LETTERS
Letters
Sirs,
Platelet monoamine uptake in depressionprimary o r secondary phenomenon?
Recent studies in biological psychiatry have focused extensively on peripheral amine receptor function and radioligand binding. The difficulty with interpreting changes noted is their relationship to central receptor function. Professor Turner has rightly drawn attention to this dilemma when he suggested that perhaps the decrease in V, , , of platelet serotonin uptake in depression is related to excessive cortisol secretion also observed in that disorder (Turner, 1986). He cites recent pharmacological evidence to show that this maybe the case. Both ACTH, which stimulates cortisol release from the adrenal cortex, and the synthetic glucocorticoid dexamethasone cause a reduction in V,,, of platelet 5-HT uptake (Chan and Lee, 1985). In contrast adrenalectomy , which will reduce cortisol concentrations, rather than increasing V,,,, causes a reduction (Tukianen, 1981; Lee and Chan, 1984). Furthermore the role of glucocorticoids in modulating this effect was confirmed in experiments which showed that triamcinolone but not deoxycorticosterone restored active uptake of 5-HT, with a V,,, approaching that of sham operated animals (Lee and Chan, 1984). These studies argue against an inverse relationship between V,,, of 5-HT uptake and corticosteroid concentrations. Clinical studies of this relationship are sparsely reported in the literature. One study which impinges on this issue examined platelet 5HT uptake characteristics in dexamethasone suppressors and non-suppressors of plasma cortisol (Meltzer et al, 1983). Both suppressors and non-suppressors had significantly reduced V,,, values compared to controls, but neither K, of V,,, were significantly different between suppressors and non-suppressors. While one study does not refute a hypothesis the evidence of an epiphenomenon is not supported. Dr. Healy's comments (Healy, 1986) are pertinent: the study of peripheral receptor function is valid, even if an epiphenomenon, since they maybe statedependent or yield diagnostic correlates. At the same time the problem of the relationship to central receptor changes (if any) remains.
Yours faithfully,