An investigation was undertaken to study the kinetics and
possible cellular control mechanisms for imipramine HCl metabolism
in the isolated perfused rat liver. The isotope ¹⁴C-imipramine
was used and quantification was done by liquid scintillation
counting. Analysis for imipramine (IMI), desmethylimipramine
(DMI), free hydroxy (OH), glucuronide (G) and N-oxide (N-0)
metabolites was done on the perfusate, bile and liver.
The rate of IMI metabolism was found to be dependent on
two major enzymatic routes, N-demethylation (formation of DMI)
and aromatic hydroxylation (formation of G, OH) of imipramine
and one minor enzymatic route, N-oxidation (N-O). The rate of
aromatic hydroxylation of IMI was found to be inhibited after
thirty minutes, with IMI concentration 2 X 10 ⁻⁵M. This inhibition
of aromatic hydroxylation could not be detected if the perfusate
half-life for IMI (t½=18.5 minutes) was the only parameter
monitored. After incubation periods of fifteen, thirty and sixty 80 per cent and the remainder of IMI was in the perfusate. The dose of IMI was varied (0.5 X 10⁻⁵ M, 1 X 10⁻⁵ M and 2 X 10⁻⁵ M)
for metabolism by the perfused rat liver. The incubation time
was kept constant at fifteen minutes. The rate of imipramine
metabolism (formation of DMI and GOH) followed first order kinetics when the dose of IMI was 0.5 X 10⁻⁵ M or 1 X 10⁻⁵ M. Increasing
the dose of IMI to 2 X 10⁻⁵ M slightly suppressed the formation
of DMI and the formation of GOH followed zero order kinetics.
It was found that the endogenous DMI formed from IMI metabolism
inhibited the formation of GOH after fifteen minutes and
thirty minutes of IMI metabolism as shown by the following results.
DMI (1.65, 3.33, 6.66 or 13.32 X 10⁻⁶ M) was preincubated prior
to addition of IMI. DMI (1.65 or 3.33 X 10⁻⁶ M) was found to
specifically inhibit aromatic hydroxylation of IMI. Higher concentration of DMI (6.66 or 13.32 X 10⁻⁶ M) inhibited the formation
of GOH and DMI. Ethyl alcohol (1 mM) preincubated prior to addition
of 1 X 10⁻⁵ M of IMI specifically inhibited DMI formation. No
inhibition of GOH occurred. Ethyl alcohol (1 mM) caused inhibition
of formation of DMI from IMI metabolism when the dose of IMI was
2 X 10⁻⁵ M. The incubation time for IMI metabolism was fifteen
and sixty minutes. With this decrease of DMI formation, the
formation of GOH increased after fifteen or sixty minutes
of incubation time. From these experiments it was concluded that
suppression of aromatic hydroxylation of imipramine was due to
the formation of endogenous DMI formed from IMI metabolism.
Optimal conditions were found to study possible cellular control mechanisms for IMI metabolism in the isolated perfused
rat liver. The dose of IMI was 1 X 10⁻⁵ M and the incubation
time was fifteen minutes. Dibutyryl cyclic AMP (2 X 10⁻⁶ M) caused
inhibition of IMI metabolism. DMI formation was inhibited 28 per
cent while GOH formation was inhibited 29 per cent. NADPH (1.1 X
10⁻⁶ M) or NADH (1.3 X 10⁻⁶ M) was found to inhibit imipramine
metabolism. GOH and DMI were both inhibited. Succinic acid
(1.6 X 10⁻³ M) was found to inhibit DMI formation but not GOH. / Medicine, Faculty of / Anesthesiology, Pharmacology and Therapeutics, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/41271 |
| Date | January 1973 |
| Creators | Moldowan, Mervin John |
| Publisher | University of British Columbia |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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