Experimental diabetes upregulates the expression of uretereral endothelin receptors

Contractile effects of endothelins on isolated human ureter

The aim of our study was to investigate mechanism of action of endothelins 1, 2 and 3 on spontaneous activity, tone and intraluminal pressure of human ureter. Both longitudinal tension and intraluminal pressure were recorded from the isolated segments of proximal human ureter. Endothelins 1, 2 and 3 (5.35x10(-11) M - 5.05x10(-8) M) produced concentration-dependent tonic contraction and sustained increase in intraluminal pressure of isolated preparations of human ureter. Endothelins 1 and 3 produced also concentration-dependent inhibition of spontaneous, phasic contractions of the isolated preparations. Selective antagonist of ET(A) receptors BQ123 and selective antagonist of ET(B) receptors BQ788 produced significant inhibition of endothelin-1-induced tonic contraction (pA(2)=8.80 and 6.55, respectively) and increase in intraluminal pressure (pA(2)=8.68 and 7.02, respectively), while they did not affect endothelin-1-induced inhibition of spontaneous activity. Endothelin 1 produces increase in tone and intraluminal pressure of isolated human ureter acting on both ET(A) and ET(B) receptors, the first one being functionally more important. Only endothelins 1 and 3 inhibit spontaneous, phasic activity of human ureter, but this effect was not blocked by selective antagonists of ET(A) and ET(B) receptors.

Ethanol extracts of Rehmannia complex (Di Huang) containing no Corni fructus improve early diabetic nephropathy by combining suppression on the ET-ROS axis with modulate hypoglycemic effect in rats

AIM

Liuwei Dihuang (Rehmannia complex, RC) decoction, a classic prescription of Traditional Chinese Medicine (TCM), has been used in treating diabetic nephropathy (DN). Among the 6 crude medicines which contains Corni fructus is recognized as the active fraction for its effectiveness. We aimed to investigate, first, if without Corni fructus a modified RC could be still effective, second, if the ethanol extracts could be better than that of water extract and third, the beneficial effect is mainly stemmed from suppressing the endothelin (ET-1) pathway associated with a moderate hypoglycemic effect.

METHODS AND MATERIALS

Diabetes for 8 weeks was induced by a single dose of streptozotocin (STZ, 65 mg/kg, i.p.) in rats and treated with RC extracts in either 95%, 70% ethanol or water separately during 5-8th week. The efficacy of extracts was compared with aminoguanidine (AMG).

RESULTS

An increase in albumin and creatinine in 24h urine, blood urea nitrogen (BUN) was found in STZ rats. Oxidative stress was found in renal cortex in association with upregulated plasma ET-1 and mRNA of ETA, decreased MMP 2,9 (matrix matelloproteinases) and increased hydroxyproline.

CONCLUSIONS

The RC without Corni fructus was very effective in alleviating DN and ethanol extracts provided greater effects against water extracts. The efficacy in alleviating DN is attributed to normalizing the activated ET system, oxidative stress and MMP 2,9 in combination with a moderate hypoglycemic activity.

Differential regulation of endothelin secretion and endothelin receptor mRNA levels in JAR, JEG-3, and BeWo choriocarcinoma cell lines and in human trophoblasts, their nonmalignant counterpart

Endothelin (ET) secretion and expression of both ET-A and ET-B receptor subtypes have been found in a number of primary cancers. The present study tested (1) whether choriocarcinoma cells and their nonmalignant counterpart, the trophoblast, secrete ET-1 and express ET-A and ET-B receptors; (2) whether ET-1 secretion and receptor mRNA levels are regulated by the same factors in nonvascular tissues as in vascular tissues; and (3) whether such regulation is similar in malignant and nonmalignant cells. All cells secreted ET-1 in similar amounts (approximately 0.8 fmol/10(6) cells per 24 h) and secretion was unaffected by culture and treatment. Whereas ET-B accounted for almost all (>98%) ET receptor transcripts in the choriocarcinoma cells, the trophoblasts expressed about 20% ET-A receptor mRNA. During control cultures, ET-B mRNA levels rose in choriocarcinoma, with the greatest relative increase (6-fold; P < 0.05 vs 0 h) in BeWo, whereas in trophoblasts, ET-A mRNA transiently changed after 24 and 48 h. Treatment with dexamethasone and glucose did not alter the mRNA levels in all cells. Insulin induced changes (P < 0.05) in ET-B mRNA levels in BeWo (+90 and +60% after 24 and 48 h, respectively) and JEG-3 (-70%), but not in JAR and trophoblast cells. We conclude that malignant transformation affects the responsiveness of the endothelin receptor system to external stimuli and that the regulation of the endothelin system differs in vascular and nonvascular tissues.

Gene expression, localization, and pharmacological characterization of endothelin receptors in diabetic rat bladder dome

As there are significant amounts of functional endothelin receptors in the mammalian urinary tract, we examined the effect of experimental diabetes on the expression of endothelin receptors and their mRNAs in the rat bladder dome. The density of endothelin receptors in the rat bladder dome was higher (8 and 16 weeks following the onset of diabetes) than in age-matched controls. Insulin treatment, started 8 weeks after the induction of diabetes, partially reversed the endothelin receptor alterations. The pharmacological profile of the endothelin receptors in the bladder dome was similar in all groups and was consistent with the predominance of the endothelin ET(A) receptor subtype (ET(A):ET(B)=approximately 4:1). Autoradiographic studies demonstrated that the endothelin receptors were located in all tissue components of the bladder, including epithelial and muscular layers. Semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) data indicated that diabetes increased the expression level of gene transcripts for both endothelin receptor subtypes and that insulin treatment reversed the mRNA upregulation.

Endothelin and free radicals modulate microvascular responses in streptozotocin-induced diabetic rats

The quantitative contribution of endothelin and free radicals in modulating peripheral endothelial and smooth muscle-dependent vascular responses in 4 weeks streptozotocin-induced diabetic rats was investigated. Skin blood flow was monitored in base of blisters raised on the hind footpad. Smooth muscle-dependent vasodilation was tested using sodium nitroprusside (SNP). Endothelial-mediated inflammatory responses were induced via either electrical stimulation (ES) of the sciatic nerve or substance P (SP) perfusion over the blister base. Role of endothelin and free radicals was examined using ET-A or ET-B receptor antagonists (BQ-123 or BQ-788) and superoxide anions or hydroxyl radicals scavengers (superoxide dismutase (SOD) or N-acetyl cysteine (NAC)). Diabetic rats showed a significant reduction (75%) in SNP responses that coincided with a 70 and 60% reduction in responses to ES and SP. Their basal plasma extravasation (PE) was significantly higher while PE response to SP was significantly reduced. BQ-788, was more potent than BQ-123, improving responses to ES and SP in diabetic rats by 85%. Likewise, NAC was more potent than SOD normalizing the ES response and improving SP response by 85%. Combined treatment with BQ-123 and SOD normalized all vasodilatation responses in diabetic rats. BQ-123 and BQ-788 were equally potent normalizing the PE responses to SP whereas SOD and NAC had no effect. We conclude that endothelin and free radicals play a role in altering microvascular function in diabetes and that their effect could be reversed early in the disease.

Effects of insulin treatment on diabetes-induced alterations in endothelin receptors in rat ureter

BACKGROUND

The present investigation was undertaken to examine the effect of insulin treatment on diabetes-induced alterations in endothelin (ET) receptors in rat ureters.

METHODS

The biochemical properties of ET receptors were examined in rat ureters from the following groups: 8 weeks diabetic (D8); 8 weeks age-matched control (C8); 16 weeks diabetic (D16); 16 weeks diabetic-insulin treated (insulin started 8 weeks after the onset of diabetes) (DI16); and 16 weeks age-matched control (C16). Diabetes was induced by the i.v. injection of 65 mg/kg streptozotocin (STZ).

RESULTS

The densities of ET receptors (Bmax values), as determined by saturation experiments with [125I]-ET-1, in the ureteral plasma membranes of D8, C8, D16, DI16 and C16 were 91.7 +/- 10.1, 42.1 +/- 7.2, 71.1 +/- 2.4, 51.5 +/- 6.3 and 45.1 +/- 3.3 fmol/mg of protein, respectively. [125I]-ET-1 binding to the ET receptors in rat ureteral membrane particulates was inhibited by ET-1 (non-selective), ET-3 (ET(B/C selective), BQ610 (ET(A) selective) and IRL 1620 (ET(B) selective) with the following rank order of Ki values: ET-1 < BQ 610 < ET-3 << IRL 1620. The pharmacological profile of the ET receptors was similar in all groups examined and was consistent with the predominance of the ET(A) receptor subtype in the ureteral membrane particulates. The subtype specificity of ET receptors in the ureteral tissues is confirmed with inhibition data obtained from similar binding studies in cloned human ET(A) and ET(B) receptors.

CONCLUSION

The data indicate that diabetes results in an up-regulation of ET receptors in the rat ureter, which is normalized by insulin treatment.