Contribution of nitric oxide to the beneficial effects of enalapril in the fructose-induced hyperinsulinemic rat

The Relation between Fructose-Induced Metabolic Syndrome and Altered Renal Haemodynamic and Excretory Function in the Rat

This paper explores the possible relationships between dietary fructose and altered neurohumoral regulation of renal haemodynamic and excretory function in this model of metabolic syndrome. Fructose consumption induces hyperinsulinemia, hypertriglyceridaemia, insulin resistance, and hypertension. The pathogenesis of fructose-induced hypertension is dubious and involves numerous pathways acting both singly and together. In addition, hyperinsulinemia and hypertension contribute significantly to progressive renal disease in fructose-fed rats. Moreover, increased activity of the renin-angiotensin and sympathetic nervous systems leading to downregulation of receptors may be responsible for the blunted vascular sensitivity to angiotensin II and catecholamines, respectively. Various approaches have been suggested to prevent the development of fructose-induced hypertension and/or metabolic alteration. In this paper, we address the role played by the renin-angiotensin and sympathetic nervous systems in the haemodynamic alterations that occur due to prolonged consumption of fructose.

Effect of myricetin on blood pressure and metabolic alterations in fructose hypertensive rats

Fructose feeding induces a rise in blood pressure in normal rats and is associated with insulin resistance, hyperinsulinemia, and hypertriglyceridemia. We have examined the effect of myricetin (100 and 300 mg/kg, p.o. for 6 weeks) isolated from Vitis vinifera Linn. (Vitaceae) on systolic blood pressure (SBP), vascular reactivity, serum glucose, triglycerides, cholesterol, and insulin in fructose-induced hypertension. Myricetin reduced systolic blood pressure and vascular reactivity changes to catecholamines and reversed the metabolic alterations induced by fructose. The cumulative concentration-response curve (CCRC) of Ang II was shifted toward the right in rats treated with myricetin, using isolated strips of ascending colon. The results suggest that myricetin could prevent the development of high blood pressure induced by a diet rich in fructose, probably by reversing the metabolic alterations induced by fructose. In conclusion, myricetin has antihypertensive action in the fructose model.

Effect of Solanum torvum on blood pressure and metabolic alterations in fructose hypertensive rats

ETHNOPHARMACOLOGICAL RELEVANCE

Solanum torvum (Solanaceae) is a plant used in Cameroon ethnomedicine for the treatment of hypertension.

AIM OF THE STUDY

The present study was aimed to determine the effect of ethanolic extract of Solanum torvum (100 and 300 mg/kg; p.o. for 6 weeks) on systolic blood pressure (SBP), vascular reactivity, serum glucose, triglycerides, cholesterol, insulin and uric acid in fructose-induced hypertension.

MATERIALS AND METHODS

The effect of ethanolic extract of Solanum torvum (100 and 300 mg/kg; p.o. for 6 weeks) on fructose (10%) induced rise in blood pressure was tested by invasive and non-invasive measurements and the biochemical parameters were studied by using standard kits.

RESULTS

Ethanolic extract of Solanum torvum reduced systolic blood pressure, vascular reactivity changes to catecholamines and reversed the metabolic alterations induced by fructose. The cumulative concentration response curve (CCRC) of Angiotensin II (Ang II) using isolated strip of ascending colon was shifted towards right in rats treated with ethanolic extract of Solanum torvum.

CONCLUSIONS

In conclusion, ethanolic extract of Solanum torvum could prevent the development of high blood pressure induced by a diet rich in fructose probably by reversing the metabolic alterations induced by fructose.

Increased endothelial nitric-oxide synthase expression reduces hypertension and hyperinsulinemia in fructose-treated rats

Endothelial dysfunction and decreased production of nitric oxide (NO) by endothelial NO synthase (eNOS) are implicated in the pathogenesis of hypertension and insulin resistance. Because the potential influence of increased eNOS expression/activity on these parameters is unclear, the present study examined the effects of eNOS gene therapy on insulin resistance and blood pressure alterations in a fructose-induced hypertension model in rats. As predicted, 2 weeks of fructose consumption in the drinking water resulted in elevated systolic blood pressure and insulin resistance. These and other physiologic alterations were reversed within 2 weeks after a single intravenous injection of a vector containing the human eNOS cDNA (pcDNA3.1-eNOS), whereas injection of an empty vector (pcDNA3.1) was without effect. In support of the beneficial effects of pcDNA3.1-eNOS treatment being because of enhanced eNOS expression and activity, increased eNOS protein levels were documented in aorta, liver, kidney, and heart of fructose-treated rats injected with pcDNA3.1-eNOS, and corresponding elevations in nitrite/nitrate and cGMP concentrations were observed in urine. Furthermore, pcDNA3.1-eNOS treatment prevented fructose-induced decreases in expression levels of insulin receptor substrate-1, the p110 catalytic subunit of phosphatidylinositol 3-kinase, phosphorylated Akt, and phosphorylated AMP-activated protein kinases in liver, aorta, and skeletal muscle. The results of this study cumulatively indicate that gene therapy with human eNOS decreased fructose-induced hypertension and insulin resistance in rats and suggest potential signaling pathways that mediate these effects. These data highlight the potential utility of eNOS gene therapy in the treatment of hypertension and insulin resistance.

Potential role of kinins in the effects of taurine in high-fructose-fed rats

The present work investigates the involvement of kinins in the effects of taurine in fructose-fed hypertensive rats. The effects of taurine on blood pressure, plasma glucose, insulin, and the insulin sensitivity index were determined. Angiotensin-converting enzyme (ACE) activity and nitrite content in plasma, plasma and tissue kallikrein activity, and taurine content were also investigated. The blood pressure changes in response to the coadministration of inhib itors of the synthesis of nitric oxide (NO), prostaglandins (PGs), or a kinin receptor blocker along with taurine was also evaluated. Fructose-fed rats had higher blood pressure and elevated plasma levels of glucose and insulin. Kallikrein activity, taurine, and nitrite contents were significantly lower in fructose-fed rats as compared with controls. The increases in systolic blood pressure, hyperglycemia, and hyperinsulinemia were controlled by taurine administration in fructose-fed rats. ACE activity was lower, while nitrite and taurine content and kallikrein activity were higher, in taurine-supplemented rats as compared with fructose-fed rats. A significant increase in blood pressure was observed in rats cotreated with the inhibitors Hoe 140 (a kinin receptor blocker), L-NAME (a NO synthase inhibitor), or indo metha cin (a PG synthesis inhibitor) with taurine for 1 week as compared with taurine-treated fructose-fed rats. This suggests that the antihypertensive effect of taurine in fructose-fed rats was blocked by the inhibitors. Augmented kallikrein activity and, hence, increased kinin availability may be implicated in the effects of taurine in fructose-fed hypertensive rats.Key words: kallikrein, nitric oxide, angiotensin-converting enzyme, blood pressure, taurine.

Leaf methanol extract of Bidens pilosa prevents and attenuates the hypertension induced by high-fructose diet in Wistar rats

Chronic fructose treatment in rats has repeatedly been shown to elevate blood pressure in association with insulin resistance and hyperinsulinemia. The purpose of the current study was to investigate the effect of the leaf methanol extract of Bidens pilosa on systolic blood pressure (SBP) and plasma glucose, insulin, cholesterol, triglycerides and creatinine levels in rats with fructose-induced hypertension. Wistar rats that drank a 10% fructose solution for 3-6 weeks showed significant increase not only in plasma insulin and cholesterol levels but also in SBP. B. pilosa extract was able to prevent the establishment of hypertension and lower elevated blood pressure levels. The extract also reduced the highly elevated plasma insulin levels provoked by the high fructose diet. These results suggest that the leaf methanol extract of B. pilosa exerts its antihypertensive effect in part by improving insulin sensitivity.

The effects of losartan and fosinopril in hypertensive type 2 diabetic patients

The aim of this study is to evaluate the effects of losartan on blood pressure (BP), creatinine clearance (Ccr) and urinary albumin excretion (UAE), and to assess metabolic parameters in comparison with ACEI. Thirty-three type 2 diabetic hypertensive patients were enrolled in the study. Twenty patients were randomized to receive 50 mg/day losartan and 13 patients to 10 mg/day fosinopril. Patients were studied at baseline and after 1 and 6 months. BP was significantly decreased in both groups at the end of the 1st and 6th month to a similar extent. Ccr had fallen in both groups at the end of 1st and 6th months. The effect of each drug on Ccr was similar (64.2+/-70.6 and 42.8+/-53.8 ml/min, respectively, NS). In the subgroup with microalbuminuria at baseline, UAE rate was lower in both groups at the end of the 1st and 6th months. However, when compared with the end of 1st month, the antiproteinuric effect of losartan was slightly decreased at the end of 6th month. Metabolic parameters did not change with either drug. Both drugs were well tolerated. Thus the antihypertensive effects of the two drugs were comparable. In conclusion, this study confirms the efficacy and safety of losartan as an antihypertensive drug in diabetic patients.

Enalapril acts through release of nitric oxide in patients with essential hypertension

BACKGROUND

Endothelial dysfunction has been proposed as an etiological agent in the pathogenesis of essential hypertension. Amongst the various antihypertensive drugs, angiotensin converting enzyme inhibitors (ACEI) have been implicated in modifying the vascular endothelium by the release of mediators that include bradykinin, nitric oxide, prostaglandins and thromboxane A2.

MATERIALS AND METHODS

To study the mechanism of action of enalapril, an ACEI, serum reactive nitrite intermediates (RNI) and citrulline, by products of nitric oxide metabolism were measured before and after treatment with enalapril in 25 consecutive patients of essential hypertension.

RESULTS

Following treatment serum RNI intermediate increased from a pretreatment value of 164.5 +/- 20.2 nmol/mL to a post treatment value of 266.9 +/- 47.3 nmol/mL (p < 0.05), however there was no significant change in the levels of citrulline (p > 0.1). There was no significant correlation between the severity of hypertension and serum RNI. Serum RNI levels were lower in the postmenopausal women but did not reach statistical significance.

CONCLUSIONS

It is postulated that enalapril exhibits its antihypertensive property through release of nitric oxide.

Effects of the aqueous and methylene chloride extracts of Bidens pilosa leaf on fructose-hypertensive rats

We investigated the effects of the aqueous (150-350 mg/kg) and methylene chloride (150-300 mg/kg) extracts of Bidens pilosa on fructose-induced hypertension in rats. Food and liquid intake were measured as well as systolic blood pressure and plasma levels of glucose, insulin, cholesterol, triglycerides and creatinine. Fructose feeding for 6 weeks induced hypertension, hyperinsulinemia and increased plasma triglyceride levels in male Wistar rats. The aqueous and methylene chloride extracts of B. pilosa reversed the high blood pressure and hypertriglyceridemia developed due to fructose feeding but did not have any effects on plasma levels of insulin and glucose. High doses of the extracts reduced plasma creatinine levels and tended to increase plasma cholesterol. These results suggest that the extracts of B. pilosa possess hypotensive effects whose mechanism of action is not related to insulin sensitivity.

Effect of inhibition of nitric oxide synthase on blood pressure and renal sodium handling in renal denervated rats

The role of sympathetic nerve activity in the changes in arterial blood pressure and renal function caused by the chronic administration of N G-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthesis, was examined in sham and bilaterally renal denervated rats. Several studies have demonstrated that sympathetic nerve activity is elevated acutely after L-NAME administration. To evaluate the role of renal nerve activity in L-NAME-induced hypertension, we compared the blood pressure response in four groups (N = 10 each) of male Wistar-Hannover rats weighing 200 to 250 g: 1) sham-operated vehicle-treated, 2) sham-operated L-NAME-treated, 3) denervated vehicle-treated, and 4) denervated L-NAME-treated rats. After renal denervation or sham surgery, one control week was followed by three weeks of oral administration of L-NAME by gavage. Arterial pressure was measured weekly in conscious rats by a tail-cuff method and renal function tests were performed in individual metabolic cages 0, 7, 14 and 21 days after the beginning of L-NAME administration. L-NAME (60 mg kg-1 day-1) progressively increased arterial pressure from 108 +/- 6.0 to 149 +/- 12 mmHg (P<0.05) in the sham-operated group by the third week of treatment which was accompanied by a fall in creatinine clearance from 336 +/- 18 to 222 +/- 59 microl min-1 100 g body weight-1 (P<0. 05) and a rise in fractional urinary sodium excretion from 0.2 +/- 0. 04 to 1.62 +/- 0.35% (P<0.05) and in sodium post-proximal fractional excretion from 0.54 +/- 0.09 to 4.7 +/- 0.86% (P<0.05). The development of hypertension was significantly delayed and attenuated in denervated L-NAME-treated rats. This was accompanied by a striking additional increase in fractional renal sodium and potassium excretion from 0.2 +/- 0.04 to 4.5 +/- 1.6% and from 0.1 +/- 0.015 to 1.21 +/- 0.37%, respectively, and an enhanced post-proximal sodium excretion compared to the sham-operated group. These differences occurred despite an unchanged creatinine clearance and Na+ filtered load. These results suggest that bilateral renal denervation delayed and attenuated the L-NAME-induced hypertension by promoting an additional decrease in tubule sodium reabsorption in the post-proximal segments of nephrons. Much of the hypertension caused by chronic NO synthesis inhibition is thus dependent on renal nerve activity.

Contribution of bradykinin to the beneficial effects of ramipril in the fructose-fed rat

The contribution of nondegraded bradykinin to the metabolic effects of the angiotensin-converting enzyme (ACE)-kininase II inhibitor ramipril was evaluated in rats rendered hypertensive, hyperinsulinemic, and hypertriglyceridemic by a fructose-enriched diet. The response of blood pressure, insulin, and triglyceride levels to concomitant administration of ramipril and the bradykinin antagonist HOE 140 was studied. Rats that received ramipril, HOE 140, or not treated at all served as controls. Treatment with ramipril reduced levels of both insulin (from 6.6 +/- 2.0 to 3.6 +/- 1.7 ng/ml; p < 0.05) and triglycerides (from 292 +/- 88 to 164 +/- 35 mg/dl; p < 0.001) as well as blood pressure (from 144 +/- 6 to 116 +/- 6 mm Hg; p < 0.001). In contrast, treatment with HOE 140 did not alter any of these parameters. The combined treatment, however, blunted the beneficial metabolic effects of ramipril on insulin (7.8 +/- 4.4 ng/ml before and 7.7 +/- 2.9 ng/ml after treatment) and triglycerides (290 +/- 135 mg/dl before and 285 +/- 152 mg/dl after treatment), whereas the hypotensive effect of ramipril was preserved (151 +/- 8 mm Hg before and 122 +/- 6 mm Hg after treatment (p < 0.001). The data suggest that whereas the hypotensive effect is mostly angiotensin-II dependent, the advantageous metabolic affect of ramipril is highly dependent on the accumulation of bradykinin.

Sympathetic functions in NG-nitro-L-arginine-methyl-ester-induced hypertension: modulation by the renin-angiotensin system

BACKGROUND

Nitric oxide and angiotensin II have been shown to attenuate cardiac beta-adrenergic inotropism.

OBJECTIVE

To study sympathetic presynaptic and post-synaptic functions after chronic nitric oxide synthesis blockade with NG-nitro-L-arginine-methyl-ester (L-NAME, for 40 days) in association with renin-angiotensin system blockade (during the last 12 days) in order to evaluate the possible physiological interactions between these systems.

METHODS

Haemodynamic parameters in conscious rats were assessed. Release of noradrenaline from isolated atria and cardiac beta-adrenergic-adenylyl cyclase pathway in rats of sham-treated and L-NAME-treated groups, with or without losartan or enalaprilat treatment, were assessed.

RESULTS

L-NAME-treated rats developed a time-dependent increase in blood pressure associated with increased plasma adrenaline levels whereas plasma noradrenaline and cardiac catecholamine levels were similar to those in sham-treated rats. Field-stimulated release of noradrenaline, cardiac beta-adrenoceptor density and affinity and isoproterenol-stimulated formation of cyclic AMP were similar in sham and L-NAME-treated rats. However, Gpp(NH)p, NaF and forskolin-stimulated adenylyl cyclase activity were greater in L-NAME rats although Gs and Gi protein levels were similar in sham-treated and L-NAME-treated rats. Losartan and enalaprilat treatments exerted equipotent angiotensin-pressor response blockade and hypotensive effects whereas catecholamine levels were not altered. Interestingly, only losartan treatment acted to reduce the increased Gs-adenylyl cyclase activity in L-NAME rats, without alteration of G protein levels.

CONCLUSIONS

The nitric oxide synthase blockade-induced hypertension seems to be associated with increased adrenal-medullary system and renin-angiotensin system activities. The increased Gs-adenylyl cyclase activity after chronic inhibition of formation of nitric oxide suggests that nitric oxide plays a modulatory role in formation of cyclic AMP, to which angiotensin II seems to contribute through an angiotensin II type 1 receptor-mediated mechanism.