Hyperglycemia induced by the 5-HT receptor agonist, 5-methoxytryptamine, in rats: involvement of the peripheral 5-HT2A receptor.
The effects of the 5-HT receptor agonist, 5-methoxytryptamine, on plasma glucose levels were investigated in rats. 5-Methoxytryptamine induced a significant hyperglycemia above the dosage of 1 mg/kg. 5-Methoxytryptamine-induced hyperglycemia was antagonized by pretreatment with the 5-HT1 and 5-HT2 receptor antagonist, methysergide, or the 5-HT2A receptor antagonist, ketanserin, whereas the 5-HT3 and 5-HT4 receptor antagonist, tropisetron, and the 5-HT4 receptor antagonist, SDZ 205-557 (2-methoxy-4-amino-5-chloro-benzoic acid 2-(diethylamino) ethyl ester), showed no effect. In addition, the peripheral 5-HT2 receptor antagonist, xylamidine, reduced 5-methoxytryptamine-induced hyperglycemia. These results suggest that 5-methoxytryptamine-induced hyperglycemia is mediated by the peripheral 5-HT2A receptor, although it has a high affinity for the 5-HT4 receptor. Adrenodemedullation abolished the 5-methoxytryptamine-induced hyperglycemia. 5-Methoxytryptamine did not affect the blood levels of the pancreatic hormones, insulin and glucagon. The hyperglycemia induced by 5-methoxytryptamine was not affected by pretreatment with dexamethasone which inhibits corticosterone release. These results indicate that 5-methoxytryptamine-induced hyperglycemia is elicited by a facilitated adrenaline release from the adrenal gland. Therefore, it is suggested that the 5-HT2A receptor may be partly involved in the pharmacological effects induced by the 5-HT4 receptor agonist, 5-methoxytryptamine.
Yamada
J
J
Department of Pharmacology, Kobe Pharmaceutical University, Japan.
Sugimoto
Y
Y
Yoshikawa
T
T
Horisaka
K
K
D008735:5-Methoxytryptamine / Q000494:pharmacology*; D000313:Adrenal Medulla / Q000502:physiology; D000818:Animals; D001786:Blood Glucose / Q000032:analysis*; D003907:Dexamethasone / Q000494:pharmacology; D005934:Glucagon / Q000097:blood; D007328:Insulin / Q000097:blood; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D044402:Receptor, Serotonin, 5-HT2A; D011985:Receptors, Serotonin / Q000187:drug effects* / Q000502:physiology; D012702:Serotonin Antagonists / Q000494:pharmacology*; D017366:Serotonin Receptor Agonists / Q000494:pharmacology*
D001786:Blood Glucose; D007328:Insulin; D044402:Receptor, Serotonin, 5-HT2A; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D008735:5-Methoxytryptamine; D003907:Dexamethasone; D005934:Glucagon