Renal effects of prostaglandin inhibition during increases in renal venous pressure

The role of prostaglandins (PGs) in mediating the hemodynamic and natriuretic responses to increases in renal interstitial pressure (RIP) induced by altering renal venous pressure (RVP) from control (3.6 +/- 0.6) to 15 and 30 mmHg was examined before and after PG inhibition in pentobarbital sodium-anesthetized dogs. These elevations of RVP resulted in RIP increasing from control (6 +/- 1) to 11 +/- 1 and 23 +/- 2 mmHg, respectively, without altering mean arterial pressure (MAP), renal blood flow (RBF), and glomerular filtration rate (GFR). Sodium excretion increased only when RVP reached 30 mmHg. During the inhibition of PG synthesis, 15 mmHg RVP induced a 10% decrease in RBF, and 30 mmHg RVP induced a further 20% decrease in RBF and a 50% decrease in GFR. PG synthesis inhibition did not alter either the RIP or the sodium excretory response. In conclusion, the natriuresis associated with the RIP increases induced by increasing RVP appears to be independent of PG synthesis. PGs, however, appear to be important for the maintenance of RBF and GFR during increased RVP. These findings suggest that different mechanisms are involved in the hemodynamic and natriuretic responses to arterial vs. venous pressure changes.

Mediatory role of endothelium-derived nitric oxide in renal vasodilatory and excretory effects of bradykinin

Intrarenal infusions of 5 ng/kg/min bradykinin (BK) in 5 mg/kg intravenous bolus meclofenamate-treated anesthetized dogs significantly increased renal blood flow, diuresis, natriuresis, and kaliuresis. All these effects were abolished by the simultaneous intrarenal infusion of a competitive inhibitor of nitric oxide synthesis, NG-monomethyl-L-arginine (LNMMA). Furthermore, the intrarenal infusion of this inhibitor alone also produced a significant decrease in basal renal blood flow. The administration of L-arginine, a precursor of nitric oxide, prevented the inhibitory effect of LNMMA on the renal vasodilatory and excretory response to BK. Glomerular filtration rate and mean arterial pressure did not change throughout the experiment. It is concluded that the renal vasodilatory and excretory responses to intrarenal BK in meclofenamate-treated dogs are largely dependent on endothelium-derived nitric oxide.

Role of prostaglandins and endothelium-derived relaxing factor on the renal response to acetylcholine

Acetylcholine (ACh) stimulates the endothelial release of prostacyclin and endothelium-derived relaxing factor (EDRF). However, the relative participation of these substances in mediating the renal effects of ACh remains undefined. To elucidate this issue, we studied the modifications of renal responses to intra-renal ACh infusion (25 ng.kg-1.min-1) produced by blocking the synthesis of EDRF and/or prostaglandins (PG) in anesthetized dogs. ACh induced a significant increase in renal blood flow (RBF) (34%), urine volume (UV) (450%), and urinary sodium excretion (UNaV)(259%), which remained unaltered after blocking the synthesis of EDRF [NG-monomethyl-L-arginine (LNMMA), 50 micrograms.kg-1.min-1 intrarenal] or PG (meclofenamate, 5 mg/kg iv). However, the simultaneous administration of meclofenamate and LNMMA prevented the ACh-induced increase in RBF and UV but not in UNaV. The concomitant infusion of L-arginine but not D-arginine prevented these blocking effects of LNMMA. It was concluded that the ACh-induced increases in RBF and UV, but not UNaV, are mediated by both PG and EDRF. The hemodynamic and diuretic effect of either one of these mediators can be fully compensated during the blockade of the other.

Evidences for the existence of endothelium-derived relaxing factor in the renal medulla

The basal levels of cGMP in renal medulla slices were enhanced when the slices were stimulated with both endothelium-dependent (acetylcholine) and endothelium-independent (molsidomine) vasodilators. When preincubated with NG-mono-methyl-L-arginine, a specific inhibitor of endothelium-derived relaxing factor, only the acetylcholine-stimulated increase was completely abolished. Furthermore, a preincubation with L-arginine, a selective precursor of endothelium-derived relaxing factor, enhanced the cGMP levels. The results indicate that the renal medulla, presumably the endothelial cells of the vasa recta, is able to produce endothelium-derived relaxing factor.

Quantitation of the in vivo kidney volume with cine computed tomography

The authors examined the utility of cine computerized tomography (CT) for noninvasive determination of whole kidney, cortical, and medullary volumes. The right kidneys of 14 anesthetized dogs were scanned after an intravenous bolus injection of iohexol, and their volumes determined after boundary identification. After the scans, the kidneys were excised at postmortem examination and their volumes determined by fluid displacement. The mean (+/- standard error of the mean [SEM]) postmortem and in vivo renal volumes were 66.1 +/- 2.2 cc and 78.2 +/- 2.4 cc, respectively (r = 0.86; P less than 0.001). The difference was consistent with the blood, filtrate, and urine contents of the in vivo kidney. The in vivo cortical and medullary volumes correlated poorly with their postmortem volumes because of difficulties in boundary definition. These results demonstrate the feasibility for fast and reliable in vivo whole kidney volume quantitation by cine CT.

Effect of captopril on renal function in hypertensive dogs with unilateral renal artery stenosis, studied with radionuclide dynamic scintigraphy

The kidneys of five hypertensive dogs with experimental unilateral renal artery stenosis were examined by 99mTc-diethylenetriaminepentaacetic acid (DTPA) and 131I-hippuran radionuclide dynamic scintigraphy at 10 and 40 min (respectively) following the administration of intravenous bolus injections of captopril. Doses of 0.2, 0.5, and 1.0 mg/kg captopril reduced mean arterial pressure by 33 +/- 4, 31 +/- 7, and 51 +/- 4 mm Hg and increased plasma renin activity by 40.1 +/- 9.8, 57.6 +/- 3.2, and 34.4 +/- 15.2 ng A1/mL/h, respectively. The time-activity curves of both 99mTc-DTPA and 131I-hippuran indicated that renal excretory function in the stenotic kidney was compromised with all three doses of captopril. However, if nitroprusside was used to reduce the mean arterial pressure to a level comparable to that with captopril, there was no appreciable increase in plasma renin activity and renal excretory function was only partially affected in the stenotic kidney. One hour after the administration of 0.5 mg/kg captopril, the function of the stenotic kidneys was partially restored and, by two hours, the time-activity curves were comparable to control scans. These data demonstrate a reversible, time-limited suppression of stenotic kidney function by captopril in renovascular hypertension and provide support for the use of captopril in the diagnosis of renovascular hypertension by radionuclide dynamic scintigraphy.

Effects of NG-monomethyl-L-arginine and L-arginine on acetylcholine renal response

Intrarenal infusion of acetylcholine in meclofenamate-treated dogs significantly increased renal blood flow, diuresis, and natriuresis. Intrarenal infusions of either NG-monomethyl-L-arginine (inhibitor of endothelium-derived relaxing factor formation), or L-arginine (precursor of endothelium-derived relaxing factor formation) did not modify basal levels of those parameters. However, the infusion of NG-monomethyl-L-arginine inhibited the acetylcholine-induced increases in renal blood flow and diuresis without affecting natriuresis, which increased significantly. The infusion of L-arginine failed to further enhance hemodynamic and excretory effects elicited by acetylcholine. The concomitant infusion of L-arginine and NG-monomethyl-L-arginine did not change renal blood flow, urine flow, or sodium excretion rate. L-Arginine administration prevented the inhibitory effect of NG-monomethyl-L-arginine on acetylcholine-induced renal vasodilatation and diuresis. Glomerular filtration rate and mean arterial pressure did not change throughout the experiment. The results indicate that the vasodilatory and diuretic responses to intrarenal acetylcholine in meclofenamate-treated dogs are largely dependent on endothelium-derived relaxing factor.

Role of prostaglandins in the renal response to calcium infusion

The effects of intrarenal infusions of calcium gluconate (10 and 100 micrograms Ca.kg-1.min-1) on renal hemodynamics and on renal excretory function were studied in anesthetized mongrel dogs. In one group, the two doses of calcium were infused for 30 min each (1 ml/min). In a second group, the same doses were administered 30 min after the start of an infusion of prostaglandin (PG) inhibitors (intrarenal indomethacin, 10 micrograms.kg-1.min-1, or intravenous bolus injection of meclofenamate, 5 mg/kg). No change with physiological significance was observed during the infusion of 10 micrograms Ca.kg-1.min-1. However, the infusion of 100 micrograms Ca.kg-1.min-1 induced increases (P less than 0.05) in glomerular filtration rate (50%), sodium excretion rate (180%), and fractional excretion of sodium (160%), with respect to control precalcium values. All these changes were prevented by the concurrent administration of PG synthesis inhibitors. Urinary PGE2 and 6-keto-PGF1 alpha increased 220 and 85%, respectively, during the infusion of 100 micrograms Ca.kg-1.min-1, but both decreased (P less than 0.05) below basal levels during the concurrent administration of PG synthesis inhibitors. The infusion of 100 micrograms Ca.kg-1.min-1 decreased (P less than 0.05) renal blood flow by 16% during the administration of PG synthesis inhibitors. These results suggest that PGs are mediating the increase in hemodynamic and excretory factors induced by the intrarenal infusion of 100 micrograms Ca.kg-1.min-1.

Renal functional reserve and microalbuminuria in offspring of hypertensive parents

Renal functional reserve, microalbuminuria, and plasma atrial natriuretic factor were measured in 21 offspring (9.5 +/- 0.5 years of age, mean +/- SEM) of hypertensive parents and in eight children (10 +/- 0.5 years of age) with no family history of hypertension who were used as a control group. Renal functional reserve was evaluated by measurement of the changes in creatinine clearance after an oral protein load of 45 g/m2. Atrial natriuretic factor levels were determined before and 60 minutes after the protein load, and microalbuminuria in fractional urine before and 120 minutes after the same stimulus as well as in a 24-hour urine collection. All children in the control group significantly increased their creatinine clearance after the protein load (preload, 122 +/- 12; 60 minutes, 144 +/- 9; 120 minutes, 154 +/- 11; 180 minutes, 144 +/- 9 ml/min/1.73 m2; all values were significant vs. preload, p less than 0.005). In contrast, only 13 of 21 offspring of hypertensive parents increased their creatinine clearance to values within 2 SD of the increase shown by the control group (preload, 144 +/- 11; 60 minutes, 153 +/- 7; 120 minutes, 202 +/- 13 ml/min/1.73 m2; p less than 0.001 vs. preload; 180 minutes, 214 +/- 19 ml/min/1.73 m2, p less than 0.001 vs. preload). The remaining eight offspring of hypertensive parents showed no detectable changes (nonresponders) (preload, 189 +/- 18; 60 minutes, 146 +/- 11; 120 minutes, 170 +/- 14; 180 minutes, 168 +/- 13 ml/min/1.73 m2; all values p = NS). No changes in atrial natriuretic factor after the protein load were observed in any group. Offspring of hypertensive parents presented higher microalbuminuria levels in 24-hour urine specimens (3.1 micrograms/min, tolerance factor [TF]2.2) than controls (2.1 micrograms/min, TF 1.5) (p less than 0.05). Although microalbuminuria increased significantly after the water load in the control group (p less than 0.05) and in the offspring of hypertensive parents (p less than 0.01), it returned to baseline at 120 minutes in the former but not in the latter (p less than 0.05 vs. baseline). The lack of renal functional reserve in nonresponders was significantly related (p less than 0.05) to the presence of higher levels of microalbuminuria. We conclude that the absence of renal functional reserve and increased microalbuminuria in some normotensive children who are offspring of essential hypertensive parents can indicate that subtle alterations in renal function may precede the onset of clinical hypertension.

Distribution of prostaglandins E2 and 6-keto-F1 alpha production in dog kidneys

Little is known about the distribution of prostaglandin E2 (PGE2) and prostacyclin (PGI2) production in the canine kidney. To determine the basal and stimulated profiles of PGE2 and PGI2 production along the corticomedullary axis of the dog kidney, a slice (0.5 mm thick, 10-50 mg) was obtained from six equally spaced zones along the axis (zone 1, medullary crest; zones 2 and 3, inner medulla; zone 4, outer medulla; and zones 5 and 6, cortex) and was divided into equal halves. One half of the slice was incubated with Krebs-Ringer buffer containing arachidonic acid (6.6 x 10(-4) M), bradykinin (9.4 x 10(-6) M), or indomethacin (10(-5) M), whereas the remaining half of each slice was similarly incubated in Krebs-Ringer buffer alone. The production of PGE2 and 6-keto-PGF1 alpha (the stable metabolite of PGI2) was determined by radioimmunoassay. Under basal conditions, both PGE2 and 6-keto-PGF1 alpha were highest in the innermost zones of the inner medulla (PGE2, 3,328 +/- 549 pg/mg; 6-keto-PGF 1 alpha, 1,611 +/- 129 pg/mg) and decreased exponentially to low levels in the cortex (PGE2, undetectable; 6-keto-PGF1 alpha, 13 +/- 2 pg/mg); this production was inhibited by indomethacin. Arachidonic acid significantly increased the production of PGE2 in all zones of the kidney and the production of 6-keto-PGF1 alpha only in zones 3-6.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of renin release by intrarenal calcium infusion

The effects of intrarenal infusions of calcium gluconate (10 and 100 micrograms Ca/kg/min) on renin secretion were studied in anesthetized mongrel dogs. In one group, the two doses of calcium were infused for 30 minutes each (1 ml/min). In a second group, the same doses were administered 30 minutes after the start of infusion of prostaglandin synthesis inhibitors (indomethacin 10 micrograms/kg/min intrarenal or injection of meclofenamate 5 mg/kg i.v. bolus). Mean arterial pressure, renal blood flow, and glomerular filtration rate remained unchanged during the infusion of calcium in both groups. The infusion of 10 micrograms Ca/kg/min increased renin secretion 77% and sodium excretion 123%. During the infusion of 100 micrograms Ca/kg/min, renin secretion was not different from precalcium values, whereas urinary 6-keto-PGF1 alpha, urine flow, sodium, potassium, and calcium excretion rates were increased (p less than 0.05). During the administration of prostaglandin synthesis inhibitors, the urinary 6-keto-PGF1 alpha levels were reduced, and the infusion of 10 micrograms Ca/kg/min failed to increase renin secretion, sodium excretion, or 6-keto-PGF1 alpha excretion rates. The infusion of 100 micrograms Ca/kg/min during prostaglandin synthesis inhibition did not modify urine flow or sodium excretion; however, potassium and calcium excretions increased. It is concluded that 1) the intrarenal infusion of small doses of calcium gluconate is capable of stimulating renin secretion through a prostaglandin-mediated mechanism, and 2) the stimulation of renin secretion as well as the increase in sodium excretion induced by calcium are independent of hemodynamic alterations.

Characterization of the renal effects of an intravenous calcium gluconate infusion in normotensive volunteers

The effects on renal function of an intravenous infusion of calcium gluconate at subpressor doses have been investigated in a group of seven normotensive male volunteers. In the absence of changes in blood pressure, the calcium gluconate induced a significant increase in renal plasma flow and the glomerular filtration rate (P less than 0.01) with a significant fall in the filtration fraction (P less than 0.01). Both diuresis and natriuresis increased significantly (P less than 0.01), plasma renin activity fell (P less than 0.01) and the urinary excretion of 6-keto prostaglandin F1 alpha (PGF1 alpha) and prostaglandin E2 (PGE2) increased (P less than 0.01). These results indicate that calcium infusion at subpressor doses has renal vasodilating, diuretic and natriuretic properties that appear to be facilitated by an increase in the renal production of vasodilatory and natriuretic prostaglandins.

Intrarenal mechanisms that regulate sodium excretion in relationship to changes in blood pressure

Because pressure-related natriuresis may be central to the regulatory role of the kidney on blood pressure, it is important to understand the relationship of humoral systems involved in the control of renal hemodynamics and tubular function. The preglomerular endothelial synthesis of prostaglandin I2 and endothelium-derived relaxing factor seem to modulate autoregulatory control by the afferent arterioles and the release of renin by the juxtaglomerular apparatus. The release of renin is followed by an increase in angiotensin II in the renal interstitium, which is responsible for adjusting the vascular tone of the efferent arterioles and vasa recta and for stimulating proximal tubular reabsorption of sodium. Variations in medullary circulation induced by angiotensin II could alter medullary interstitial pressure and the medullary production of prostaglandins E2 and I2 and, ultimately, could modulate sodium reabsorption in the medullary thick ascending limbs and the collecting ducts.

Alterations in blood pressure by derangement of the mechanisms that regulate sodium excretion

Understanding the sequence of events responsible for pressure-related natriuresis and their pathophysiologic alterations may be useful in distinguishing various types of essential hypertension of renal origin. The perturbation of a distal step in the sequence is likely to be reflected in a simple physiologic defect. For instance, pathophysiologic alterations in the medullary production of prostaglandin E2 might directly influence natriuresis and diuresis because of its modulatory effect on tubular reabsorption of sodium and water. Perturbation of more proximal steps in the sequence could influence all the distal events as well. For instance, prostaglandin I2 and endothelium-derived relaxing factor may be produced by the preglomerular vasculature in response to alterations in renal perfusion pressure and may modulate the release of renin from the juxtaglomerular cells. Thus, variations in the production of prostaglandin I2 or endothelium-derived relaxing factor may be reflected by various renal vascular, tubular, and systemic homeostatic events related to the renin-angiotensin system.

Effects of atrial natriuretic peptide on renal medullary prostaglandin E2 production

Like arachidonic acid (AA) and bradykinin (BK), the intrarenal administration of atrial natriuretic peptide (ANP) has been shown to increase the urinary excretion of prostaglandin E2 (PGE2). In the present study, the direct in vitro effects of ANP on PGE2 production were compared with those of AA and BK. Canine renal inner medullary slices were preincubated for 30 min and washed in aerated Krebs-Ringer buffer (37 degrees C). During the final incubation period, with the use of varied concentrations of AA, BK, or ANP in Krebs-Ringer buffer, samples were obtained at 0 and 30 min to be used for radioimmunoassay of PGE2. Although the rate of PGE2 production was significantly increased 11-fold with AA and threefold with BK, it was unaffected by four different doses of ANP (10(-5) to 10(-11) M). Furthermore, the production of PGE2 during basal and stimulated (BK or AA) conditions was significantly blocked by indomethacin but not by ANP. These results indicate that ANP had no direct stimulatory or inhibitory effect on the medullary production of PGE2.

Effect of renal interstitial infusion of arachidonic acid on proximal sodium reabsorption

The effect of prostaglandins (PGs) on proximal sodium reabsorption has not been fully defined. The objective of the present study was to determine the response of proximal tubular sodium reabsorption to infusions of arachidonic acid and specific PGs into the renal interstitium in rats. Renal interstitial infusions of arachidonic acid as well as the individual PGs, I2, E2, and F2 alpha, were employed to elevate the concentration of these PGs in the kidney. Infusion of 10(-4) M arachidonic acid elicited a marked increase of urinary excretion of 6-keto-PGF1 alpha (a stable metabolite of PGI2) from 260.1 +/- 52.7 to 507.4 +/- 129.5 pg/min (P less than 0.05) and a smaller increase of PGE2 from 18.4 +/- 11.2 to 25.9 +/- 10.9 pg/min (P less than 0.05). When micropuncture samples were obtained from superficial late proximal tubules, infusion of arachidonic acid increased the fractional delivery of sodium (FDNa) from 47.8 +/- 5.9 to 58.3 +/- 4.6% (n = 6, P less than 0.01). In the presence of indomethacin, arachidonic acid failed to augment FDNa. Infusion of 10(-5) M PGI2 also increased FDNa from 51.4 +/- 3.4 to 64.0 +/- 4.4% (n = 10, P less than 0.01). PGF2 alpha did not change FDNa and PGE2 decreased it from 53.1 +/- 5.4 to 37.4 +/- 3.3% (n = 8, P less than 0.01). In summary, the present study demonstrates that renal interstitial infusion of arachidonic acid decreases sodium reabsorption by the superficial proximal tubules possibly through the stimulation of PGI2 production.

Effect of atriopeptin II on contrast medium-induced changes in renal blood flow

Volume expansion has been shown to attenuate the vaso-constrictive effects of contrast medium. Since endogenous circulating levels of atrial natriuretic peptides are elevated during volume expansion and since atrial natriuretic peptides have been shown to blunt or block the vasoconstrictive effects of various pharmacologic agents, we examined the effect of atriopeptin II infusion on contrast medium-induced alterations in renal blood flow. Transient changes in renal blood flow were measured with an electromagnetic flow probe following bolus injections of the contrast medium, sodium meglumine diatrizoate (Renovist II, 2 ml/4 sec), into the renal arteries of dogs. Under control conditions (that is, saline vehicle), the bolus of contrast medium caused an initial 15 to 21% increase in renal blood flow at 14 to 21 seconds, followed by a subsequent 5 to 13% decrease in renal blood flow at 43 to 59 seconds after injection. Infusion of atriopeptin II (0.05 pg/kg/min) into the renal artery did not alter arterial blood pressure, glomerular filtration rate, or baseline renal blood flow, but did produce increases in urine flow rate and clearance of sodium. The infusion of atriopeptin II attenuated the contrast medium-induced reduction in RBF, but the infusion of a threshold dose of bradykinin (1 ng/kg/min) had no effect. These results suggest that low doses of atriopeptin II can selectively attenuate the vasoconstrictive effects of contrast medium on renal blood flow without influencing systemic hemodynamics.

Natriuretic response to volume expansion in polycystic kidney disease

Hypertension is an early manifestation of autosomal dominant polycystic kidney disease (ADPKD). Whether polycystic kidneys have an intrinsic abnormality that leads to sodium retention, volume expansion, and hypertension is uncertain. We studied the natriuretic response to a 4-hour infusion of physiologic saline at a rate of 6.5 ml/kg per hour in 10 patients with ADPKD who had normal renal function and 10 gender- and age-matched control subjects. Baseline 24-hour urinary excretions of sodium and potassium were similar in both groups. The baseline filtration fraction was significantly higher in the patients with ADPKD than in the control subjects. During the infusion of saline, no significant changes in blood pressure, clearance of inulin, or clearance of p-aminohippuric acid were detected. The increase in fractional excretion of sodium over baseline was significantly higher in the patients with ADPKD than in the control subjects. The pressure-natriuresis regression line was significantly shifted to the right in patients with ADPKD who had hypertension. The fractional excretion of potassium was significantly lower in patients with ADPKD than in control subjects. No significant differences in plasma renin activity, aldosterone, or atrial natriuretic factor were detected between the two groups. These observations suggest the presence of subtle abnormalities in the management of renal sodium that might contribute to the development and maintenance of hypertension in patients with ADPKD.

Hemodynamic effects of chronic infusion of rANP in renal hypertensive rats

The purpose of this study was to evaluate the hemodynamic effects induced by an infusion of synthetic rat atrial natriuretic peptide (rANP, 0.5 micrograms/h iv) during 5 consecutive days in conscious normotensive and two-kidney, one-clip hypertensive (2K,1C) rats. Changes in plasma ANP (pANP) levels and plasma renin activity (PRA) were also determined. The administration of ANP in 2K,1C rats induced a significant decrease in mean arterial pressure (MAP) from 169 +/- 3 to 138 +/- 3, and 149 +/- 3 mmHg by 2 and 5 days of infusion, respectively. This hypotension was accompanied by a significant fall in cardiac index (CI) from 400 +/- 16 to 348 +/- 14 ml.min-1.kg-1 after 2 days of ANP treatment. However, CI returned to the basal levels at the third day, and a significant decrease in total peripheral resistance (TPR) was observed by 3 and 5 days of ANP infusion. The administration of the same dose of ANP in normotensive rats did not induce changes in MAP, but CI decreased (P less than 0.001) transitorily during the first 2 days and returned to control values thereafter. Basal pANP levels were significantly elevated in the hypertensive animals (176 +/- 40 pg/ml) when compared with the normotensive rats (82 +/- 10 pg/ml). The ANP infusion resulted in lower (P less than 0.05) pANP levels in hypertensive (1,017 +/- 234 pg/ml) than in normotensive rats (3,466 +/- 975 pg/ml). PRA did not change in any group during the administration of ANP.(ABSTRACT TRUNCATED AT 250 WORDS)

Blunted pressure natriuresis in the Brattleboro diabetes insipidus rat

Antidiuretic hormone is known to stimulate the renal synthesis of prostaglandins. These autacoids, in turn, modulate the pressure natriuresis phenomenon. Accordingly, the present study was done to test the hypothesis that, in the absence of antidiuretic hormone and antidiuretic hormone-dependent prostaglandin synthesis, the pressure natriuresis response is blunted. Experiments were performed on Brattleboro diabetes insipidus rats (n = 7) and Long Evans control rats (n = 14). A change in perfusion pressure in the Long Evans rats from 89.3 +/- 1.0 to 108.7 +/- 1.1 mm Hg (p less than 0.05) was associated with significant increases in the fractional excretion of sodium (1.1 +/- 0.2 to 2.3 +/- 0.3%) and the urinary prostaglandin excretion (32.6 +/- 6.8 to 56.6 +/- 10.0 pg/min). In contrast, a similar change in perfusion pressure in the diabetes insipidus rat from 88.6 +/- 1.4 to 106.2 +/- 1.5 mm Hg (p less than 0.05) resulted in no significant increases in either sodium or prostaglandin excretions. Treatment of a third group of diabetes insipidus rats (n = 9) with 1-desamino-8-D-arginine vasopressin (1 microgram/day) restored the natriuretic response to increases in renal perfusion pressure. Treated diabetes insipidus and Long Evans control rats had comparable natriuretic responses to increases in renal perfusion pressure. Untreated diabetes insipidus rats, on the other hand, had blunted responses. In summary, the pressure natriuresis response in diabetes insipidus rats is blunted compared with Long Evans control rats. We conclude that antidiuretic hormone is necessary for the complete expression of the pressure natriuresis response.

Converting enzyme inhibition in chronic renal failure

Ten patients with chronic renal failure whose hypertension was controlled with triple drug therapy consisting of propranolol-hydralazine-furosemide were switched to the angiotensin-converting enzyme (ACE) inhibitor captopril for a period of 12 months. Control of hypertension was similar with both antihypertensive regimens. Clearance of inulin and of paraaminohippuric acid increased during the first 3 months of captopril therapy and remained stable thereafter. Moreover, the decline in the reciprocal of serum creatinine over time observed during triple drug therapy was arrested during therapy with the ACE inhibitor. If the salutary effects of captopril are sustained, the results obtained in the current studies would suggest that control of hypertension by ACE inhibition may be effective in slowing progression of renal failure. Future studies to answer this important question are necessary.

Proximal tubule response in aldosterone escape

The response of the proximal tubule to chronic aldosterone administration (15 micrograms.kg-1.day-1) was evaluated in eight conscious female mongrel dogs. Temporal profiles between hemodynamic and hormonal changes and the fractional excretions of sodium and lithium were established. Aldosterone infusion resulted in a significant decrease in urinary sodium excretion from 9.2 +/- 1.3 to 5.8 +/- 0.9 meq/h after 1 day, returning to normal by the 5th day. These changes in urinary sodium excretion were associated with significant elevations of the mean arterial pressure (MAP) from 105 +/- 5 to 111 +/- 6 mmHg and plasma atrial natriuretic factor concentrations (ANF) from 30 +/- 2 to 57 +/- 7 pg/ml beginning the 1st day of infusion. Plasma renin activity (PRA), on the other hand, was depressed by aldosterone, falling below the level of detectability. The fractional excretion of lithium increased significantly by day 2 of aldosterone infusion (from 29 +/- 3 to 44 +/- 6%), reflecting the proximal tubular response to the above changes. We conclude that the proximal tubule responds to increases in MAP and ANF and decreases in PRA during aldosterone infusion by decreasing sodium reabsorption. Subsequent nephron segments must also respond to the volume expansion produced by aldosterone, since the sustained proximal tubule natriuretic response is insufficient to explain all of escape.

Stimulation of plasma renin activity by captopril in renovascular hypertensive conscious dogs

The increase in plasma renin activity induced by captopril is used in the clinical evaluation of renovascular hypertensive patients. This increase in plasma renin activity could result from either the concomitant fall in systemic pressure or other effects of captopril, such as the removal of an angiotensin II inhibitory effect on renin release, the increased production of bradykinin or prostaglandins, etc. To examine the effect captopril has on plasma renin activity, independent of changes in systemic pressure, captopril (5, 10 and 50 micrograms/kg iv) was administered to conscious dogs before and following the development of 1 clip-2 kidney Goldblatt hypertension. Plasma renin activity, under normal conditions remained unchanged, while during hypertension it increased 2.0, 2.8 and 3.5 fold respectively in response to the three doses of captopril. These results suggest that the development of renovascular hypertension sensitized the kidney to release renin when challenged by captopril and that the effect is independent of changes in systemic pressure.

Control of hypertension with the angiotensin converting enzyme inhibitor captopril reduces glomerular proteinuria

Recent experimental and clinical data have suggested that angiotension converting enzyme (ACE) inhibitors may decrease glomerular proteinuria by specific effects on the glomerulus. We studied a group of 15 adult patients with chronic renal failure and proteinuria due to various glomerulopathies. These patients had mild to moderate hypertension which was effectively controlled with conventional antihypertensive therapy. We then treated the patients with captopril, maintaining a similar dietary protein and salt intake. After 6 months of study, proteinuria was reduced significantly without reduction in inulin or para-aminohippurate clearance. This supports the concept that captopril may have salutary effects on the glomerulus, independently of its effect on systemic blood pressure.