An electron microscopic and biochemical study of the effects of cyclic 3', 5'-AMP, ergotamine or propranolol on the lysosomes of newborn rat hepatocytes.

The effects of cyclic 3',5'-AMP, ergotamine or propranolol on newborn rat liver were studied by using biochemical assays, electron microscopy and quantitative morphometry. Cyclic AMP enhanced the normal postnatal rise in the glycogen-hydrolysing activity of acid alpha 1, 4 glucosidase but had no effect on the maltose-hydrolysing activity of the enzyme. The results suggest that these activities may be due to different enzymes. Propranolol prevented the postnatal increase in the glycogen-hydrolysing activity of acid glucosidase and the breakdown of lysosomal glycogen, indicating that these phenomena represent beta-adrenergic functions in newborn rats. Ergotamine also inhibited the postnatal increase in this activity and the lysosomal glycogen mobilization. A reasonable explanation for these results is that ergotamine interferes with the action or formation of cyclic AMP.     

Glycogen autophagy in newborn rat hepatocytes

Glycogen autophagy in newborn rat hepatocytes was studied by using enzyme determinations and electron microscopy. Cyclic AMP induced glycogen autophagy in these cells. Glycogen-hydrolyzing acid glucosidase activity increased whereas acid mannose 6-phosphatase activity decreased in the liver of these animals. Parenteral glucose, which prevents postnatal glucagon secretion and tissue cyclic AMP elevation, and propranolol which antagonizes cyclic AMP, inhibited glycogen autophagy. Glucosidase activity decreased and phosphatase activity increased. These findings raise the possibility that cyclic AMP-induced autophagic mechanisms in newborn rat hepatocytes are associated with changes in the activity of acid mannose 6-phosphatase.     

Electron microscopic demonstration of glycogen and phosphorylase activity in rat hepatocytes

Synopsis The effect of fixation with a bicarbonate-buffered solution of paraformaldehyde and polyvinyl pyrrolidone (PVP) on the ultrastructural demonstration of glycogen and phosphorylase activity in rat hepatocytes has been studied. Phosphorylase was demonstrated by the precipitation of liberated phosphate ions with ferrous ions. 7.5% PVP was included in all steps in the procedure before post-fixation in osmium tetroxide.Glycogen particles were well preserved. Structures connecting membranes and glycogen particles were also evident. Phosphorylase activity was rapidly inhibited by the fixative; the fixation time was, therefore, kept very short. The final reaction product was localized on glycogen particles and on endoplasmic membranes in association with glycogen particles. The results support the view that endoplasmic membranes are involved in the metabolism of glycogen in hepatocytes.Paper presented at a symposium The changing directions of carbohydrate histochemistry at the Fifth International Congress of Cytochemistry and Histochemistry in Bucharest, Romania on 1 September 1976.     

Chick hepatic lectins: An electron microscopic study on isolated hepatocytes during development

We studied the carbohydrate recognition systems of hepatocytes isolated from 16-day-old embryos, 19-day-old embryos and chicks within 24 h of hatching. We localized and quantified at the ultrastructural level the binding sites for glycoproteins exposing terminal N-acetylglucosamine (GlcNAc), mannose and N-acetylgalactosamine (GalNAc) residues by means of protein-gold complexes. Binding sites specific for GlcNAc and mannose residues are present on hepatocytes from embryos and chicks. On the contrary GalNAc specific binding sites are exclusively observed on cells from 16-day-old embryos. The number and distribution of gold particles on hepatocyte cell surfaces depend on the binding sites and the age considered. We describe a modulation in the number of GlcNAc, and mannose specific receptors present on the cell surface between the embryonal stage and neonatal life.     

An electron microscopic study of cultured rat testicular fragments

Summary Fragments of testicular tissue of 26-day-old rats were grown as organ cultures during one to six weeks. Electron microscopic studies showed that these tissues can be maintained in vitro for prolonged periods of time, although the most differentiated elements (Leydig and spermatic cells other than spermatogonia) fail to continue their development and degenerate rather rapidly. The connective tissue structures preserve their usual architecture, but the basal membrane of the tubules appears extremely folded and detached from the epithelium. After four weeks in culture, spermatogonia without differentiating are still present, and among them the presence of a more primitive type is noted. Sertoli cells are well preserved and ultrastructurally they present the characteristics of the adult type. The possibility exists that differentiation of these two lines of cells may be achieved in vitro if the factors necessary for their growth and differentiation are recognized and incorporated in the culture system.     

Energy depletion and autophagy. Cytochemical and biochemical studies in isolated rat hepatocytes

Summary In this paper, data dealing with the sensitivity of autophagy towards partial ATP depletion in isolated rat hepatocytes are reviewed. Partial reduction of intracellular ATP causes: (1) a decrease of proteolytic flux; (2) a decrease in uptake of cytosolic components into the autophagic-lysosomal compartment; (3) either a decrease or no change in the ratio between volume densities of autophagosomes and lysosomes, depending on whether or not the cytosolic phosphate potential is affected; and (4) impairment of the lysosomal proton pump. It is concluded that the consecutive steps of autophagy all respond to relatively small changes of intracellular ATP concentration.     

The pituitary cleft of the rat: An electron microscopic study

The epithelium of the pituitary cleft and its colloid have been studied at the ultrastructural level in normal, adrenalectomized, castrated, dehydrated and lactating adult rats. Both control and experimental animals showed cells in different stages of degradation inside the cleft and mixed with the colloid. These exfoliated cells seems to have originated from the cleft's epithelium or the adjacent granular cells.In adrenalectomized and castrated rats the rostral epithelium of the cleft had large intercellular spaces that in some instances appeared to open directly into the cleft. Occasionally the adenohypophysial canaliculi of the adrenalectomized rats were also seen connecting with the cleft. In lactating and castrated animals dark cells appeared more frequently in the rostral and caudal epithelium of the cleft.The results obtained suggest that the colloid is originated at least in part by involuted pituitary cells. There is also evidence that the follicular cavities of the Pars distalis and the cleft are continuous structures.