Light and electron microscopical studies on the appearance of a marginal layer and colloid in the pituitary cleft in young rats.

Studies on the marginal zone and colloid of the pituitary cleft in pituitaries of rats aged 2 to 88 days were performed by light and electron microscopy. From 10 days of age the intermediate lobe could be divided into two parts, i.e., the marginal layer and the intermediate lobe proper. The former part consisted of agranular cells facing the cleft; the latter part comprised granular cells stained with PAS-lead hematoxylin. In addition, the former part was separated from the latter by a basal lamina. In 2 and 6-day-old animals, however, there was neither a rising of the marginal layer nor an occurrence of the basal lamina, although the agranular cells and the granular cells could be distinguished in the intermediate lobe. Accordingly, it appears that the marginal layer of the intermediate lobe beings to occur after 6 days of age. The PAS reactivity of the colloid in the pituitary cleft was generally weakly positive up to 20 days of age, and then from 26 days onward the reactivity became stronger, being strongly positive in 74 and 88-day-old rats. Consequently, it is suggested that the PAS positive substances begin to be stored in the cleft after birth and increase with the advance of age.