Hemodynamic basis for glomerular injury in rats with desoxycorticosterone-salt hypertension

Micropuncture and/or morphologic studies were performed in seven groups of uninephrectomized (UNX) adult male Munich-Wistar rats. Control groups 1, 3, and 6 received standard (24% protein) chow and tap water. Groups 2, 4, and 5 received weekly injections of desoxycorticosterone pivilate (DOC) and 1% saline for drinking, groups 2 and 4 were fed standard chow, and Group 5 a diet containing 6% protein. Group 7 received DOC, salt, and standard chow for 3 wk followed by withdrawal of DOC and salt for an additional 6 wk. 10-14 d after UNX, groups 1 and 2 exhibited similar single nephron glomerular filtration rates (SNGFR) and initial glomerular plasma flow rates (QA). Group 2 had higher mean arterial pressure (AP) and glomerular capillary hydraulic pressure (PGC) than group 1. 3-4 wk after UNX, group 4 exhibited further elevations in AP and PGC as compared with groups 2 and 3. SNGFR and QA were similar in groups 3 and 4, but these average values were greater than typical for normal rats. Group 4 also demonstrated increased urinary protein excretion. Morphologic evaluation of glomeruli in groups 2 and 4 revealed mesangial expansion and focal intraglomerular hemorrhage whereas glomeruli of groups 1 and 3 were essentially normal. Values for AP and PGC in group 5 were not different than group 3 but significantly lower than group 4. QA and SNGFR were lower in group 5 (low protein) than in groups 3 and 4. Furthermore, proteinuria and glomerular structural lesions were abolished in group 5. Morphologic studies performed in groups 6 and 7 showed that early DOC-SALT lesions progress to focal glomerular sclerosis. These studies suggest that continued elevations in glomerular capillary flows and pressures predispose to glomerular injury in this model of systemic arterial hypertension.     

Control of glomerular hypertension limits glomerular injury in rats with reduced renal mass.

Micropuncture and morphologic studies were performed in four groups of male Munich-Wistar rats after removal of the right kidney and segmental infarction of two-thirds of the left kidney. Groups 1 and 3 received no specific therapy. Groups 2 and 4 were treated with the angiotensin I converting enzyme inhibitor, enalapril, 50 mg/liter of which was put in their drinking water. All rats were fed standard chow. Groups 1 and 2 underwent micropuncture study 4 wk after renal ablation. Untreated group 1 rats exhibited systemic hypertension and elevation of the single nephron glomerular filtration rate (SNGFR) due to high average values for the mean glomerular transcapillary hydraulic pressure difference and glomerular plasma flow rate. In group 2 rats, treatment with enalapril prevented systemic hypertension and maintained the mean glomerular transcapillary hydraulic pressure gradient at near-normal levels without significantly compromising SNGFR and the glomerular capillary plasma flow rate, as compared with untreated group 1 rats. Groups 3 and 4 were studied 8 wk after renal ablation. Untreated group 3 rats demonstrated persistent systemic hypertension, progressive proteinuria, and glomerular structural lesions, including mesangial expansion and segmental sclerosis. In group 4 rats, treatment with enalapril maintained systemic blood pressure at normal levels over the 8-wk period and significantly limited the development of proteinuria and glomerular lesions. These studies suggest that control of glomerular hypertension effectively limits glomerular injury in rats with renal ablation, and further support the view that glomerular hemodynamic changes mediate progressive renal injury when nephron number is reduced.     

Functional effects on glomerular hemodynamics of short-term chronic cyclosporine in male rats.

We evaluated the effects of chronic cyclosporine (CsA) administration on the determinants of nephron filtration rate (SNGFR) using micropuncture techniques (mp) in male Munich-Wistar rats. Animals received CsA (30 mg/kg SQ) in olive oil daily for 8 d before mp. Controls (PFC) were pair fed. SNGFR, glomerular capillary hydrostatic pressure gradient (delta P), nephron plasma flow (SNPF), plasma protein oncotic pressure (pi A), and glomerular ultrafiltration coefficient (LpA) were quantitated in each experiment. CsA was associated with a lower SNGFR due to decreases in SNPF and a major reduction in delta P but no decrease in LpA. Plasma volume expansion (PVE) caused SNGFR, delta P, and SNPF to increase in both CsA and PFC without eliminating the differences between CsA and PFC. CsA/PVE rats responded normally to angiotensin II (AII) infusion indicating that the low delta P associated with CsA is not due to unresponsiveness to AII. Prior renal denervation caused SNGFR and SNPF to increase in CsA-treated animals but failed to alter the reduction in glomerular capillary pressure after CsA or to eliminate the glomerular hemodynamic differences between treated animals and pair-fed controls. This constellation of glomerular hemodynamic abnormalities suggests that the renal effect of short-term chronic CsA administration is mediated primarily by a reduction in the afferent effective filtration pressure resulting from an imbalance between pre- and postglomerular vascular resistances.     

Mechanisms underlying transition from acute glomerular injury to late glomerular sclerosis in a rat model of nephrotic syndrome.

Functional and morphologic measurements were performed in Munich-Wistar rats after a single central venous injection of puromycin aminonucleoside (PA) or saline vehicle (sham). During phase I, PA rats exhibited overt nephrotic syndrome and impaired glomerular filtration, primarily due to a reduction in the glomerular capillary ultrafiltration coefficient. The morphologic counterpart of the latter consisted of effacement of glomerular epithelial cell foot processes and decrease in the number of filtration slit diaphragms. Administration of the angiotensin I converting enzyme inhibitor (CEI) enalapril to PA rats did not ameliorate glomerular dysfunction. During phase II, PA rats exhibited spontaneous resolution of proteinuria, impaired function, and morphologic abnormalities. However, PA rats now demonstrated marked glomerular capillary hypertension and continued, albeit lesser, reductions in the ultrafiltration coefficient. Concurrent CEI administration modestly lowered systemic arterial pressure, and normalized the glomerular capillary hydraulic pressure and ultrafiltration coefficient. Additional rats were studied during phase III, 70 wk after injection. In PA rats, prior glomerular hypertension was associated with development of recurrent proteinuria and extensive glomerular sclerosis, whereas concurrent CEI administration limited these parameters to values comparable to those in sham rats. Glomerular hypertension thus may explain the development of glomerular sclerosis and renal failure long after an episode of acute glomerular injury.     

Chronic glucocorticoid therapy amplifies glomerular injury in rats with renal ablation.

Functional and/or structural measurements were performed in eight groups of Munich-Wistar rats after five-sixths nephrectomy. Groups 1 and 5 received no therapy. Groups 2 and 6 received daily doses of methylprednisolone (MP). Groups 3 and 7 received MP plus the angiotensin I converting enzyme inhibitor (CEI), benzazepril. Groups 4 and 8 received CEI alone. Groups 1 through 4 underwent micropuncture study 2 wk after renal ablation. Untreated group 1 rats exhibited systemic hypertension and elevation of the single nephron glomerular filtration rate due to glomerular capillary hyperperfusion and hypertension. Administration of MP in group 2 resulted in comparable systemic hypertension, with further elevation of the single nephron glomerular filtration rate due to even higher values for glomerular perfusion and hydraulic pressure. Concurrent treatment with CEI in groups 3 and 4 controlled systemic and glomerular hypertension despite equivalent renal ablation and, in group 3, comparable doses of MP. Groups 5 through 8 were followed for 12 wk. Untreated group 1 rats demonstrated continued systemic hypertension, progressive proteinuria, and eventual glomerular sclerosis. Addition of MP in group 6 dramatically accelerated the development of proteinuria and glomerular sclerosis, while CEI (groups 7 and 8) afforded striking protection against disease progression. Thus, potent vasodilator glucocorticoids may amplify hemodynamically mediated glomerular injury, whereas control of systemic and glomerular hypertension prevents this undesirable consequence of chronic steroid therapy.     

Mechanism of Glomerulotubular Balance in the Setting of Heterogeneous Glomerular Injury: PRESERVATION OF A CLOSE FUNCTIONAL LINKAGE BETWEEN INDIVIDUAL NEPHRONS AND SURROUNDING MICROVASCULATURE

Autologous immune complex nephropathy (AICN), an experimental model for human membranous glomerulopathy, is characterized by marked heterogeneity in function from glomerulus to glomerulus. However, the fraction of the filtered load of fluid reabsorbed by the proximal tubule remains nearly constant from nephron to nephron, despite wide variation in single nephron glomerular filtration rate (SNGFR). To define the physiological mechanisms responsible for this marked variation in SNGFR values within a given kidney and for the remarkable preservation of glomerulotubular balance, the various determinants of fluid exchange across glomerular and peritubular capillary networks were evaluated in Munich-Wistar rats with AICN. For comparison, similar measurements were obtained in rats with the functionally more homogeneous lesion of heterologous immune complex nephropathy. In AICN rats studied ~5 mo after injection of renal tubule epithelial antigen (Fx1A), a high degree of glomerulus-proximal tubule balance was found, despite marked variations in SNGFR values within a single kidney. These changes were associated with marked heterogeneity in immunoglobulin and complement deposition within and among glomeruli. Although mean capillary hydraulic pressure and Bowman's space hydraulic pressure ranged widely from glomerulus to glomerulus, the mean glomerular transcapillary hydraulic pressure difference was remarkably uniform among these functionally diverse glomeruli and could not, therefore, be implicated as the cause of the dispersion in SNGFR values. The two remaining determinants of SNGFR, namely, glomerular plasma flow rate (Q_A) and ultrafiltration coefficient (K_f), varied markedly from glomerulus to glomerulus, but always in direct proportion to SNGFR, and proved to be responsible for the marked variation in SNGFR.     

Therapeutic advantage of converting enzyme inhibitors in arresting progressive renal disease associated with systemic hypertension in the rat.

Micropuncture and morphologic studies were performed in six groups of male Munich-Wistar rats after removal of the right kidney and segmental infarction of two-thirds of the left kidney. Groups 1 and 4 received no specific therapy. Groups 2 and 5 were treated with the angiotensin I-converting enzyme inhibitor, enalapril, 50 mg/liter, in the drinking water. Groups 3 and 6 were treated with reserpine (5 mg/liter), hydralazine (80 mg/liter), and hydrochlorothiazide (25 mg/liter). All rats were fed standard chow. Groups 1-3 underwent micropuncture study 4 wk after renal ablation. Untreated group 1 rats exhibited systemic hypertension and elevation of the single nephron glomerular filtration rate (SNGFR) due to high average values for the mean glomerular transcapillary hydraulic pressure gradient (delta P) and glomerular plasma flow rate (QA). In group 2 rats, treatment with enalapril prevented systemic hypertension and maintained delta P at near-normal levels without significant reduction in SNGFR and QA. In contrast, triple drug therapy normalized systemic hypertension, but failed to lower delta P in group 3 rats. Groups 4-6 were followed for 12 wk after renal ablation. Untreated group 4 rats demonstrated continuous systemic hypertension, progressive proteinuria, and glomerular structural lesions, including mesangial expansion and frequent areas of segmental sclerosis. In group 5 rats, treatment with enalapril maintained systemic blood pressure at normal levels over the 12-wk period and dramatically limited the development of proteinuria and glomerular lesions. Despite equivalent systemic blood pressure control in group 6 rats, failure of triple drug therapy to control glomerular hypertension was associated with progressive proteinuria and glomerular lesions comparable to those seen in untreated group 4 rats. Thus, unless glomerular capillary hypertension is corrected, control of systemic blood pressure is insufficient to prevent progressive renal injury in rats with reduced renal mass.     

"Intact nephrons" as the primary origin of proteinuria in chronic renal disease. Study in the rat model of subtotal nephrectomy

Single nephron filtration rate of albumin (SNGFRAlb) was measured in remnant nephrons of Munich-Wistar rats 4-6 wk after subtotal nephrectomy (NPX). Serial thin-section histological analysis was then conducted on the same glomeruli by light microscopy. SNGFRAlb ranged from 1 to 15 times normal. However, a direct relationship between abnormalities of structure and function was not seen, e.g. the glomeruli with the fewest structural abnormalities and marked hyperfiltration often had the highest SNGFRAlb. Moreover, the majority of glomeruli had minimal structural abnormalities. Normalization of the markedly elevated glomerular capillary pressure (PGC) in these glomeruli was accomplished by acute intravenous infusion of verapamil, which decreased SNGFRAlb by 9-83% without affecting the single nephron filtration rate of water (SNGFRH2O). 1-2 wk after subtotal NPX, all glomeruli were hyperfiltering and had elevated PGC. The fractional clearance of larger (greater than 36 A) dextrans was selectively increased in these glomeruli that lacked discernible damage by light microscopy. Verapamil normalized PGC, reduced proteinuria to 48 +/- 4% of baseline, and improved glomerular size selectivity without altering SNGFRH2O. Proteinuria after subtotal NPX thus originates largely from glomeruli with minimal structural abnormalities. The defect in size selectivity is largely attributed to the prevailing high PGC, producing large, nonselective channels on the glomerular capillary wall. The observations raise the possibility that in chronic renal diseases, the reduction in proteinuria often seen after therapeutic measures, including antihypertensive medication, may reflect their functional effect on the relatively intact glomeruli rather than their structure-sparing effect on severely damaged glomeruli, which contribute little to the proteinuria.     

Glomerular actions of endothelin in vivo.

In Munich-Wistar rats, a micropipette was inserted into a first-order branch of the left main renal artery and continuously infused with human/porcine endothelin (0.4 ng/min). Micropuncture measurements revealed substantial differences within the cortical microcirculation of the same left kidney: SNGFR was some 35% lower in glomeruli exposed to endothelin compared with non-endothelin-perfused glomeruli (P less than 0.005). Similarly, glomerular plasma flow rate was some 38% lower in the endothelin-exposed glomeruli (P less than 0.001). The hypoperfusion and hypofiltration in the endothelin-exposed glomeruli reflected an increase in resistances in the afferent and efferent arterioles. There was no difference in the value of the glomerular capillary ultrafiltration coefficient between the two populations of glomeruli. We also studied kidneys that underwent 25 min of renal artery clamping 48 h before study. Antiendothelin antibody infused into one of the branches of the main renal artery ameliorated the vasoconstriction characteristic of postischemic nephrons: within the cortical microcirculation, the SNGFR in glomeruli exposed to antiendothelin antibody was 27.0 +/- 3.1 nl/min as compared with 17.4 +/- 1.7 measured in glomeruli not perfused with the antibody (P less than 0.001). Similarly, glomerular plasma flow rate was higher in the glomeruli exposed to antiendothelin antibody (128.7 +/- 14.4 nl/min vs. 66.6 +/- 5.6, P less than 0.005). Resistances in both the afferent and efferent arterioles were substantially lower in the antibody-exposed glomeruli. It is, therefore, suggested that endothelin, presumably released from damaged endothelium, may play an important intermediary role in the hypoperfusion and hypofiltration observed in postischemic kidneys.     

Effects of treatment with angiotensin-converting enzyme inhibitor (ACEI) or angiotensin II receptor antagonist (AIIRA) on renal function and glomerular injury in subtotal nephrectomized rats

The aim of this study was to determine if treatment with angiotensin-converting enzyme inhibitors (ACEI) or angiotensin II receptor antagonists (AIIRA) might decrease urinary albumin excretion and prevent glomerular enlargement and glomerulosclerosis in subtotal (5/6) nephrectomized rats. Morphometric image analysis of glomeruli was also performed in the subtotal nephrectomized rats. The nephrectomized rats were treated with ACEI (enalapril 100mg/l), AIIRA (L-158,809 10 mg/l) or TRX (reserpine 5 mg/l, hydralazine 80 mg/l, and hydrochlorothiazide 25 mg/l) and euthanized at 16 weeks after renal ablation. Treatments were started at 2 weeks (early treatment: Group I) or 8 weeks (later treatment: Group II) after the ablation. ACEI and AIIRA treatments were equally and significantly effective in limiting albuminuria and progression of glomerular sclerosis. TRX was also as effective in decreasing urinary albumin excretion and preserving the renal function as ACEI or AIIRA in Group I. The improvement of albuminuria, glomerular enlargement and sclerosis after these treatments in Group II was significantly less than that in Group I. It appears that the early treatment with angiotensin converting enzyme inhibitor, angiotensin II receptor antagonist or reserpine, hydralazine and hydrochlorothiazide (TRX) may prevent glomerular injury in human patients with renal hypertension. J. Clin. Lab. Anal. 11:53–62. © 1997 Wiley-Liss, Inc.     

Hepatocyte growth factor-stimulating endothelial cell growth and accelerating glomerular capillary repair in experimental progressive glomerulonephritis

Hepatocyte growth factor (HGF) is one of the major growth factors that stimulate the growth and the migration of vascular endothelial cells. In this study, we examined the beneficial effects of HGF for glomerular repair in an experimental progressive glomerulonephritis (GN) model prepared by injecting both anti-Thy-1.1 antibody (day 0) and habu-snake venom (day 1) in rats. The rats received continuous intraperitoneal administration of recombinant human HGF (80 microg/100 g/day) or vehicle control at an early stage (day 2 to day 9), after severe glomerular injury. The vehicle-infused control rats initially showed severe mesangiolysis with large ballooning (day 2), followed by the prominent proliferation of mesangial cells with minimal capillary regeneration (day 5 to week 2), and global sclerosis with chronic renal failure (week 4 to week 8). Although mesangiolysis with large ballooning and mesangial cell proliferation were also observed in the HGF-infused rats, glomerular capillary regeneration with marked endothelial cell proliferation occurred during HGF administration from day 2 to day 9. Subsequently, the glomerulus was repaired with the development of the capillary network and the reduction of mesangial hypercellularity from week 2 to week 4, and almost all of the glomeruli showed a normal structure by week 8. The HGF-treated rats showed significantly better renal functions (Cr: 0.3 +/- 0.1 vs. 3.5 +/- 1.1 mg/dl in control, p < 0.001), less proteinuria (21.2 +/- 8.0 mg/day vs. 421.4 +/- 45.1 mg/day in control, p < 0.001) and less glomerular sclerosis at week 8 than the vehicle-infused rats. We conclude that HGF accelerated glomerular repair through the growth of capillary endothelial cells and capillary regeneration in experimental progressive GN. Administering HGF is a logical and efficient strategy for treating progressive GN with severe capillary destruction.     

Control of glomerular hypertension by insulin administration in diabetic rats.

Micropuncture studies were performed in Munich Wistar rats made diabetic with streptozotocin and in normal control rats. Diabetic rats received daily ultralente insulin to maintain moderate hyperglycemia (approximately 300 mg/dl). Group 1 diabetic rats studied after routine micropuncture preparation exhibited elevation of the single nephron glomerular filtration rate (SNGFR) due to increases in the glomerular transcapillary hydraulic pressure difference and glomerular plasma flow rate. In group 2 diabetic rats infusion of insulin to achieve acute blood glucose control normalized the glomerular transcapillary pressure gradient while increasing the glomerular ultrafiltration coefficient, so that SNGFR remained elevated. Persistent elevation of SNGFR despite normalization of the transcapillary pressure gradient was also observed in group 3 diabetic rats infused with insulin plus sufficient dextrose to maintain hyperglycemia. These studies indicate that glomerular capillary hypertension in diabetes is an acutely reversible consequence of insulin deficiency and not the result of renal hypertrophy.     

Glomerular and tubular dynamics in mercuric chloride-induced acute renal failure

Mercuric chloride (HgCl2)-induced acute renal failure has received considerable investigative attention but little agreement as to its pathogenesis. A source of some disagreement has been the lack of direct glomerular dynamics measurements in this disorder. We examined glomerular dynamics, tubular integrity, and whole kidney function at 24 hours in Munich-Wistar rats given either HgCl2, 3.5 mg/kg, or a similar volume of 0.9% saline solution intramuscularly. Arterial blood pressure was elevated in HgCl2-injected rats, but renal blood flow and its distribution were similar to those of controls. Inulin clearance, however, was reduced by 89% in HgCl2-injected animals. Glomerular dynamics experiments demonstrated similar glomerular plasma flow (QA) and glomerular capillary and tubular pressures in control and HgCl2-injected animals but a higher net afferent ultrafiltration pressure and lower ultrafiltration coefficient (Kf) in the HgCl2-injected group. Single-nephron glomerular filtration rate (SNGFR), when measured from Bowman's space and HgCl2-injected rats, was similar to that measured from late proximal tubules in controls. However, SNGFR determined from the later proximal tubule in HgCl2-injected rats was only one third of that measured from Bowman's space. QA estimated from glomerular counting was similar to that calculated from Bowman's space SNGFR in HgCl2-injected rats. 3H-inulin microinjection experiments confirmed the presence of tubular fluid backleak suggested by the discrepancy in Bowman's space and late proximal tubular SNGFR measurements. It is concluded that at 24 hours in low-dose HgCl2-induced acute renal failure, tubular fluid backleak is the major pathogenetic factor, with a decline in Kf having a potential secondary role.     

Glomerular injury in uninephrectomized spontaneously hypertensive rats. A consequence of glomerular capillary hypertension.

Micropuncture and/or morphologic studies were performed in intact Wistar-Kyoto rats (WKY) (group 0), intact spontaneously hypertensive rats (SHR) (groups 1 and 5), uninephrectomized (UNX) WKY (groups 2 and 6), and UNX SHR (groups 3 and 4, 7 and 8). UNX was performed when rats were 5 wk of age. Groups 0-4 were observed for 34 wk after which whole kidney clearance and morphologic studies were performed. Groups 5-8 underwent micropuncture study at 10 wk of age. Groups 4 and 8 were fed a diet containing 6% protein. All other rats ingested standard laboratory diet. 5 wk after UNX, normotensive group 6 had higher single nephron glomerular filtration rate (SNGFR) and initial glomerular plasma flow rate (QA) than intact, hypertensive group 5. Glomerular transcapillary hydraulic pressure difference (delta P) was similar in these two groups. Hypertensive group 7 exhibited less elevation in SNGFR and QA than group 6, but delta P was significantly increased. The presence of glomerular capillary hypertension in UNX SHR at 10 wk was associated with the development of significant proteinuria and an increased incidence of mesangial expansion and glomerular sclerosis at 7 mo (group 3) as compared with groups 0, 1, and 2. Protein restriction prevented the development of increased delta P in UNX SHR (group 8) and also conferred long-term protection from increased urinary protein excretion and glomerular injury (group 4). These studies suggest that glomerular capillary hypertension predisposes to glomerular injury in this model of hypertension with reduced renal mass.     

Prevention of diabetic glomerulopathy by pharmacological amelioration of glomerular capillary hypertension.

Two groups of adult male Munich-Wistar rats and a third group of nondiabetic age-matched and weight-matched normal control rats underwent micropuncture study 1 mo, and morphologic studies 14 mo, after induction of streptozotocin diabetes or sham treatment. All animals were fed standard rat chow. Diabetic rats received daily ultralente insulin to maintain stable moderate hyperglycemia (approximately 350 mg/dl). In addition, one group of diabetic rats was treated with the angiotensin I converting enzyme inhibitor, enalapril, 15 mg/liter of drinking water. Average kidney weight, whole kidney and single-nephron glomerular filtration rate, and glomerular plasma flow rate were elevated to similar values in both groups of diabetic rats, relative to normal control rats. Non-enalapril-treated diabetic rats exhibited significant elevations in mean glomerular capillary hydraulic pressure and transcapillary hydraulic pressure gradient, compared with the other groups studied, and only this group eventually developed marked and progressive albuminuria. Likewise, histological examination of the kidneys at 14 mo disclosed a high incidence of glomerular structural abnormalities only in non-enalapril-treated diabetic rats. These findings indicate that prevention of glomerular capillary hypertension in rats with diabetes mellitus effectively protects against the subsequent development of glomerular structural injury and proteinuria. This protection is afforded despite pronounced hyperglycemia and elevated levels of glucosylated hemoglobin, further supporting our view that hemodynamic rather than metabolic factors predominate in the pathogenesis of diabetic glomerulopathy.     

Permselectivity of the glomerular capillary wall. Studies of experimental glomerulonephritis in the rat using dextran sulfate.

To determine whether the increased filtration of serum proteins after glomerular injury is the consequence of altered electrostatic properties of the glomerular capillary wall, we measured fractional clearances of the anionic polymer, dextran sulfate, in nine Munich-Wistar rats in the early autologous phase of nephrotoxic serum nephritis (NSN). In agreement with previous studied from this laboratory, whole kidney and single nephron glomerular filtration rates were normal in NSN rats despite histological evidence of glomerular injury, and despite a marked reduction in the glomerular capillary ultrafiltration coefficient to approximately one-third of normal. In the companion study (9), it was shown that in NSN rats the mean fractional clearances of neutral dextrans over the range of effective molecular radii from 18 to 42 A were reduced, compared to normla. In contrast, in the present study the mean fractional clearances for dextran sulfate over the same range of molecular radii were significantly greater than those found previously for normal Munich-Wistar rats. The fractional clearance of dextran sulfate molecules of the same molecular radius as serum albumin (approximately 36 A) was increased markedly, from 0.015 +/- 0.005 (SEM) in nonnephritic controls to 0.24 +/- 0.03 in NSN (P less than 0.001). The sialoprotein content of glomeruli, estimated by the colloidal iron reaction, was reduced in NSN rats as compared to normal controls. It is concluded that the abnormal filtration of anionic serum proteins, such as albumin, seen in glomerulopathies is, at least in part, the consequence of loss of fixed negative charges from the glomerular capillary wall.     

Impaired autoregulation of glomerular capillary hydrostatic pressure in the rat remnant nephron.

In the present micropuncture study, the autoregulation of glomerular capillary hydrostatic pressure (PG) in Munich-Wistar rats 24 h after 75% nephrectomy (Nx) or sham operation (Sh) was investigated. The effect of varying renal perfusion pressure (RPP) on paired determinations of directly measured PG was evaluated in glomeruli of nephrons in which distal fluid delivery was present (unblocked). Autoregulation of PG in Sh glomeruli with unblocked tubules occurred at RPP values between 99.5 +/- 1.0 and 132.1 +/- 1.0 mmHg. In contrast, in Nx glomeruli with unblocked tubules PG increased by 0.32 +/- 0.07 mmHg/mmHg increase in RPP over this same range of RPP (P less than 0.0001). To determine whether enhanced prostaglandins synthesis was responsible for the altered regulation of PG in Nx glomeruli, we repeated the micropuncture measurements in a setting of prostaglandin synthesis inhibition. Although prostaglandins synthesis inhibition did not affect the autoregulation of PG in Sh glomeruli, it did normalize the autoregulatory capacity for PG of Nx glomeruli with unblocked tubules. Thus, acute Nx is associated with a significant loss of the autoregulatory capacity for PG and this impairment appears to be related to a prostaglandin-mediated alteration of the responsiveness of the vascular effector site for autoregulation.     

Renal vasoconstriction caused by short-term cholesterol feeding is corrected by thromboxane antagonist or probucol.

Recent studies indicate that short-term cholesterol feeding causes vascular hyperreactivity and/or increased tone in certain vascular beds. The present study in rats examined the effect of 3 wk of cholesterol-supplemented diet (CSD) on renal hemodynamics. We tested the hypothesis that LDL oxidized in vivo is causally related to increased renal vascular tone by adding the antioxidant drug probucol to the CSD (CSD + P). Micropuncture of surface nephrons in the CSD rats demonstrated that single nephron glomerular filtration rate (SNGFR) and single nephron afferent plasma flow (QA) were markedly lower than in normal rats, whereas glomerular capillary pressure (PGC), afferent arteriolar resistance (RA), and single nephron filtration fraction (SNFF) were higher. In the CSD + P animals, almost all of these hemodynamic abnormalities were absent. TXB2 and PGE2 were increased in proximal tubule fluid and urine in the CSD rats, but normal in the CSD + P group. Infusion of a TXA2 receptor antagonist into the suprarenal aorta of CSD rats caused a rapid return to normal of RBF (renal blood flow), GFR (glomerular filtration rate), SNGFR, QA, RA, PGC, and Kf (ultrafiltration coefficient). Our observations demonstrate that cholesterol feeding leads to renal vasoconstriction, which appears to be mediated largely by increased TXA2 production. The fact that probucol prevented the hemodynamic abnormalities as well as the increased TX production is consistent with the hypothesis that LDL oxidized in vivo initiates events leading to TX mediated vasoconstriction.     

Interaction between alpha 2-adrenergic and angiotensin II systems in the control of glomerular hemodynamics as assessed by renal micropuncture in the rat.

The hypothesis that renal alpha 2 adrenoceptors influence nephron filtration rate (SNGFR) via interaction with angiotensin II (AII) was tested by renal micropuncture. The physical determinants of SNGFR were assessed in adult male Munich Wistar rats 5-7 d after ipsilateral surgical renal denervation (DNX). DNX was performed to isolate inhibitory central and presynaptic alpha 2 adrenoceptors from end-organ receptors within the kidney. Two experimental protocols were employed: one to test whether prior AII receptor blockade with saralasin would alter the glomerular hemodynamic response to alpha 2 adrenoceptor stimulation with the selective agonist B-HT 933 under euvolemic conditions, and the other to test whether B-HT 933 would alter the response to exogenous AII under conditions of plasma volume expansion. In euvolemic rats, B-HT 933 caused SNGFR to decline as the result of a decrease in glomerular ultrafiltration coefficient (LpA), an effect that was blocked by saralasin. After plasma volume expansion, B-HT 933 showed no primary effect on LpA but heightened the response of arterial blood pressure, glomerular transcapillary pressure gradient, and LpA to AII. The parallel results of these converse experiments suggest a complementary interaction between renal alpha 2-adrenergic and AII systems in the control of LpA.     

Mechanism of preservation of glomerular perfusion and filtration during acute extracellular fluid volume depletion. Importance of intrarenal vasopressin-prostaglandin interaction for protecting kidneys from constrictor action of vasopressin.

Glomerular circulatory dynamics were assessed in 60 adult anesthetized rats, which were either deprived or not deprived of water for 24-48 h. Water-deprived rats (n = 21) were characterized by a depressed level of single nephron glomerular filtration rate (SNGFR) when compared with nonwater-deprived controls (n = 8) (23.2 +/- 1.3 vs. 44.8 +/- 4.1 nl/min). This was primarily due to decreased glomerular plasma flow rate (71 +/- 5 vs. 169 +/- 23 nl/min) and glomerular capillary ultrafiltration coefficient (0.028 +/- 0.003 vs. 0.087 +/- 0.011 nl/[s . mmHg]). Infusion of saralasin to these water-deprived rats resulted in significant increases in plasma flow rate and ultrafiltration coefficient, and decline in arteriolar resistances. Consequently, SNGFR increased by approximately 50% from pre-saralasin levels. When water-deprived saralasin-treated rats were given a specific antagonist to the vascular action of arginine vasopressin (AVP), d(CH2)5Tyr(Me)AVP, a fall in systemic blood pressure occurred, on average from 102 +/- 5 to 80 +/- 5 mmHg, unaccompanied by dilation of renal arterioles, so that both plasma flow rate (129 +/- 8 vs. 85 +/- 13 nl/min) and SNGFR (31.0 +/- 2.9 vs. 18.2 +/- 4.4 nl/min) decreased. This more selective extrarenal constrictor action of AVP was further documented in additional studies in which cardiac output and whole kidney blood flow rate were simultaneously measured. In water-diuretic rats, administration of a moderately pressor dose of AVP (4 mU/kg per min) resulted in a significant rise in kidney blood flow rate (from 8.8 +/- 1.2 to 9.6 +/- 1.3 ml/min). The higher kidney blood flow rate occurred despite a fall in cardiac output (from 111 +/- 7 to 98 +/- 9 ml/min), and was associated with a significant increase in the ratio of systemic vascular to renal vascular resistance (on average from 0.083 +/- 0.014 to 0.106 +/- 0.019). Furthermore, infusion of d(CH2)5Tyr(Me)AVP to water-deprived animals (n = 6) to antagonize endogenous AVP resulted in systemic but not renal vasodilation, so that kidney blood flow rate fell (by approximately 30%), as did systemic-to-renal resistance ratio (by approximately 30%). When the above two experiments were repeated in indomethacin-treated animals, exogenous AVP administration in water-diuretic rats (n = 6) and antagonism of endogenous AVP in water-deprived rats (n = 7) caused, respectively, parallel constriction and dilation in systemic and renal vasculatures. The net effect was unaltered systemic to renal vascular resistance ratio in both cases. These results indicate that (1) unlike angiotensin II, AVP maintains glomerular perfusion and filtration in acute extracellular fluid volume depletion by a more selective constriction of the extrarenal vasculature. (2) The relative renal insensitivity to the vasoconstrictor action of AVP appears to be due to an AVP-induced release of a potent renal vasodilator, sensitive to indomethacin, presumably prostaglandins.