Chronic oral administration of arginine induces GH gene expression and insulin resistance.
Arginine (Arg) presents a potent growth hormone (GH) releasing activity. In vivo and in vitro studies carried out in our laboratory have demonstrated that acute treatment with Arg also increases GH gene expression. Taking into account the recognizable diabetogenic role of GH and that Arg increases insulin release, this study aimed at evaluating the effects of oral chronic administration of Arg on GH gene expression, by Northern blotting analysis, and on the insulin sensitivity, by means of the Insulin Tolerance Test (ITT), blood glucose decay rate (kitt) and insulin plasma concentration. We demonstrated that rats that consumed Arg ( approximately 35 mg/day) in drinking water, during 4 weeks, presented an increase in GH mRNA content (p < 0.01), a decreased peripheral response to insulin, as shown by the reduced blood glucose decay rate (p < 0.05), and a higher insulin plasma concentration (p < 0.01) than control group. Arg treatment did not modify the animals' food and water intake, while it decreased the heart rate and the arterial blood pressure compared to control group (p < 0.05). According to the results presented herein we conclude that chronic oral administration of arginine increases GH gene expression and induces insulin resistance. The arterial blood pressure decrease has already been pointed out in the literature, and seems to occur in response to the dilating effect of nitric oxide generated from Arg, as well as from NO generation in central and peripheral neuronal populations that express NOS and are involved in the autonomic regulation of the cardiac function.
de Castro Barbosa
Thais
T
Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of São Paulo, 05508-900, São Paulo, SP, Brazil.
Lourenço Poyares
Leonice
L
Fabres Machado
Ubiratan
U
Nunes
Maria Tereza
MT
D000284:Administration, Oral; D000818:Animals; D001120:Arginine / Q000008:administration & dosage* / Q000494:pharmacology; D001786:Blood Glucose / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D001835:Body Weight / Q000187:drug effects; D004326:Drinking / Q000187:drug effects; D004435:Eating / Q000187:drug effects; D015870:Gene Expression / Q000187:drug effects; D013006:Growth Hormone / Q000235:genetics*; D006339:Heart Rate / Q000187:drug effects; D007328:Insulin / Q000097:blood; D007333:Insulin Resistance / Q000235:genetics*; D008297:Male; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
D001786:Blood Glucose; D007328:Insulin; D012333:RNA, Messenger; D013006:Growth Hormone; D001120:Arginine