Article date: July 1977
By: G. CURZON, J.C.R. FERNANDO in Volume 60, Issue 3, pages 401-408
1 An investigation was made into the effects of drugs which alter insulin secretion on the concentrations of tryptophan and other aromatic amino acids in plasma and brain and on 5‐hydroxytryptamine (5‐HT) and 5‐hydroxyindoleacetic acid (5‐HIAA) in train. Drugs used were streptozotocin, propranolol, tolbutamide and phentolamine.
2 Tolbutamide and phentolamine increased the plasma insulin concentrations by 100% and 300% respectively but with little effect on the brain/plasma ratios for the aromatic amino acids. Previously propranolol was found to decrease plasma insulin by 50% without altering the above ratios. The ratios were decreased by streptozotocin but only when plasma insulin fell by more than 50%.
3 Phentolamine and propranolol did not alter the brain/plasma ratios for the aromatic amino acids in streptozotocin‐treated rats.
4 The results suggest that only large changes of insulin secretion e.g. those associated with food intake or aminophylline injection are likely to alter appreciably the brain/plasma ratios for the aromatic amino acids.
5 Tolbutamide displaced tryptophan from its binding to plasma albumin and increased brain 5‐HIAA probably by inhibiting 5‐HIAA efflux from brain. The other drugs did not alter brain 5‐HT or 5‐HIAA concentrations.
DOI: 10.1111/j.1476-5381.1977.tb07515.x
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