The effects of embryonic pars distalis grafts on the development of hypophysectomized chick embryos

Hypophysectomized nine-day old embryos received one or two grafts of embryonic, ten-day old pars distalis to the chorio-allantois. At the end of 20 days of incubation, all embryos were killed and no differences between the hypophysectomized embryos having one or two grafts were noted. Normal survival was 72%, but only 6% of the hypophysectomized embryos survived and the survival of grafted embryos was 60%. The rate of maturation of the extraembryonic membranes of hypophysectomized embryos was slower than normal, but the rate in grafted embryos was normal. In hypophysectomized embryos, the vitelline and chorio-allantoic circulation did not collapse nor was the yolk sac retracted; however, these changes did occur in grafted embryos. The mean body weight of hypophysectomized embryos (8.9 gm) was 45% of normal and that of treated embryos was 63% of normal. The normal paired thyroid glands weighed 2.2 mg, but those of hypophysectomized embryos weighed 0.5 mg and the size and number of follicles and the amount of colloid were reduced in pituitaryless embryos. The thyroid glands of treated embryos weighed 1.2 mg and showed normal histology. The paired testes of normal embryos weighed 4.6 mg, but those of hypophysectomized embryos weighed 1.6 mg and the size of the seminiferous cords and the amount of interstitial tissue were reduced. The testes of treated embryos weighed 3.1 mg and showed normal histology. The normal left ovaries weighed 4.4 mg, but those of pituitaryless embryos weighed 2.7 mg and the thickness of the cortex and medulla was reduced. The ovaries of embryos with grafts weighed 4.2 mg and showed normal histology. The normal paired adrenal glands weighed 4.5 mg, but those of hypophysectomized embryos weighed 2.6 mg. The adrenals of treated embryos weighed 3.7 mg. The cortical cords and chromaffin tissue normally comprised 44% and 33% of the glands and 23% was nonparenchymal space (NPS). In hypophysectomized embryos the cortical component was 31% and the chromaffin and NPS were 40% and 29%. In treated embryos the percents were 43, 31 and 26. This study demonstrated that most of the defects of hypophysectomized embryos are due to the absence of the hormones of the pars distalis and that an ectopic embryonic pars distalis secretes normal amounts of a somatotrophic, a thyrotrophic, a gonadotrophic, and an adrenocorticotrophic hormone.