Facilitating effect of insulin on brain 5-hydroxytryptamine metabolism.
In this study we investigated the effect of insulin on striatal 5-hydroxytryptamine and tryptamine in streptozotocin-diabetic and in normal rats. Streptozotocin-diabetic rats show a reduction in rat striatal tryptophan, 5-hydroxytryptamine, and 5-hydroxyindole acetic acid, an effect observed at 7 or 14 days after the treatment began. In addition, the accumulation of striatal tryptamine in pargyline-treated rats was reduced at 14 days. Insulin administration produced an increase in rat striatal tryptophan concentration that was observed within 2 h following its administration. By 6 h, however, the striatal tryptophan concentrations were significantly reduced. No changes in rat striatal 5-hydroxytryptamine were observed following the insulin administration, but the treatment induced significant increases in 5-hydroxyindole acetic acid that were observed at 2, 3, 4, and 6 h after insulin administration. The administration of insulin to diabetic rats had a tendency to reverse the decreases in 5-hydroxytryptamine metabolism observed in these animals. Treatment with tryptophan (12-25 mg kg-1) markedly increased rat striatal tryptophan, but did not affect 5-hydroxytryptamine metabolism, an effect that was only observed after the administration of higher doses (50-100 mg kg-1). This is in contrast to the effect of insulin that produces a lesser increase in striatal tryptophan accompanied by an increase in 5-hydroxytryptamine metabolism, indicating that in addition to the increase in tryptophan availability that it produces, it also possesses some other facilitatory effect on 5-hydroxytryptamine metabolism.
D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism*; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000378:metabolism*; D013997:Time Factors; D014363:Tryptamines / Q000378:metabolism; D014364:Tryptophan / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology
D001786:Blood Glucose; D007328:Insulin; D014363:Tryptamines; D012701:Serotonin; C030820:tryptamine; D006897:Hydroxyindoleacetic Acid; C025166:tryptophan ethyl ester; D014364:Tryptophan