Gonadal regulation of pituitary hormone mRNA levels in male rats.
The control of anterior pituitary hormone gene expression by testosterone in male rat pituitaries in vivo was investigated using dot-blot mRNA-cDNA hybridization assays. Common alpha subunit mRNA levels doubled by 2 days after orchidectomy and rose progressively to reach plateau levels three to four times intact control values by 2 weeks. LH-beta mRNA increased significantly (congruent to 50%) within 12 h, and thereafter progressively to seven times intact control values by 3 weeks after orchidectomy. The changes in alpha mRNA were likely to have occurred in gonadotrophs and not thyrotrophs, since TSH-beta mRNA levels were unaltered by orchidectomy. LH subunit mRNA changes were accompanied by an initial (1-4 days) decrease in pituitary LH content; thereafter, pituitary LH increased in parallel with and by a similar magnitude to the LH-beta mRNA. Serum LH rises occurred before significant increases in LH subunit mRNA after orchidectomy. The lack of temporal correlation between mRNA levels and serum and pituitary LH in the early stages after removal of testosterone feedback contrasts with the good correlation when a new steady state was achieved after 3-4 weeks, and indicates differing kinetics for changes in these aspects of gonadotroph function. An inhibitory effect of testosterone on LH subunit gene expression was confirmed by prevention of the rise in alpha and LH-beta mRNAs when treatment commenced immediately after castration. However, pituitary LH content and serum LH levels were reduced relative to control values, suggesting additional inhibitory actions of testosterone on translational and post-translational events in gonadotrophs.(ABSTRACT TRUNCATED AT 250 WORDS)
Abbot
S D
SD
Department of Medicine, University of Birmingham, Edgbaston.
Docherty
K
K
Clayton
R N
RN
D000818:Animals; D005246:Feedback; D013006:Growth Hormone / Q000032:analysis / Q000097:blood / Q000235:genetics; D007986:Luteinizing Hormone / Q000032:analysis / Q000097:blood / Q000235:genetics; D008297:Male; D009919:Orchiectomy; D010902:Pituitary Gland / Q000032:analysis; D010907:Pituitary Hormones / Q000032:analysis / Q000097:blood / Q000235:genetics*; D011388:Prolactin / Q000032:analysis / Q000097:blood / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013737:Testis / Q000502:physiology*; D013739:Testosterone / Q000494:pharmacology; D013972:Thyrotropin / Q000032:analysis / Q000097:blood / Q000235:genetics; D013997:Time Factors
D010907:Pituitary Hormones; D012333:RNA, Messenger; D013739:Testosterone; D011388:Prolactin; D007986:Luteinizing Hormone; D013972:Thyrotropin; D013006:Growth Hormone