On the Postnatal Histogenesis of the Anterior Pituitary of the Rat

Abstract

A histogenetic study was done on the anterior pituitary of rats of both sexes progressing in age from birth to maturity. The results obtained were as follows:
1. The parenchymatous cells of the rat anterior pituitary were composed essentially of chromophobe, acidophile and basophile cells. Two distinct cell types of basophils (delta- and beta-cells) could be distinguished by the application of the periodic acid-SCHIFF technique and GOMORI's aldehyde-fuchsin method.
2. Chromophobes were generally small in size and contained fine filamentous material but no coarse secretion granules in the cytoplasm. Their cell boundaries were not as clearly defined as in the chromophils. The nuclei of chromophobes, round or oval in shape, contained relatively few chromatin particles and usually one or two acidophilic nucleoli. These cytological characteristics indicate that the chromophobes are in an undifferentiated state.
3. Acidophils, though not as abundant as in adults, could already be identified by the presence of acidophilic granules in the cytoplasm immediately after birth. Acidophils were frequently observed to contain negative images of the Golgi apparatus in juxta-nuclear regions as cap-like figures and basophilic filamentous materials suggesting the presence of ribonucleic acid. As the animals approached maturity acidophils gradually became densely packed with cytoplasmic granules. On the whole there was a greater increase in the number of acidophils during growth and development of females than in males, therefore the number of acidophils in adult females exceeded that in males.
4. Beta-cells characterized by the presence of cytoplasmic granules which react positively with the PAS reagent and aldehyde-fuchsin showed well-defined but irregularly shaped cell boundaries. These cells could be recognized from the earliest post-natal period. Their cytoplasmic granules gradually increased with age. In adult females most basophils were beta-cells, while in adult males delta-cells were predominant.
5. Delta-cells were large in size, oval or round in shape, and had distinct cell boundaries. Their fine cytoplasmic granules which react positively with the PAS reagent and aldehyde-fuchsin were distributed throughout the cytoplasm except in the GOLGI area. Some of these cells were densely granulated especially in the peripheral zone of the cytoplasm. The negative image of the GOLGI apparatus of delta-cells was seen in the juxta-nuclear region as a clear, granule-free, circular area with a red centrum by the PAS technique or a dark blue centrum by the azan stain modified by MARTINS. In adult males, delta-cells were frequently found in the ventral area of the anterior lobe and the upper region adjacent to RATHKE's residual cleft. In adult females, on the other hand, delta-cells which were smaller in size and less granulated than those of adult males were located in the central region of the anterior lobe. In addition, most basophils of adult females were not delta-cells, but beta-cells.
6. During the earliest postnatal life, delta-cells were scarce in number, small in size and showed feeble stainability for various dyes. In males, they became numerous and more densely granulated towards maturity. On the other hand, in females, they attained the maximum number on the 30th day, and decreased rapidly thereafter.
7. Between the 35th and 45th day a remarkable change took place in deltacells of the females. During this period degranulation of delta-cells was observed. In addition, the majority of degranulated delta-cells was small in size when compared with delta-cells of the previous stage and had pycnotic nuclei, although delta-cells of the 30-day old female were similar in cytological details to those of males at the same age.
8. According to PURVES and GRIESBACH (1954, 1955) and SIPERSTEIN, NICHOLS. GRIESBACH and CHAIKOFF (1954), two specific types of delta-cells were distinguishable in the rat anterior pituitary.