Glucocorticoid regulation of proopiomelanocortin gene expression in the pituitary gland of hypothalamopituitary intact and hypothalamopituitary disconnected sheep.
Proopiomelanocortin (POMC) gene expression in the anterior pituitary (AP) gland has previously been shown to be positively regulated by CRF and AVP and negatively regulated by glucocorticoids. In the neurointermediate lobe (NIL) of the pituitary, however, POMC gene expression is under tonic inhibitory dopaminergic control. In the present study we have used hypothalamopituitary intact (HPI), ovariectomized (OVX), and OVX/hypothalamopituitary disconnected (OVX/HPD) ewes to examine direct (i.e. nonhypothalamic) effects of glucocorticoids on POMC gene expression in both the AP and the NIL. There was no difference between POMC mRNA levels in intact and OVX sheep. In intact animals treated with dexamethasone, AP POMC mRNA levels were half those of controls. POMC mRNA levels were increased 3-fold in OVX/HPD sheep, compared with OVX, and lowered by dexamethasone to half OVX/HPD levels. In the NIL, hypothalamopituitary disconnection resulted in slightly higher mean POMC mRNA levels than in intact animals but the large intragroup variation did not allow a significant change. Dexamethasone administration had no effect on NIL levels of POMC mRNA in intact or OVX/HPD sheep.
Mercer
J E
JE
Medical Research Centre, Prince Henry's Hospital, Melbourne, Australia.
Clements
J A
JA
Clarke
I J
IJ
Funder
J W
JW
D000818:Animals; D003907:Dexamethasone / Q000494:pharmacology; D005260:Female; D015870:Gene Expression / Q000187:drug effects*; D005938:Glucocorticoids / Q000494:pharmacology*; D007031:Hypothalamus / Q000502:physiology*; D009693:Nucleic Acid Hybridization; D010052:Ovariectomy; D010902:Pituitary Gland / Q000378:metabolism*; D010903:Pituitary Gland, Anterior / Q000378:metabolism; D010904:Pituitary Gland, Posterior / Q000378:metabolism; D011333:Pro-Opiomelanocortin / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism; D012756:Sheep
D005938:Glucocorticoids; D012333:RNA, Messenger; D011333:Pro-Opiomelanocortin; D003907:Dexamethasone