L-arginine-induced growth hormone secretion is not influenced by co-infusion of the nitric oxide synthase inhibitor N-monomethyl-L-arginine in healthy men.
In animals, it has been demonstrated that nitric oxide (NO) is a potent neuroregulatory substance. By intravenous infusion, L-arginine is converted to NO and citrulline, but it is unknown whether NO is responsible for the GH stimulating effect of L-arginine in humans. We investigated whether intravenous infusion of the NO synthase inhibitor N-monomethyl-L-arginine (L-NMMA) influenced L-arginine stimulated GH secretion. Ten healthy men, aged 28.6 +/- 1.9 (mean +/- SEM) years were examined twice. L-arginine was infused intravenously in a dose of 0.5 g/kg, max 35 g, from 0 to 30 min, accompanied by either: (1) L-NMMA from -5 to 0 min, in a dose of 3 mg/kg, max 250 mg, and in a dose of 3.5 mg/kg, max 250 mg from 0 to 60 min; or (2) a saline infusion. Heart rate increased (P = 0.032), and diastolic blood pressure decreased (P < 0.001) in the two situations. Plasma cGMP was unchanged and identical in the two situations (P = 0.679). Urine cGMP/creatinine ratio increased during both examinations (P = 0.041). Growth hormone secretion increased significantly during L-arginine infusion (P = < 0.001) without any effect of L-NMMA (P = 0.848). We did not find evidence that NO influences GH secretion. It remains to be tested, however, whether a higher dose of L-NMMA may influence L-arginine stimulated GH secretion.
Fisker
S
S
Medical Department M (Endocrinology and Diabetes), Aarhus University Hospital, Denmark.
Nielsen
S
S
Ebdrup
L
L
Bech
J N
JN
Christiansen
J S
JS
Pedersen
E B
EB
Jørgensen
J O
JO
D000328:Adult; D000704:Analysis of Variance; D001120:Arginine / Q000008:administration & dosage / Q000494:pharmacology*; D004347:Drug Interactions; D019382:Human Growth Hormone / Q000097:blood / Q000378:metabolism*; D006801:Humans; D007262:Infusions, Intravenous; D008297:Male; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D012016:Reference Values; D013997:Time Factors; D019323:omega-N-Methylarginine / Q000008:administration & dosage / Q000494:pharmacology*
D019382:Human Growth Hormone; D019323:omega-N-Methylarginine; D001120:Arginine; D019001:Nitric Oxide Synthase