Biomedical subjects

W C Parks

Publications and source records attributed to W C Parks.

112 records · Page 7Linked to original sources

PubMed1982

Insulin mediates the stimulation of pyruvate kinase by a dual mechanism.

A radioimmunoassay specific for liver pyruvate kinase was used to determine the mechanism(s) involved in the insulin stimulation of this enzyme activity in chronically diabetic rats. Rats, made diabetic with alloxan, were fed on a high-carbohydrate (50%-sucrose) fat-free diet and treated with insulin for 12, 36 or 60 h. Livers were removed at the various times, a piece was kept for determination of glycogen, and the remainder was homogenized. The 100000 g supernatant was prepared and used for determination of pyruvate kinase activity and quantity. Glycogen increased to a maximum of approx. 7% by 12 h after insulin treatment, and was maintained at this elevated value for 60 h. Liver pyruvate kinase activity, which is depressed in diabetes, did not respond to insulin until 36 h of treatment, with a more substantial increase occurring by 60 h. Radioimmunoassay data indicated that the increase in activity was concomitant with a substantial increase in the quantity of the enzyme and a moderate increase in its specific activity. These results demonstrate that a dual mechanism, i.e. an increase in both the quantity and specific activity of the enzyme, regulates the insulin-mediated stimulation of liver pyruvate kinase in the diabetic rat.

Animals↗

PubMed1981

Rapid alterations induced by insulin in hepatocyte ultrastructure and glycogen levels.

The speed with which insulin alters hepatocyte ultrastructure and glycogen levels in insulin-deficient rats has been studied. Insulin deficiency was induced with alloxan, followed by insulin treatment with regular and NPH insulin. Rats were killed at various times after the insulin injection, blood samples were obtained, plasma glucose levels were determined, and liver samples were prepared for electron microscopy and glycogen determinations. Plasma glucose levels in insulin-deficient rats declined to normal values by 4 hours post insulin, returning to insulin-deficient levels by 8 hours post insulin. Hepatic glycogen was considerably reduced in the insulin-deficient rats. By 1 hour post insulin hepatic glycogen increased, reached maximal levels by 8 hours, then declined to insulin-deficient levels by 36 hours. The ultrastructural appearance of both centrilobular and periportal hepatocytes from insulin-deficient rats showed abundant vesicular smooth endoplasmic reticulum (SER), decreased rough endoplasmic reticulum (RER), and enlarged RER intracisternal spaces. One-half hour post insulin, centrilobular hepatocytes were unchanged. In periportal hepatocytes, however, vesicular SER was no longer visible, the RER intracisternal spaces appeared normal, and the amount of RER had increased. By 1 hour post insulin the centrilobular hepatocytes showed similar ultrastructural changes. These changes became more pronounced in the next few hours and remained through 24 hours. By 36 hours both centrilobular and periportal hepatocytes appeared similar to those in the insulin-deficient rat. These results demonstrate the rapid and lobular-specific effects insulin has on the hepatocyte.

Animals↗

PubMedDate not supplied

Matrix metalloproteinases in repair.

During repair, many different matrix metalloproteinases are produced by multiple cell types residing in various compartments within the wound environment. This diversity of enzymes, coupled with discreet cellular expression, implies that different matrix metalloproteinases serve different functions, acting on a variety of substrates, during wound healing. With few exceptions, however, the actual function and spectrum of functions of matrix metalloproteinases in vivo is not known. Even with the advent of genetically defined animal models, few studies have rigorously addressed the substrates and role of matrix metalloproteinases in wound repair. Before we can understand the role of matrix metalloproteinases in ulceration and disease, we need to determine the function these enzymes serve in normal tissues and repair.

Animals↗

PubMedDate not supplied

In situ hybridization of human erythropoietin in pre- and postnatal kidneys.

Due to the transient transcription of the gene of erythropoietin (EPO) in response to hypoxic stimuli, localization within the cell of origin in humans has not been possible. Under acutely induced transcription of the EPO gene, through severe bleeding (hematocrit < 10%), EPO transcripts were detected within renal interstitial cells in rodents. However, by immunohistochemistry or tissue culture, human tubular epithelial cells or glomerular mesangium have been shown to produce EPO, suggesting a species difference. Aiming to investigate the precise location of EPO in intact human kidneys, 38 fetal, infant, and adult kidneys were examined by in situ hybridization. Kidneys from patients with conditions predisposing to severe hypoxia and/or induced polycythemia were utilized, because under these conditions active EPO mRNA synthesis is expected. We found specific EPO mRNA transcripts within a small population of cortical interstitial cells of near-term or postnatal kidneys.

Adult↗