A compound's toxicological property has been linked to metabolic pathways, which often differ in various species. For that reason the correlation between toxicity and metabolism has been observed to obtain a clear insight into cellular metabolism, both in vitro and in vivo conditions. In vitro experiment In vitro studies on liver preparations from rats and other rodents revealed that hydroxylation is the major process during the metabolism of NRB. Furthermore, the metabolites between the sexes of the rat seemed to deviate from one another. First and foremost when NRB had been incubated with the liver S9 fraction, a few metabolic products were observed. The S9 fraction has been defined as "Supernatant fraction obtained from an organ (usually liver) homogenate by centrifuging at 9000 g for 20 minutes in a suitable medium; this fraction contains cytosol and microsomes." The S9 fraction consists of two components: the microsomes component which incorporates cytochrome P450 isoforms (phase I metabolism) and the cytosolic component which contains transferases (phase II metabolism). A mixture of four active endo-isomers of NRB (U, V, W en Y) formed four major metabolites in rat liver S9 and cytosolic preparations after incubation. The isomers are separately not pure compounds, but research with pure V isomer and a mixture of U and V isomers pointed out that each isomer undergoes metabolism to be formed into a single product in rat. Mass spectrometry confirmed that all metabolites had a mass consistent with a hydroxylated metabolite of NRB. Because female rats are more sensitive to NRB than the male species, the level of metabolites are higher in females than in males. The same metabolites were found in guinea pigs, although the levels of metabolism in these rodents are considerately lower compared to those in rats. In mice two metabolites were detected: one metabolite of the V isomer (V1) which was also found in the rat preparations and another, new metabolite of the V isomer (V2). (Figure 7.1) These data acknowledge the link between the susceptibility to NRB and the production of different types and different levels of metabolites. In vivo experiment After collecting blood from rats 10 and 30 minutes after oral administration, plasma and red blood cell fractions were analyzed in search for either parent compounds or hydroxylated metabolites. However, neither were found, which either means that the absorption did not take place or the compounds underwent a quick clearance from the body. Whole blood samples certainly showed traces of the parent compound and a metabolite (M3) with molecular mass of 226, in samples from both female and male rats. The level in which this metabolite occurred, appeared to be once again higher in the female rats than in the male species. M3 was not found in any other rat or mouse tissue. This suggests that M3 may be formed by gut microflora in rats. After NRB had orally been administered, an examination of both rat and mouse liver revealed traces of the parent compound. Comparing the metabolite levels in both sexes and species, a significantly higher amount was discovered in the female rats than in the male rats or the mice. HPLC chromatograms liver preparations from female of and male rats, display the detection of four metabolites (U1, V1, M1, M2). (Figure 7.2) Mass spectrometry had been used to identify these and easily so, because the hydroxylated metabolites were +16 amu higher than NRB. These studies confirmed that the metabolites were identical to those found in the in vitro preparations. The metabolites were not found in mouse liver preparations. Moreover, neither NRB parent compound nor its metabolites were discovered in the heart after oral administration in rats as well as mice. This lack of detectable metabolites implies that NRB is able to induce a lethal effect at extremely low levels.
Norbormide
Nandrolone caproate
Nandrolone
Norethandrolone
Nandrolone hydrogen succinate
Nandrolone propionate
Nandrolone sulfate
Oxandrolone