Characteristics of Protein Synthesis in the Anterior Pituitary of White Plymouth Rock Dwarf Chicken

Anterior pituitaries from White Plymouth Rock normal and dwarf chickens were incubated with 14C-leucine, and the radioactivity of labeled proteins was counted after separation by disc electrophoresis. Rates of each protein synthesis and release into incubation medium were represented with disintegration per minute (dpm) per 100g body weight per 2 hours (Fig. 4-7). The whole content of each protein in the anterior pituitary was determined by a densitometry using the same parameter as described above (Fig. 8).The profile of disc electrophoretic pattern of the anteior pituitary was essentially the same during the growth periods from embryo to adult. There were no qualitative differences in the profiles among sexes, normal, and dwarf chickens, growth hormone (GH), prolactin (PL), slow protein (SP), and some blood proteins being detected (Fig. 1-2). GH synthesis rate decreased with age and was higher in the dwarf than in the normal. GH release rate did not change appreciably in all chicken groups. GH content was approximately parallel to synthetic activity (Fig. 4, 8). PL synthesis also decreased with age and was somewhat high in dwarfs. There were no notable differences in PL release and content among male, female, normal, and dwarf chickens (Fig. 5, 8). Changes in synthesis and release of SP were similar to those of GH (Fig. 6). SP accumulation in the dwarf pituitary was evident at 13 and 20 weeks of age (Fig. 8). It was confirmed that this prominent protein was confined in the caudal lobe of the chicken anterior pituitary (Fig. 3). Total protein synthesis in the pituitary decreased with age, and was higher in the dwarf than in the normal probably reflecting enhanced synthesis of SP, GH, and PL in the dwarf (Fig. 7).There were no distinct differences in rates of 3H-1-leucine incorporation into muscle, liver, and kidney proteins between the normal and the dwarf chickens (Table 2). This, along with data on amino acid pool suggests that the enhanced protein synthesis including GH would be peculiar to the dwarf anterior pituitary and closely associated with a development of the dwarfism. In view of the present experimental evidence, it seems unlikely that the depression of GH synthesis and or release is the cause of the dwarfism as has been reported in mammals.