Helen D. Wilson

Effect of Insulin and Oral Glutathione on Glutathione Levels and Superoxide Dismutase Activities in Organs of Rats With Streptozocin-Induced Diabetes

The effect of insulin or glutathione treatment on glutathione content of liver and jejunal mucosa and on superoxide dismutase (SOD) activity of liver, kidney, and erythrocytes was investigated in pair-fed animals with streptozocin (STZ)-induced diabetes. Diabetes lowered hepatic glutathione concentration, but glutathione concentration of the jejunal mucosa was not affected. Insulin, but not oral glutathione, restored hepatic glutathione concentration to normal levels. Diabetes depressed activity of the cytosolic form of SOD in liver, kidney, and erythrocyte. Treatment of diabetic rats with oral glutathione or intramuscular insulin increased cytosolic SOD activity of renal cortex and liver (but not erythrocytes) to control levels. These results suggest a link between glutathione metabolism and cytosolic SOD activity in diabetes.

Vitamin D Dependence of In Vivo Calcium Transport and Mucosal Calcium Binding Protein in Rat Large Intestine

Dependence of large intestinal calcium transport on vitamin D has been examined in vitro in colon only. The authors studied calcium fluxes in cecum and colon in vivo by perfusion with 1.6 mM calcium chloride in saline. Tracer 45Ca either was injected parenterally 24 hr before study or was added to the perfusates. For 8--10 wk after weaning, rats had been fed a rachitogenic diet; 48 and 24 hr before study, 50% of the animals were treated with 20,000 IU vitamin E2. In a separate set of animals, mucosal calcium binding protein was analyzed by the Chelex assay method. In comparison with vitamin D-deficient rats, the colon of vitamin D-treated rats showed higher lumen-to-plasma flux and lower plasma-to-lumen flux and net absorption instead of net secretion. In cecum, calcium transport was not significantly altered by vitamin D treatment. Mucosal calcium binding protein was higher in cecum than in colon in both groups and was higher in vitamin-D-treated than in vitamin D-deficient animals in both segments. The current study shows that in the rat colon calcium fluxes both into and out of the lumen as well as net transport are significantly by vitamin D treatment, but that cecal transport rates are not affected. In both cecum and colon, mucosal calcium binding protein increases with vitamin D treatment.

Intestinal Calcium Binding Protein in the Diabetic Rat

A SPECIFIC duodenal calcium binding protein (CaBP) has been implicated in calcium absorption in many animal species1 and adaptation of duodenal adsorption to increased calcium intake is accompanied by its increase. Vitamin D deficiency depletes and repletion restores CaBP with corresponding changes in duodenal absorption. The exact role of CaBP in calcium absorption has, however, not yet been defined. We studied calcium absorption in the diabetic rat, in which model system previous studies have shown enhanced carbohydrate and amino acid absorption2,3, and found decreased duodenal but normal ileal absorption4. Since CaBP may be important in duodenal calcium absorption, we report here studies of CaBP in rats made diabetic with alloxan.

Calcium Intake Regulates 1,25-Dihydroxy-Vitamin D Formation in the Diabetic Rat

Duodenal calcium absorption and serum 1,25-dihydroxyvitamin D [1,25-(OH)2D] concentrations are decreased and body growth is arrested in the streptozotocin-diabetic rat taking commercial chow with high (1.2–2%) calcium content. Treatment with insulin restores 1,25-(OH)2D3, calcium absorption, and body growth to normal. We hypothesized that the depressed 1,25-(OH)2D3 in diabetics is due in part to the minimal requirement for vitamin-D-mediated intestinal calcium transport under conditions of arrested growth and high calcium intake. We tested this hypothesis by comparing the response of serum 1,25-(OH)2D3 concentration to low (0.02%) and normal (0.5%) calcium diets in control and streptozotocin-diabetic rats. To evaluate response to short-term insulin treatment, serum 1,25-(OH)2D3 was measured after 12 or 36 h of treatment. Serum 1,25-(OH)2D3 concentrations in the 0.5% calcium diet groups were 175, 25, and 120 pg/ml for control, diabetic, and insulin-treated 36-h groups, respectively. Low calcium diets increased concentration to 625, 100, and 370 pg/ml for controls, diabetics, and insulin-treated 36-h groups, respectively. In conclusion, the diabetic retains the ability to respond to calcium deficiency, even in the insulin-deficient state. Low calcium intake, in addition to enhancing 1,25-(OH)2D3 formation in diabetics, also modulates the response to insulin treatment. These studies demonstrate that the regulatory factor(s) suppressing serum, 1,25-(OH)2D3 in diabetes is not simply insulin deficiency per se. Implications of these findings for diabetes are discussed.

Jejunal sodium transport in the rat: Effects of alloxan diabetes

Abstract A previous study has shown that, in the presence of relatively high concentrations of glucose (16 mM), net transport of Na+ and glucose is greater in jejunal sacs prepared from diabetic than control rats. This increase in Na+ transport may be caused by (a) the increased transport of glucose, or (b) differences in glucose metabolism between controls and diabetics. We examined effects of alloxan diabetes on jejunal Na+ transport using a low concentration (1 mM) of a non-metabolized hexose, 3-O- methyl- d - glucose . Net transport of Na+ into the serosal medium (all data μmoles/g wet wt of sac per h) was greater in everted sacs from diabetic (30) than control (15) rats. Mucosal-to-serosal flux of Na+ was also greater in sacs from diabetic rats (213 vs 176), but serosal-to-mucosal fluxes did not differ significantly (151 vs 142). Serosal transport of 3-O- methyl- d - glucose was three times greater in sacs from diabetic rats (6.2 vs 2.4). Thus, jejunal Na+ transport is increased in diabetes, independently of the presence of high concentrations of glucose. In these studies, the increase in Na+ transport is of sufficient magnitude to explain the stimulation of hexose absorption in diabetes. Alternatively, the magnitude of the stimulation of hexose transport could not explain effects of Na+ movements.

Increased intestinal growth in the streptozotocin-diabetic rat occurs prior to changes in hormone secretion

Depressed somatic growth in the rat with streptozotocin diabetes is associated with greatly enhanced intestinal growth. In patients with diabetes mellitus, growth hormone is elevated. Therefore, we measured the association between gut growth and serum growth hormone in the streptozotocin-diabetic rat. At 10 days growth hormone did not differ in control, untreated diabetic and insulin-treated diabetic groups. At 20 days of diabetes, growth hormone was elevated in untreated diabetic groups, but depressed to control levels by insulin. Intestinal growth was markedly elevated in all diabetic groups by 10 days, prior to the increases in hormone levels. We conclude that the enhanced intestinal growth in diabetes is probably independent of growth hormone.

Diabetes and Renal Calcium Binding Protein in the Rat

Abstract Renal calcium binding protein (CaBP), a vitamin D-dependent protein of 28,000 M r, may be involved in calcium transport by cells of the renal tubule. The streptozotocin-diabetic rat is hypercalciuric and shows markedly decreased concentration of 1,25-dihydroxy-cholecalciferol [1,25-(OH)2D3] in serum and of CaBP in small intestine. To examine the relationship of renal CaBP in diabetes to 1,25-(OH)2D3 and urinary calcium excretion, renal CaBP, serum 1,25-(OH)2D3, and urinary calcium were measured in control, diabetic, and insulin–treated diabetic rats. Treatment of the diabetic rat with insulin decreased urinary calcium excretion and elevated 1,25-(OH)2D3 toward normal. Renal CaBP was found to be the same in controls and diabetics despite a tenfold difference in concentration of 1,25-(OH)2D3 in serum, and to be unaffected by insulin treatment, which elevated 1,25-(OH)2D3 by a factor of 7 above untreated diabetics. It is concluded that in the diabetic rat either (1) the threshold concentration of 1,25-(OH)2D3 for inducing synthesis of renal CaBP is set at a much lower level than that for intestinal CaBP, or (2) since both 1,25-(OH)2D3 and renal CaBP are produced in the kidney, 1,25-(OH)2D3 exerts a paracrine effect on renal CaBP production because of its high local concentration. The increased urinary calcium excretion in the untreated streptozotocin-diabetic rat is not secondary to an alteration in renal CaBP.

Intestinal Resection and Calcium Absorption in the Rat

Summary Calcium transport was measured in duodenum and ileum of young rats 7-9 days post 70% resection of mid-small intestine. Duodenal calcium absorption per unit weight of mucosa was depressed to half that of transected controls because of decreased flux out of the lumen. Since absorption per cm segment length of duodenum was also depressed in resected as compared with transected animals, the mucosal hyperplasia secondary to resection did not compensate for decreased absorption per unit weight of mucosa. Ileum of resected animals showed net calcium secretion in comparison with net absorption in transected controls. Possible causes for depression of calcium absorption include abnormal vitamin D metabolism with decreased enterohepatic cycling of polar vitamin D metabolites or immaturity of rapidly proliferating mucosal cells. We thank Fred Kirchner, Radiation Research Laboratory, University of Iowa, for advice regarding the intestinal resections.

Rat Large Bowel Maintains Calcium Transport after Small Bowel Resection

Because of the marked defect in calcium transport by the residual duodenum and ileum of the rat 10 days after 70% resection of mid-small intestine, we examined the calcium transport response by large intestine at this time. Although net cecal calcium absorption was decreased by one third in resected rats as compared with transected controls, total net cecal absorption was maintained because of the small growth response. Colonic calcium transport was the same in transected and resected groups, despite greater segment growth in the resected group. In comparison to the marked abnormality in calcium transport by the residual small intestine secondary to resection, the effect on the large intestine was minimal.

Effects of dietary protein on body weight, mucosal growth, and calcium absorption in the rat.

Previous studies of dietary protein intake and calcium balance demonstrate decreased fecal calcium excretion with high-protein diets. To determine whether a duodenal or ileal calcium transport response could account for these findings, we examined calcium transport by these two segments directly byin situ perfusion. Weight-matched growing rats were pair-fed isocaloric diets for 6–8 days containing 89% protein (casein), 39% protein, or 0% protein. Sucrose was substituted for the decreased casein in the 39% and 0% protein diets. Each diet also contained 5% fat, a mineral mix, and vitamins. Calcium content of all diets was 0.5%. Body weight was maintained by the 39% protein group; weight loss was 5% for the 89% protein group and 18% for the 0% protein group. Smallintestinal weight as a percentage of body weight was the same for the three groups. For both the duodenum and the ileum, mucosal dry weight per centimeter was greater in the 39% protein group than either the 89% protein or 0% protein group. Calcium absorption per gram dry weight of mucosa (absorptive specific activity) was the same for all diet groups, but because of the greater mucosal weight per unit length in the 39% protein group, absorption per centimeter was increased in this group. In conclusion, although we found no direct relation between dietary protein and mucosal absorptive specific activity for calcium, calcium absorption was determined by the amount of mucosa which was dependent on protein intake and reflected the nutritional status of the body.