Is There a Relationship between Baseline and Treatment-Associated Changes in [3H]-IMI Platelet Binding and Clinical Response in Major Depression?
A peripheral model for the central 5-HT neuron is the characterization of platelet imipramine binding. We studied an outpatient major depressive cohort who fulfilled Research Diagnostic Criteria for agitation. After a 1-week placebo lead-in, subjects were blindly randomized to either imipramine (IMI) of fluoxetine (FLU) during an 8-week, double-blind study period. Thirty-three subjects (15 IMI, 18 FLU) provided both baseline and endpoint samples for the platelet [3H]-IMI assay. Depression efficacy was comparable across the two treatments, whereas FLU was significantly more effective in reducing secondary anxiolysis (p = .023). Discontinuations due to an adverse event were significantly more frequent with IMI than FLU (p < .01). Baseline affinity (KD) was mildly predictive of change in the HAMD (r = -.22; p = .07). Whereas baseline to endpoint density (Bmax) changes (Δ) were similar for IMI (183 ± 329 fmol/mg) and FLU (196 ± 402 fmol/mg), a statistically significant treatment difference in ΔKD emerged (IMI -0.005 ± 0.010 pmol/ml versus FLU 0.08 ± 0.013 at p = .004). Moreover, the changes in KD and HAMD17 trended to a positive correlation among only the FLU-treated subjects (4 = 0.406, p = .095). The Clinical effects of 5-HT-based selective antidepressant may be reflected by dynamic changes in the platelet 5-HT uptake apparatus. These data suggest that the baseline confirmational status of the [3H]-IMI:5-HT transporter may reflect a "capacity" for a treatment response.