Charles F. Howard

Changes in Islet Cell Composition During Development of Diabetes in Macaca nigra

The islets of Langerhans in sections from the pancreas tail of Macaca nigra were stained by antiserum to insulin, glucagon, or somatostatin. The area of stained cells per total area of the islets was determined by a computerized photometric method. Insulin of the beta cells occupied 77% of the islet area in nondiabetic (ND) monkeys and decreased to 62% in monkeys in the earliest stages of metabolic deterioration, i.e., hormonally impaired (HI) monkeys. At the later stage of borderline diabetes (BD), monkeys had only 39% of the islet area occupied by insulin and the area was diminished to 1% in diabetic (D) monkeys. Islets in HI monkeys had an unusual pattern in which only the beta cells in the periphery of islets were stained. Glucagon in the alpha cells stained 7% of the islet area in ND monkeys, but the area was almost doubled to 13% in HI monkeys; the percentage decreased to about 5% in BD and 3% in D monkeys. Somatostatin accounted for 5% of the islet area in ND monkeys, was slightly greater at 7% in HI monkeys, and decreased to 3% in BD and 2% in D monkeys. Alterations in percentages of secretory cells correlated with several of the metabolic and clinical Changes.

Aortic atherosclerosis in normal and spontaneously diabetic Macaca nigra

Aortic atherosclerosis is minimal in normal Macaca nigra; development of atherosclerosis correlates with increasing severity of diabetes mellitus. The extent of aortic involvement (plaque plus sudanophilia) was quantified and compared with metabolic and clinical parameters. Increasing atherosclerosis correlated with decreasing ability to clear glucose in a tolerance test (P less than 0.01), decreasing insulin (P = 0.02), and increasing glucose (P less than 0.01) and triglycerides (P less than 0.01). A diabetic index, established as a summation of several metabolic measurements, correlated with atherosclerosis at P less than 0.001. On the average, involvement of the thoracic aorta was about 3-fold greater than in the abdominal portion; involvement reached over 40% in severely diabetic monkeys. Atherosclerosis development is unique in these monkeys since they consume a natural ration low in fat and cholesterol. Serum cholesterol did not correlate with diabetes or artherosclerosis. Increasing age alone was associated with slight sudanophila, some intima-media thickening, and occasional small lesions. However, only with increasing severity of diabetes was there significant atherosclerosis.

Aortic lipogenesis during aerobic and hypoxic incubation.

Abstract Atherosclerotic rabbit aortas incorporate more [2- 14 C]glucose into lipids when incubated under hypoxic than aerobic conditions. This increase results from greater radiosubstrate incorporation into the glycerol moiety of glycerides and phospholipids. Fatty acids are synthesized mainly by elongation; synthesis of all fatty acids is less during hypoxia. Though the total amount of [1- 14 C]acetate incorporated into lipids is the same during both incubation conditions, there is a redistribution so that this substrate equilibrates more into phospholipid glycerol during hypoxia. Fatty acid synthesis from [1- 14 C]acetate is primarily by elongation and decreases during hypoxic incubation.

Correlations of aortic histology with gross aortic atherosclerosis and metabolic measurements in diabetic and nondiabetic Macaca nigra

We studied the aortic histology of 28 Macaca nigra males and females, from 6 to more than 20 years old, normal and manifesting various degrees of spontaneous diabetes. Correlations of several metabolic and hormonal indicators of diabetes severity with gross and microscopic findings in the aortas demonstrated direct associations with the severity of atherosclerosis. Mild to relatively severe aortic lesions were present. These monkeys showed many changes similar to those observed in medium and large arteries of diabetic humans. Intimal proliferation, prominent extracellular fibers as part of the intimal thickening, and lipid deposition--mostly in extracellular locations--were particularly evident. Significant relationships were observed when glucose clearance, insulin secretion, and fasting glucose levels were correlated with all aortic microscopic findings. Cholesterol concentrations had no correlation with the histological state of the aortas, and triglyceride levels correlated only with aortic lipid content and intimal thickness. Aortic pathologic changes increased with age; diabetics had significantly greater changes than nondiabetics. Macaca nigra can be useful in the study of how diabetes affects the development of atherosclerosis without the influence of an atherogenic diet.

Metabolism of Arachidonic Acid by Macaque Platelets Implications for Studies on Atherosclerosis

The metabolism of [1-14C]arachidonic acid [( 1-14C]AA) by washed platelets from macaques and human subjects was investigated. The results were as follows: At substrate levels of 1 microM, similar amounts of prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2 alpha), prostaglandin D2 (PGD2), and thromboxane A2 (TXA2), measured as thromboxane B2 (TXB2), were produced from [1-14C]AA by platelets from rhesus, Celebes black, and cynomolgus macaques and humans. An increase in the AA concentration from 1 microM to 20 microM decreased the TXB2: PGD2 ratio (aggregator: antiaggregator) from greater than 5 to less than 2 in all series. In the human series, the ratio decrease was due to an increase in PGD2 production; in the macaque series, PGD2 production increased and TXB2 production decreased. Under basal conditions and at 1 microM AA concentrations, the amounts of prostaglandins and thromboxanes produced by platelets from male and female rhesus macaques were the same. An increase in substrate concentration from 1 microM to 20 microM AA decreased TXB2 production and increased PGD2 production to the same extent in platelets from male and female rhesus macaques. Imidazole increased prostaglandin production and decreased TXB2 production by platelets from both male and female rhesus macaques. The TXB2: PGD2 ratios were reduced below 1.5; there was no difference between the ratios in the two series. In the presence of 1 mM imidazole, greater amounts of prostaglandins and thromboxanes were produced in the male than in the female series. These data indicate that macaques platelets are a suitable model for the study of AA metabolism in human platelets.

Reaction patterns of islet-cell autoantibodies in Macaca nigra.

Circulating islet-cell autoantibodies (ICAAs) that reacted specifically with cytoplasmic components have been found in the blood of prediabetic Macaca nigra. The three distinct reaction patterns observed involved the majority of islet cells throughout the islet; a moderate number of cells, mainly at the islet periphery and around the vasculature; and a few cells scattered throughout the islet. Pancreas sections incubated with sera containing ICAAs followed with peroxidase-conjugated antibody were then reacted with antiinsulin, antiglucagon, or antisomatostatin antisera. The pattern associated with most of the islet cells was shown to be reactive to beta cells and was termed B-ICAA; the pattern with cells at the periphery was identified as alpha cells (A-ICAA); and the scattered cells contained somatostatin (D-ICAA). None of the three islet hormones were able to block ICAA reaction after overnight incubation, so the ICAAs are not anti-islet hormone antibodies. The vaned reactions with antigens of different secretory cells indicate release of a variety of immunogens from islet cells as they necrose and cause the formation of different ICAAs.

Effects of ADP and epinephrine on Macaque and human platelets. Implications for studies on human atherosclerosis

The ranges for near-threshold ADP concentrations for the aggregation of macaque and human citrated platelets overlapped. The minimum concentrations of epinephrine, 0.05 microM to 1.0 microM, that at least doubled the aggregation response at threshold ADP concentrations were comparable for macaque and human citrated platelets. Epinephrine (1.0 microM to 10 mM) alone never aggregated macaque citrated platelets. Biphasic aggregation occurred with both macaque and human citrated platelets. The addition of heparin to a final concentration of 2.2 units/ml had no effect on the threshold ADP concentrations or the sensitivity of macaque or human citrated platelets to epinephrine. One microM phentolamine eliminated the potentiating effect of 1 microM epinephrine on ADP-induced aggregation of macaque and human citrated platelets. The threshold concentrations of ADP for macaque platelets were sharply reduced when heparin was used as an anticoagulant rather than citrate. However, epinephrine induced a similar increase in aggregability with both citrated and heparinized platelets, 0.55 +/- 0.09 SEM% and 0.44 +/- 0.09 SEM%, respectively. These data indicate that macaque and human platelets behave in a similar manner in response to ADP and that epinephrine potentiates the ADP-induced aggregation of macaque and human platelets equally well.

Lipoprotein patterns in nondiabetic, borderline diabetic, and diabetic Macaca nigra

Lipoproteins were isolated by sequential ultracentrifugation, and the concentrations and compositions were determined in nondiabetic (ND), borderline diabetic (BD), and diabetic (D) Macaca nigra males consuming a chow ration. The total concentrations and components of the VLDL and IDL increased significantly with metabolic deterioration (P less than 0.01). Concentrations and components of LDL increased in the BD and D monkeys, but changes were not statistically significant. The HDL2 and HDL3 particles were virtually unchanged among the three different metabolic groups. The VLDL was the major carrier of the triglycerides, especially in D monkeys. Cholesterol was present predominantly in the LDL. The LDL-cholesterol to HDL-cholesterol ratio increased in the BD and D monkeys, owing mainly to increases in the LDL-cholesterol content. Apoprotein antisera showed apoprotein B in the VLDL, IDL, and LDL, apoprotein E in the VLDL and IDL, and apoprotein A-I in the HDL2 and HDL3 fractions. Because Macaca nigra consume a nonatherogenic, low-cholesterol, low-fat ration, the changes in lipoproteins, particularly in VLDL and IDL, are attributable to metabolic alterations associated with diabetes.