PPAR gamma activation protects the brain against microvascular dysfunction in sepsis

Sepsis is a severe disorder characterized by systemic inflammatory responses in the presence of an infection and may progress to multiple organ dysfunction and death. Alterations in cerebral microcirculation fulfill a crucial role in the pathogenesis of severe sepsis, and include a decrease in capillary density and disturbances in leukocyte movement along capillaries. Nevertheless, the mechanisms involved in sepsis-associated cerebral microcirculatory alterations have so far not been defined. We investigated the effect of the peroxisome proliferator-activated receptor gamma (PPARγ) selective agonist rosiglitazone on leukocyte/endothelial cell interaction and functional capillary density in the brain in the cecal ligation and puncture (CLP) model of sepsis. Anti-inflammatory effects of rosiglitazone on the cerebral microcirculation were marked. Functional capillary density increased and leukocyte rolling and adhesion were decreased in animals submitted to CLP and treated with rosiglitazone. Our data provide evidence for involvement of PPARγ activation in leukocyte-endothelium interactions and alterations in capillary density. Improved cerebral perfusion in animals treated with rosiglitazone, suggests that PPARγ activation is protective against cerebral microvascular dysfunction in sepsis.

Uric acid levels are associated with microvascular endothelial dysfunction in patients with Type 1 diabetes

AIMS

Recent data identified uric acid as an independent risk factor for cardiovascular disease. The aim of the present study was to assess the association between uric acid and endothelial dysfunction in 57 patients with Type 1 diabetes and 53 healthy control subjects.

METHODS

Microvascular endothelial function was evaluated using laser Doppler perfusion monitoring coupled with pharmacological (iontophoretic administration of acetylcholine and sodium nitroprusside) and physiological (post-occlusive reactive hyperaemia and thermal hyperaemia) stimuli.

RESULTS

Uric acid was higher in subjects without diabetes than in those with diabetes (P = 0.03). Microvascular vasodilator response to acetylcholine was significantly reduced in Type 1 diabetes (P = 0.002) and was correlated to disease duration (r = -0.3, P = 0.01), triglyceride (r = -0.37, P = 0.005), insulin dose (r = -0.28, P = 0.03), fasting plasma glucose levels (r = -0.3, P = 0.02), HbA(1c) (r = -0.34, P = 0.001) and uric acid (r = -0.3, P = 0.005). On stepwise multivariate analysis, age, HbA(1c) and uric acid were the most important independent variables that were associated with the endothelium-dependent response in Type 1 diabetes (P = 0.02).

CONCLUSIONS

Glycaemic control and uric acid in the normal range were the most important contributing factors to the decreasing endothelium-dependent responses associated with Type 1 diabetes. Consequently, uric acid could be a new potential marker of microvascular endothelial dysfunction in these patients. Further studies are required to explore the clinical relevance of the relationship between uric acid levels, oxidative stress and endothelial dysfunction in patients with Type 1 diabetes, as well as whether treatment with uric acid-lowering drugs for slight elevations in uric acid would benefit these patients.

Chronic dynamic exercise increases apolipoprotein A-I expression in rabbit renal cortex as determined by proteomic technology

OBJECTIVE

We have shown previously that exercise training enhances endothelium-dependent and endothelium-independent vascular relaxation in rabbit kidney. This study aimed to investigate protein expression changes in the rabbit renal cortex induced by chronic dynamic exercise.

DESIGN

Kidneys were obtained from New Zealand rabbits either confined to pens (n = 8) or trained on a treadmill (0% grade) for 5 days/week at a speed of 18 m/min for 60-min periods over 12 weeks (n = 8). Expression of proteins in the renal cortex was determined by colloidal Coomassie blue staining after two-dimensional polyacrylamide gel electrophoresis. Differential protein spots were excised and digested with trypsin, and peptides were sequenced by electrospray ionization-ion trap mass spectrometry.

RESULTS

Two pairs of matching differentially stained spots displayed an approximate threefold increase in trained compared with sedentary animals. These four spots presented a molecular mass of 23 kDa but different pI values. Mass spectrometric analyses revealed the pairs of matching spots as being rabbit apolipoprotein A-I.

CONCLUSION

Chronic dynamic exercise increases apolipoprotein A-I expression in the rabbit renal cortex. This fact could be involved in the alterations observed in the renal circulation after exercise training.

Endothelial function in patients with type 1 diabetes evaluated by skin capillary recruitment

The aim of the present study was to evaluate skin capillary density and recruitment of the upper and lower extremities of patients with type 1 diabetes under chronic treatment without clinical manifestations of diabetes-related complications. This cross-sectional observational study included 59 (27.1+/-10.6 years) consecutive outpatients with type 1 diabetes [duration 10 (1; 45) years] and 41 age- and sex-matched healthy controls. We used intravital video-microscopy to measure basal and maximal (during venous congestion) skin capillary densities as well as capillary recruitment using post-occlusive reactive hyperemia (PORH) in the dorsum of the fingers and toes. Mean capillary density (MCD) of the fingers at baseline was not different between controls and patients (123.02+/-22.6 and 132.3+/-28.9 capillaries/mm(2), respectively; P=0.08). In contrast, baseline MCD of the toes was lower in controls, when compared to patients (84.6+/-19.8 and 96.2+/-23.4 capillaries/mm(2), respectively; P=0.01). Capillary recruitment during PORH (% increase of the number of capillaries/mm(2)) was significantly higher in controls compared to patients both in fingers [7 (-8; 33) and -1.0 (-35, 13), respectively; P=0.000] and toes [6 (-20; 46) and 0 (-24; 20), respectively; P=0.000]. During venous occlusion, capillary density increase (% increase of the number of capillaries/mm(2)) was also higher in controls compared to patients both in fingers [3 (-14; 23) and 0.0 (-30; 29.2), respectively; P=0.02] and toes [9.3 (-18; 51) and -7 (-34; 22), respectively; P=0.000]. Our results showed that patients with type 1 diabetes, although not presenting skin capillary rarefaction, display skin microvascular functional alterations in both extremities characterized by an absence of capillary reserve.

Metformin prevents the impairment of endothelium-dependent vascular relaxation induced by high glucose challenge in rabbit isolated perfused kidneys

High glucose concentrations are involved in the development of diabetic-associated vascular complications. We have previously reported that acute high glucose challenge, corresponding to post-prandial glycemia levels observed in patients with type 2 diabetes, blunts ACh-induced endothelium-dependent relaxation of the renal circulation of non-diabetic rabbits. Isolated perfused kidneys from non-diabetic rabbits were acutely exposed (3 h) to normal (5.5 mM--control group) or high (15 mM) D-glucose concentrations in the presence or absence of a continuous infusion of metformin (20 or 100 microM). Renal vascular reactivity was evaluated with endothelium-dependent (acetylcholine, ACh) and -independent (sodium nitroprusside, SNP) vasodilating agents. ACh-induced maximal renal vasodilation was reduced by high glucose infusion (15 mM) in comparison to the control group (25+/-3% and 41+/-3% respectively; P<0.01), being restored to 41+/-4% and 43+/-2% by a simultaneous 3-h infusion of 20 or 100 microM of metformin respectively (P>0.05). Perfusion of the kidneys with the angiotensin II-converting enzyme inhibitor captopril (10 microM) also significantly prevented the deleterious effects of high glucose challenge in the renal circulation. The use of a continuous infusion of N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 microM) did not affect the protective effect of metformin in the renal circulation (39+/-4%; P>0.05), while tetraethylammonium (TEA, 10 mM) partially blunted this effect (33+/-4, P<0.01). Renal vasodilation induced by SNP was not modified by simultaneous infusion of high glucose and/or metformin. It is concluded that the impairment of ACh-induced endothelium-dependent renal vasodilation observed after acute exposure to high glucose concentrations is abolished by metformin administration. These alterations of renal vascular reactivity can be accounted for, at least in part, by the activation of the renal renin-angiotensin system during hyperglycemia. The protective effects of metformin present some EDHF-dependent component and are not related to metabolic pathways dependent on nitric oxide.

Effects of centrally acting antihypertensive drugs on the microcirculation of spontaneously hypertensive rats

We investigated the acute effects of centrally acting antihypertensive drugs on the microcirculation of pentobarbital-anesthetized spontaneously hypertensive rats (SHR). The effects of the sympatho-inhibitory agents clonidine and rilmenidine, known to activate both alpha2-adrenoceptors and nonadrenergic I1-imidazoline binding sites (I1BS) in the central nervous system, were compared to those of dicyclopropylmethyl-(4,5-dimethyl-4,5-dihydro-3H-pyrrol-2-yl)-amine hydrochloride (LNP 509), which selectively binds to the I1BS. Terminal mesenteric arterioles were observed by intravital microscopy. Activation of the central sympathetic system with L-glutamate (125 microg, ic) induced marked vasoconstriction of the mesenteric microcirculation (27 +/- 3%; N = 6, P < 0.05). In contrast, the marked hypotensive and bradycardic effects elicited by intracisternal injection of clonidine (1 microg), rilmenidine (7 microg) and LNP 509 (60 microg) were accompanied by significant increases in arteriolar diameter (12 +/- 1, 25 +/- 10 and 21 +/- 4%, respectively; N = 6, P < 0.05). The vasodilating effects of rilmenidine and LNP 509 were two-fold higher than those of clonidine, although they induced an identical hypotensive effect. Central sympathetic inhibition elicited by baclofen (1 microg, ic), a GABA B receptor agonist, also resulted in vasodilation of the SHR microvessels. The acute administration of clonidine, rilmenidine and LNP 509 also induced a significant decrease of cardiac output, whereas a decrease in systemic vascular resistance was observed only after rilmenidine and LNP 509. We conclude that the normalization of blood pressure in SHR induced by centrally acting antihypertensive agents is paralleled by important vasodilation of the mesenteric microcirculation. This effect is more pronounced with substances acting preferentially (rilmenidine) or exclusively (LNP 509) upon I1BS than with those presenting important alpha2-adrenergic activity (clonidine).

Cardiovascular properties of yangambin, a lignan isolated from Brazilian plants

Yangambin was initially selected from a number of lignans isolated from Brazilian plants for its ability to antagonize Platelet-Activating Factor (PAF, 1-O-hexadecyl-2-acetyl- sn-glyceryl-3-phosphorylcholine)-induced biological effects. Subsequently it was shown that, besides its antagonistic properties at PAF receptors, yangambin also prevents the cardiovascular collapse observed during anaphylactic and endotoxic/septic shocks, as well as the vascular and cardiac hyporesponsiveness to catecholamines in endotoxic shock. It is suggested that this naturally occurring compound could be of potential interest in the adjunctive management of the above mentioned pathologies. In the present article, we review the main studies investigating the pharmacological properties of yangambin related to the cardiovascular function.

Protective effects of yangambin on cardiovascular hyporeactivity to catecholamines in rats with endotoxin-induced shock

The protective effects of a new, selective, plant-derived platelet-activating factor (PAF) antagonist, yangambin, on the cardiovascular alterations and mortality due to endotoxic shock were investigated in anaesthetized rats. We also studied the involvement of PAF in the induction of the vascular and cardiac hyporesponsiveness to adrenergic stimulation observed during endotoxaemia. The animals were sensitized to the lethal effects of Escherichia coli lipopolysaccharide (LPS) with D(+)-galactosamine (50 mg/kg, i.v.) 15 min before LPS injection. LPS (3 mg/kg, i.v.) induced a progressive and marked decrease in mean arterial blood pressure from 85+/-4 to 30+/-3 mmHg and a reduction of cardiac output (CO) from 180+/-7 to 37+/-3 ml/min (120 min) accompanied by a maintenance of systemic vascular resistance, suggesting that cardiovascular collapse resulted mainly from myocardial depression. The maximum pressor responses to noradrenaline (0.3-3.0 microg/kg, i.v.) fell from 72+/-9 (control) to 5+/-1 mmHg (LPS) while the CO responses decreased from 81+/-5 to 8+/-3 ml/min. Pre-treatment with yangambin (30 mg/kg, i.v.) or with WEB 2086 (5 mg/kg, i.v.), a reference PAF receptor antagonist, completely prevented the LPS-induced cardiovascular collapse and abolished the sharp reductions of the arterial blood pressure and CO responses to noradrenaline observed during endotoxaemia. Post-treatment with yangambin 90 min after LPS administration did not reverse the arterial hypotension, cardiac failure or cardiovascular hyporesponsiveness to catecholamines. Finally, the acute (150 min) survival rates of endotoxic shock increased from 0% (LPS group) to 100% in the groups pretreated with either yangambin or WEB 2086. The long-term (7-day) survival also increased from 0% (LPS group) to 85% (yangambin pre-treatment group). In conclusion, these data suggest a role for PAF in the pathogenesis of endotoxin-induced vascular and cardiac hyporesponsiveness to catecholamines and confirm its involvement in the complex cascade of multiple mediators released during endotoxic/septic shock. Yangambin proved to be an effective pharmacological agent against cardiovascular collapse and mortality in endotoxin shock.

Cardiovascular effects of chronic ifenprodil in a model of central sympathetic stimulation

In the present study we investigated the effects of a long-term treatment (14 days) with ifenprodil on the excitatory haemodynamic responses induced by central pharmacological stimulation in anaesthetised rabbits. The intracerebroventricular injection of L-glutamate (3 mg/kg) induced important rises in dP/dtmax (32.9%), mean arterial pressure (42.6%) and in the myocardial oxygen consumption index: the triple product (84.2%). Ifenprodil (1.5, 3 and 6 mg/kg/day, i.p.) reduced the increases in myocardial oxygen demand induced by intracerebral L-glutamate in a dose-related manner. Interestingly, ifenprodil also reduced in a dose-dependent manner the maximum values of the oxygen demand indices reached during the central nervous system stimulation. These results indicate that the long-term treatment with ifenprodil can reduce the myocardial oxygen consumption induced by central nervous system stimulation without significant depression of the resting cardiac function. This favourable effect of ifenprodil is in fact a consequence of the association of mild inhibitory effects on the three parameters taken into account in the triple product index of myocardial oxygen consumption.

Investigation of the haemodynamic effects of Phoneutria nigriventer venom in anaesthetised rabbits

The haemodynamic alterations induced by the central and peripheral administration of the armed spider (Phoneutria nigriventer) venom (PNV) were investigated in anaesthetised rabbits. The intracerebroventricular injection of increasing doses of PNV (30 and 100 microg/kg) elicited a biphasic cardiovascular response characterised by a brief hypotension (1-3 min) followed by a marked and sustained (more than 30 min) increase in mean arterial pressure (61 +/- 5 and 61 +/- 10%, respectively) and in systemic vascular resistance (135 +/- 21 and 161 +/- 37%) accompanied by mild increases in cardiac contractility. Systemic alterations such as salivation and muscular fasciculation were also observed. At the opposite, the dose of 100 microg/kg of PNV injected intravenously produced only a hypotensive effect (29 +/- 4% decrease in mean arterial pressure) and a decrease in vascular resistance (38 +/- 5%). Nevertheless, a much higher dose of PNV (1 mg/kg) injected intravenously produced a hypertensive response analogous to the one observed upon central administration. The central hypertensive response induced by PNV was not affected by preteating the animals with selective antagonists of receptors of different neurotransmitters or endogenous mediators such as: acethylcoline muscarinic, bradykinin B2, angiotensin II AT1 receptors and also antagonists of the excitatory amino acid receptors of the central nervous system. Nevertheless, the intravenous pretreatment with the selective alpha1-adrenergic receptor antagonist prazosin significantly blunted the excitatory cardiovascular response evoked by the central injection of PNV. It is concluded that PNV can induce central as well as peripheral haemodynamic effects. The central component seems to be mediated by the activation of cardiovascular centres which in turn lead to an increase in the sympathetic outflow to the periphery, whereas the peripheral component can be accounted for either by direct activation of the vascular alpha1-adrenergic receptors or by catecholamine release from the sympathetic nerve endings.

Involvement of platelet-activating factor in the modulation of vascular tone in the isolated perfused rabbit kidney

The hypothesis that platelet-activating factor (PAF) plays a role in the modulation of the vasomotor tone and blood pressure was put forward by our group in previous in vivo studies in anaesthetised rabbits. The present study was undertaken to investigate the putative role of this lipid mediator in the vascular reactivity of the renal circulation, using the experimental model of the isolated perfused rabbit kidney. Dose-response curves to noradrenaline-induced vasoconstriction were performed before and after continuous infusions of two different PAF-receptor antagonists (WEB 2086 and yangambin) and of the phospholipase A2 inhibitor mepacrine. The increases in renal perfusion pressure elicited by noradrenaline were potentiated by all the above-mentioned treatments in a dose-dependent manner. Moreover, prostaglandin F2alpha-induced vasoconstriction was also potentiated by the administration of the PAF receptor antagonists and mepacrine. Furthermore, the administration of PAF into the renal circulation induced dose-related and long-lasting vasodilator responses, which were blocked by the PAF receptor antagonists. Nevertheless, PAF-induced renal vasodilation was also abolished by a pretreatment with mepacrine or with the cyclooxygenase inhibitor indomethacin, suggesting that it enhances the secondary formation of vasodilator arachidonic acid metabolites. The data indicate that PAF is involved in the modulation of the vasomotor tone in the renal circulation, through the release of cyclooxygenase products, constituting an additional mechanism of modulation of smooth muscle cell contractility to the ones exerted by well-known vasoactive substances of endothelial origin such as nitric oxide.

Pyridostigmine blunts the increases in myocardial oxygen demand elicited by the stimulation of the central nervous system in anesthetized rats

The purpose of the present work was to verify the effect of pyridostigmine bromide, a reversible cholinesterase inhibitor, on the increases in cardiac work and myocardial oxygen demand produced by central sympathetic stimulation in pentobarbital-anesthetized Wistar rats. The pharmacological stimulation of the central nervous system with L-glutamate (1 mg/kg, intracerebroventricular) elicited marked increases in arterial pressure, dP/dt(max), rate-pressure product, and triple product, reproducing the cardiovascular alterations observed during physical effort and stressful situations. The oral administration of pyridostigmine bromide (5, 10 and 20 mg/kg) 2 hours before central stimulation blunted the increases in mean arterial pressure, dP/dt(max), and triple product elicited by glutamate (29, 28 and 57% for 5 mg/kg; 26, 23 and 46% for 10 mg/kg and 19, 17 and 37% for 20 mg/kg, respectively) when compared to the control group (41, 49 and 106%, respectively; p < 0.05). Our results also showed that the activity of plasmatic cholinesterase was effectively inhibited by pyridostigmine bromide. In conclusion, the increases in endogenous acetylcholine induced by cholinesterase inhibition blunted the centrally-evoked increases in myocardial oxygen demand in anesthetized rats. This effect could represent a cardioprotective action in a situation of ischemic heart disease.

The acute increases in vasomotor tone and blood pressure induced by carotid artery occlusion are modulated by platelet-activating factor (PAF) independently of nitric oxide release

The purpose of the present study was to investigate the involvement of nitric oxide (NO) in the modulatory role of platelet-activating factor (PAF, 1-O-hexadecyl-2-acetyl-sn-glyceryl-3-phosphorylcholine), a vasoactive phospholipid mediator synthesized by endothelial cells, on the vascular tone and arterial blood pressure. In pentobarbitone-anaesthetized rabbits, unloading of the carotid sinus baroreceptors by a bilateral carotid artery occlusion elicited a reflex rise in systemic vascular resistance, which was markedly potentiated by pretreating the animals with the PAF receptor antagonist WEB 2086 ([3-4-(2-chlorphenyl-)-9-methyl-6H-thieno-3,2-f-1,2,4-triazolo-4,3 -alpha-1,4 -diazepin-2-yl-(4-morpholinyl)-1-propanone]; 5 mg/kg, i.v.). In contrast, the inhibition of the biosynthesis of NO via NO synthase using N omega-nitro-L-arginine methyl ester (L-NAME) neither affected the systemic vasoconstriction induced by carotid artery occlusion nor modified the potentiating effect of WEB 2086. The haemodynamic alterations induced by L-NAME administration were corrected by continuous infusions of the directly-acting vasodilators sodium nitroprusside or diazoxide. The results of the present study confirm previous studies from our group suggesting the involvement of PAF in a negative feedback mechanism effective in the local regulation of vasomotor tone in anaesthetized rabbits, but exclude the participation of NO in this process.

Pharmacological evidence of a role for platelet activating factor as a modulator of vasomotor tone and blood pressure

The purpose of the present study was to investigate the role of platelet-activating factor (PAF, 1-O-hexadecyl-2-acetyl-sn-glyceryl-3-phosphorylcholine), a phospholipid mediator synthesized by endothelial and smooth muscle cells, in the modulation of vascular tone and blood pressure. In pentobarbitone-anaesthetised rabbits, unloading of the carotid sinus baroreceptors by a bilateral carotid artery occlusion elicited a reflex rise in arterial pressure which was markedly potentiated by pretreating the animals with the PAF receptor antagonists WEB 2086 [3-4-(2-chlorphenyl)-9-methyl-6H-thieno-3,2f-1,2,4-triazolo-4, 3 a-1,4-diazepin-2-yl-(4-morpholinyl)-I-propanone; 2, 5 or 10 mg kg-1, i.v.] or BN 52021 (ginkgolide B; 0.1, 0.3 or 1.0 mg kg-1, i.v.). The increases in systemic vascular resistance induced by noradrenaline (30 micrograms kg-1, i.v.) or by the central activation of the sympathetic nervous system with glutamate (1 mg kg-1, intracerebroventricular) were also significantly potentiated in animals pretreated with WEB 2086 (5 mg kg-1, i.v.). In contrast, pretreatment with the cyclooxygenase inhibitor indomethacin (3 mg kg-1, i.v.) did not affect the haemodynamic actions of noradrenaline, thus excluding the possibility that prostacyclin may modulate the potentiating effect. To further confirm that PAF is released during systemic vasoconstriction, the cardiovascular PAF receptors were desensitized by the daily administration of PAF (3 micrograms kg-1, i.v.) for seven days. This procedure significantly reduced the intensity and duration of the hypotensive response to a subsequent PAF injection (3 micrograms kg-1, i.v.). In desensitized animals, the hypertensive response to bilateral carotid artery occlusion was potentiated to the same extent as in the animals treated with PAF receptor antagonists. Inhibition of PAF biosynthesis by pretreatment of the animals with the phospholipase A2 inhibitor mepacrine (5 mg kg-1, i.v.) also enhanced the increase in blood pressure elicited by carotid artery occlusion. We conclude that PAF is involved in the acute but not basal modulation of vasomotor tone and, hence, arterial pressure, probably by a negative feedback mechanism triggered by important increases in the vascular tone.