LY248686 is an inhibitor of serotonin (S-hydroxytryptamine; 5-HT) and norepinephrine (NE) uptake in synaptosomal preparations of hypothalamus and cerebral cortex, and 5-HT uptake in human blood platelets, with inhibitor constants near nanomolar concentrations. Upon administration to rats 1 hour before sacrifi ce, LY248686 caused dose-dependent and parallel decreases of 5-HT and NE uptake in hypothalamus homogenates ex vivo. LY248686 is a positive enantiomer and was slightly more potent than its negative isomer, LY248685, as an inhibitor of 5-HT uptake. Both isomers were only weak inhibitors of dopamine (DA) uptake in striatal synaptosomes. The inhibitory effects on 5-HT and NE uptake after a single administration of LY248686 KEY WORDS: Uptake; Inhibitor; Serotonin; Norepineph rineThe extent of inhibition of serotonin (5-hydroxytrypta mine; 5-HT) and norepinephrine (NE) uptake by the tricyclic tertiary amine-containing antidepressant drugs depends on their relative degrees of metabolic N-demethylation. Amitriptyline, an inhibitor of 5-HT and NE uptake in nerve-ending preparations (synap tosomes), is converted in vivo to nortriptyline, a po tent and selective inhibitor of NE uptake, while imipra mine, a selective inhibitor of 5-HT uptake, is converted to desipramine, another potent and selective inhibitor

lit fiuoxetine, the N-demethylated metabolite ."" uoxetine exists in R-and S-enantiomeric fonns. S-Norfluoxetine inhibited serotonin (5-HT) uptake and I'Hlptlroxetine binding to 5-HT uptake sites with a pKi of 7.86 and 8.88 or 14 and 1.3 nM, respectively, whereas l-norfluoxetine was 22 and 20 times, respectively, less pDltnt. R-and S-Norfluoxetine were less potent than the tlmSponding enantiomers of fluoxetine as inhibitors of WMpinephrine uptake and [3HJtomoxetine binding to WMpinephrine uptake sites. Ex vivo studies showed that S-norfluoxetine inhibited 5-HT uptake with an ED50 of 3 "8!kg intraperitoneally, 4.7 mglkg subcutaneously, and lEY WORDS: Fluoxetine; Norfluoxetine; Enantiomers; Strotonin 5-HT; Uptake; Inhibitors Ruoxetine, a selective inhibitor of serotonin (5-hydroxy lIyptamine, 5-HT) uptake (Wong et aI., 1974(Wong et aI., , 1975, has been successfully developed as an antidepressant drug (Feighner 1983;Beasley et al. 1990). Fluoxetine is de ftIoped and is marketed as the racemate, i.e., the R (-) and 5 (+) enantiomers of equal amounts. Both enantiomers inhibit 5-HT uptake and effectively pro duce functional responses associated with an increased S-HT transmission. There are no major differences in potency between R-and S-fluoxetine, and their eudis IIic ratio is close to unity (Wong et al., 1985(Wong et al., , 1990 9 mglkg orally (7.3, 11.4 and 21.9 Jimollkg, respectively), while the ED50 for R-norfluoxetine exceeded 20 mglkg intraperitoneally (48.6 Jimollkg). Inhibition of 5-HT uptake in cerebral cortex ex vivo and decrease in 5-HIAA levels in hypothalamus persisted for 24 hours after administration of S-norfluoxetine as demonstrated with the administration of fluoxetine. Thus, S-norfluoxetine is the active N-demethylated metabolite responsible for the persistently potent and selective inhibition of 5-HT uptake in vivo. Robertson et aI. 1988). Enzymatic N-demethylation is an early step of fluoxetine metabolism, and the de methylated compound norfluoxetine (Fig. 1) is a major metabolite (Parli and Hicks 1974; Lemberger et aI. 1978;Beasley et al. 1990) in laboratory animals and in man. Norfluoxetine is also a potent and selective inhibitor of 5-HT uptake (Wong et aI. 1975; Horng and Wong 1976;Fuller et al. 1978). In the present communication, we report the pharmacologic pro&les of R-and S-norfluox etine, which have been recently synthesized in high enantiomeric purity. In contrast with the two enan tiomers of fluoxetine, however, we have found that S-norfluoxetine is over 20-fold more potent than the R enantiomer as an inhibitor of 5-HT uptake both in vitro and in vivo. MATERIALS AND METHODSMale Sprague-Dawley rats weighing between 100 and 150 g (Harlan Industries, Cumberland, IN) were housed in a room with a 12-hour dark/light cycle at 23°C, and

Duloxetine (LY248686, [+]-N-methyl-3-(1-napthalenyloxy)-2-thiophene-propanamine) is a potent dual inhibitor of serotonin (5-hydroxytryptamine, 5-HT) and norepinephrine (NE) uptake in hypothalamus and cerebral cortex of rat brain (Wong et al. 1993; Fuller et al. 1994). Consistent with the dual mechanisms of inhibiting 5-HT and NE uptake, duloxetine at 15 mg/kg IP produced large increases in extracellular levels of 5-HT (250%) and NE (1,100%) 30 minutes after systemic administration. Levels of 3-methoxy-4-hydroxy-phenylethyleneglycol (MHPG) and 5-hydroxyindoleacetic acid (5-HIAA), metabolites of NE and 5-HT, respectively, were reduced, whereas those of dopamine (DA) and its metabolite 3, 4-dihydroxyphenylacetic acid (DOPAC) were not significantly altered. Duloxetine at 7 mg/kg produced less pronounced increases while no consistent effects were observed at 4 mg/kg. In this dose range, duloxetine inhibited 5-HT uptake in platelets ex vivo without inhibiting striatal dopamine (DA) uptake. In the present study we also found that the primary amine (a racemate) of duloxetine is about one-fourth as active as duloxetine to inhibit 5-HT and NE uptake. The potential primary amine metabolite of duloxetine might contribute, in part, to the inhibition of 5-HT and NE uptake in vivo. Thus the ability to produce robust increases of extracellular 5-HT and NE levels suggests that duloxetine may potentially be a highly effective antidepressant agent.

Anemia was induced in weanling Sprague Dawley rats either by feeding an iron-deficient diet or by chronic phlebotomy. The erythroid regenerative response was then evaluated before and after a hemolytic event, and results were compared with those of a third group of control nonphlebotomized rats fed an iron-replete diet. Diet and phlebotomy groups developed a similar degree of anemia (mean hemoglobin concentration 7.9 g/dL and 7.8 g/dL, respectively; controls, 13.9 g/dL) and hypoferremia (mean serum iron concentration 25.4 microgram/dL and 34.9 microgram/dL, respectively; controls, 222.0 microgram/dL). However, the anemia in diet rats was nonregenerative (reticulocyte count, 83.1 X 10(3) cells/microliter) and associated with bone marrow erythroid hypoplasia; whereas the anemia in phlebotomy rats was regenerative (reticulocyte count, 169.6 X 10(3) cells/microliter) and associated with bone marrow erythroid hyperplasia. Thrombocytosis was seen in diet rats (1,580 X 10(3) cells/microliter) but not phlebotomy rats (901 X 10(3) cells/microliter) when compared with controls (809 X 10(3) cells/microliter). To further evaluate the regenerative capability, phenylhydrazine (PHZ) was administered to induce hemolysis. Erythrocyte mass declined approximately 25% in all groups, including controls. The reticulocytosis (265.3 X 10(3) cells/microliter) seen in phlebotomy rats was earlier and significantly greater than that seen in either diet or control rats. Hemoglobin concentration returned to pre-PHZ concentrations (7.9 g/dL) in phlebotomy rats within 4 days posthemolysis. In diet rats, the maximal regenerative response (176.3 X 10(3) cells/microliter) was not seen until 8 days posthemolysis, and hemoglobin (7.5 g/dL) did not return to pre-PHZ concentrations during the 8-day study. In many aspects, the anemia seen following diet- or phlebotomy-induced iron deficiency was similar. However, the erythroid regenerative capability varied depending on the mechanism by which anemia was induced and furthermore altered the efficiency of hemoglobin production following a hemolytic event. These results suggest that the availability of iron in the diet may modulate the pathogenesis of iron deficiency anemia.

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