title: Effects of age on GH responses to growth hormone-releasing factor in rats.
abstract: This paper aims to investigate the growth hormone (GH) responses to the growth hormone releasing factor-44 (GRF-44) in young and adult rats in vitro and in vivo. Male Wistar rats aged 28 days and 6 months were used. In pentobarbital anesthetized young rats, an intravenous administration of GRF-44 at a dose of 25 ng/100 g b.w. resulted in an 11.4 fold rise in the serum GH level at 5 min after GRF-44 injection. On the other hand, in adult rats the same dose of GRF-44 did not elicit a significant rise in the serum GH level. However, GH secretion in response to GRF-44 at a dose of 250 ng/100 g b.w. was not attenuated in adult rats. Isolated pituitary cells obtained from young and adult rats were incubated for 3 days. The addition of GRF-44 at a concentration of 5 ng/ml to the cultured pituitary cells from young rats caused a 3.2 fold increase in GH content in the medium. On the other hand, the same dose of GRF-44 added to the cultured pituitary cells from adult rats resulted in only a 2.3 fold increase in GH content. These data indicate that the sensitivity of somatotrophs to GRF may be diminished with age.
mesh_terms: D000375:Aging; D000818:Animals; D002478:Cells, Cultured; D013006:Growth Hormone / Q000096:biosynthesis*; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology*; D008297:Male; D010446:Peptide Fragments / Q000494:pharmacology*; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D010446:Peptide Fragments; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone