Relation of glomerular injury to preglomerular resistance in experimental hypertension

Glomerulosclerosis: are we any wiser?

Chronic renal failure (CRF) is characterized histologically by progressive glomerulosclerosis (GS) and tubulo-interstitial scarring (TIS). Recently, research has focused on the study of the pathophysiology of GS. Most advances in this field have been derived from the study of various experimental models of CRF and GS in the rat. In this paper, I will review some of the concepts and hypotheses put forward to explain progressive GS and examine their relevance to glomerular scarring and CRF in humans.

Long-term improvement in renal function after short-term strict blood pressure control in hypertensive nephrosclerosis

Seventy-nine hypertensive nephrosclerosis patients entered a prospective randomized single-blind study to 1) establish the pattern of decay of renal function in this population and the variability therein and 2) to determine if strict diastolic blood pressure (DBP) control (less than or equal to 80 mm Hg) is more effective than conventional levels (90-95 mm Hg) in conserving renal function. Because of unexpected significant improvement in renal function in patients from both groups, which changed the perspectives on the course of this disease as described herein, this report is being published before completion of the trial. The selection criteria were 1) serum creatinine concentration of 1.6-7.0 mg/dl, 2) glomerular filtration rate of less than 70 ml/min/1.73 m2, and 3) absence of diseases (other than hypertension) known to destroy renal function. Renal function was assessed by glomerular filtration rate [( 125I]iothalamate clearance) and serum creatinine concentration. Before randomization, DBP was aggressively treated to reduce it to less than 80 mm Hg. Twenty-two subjects (14 in the strict DBP control group and eight in the conventional DBP control group) have been enrolled in the study for 36 months. In contrast to results from previous studies in humans and rats, renal function improved in both patient groups. Thus, irrevocable progression of renal damage after onset of renal failure from high blood pressure does not necessarily occur, and in fact, long-term improvement of renal function resulted from the effects of the study itself.(ABSTRACT TRUNCATED AT 250 WORDS)

Sex and the single kidney

Micropuncture measurements revealed that approximately 9 to 10 months after uninephrectomy and maintenance on a high-protein diet, glomerular capillary BP was significantly higher in male than in virgin female rats. This might account for the greater susceptibility of the male to age- and ablation-induced glomerular damage reported by others, although at the time of the present studies, significant reduction in function and worsening in glomerulosclerosis in males v females was barely evident. In a second group of chronically uninephrectomized females, the effects of multiple (five) consecutive pregnancies and lactations were investigated and did not indicate any severe deleterious long-term effects of pregnancy on the glomeruli in this model of underlying renal compromise. Variable responses to an acute intravenous glycine challenge which did not correlate well with the extent of glomerular damage were observed in each group, suggesting that this test may not always be informative regarding underlying glomerular disease.

Mechanisms of hypertensive glomerular injury

Systemic hypertension complicates the course of most patients with chronic renal failure and accelerates the progression of experimental and clinical glomerular disease. Based on recent experimental studies, it is suggested that at similar levels of systemic hypertension, glomerular injury only develops when pre-glomerular resistances are ineffective, thus allowing the development of glomerular hypertension. The mechanisms by which the hemodynamic stress of elevated intracapillary flows and pressures leads to progressive glomerular damage, particularly to the development of focal glomerulosclerosis is currently unknown. Endothelial cell injury, increased mesangial traffic or trapping of macromolecules and epithelial cell injury, or a combination, appear to occur early, followed by in situ inflammatory and microthrombotic mechanisms. This may explain why various therapeutic approaches, whether dietary or pharmacologic, can have salutory effects despite their diverse mechanisms of action.

Glomerular filtration and volume regulation in gravid animal models

The gestational increase in glomerular filtration rate (GFR) that occurs in the normal rat is the result exclusively of an increase in plasma flow rate, and there is no sustained increase in glomerular capillary blood pressure during a normal pregnancy. The factor or factors that initiate the gestational renal vasodilatation (and plasma volume expansion) are maternal, not fetoplacental in origin. Apart from ruling out prostaglandins as an initiating agent, animal studies have not yet defined the precise nature of the initiating factors; it is unlikely that the gestational plasma volume expansion can be the sole cause of the increased GFR seen in pregnancy. The normal kidney in pregnancy exhibits substantial renal reserve to amino acid infusion, despite being already vasodilated by the gestational stimulus. The renal volume-sensing and control system of tubuloglomerular feedback is fully operative in pregnancy, and appears to be 'reset' to perceive the expanded plasma volume of pregnancy as normal. This observation agrees with many other indications that the sensors perceiving and controlling intravascular volume are reset during a normal pregnancy to enable the mother to accommodate the increased plasma volume without provoking a natriuretic response. Multiple pregnancies do not have any cumulative, long-term deleterious effects on renal function, either when the underlying function is normal or when it has been compromised by removal of renal mass plus high-protein feeding. In the short-term, pregnancy does not worsen kidney function when underlying glomerulonephritis is present. Therefore, the hyperfiltration of pregnancy does not appear to be a damaging entity, unlike other hyperfiltration states studied in the male rat. Still unknown is the mechanism by which pregnancy does worsen underlying glomerular disease in some women. The preliminary data in the rat, presented above, suggest that the exacerbating influence may be something other than the glomerular haemodynamic changes of pregnancy.

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.