Adrenalectomy: its effects on systemic tryptophan metabolism in normal and protein malnourished rats

Rats born to dams fed either a low protein diet (8% casein) or a normal diet (25% casein) started 5 weeks prior to conception and continued through lactation were bilaterally adrenalectomized or received a sham-operation at 30 days of age. At 60 days of age, the systemic tryptophan metabolism of th 8% and 25% adrenalectomized rats was compared to the sham-operated controls of each diet group. While adrenal ablation produced significant decreases in the brain serotonin and metabolite concentrations and marked increases in brain tryptophan concentrations for both diet groups compared to their respective controls, these substances remained significant higher in all malnourished rats than in the well-nourished groups. Also, the major modulator of the peripheral metabolic pathways which regulates the availability of free plasma tryptophan (total tryptophan, albumin, and nonesterified fatty acid concentrations) was the nutritional status of the rats rather than their treatment condition. Only plasma corticosterone concentrations showed changes (significantly decreases) as a consequence of adrenal ablation for either diet group. Overall, the data indicated that under physiological conditions the adrenal cortex has an important function in determining brain tryptophan utilization, whereas its role in regulating peripheral tryptophan metabolism is minimal.