Superoxide dismutase and oxidative stress in Dahl salt-sensitive and -resistant rats

The roles of oxidative stress and renal superoxide dismutase (SOD) levels and their association with renal damage were studied in Dahl salt-sensitive (S) and salt-resistant (R)/Rapp strain rats during changes in Na intake. After 3 wk of a high (8%)-Na diet in S rats, renal medullary Cu/Zn SOD was 56% lower and Mn SOD was 81% lower than in R high Na-fed rats. After 1, 2, and 3 wk of high Na, urinary excretion of F(2)-isoprostanes, an index of oxidative stress, was significantly greater in S rats compared with R rats. Plasma F(2)-isoprostane concentration increased in the 2-wk S high Na-fed group. After 3 wk, renal cortical and medullary superoxide production was significantly increased in Dahl S rats on high Na intake, and urinary protein excretion, an index of renal damage, was 273 +/- 32 mg/d in S high Na-fed rats and 35 +/- 4 mg/d in R high Na-fed rats (P < 0.05). In conclusion, salt-sensitive hypertension in the S rat is accompanied by marked decreases in renal medullary SOD and greater renal oxidative stress and renal damage than in R rats.

Role of abnormal nitric oxide systems in salt-sensitive hypertension

A large percentage of human hypertensive patients are salt sensitive, referring to the dependence of hypertension on sodium intake, but the cause of the salt sensitivity is not known. Although several mechanisms may contribute to salt-sensitive hypertension, the nitric oxide (NO) system appears to play a major role. Studies in humans and Dahl salt-sensitive (S) rats indicate that NO production is decreased during hypertension. Intravenous L-arginine infusion in Dahl S rats increases NO production and prevents salt-sensitive hypertension. In the Dahl salt-resistant (R) rat, NO production by both inducible NO synthase (iNOS) and neuronal NOS (nNOS) help to prevent salt-sensitive hypertension. Experimental evidence is summarized, indicating that the Dahl S rat has a deficient production of NO by nNOS, although NO production by iNOS appears to moderately decrease salt sensitivity. Other evidence about the importance of NO in salt-sensitive hypertension is reviewed, including the role of the renal NO system.

Mechanisms of salt-sensitive hypertension: role of inducible nitric oxide synthase

The goal of this study was to determine the role of inducible nitric oxide synthase (iNOS) in the arterial pressure, renal hemodynamic, renal excretory, and hormonal changes that occur in Dahl/Rapp salt-resistant (R) and salt-sensitive (S) rats during changes in Na intake. Thirty-two R and S rats, equipped with indwelling arterial and venous catheters, were subjected to low (0.87 mmol/day) or high (20.6 mmol/day) Na intake, and selective iNOS inhibition was achieved with intravenous aminoguanidine (AG, 12.3 mg. kg(-1). h(-1)). After 5 days of AG, mean arterial pressure increased to 121 +/- 3% control in the R-high Na AG rats compared with 98 +/- 1% control (P < 0.05) in the R-high Na alone rats, and S-high Na rats increased their arterial pressure to 123 +/- 3% control compared with 110 +/- 2% control (P < 0.05) in S-high Na alone rats. AG caused no significant changes in renal hemodynamics, urinary Na or H(2)O excretion, plasma renin activity, or cerebellar Ca-dependent NOS activity. The data suggest that nitric oxide produced by iNOS normally helps to prevent salt-sensitive hypertension in the Dahl R rat and decreases salt sensitivity in the Dahl S rat.

A High Salt Diet Increases Renal Nitrotyrosine Formation and Urinary Excretion of F 2 -Isoprostanes and Protein in Dahl Salt-Sensitive Rats

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Superoxide formation causes tissue injury in many disease processes, and interaction between superoxide and nitric oxide forms peroxynitrite, a very strong oxidant. An index of peroxynitrite damage to tissues is nitrotyrosine formation. Also, F 2 -isoprostanes have been shown to be a reliable marker of oxidative stress in vivo. Recently, oxidative stress was shown to contribute to the maintenance of hypertension in the SHR; however, whether oxidative stress is involved in the renal damage that occurs in Dahl salt-sensitive (S) hypertension is not clear. Our goal was to determine the role of oxidative stress in the renal damage that occurs in Dahl S/Rapp rats on high Na intake by determining the urinary excretion of F 2 -isoprostanes and renal nitrotyrosine formation and determining urinary protein excretion as an index of renal damage. Studies were conducted in S rats on a low salt (0.3% NaCl) or a high salt (8% NaCl) diet for 3 weeks. After 3 weeks urine was collected continuously for 24 hours, and urinary F 2 -isoprostane concentration was measured with a gas chromatography/mass spectrometric assay. Renal nitrotyrosine formation was determined by immunohistochemistry and urinary protein excretion by the Bradford method. We found that high Na intake significantly increased urinary F 2 -isoprostane excretion to 24.2±1.7 ng/day compared with 9.7±0.8 ng/day in rats on a low Na diet, P<0.05. Renal glomerular nitrotyrosine was prevalent in the high Na group compared to the low Na group. Urinary protein excretion was 274±32 mg/day in high Na rats and 55±11 mg/day in low Na rats, P<0.05. The results suggest that oxidative stress is significantly increased in Dahl S rats on a high salt diet, which possibly contributes to the progression of renal damage.

The Role of Oxidative Stress in Dahl Salt-Sensitive Hypertension

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High sodium intake in the Dahl salt-sensitive (S) rat causes hypertension and renal damage. Our goal was to determine if long-term iv infusion of Tempol, a superoxide dismutase mimetic, would ameliorate the hypertension and reduce renal damage in Dahl S rats subjected to high sodium intake. Dahl S/Rapp rats with indwelling arterial and venous catheters were maintained by iv infusion for 3 weeks on either high Na(20.6 mEq/day)(HN), high Na + Tempol(125μmol/kg/h)(HNT)or low Na(0.9 mEq/day) + Tempol(LNT). Arterial pressure was measured 24 hours/day, and as seen in the figure, was significantly decreased in high Na S rats by Tempol. † -P<.05 compared to HNT, * -P<.05 compared to LNT. At the end of 3 weeks, rats were anesthetized with isoflurane, and kidneys were removed for histological examination. At this time, the percentage of glomeruli with either focal or global sclerosis in HN, HNT and LNT rats was 3.4±0.8 * †, 1.4±0.4 † and 0.6±0.08, respectively, and glomerular cross-sectional area (mm 2 ) was 14.3±0.4,12.9±0.5 and 12.2±0.6. Therefore, Tempol significantly reduced arterial pressure and indices of renal damage, glomerular sclerosis and glomerular cross-sectional area. These data suggest that oxidative stress significantly increases arterial pressure and exacerbates renal damage in salt-sensitive Dahl rats during increased sodium intake.

Role of neuronal nitric oxide synthase in Dahl salt-sensitive hypertension

The goal of this study was to determine the role of neuronal nitric oxide synthase (nNOS) in the arterial pressure, renal hemodynamic, and renal excretory changes that occur in Dahl salt-resistant (DR) and salt-sensitive (DS) rats during changes in Na intake. Fifty-three DR and DS rats/Rapp strain of 7 to 8 weeks of age with indwelling arterial and venous catheters were subjected to low (0.87 mmol/d) or high (20.6 mmol/d) Na intake beginning 2 days before the start of the control period. Measurements were made during a 5-day control period followed by a 5-day period of nNOS inhibition with intravenous 7-nitroindazole (7NI, 1.67 mg. kg-1. h-1) or vehicle infusion. After 5 days of 7NI, mean arterial pressure increased to 120+/-6% control in the DR-high Na, 7NI rats compared with 98+/-1% control (P<0.05) in the DR-high Na alone rats. After 5 days of 7NI, DS-high Na rats, which had a control arterial pressure 31 mm Hg higher than the comparable DR rats, increased their arterial pressure to 114+/-3% control, which was not significantly different from the DS-high Na alone pressure of 110+/-2% control. No significant changes occurred in glomerular filtration rate, effective renal plasma flow, urinary Na excretion, or urine volume because of 7NI. However, plasma renin activity decreased significantly in DR and DS rats on low Na intake with 7NI infusion. The data demonstrate that the highly salt-resistant DR rat became salt-sensitive during nNOS inhibition with 7NI. However, the arterial pressure of the DS rat was not affected by 7NI. This suggests that nitric oxide produced by nNOS in the DR rat normally helps to prevent salt-sensitive hypertension and that low functional levels of nNOS in the DS rat may contribute to its salt-sensitivity.

Dynamics of extracellular fluid volume changes during hyperproteinemia

The dynamics of fluid volume distribution between the blood and interstitium during hyperproteinemia were studied in 12 anephric, conscious dogs during several states of hydration. After recovery from splenectomy and unilateral nephrectomy, plasma protein concentration was elevated to 8.4-8.7 g/dl by daily intravenous infusion of 330 ml of previously collected autologous plasma for 11 days. The remaining kidney was then removed, and the next day lactated Ringer solution equivalent to 10 or 20% of body weight was infused intravenously. By the end of the 25-h postinfusion period, Ringer infusion had increased circulating protein mass 20.9 +/- 9.1% (mean +/- SE) in the 10% group (P < 0.05) and decreased it 10.5 +/- 3.3% in the 20% group (P < 0.05). The average increase in blood volume and arterial pressure during the postinfusion period was 27.4 +/- 2.5 and 20.7 +/- 3.7%, respectively, in the 10% group but only 17.8 +/- 2.4 and 12 +/- 1.6% in the 20% group (all changes significant compared with respective control). The relationship between blood volume and sodium space was similar to that found during normoproteinemia, such that elevations in sodium space of 40-50% increased blood volume but greater elevations in sodium space caused no further increases in blood volume. Overhydration during chronic hyperproteinemia causes hypervolemia and hypertension, but, in contrast to those in short-term studies, the increases in blood volume and arterial pressure are not greater than those achieved during normoproteinemia.

Chronic lymph flow responses to hyperproteinemia

The long-term responses of lymph flow, lymph protein transport, and the permeability-surface area (PS) product to hyperproteinemia have been studied in conscious dogs. Plasma protein concentration (PPC) was increased by daily intravenous infusion of previously collected autologous plasma for 9 days. Lymph flow was determined by collecting lymph chronically from a lymphatic afferent to the popliteal node in the hind leg. Compared with the average value during the normal-PPC period, the following changes occurred during 10 days of high PPC: lymph flow decreased from 12.3 +/- 1.1 to 3.8 +/- 0.6 microl/min, lymph protein transport decreased from 241 +/- 24 to 141 +/- 21 microg/min, PS product decreased from 4.7 +/- 0.5 to 3.0 +/- 0.5 microl/min, PPC increased from 7.1 +/- 0.1 to 8.8 +/- 0.4 g/dl, lymph protein concentration increased from 1.9 +/- 0.1 to 3.8 +/- 0.1 g/dl, plasma colloid osmotic pressure increased from 18. 6 +/- 0.8 to 24.2 +/- 2.1 mmHg, and lymph colloid osmotic pressure increased from 4.8 +/- 0.2 to 10.4 +/- 0.7 mmHg. In conclusion, long-term hyperproteinemia in dogs resulted in chronic decreases in lymph flow, lymph protein transport, and the PS product and chronic increases in lymph protein concentration and lymph colloid osmotic pressure. The marked decrease in lymph flow during hyperproteinemia decreased lymph protein transport and thus contributed to the increase in lymph protein concentration. In addition, the decreases in PS product and lymph protein transport suggest that transcapillary protein flux decreases during hyperproteinemia.

Cardiovascular-renal responses to long-term nitric oxide inhibition during angiotensin II-AT1 receptor inhibition

A previous study in conscious dogs showed that the normal hypertensive response to short-term nitric oxide synthesis inhibition was markedly attenuated during angiotensin II-AT1 receptor inhibition. However, whether angiotensin plays an important cardiovascular role in the dog during long-term nitric oxide synthesis inhibition has not been determined and was therefore the goal of this investigation. Studies were conducted in 16 conscious dogs that received angiotensin AT1 receptor inhibition with L158809 (N = 8) or vehicle (N = 8) for 12 d. During the last 6 d of this infusion, nitric oxide synthesis was inhibited by infusing NG-nitro-L-arginine methyl ester intravenously at 37.1 nmol/kg/min. In both the AT1 and vehicle groups, nitroarginine infusion significantly decreased the acetylcholine depressor response, glomerular filtration rate, renal plasma flow, and heart rate, and increased arterial pressure and renal vascular resistance in a similar manner, whereas it caused little change in the urinary excretion of sodium and water or in plasma renin activity. In conclusion, the long-term responses of arterial pressure, renal hemodynamics, and the renal excretion of sodium and water to nitric oxide synthesis inhibition were not significantly influenced by blockade of angiotensin AT1 receptors with L158809 in the dog.

Role of nitric oxide in the arterial pressure and renal adaptations to long-term changes in sodium intake

The goals of this study were to determine whether long-term nitric oxide (NO) synthesis inhibition in dogs results in an increase in the sodium sensitivity of arterial pressure and whether changes in plasma renin activity or the plasma concentrations of arginine vasopressin (AVP) and aldosterone play an important role in this hypertension. Studies were conducted in a control group and groups that received NO inhibition with N(G)-nitro-L-arginine methyl ester (L-NAME) at 10 or 25 microg x kg(-1) x min(-1). Each group was challenged with normal, low, and high sodium intake for periods of 5 days each. Urinary nitrate + nitrite excretion (UNOx) more than doubled in the control group during high sodium intake. In both L-NAME groups, UNOx decreased significantly, there was a hypertensive shift in the relation between urinary sodium excretion and arterial pressure, and urinary sodium excretion remained normal even in the high-sodium intake period. L-NAME infusion did not change the sodium sensitivity of arterial pressure or plasma renin activity, plasma aldosterone, and plasma AVP. In conclusion, the data suggest that, in dogs, increases in NO synthesis are not necessary to excrete a chronic sodium load, and decreases in NO do not increase the sodium sensitivity of arterial pressure.

Role of nitric oxide in regulation of long-term pressure-natriuresis relationship in Dahl rats

The aim of this study was to determine the role of nitric oxide (NO) in the development of salt-induced hypertension in the Brookhaven strain of Dahl rats. Six- to seven-week-old conscious salt-sensitive (S) and salt-resistant (R) rats with indwelling arterial and venous catheters received low-, normal-, and high-sodium intakes sequentially over a 16-day period, and L-arginine was infused intravenously at 2 or 4 mg.kg-1.min-1 over this time. The S rats had an impaired NO production as evidenced by a decreased urinary nitrate plus nitrite excretion. The administration of the low or high dose of L-arginine increased the whole body NO production of the S rats to that of the control R rats, and the high dose of L-arginine prevented the shift of long-term pressure-natriuresis relationship, the elevation of arterial pressure, and the increase in salt sensitivity of arterial pressure in the S rats. The sodium and water balances were not different between the age-matched R and S rats. In conclusion, a continuous infusion of L-arginine prevented both the changes in the pressure-natriuresis relationship and the development of salt-induced hypertension in Dahl S rats.

Overall hemodynamic studies after the chronic inhibition of endothelial-derived nitric oxide in rats

Previous studies have demonstrated that an acute intravenous administration of nitro-L-arginine methyl ester (L-NAME) causes a sustained hypertension and widespread vasoconstriction. However, little information is available regarding the chronic effect of L-NAME on circulatory hemodynamics. Therefore, the purpose of the present study was to characterize both the systemic and regional hemodynamics after the chronic inhibition of endothelium-derived nitric oxide in male Sprague Dawley rats. The rats were divided into two groups: control (n = 8) and L-NAME (n = 8). The rats in the control group received only tap water and the rats in the L-NAME group received oral L-NAME solution at a dose of 0.1 mg/mL in the drinking water ad libitum. Four weeks after L-NAME or tap water treatment the rats were anesthetized with inactin, and mean arterial blood pressure, cardiac output, and individual organ flows were measured. Cardiac output and individual organ flows were measured using radioactive microspheres. Chronic administration of L-NAME resulted in a significant increase in mean arterial blood pressure from a control value of 118 +/- 4 mm Hg to 174 +/- 8 mm Hg (P < .01). Cardiac output decreased from a control value of 29 +/- 2 mL/min/100 g to 20 +/- 2 mL/min/100 g (P < .01) and total peripheral resistance increased from a control value of 4.3 +/- 0.3 mm Hg/mL/min/100 g to 9.7 +/- 1.4 mm Hg/mL/min/100 g (P < .01). In addition, chronic L-NAME treatment resulted in a widespread vasoconstriction and decrease in regional blood flows.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms involved in the cardiovascular-renal actions of nitric oxide inhibition

The roles of the sympathetic nervous system, angiotensin II, and arginine vasopressin in the cardiovascular-renal responses to nitric oxide synthesis inhibition were examined in eight conscious dogs equipped with arterial and venous catheters and a nonoccluding bladder catheter. Nitric oxide inhibition was achieved by intravenous infusion of NG-nitro-L-arginine methyl ester (L-NAME) at 37.1 nmol/kg per minute for 140 minutes in the control group. The same dogs, after a 1-week recovery, were pretreated for 2 days with either prazosin for alpha 1 blockade, prazosin plus propranolol for alpha 1 plus beta blockade, L-158,809 for angiotensin receptor blockade, or d(CH2)Tyr(Me)arginine vasopressin for vasopressin-V1 blockade, and the L-NAME infusion was repeated. After 140 minutes of L-NAME infusion into the control group, mean arterial pressure and renal vascular resistance had increased 16% and 71%, and renal blood flow, glomerular filtration rate, urine flow, and urinary sodium excretion had decreased 33%, 16%, 61%, and 64%, respectively. The decrement in renal blood flow and glomerular filtration during L-NAME administration was unaffected by any of the neurohumoral blockers. During V1 blockade L-NAME resulted in only a 3% increase in arterial pressure, attenuation of the renal vascular resistance response, and almost total elimination of the decrease in urine flow. During angiotensin blockade the L-NAME-induced increase in arterial pressure was markedly attenuated, and the decrease in urinary sodium excretion was attenuated in the alpha 1 plus beta blockade group.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitric oxide regulates renal hemodynamics and urinary sodium excretion in dogs

The goal of this study was to determine whether nitric oxide has a long-term role in the control of renal hemodynamics and the relation between arterial pressure and urinary sodium excretion. Studies were conducted over a 25-day period in seven conscious dogs equipped with indwelling vascular catheters and an electromagnetic flow probe on the iliac artery. Nitric oxide synthesis was inhibited by continuous intravenous infusion of NG-nitro-L-arginine methyl ester at 37.1 nmol/kg per minute, and the effects of low, normal, and high sodium intakes were determined. Significant nitric oxide synthesis inhibition was evidenced by a decrease in the depressor and flow responses to systemic acetylcholine administration. During the normal sodium intake plus nitro-arginine period, arterial pressure increased to hypertensive levels, averaging 120 +/- 4% of control; renal vascular resistance increased to an average of 134 +/- 8% of control; glomerular filtration rate and renal plasma flow decreased to 83 +/- 3% and 81 +/- 3% of control, respectively; and no changes occurred in filtration fraction, plasma renin activity, plasma concentrations of aldosterone and cortisol, urinary sodium excretion, sodium balance, fractional excretion of sodium, urine volume, and volume balance. Arterial pressure increased further to 130 +/- 3% of control during high salt intake, and sodium balance was achieved at each sodium intake despite the increase in arterial pressure because of a hypertensive shift in the relation between urinary sodium excretion and arterial pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term cardiovascular role of nitric oxide in conscious rats

The goal of this study was to determine the arterial pressure and renal excretory responses to a continuous intravenous infusion of 7.4 nmol/kg per minute of the nitric oxide synthesis inhibitor NG-nitro-L-arginine methyl ester (L-NAME) in conscious rats. Studies were conducted in six groups of Sprague-Dawley rats with indwelling arterial and venous catheters over periods lasting 12 to 26 days. In the first group of rats, L-NAME infusion for 9 days caused a sustained increase in arterial pressure, and on the ninth day arterial pressure was increased 29 mm Hg. Infusion of L-NAME at the higher dose of 37 nmol/kg per minute for 9 days caused no greater increase in arterial pressure than the lower dose. Sodium and volume balances and phenylephrine pressor sensitivity were unchanged during L-NAME administration at 7.4 nmol/kg per minute; plasma renin activity increased 2.5-fold, but the vasodepressor and vasodilator responses to acetylcholine and bradykinin were unchanged. Arterial pressure remained significantly increased 7 days after L-NAME was stopped, but in another group of rats, intravenous L-arginine infusion caused arterial pressure to return to control within 1 day. This same dose of L-arginine was administered for 7 days intravenously, and neither arterial pressure nor sodium balance changed. In other groups of rats, L-arginine was administered in conjunction with L-NAME; this prevented any change in arterial pressure, whereas D-arginine did not. In conclusion, the data suggest that continuous intravenous infusion of L-NAME causes sustained increases in arterial pressure in conscious rats without any sodium or water retention. The hypertension is accompanied by increases in plasma renin activity and can be prevented with intravenous L-arginine administration.

Role of endothelium-derived nitric oxide in control of renal microvasculature in aging male rats

The objective of this study was to evaluate the role of nitric oxide (NO) in the regulation of whole kidney and glomerular hemodynamics during aging. After 2 wk of oral treatment with N-nitro-L-arginine methyl ester (L-NAME; 4.5 mg.kg body wt-1.day-1) to inhibit NO synthesis, male rats, aged 3-5, 13-15, and 21-24 mo, were studied by micropuncture. Blood pressure increased by 50% in old (21-24 mo) rats with L-NAME but only 20-30% in the two younger groups. With L-NAME, renal vascular resistance increased fivefold in old rats but only twofold in younger groups. Glomerular capillary pressure increased 20-30% in younger L-NAME rats and 60% in older rats. Afferent and efferent resistances increased dramatically, and the glomerular capillary ultrafiltration coefficient decreased in all L-NAME-treated rats but most strikingly in the 21- to 24-mo-old group. Acute infusion of L-arginine significantly attenuated the effects of NO synthase inhibition on arterial pressure and renal hemodynamics in both young and old rats. This study confirms that NO synthesis blockade has a greater effect on renal hemodynamics in aging rats and implies that NO may play a progressively more important role in controlling renal function with advancing age.

Cardiovascular responses to long-term blockade of nitric oxide synthesis

The goal of this study was to determine if there is a basal release of nitric oxide that affects long-term arterial pressure regulation in dogs. Studies were conducted over a 23-day period in eight conscious dogs with indwelling catheters. Nitric oxide synthesis was blocked by continuous intravenous infusion of nitro-L-arginine-methyl ester at 37.1 nmol/kg per minute for 11 days. Arterial pressure increased to 120 +/- 4% of control on the first day, decreased for a few days, and then increased to a maximum value of 122 +/- 6% of control on day 7. Bradycardia was sustained throughout the entire nitro-arginine period. Blockade of nitric oxide synthesis was evidenced by attenuated pressure and flow responses to systemic acetylcholine infusion. The pressor response to phenylephrine was increased for only 1 day, and the hypotensive effects of nitroprusside were enhanced. Also, the variability of arterial pressure was significantly increased during nitro-arginine. Sodium and water balances were positive the first day of nitro-arginine infusion but were unchanged for the entire nitro-arginine period. In conclusion, the data suggest that blockade of the basal release of nitric oxide in dogs causes an increase in the long-term level of arterial pressure without any sustained sodium or water retention.

Role of nitric oxide in long-term angiotensin II-induced renal vasoconstriction

In vitro studies have indicated that nitric oxide may play an important role in modulating the renal vascular actions of angiotensin II (Ang II). However, the physiological importance of this interaction in the long-term regulation of renal hemodynamics is unknown. Therefore, the goal of this study was to determine if long-term Ang II-induced renal vasoconstriction was potentiated by nitric oxide synthesis inhibition. The intrarenal effects of Ang II were examined in eight unilaterally nephrectomized, conscious dogs before and after systemic inhibition of nitric oxide synthesis. Ang II infusion into the renal artery at 0.5 ng/kg per minute resulted in decreases in renal plasma flow of 15% and 9% after 3 and 5 days, respectively. During this time, glomerular filtration rate decreased 12% after 3 days of angiotensin but was not significantly changed after 5 days. After 4 days of recovery from Ang II, nitric oxide synthesis was inhibited with intravenous NG-nitro-L-arginine-methyl ester (L-NAME) at 10 micrograms/kg per minute for 5 days, and this caused a significant decrease in renal plasma flow but no change in glomerular filtration rate. Infusion of Ang II into L-NAME-pretreated dogs for an additional 5 days further decreased renal plasma flow and glomerular filtration 14% and 11%, respectively. However, the effects of Ang II and L-NAME on renal plasma flow were only additive on days 3 and 5 of this period, and the effects on glomerular filtration were additive on day 3 but were potentiated on day 5.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic effects of hyperproteinemia on blood volume and lymph protein concentration

The long-term effects of hyperproteinemia on blood volume and lymph protein concentration were studied in six conscious dogs over a 17-day period. Plasma protein concentration (PPC) was increased by daily intravenous infusion of approximately 300 ml of previously collected autologous plasma. By day 17 PPC had increased 2.4 g/dl, and plasma colloid osmotic pressure had increased 51%; however, blood volume was not changed. Also, at this time sulfate space, an index of extracellular fluid volume, had increased 12%, prenodal lymph protein concentration had increased from 1.6 to 5.1 g/dl, mean arterial pressure was unchanged, circulating protein mass was increased, and plasma sodium concentration was decreased slightly. In conclusion, the increase in lymph protein concentration during hyperproteinemia may indicate that interstitial fluid protein concentration also increased. This, in turn, would help to prevent any increase in the transcapillary colloid osmotic pressure gradient and thus attenuate any changes in blood volume.

Mechanism of decreased cardiac output during ANP infusion in conscious anephric dogs

Atrial natriuretic peptide (ANP) may decrease cardiac output (CO) by lowering circulating blood volume (BV) or by altering the vasculature in a manner that would decrease venous return. The purpose of this study was to determine the role of decreased BV in mediating the decrease in CO during acute infusion of ANP. BV was measured by dilution of 51Cr-labeled red blood cells in seven trained conscious splenectomized dogs studied after unilateral (UNX) and total (TNX) nephrectomy. BV, hematocrit (Hct), CO, mean arterial pressure (MAP), and total peripheral resistance (TPR) were determined during a 90-min control period and 270 min of infusion of ANP (20 ng.kg-1.min-1 iv). In UNX dogs, ANP decreased BV from 60.9 +/- 1.4 to 58.6 +/- 1.4 ml/kg and increased Hct from 39.3 +/- 1.8% to 41.1 +/- 1.8% (P less than 0.05). MAP was not changed and CO fell to a low that was 86 +/- 2% of control (P less than 0.05) 240 min after starting ANP. TPR increased significantly during ANP infusion. All variables returned to control after ANP was stopped. In the same dogs studied 24 h after TNX, MAP averaged 111 +/- 5 mmHg during control and did not change during ANP infusion. CO fell to a low of 82 +/- 3% of control (P less than 0.05) after 120 min of infusion and remained reduced until after the ANP was stopped.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic lymph flow and transcapillary fluid flux during angiotensin II hypertension

The roles of the transvascular fluid flux and lymph flow in the distribution of extracellular fluid volume during angiotensin II (ANG II) hypertension were evaluated in 11 conscious dogs. Similarly, the factors regulating the distribution of plasma protein across the microvasculature were assessed. By the second day of ANG II infusion, the thoracic duct lymph flow had increased 58% above control, transcapillary fluid flux had increased 45%, and plasma volume, sulfate space, and interstitial fluid volume remained close to control. In addition, the thoracic duct lymph protein transport had increased 34%, and the accompanying increase in transcapillary protein flux prevented any change in plasma protein mass. Also, at this time, the lymph flow and protein transport from subcutaneous tissue in the hind limb were not increased, and the permeability-surface area product of this region decreased 40%. The origin of the increased thoracic duct lymph flow on day 2 probably was from the splanchnic bed. In conclusion, the increased lymph flow during ANG II hypertension compensated for the increase in transcapillary fluid flux, thus preventing edema formation.

Effects of hypoproteinemia on blood volume and arterial pressure of volume-loaded dogs

Studies were performed in 14 conscious, anephric dogs to clarify the role of blood volume in the genesis of hypertension. The dogs were splenectomized and had plasma protein concentration (PPC) reduced to 2.7 g/dl by daily plasmapheresis for 9 days. This hypoproteinemia resulted in a 20% decrease in both blood volume and mean arterial pressure. On the 10th day the dogs were nephrectomized. On the 11th day after a 3-h control period with plasmapheresis, lactated Ringer equivalent to 10 or 20% of body weight was intravenously infused. By 25 h postinfusion blood volume had not increased, and the dogs were still hypotensive. At 25 h plasma protein mass was returned to normal by intravenous infusion of autologous plasma, the average blood volume of the three low PPC groups increased approximately 50%, and the arterial pressure increased greater than 60%. The decrease in PPC shifted the regression of blood volume on sodium space down the blood volume axis. In conclusion, the dependence of arterial pressure on blood volume was demonstrated by the decrease in both blood volume and arterial pressure after PPC reduction, the constancy of blood volume and pressure during Ringer infusion, and the increase in both volume and pressure after plasma infusion.

Chronic transvascular fluid flux and lymph flow during volume-loading hypertension

The chronic roles of the transcapillary fluid flux and lymph flow in the distribution of extracellular fluid volume during volume-loading hypertension were investigated in five conscious dogs. Similarly, the distribution of plasma proteins across the microvasculature was evaluated. During the early phases of volume-loading hypertension the fluid balance was positive, which caused the extracellular fluid volume and the plasma volume to increase 25 and 15%, respectively. The thoracic duct lymph flow more than doubled, but the increase in transcapillary fluid flux was even greater. Therefore the interstitial fluid volume increased 30%. This fluid shift from the vasculature into the interstitium probably prevented an even greater rise in arterial pressure. In addition, the transcapillary protein flux more than doubled, but the accompanying increase in lymph protein transport prevented any change in plasma protein mass. During the latter part of the saline-infusion period, the lymph flow declined toward its control, which caused a net transfer of fluid into the interstitium. In conclusion, the transcapillary fluid flux and lymph flow play significant roles in extracellular fluid volume distribution.

Computer models for designing hypertension experiments and studying concepts

This paper demonstrates how computer models along with animal experiments have been used to work out the conceptual bases of hypertensive mechanisms, especially the following: (1) The renal-fluid volume pressure control mechanism has a feed-back gain for pressure control of infinity. Therefore, the chronic level to which the arterial pressure is controlled can be changed only by altering this pressure control mechanism. (2) An increase in total peripheral resistance is not sufficient by itself to cause hypertension. The only resistances in the circulatory system that, when increased, will cause hypertension are those along a restricted axis from the root of the aorta to Bowman's capsule in the kidneys. (3) Autoregulation in the peripheral vascular beds does not increase the arterial pressure in hypertension. However, autoregulation can convert high cardiac output hypertension into high peripheral resistance hypertension. (4) In a computer simulation that cannot yet be performed in animals, a simulated hypertension caused by a combination of increased renal afferent and efferent arteriolar resistances has characteristics that match almost exactly those of essential hypertension.

Renal hemodynamic, fluid volume, and arterial pressure changes during hyperproteinemia

The chronic effects of hyperproteinemia on renal hemodynamics, fluid volume, and arterial pressure were determined in six conscious dogs over a 32-day period. Plasma protein concentration was increased by intravenous infusion of approximately 300 ml/day of previously collected autologous plasma, and the responses to changes in sodium intake were studied. By the end of a 9-day period of hyperproteinemia and normal sodium intake, plasma protein concentration had increased 2.2 g/dl, plasma colloid osmotic pressure had increased 7-8 mmHg, mean arterial pressure had increased 12 mmHg, glomerular filtration rate (GFR) had increased 15%, estimated renal plasma flow (ERPF) had increased 51% primarily due to renal vasodilatation, and filtration fraction had decreased 23%. Also, sodium balance was negative, water balance was positive, sodium iothalamate space had increased, plasma sodium concentration had decreased, and the relationship between mean arterial pressure and urinary sodium excretion was shifted to the right along the arterial pressure axis. In conclusion, long-term increases of plasma protein concentration result in a marked increase in ERPF as well as significant increases in GFR, extracellular fluid volume, and arterial pressure.