The Effect of Experimental Diabetes Mellitus and Insulin Replacement on Hepatic Ultrastructure and Protein Synthesis

Abstract

A B S T R A C T The following study was conducted in order to define the specific alterations in hepatic ultrastructure responsible for the decrease in hepatic protein synthesis associated with experimental diabetes. Rats received intravenous alloxan (70 mg/kg) and 48 h later were either sacrificed or given insulin for 1, 2, 4, 6, or 24 h. Specimens for electron microscopic evaluation and morphometric analysis were taken from the same livers used to isolate ribosomes for measurement of in vitro protein synthesis. Our results show that hepatocytes from animals with untreated alloxan diabetes show varying degrees of disorganization and loss of rough endoplasmic reticulum (RER) which is directly related to the severity of the alloxan diabetes. A significant correlation existed between the severity of ultrastructural changes as judged by the loss of both membrane and polysome components of the RER and degree of inhibition of protein synthesis (P < 0.001). Abnormalities of hepatic ultrastructure and protein synthesis were reversed within 24 h of insulin administration. The data are consistent with the view that it is the relative decrease in hepatic polysomes that results from the loss of RER in alloxan diabetes that is responsible for the decrease in hepatic protein synthesis.

Correlation of albumin production rates and albumin mRNA levels in livers of normal, diabetic, and insulin-treated diabetic rats.

“…Other studies with perfused livers (6) or isolated hepatocytes (7) indicated an impaired secretion of proteins in diabetic rats. Such a defect may relate to the marked disruption and disorganization of the rough endoplasmic reticulum observed in liver of diabetic rats (8)(9)(10), as export proteins are synthesized almost exclusively on the rough endoplasmic reticulum (11).…”

The ECK fistula in animals and humans

“…The hepatic protection in eviscerated animals 52 was almost identical to that observed with intraportal insulin therapy after portacaval shunt 10,11 and was indistinguishable from the hepatic protection provided by insulin in diabetic rats. 54 In hepatocyte tissue culture systems, many investigators have described analogous insulin effects. [55][56][57][58] The role of insulin in maintaining hepatocyte mitochondrial metabolism has also been emphasized.…”

Effect of duration of insulin deficiency on membrane-bound and free ribosomes from livers of diabetic rats

“…Details of the preparation of liver samples for electron microscopy have been recently reported from this laboratory [2,3]: quantitative characterization of the RER was based on the methods of Loud [14] and Weibel [15].…”

“…In contrast to the effect of diabetes on bound ribosomes, there was no change in protein synthetic activity of free polyribosomes isolated from livers of rats, 3, 7 or 28 days after induction of diabetes. Thus, the effect of any given degree of diabetes on hepatic protein synthesis appears to vary with the population of hepatic ribosomes being studied, and with duration of insulin deficiency.Key words: Insulin deficiency, protein synthesis, hepatic ribosomes, diabetic ribosomes.Previous studies from our laboratory have indicated that in vitro hepatic protein synthesis was decreased in rats with acute and severe experimental diabetes mellitus [1,2], and that this decrease in protein synthesis was accompanied by a marked loss and disruption of the hepatocyte rough endoplasmic reticulum [2]. Upon further analysis [3] it became clear that the decrease in total hepatic protein synthesis was limited to the bound polyribosome fraction.…”

“…Previous studies from our laboratory have indicated that in vitro hepatic protein synthesis was decreased in rats with acute and severe experimental diabetes mellitus [1,2], and that this decrease in protein synthesis was accompanied by a marked loss and disruption of the hepatocyte rough endoplasmic reticulum [2]. Upon further analysis [3] it became clear that the decrease in total hepatic protein synthesis was limited to the bound polyribosome fraction.…”