Drugs altering insulin secretion: effects on plasma and brain concentrations of aromatic amino acids and on brain 5-hydroxytryptamine turnover.
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 brain. 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.
D000596:Amino Acids / Q000097:blood / Q000378:metabolism*; D000818:Animals; D001923:Brain Chemistry / Q000187:drug effects*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D007328:Insulin / Q000097:blood / Q000378:metabolism*; D000078790:Insulin Secretion; D008297:Male; D010646:Phentolamine / Q000494:pharmacology; D010649:Phenylalanine / Q000378:metabolism; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D012701:Serotonin / Q000378:metabolism*; D013311:Streptozocin / Q000494:pharmacology; D014044:Tolbutamide / Q000494:pharmacology; D014364:Tryptophan / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism
D000596:Amino Acids; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D012701:Serotonin; D014443:Tyrosine; D010649:Phenylalanine; D006897:Hydroxyindoleacetic Acid; D013311:Streptozocin; D014364:Tryptophan; D014044:Tolbutamide; D011433:Propranolol; D010646:Phentolamine