Leptin alters the response of the growth hormone releasing factor- growth hormone--insulin-like growth factor-I axis to fasting.
Proper nutritional status is critical for maintaining growth and metabolic function, playing an intimate role in neuroendocrine regulation. Leptin, the recently identified product of the obese gene, may very well be an integral signal which regulates neuroendocrine responses in times of food deprivation. The present study examines leptin's ability to regulate hormonal synthesis and secretion within the GRF-GH-IGF axis in the adult male rat during almost 3 days of fasting. Serum levels of GH and IGF-I were drastically suppressed by fasting. Daily leptin administration was able to fully prevent the fasting-induced fall in serum GH. Leptin failed to restore IGF-I to control levels, however, suggesting possible GH resistance. Fasting caused an insignificant increase in GH mRNA, while leptin injections significantly increased steady-state levels of this message. The GRF receptor (GRFr) message was not altered with fasting or leptin treatment. Leptin also exhibited effects at the hypothalamic level. Fasting induced a sharp fall in GRF mRNA expression and leptin injections partially prevented this fall. However, there were no observed changes in the hypothalamic GRF content. These results provide evidence that leptin may function as a neuromodulator of the GRF-GH-IGF axis communicating to this hormonal system the nutritional status of the animal.
LaPaglia
N
N
Department of Medicine, Loyola University Chicago, Stritch School of Medicine, Maywood, Illinois 60153, USA.
Steiner
J
J
Kirsteins
L
L
Emanuele
M
M
Emanuele
N
N
D000818:Animals; D015152:Blotting, Northern; D005215:Fasting / Q000502:physiology*; D013006:Growth Hormone / Q000097:blood* / Q000235:genetics; D013007:Growth Hormone-Releasing Hormone / Q000235:genetics / Q000378:metabolism*; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D020738:Leptin; D008297:Male; D010902:Pituitary Gland / Q000378:metabolism; D011506:Proteins / Q000494:pharmacology*; D012333:RNA, Messenger / Q000032:analysis; D011863:Radioimmunoassay; D051381:Rats; D017207:Rats, Sprague-Dawley; D018013:Receptors, Neuropeptide / Q000235:genetics; D018017:Receptors, Pituitary Hormone-Regulating Hormone / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction
D020738:Leptin; D011506:Proteins; D012333:RNA, Messenger; D018013:Receptors, Neuropeptide; D018017:Receptors, Pituitary Hormone-Regulating Hormone; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone; C048250:somatotropin releasing hormone receptor