A. Martelli et al., LOW CLASTOGENIC ACTIVITY IN-VIVO OF THE N-NITROSO DERIVATIVES OF 5 BETA-ADRENERGIC-BLOCKING DRUGS PROVED TO BE POTENT GENOTOXINS IN-VITRO, Toxicology letters, 73(3), 1994, pp. 185-191
The N-nitroso derivatives formed by the in vitro reaction of 5 beta-ad
renergic-blocking drugs with sodium nitrite and previously found to in
duce DNA fragmentation and repair in primary cultures of both rat and
human hepatocytes were tested for their ability to exert a clastogenic
effect in vivo. In partially hepatectomized rats given by gavage a si
ngle dose of 1000 mg/kg, all 5 N-nitroso derivatives caused a statisti
cally significant increase in the frequency of micronucleated hepatocy
tes, the clastogenic potencies of NO-propranolol, NO-metoprolol, and N
O-nadolol being slightly greater than those of NO-atenolol and NO-sota
lol. In contrast, none of them produced a significant increase in the
frequency of micronucleated polychromatic erythrocytes in the bone mar
row and the spleen. For all 5 N-nitroso derivatives the in vivo clasto
genic potency, i.e. the ratio between the number of micronuclei observ
ed in the liver and the dose administered, was markedly lower than the
in vitro DNA-damaging potency calculated as the ratio between the amo
unt of DNA fragmentation and the concentration tested. This suggests a
preferential detoxification in vivo of the 5 N-nitroso derivatives.