Metabolism of [14C]methamphetamine in man, the guinea pig and the rat

1. The metabolites of (+/-)-2-methylamino-1-phenyl[1-(14)C]propane ([(14)C]methamphetamine) in urine were examined in man, rat and guinea pig. 2. In two male human subjects receiving the drug orally (20mg per person) about 90% of the (14)C was excreted in the urine in 4 days. The urine of the first day was examined for metabolites, and the main metabolites were the unchanged drug (22% of the dose) and 4-hydroxymethamphetamine (15%). Minor metabolites were hippuric acid, norephedrine, 4-hydroxyamphetamine, 4-hydroxynorephedrine and an acid-labile precursor of benzyl methyl ketone. 3. In the rat some 82% of the dose of (14)C (45mg/kg) was excreted in the urine and 2-3% in the faeces in 3-4 days. In 2 days the main metabolites in the urine were 4-hydroxymethamphetamine (31% of dose), 4-hydroxynorephedrine (16%) and unchanged drug (11%). Minor metabolites were amphetamine, 4-hydroxyamphetamine and benzoic acid. 4. The guinea pig was injected intraperitoneally with the drug at two doses, 10 and 45mg/kg. In both cases nearly 90% of the (14)C was excreted, mainly in the urine after the lower dose, but in the urine (69%) and faeces (18%) after the higher dose. The main metabolites in the guinea pig were benzoic acid and its conjugates. Minor metabolites were unchanged drug, amphetamine, norephedrine, an acid-labile precursor of benzyl methyl ketone and an unknown weakly acidic metabolite. The output of norephedrine was dose-dependent, being about 19% on the higher dose and about 1% on the lower dose. 5. Marked species differences in the metabolism of methamphetamine were observed. The main reaction in the rat was aromatic hydroxylation, in the guinea pig demethylation and deamination, whereas in man much of the drug, possibly one-half, was excreted unchanged.     

Metabolism of two PGF2 alpha analogues in primates: 15(S)-15-methyl-delta 4-cis-PGF1 alpha and 16,16-dimethyl-delta 4-cis-PGF1 alpha.

The metabolism of the prostaglandin F2 alpha analogues, 15-methyl-delta 4-cis-PGF1 alpha and 16,16-dimethyl-delta 4-cis-PGF1 alpha, has been investigated in the cynomologus monkey and the human female. The two analogues, tritium labelled in the 9 beta-position, were administered by intramuscular injections into the monkeys and by subcutaneous injections into the human. Excretion of tritium labelled products were followed in urine (in both species) and feces (in monkeys only) and several metabolites were identified by GC/MS. The analogues were found to be resistant to the 15-hydroxy dehydrogenase and furthermore the degradation by beta-oxidation was delayed. About 13% of the given dose of 15-methyl-delta 4-cis-PGF1 alpha was excreted unchanged into urine and feces from the monkey. The corresponding figure for 16,16-dimethyl-delta 4-cis-PGF1 alpha was about 20%. In addition, a large part of the metabolites had the carbon skeleton intact and were only metabolized by omega-oxidation. The relative resistance to degradation of these two analogues is likely to be the basis for their prolonged pharmacological activity.     

Species differences in the metabolism of norephedrine in man, rabbit and rat

1. (+/-)-2-Amino-1-phenyl[1-(14)C]propan-1-ol ([(14)C]norephedrine) was administered orally to man, rat and rabbit and the metabolites excreted in the urine were identified and measured. Pronounced species differences in the metabolism of the drug were found. 2. Three male human subjects, receiving 25mg each of [(14)C]norephedrine hydrochloride, excreted over 90% of the (14)C in the first day. The main metabolite was the unchanged drug (86% of the dose) and minor metabolites were hippuric acid and 4-hydroxynorephedrine. 3. In rats given 12mg of the drug/kg almost 80% of the (14)C administered was excreted in the first day. The major metabolites in the urine were the unchanged drug (48% of the dose), 4-hydroxynorephedrine (28%) and trace amounts of side-chain degradation products. 4. Rabbits given 12mg of the drug/kg excreted 85-95% of the dose of (14)C in the urine in the first 24h after dosing. The major metabolites in the urine were conjugates of 1,2-dihydroxy-1-phenylpropane (31% of the dose) and of 1-hydroxy-1-phenylpropan-2-one (27%) and hippuric acid (20%). The unchanged drug was excreted in relatively small amounts (8%).     

Bioconversion of Stemodia maritima diterpenes and derivatives by Cunninghamella echinulata var. elegans and Phanerochaete chrysosporium

Stemodane and stemarane diterpenes isolated from the plant Stemodia maritima and their dimethylcarbamate derivatives were fed to growing cultures of the fungi Cunninghamella echinulata var. elegans ATCC 8688a and Phanerochaete chrysosporium ATCC 24725. C. echinulata transformed stemodin (1) to its 7alpha-hydroxy- (2), 7beta-hydroxy- (3) and 3beta-hydroxy- (4) analogues. 2alpha-(N,N-Dimethylcarbamoxy)-13-hydroxystemodane (6) gave 2alpha-(N,N-dimethylcarbamoxy)-6alpha,13-dihydroxystemodane (7) and 2alpha-(N,N-dimethylcarbamoxy)-7alpha,13-dihydroxystemodane (8). Stemodinone (9) yielded 14-hydroxy-(10) and 7beta-hydroxy- (11) congeners along with 1, 2 and 3. Stemarin (13) was converted to the hitherto unreported 6alpha,13-dihydroxystemaran-19-oic acid (18). 19-(N,N-Dimethylcarbamoxy)-13-hydroxystemarane (14) yielded 13-hydroxystemaran-19-oic acid (17) along with the two metabolites: 19-(N,N-dimethylcarbamoxy)-2beta,13-dihydroxystemarane (15) and 19-(N,N-dimethylcarbamoxy)-2beta,8,13-trihydroxystemarane (16). P. chrysosporium converted 1 into 3, 4 and 2alpha,11beta,13-trihydroxystemodane (5). The dimethylcarbamate (6) was not transformed by this microorganism. Stemodinone (9) was hydroxylated at C-19 to give 12. Both stemarin (13) and its dimethylcarbamate (14) were recovered unchanged after incubation with Phanerochaete.     

Metabolism of NG,NG-and NG,N'G-dimethylarginine in rats

The metabolic fates of NG,NG-and NG,N'G-dimethylarginines in rats were investigated isotopically and novel metabolites, alpha-keto-delta-(N,N-dimethylguanidino)-and alpha-keto-delta-(N,N'-dimethylguanidino)valeric acids and gamma-(N,N-dimethylguanidino)-and gamma-(N,N'-dimethylguanidino)butyric acids were identified. In the case of the rats injected with NG,NG-dimethyl-L-[1,2,3,4,5-14C]arginine, about 13% of the radioactivity was recovered in the first 12-h urine and was distributed in the following metabolites (relative ratios): unchanged NG,NG-dimethyl-L-arginine (35.2%), gamma-(N,N-dimethylguanidino)butyric acid (18.4%), alpha-keto-delta-(N,N-dimethylguanidino)valeric acid (16.4%), and N alpha-acetyl-NG,NG-dimethyl-L-arginine (8.5%). The radioactivity retained in the tissues was found mainly in citrulline and was further distributed in ornithine, arginine, and glutamic acid and even in protein-bound arginine. In the case of NG,N'G-dimethyl-L-[1,2,3,4,5-14C]arginine-injected rats, about 75% of the radioactivity was excreted in the first 12-h urine and was recovered in the following metabolites (relative ratios): N alpha-acetyl-NG,N'G-dimethyl-L-arginine (48.4%), unchanged NG,N'G-dimethyl-L-arginine (23.7%), alpha-keto-delta-(N,N'-dimethylguanidino)valeric acid (20.2%), and gamma-(N,N'-dimethylguanidino)butyric acid (9.6%). In the tissues, most of the radioactivity was associated with unchanged NG,N'G-dimethyl-L-arginine. These findings show that both dimethylarginines are metabolized by a pathway forming the corresponding alpha-ketoacid analogs and the oxidatively decarboxylated products of the alpha-ketoacids in addition to the N alpha-acetyl conjugates identified previously (K. Sasaoka, T. Ogawa, and M. Kimoto (1982) Arch. Biochem. Biophys. 219, 454-458), and NG,NG-dimethyl-L-arginine is catabolized by an additional pathway leading to the formation of citrulline and its metabolically related amino acids. By considering their catabolism, an attempt to use urinary dimethylarginines as an index of in vivo breakdown of tissue proteins is invalid at least in rats.     

Evaluation of isotope ratio (IR) mass spectrometry for the study of drug metabolism

Isotope ratio (IR) mass spectrometry was evaluated for the study of drug metabolism and balance using 13C, 15N2-labelled antipyrine (AP) as a test drug. Rats were given 40 mg kg-1 (13C,15N2)AP intraperitoneally. Breath, urine, faeces and blood were collected. Except for breath, samples were combusted in sealed quartz tubes. The resulting CO2 and N2 were analysed for excess 13C and 15N, relative to pre-dose samples, by IR mass spectrometry. In addition, blood levels of AP and cumulative excretion of urinary AP metabolites were determined by gas chromatography/mass spectrometry/selected ion monitoring (GC/MS/SIM) and high-performance liquid chromatography (HPLC) respectively. Excess 13C and 15N levels in blood were comparable with observed levels of AP, and urinary recoveries of 13C (42%) were in good agreement with those calculated from HPLC data (45%). N-Demethylation, one of the important pathways of AP metabolism, was most rapidly determined by excess 13CO2 excretion in breath (8%). The IR mass spectral analysis complemented gas chromatographic/mass spectrum and HPLC analyses, and was less complex.     

The metabolic fate of amphetamine in man and other species

1. The fate of [(14)C]amphetamine in man, rhesus monkey, greyhound, rat, rabbit, mouse and guinea pig has been studied. 2. In three men receiving orally 5mg each (about 0.07mg/kg), about 90% of the (14)C was excreted in the urine in 3-4 days. About 60-65% of the (14)C was excreted in 1 day, 30% as unchanged drug, 21% as total benzoic acid and 3% as 4-hydroxyamphetamine. 3. In two rhesus monkeys (dose 0.66mg/kg), the metabolites excreted in 24h were similar to those in man except that there was little 4-hydroxyamphetamine. 4. In greyhounds receiving 5mg/kg intraperitoneally the metabolites were similar in amount to those in man. 5. Rabbits receiving 10mg/kg orally differed from all other species. They excreted little unchanged amphetamine (4% of dose) and 4-hydroxyamphetamine (6%). They excreted in 24h mainly benzoic acid (total 25%), an acid-labile precursor of 1-phenylpropan-2-one (benzyl methyl ketone) (22%) and conjugated 1-phenylpropan-2-ol (benzylmethylcarbinol) (7%). 6. Rats receiving 10mg/kg orally also differed from other species. The main metabolite (60% of dose) was conjugated 4-hydroxyamphetamine. Minor metabolites were amphetamine (13%), N-acetylamphetamine (2%), norephedrine (0.3%) and 4-hydroxynorephedrine (0.3%). 7. The guinea pig receiving 5mg/kg excreted only benzoic acid and its conjugates (62%) and amphetamine (22%). 8. The mouse receiving 10mg/kg excreted amphetamine (33%), 4-hydroxyamphetamine (14%) and benzoic acid and its conjugates (31%). 9. Experiments on the precursor of 1-phenylpropan-2-one occurring in rabbit urine suggest that it might be the enol sulphate of the ketone. A very small amount of the ketone (1-3%) was also found in human and greyhound urine after acid hydrolysis.     

The metabolic fate of (2-14C)folic acid and a mixture of (2-14C)- and (3'',5'',9-3h)-folic acid in the rat.

The metabolism of [2-14C]folic acid over 13 days and a mixture of [2-14C]- and [3',5',9-3h]-folic acid in rats over a 6-day period is described. Both 14C and 3H are excreted in urine over the 6-day period, but 3H and 14C are only detectable in faeces for 2 days. A breakdown product of folic acid labelled with 3H only was found in some urine samples, but no metabolite corresponding to the part of the molecule containing 14C was detected. These experiments show that in the whole animal a substantial portion of orally administered folic acid undergoes scission shortly after administration [Blair Biochem. J. (1957) 68, 385-387] and that the retained folates are a shortage form for folate monoglutamates.     

Metabolism of two PGF2α analogues in primates: 15(S)-15-methyl-Δ4-cis-PGF1α and 16,16-dimethyl-Δ4-cis-PGF1α

The metabolism of the prostaglandin F_2α analogues, 15-methyl-Δ⁴-$\text{cis}$-PGF_1α and 16,16-dimethyl-Δ⁴-$\text{cis}$-PGF_1α, has been investigated in the cynomolgus monkey and the human female. The two analogues, tritium labelled in the 9β-position, were administered by intramuscular injections into the monkeys and by subcutaneous injections into the human. Excretion of tritium labelled products were followed in urine (in both species) and feces (in monkeys only) and several metabolites were identified by GC/MS. The analogues were found to be resistant to the 15-hydroxy dehydrogenase and furthermore the degradation by β-oxidation was delayed. About 13% of the given dose of 15-methyl-Δ⁴-$\text{cis}$-PGF_1α was excreted unchanged into urine and feces from the monkey. The corresponding figure for 16,16-dimethyl-Δ⁴-$\text{cis}$-PGF_1α was about 20%. In addition, a large part of the metabolites had the carbon skeleton intact and were only metabolized by ω-oxidation. The relative resistance to degradation of these two analogues is likely to be the basis for their prolonged pharmacological activity.     

Metabolites of octoclothepin eliminated in human and rat urine

1. Four metabolites and unchanged octoclothepin were extracted with dichloroethane from the urine of humans given octoclothepin. These substances were isolated and purified by column and thin-layer chromatography. 2. By chromatographic, spectrophotometric and polarographic analysis, unchanged octoclothepin and three of the metabolites were identified (noroctoclothepin, noroctoclothepin S-oxide and octoclothepin S-oxide). 3. The presence of glucuronides in human urine was proved. 4. The same metabolites and unchanged octoclothepin were also found in rat urine by chromatography.     

The metabolism of arylazoisoxazolones by rats and dogs

1. When rats were given a single oral dose of the lipid-soluble fungicide 4-(2-chlorophenylhydrazono)-3-methyl[4-(14)C]isoxazol-5-one ([(14)C]drazoxolon), about 75% of the label was excreted in the urine and 13% in the faeces in 96hr. An additional 7% of the radioactivity was recovered as (14)CO(2) in 48hr. 2. About 8% of the label was excreted by rats in the bile in 0-24hr. and an additional 6% was excreted by the same route in 24-48hr. 3. When dogs were given a single oral dose of [(14)C]drazoxolon about 35% of the label was excreted in the urine and a similar amount was excreted in the faeces in 96hr. 4. The major metabolites in the urine of the rat and the dog were identified as 2-(2-chloro-4-hydroxyphenylhydrazono)acetoacetic acid (dog, 14%), the corresponding ether glucosiduronic acid (dog, 12%; rat, 13%) and ester sulphate (rat, 65%). 5. When rats were given a single oral dose of 3-methyl-4-([U-(14)C]phenylhydrazono)isoxazol-5-one about 75% of the label was excreted in the urine and 15% in the faeces in 96hr. The major metabolite in the urine was identified as the ester sulphate conjugate of 2-(4-hydroxyphenylhydrazono)-acetoacetic acid. 6. Reduction of the azo link was of minor quantitative significance. 7. These results are discussed in their relation to species differences in the toxicity of these compounds.     

Decreased rate of metabolism induced by a shift of the double bond in prostaglandin F 2alpha from the delta5 to the delta4 position.

The synthesis of an isomer of prostaglandin F 2alpha,9alpha,11alpha,15(S)-trihydroxyprosta-4-cis,13-transdienoic acid is described. The metabolism of this compound in the rat has been investigated. The rate of degradation by beta-oxidation was slowed down considerably. Thus 10-20% of the injected isomer was excreted in the urine unchanged indicating a longer half-life in the circulation than for prostaglandin F 2alpha. More over 2% was excreted as C20 metabolites, 11-18% as C18 metabolites and 8-15% as C16 metabolites. This relative resistance to degradation by beta-oxidation is of considerable biochemical and pharmacological interest.     

Identification of fendiline metabolites in human urine

After oral application of 14C labelled fendiline, 13 metabolites of this drug could be identified in human urine. Only traces of parent fendiline were excreted in the urine. The main pathway of metabolism is hydroxylation of phenyl groups with subsequent glucuronidation and sulphation. On the other hand, oxidative dealkylation occurs with the amino group remaining at the 3,3-diphenylpropyl moiety and p-hydroxyacetophenone being formed almost entirely from the 1-phenylethyl group.     

Cluster Roots of Leucadendron laureolum (Proteaceae) and Lupinus albus (Fabaceae) Take Up Glycine Intact: An Adaptive Strategy to Low Mineral Nitrogen in Soils?

BACKGROUND AND AIMS: South African soils are not only low in phosphorus (P) but most nitrogen (N) is in organic form, and soil amino acid concentrations can reach 2.6 g kg(-1) soil. The Proteaceae (a main component of the South African Fynbos vegetation) and some Fabaceae produce cluster roots in response to low soil phosphorus. The ability of these roots to acquire the amino acid glycine (Gly) was assessed. METHODS: Uptake of organic N as 13C-15N-Gly was determined in cluster roots and non-cluster roots of Leucadendron laureolum (Proteaceae) and Lupinus albus (Fabaceae) in hydroponic culture, taking account of respiratory loss of 13CO2. KEY RESULTS: Both plant species acquired doubly labelled (intact) Gly, and respiratory losses of 13CO2 were small. Lupin (but not leucadendron) acquired more intact Gly when cluster roots were supplied with 13C-15N-Gly than when non-cluster roots were supplied. After treatment with labelled Gly (13C : 15N ratio = 1), lupin cluster roots had a 13C : 15N ratio of about 0.85 compared with 0.59 in labelled non-cluster roots. Rates of uptake of label from Gly did not differ between cluster and non-cluster roots of either species. The ratio of C : N and 13C : 15N in the plant increased in the order: labelled roots < rest of the root < shoot in both species, owing to an increasing proportion of 13C translocation. CONCLUSIONS: Cluster roots of lupin specifically acquired more intact Gly than non-cluster roots, whereas Gly uptake by the cluster and non-cluster roots of leucadendron was comparable. The uptake capacities of cluster roots are discussed in relation to spatial and morphological characteristics in the natural environment.     

The biochemical pathway for the breakdown of N4-ethyl-L-asparagine in the bacterium Pseudomonas stutzeri.

N4-Ethyl-L-[u-14C]asparagine and L-[U-14C]aspartate give identical metabolites, mainly intermediates of the tricarboxylic acid cycle and related amino acids, in whole cells of Pseudomonas stutzeri. The labelled asparagine derivative is converted into [14C]-aspartate by cell-free extracts, and this reaction, which has an optimum pH of 8.8 +/- 0.2, is neither inhibited by unlabelled asparagine nor enhanced by unlabelled 2-oxoglutarate. No labelled keto acid corresponding to N4-ethylasparagine was detected in either whole cells or cell-free extracts. Thus N4-ethyl-L-asparagine, like asparagine, must be broken down by hydrolysis, at least in this bacterium.     

N6-Trimethyl-lysine metabolism. 3-Hydroxy-N6-trimethyl-lysine and carnitine biosynthesis.

Rats injected with N6-[Me-3H]trimethyl-lysine excrete in the urine five radioactively labelled metabolites. Two of these identified metabolites are carnitine and 4-trimethylammoniobutyrate. A third metabolite, identified as 5-trimethylammoniopentanoate, is not an intermediate in the biosynthesis of carnitine; the fourth and major metabolite, N2-acetyl-N6-trimethyl-lysine, is not a precursor of carnitine. The remaining metabolite (3-hydroxy-N6-trimethyl-lysine) is converted into trimethylammoniobutyrate and carnitine by rat liver slices and into trimethylammoniobutyrate by rat kidney slices. In rat liver and kidney-slice experiments, radioactivity from DL-N6-trimethyl-[1-14C]lysine and DL-N6-trimethyl-[2-14C]lysine was incorporated into N2-acetyl-N6-trimethyl-lysine and 3-hydroxy-N6-trimethyl-lysine, but not into trimethylammoniobutyrate or carnitine. A procedure was devised to purify milligram quantities of 3-hydroxy-N6-trimethyl-lysine from the urine of rats injected chronically with N6-trimethyl-lysine (100 mg/kg body wt. per day). The structure of 3-hydroxy-N6-trimethyl-lysine was confirmed chemically and by nuclear-magnetic-resonance spectrometry [Novak, Swift & Hoppel (1980) Biochem. J. 188, 521--527]. The sequence for carnitine biosynthesis in liver is: N6-trimethyl-lysine leads to 3-hydryxy-N6-trimethyl-lysine leads to leads to 4-trimethylammoniobutyrate leads to carnitine.     

13C n.m.r. studies of gluconeogenesis in rat liver suspensions and perfused mouse livers

Our early 31P n.m.r. studies of compartmentation in suspensions of rat liver cells have been extended by following fructose-1-phosphate peaks, known to be in the cytosol, which gave the same pH as the Pi peak previously assigned to the cytosol. Gluconeogenesis have been followed from [13C]glycerol labelled at C1,3 or at C2 and from labelled [3-13C]alanine. With the glycerol substrate it was possible to follow the label into alpha-glycerophosphate and to determine its distribution in the glucose formed. To a first approximation (i.e. 90%) the glucose level could be followed from its original glycerol position, e.g. [1,3-13C]glycerol to strongly labelled positions 1, 3, 4 and 6 of glucose. Slightly more than 10% of the label was scrambled (i.e. 10% movement of C2 to C1 and ca. 10% of C1 was lost, the remainder being unchanged). These are consistent with a flux through the pentose shunt, dominated by the transketolase pathway. With [3-13C]alanine, about 14 resonances are assigned to different carbons of the intermediates beta-hydroxybutyrate, acetoacetate, lactate, pyruvate, glutamate, glutamine, asparate, as well as C2-alanine, while another 7 resonances are observed from the different anomeric carbons of glucose. The effects of thyroid hormone treatment of the rats upon numerous in vivo rates are clearly observed and will be illustrated.     

The metabolism of four sulphonamides in cows

1. The metabolism of sulphanilamide, sulphadimidine (4,6-dimethyl-2-sulphanilamidopyrimidine), sulphamethoxazole (5-methyl-3-sulphanilamidoisoxazole) and sulphadoxine (5,6-dimethoxy-4-sulphanilamidopyrimidine) given by intravenous injection has been examined in cows. 2. The sulphonamides were present mainly as unchanged drugs in blood samples collected 2h after administration. 3. The sulphonamides were excreted in the milk partly as unchanged drugs and partly as conjugated metabolites whereas only small amounts were excreted as the N(4)-acetyl derivatives. 4. The unchanged drug and the N(4)-acetyl derivative were the major constituents in urine samples after administration of sulphanilamide, sulphamethoxazole and sulphadoxine. 5. Besides the unchanged drug, the N(4)-acetyl derivative and the conjugated metabolites, three further metabolites of sulphadimidine were isolated from urine samples and identified. They were 5-hydroxy-4,6-dimethyl-2-sulphanilamidopyrimidine, 4-hydroxymethyl-6-methyl-2-sulphanilamidopyrimidine and sulphaguanidine.     

The metabolism of N-triphenylmethylmorpholine in the dog and rat

1. Rats were given N-triphenyl[(14)C]methylmorpholine, triphenyl[(14)C]carbinol, N-triphenylmethyl[G-(3)H]morpholine or [G-(3)H]morpholine as single oral doses; the routes of excretion were examined. 2. Dogs were given single oral doses of N-triphenyl[(14)C]methylmorpholine. 3. (14)C-labelled metabolites were excreted mainly in the faeces in both rats and dogs; no (14)CO(2) was expired and less than 3% remained in the carcass and skin after 96hr. 4. (3)H-labelled metabolites were excreted rapidly in urine; part of the label was found in the expired gases and over 10% remained in the carcass and skin after 96hr. 5. Differences in excretion pattern between the sexes were noticed in rats but not in dogs. 6. N-Triphenylmethylmorpholine was rapidly hydrolysed to form triphenylcarbinol and morpholine in the stomach; morpholine was absorbed rapidly and excreted largely unchanged, though some was degraded, since some of the (3)H was found in water. 7. Triphenylcarbinol was absorbed only slowly and was oxidized to p-hydroxyphenyldiphenylcarbinol. 8. Both triphenylcarbinol and its p-hydroxy derivative were found in urine, bile and faeces in the free form and conjugated with glucuronic acid. The proportion of conjugates was higher in rat bile than in faeces. 9. Traces of o-hydroxyphenyldiphenylcarbinol and m-hydroxyphenyldiphenylcarbinol were detected as metabolites both free and conjugated.     

The synthesis of [14C]streptozotocin and its distribution and excretion in the rat

[(14)C]Streptozotocin was synthesized specifically labelled at three positions in the molecule. The biological activity of synthetic streptozotocin was characterised by studies in vivo of its diabetogenic activity and its dose-response curves. After this characterization the excretion pattern of all three labelled forms of streptozotocin was studied. With [1-(14)C]streptozotocin and [2'-(14)C]streptozotocin the injected radioactivity was excreted (approx. 70% and 80% respectively) mainly in the urine, the greater part of the excretion occurring in the first 6h period; small amounts (approx. 9% and 8% respectively) were found in the faeces. In contrast, with [3'-methyl-(14)C]streptozotocin a much smaller proportion (approx. 42%) of the injected radioactivity was excreted in the urine, the major proportion appearing in the first 6h, whereas approx. 53% of the injected radioactivity was retained in the carcasses. In whole-body radioautographic studies very rapid renal clearance and hepatic accumulation of the injected radioactivity was observed with all three labelled forms of the drug. There was some evidence for biliary and intestinal excretion. Major differences were apparent in the tissue-distribution studies, with each of the three labelled forms, particularly with [3'-methyl-(14)C]streptozotocin. There was no accumulation of [1-(14)C]streptozotocin in the pancreas for the 6h period after administration. However, with [3'-methyl-(14)C]streptozotocin (and also [2'-(14)C]streptozotocin) there was evidence of some pancreatic accumulation after 2h. The results indicate that streptozotocin is subjected to considerable metabolic transformation and to rapid renal clearance. The implication of these suggestions is evaluated with particular reference to the diabetogenic action of streptozotocin.