Abstract. Effects of the serotonergic anxiolytic buspirone on plasma glucose and glucoseinduced hyperglycemia were studied in mice. Buspirone did not affect plasma glucose levels of non-fasted mice, while it increased serum insulin levels. In fasted mice, buspirone significantly reduced glucose-induced hyperglycemia and enhanced insulin release elicited by glucose. This suggests that buspirone enhances insulin release, resulting in inhibition of glucose-induced hyperglycemia. The major metabolite of buspirone, 1-(2-pyrimidinyl)piperazine (1-PP) increased serum insulin levels and induced a slight hypoglycemia in non-fasted mice. 1-PP decreases glucose-induced hyperglycemia and amplifies insulin release elicited by glucose in fasted mice. Since buspirone is mainly metabolized to 1-PP and formation of 1-PP occurs quickly, the inhibitory effect of buspirone on glucose-induced hyperglycemia is likely mediated by 1-PP.
Benzodiazepine derivatives are widely used for anxiety, by the facilitation of GABA neurotransmission. It is well known that serotonin (5-HT) is involved in several neurological functions.1) The 5-HT 1A receptor is related to emotion and the 5-HT 1A receptor agonists induce anxiolytic and antidepressant effects in humans and animals. 2,3) Buspirone is known to be a 5-HT 1A receptor agonist and is used to treat anxiety.2) Stress induces several neuroendocrinological effects such as activation of the hypothalamus-pituitary-adrenal (HPA) axis and elicits activation of sympathetic tone. 4,5) Hyperglycemic responses to stress are recognized as an index of the sympathetic nervous system. 4) Stress induces changes in emotion and mood. 5) Recently, it was reported that the 5-HT 1A receptor agonist might be effective for stress-induced behavioral depressant symptoms. 2)Previous reports demonstrated that 5-HT receptor is involved in glucose regulation. The 5-HT 1A receptor agonist 8-OH-DPAT elicits hyperglycemia in rats and mice.6,7) The 5-HT 1A receptor partial agonist buspirone and ipsapirone elevate the glucose levels of rats. 8,9) These effects of 5-HT 1A receptor agonists are considered due to facilitating adrenaline release from the adrenal medulla.10,11) However, there may be species differences in the effects of buspirone on glucose levels between rats and mice. We previously reported that buspirone did not elevate glucose levels of mice and it increases serum insulin levels.12) In addition, buspirone reduces glucose-induced hyperglycemia in mice by increasing insulin levels. 12)It is well known that stress elicits hyperglycemia and stress-induced hyperglycemia may be a factor in contributing to diabetes. 4,13) Since buspirone is available in stressed-patients with accompanying with anxiety, the possibility that buspirone may also suppress stress-induced hyperglycemia is postulated. However, it is not clear whether buspirone modifies stress-elevated hyperglycemia. In this paper, we examined the effects of buspirone on stress-induced hyperglycemia and involvement of insulin in the effects of buspirone. MATERIALS AND METHODS AnimalsMale ddY mice weighing 28-32 g were obtained from SLC Japan Inc (Japan). Mice were fed with free access to food and water and they were housed under a controlled 12-h/12-h light-dark cycle (light from 7:00 a.m. to 7:00 p.m.), with room temperature at 23Ϯ1°C and humidity at 55Ϯ5%. For experiments with glucose, mice were fasted for 20 h. The experimental procedure was approved by the Kobe Pharmaceutical University Animal Care and Use Committee.Drug Treatment Buspirone HCl, 1-(2-pyrimidinyl)-piperazine (1-PP) HCl were obtained from Sigma (U.S.A.). Drugs were dissolved in saline. Buspirone and 1-PP were injected s.c. 30 min before immobilization stress.Immobilization and Determination of Plasma Glucose and Insulin Levels Mice were restrained by placing in individual wire cages (3.5 cmϫ8.3 cmϫ2.3 cm). After immobilization for 15, 30, 60 and 120 min, mice were immediately decapitated and blood ...
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