Peroxisomes in the absorptive cells of normal, rachitic, and vitamin-D replete chick intestine: ultrastructure and histochemistry

Identification of glyoxylate cycle enzymes in chick liver--the effect of vitamin D3: cytochemistry and biochemistry

Information regarding the presence of the glyoxylate cycle in chick liver was sought. This metabolic pathway has long been thought to be absent from vertebrate tissues. Previous studies in other tissues have shown that, when present, this pathway is sensitive to vitamin-D. Thus, the effect of long-term vitamin-D deficiency and subsequent vitamin-D replacement on liver structure was studied by light microscopy. In addition, specific biochemical assays for the presence of glyoxylate cycle enzymes were performed. Light microscopy of lipid extracted tissues, light microscopic histochemistry, and quantitative histochemistry showed that the hepatocytes from vitamin-D-deficient animals contained primarily lipid. Hepatocytes from normal and vitamin-D-replete livers contained primarily carbohydrate as judged by their staining with periodic acid-Schiff (PAS). Also, malate synthase positive peroxisomes were seen in hepatocytes from normal and vitamin-D-treated chicks. Structures positive for this glyoxylate cycle enzyme were rarely seen in the hepatocytes from vitamin-D-deficient animals. Biochemical analyses showed the presence of the two unique glyoxylate cycle enzymes, isocitrate lyase and malate synthase, in chick hepatocytes. The activity of these enzymes was markedly increased in the vitamin-D-replete livers. In addition, chick hepatocytes demonstrated the capacity to oxidize fatty acid in the presence of cyanide. This activity, which is characteristic of peroxisomal B-oxidation rather than mitochondrial, was stimulated by vitamin-D treatment. Lastly, incubation of chick liver in the presence of a fatty acid substrate (palmitate) led to higher tissue glycogen content. The latter was further increased in liver from vitamin-D-replete animals. These data show the presence of glyoxylate cycle enzymes in a higher vertebrate and indicate that this tissue is endowed with the capacity to convert lipid to carbohydrate.

Electron microscopic cytochemical localization of a basolateral calcium adenosine triphosphatase in vitamin D replete chick enterocytes

A cytochemical technique for the electron microscopic localization of calcium adenosine triphosphatase (Ca-ATPase) was utilized to localize this enzyme in the enterocytes of rachitic and vitamin D-replete chicks. In animals treated with cholecalciferol (CC, vitamin D3), an electron-dense reaction product was located along the basolateral membranes of the absorptive cells within 72 hr after injection. Similarly, a reaction product was identified in association with the basolateral membranes within 24 hr after injection of 1,25-dihydroxycholecalciferol, the active metabolite of vitamin D. A microvillar reaction product was not seen in either of these two groups. Electron-dense reaction products were also seen in association with mitochondria and scattered throughout the cytoplasm of these enterocytes. The Ca-ATPase reaction product was dependent upon the presence of medium calcium and substrate (ATP), was inhibited by vanadate, and was heat labile. In the rachitic animals, a reaction product indicative of Ca-ATPase activity was not seen in association with either the basolateral membranes or the mitochondria. These data appear to indicate that an energy-requiring calcium-activated membrane pump plays a role in the flux of calcium across the enterocytes of the small intestine.