of HbFe3+ were formed per mol of N-hydroxy-ABP in 5 min, indicating that with increasing N-hydroxy-ABP concn side-reactions increased. 3. After incubation of N-hydroxy-ABP (1.72 mM) with rat Hb (7.66 mM HbFe2+), nitroso-BP disappeared with a half-life of 1 min, maximal HbFe3+ of 72% occurred at 47 min, and the concn of 4-aminobiphenyl (ABP) increased at a rate of 51 nmol/ml per h. 4. In rats injected with 0.24 mmol/kg ABP, HbFe3+ concn plateaued at 56% after 75 min, indicating an equilibrium between HbFe3+ formation and HbFe3+ reduction. Such equilibrium was simulated by titrating rat blood in vitro with N-hydroxy-ABP for 1 h. 5. The long-lasting HbFe3+ formation by ABP in rat results from a cycle of activation of ABP to N-hydroxy-ABP, its rapid co-oxidation with HbFe2+ to form HbFe3+ and nitroso-BP, and binding of nitroso-BP to erythrocyte thiol groups. ABP is released from the Hb adduct and enters a new cycle of activation and inactivation, until terminated by ring-hydroxylation.

1. 3H-4-Aminobiphenyl (ABP, 5 mg) given i.p. to rat had elimination half-lives of 15.6, 17 and 17 h, respectively, for urinary, faecal and total 3H elimination. 14C-ABP administered orally to rats at 100 mg/kg gave elimination half-lives of 31, 36.7 and 34 h, respectively, for urinary, faecal and total 14C elimination. 2. Semi-log plots of percentage dose remaining in the body versus time indicated that: (i) 82% of 3H activity was excreted in 36 h with a half-life of 14.4 h and 18% with a half-life of 46.2 h, and (ii) 77% of 14C activity was excreted in 48 h with a half-life of 15 h and 23% with a half-life of 180 h. 3. After i.p. injection of 10 mg/kg 14C-ABP to rats, ferrihaemoglobin (HbFe3+) concn increased to 60% in 2 h, accompanied by accumulation of 14C activity in erythrocytes, indicating that the active metabolite, N-hydroxy-4-aminobiphenyl (N-hydroxy-ABP) had oxidized haemoglobin-Fe2+ (HbFe2+) and was bound to the erythrocyte. 4. ABP given i.p. to rats at 0.24 mmol/kg rapidly appeared in blood, disappeared with a half-life of 30 min, and blood concn plateaued at 30 nmol/ml. The concn of 4-acetyl-aminobiphenyl (AABP) plateaued at 17 nmol/ml after 15 min, indicating a dynamic equilibrium between N-acetylation of ABP and N-deacetylation of AABP. The concn of 4'-hydroxy-4-acetylaminobiphenyl (4'-hydroxy-AABP) increased slowly at 1.65 nmol/h. 5. AABP given i.p. to rats at 0.88 mmol/kg slowly appeared in the blood, accompanied by the appearance of ABP and 4'-hydroxy-AABP and formation of HbFe3+. After 4 h the concn of AABP and ABP was 27-35 mmol/ml, indicating a dynamic equilibrium between N-deacetylation of AABP and acetylation of ABP. Neither N-hydroxy-ABP nor N-hydroxy-4-acetylaminobiphenyl (N-hydroxy-AABP) were found.