[The developmental changes of GHR and IGF-1R gene expressions in porcine hypothalamus and pituitary].
GH and IGF-1 may serve as negative feedback factors to regulate GH secretion from pituitary by binding to their respective receptors in hypothalamus and/or pituitary. In order to evaluate the line-specific developmental patterns of negative feedback regulation of GH secretion, Erhualian (EHL) and Large White (LW) pigs with significant difference in growth rate were employed in present study to investigate the developmental changes of GH receptor (GHR) mRNA and type-1 IGF receptor (IGF-1R) mRNA in hypothalamus and pituitary from birth till 180 days of age by relative quantitative RT-PCR. Pigs were sampled at birth, 3 , 20, 30, 90, 120 and 180 days of age respectively. Hypothalamic GHR mRNA was expressed according to an age-dependent manner, being low at birth, then increased steadily till day 120, followed by a decrease (P < 0.05) at the age of 180 days, suggesting that the sensitivity of hypothalamus to the GH negative feedback influence increase steadily during fast-growing period. LW boars expressed higher level of GHR mRNA than EHL boars (P < 0. 05) in hypothalamus. In pituitary, however, the GHR mRNA level was not significantly correlated with the breeds and age. The results suggested that GH might act mainly at the level of hypothalamus to regulate GH secretion. In contrast, the expression of IGF-1R mRNA exhibited line-specific developmental patterns in pituitary but not in hypothalamus. Hypothalamic expression of IGF-1R mRNA was abundant but did not show significant differences between ages, groups or lines. In pituitary, however, the IGF-1R mRNA expression was found to be high at birth both in EHL and LW pigs, subsequently declined till day 20, then followed by a slow rise reaching the second peak at the age of 90 days. At the age of 180 days, the pituitary IGF-1R mRNA level was higher in EHL pigs than that in LW pigs (P < 0.05), but the opposite was true at the age of 30 and 90 days. These results suggest that the site for receiving the feedback signal of IGF-1 is more likely in pituitary rather than in hypothalamus in the pig.
Key Laboratory of Animal Physiology & Biochemistry, Ministry of Agriculture, Nanjing Agricultural University, Nanjing 210095, China.
Jin-Xian
JX
Xu
Dong
D
Xia
Ru-Qian
RQ
Zhao
Qing-Fu
QF
Xu
Xi-Hui
XH
Wei
Jie
J
Chen
D000367:Age Factors; D000818:Animals; D005260:Female; D015870:Gene Expression; D007031:Hypothalamus / Q000378:metabolism*; D010902:Pituitary Gland / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D017526:Receptor, IGF Type 1 / Q000235:genetics*; D011986:Receptors, Somatotropin / Q000235:genetics*; D013552:Swine
D012333:RNA, Messenger; D011986:Receptors, Somatotropin; D017526:Receptor, IGF Type 1