Experimental diabetes mellitus inhibits prostacyclin synthesis by the rat penis: pathological implications

Summary In view of the marked increase in blood flow into the penis during erection and the association of diabetes mellitus with impotence, we used the diabetic rat model to investigate the possibility that: (a) the penis may produce prostacyclin; and (b) prostacyclin secretion may be decreased in diabetes. Rats given a high dose of streptozotocin (120 mg/kg body weight) developed acute ketotic diabetes and were killed after 48 h. Animals given a low dose of streptozotocin (65 mg/ kg body weight) developed non-ketonuric diabetes and were killed after 7 or 62 days. Aortic rings and penile tissue discs were incubated in buffer, which was assayed for 6-oxo-pros-taglandin F₁, the stable and spontaneous breakdown product of prostacyclin. Penile tissue from control, ketotic and non-ketonuric (7 days) animals released similar quantities of prostacyclin, whereas that from long-term non-ketonuric animals (62 days) produced significantly less prostacyclin. Production of this prostanoid by the aortic rings paralleled these changes. We conclude that: (a) penile tissue releases prostacyclin in quantities comparable to those of the aorta; (b) long-term diabetes leads to diminished prostacyclin release by penile and aortic tissue: the former may contribute to the pathogenesis of diabetic impotence; and (c) since short-term ketotic diabetes does not inhibit aortic or penile prostacyclin release, duration of diabetes rather than its severity is responsible for diminished prostacyclin release.     

Inhibition by hydrocortisone of prostacyclin synthesis by rat aorta and its reversal with RU486

A rat aortic explant culture system was developed for the investigation of the effects of hydrocortisone (HC) and the glucocorticoid antagonist, RU486, on prostacyclin (PGI2 synthesis. HC, but not aldosterone, progesterone, 17 beta-estradiol, or testosterone, inhibited spontaneous, epinephrine-stimulated and U46619 (an analog of thromboxane A2)-stimulated PGI2 synthesis by cultured aortic explants in a concentration- and time-dependent manner. Adequate inhibition of aortic explant PGI2 synthesis by physiological concentrations of HC was achieved after an 18-h culture. An 18-h time course was employed in subsequent experiments. In contrast, HC had no effect on arachidonic acid-stimulated PGI2 synthesis. Protein synthesis inhibitors, actinomycin D and cycloheximide, had no effect on the inhibitory action of HC on epinephrine- and U46619-induced release of PGI2. They exerted a direct inhibitory effect on aortic PGI2 synthesis. Arachidonic acid stimulated PGI2 release by the explants and was unaffected either by HC or by treatment with cycloheximide or actinomycin D. RU486 blocked the inhibitory action of HC on aortic PGI2 synthesis in a dose-dependent manner. Thus, the inhibitory effect of HC on vascular PGI2 synthesis is probably mediated through an inhibition of phospholipase A2 and not cyclooxygenase or other PGI2 synthase systems; furthermore, this inhibitory effect is not dependent upon de novo protein synthesis. RU486 antagonizes the inhibitory effect of HC. The inhibition of vascular PGI2 by hydrocortisone has implications in the pathogenesis of steroid-related hypertension and atherosclerosis and the antiinflammatory effect of steroids.     

Urinary metabolites of thromboxane and prostacyclin in diabetes mellitus

The in vivo synthesis of thromboxane A2 and prostacyclin was estimated in 23 diabetics through measurements of the major urinary metabolites 2,3-dinor-thromboxane B2 and 2,3-dinor-6-keto-PGF 1 alpha utilizing gas chromatography-mass spectrometry. Mean excretion was similar to that in non-diabetic subjects. The possible influence of hyperglycemia on the excretion of 2,3-dinor-thromboxane B2 and 2,3-dinor-6-keto-PGF 1 alpha was evaluated in three ways: by measuring excretion before and during an acute 9-h normalization of hyperglycemia through an artificial pancreas (Biostator) as well as by comparing excretion before and 7-12 days or 40-180 days after the initiation of insulin treatment. Despite significant reducing effects on hyperglycemia or on levels of hemoglobin A 1c, no effects on the excretion of the thromboxane and prostacyclin metabolites could be found. Abnormal formation of thromboxane or prostacyclin is not a generalized feature of the diabetic state.     

Teratogenic effects of diabetes mellitus in the rat. Prevention by vitamin E

Summary We wanted to determine whether administration of vitamin E could reduce the production of free radicals which could play a role in the teratogenic effects of diabetes mellitus. Diabetes was induced in Wistar rats by the intravenous administration of streptozotocin. The animals were divided into six groups: one with no supplement (D) and two, supplemented during pregnancy either with oral vitamin E (150 mg/day) (D + E) or with a placebo (safflower oil) (D + O). Three other groups were kept under the same conditions, but were treated with insulin: D + I, D + I + E and D + I + O. There were three groups of matched controls: C, C + E and C + O. All animals were killed on day 11.5 of pregnancy. In C animals the percentages of reabsorptions and malformations were 1.3 and 2%, respectively, comapred with 23.6, 24.3, 6.2 and 13.2%, respectively in D and D + I groups. The crown-rump length, number of somites, and protein and DNA content were higher in C animals than in the diabetic rats, independent of insulin treatment. When vitamin E was administered no changes in these parameters were observed in C and D + I animals; however, in the D mothers it reduced the rate of embryo malformations to 4.6% and increased the crown-rump length and the number of somites. However, vitamin E did not modify the protein and DNA content and the percentage of reabsorptions. In conclusion, administration of vitamin E to diabetic animals decreases the rate of embryo malformations and increases their size and maturation, supporting a role for free radicals in the teratogenic effects of diabetes.     

Reduced serum-stimulatory activity on prostacyclin production by cultured aortic endothelial cells in diabetes mellitus

Reduced prostacyclin (PGI2) production by the vascular wall has been proposed as a possible cause of macro- or microangiopathy in diabetes mellitus. In the present study, we confirmed the stimulatory activity on PGI2 (PSA) production in plasma-derived serum (PDS) by cultured aortic endothelial cells. Furthermore, the abnormality of PSA was examined in diabetic PDS. PSA in PDS from non-insulin-dependent diabetics significantly decreased as compared with that in PDS from age-matched control subjects. There was no difference in PSA in PDS between diabetic patients with and without vascular complications such as retinopathy and nephropathy. In addition, after treatment with dialysis, PSA in diabetic PDS was still not restored to that in normal PDS. These findings suggest that relatively heat-stable (56 degrees C, 30 min) and nondialyzable PGI2 stimulatory substance(s) may decrease in diabetic PDS. It is concluded that a reduction in PDS-stimulated PGI2 production by the vascular wall can play an important role in the pathogenesis of vascular lesions in diabetes mellitus.     

Preventive effects of ophiopogon-polysaccharide on apiponectin in gestational diabetes mellitus rat

ObjectiveTo investigate the effect of ophiopogon-polysaccharide on adiponectin (APN) in gestational diabetic mellitus rat.MethodsThe model of gestational diabeties mellitus rat were established with streptozotocin by intraperitoneal injection. Model rats were randomly divided into ophiopogon-polysaccharide 125 mg/kg group, 250 mg/kg group, 500 mg/kg group, GDM group and normal pregnancy group (n=10). Ophiopogon-polysaccharide was given by intragastric administration for 14 days. The fasting blood glucose levels of rats at the 0, 7, 14 day were detected respectively. The serum insulin level and APN in fat tissue and placenta were detected at the 14 day.ResultsThe fasting blood glucose level, serum insulin level and APN mRNA in fat tissue and placenta were significantly decreased in gestational diabetes rats treated by ophiopogon-polysaccharide compared with model group (P < 0.05).ConclusionsOphiopogon-polysaccharide could decrease the fasting blood glucose level and serum insulin level, and improve APN mRNA in fat tissue and placenta.     

Hydrolase activities in the rat aorta. I. Effects of diabetes mellitus and insulin treatment.

Vascular disease in diabetics could arise in part from altered vessel wall catebolism. Specific activities of hydrolases in aortic smooth muscle cells from rats with streptozotocin-induced diabetes were measured. Enyzmes included: neutral alpha-glucosidase, alpha-mannosidase, and lysosomal N-acetyl beta-glucosaminidase, beta-galactosidase, cathepsin C, acid alpha-glucosidase, and acid cholesteryl esterase. After 4,8, and 11 weeks of diabetes, activities of all enzymes studied were decreased significantly in diabetic vessels, decreases ranging from 15% for cathepsin C to 62% for alpha-mannosidase. After 3 weeks of diabetes, insulin treatment for 1 week restored enzyme levels to normal. After 7 weeks of diabetes, 1 week of insulin treatment did not restore enzyme levels fully to normal (acid cholesteryl esterase was unchanged); 4 weeks of insulin did. Acid phosphatase and N-acetyl beta-glucosaminidase activities were reduced markedly in histochemical studies of diabetic aortas at all time periods and were restored by insulin treatment. Alloxan-induced diabetes gave results similar to those with streptozotocin. Significant decreases of aortic hydrolase activities, including those of lysosomes, occur in experimental diabetes mellitus and could contribute to accumulation of substrates in vascular smooth muscle cells.     

Dose-related opposite effects of hydrocortisone on hepatocyte proliferation in the rat

To evaluate the role of glucocorticoids in the regulation of hepatocyte proliferation, high doses (6.25 mg/kg or more) and low doses (1.25 mg/kg or less) of hydrocortisone were injected into various categories of rats which had very different levels of proliferation. We used: (a) suckling rats whose stable unsynchronized proliferation can be stimulated and synchronized by acute inflammation or cyproterone feeding; (b) adult rats with a low level of proliferation, and (c) 2/3 hepatectomized rats during the first period of synchronized proliferation or during the second period of lower and unsynchronized proliferation. The kinetics of the labelling index and mitotic index were observed after hydrocortisone injection. High doses inhibited proliferation, as already found by many investigators. This effect was observed in suckling and hepatectomized rats and during acute inflammation in suckling or adult rats. Low doses had no inhibitory activities and, on the contrary, stimulated proliferation in some situations. The highest stimulations were observed during the early period after 2/3 hepatectomy or in combination with acute inflammation either in suckling rats or in 2/3 hepatectomized rats during the late period of regeneration. In all these situations hydrocortisone was a cofactor active during the early G₁-phase. In contrast, in normal suckling rats a slight stimulation was observed due to an action at the G₀-G₁ transition. No such effect was found in adult rats. Our data show that doses of hydrocortisone in the therapeutic range or close to physiological values do not inhibit and, on the contrary, can stimulate hepatocyte proliferation.     

Influence of diabetes on enzyme activities in rat aorta

The activities of hexokinase, glucose-6-phosphate dehydrogenase, hydroxyacyl-CoA-dehydrogenase, adenylate kinase and glutathione reductase were determined in the aorta of rats made diabetics with streptozotocin for over two weeks and in noninjected controls. Adenosinetriphosphate (ATP) and total adenine nucleotide content were also measured. Glutathione reductase activity was not significantly changed in the diabetic aorta whereas the activities of glucose-6-phosphate dehydrogenase, hydroxyacyl-CoA-dehydrogenase and adenylate kinase were all increased. Hexokinase activity was significantly decreased in diabetic rat aorta. When measured after incubation in vitro for 2 h with 5.6 mmol/l glucose, the ATP-concentration was reduced in the diabetic aorta while the total concentration of adenine nucleotides was unchanged. Insulin treatment started three days after induction of diabetes with streptozotocin and continued for twelve days restored the growth rate of the rats but their glucose metabolism was not completely normalized. After insulin treatment no significant differences between diabetic and normal rats were found in the aortic activities of glucose-6-phosphate dehydrogenase, hydroxyacyl-CoA-dehydrogenase, adenylate kinase or in the ATP content.     

Hydrolase activities in the rat aorta. II. Effects of hypertension alone and in combination with diabetes mellitus

Hypertension is an important risk factor for atherosclerosis and often occurs in association with diabetes mellitus. Specific activities of hydrolases in homogenates of aortas from rats with renal-clip hypertension, normotension following a period of hypertension, and hypertension combined with streptozotocin-induced diabetes mellitus were measured. Enzymes included: neutral alpha-glucosidase, and lysosomal N-acetyl-beta-glucosaminidase, beta-galactosidase, cathepsin C, acid alpha-glucosidase, and acid cholesteryl esterase. After 6 or 12 weeks of hypertension, specific activities of all enzymes measured were significantly increased, levels ranging from 24% above normal for cathepsin C to 351% above normal for N-acetyl-beta-glucosaminidase. Six weeks of normotension following 6 weeks of hypertension resulted in restoration to normal of four of the six enzyme activities; the remaining two enzymes were significantly below normal levels. Combined hypertension and diabetes mellitus showed smooth muscle cell levels of four of the five hydrolases measured to be significantly lower than those present with hypertension alone. In every instance, histochemical studies of aortas showed acid phosphatase and N-acetyl-beta-glucosaminidase activities which corresponded to the biochemical findings. These findings indicate profound and discrete effects of two clinical risk factors on vascular smooth muscle cell lysosomes.     

锌防治糖尿病的作用机制

自20世纪80年代,锌的类胰岛素作用越来越受到国内外学者的关注。本文简要介绍了锌及其配合物的类胰岛素作用及其与糖尿病的关系,并初步总结了锌对糖尿病防治作用的机制,包括参与胰岛素的合成与分泌、促进酪氨酸蛋白激酶磷酸化、抗氧化、改善免疫功能等。随着对锌及其配合物抗糖尿病作用及作用机制研究的不断深入,该类化合物必将拥有越来越广阔的应用前景。     

空腹血糖和糖化血红蛋白用于筛查糖尿病的研究

目的评估空腹血糖(FPG)和糖化血红蛋白(HbA1c)在筛查糖尿病(DM)和糖耐量受损(IGT)中的应用价值。方法北京地区研究对象1118名,为明确DM诊断而就诊者和DM高危人群接受DM筛查者,男489名,女629名,平均48±12岁,行口服葡萄糖耐量试验(OGTT)并测定HbA1c。结果按照1999年WHO的DM诊断标准,本研究人群糖耐量正常(NGT)、空腹血糖受损(IFG)、IGT、IGT合并IFG和DM者分别为510、35、155、52、366例。采用受试者工作特征曲线(ROC曲线)判断,与以OGTT诊断的DM状态相关的FPG临界点为6.2mmol/L,敏感性和特异性分别为85.0%和90.4%,曲线下面积0.943(95%CI0.927～0.959),阳性似然比8.9,阴性似然比0.2;与以OGTT诊断的DM状态相关的HbA1c临界点为6.2%,敏感性和特异性分别为86.6%和77.5%,曲线下面积0.896(95%CI0.876～0.916),阳性似然比3.9,阴性似然比0.2。与IGT状态相关的FPG临界点为5.1mmol/L,敏感性和特异性分别为65.2%和68.3%,曲线下面积为0.729,阳性似然比2.1,阴性似然比0.5。与IGT状态相关的HbA1c临界点为5.7%,敏感性和特异性分别63.3%和56.5%,曲线下面积为0.634,阳性似然比1.5,阴性似然比0.7。结论6.2mmol/L6.2%时应进一步行OGTT了解2h血糖以明确有无DM,FPG和HbA1c不适用于筛查IGT人群。     

Fasting hyperglycemia normalizes oxidative and nonoxidative pathways of insulin-stimulated glucose metabolism in noninsulin-dependent diabetes mellitus

The present studies were undertaken to determine whether fasting hyperglycemia can compensate for decreased insulin-stimulated glucose disposal, oxidation, and storage in noninsulin-dependent diabetes mellitus (NIDDM) as well as to determine whether hyperglycemia normalizes insulin-stimulated skeletal muscle glycogen synthase and pyruvate dehydrogenase (PDH) activities. To accomplish this, we used the glucose clamp technique with isotopic determination of glucose disposal and indirect calorimetry for measuring the pathways of glucose metabolism, and vastus lateralis muscle biopsies to determine the effects of insulin on glycogen synthase and PDH activities. Nine patients with NIDDM and eight matched non-diabetic subjects were infused with insulin (40 mU/m2.min) while plasma glucose was maintained at the prevailing fasting concentration. During insulin infusion, rates of glucose disposal, storage, and oxidation were the same in the two groups. Insulin infusion significantly activated glycogen synthase fractional velocity to the same extent in NIDDM (0.210 +/- 0.056 vs. 0.332 +/- 0.079) and controls (0.192 +/- 0.036 vs. 0.294 +/- 0.050). Insulin infusion increased PDH fractional velocity in controls (from 0.281 +/- 0.022 to 0.404 +/- 0.038), but not in NIDDM (from 0.356 +/- 0.043 to 0.436 +/- 0.060), although the activity of PDH during insulin infusion did not differ between the groups. We conclude that prevailing fasting hyperglycemia normalizes the nonoxidative and oxidative pathways of insulin-stimulated glucose in metabolism in NIDDM and may act as a homeostatic mechanism to normalize muscle glucose metabolism.