Effects of ornithine alpha-ketoglutarate on insulin secretion in rat pancreatic islets: implication of nitric oxide synthase and glutamine synthetase pathways.
Ornithine alpha-ketoglutarate (OKG) administration in human subjects elicits insulin secretion. We investigated whether this action was related to an effect of OKG on islets of Langerhans, and addressed the underlying mechanisms of action. For this purpose the influence of OKG on insulin secretion was measured in isolated rat islets of Langerhans under two different conditions. In incubated islets, OKG (0.25 to 2.5 mmol/l) significantly and dose-relatedly increased insulin secretion (1.7- to 4.2-fold; P<0.05 v. basal). To study the kinetics of OKG-stimulated insulin secretion, perifusion experiments were performed, which showed that OKG affected insulin secretion in both initial and later phases. Experiments using alpha-ketoglutarate (alpha-KG) (1 mmol/l) or ornithine (Orn) (2 mmol/l) alone, in concentrations equal to that of OKG, showed that the OKG-induced insulin secretion could not be obtained by either component alone, suggesting that an alpha-KG-Orn interaction is mandatory for the insulin-secreting effect to occur. Since data obtained in vivo suggest that effects of OKG may depend on the synthesis of NO, glutamine and/or polyamines, three metabolic pathways potentially involved in insulin secretion, we then evaluated their contribution by means of their respective inhibitors: l-NG-nitroarginine methyl ester (l-NAME), methionine sulfoximine (MSO) and difluoromethylornithine (DFMO). Both l-NAME and MSO were able significantly to reduce OKG-induced insulin secretion (30 and 40 % respectively; P<0.05), while DFMO was ineffective. Thus OKG is an effective stimulator of insulin secretion, requiring the joint presence of both Orn and alpha-KG, and acting mainly via the synthesis of NO and glutamine. A better understanding of OKG insulino-secretory properties and its mechanisms of action are a prerequisite for its use in insulin-compromised situations.
Schneid
Christina
C
INSERM U-341, Service de Diabètologie, Hôpital Hôtel-Dieu, Paris, France.
Darquy
Sylviane
S
Cynober
Luc
L
Reach
Gérard
G
De Bandt
Jean-Pascal
JP
D000818:Animals; D046508:Culture Techniques; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008717:Methionine Sulfoximine / Q000494:pharmacology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009952:Ornithine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000187:drug effects*; D013268:Stimulation, Chemical
D004791:Enzyme Inhibitors; D007328:Insulin; D008717:Methionine Sulfoximine; C002118:ornithine alpha-ketoglutarate; D009952:Ornithine; D019001:Nitric Oxide Synthase; D005974:Glutamate-Ammonia Ligase; D019331:NG-Nitroarginine Methyl Ester