Effect of diabetic hyperglycemia and other sugars on plasma dopamine-beta-hydroxylase activity.

The plasma glycoprotein, dopamine-beta-hydroxylase (DBH), is present in markedly increased amounts in experimental, streptozocin (STZ)-diabetic rats, reaching a maximum at about the first week and maintaining a plateau for several months afterward. High glycemia values are observed simultaneously. Insulin treatment is observed to keep the glycemia and plasma DBH activity values at levels seen in control rats. The heterologous half-life of DBH in STZ-diabetic rats is significantly increased compared with that of control animals. The glucose analogue, 2-deoxy-D-glucose, has a similar effect on plasma DBH activity levels, eliciting high glycemia values. In STZ-diabetic animals, this increase is more significant, as if it were the additive effect of the two sugars. Other sugars that can compete for glycoprotein catabolic receptors can also modulate the plasma DBH activity levels. The lack of effect of galactose on DBH levels, together with the induced increase of DBH by alpha-methyl-D-mannoside and, to a lesser extent, by inulin, suggest an important rate for the mannose/glucose/N-acetyl glucosamine/fructose receptor in the catabolic clearance of DBH from plasma and explain the abnormal values seen for DBH in diabetes mellitus.

Pressure-diuresis in volume-expanded rats. Cortical and medullary hemodynamics.

This study evaluated whether pressure-diuretic and pressure-natriuretic responses are associated with alterations in vasa recta hemodynamics. Autoregulation of cortical and papillary blood flow was studied using a laser-Doppler flowmeter in volume-expanded and hydropenic rats. Superficial cortical flow and whole kidney renal blood flow were autoregulated in volume-expanded rats and decreased by less than 10% after renal perfusion pressure was lowered from 150 to 100 mm Hg. In contrast, papillary blood flow was not autoregulated and fell by 24 +/- 2%. The failure of papillary blood flow to autoregulate was due to changes in the number of perfused vessels as well as to alterations in blood flow in individual ascending and descending vasa recta. Pressure in vasa recta capillaries increased from 6.8 +/- 0.8 to 13.8 +/- 1.2 mm Hg after renal perfusion pressure was elevated from 100 to 150 mm Hg, and renal interstitial pressure rose from 7.4 +/- 0.8 to 12.3 +/- 1.4 mm Hg. In hydropenic rats, papillary blood flow was autoregulated to a significant extent, but it still decreased by 19% after renal perfusion pressure was lowered from 150 to 100 mm Hg. The pressure-diuretic and pressure-natriuretic responses in hydropenic rats were blunted in comparison to those observed in volume-expanded rats. These findings indicate that the pressure-diuretic and pressure-natriuretic responses are associated with changes in vasa recta hemodynamics and renal interstitial pressure.

Importance of nitric oxide and prostaglandins in the control of rat renal papillary blood flow.

The role of nitric oxide and prostaglandins in the control of rat renal papillary blood flow has been studied in anesthetized Munich-Wistar rats by use of laser Doppler flowmeter. Acute administration of N omega-nitro-L-arginine methyl ester (L-NAME) 10 mg/kg IV (n=8) increased mean arterial pressure by 27.8 +/- 3.6%, decreased papillary blood flow by 39.4 +/- 3.8%, and decreased renal blood flow by 47.4 +/- 1.9%. The subsequent administration of indomethacin (7.5 mg/kg IV) further decreased papillary blood flow (35.2 +/- 2.5%) without significant changes in mean arterial pressure or renal blood flow. In a second group (n = 6), administration of indomethacin before L-NAME decreased papillary blood flow by 39.6 +/- 2.1% without significantly altering mean arterial ressure or renal blood flow. The subsequent injection of L-NAME further decreased papillary blood flow (32.9 +/- 1.8%) and renal blood flow (49.8 +/- 6.6%) while increasing mean arterial pressure to a level not significantly different from that found in the first group. Autoregulation studies showed that L-NAME but not indomethacin reduced the renal perfusion pressure-renal blood flow relationship without altering autoregulation. However, both nitric oxide and prostaglandins importantly affected the renal perfusion pressure-papillary blood flow relationship because L-NAME and indomethacin significantly decreased this relationship in an additive fashion. Although both drugs reduced the sensitivity of the pressure-papillary flow relationship, only L-NAME affected autoregulation so that papillary blood flow was autoregulated at higher renal perfusion pressures. Thus, the present results indicate that both nitric oxide and prostaglandins control a similar percentage of rat renal papillary blood flow, but nitric oxide seems to be more important than prostaglandins as a mediator of the pressure-blood flow relationship. In contrast, only nitric oxide modifies the renal blood flow level, although it does not disturb whole-kidney blood flow autoregulation.

Effects of chronic increased salt intake on nitric oxide synthesis inhibition-induced hypertension.

OBJECTIVE AND METHOD: Experimental evidence suggests that endogenous nitric oxide plays an important role in the homeostatic response to an increase in sodium intake. In the present study we evaluated the influence of a high sodium intake (1% NaCl as drinking water) on arterial hypertension induced by long-term (6-7 weeks) inhibition of nitric oxide synthesis [NG-nitro-L-arginine methyl ester (L-NAME), 75 mg/100 ml in the drinking fluid] in rats. RESULTS: Treatment with L-NAME induced progressive elevations in tail-cuff systolic blood pressure, but there were no differences between rats drinking tap water and rats drinking 1% NaCl. Direct measurement of blood pressure at the end of the treatment confirmed the hypertension and the lack of differences between the two groups treated with L-NAME. Metabolic studies performed at the end of L-NAME treatment showed a reduced glomerular filtration rate and elevated urinary excretion of immunoreactive endothelin in the two hypertensive groups treated with L-NAME. Drinking intake, diuresis and natriuresis were significantly higher only in the L-NAME group drinking 1% NaCl. Both groups treated with L-NAME showed an accelerated and increased diuretic and natriuretic response to an isotonic 0.9% NaCl load (2.5 ml/100 g body weight, intraperitoneally). At the end of the study ventricular hypertrophy was observed in both L-NAME groups. CONCLUSION: The present results indicate that the time-dependent elevation in blood pressure produced by long-term inhibition of nitric oxide production is not affected by an increased sodium intake. However, salt supplementation induced the development of a polyuria and polydipsia syndrome in rats treated with L-NAME. The elevated excretion of endothelin in both groups treated with L-NAME suggests the possible participation of endothelin in the development of L-NAME hypertension.

Role of renin-angiotensin system in the impairment of baroreflex control of heart rate in renal hypertension.

Studies of the baroreceptor heart rate reflex were performed in two-kidney, one clip (2K1C) hypertensive rats to evaluate the relative importance of two factors--high blood pressure and high angiotensin II circulating levels--on impairment of the baroreflex, present in the acute phase of this model of hypertension. The sensitivity of baroreceptor reflex was determined by the slope of the relationship between changes in mean arterial pressure (MAP) and changes in heart rate in response to injections of phenylephrine and nitroprusside. Bradycardic and tachycardic responses were analyzed separately. In basal conditions, the slope of the MAP-heart rate relationship in 2K1C hypertensive animals was significantly lower than in control animals, both for tachycardic and bradycardic responses. Lowering of blood pressure with captopril to normotensive levels in the 2K1C animals significantly increased baroreflex gain in bradycardic responses to the level found in normotensive rats. Normalization of blood pressure with nitroprusside did not change baroreflex sensitivity. Infusion of angiotensin II at a dose that did not change MAP, previously normalized with captopril, completely reverted the effect of this agent on baroreflex sensitivity. Our data indicate that, in 2K1C hypertensive rats, decreased baroreflex sensitivity is mediated, at least in part, by high angiotensin II circulating levels. Elevated blood pressure per se is of secondary importance.

Effect of endothelin blockade on pressure natriuresis in nitric oxide-deficient hypertensive rats.

OBJECTIVE: Chronic inhibition of nitric oxide synthesis has been shown to cause arterial hypertension and an important blunting of the pressure diuresis and natriuresis response. The mechanisms mediating these abnormalities are not completely established. We therefore studied the effects of endothelin on these alterations. MATERIALS AND METHODS: Pressure diuretic and natriuretic relationships were evaluated in rats treated chronically (3 weeks) with the nitric oxide synthesis inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME; 40 mg/kg per day), alone or in combination with bosentan sodium salt (acute treatment: 10 mg/kg, intravenously; chronic treatment: 10 mg/kg per day). RESULTS: Chronic treatment with L-NAME significantly elevated mean arterial pressure (143.7 +/- 2.8 mmHg versus 102.8 +/- 1.6 in controls), reduced the glomerular filtration rate and renal blood flow and shifted the pressure diuretic and natriuretic responses to the right. Treatment with bosentan, either acute or chronically, did not attenuate the arterial hypertension of the L-NAME-treated rats but normalized the glomerular filtration rate and renal blood flow. In spite of the normalization of renal hemodynamics, the pressure diuretic and natriuretic responses of the bosentan-treated groups were not normalized, although chronic bosentan significantly improved the pressure natriuretic response. CONCLUSIONS: These results indicate that endothelin participates in the renal hemodynamic and excretory alterations that follow chronic inhibition of nitric oxide synthesis. However, the arterial hypertension is not mediated by endothelin activation.

Role of protein kinase C in mesenteric pressor responses of rats with portal hypertension.

1. Hyporesponsiveness to vasoconstrictors is a characteristic abnormality of liver diseases of uncertain origin. In the present study, we have evaluated the involvement of protein kinase C (PKC) in the reduced pressor response to methoxamine (MTX) of a rat model of portal hypertension induced by partial portal vein ligation (PVL). Experiments were performed in the isolated and perfused mesentery. 2. The pressor response to MTX was reduced in PVL compared to that of control animals (Sham) and pretreatment with NG-nitro-L-arginine (L-NOARG, 10(-4) M) or removal of the endothelium potentiated the response of both groups. However, only removal of the endothelium completely eliminated the reduced pressor response to MTX of the PVL vessels. 3. Pretreatment of the mesentric vessels with calphostin C (10(-6) M), a PKC inhibitor, reduced the response to MTX of Sham to a level similar to that of untreated PVL vessels, but did not change that of PVL animals. 4. Mesenteric pressor responses to a PKC activator, phorbol 12,13-dibutyrate (PDBu), were similar in vessels from both PVL and Sham rats and pretreatment with L-NOARG or removal of the endothelium enhanced those responses while indomethacin (10(-5) M) decreased them. In all cases, the responses to PDBU were similar in PVL vessels compared to Sham. 5. These results indicate that the reduced pressor response to MTX of the mesenteric vascular bed of PVL rats is due to an endothelial alteration, compatible with an enhanced production of nitric oxide. The lack of response to calphostin C in PVL vessels suggests an impairment in agonist-induced PKC activation. Since direct activation of PKC induces a normal pressor response, it is concluded that the endothelial alteration interacts with the mechanism producing PKC activation, which results in a lower pressor response of the PVL mesenteric vaculature.

Role of the renin-angiotensin system in the development of thyroxine-induced hypertension.

OBJECTIVE: We evaluated the influence of chronic blockade of the renin-angiotensin system on hypertension induced by long-term thyroxin (T4) administration. To this end, we determined the effects of chronic treatment with captopril on blood pressure, cardiac hypertrophy and other renal and metabolic variables of hypertensive hyperthyroid rats. METHODS: T4 was administered s.c. at 0.38 mumol/kg per day and captopril was given in the drinking water (1.38 mmol/l). Both treatments were maintained for 6 weeks. Control rats received tap water. After the treatment period, the rats were placed in metabolic cages. Later, blood pressure was measured in conscious rats by intra-arterial determination. RESULTS: T4-treated rats showed an increased mean arterial pressure (MAP) whereas, in rats treated with T4 plus captopril, MAP was similar to that of the control group. Captopril did not affect the increased heart rate or ventricular weight/body weight ratio of hyperthyroid rats, but it improved the reduced creatinine clearance of these animals. CONCLUSIONS: The elevation in blood pressure produced by long-term T4 administration was prevented by chronic blockade of the renin-angiotensin system. Captopril improved the renal function of hyperthyroid rats, but did not affect the relative cardiac hypertrophy of these animals.

Nitric oxide, the kidney, and hypertension.

The acute administration of nitric oxide (NO) synthesis inhibitors reduces the renal capacity to excrete sodium under normal or volume expanded conditions and increases renovascular resistances in the absence of changes in systemic blood pressure (BP). This indicates a sensitivity of renal vasculature higher than that of systemic vessels to NO synthesis inhibition. Medullary circulation is the renovascular territory most dependent on NO availability. Thus, alterations in medullary blood flow seems to account for the blunted pressure-natriuresis and sodium retention during acute NO synthesis inhibition. By contrast, during chronic administration of L-arginine analogs, systemic BP rises and overrides initial sodium retention by a resetting of the pressure-natriuresis relationship. This BP increase appears to be dependent on an overexpression of the actions of vasoconstrictor systems due to an imbalance created by the diminished NO production. Prolonged NO synthesis inhibition not only elevates BP, but also produces renal vascular and parenchymal damage. Antihypertensive therapy impedes BP elevation and ameliorates kidney deterioration. Finally, there is evidence of the possibility that a certain alteration in the L-arginine-NO pathway exists in genetic models and in human essential hypertension. In conclusion, according to the data contained in the literature, NO plays a significant role in the regulation of systemic and renal hemodynamics and excretory function, and could participate in the development of hypertension.

Chronic effects of nitric oxide and prostaglandin inhibition on pressure diuresis and natriuresis in rats.

The long-term interaction between nitric oxide (NO) and prostaglandins (PGs) in the pressure diuresis and natriuresis response has been studied. Experiments were performed in rats with chronic (8 weeks) inhibition of NO (NG-nitro L-arginine methyl Ester, L-NAME, 40 mg/kg/day) with or without simultaneous PGs synthesis blockade (indomethacin, 1 mg/kg/day). A time control group with no treatment was studied in parallel. At the end of this period, the animals were anesthetized and renal hemodynamics and excretion were studied at three levels of renal perfusion pressure (RPP; 100, 125 and 150 mm Hg). Renal blood flow, glomerular filtration rate, diuresis and natriuresis were lower at the three RPP levels in both L-NAME-treated groups than in the control or indomethacin-treated animals. Simultaneous administration of indomethacin plus L-NAME did not further modify the hemodynamic or excretory responses observed in the L-NAME-treated animals. These results show that chronic NO inhibition impairs the renal excretory response to changes in renal perfusion pressure, and simultaneous NO and prostaglandin synthesis inhibition does not reduce those responses further. It is concluded that, on a long-term basis, a preserved NO production, but not prostaglandin production, is critical for a normal pressure diuretic and natriuretic mechanism.

Mechanisms of the increased pressor response to vasopressors in the mesenteric bed of nitric oxide-deficient hypertensive rats.

In the present study we analyzed mesenteric vascular reactivity of chronic nitric oxide (NO)-deficient hypertensive rats (NW-nitro-L-Arginine Methyl Ester, L-NAME, 50 mg/kg/day, oral, 3 weeks). Perfusion pressure changes in response to cumulative additions of methoxamine and KCl were significantly increased in the mesenteric vessels of the L-NAME-treated as compared with vessels of the controls. Verapamil reduced the responses to methoxamine, but those of the hypertensive rats were still enhanced. In contrast, responses to KCl were almost completely abolished by verapamil. In mesenteric vessels perfused with zero calcium and high-potassium Krebs, pressor responses to the re-addition of calcium were also significantly enhanced in the hypertensive rats compared to the controls. Vasodilator responses to acetylcholine in KCl-preconstricted vessels, while still significant, were reduced in the L-NAME-treated rats. In this case, acute inhibition of NO blocked the vasodilator responses to acetylcholine and abolished the differences between the two groups. In methoxamine-preconstricted vessels and in the presence of acute inhibition of NO and prostaglandins, vasodilator responses to acetylcholine were significantly greater in the hypertensive vessels than in controls. In conclusion, the mesenteric vessels of L-NAME hypertensive rats show an enhanced response to vasopressors which is related to calcium entry. These data also reveal the existence of an enhanced role of a NO and prostaglandin-independent vasodilator factor, probably endothelium-derived hyperpolarizing factor that may play a compensatory role in the deficiency of NO.

Synergistic interaction of diazepam with 3',5'-cyclic adenosine monophosphate-elevating agents on rat aortic rings.

We investigated the effect of the phosphodiesterase type 4 (PDE4) inhibitory activity of diazepam on the arterial wall. To this purpose, we examined the interaction of diazepam with 3',5'-cyclic adenosine monophosphate (cyclic AMP)-elevating agents on vasodilatation and cyclic AMP levels in rat aortic rings precontracted with phenylephrine. The involvement of benzodiazepine receptors was also studied. Diazepam (5-100 microM) produced a relaxation of this preparation which was neither mimicked by gamma-aminobutyric acid (GABA), nor antagonized by flumazenil and 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide (PK 11195), inhibitors of central or peripheral type benzodiazepine receptors, respectively. The diazepam-induced relaxation was potentiated by the presence of isoprenaline (10 nM), forskolin (50 nM) or milrinone (0.1 microM). Furthermore, diazepam increased the enhancement of cyclic AMP levels induced by these three agents in this tissue. Our results demonstrate a functional and biochemical synergistic interaction of diazepam with cyclic AMP-elevating agents on rat aortic rings.

Sympathoadrenal activity and plasma glucose effects on plasma dopamine-beta-hydroxylase levels in rats.

Plasma dopamine-beta-hydroxylase (DBH) activity is a controversial index of sympathoadrenal function. In our results, the half-life of bovine DBH administered by cardiac puncture to Wistar rats was dependent on plasma glucose values, being 60 min for controls, 96 min for streptozotocin (STZ)-diabetic animals (p less than 0.02) and 33 min for insulin-treated normal rats (p less than 0.01). In experimental situations with low plasma glucose levels, DBH activity was also diminished with respect to controls (glucose: 103.6 +/- 2.2 mg%, DBH: 9.7 +/- 0.5 U/ml). After fasting, glucose was 60.8 +/- 1.5 mg% (p less than 0.001) and plasma DBH 6.4 +/- 0.3 U/ml (p less than 0.001); fasting plus cold exposure also decreased glucose (66.2 +/- 1.4 mg%, p less than 0.001) and plasma DBH (6.7 +/- 0.2 U/ml; p less than 0.001). In both situations, there was an increase in exocytosis from sympathoadrenal tissues; however, no increase in plasma DBH levels was observed, because plasma glucose being diminished it was unable to compete at the catabolic receptor level. When normal plasma glucose levels take place, plasma DBH is essentially constant, poorly reflecting a moderate increase or decrease in exocytosis from tissues, as was the case in our animals with 48 h of cold exposure. When chemical sympathectomy (6-OH-dopamine) or bilateral adrenalectomy was performed there was a compensatory mechanism between them. Plasma DBH does not change significantly in these situations if plasma glucose values are normal. From these results, the most important physiological influence on plasma DBH activity is the glucose plasma levels. Plasma DBH values not being a useful index of sympathoadrenal activity if, at the same time, the plasma glucose levels are not considered.

Diazepam reduces action potential duration in guinea-pig papillary muscle by a cAMP-dependent mechanism.

In this study, we have analyzed the role of cyclic AMP (cAMP) as the mediator of the decrease in action potential duration induced by diazepam. Diazepam (1-100 microM) reduced, in a dose-dependent manner, the duration of intracellular action potential recorded in the papillary muscle obtained from the right ventricle of the guinea pig heart. This effect was mimicked by the analog of cyclic AMP, 8-Br-cAMP (100 microM), but not by gamma-amino-butyric acid (GABA). Also, the selective antagonist of the benzodiazepine receptors, flumazenil did not modify the effect of diazepam. The diazepam-induced shortening of action potential duration was partially antagonized by the inhibitor of cAMP synthesis carbachol (1 microM) or the blocker of the cAMP-dependent protein kinase A, Rp-cAMP[S] (1 microM). These results indicate that cyclic AMP is involved in the diazepam-induced shortening of the action potential duration of the guinea pig papillary muscle.

Hemodynamic effects of hypertonic saline in the conscious rat.

The present study examines the role of vasopressin and the sympathetic nervous system on the hemodynamic effects of an infusion of hypertonic saline (NaCl 1.5 M) in conscious rats. The cardiovascular response to hypertonic saline was similar in both untreated and hexamethonium-pretreated rats. Mean arterial pressure increased by 15 mmHg as a consequence of the elevation of total peripheral resistance, while cardiac index was decreased. The administration of an antagonist to the pressor activity of vasopressin in rats with intact reflexes, partially decreased mean arterial pressure and total peripheral resistance and increased cardiac index toward basal values. In contrast, the hemodynamic response to hypertonic saline was totally reverted when the vasopressin antagonist was injected in the hexamethonium-pretreated rats. The results of the present study indicate that the hypertensive response induced by hypertonic saline in conscious rats is due to the vasoconstrictor effects of both vasopressin and the sympathetic nervous system.

Omapatrilat normalizes renal function curve in spontaneously hypertensive rats.

BACKGROUND: The present study was designed to analyze the chronic renal response to omapatrilat, a new vasopeptidase inhibitor, in spontaneously hypertensive rats (SHR). To that end, the renal and blood pressure response to a 4-day salt loading protocol was analyzed and the respective chronic renal curves constructed. RESULTS: In non treated animals, and under normal sodium intake (around 2 mEq/day), mean arterial pressure (MAP), was significantly higher in the SHR as compared with the controls (WKY). After increasing salt intake (8 times normal), MAP did not change significantly in any group and the animals reached a normal sodium balance in four days. In a second group of animals, omapatrilat was given orally for 15 days at the dose of 40 mg/kg/day in the drinking water. In these omapatrilat-treated animals, and under normal sodium intake, MAP was significantly lower in both groups, although the antihypertensive effect was much greater in the SHR, so that the MAP of the SHR group was completely normalized and similar to the WKY-treated group. The subsequent elevation of sodium intake did not significantly elevate MAP in any group and the animals could manage the sodium excess as well as the non treated groups. CONCLUSIONS: These results indicate that chronic treatment with omapatrilat normalizes blood pressure in SHR without affecting adversely the renal ability to eliminate a sodium load. Chronic treatment with omapatrilat resets the chronic pressure natriuresis relationship of the SHR to a normal level, thus without altering the normal salt-independence of this arterial hypertension model.

Pancreatitis associated with pleural-mediastinal pseudocyst, panniculitis and polyarthritis.

We describe two patients with pancreatitis. One patient had acute pancreatitis of biliary origin and presented with small joint polyarthritis and panniculitis lesions. The other patient was originally hospitalised for dyspnoea with bilateral pleural effusion, and subsequently developed migratory polyarthritis. During his hospital stay he developed panniculitis lesions and a monoclonal IgG disorder of unknown significance. Very few patients with pancreatitis develop polyarthritis and panniculitis. The appearance of pseudocysts in the pleural and mediastinal cavity in the course of pancreatitis is an infrequent complication.

[Renal effects of the chronic inhibition of nitric oxide synthesis in cirrhotic rats with ascites]. / Efectos renales de la inhibición crónica de la síntesis de óxido nítrico en ratas cirróticas con ascitis.

Previous studies have shown that acute inhibition of nitric oxide (NO) synthesis improves sodium and water excretion and increases blood pressure in cirrhotic rats with ascites, thus suggesting that NO is an important factor contributing to the arterial hypotension and sodium retention of liver cirrhosis. In the present work we have analyzed the renal effects derived from the chronic oral treatment (10 days) with aminoguanidine (AG, 100 mg/kg/day), a preferential inhibitor of inducible NO synthase (iNOS), or Nw-Nitro-L-Arginine Methyl Ester (L-NAME, 0.5 mg/kg/day), a nonselective inhibitor of NOS, in an experimental model of liver cirrhosis with ascites (carbon tetrachloride inhalation). Untreated cirrhotic rats showed lower mean arterial pressure (MAP), diuresis, natriuresis and glomerular filtration rate (GFR) and similar renal blood flow (RBF) compared with the untreated control rats. Chronic administration of AG did not modify significantly any parameter in cirrhotic and control animals. Conversely, long-term L-NAME administration to cirrhotic rats normalized MAP and significantly increased water and sodium excretion, whereas in control animals these parameters were not significantly modified. These results show that chronic NO synthesis inhibition with L-NAME, but not with aminoguanidine, improves renal perfusion pressure and increases the lower sodium and water excretion of cirrhotic rats with ascites. Thus, an enhanced production of NO is an important factor contributing to the renal sodium and water retention characteristic of liver cirrhosis.