title: Differential effect of age on transforming growth factor-beta 1 inhibition of prolactin gene expression versus secretion in rat anterior pituitary cells.
abstract: Transforming growth factor-beta 1 (TGF-beta 1) synthesized in the pituitary may act as an autocrine/paracrine regulator of lactotrope function. We examined the effects of TGF-beta 1 on PRL messenger RNA (mRNA), PRL synthesis, and PRL secretion in cultured anterior pituitary (AP) cells from rats at different ages. APs excised from ovariectomized female Sprague-Dawley rats, either young(2-3 months old; average serum PRL: 9 ng/ml), middle-aged (11-12 months old; average serum PRL: 133 ng/ml), or old (24 months old; average serum PRL: 159 ng/ml), were dispersed and cultured for 5 days. Then, cells were washed and challenged with increasing doses of TGF-beta 1 (0-100 ng/ml) for 1-48 h in serum-free medium. Northern blot analysis showed an increase in basal PRL mRNA levels, and a decrease in responsiveness to TGF-beta 1 with age. TGF-beta 1 suppressed PRL mRNA in a dose- and time-dependent manner in cells from young rats. Maximum inhibition was observed at 0.5-1 ng/ml of TGF-beta 1. At 0.5 ng/ml TGF-beta 1, significant reduction in PRL mRNA was detected at 6 h, and maximum inhibition was observed at 12-48 h post TGF-beta 1 incubation. Cells from middle-aged rats were less responsive to TGF-beta 1, whereas cells from old rats did not seem to respond under our experimental conditions. In addition to its effect on PRL mRNA in young AP cells, TGF-beta 1 dose dependently inhibited the rate of PRL synthesis, as indicated by reduced [35S]methionine incorporation into immunoprecipitated PRL. Responsiveness of PRL synthesis to TGF-beta 1 inhibition also decreased with age; however, significant inhibition by TGF-beta 1 on PRL synthesis could still be observed in old AP cells. Analysis by RIA demonstrated that young AP cells produced lower levels (15 micrograms/10(6) cells.24 h) of PRL in culture medium than old AP cells (32 micrograms/10(6) cells.24 h). TGF-beta 1 decreased medium PRL levels in old AP cells as efficaciously as in young AP cells. Significant reduction in medium PRL secreted by young AP cells was observed at 3 h when changes in both PRL mRNA and PRL synthesis were not evident. Taken together, our data suggest that TGF-beta 1 affects PRL production at multiple levels. Moreover, its inhibition on PRL synthesis and mRNA expression, but not on PRL secretion, is age-related. Thus, TGF-beta 1 may play an important role in regulating lactotrope function during aging.
authors.affiliation: Faculty of Medical Technology, National Yang-Ming University, Taipei, Taiwan, Republic of China.
authors.forename: S K
authors.initials: SK
authors.lastname: Tan
authors.forename: F F
authors.initials: FF
authors.lastname: Wang
authors.forename: H F
authors.initials: HF
authors.lastname: Pu
authors.forename: T C
authors.initials: TC
authors.lastname: Liu
mesh_terms: D000375:Aging / Q000097:blood / Q000502:physiology*; D000818:Animals; D003470:Culture Media / Q000378:metabolism; D005260:Female; D015870:Gene Expression / Q000187:drug effects*; D010052:Ovariectomy; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000378:metabolism*; D011388:Prolactin / Q000037:antagonists & inhibitors* / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
chemical_list: D003470:Culture Media; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; D011388:Prolactin