H. A. Peredo

ROLE OF HYPOTHALAMIC α2-ADRENOCEPTOR ACTIVITY IN FRUCTOSE-INDUCED HYPERTENSION

1 The aim of the present study was to investigate the effects of the α2‐adrenoceptor antagonist yohimbine on blood pressure and heart rate (HR) regulation, as well as on adrenergic and serotoninergic neurotransmission, in fructose hypertensive (F) rats. 2 The anterior hypothalamic area of control (C) and F rats was perfused with Ringers solution containing 10 and 100 µg/mL yohimbine through a microdialysis concentric probe. The effects of yohimbine on mean arterial pressure (MAP) and HR, as well as on hypothalamic dihydroxyphenylacetic acid (DOPAC) and 5‐hydroxyindole acetic acid (5‐HIAA) levels, were measured according to perfusion time. 3 Although intrahypothalamic perfusion of yohimbine increased blood pressure in C rats (ΔMAP 9 ± 1 and 11 ± 2 mmHg for 10 and 100 µg/mL yohimbine, respectively; P < 0.05 vs Ringers perfusion), the α‐adrenoceptor antagonist did not modify MAP in F. Intrahypothalamic yohimbine had no effect on HR at either concentration tested. Intrahypothalamic perfusion of 10 and 100 µg/mL yohimbine increased DOPAC levels in C rats (135 ± 6 and 130 ± 5% of basal levels, respectively; both n = 6; P < 0.05 vs Ringers perfusion), but not in F animals (115 ± 6 and 102 ± 6% of basal levels, respectively; both n = 6). In both C and F rats, yohimbine administration induced an increase in 5‐HIAA dialysate levels. 4 The results of the present study support the notion that α2‐adrenoceptor tone of the anterior hypothalamus of normotensive rats, which contributes to normal blood pressure regulation, is not involved in the control of HR in either normotensive C or hypertensive F rats. The absence of changes in MAP after yohimbine perfusion in F rats suggests that the α2‐adrenoceptor tone could be decreased in this group of rats and that this may be responsible for the maintenance of hypertension in this model. Intrahypothalamic perfusion of yohimbine increased DOPAC in the dialysate only in C rats, suggesting changes in presynaptic α2‐adrenoceptor activity in fructose‐overloaded rats. Conversely, increased 5‐HIAA levels did not differ between C and F groups.

Pioglitazone and losartan modify hemodynamic and metabolic parameters and vascular prostanoids in fructose-overloaded rats.

This study analyzes the effects of losartan (AT1 blocker) and pioglitazone (insulin sensitizer), alone and in combination, in the fructose-overloaded rat, a model of metabolic syndrome. All treatments (nine weeks) reduced blood pressure and triglyceridemia and also restored the diminished release of vasodilator prostaglandins (prostacyclin in aorta and mesenteric vascular bed and prostaglandin E2 in the latter). Pioglitazone, alone and in combination with losartan, reduced the release of the vasoconstrictor thromboxane in controls and fructose rats in both vascular preparations. In conclusion, although combination therapy and single treatments exerted similar effects, there may still be some advantage to the combined treatment.

Prostanoid production in endothelial and Kupffer liver cells from monocrotaline intoxicated rats

A single dose of monocrotaline, a pyrrolizidine alkaloid, was injected into rats in order to produce 25 (Group I) and 45 (Group II) days later a progressive and so called delayed liver injury. The present study investigated the prostanoid production of Kupffer cells and endothelial cells separated from Monocrotaline and saline (Group III) injected rat livers. Kupffer cells: formation of 6 keto Prostaglandin F1 a, the major prostacyclin metabolite, gradually decreased in Groups I vs II (P50.01) and in both Groups I and II vs Controls (P50.01). In addition Prostaglandin F2 a showed a significant increase in Groups I and II when compared to Group III, (P50.001), and Thromboxane B2 was present in both Groups of Monocrotaline treated animals, while it was not detectable in the control Group III. Endothelial cells:6ketoProstaglandin F1 a decreased in Groups I vs II. This differences was significant when compared, and compared to controls (Group III, P50.001). Prostaglandin E2 was detected only in Groups I and II. Prostaglandin F2 a and Thromboxane B2 could not be detected in any Group. Ultramicroscopy showed morphological cell damage in nonparenchymal cells in Monocrotaline intoxication in Group II, rats sacrified 45 days after the injection, while it shows normal features in those treated animals sacrified 25 days after the injection, as well as in control group. Conclusion: Asingle Monocrotaline injection produces, 25 and 45 days later, severe and progressive alterations in the prostanoid production in Kupffer and Endothelial cells, while ultramicroscopic alterations was only observed 45 days after the injection of Monocrotaline. A decreased production of vasodilators and the presence of vasoconstrictor prostanoids that can participate in the production of the circulatory derangements enhancing liver injury and portal hypertension were also observed.

A high-fat plus fructose diet produces a vascular prostanoid alterations in the rat.

In the rat, a high-fat (HF) plus fructose (F) diet produces cardiovascular and metabolic alterations that resemble human metabolic syndrome. Prostanoids (PR), cyclo-oxygenase-derived arachidonic acid metabolites, have vasoactive properties and mediate inflammation. The aim of this study was to analyse the effect of a HF+F diet on blood pressure (BP), metabolic parameters and mesenteric vascular bed PR production in male Sprague-Dawley rats. Four groups were studied over 9 weeks (n = 6 each): control (C), standard diet (SD) and tap water to drink; F+SD and 10% w/v F solution to drink; HF 50% (w/w) bovine fat added to SD and tap water; and HFF, both treatments. PR were determined by HPLC. Blood pressure was elevated in all experimental groups. Triglyceridaemia, insulinaemia and HOMA-IR were increased in the F and HF groups. HF+F animals showed elevated glycaemia, insulinaemia, HOMA-IR and triglyceridaemia. F decreased the vasodilator prostanoids PGI2 and PGE2 in the mesenteric vascular bed. Body weight was not significantly altered. In HFF, production of PGE2 , PGF2 alpha and TXB2 was elevated. The increased BP in HF and HFF could be partly attributed to the imbalance in vascular PR production towards vasoconstrictors. On the other hand, this dietary modification could induce inflammation, which would explain the elevation of PGE2 . In the F group, hypertension could be related to decreased vasodilator PRs. The simultaneous administration of HF and F in the rat produces deleterious effects greater than observed when treatments are applied separately.

Metformin reduces vascular production of vasoconstrictor prostanoids in fructose overloaded rats

Metformin is a hypoglycaemic drug currently used to increase insulin sensitivity in the treatment of type 2 diabetes and metabolic syndrome. Its main mechanism of action is through activation of AMP-activated protein kinase, an enzyme that regulates cellular and whole organ metabolism. The fructose-overloaded rat is an experimental model with features that resemble human metabolic syndrome. We have previously reported alterations in vascular prostanoids (PR) in this model. The aim of this study was to analyse the effects of metformin treatment on blood pressure, metabolic parameters and PR production in aorta and mesenteric vascular bed (MVB) from fructose-overloaded animals. Four groups of male Sprague-Dawley rats were used: control, fructose overloaded (10% w/v fructose), metformin treated (50 mg kg(-1) day(-1) ) and fructose-overloaded treated with metformin. Rats with fructose overload had significantly elevated systolic blood pressure, glycaemia, triglyceridaemia, cholesterolaemia and insulinaemia compared with controls. Except for insulinaemia, metformin limited all these increases in fructose-overloaded animals. Fructose overload reduced prostacyclin levels in aorta and MVB, but prostaglandin E(2) levels were only reduced in MVB. Metformin treatment reduced the levels of the vasoconstrictor prostaglandins, PGF(2) α and thromboxane, in both vascular preparations from fructose-overloaded rats. PGF(2) α levels were significantly reduced by metformin in controls. In conclusion, one of the mechanisms by which metformin reduced blood pressure in this model is by decreasing vasoconstrictor prostaglandin production.

DECREASED OXIDATIVE STRESS IN PREHEPATIC PORTAL HYPERTENSIVE RAT LIVERS FOLLOWING THE INDUCTION OF DIABETES

1. Oxidative stress (OS) is a biological entity indicated as being responsible for several pathologies, including diabetes. Diabetes can also be associated with human cirrhosis. Portal hypertension (PH), a major syndrome in cirrhosis, produces hyperdynamic splanchnic circulation and hyperaemia. The present study was designed to investigate the occurrence of OS in prehepatic PH rat livers following the induction of diabetes.

Sodium molybdate prevents hypertension and vascular prostanoid imbalance in fructose-overloaded rats

(1) Fructose (F) overload produces elevated blood pressure (BP), hyperglycaemia, hypertriglyceridemia and insulin resistance, resembling human metabolic syndrome. Previously, we found altered vascular prostanoid (PR) production in this model. (2) Sodium molybdate (Mo), as well as sodium tungstate, causes insulin-like effects and normalizes plasma glucose levels in streptozotocin-treated diabetic rats. We studied the effects of Mo on BP, metabolic parameters and release of PR from the mesenteric vascular bed (MVB) in F-overloaded rats. (3) Four groups of male Sprague-Dawley rats were analysed: Control, tap water to drink; F, F solution 10% W/V to drink; CMo, Mo 100 mg kg day(-1) and FMo, both treatments. After 9 weeks, the animals were killed and MVBs removed and the released PRs measured. (4) F increased BP, glycemia, triglyceridemia and insulinemia. Mo treatment prevented the increases in BP and glycemia, but did not modify triglyceridemia or insulinemia. In addition, Mo decreased BP in controls. (5) Prostaglandins (PG) F2 alpha and E2, PG 6-ketoF1 alpha and thromboxane (TX) B2 , as well as inactive metabolites of prostacyclin (PGI2 ) and TXA2 were detected. F decreased the production of vasodilator PRs PGI2 and PGE2 in MVB. Mo prevented these alterations and increased PGE2 in controls. Vasoconstrict or PRs PGF2 alpha and TXA2 release was not modified. (6) Mo treatment, beyond its known lowering effect on glycemia, prevents the reduction in the vascular release of vasodilator PR observed in this model. This could be one of the mechanisms by which Mo avoids the increase in BP caused by F overload in the rat.

[PP.12.03] EFFECTS OF LOSARTAN ON PROSTANOIDS RELEASE IN TWO MODELS OF METABOLIC ALTERATION IN THE RAT

Objective: Fructose-overload and high-fat diet in rats are experimental models that resemble human metabolic syndrome. This multifactorial alteration is associated to hypertension. The systemic renin-angiotensin system plays an important role in the regulation of vascular tone. Prostanoids (PR) are endogenous substances derived from arachidonic acid via the cyclooxygenases with vasoactive effects. The aim of this study was to analyze the effects of losartan (L, angiotensin 1 receptor antagonist) on prostanoids (PR) release by the mesenteric vascular bed (MVB) in both models of dietary alteration. Design and method: Six groups (n = 6) of male Sprague-Dawley rats were studied during 9 weeks: Control (C), standard diet (SD) and tap water to drink; fructose-overloaded (F), SD and fructose solution (10% W/V) to drink; HF diet (HF), 50% (w/w) bovine fat added to SD and tap water; C + L (CL), SD + 30 mg/Kg/day L in the drinking water; F + L (FL) 30 mg/Kg/day L in the fructose solution; and HF + L (HFL) 30 mg/Kg/day L in the drinking water. MVBs were removed and incubated and the released PRs measured by HPLC. Results: F and HF increased systolic blood pressure (SBP, mmHg, 133 ± 3, 145 ± 5 vs. C: 116 ± 2, p < 0.01 and p < 0.001). In the FL and HFL groups, L decreased SBP (102 ± 5 vs. F, 111 ± 3 vs. HF, p < 0.001 and p < 0.01). F diminished prostaglandin (PG) 6-ketoF1alpha, stable metabolite of the vasodilator prostacyclin (PGI2), (ng PR/mg tissue, 58 ± 11 vs. C: 98 ± 8, p < 0.05); and PGE2 (ng/mg, 35 ± 7 vs. C: 87 ± 6, p < 0.01). HF diet increased thromboxane (TX) B2, stable metabolite of the vasoconstrictor TXA2, (ng PR/mg tissue, 111 ± 5 vs. C: 64 ± 7, p < 0.001); and PGF2alpha (150 ± 10 vs. C: 83 ± 8, p < 0.01). In the FL group, L increased PG6-ketoF1alpha (117 ± 10 vs. F, p < 0.05) and PGE2 (104 ± 11 vs. F, p < 0.01). In the HFL group, L decreased TXB2 (66 ± 7 vs. HF, p < 0.01); and PGF2alpha (90 ± 7 vs. HF, p < 0.05). Conclusions: In conclusion, one of the possible mechanisms by which L reduced blood pressure in these models could be an improvement of endothelial function through a regulation of PR release which produced a decrease in vasoconstriction.