Abstract
Anterior pituitary glands from 65 female Hampshire and Duroc swine were assayed for growth hormone content using two criteria of their effect on immature hypophysectomized female rats: (1) increase in width of the proximal epiphysis of the tibia, and (2) gain in weight. Pituitary glands were collected from animals belonging to the following categories: fetal, immature, mature and pregnant. Each category was subdivided into four to six sub-groups and included a range of weights from fetal to 600 lb. Chemical analyses and long-bone measurements were made on all experimental animals included in the immature and mature phases. Dry matter, ether extract, nitrogen, and bone ash of the bodies of non-pregnant animals showed an increase in the total amounts of these constituents throughout the age span (1–1400 days of age) covered in this study. Dry matter, ether extract, protein, and bone ash increased at a rapid rate until the animals reach an age of about 300 days and thereafter continued to increase at a slower rate. The femur and humerus showed a rapid increase in length during the phase of rapid body growth. After growth slowed, these bones continued to increase significantly in length up to the age of 1400 days. The weight of the anterior pituitary increased rapidly until the age of 225 days, after which the rate of increase slowed but continued. The ratio of anterior pituitary weight to body weight decreased rapidly until the age of 225–300 days when the ratio became constant for the remainder of the ages studied. Growth hormone potency of a given quantity of pituitary tissue (unit potency) was significantly lower in animals less than 20 days of age than it was in older animals. The total hormone contained in the pituitary was low in fetal glands and increased throughout the life of the animal. The hormone available per kg. of body weight was high in young animals, decreased to the age of 300 days, and thereafter remained constant. No differences in pituitary potency could be ascribed to breed or reproductive state. It is concluded that reduction in growth rate at 225 days of age is due to dilution of available circulating growth hormone to the point where the body no longer responds by vigorous growth to the low concentration. Copyright © . .