Treatment of ovariectomized heifers with bovine follicular fluid specifically suppresses pituitary levels of FSH-beta mRNA.
To investigate the inhibin-induced suppression of FSH secretion by the anterior pituitary, chronically ovariectomized heifers (three per group) were treated for 56-58 h with either steroid-free bovine follicular fluid (bFF; 8 ml i.v. every 8 h) or 0.9% (w/v) NaCl (8 ml i.v. every 8 h). Blood was withdrawn at 8-h intervals for analysis of plasma concentrations of FSH and LH by radioimmunoassay. At the end of the treatment period, heifers were slaughtered and pituitary glands recovered for determination of gonadotrophin contents and levels of mRNA encoding FSH-beta, LH-beta, TSH-beta and common alpha glycoprotein hormone subunits using [32P]cDNA probes in total RNA dot and Northern blot assays. Treatment with bFF markedly suppressed plasma FSH by 85% (P less than 0.001 compared with pretreatment period), but did not affect plasma LH concentrations. Plasma FSH and LH concentrations did not vary significantly in the saline-injected control heifers. The level of FSH-beta subunit mRNA was reduced by 60% (P less than 0.001) in heifers treated with bFF, whereas no significant differences between control and bFF-treated heifers were observed in the levels of mRNA encoding LH-beta, TSH-beta or common alpha subunits. Treatments with bFF, however, did not affect pituitary content of either FSH or LH. These results support the conclusion that inhibin exerts its selective suppressive effect on the secretion of FSH by the bovine pituitary, at least in part, by directly inhibiting expression of the gene encoding the FSH-beta subunit.
Beard
A J
AJ
Department of Biochemistry & Physiology, University of Reading.
Savva
D
D
Glencross
R G
RG
McLeod
B J
BJ
Knight
P G
PG
D000818:Animals; D015152:Blotting, Northern; D001826:Body Fluids; D002417:Cattle; D005260:Female; D005640:Follicle Stimulating Hormone / Q000032:analysis / Q000097:blood / Q000235:genetics*; D037201:Follicle Stimulating Hormone, beta Subunit; D015151:Immunoblotting; D007265:Inhibins / Q000502:physiology*; D007986:Luteinizing Hormone / Q000097:blood; D008970:Molecular Weight; D006080:Ovarian Follicle / Q000502:physiology; D010052:Ovariectomy; D010903:Pituitary Gland, Anterior / Q000032:analysis*; D012333:RNA, Messenger / Q000032:analysis* / Q000235:genetics; D011863:Radioimmunoassay
D037201:Follicle Stimulating Hormone, beta Subunit; D012333:RNA, Messenger; D007265:Inhibins; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone