Effect of dietary energy and protein restriction followed by realimentation on pituitary mRNA expression of growth hormone and related genes in lambs

The objective of the current study was to evaluate the influence of dietary energy and protein restriction followed by realimentation on pituitary growth hormone (GH), growth hormone-releasing hormone receptor (GHRHR), GH secretagogue receptor (GHSR), somatostatin receptor 1 (SSTR1), somatostatin receptor 2 (SSTR2), insulin-like growth factor 1 receptor (IGF-1R), and IGF-2 mRNA expression in lambs. Forty 3-month-old native Mongolian wether lambs were selected, and randomly assigned to control group (CON), moderately energy-restricted group (MR1), moderately protein-restricted group (MR2), or severely energy- and protein-restricted group (SR). The feed restriction stage lasted for 60 days and then all groups were fed the same diet for 90 days (realimentation stage). Pituitaries were collected from four lambs in each group at the end of the two stages. Pituitary gene expression was determined by quantitative real-time reverse transcription PCR. At the end of the restriction stage, the body weight of lambs in all restricted groups was significantly lower than that in the CON group. Pituitary GH, GHRHR, GHSR and IGF-2 expression in lambs in the SR group was greater than that in the CON group (P < 0.05), whereas the mRNA expression of SSTR1, SSTR2 and IGF-1R did not change (P ≥ 0.05). At the end of the realimentation stage, the body weight of lambs in the MR1 and MR2 groups was not different from that of lambs in the CON group (P > 0.05). However, the body weight of lambs in the SR group was still lower than that in the CON group (P < 0.05). The pituitary GH expression of lambs in the SR group was still greater (P < 0.05) than that of the CON group, whereas expression of the other genes had returned to control levels. No differences were found in pituitary GH and related gene expression in lambs in the MR1 and MR2 groups compared with those in the CON group throughout the entire experiment (P > 0.05). Our results indicated that moderate dietary energy and protein restriction did not influence pituitary GH and related gene expression. Only severe energy and protein restriction caused a significant increase in pituitary GH transcription, which lasted throughout the realimentation stage.