Inhibition of insulin secretion by L-thyroxine and D-thyroxine treatment in rats under the influence of drugs affecting the adrenergic nervous system.
Both L-thyroxine and D-thyroxine induced an inhibition of glucose-induced insulin secretion with comparable time- and dose-dependent characteristics. L-thyroxine was ten times more potent than D-thyroxine. While L-thyroxine and a ten times higher dose of D-thyroxine had a similar potency in inducing hyperthermia and hypocholesterolaemia, hyperglycaemia in response to D-thyroxine was less pronounced than in response to L-thyroxine. This difference may be explained by a greater depletion of liver glycogen stores and consequently more limited capacity for provision of glucose for the circulation. The results support the view that the differences between L-thyroxine and D-thyroxine are quantitative. Adrenergic contribution to L-thyroxine- and D-thyroxine-induced inhibition of insulin secretion by rat pancreas is apparently of minor importance. Treatment of the rats with propranolol as well as with reserpine or 6-hydroxydopamine did not alleviate L-thyroxine- or D-thyroxine-induced inhibition of insulin secretion by rat pancreas.
D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D003918:Dextrothyroxine / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005947:Glucose / Q000037:antagonists & inhibitors / Q000494:pharmacology; D006892:Hydroxydopamines / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D008112:Liver Glycogen / Q000378:metabolism; D008297:Male; D016627:Oxidopamine; D010179:Pancreas / Q000294:innervation / Q000378:metabolism; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012110:Reserpine / Q000494:pharmacology; D013564:Sympathetic Nervous System / Q000187:drug effects*; D013974:Thyroxine / Q000494:pharmacology*
D001786:Blood Glucose; D006892:Hydroxydopamines; D007328:Insulin; D008112:Liver Glycogen; D003918:Dextrothyroxine; D012110:Reserpine; D016627:Oxidopamine; D011433:Propranolol; D005947:Glucose; D013974:Thyroxine