GH, GH-releasing factor and somatostatin in the growing lamb: sex differences and mechanisms for sex differences.
Factors contributing to sex differences in the somatotrophic axis were investigated in growing lambs. In the first experiment, circulating patterns of GH in venous blood, pituitary content of GH and GH mRNA, and median eminence (ME) contents of GH-releasing factor (GRF) and somatostatin (SRIF) were characterized in prepubertal ram and ewe lambs which were pair-fed to remove sex differences in feed intake. Mean and baseline plasma GH concentrations, GH pulse amplitude, and integrated plasma GH were greater in ram lambs than in ewe lambs, but GH interpulse interval did not differ between sexes. The pituitary GH content and ME contents of GRF and SRIF were greater in rams than in ewes, but steady-state levels of mRNA for GH in the pituitary gland did not differ between sexes. A second experiment investigated sex effects on the levels of SRIF in hypophysial portal blood, and found that these did not differ between sexes. We concluded that the presence of sexually dimorphic patterns of GH secretion in the growing lamb is independent of feed-intake differences between sexes. The lack of sex differences in circulating patterns of SRIF in portal plasma implies that there may be a difference in GRF secretion which may produce sexually dimorphic patterns of GH secretion in lamb.
Gatford
K L
KL
Department of Agriculture and Resource Management, University of Melbourne, Parkville, Victoria, Australia.
Fletcher
T P
TP
Rao
A
A
Egan
A R
AR
Hosking
B J
BJ
Clarke
I J
IJ
D000818:Animals; D005260:Female; D013006:Growth Hormone / Q000032:analysis / Q000097:blood / Q000235:genetics; D013007:Growth Hormone-Releasing Hormone / Q000032:analysis / Q000097:blood; D008297:Male; D008473:Median Eminence / Q000737:chemistry; D009479:Neuropeptides / Q000032:analysis / Q000097:blood*; D010902:Pituitary Gland / Q000098:blood supply / Q000737:chemistry; D012333:RNA, Messenger / Q000032:analysis; D011863:Radioimmunoassay; D012636:Secretory Rate; D012727:Sex Characteristics; D012756:Sheep / Q000097:blood / Q000254:growth & development*; D013004:Somatostatin / Q000097:blood
D009479:Neuropeptides; D012333:RNA, Messenger; D013004:Somatostatin; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone