EFFECTS OF TREATMENT WITH A LITHIUM IMIPRAMINE COMBINATION ON COMPONENTS OF ADENYLATE-CYCLASE IN THE CEREBRAL-CORTEX OF THE RAT

This study was aimed at investigating the effects of treatment with a lithium-imipramine combination on the activity of adenylate cyclase in membranes from the cerebral cortex of the rat. Treatment with (1) lithium for 2 weeks, yielding a level of lithium in serum of 0.54 ± 0.12 mmol/l, (2) imipramine for 4 weeks (10mg/kg i.p. twice per day) and (3) a combination of the two drugs reduced isoprenaline-induced stimulation of adenylate cyclase by GTP, with a greater decrement with the combined treatment. None of the treatments exerted any effect on the activity of the enzyme stimulated by GTP alone. Lithium ex vivo inhibited the calcium (Ca2+)- and Gpp(NH)p-stimulated activity of adenylate cyclase, but imipramine ex vivo did not affect the activity of adenylate cyclase, stimulated by these activators. The lithium-imipramine treatment reduced Ca2+- and Gpp(NH)p-stimulated activity of adenylate cyclase, but this was not different from that observed in the lithium-treated group. In conclusion, the β-adrenoceptor-stimulated adenylate cyclase was affected markedly by administration of lithium and imipramine together. In contrast to lithium ex vivo, imipramine ex vivo did not impair the activity of either the guanine nucleotide regulatory protein or the catalytic subunit, since no change in activity was observed in the presence of β,γ-imidoguanosine-5' triphosphate (Gpp(NH)p) or Ca2+. Furthermore, lithium ex vivo exerted its post-receptor effects on the adenylate cyclase, independent of imipramine. The decrement in activity of β-adrenergic adenylate cyclase, induced by administration of the two drugs together may partly be involved in the therapeutic action of the augmentation of antidepressants by lithium in refractory depression. © 1990.