Acute effects of hypoglycemia and hyperglycemia on hypothalamic growth hormone-releasing hormone and somatostatin gene expression in the rat.
Although previous studies have indicated that changes in the plasma glucose concentration alter GH secretion in the rat, the roles of hypothalamic GH-releasing hormone (GRH) and somatostatin (SS) in the glucose modulation of GH secretion have not yet been elucidated. We investigated the acute effects of hypo- and hyperglycemia on hypothalamic GRH and SS mRNA in the rat. Long term atrial catheters were implanted in male rats, and sequential blood sampling was performed in conscious animals. Insulin and 50% glucose were administered iv to induce hypo- and hyperglycemia, respectively. At the end of the experiment, the hypothalamus was removed, and total RNA was extracted for Northern blotting. Hypoglycemia completely inhibited pulsatile GH secretion, whereas hyperglycemia partially inhibited GH secretion. Direct effects of insulin itself on GH secretion in the insulin-induced hypoglycemia were ruled out by glucose clamp studies. Hypothalamic SS mRNA levels were increased dramatically by hypoglycemia (266 +/- 37%) and moderately by hyperglycemia (183 +/- 45%). Hypothalamic GRH mRNA levels were increased only by hyperglycemia (159 +/- 18%). The GH response to GRH was decreased dramatically by hypoglycemia and moderately by hyperglycemia. These results indicated that acute changes in the plasma glucose concentration stimulated hypothalamic SS mRNA in the rat.
Murao
K
K
First Department of Internal Medicine, Kagawa Medical School, Japan.
Sato
M
M
Mizobuchi
M
M
Nimi
M
M
Ishida
T
T
Takahara
J
J
D000818:Animals; D015870:Gene Expression; D013006:Growth Hormone / Q000378:metabolism; D013007:Growth Hormone-Releasing Hormone / Q000235:genetics* / Q000494:pharmacology; D006943:Hyperglycemia / Q000235:genetics* / Q000378:metabolism; D007003:Hypoglycemia / Q000235:genetics* / Q000378:metabolism; D007031:Hypothalamus / Q000378:metabolism / Q000502:physiology*; D008297:Male; D011673:Pulsatile Flow; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013004:Somatostatin / Q000235:genetics*; D013997:Time Factors
D012333:RNA, Messenger; D013004:Somatostatin; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone