Synthesis and release of growth hormone, prolactin, and other proteins from the anterior pituitary of normal and dwarf chickens

Abstract

Intact anterior pituitaries were excised from normal male and female chickens and from male dwarf chickens during the period of growth from 47 to 207 days after hatching. The pituitaries were incubated with l-[ 14C]leucine, and the radioactivity of the labeled leucine incorporated into certain protein fractions was counted after separation by polyacrylamidegel disc electrophoresis. Employing appropriate parameters calculated from the radioactivity counts of the proteins separated from both the incubated tissue and the incubation medium, two unit functions of the anterior pituitary, i.e., hormone synthesis and hormone release, were studied. The results showed the following: In normal chickens, GH synthesis function decreased with age in parallel with the decrease in the growth rate, indicating that GH plays a significant role in the promotion of growth in normal chickens. On the other hand, GH release function did not change during growth. Prolactin synthesis function showed a minimum value at the age of 138 days, and prolactin release function showed a peak value at 89 days. These hormone synthesis and release functions were similar in male and female chickens, in contrast to the significant differences that exist between the sexes in rats. Another prominent protein fraction, a slow-moving protein (SP), changed in a manner similar to that of GH, suggesting certain resemblances between them; the nature of this slow-moving protein is discussed. In dwarf male chickens, GH synthesis function was significantly larger than in normal chickens, and the pattern of change during growth was also different from that of the normal chickens. These differences are in odd contrast to the retarded growth of the dwarf chickens.