Messenger RNA (mRNA) levels of prolactin (PRL), growth hormone (GH), and luteinizing hormone (LH)-β subunit in the cephalic and caudal lobes of the anterior pituitary gland of the chicken during embryonic development and different reproductive stages were determined by Northern blot analysis and are related to hormone levels in plasma and each lobe. Steady-state levels of 1.4-kb transcript of PRL of the cephalic and caudal lobes increased on Days 18 and 20 of incubation, respectively. The levels were greater in the cephalic lobe than in the caudal lobe on Days 18 and 20 of incubation. Levels of PRL in each lobe show similar changes to those of mRNA levels. GH mRNA levels of both lobes started to increase on Day 16 of incubation but the levels were higher in the caudal lobe than in the cephalic lobe on Days 16-20 of incubation. Levels of GH in the cephalic lobe increased discontinuously, while those in the caudal lobe increased continuously on days of incubation. LH-β mRNA was not detected in embryos. Levels of PRL mRNA increased approximately 18-, 20-, and 3-fold in hens at 1 and 3 weeks of egg incubation and brooding stages in the hen, relative to prelaying, respectively. These levels were higher in the cephalic lobe than in the caudal lobe at all stages except for prelaying stages. Levels of PRL in each lobe displayed essentially similar changes to the mRNA levels. GH mRNA levels did not significantly vary during the cycle but were higher in the caudal lobe than in the cephalic lobe. There was no difference in LH-β mRNA levels between the two lobes but the levels were higher at prelaying and laying stages than at incubation and brooding stages. The same changes in LH concentrations in plasma as those of LH-β mRNA were found at the stages. This study shows regional differences between PRL and GH mRNA levels in the anterior pituitary gland in relation to embryogenesis and different reproductive stages.
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