Hypothalamic growth hormone-releasing factor (GRF) participates in the negative feedback regulation of growth hormone secretion.
Effects of growth hormone (GH) excess on immunoreactive hypothalamic GH-releasing factor (GRF) and somatostatin (SRIF) were studied in rats. Hypothalamic GRF content significantly reduced after 7-day daily treatment with 160 micrograms of rat GH or after inoculation of GH-secreting rat pituitary tumors, MtT-F4 for 9 or 13 days and GH3 for 3 months. Basal and 59 mM K+-evoked release of GRF from incubated hypothalami diminished, more than the content, by 43-51% in MtT-F4 tumor- or by 67-83% in GH3 tumor-bearing rats. In contrast, there was a small but significant increase in content or release of SRIF in rats harboring the GH3 or MtT-F4 tumor, respectively. These results indicate the existence of a negative feedback loop via hypothalamic GRF as well as SRIF in control of GH secretion.
Miki
N
N
Department of Medicine, Tokyo Women's Medical College, Japan.
Ono
M
M
Miyoshi
H
H
Tsushima
T
T
Shizume
K
K
D000818:Animals; D005246:Feedback; D013006:Growth Hormone / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000502:physiology*; D006706:Homeostasis; D007031:Hypothalamus / Q000502:physiology*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013004:Somatostatin / Q000502:physiology
D013004:Somatostatin; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone