Growth hormone inhibits its own secretion by acting on the hypothalamus through its receptors on neuropeptide Y neurons in the arcuate nucleus and somatostatin neurons in the periventricular nucleus.
GH secretion is regulated by hypothalamic somatostatin and GH-releasing factor. It has been postulated that GH feeds back on the hypothalamus and regulates its own secretion. We focused our attention on the action of GH in the hypothalamus in relation to GH secretion. Adult male rats were used throughout the studies, and the observation was made in conscious rats. Systemic administration of human GH induced c-fos gene expression, a marker of neuronal activity, in the hypothalamic arcuate nucleus (ARC) and the periventricular nucleus (PeV) in hypophysectomized male rats. The major cells in which c-fos gene expression was induced were neuropeptide Y (NPY) neurons in the ARC and somatostatin neurons in the PeV. GH receptor mRNA was demonstrated to be present in these neurons by in situ hybridization. The injection of a small dose of rat GH into the ARC or PeV inhibited GH secretion, whereas microinjection of IGF-I into these nuclei did not. Intracerebroventricular injection of NPY suppressed GH secretion, and this effect was abolished by anterolateral deafferentation of the medial basal hypothalamus (MBH), a procedure which disrupts the somatostatinergic input to the MBH. Taken together, these findings suggest that GH acts on NPY neurons in the ARC and somatostatin neurons in the PeV through GH receptor, and the activation of these neurons augments somatostatin release and inhibits GH secretion.
Minami
S
S
Institute of Gerontology, Nippon Medical School, Kawasaki, Japan.
Kamegai
J
J
Sugihara
H
H
Suzuki
N
N
Wakabayashi
I
I
D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D005246:Feedback; D005786:Gene Expression Regulation; D016762:Genes, fos; D013006:Growth Hormone / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D019382:Human Growth Hormone / Q000008:administration & dosage / Q000494:pharmacology; D006801:Humans; D007031:Hypothalamus / Q000166:cytology / Q000502:physiology*; D007334:Insulin-Like Growth Factor I / Q000502:physiology; D008297:Male; D008954:Models, Biological; D009474:Neurons / Q000502:physiology*; D009478:Neuropeptide Y / Q000502:physiology*; D010286:Paraventricular Hypothalamic Nucleus / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D018013:Receptors, Neuropeptide / Q000502:physiology*; D018017:Receptors, Pituitary Hormone-Regulating Hormone / Q000502:physiology*
D009478:Neuropeptide Y; D012333:RNA, Messenger; D018013:Receptors, Neuropeptide; D018017:Receptors, Pituitary Hormone-Regulating Hormone; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; C048250:somatotropin releasing hormone receptor