Regeneration of the islets of Langerhans in the guinea pig

Summary The regeneration of the islets of Langerhans in the guinea pig was studied after intravenous injection of alloxan. A number of cells in the islets was destroyed within 24 h after alloxan, but after 48 h there was a rapid proliferation of the surviving cells of the islets. This depended on the dosage of the drug as well as the timing. Electron microscopy of the islet at 48 h showed that the dividing cells had small electron dense granules and resembled a subtype of normal A cells, whose function is not yet known. There were also many agranular cells in the islet. These two groups of cells seen in the regenerating islet could be precursor cells, which could differentiate into cells. There was no evidence for transformation of duct cells or acinar cells into islet cells. None of the guinea pigs became permanently diabetic. This was probably due to inadequate dosage which resulted in only partial degeneration of the cells followed by regeneration and recovery. There was also some regeneration of the liver, kidney and the adrenal cortex following alloxan.The author is grateful to Professor R. Barer for his guidance and for providing the facilities for this study. Thanks are also due to Mrs. D. Barraclough for technical assistance and to Mrs. M. Hollingsworth for assistance with the photographsThis work was financed by a grant from the Cystic Fibrosis Research Trust     

The thyrotropic cells of the guinea pig pituitary

Summary Three different immunocytoenzymatic techniques were used to identify and characterize the thyrotropic cells in the pituitary of normal guinea pigs at the ultrastructural level (superimposition technique, immunocytochemical technique using P.A.P. and indirect immunohistoenzymatic method before embedding).These cells are characterized by a dark cytoplasm with granules ranging from 1500 to 2000 Å in diameter. The appearance of these granules is very variable: some display a marked electron density and are homogeneous but some have a less marked electron density with a more electron dense peripherally situated region.The TSH molecules are essentially confined to the granules but when the immunocytochemical reactions are carried out before embedding, positive staining is also seen in the cytoplasm and the outer surface of most of the rough endoplasmic reticulum membranes. These results are discussed.We thank D. Quief for technical assistance. This work was supported by a grant from U.E.R. III LilleAttaché de Recherche INSERM     

Functional differentiation of the anterior pituitary cells in the fetal pig

Summary The fetal porcine pituitary was investigated by means of ultrastructural immunocytochemistry (1) to identify the first cells synthesizing the adenohypophyseal hormones, (2) to follow their differentiation during fetal development, and (3) to compare their ultrastructural characteristics with those of mature adult cells.The first ACTH-cells, which produced and stored ACTH, -LPH, -MSH, and - and -endorphin in the same granules, were very numerous at day 34 and displayed a uniform morphology. At day 50 and thereafter, until the end of gestation, the ACTH-cells differed in their appearance probably reflecting various stages of differentiation of one cell type. The GH-cells gained rapidly ultrastructural features comparable to those of mature GH-cells. In contrast, in the case of PRL-cells, which appeared only at the end of the gestation period as immature elements containing very small secretory granules, the morphological maturation seemed to take place only after birth. The first cells synthesizing the glycoprotein hormones (LH, LH, FSH and TSH) displayed ultrastructural features of immature cells. At day 50, their ultrastructural organization started to show a different pattern. At the end of gestation, the TSH-cells and the gonadotropic cells displayed the ultrastructural features of mature cells.