Initiation and elongation steps of mRNA translation are involved in the increase in milk protein yield caused by growth hormone administration during lactation

Least squares mean daily milk yield (A) and protein yield (B) in control and growth hormone (GH)-treated cows over 6 d following the injection of a slow-release formulation of GH on d 0. *P<0.05; **P<0.05.

Quantitative real-time PCR (qRT-PCR) results of growth hormone (GH)-treated and control animals. Total mammary gland RNA from GH-treated and control animals was subjected to qRT-PCR analysis. Cycles to threshold (CT) values for individual animals (•) is shown for each treatment (GH and control). In some figures, some animals had the same CT value so fewer than 4 data points (•) are visible. The horizontal line (−) indicates the average gene expression within each treatment group. Genes are as defined in Table 2.

Growth hormone (GH) treatment stimulated phosphorylation of ribosomal protein S6 in the mammary gland. Lactating mammary gland lysates from GH-treated and control cows were analyzed by SDS-PAGE and Western blotting using the phosphor-specific (Ser235/236) and total antisera for ribosomal protein S6. In all cases, blots represent at least 3 independent experimental replicates. The 4 lanes for GH (1 to 4) and the 4 lanes for control (5 to 8) represent the 4 animals/treatment used in this experiment. The graph shows the phosphorylation of ribosomal protein S6 [S6 (P)] normalized for total ribosomal protein S6 content in the sample (mean±SE, n = 4/treatment); *P<0.01.

Growth hormone (GH) treatment increased the protein abundance of eukaryotic initiation factor 4E (eIF4E) in the mammary gland but did not affect the phosphorylation of eIF4E binding protein 1 (4E-BP1). The graphs show the phosphorylation of 4E-BP1 (Thr70) normalized for total 4E-BP1 content in the sample and the total eIF4E normalized for total GAPDH content in the sample. In all cases, blots are representative of at least 3 experimental replicates. The 4 lanes for GH (1 to 4) and the 4 lanes for control (5 to 8) represent the 4 animals/treatment used in this experiment. The graph shows the mean±SE, n = 4/treatment; *P<0.01.

Growth hormone (GH) treatment changed total eukaryotic elongation factor 2 (eEF2) but did not change the phosphorylation status of eEF2 and eEF2 kinase (eEF2K). Lactating mammary gland lysates from GH-treated and control cows were analyzed by SDS-PAGE and Western blotting using the phospho-specific (Ser366) eEF2K and (Thr56) eEF2. The graph shows the phosphorylation of eEF2K (Ser366) and eEF2 (Thr56) normalized for total eEF2K and total eEF2, respectively. In all cases, blots represent at least 3 experimental replicates. The 4 lanes for GH (1 to 4) and the 4 lanes for control (5 to 8) represent the 4 animals/treatment used in this experiment. The graph shows the mean±SE, n = 4/treatment; *P<0.01.