Effects of dexamethasone on the availability of l-tryptophan and on the insulin and FFA concentrations in unipolar depressed patients

Abstract

Several authors have shown that the availability of l-tryptophan ( l-TRP) in the serum is lower in patients with major depression than in controls. It has recently been reported that the administration of a dose of dexamethasone sufficient to cause cortisol suppression also caused significant decrements in the availability of l-TRP. In order to elucidate the putative pathophysiological mechanisms underlying this decreased l-TRP disposition, the authors examined 37 depressed women categorized according to the DSM-III. l-TRP, the sum of five competing amino acids (CAA), the l-TRP/CAA ratio, and insulin and free fatty acid (FFA) levels were determined both before and after oral administration of 1 mg dexamethasone. The availability of l-TRP was significantly lower in depressed women with melancholia compared with simple major and minor depressives. The baseline disposal of l-TRP was related neither to insulin nor to FFA concentrations Dexamethasone administration significantly reduced the l-TRP and l-TRP/CAA values and increased FFA and insulin levels. Postdexamethasone l-TRP and FFA levels were significantly and positively correlated.