Search

There is increasing evidence that a link between the polyol pathway and prostaglandins is important in the pathogenesis of diabetic nephropathy. The presence of the polyol pathway in the kidneys of normal animals, the galactose-fed rat, and animals with experimental diabetes has been established. While aldose reductase (AR) immunoreactive protein (AR-IRP) and AR mRNA are expressed at high levels in renal medulla, the sites of AR synthesis and regulation and metabolic consequences of AR activity in renal cortex are uncertain. The present study was conducted to test the hypothesis that AR expression and PGE2 production are coordinately regulated in glomerular mesangial cells. To test this hypothesis, we measured AR-IRP, AR mRNA, and PGE2 production in mesangial cells isolated from rats maintained on diets containing normal chow (MC-N), 50% galactose (MC-G), and 50% dextrin (MC-D). The rank order for each parameter studied (AR-IRP, AR mRNA, PGE2) was MC-N > MC-G > MC-D. Western blot analysis demonstrated that MC-N (optical density [OD] 1.0), MC-G (OD 0.59), and MC-D (OD 0.25) express AR-IRP. Slot-blot analyses demonstrated that levels of AR mRNA were greatest in MC-N (1.0), intermediate in MC-G (0.49), and lowest in MC-D (0.31). Ribonuclease (RNase) protection analyses demonstrated a similar pattern of AR mRNA expression, with MC-N at 1.0, MC-G at 0.60, and MC-D at 0.33. PGE2 production (pg/5 x 10(4) cells/30 min) was highest in MC-N (278 +/- 29), intermediate in MC-G (110 +/- 9), and lowest in MC-D (37 +/- 4).(ABSTRACT TRUNCATED AT 250 WORDS)

Increased renal production of prostaglandins (PG) may contribute to the hyperfiltration that accompanies early diabetes. It was postulated that a putative metabolic abnormality of diabetes, ie, increased flux through the polyol pathway, stimulates renal PG production and that this phenomenon can be prevented by aldose-reductase inhibition. To test this hypothesis, the effects of polyol accumulation on urinary excretion rates (UER) of PGE2 and 6-keto-PGF1 alpha were studied, using the galactose-fed rat model. UER of PGE2 and 6-keto-PGF1 alpha were measured in three groups of weanling Wistar male rats. Group 1 was maintained on normal chow (n = 6), group 2 was fed chow supplemented with 30% galactose (n = 6), and group 3 received chow supplemented with 30% galactose and 0.7% sorbinil (n = 6). Ten 24-hour urine samples were obtained from each group between 151 and 240 days on the respective diets. UER of PGE2 (P less than .001) and 6-keto-PGF1 alpha (P less than .01) were higher in group 2 than in group 1. UER of PGE2 (NS) and 6-keto-PGF1 alpha (NS), respectively, were similar in groups 1 and 3. These data indicate that flux through the polyol pathway modulates the UER of PGE2 and 6-keto-PGF1 alpha. This phenomenon may contribute to the glomerular hyperfiltration of early diabetes.

This study explores the hypothesis that the continuous ultrafiltration that accompanies continuous ambulatory peritoneal dialysis (CAPD) produces greater activation of the renin-angiotensin aldosterone axis than does the intermittent ultrafiltration that accompanies thrice weekly hemodialysis (HD). Plasma renin activity (PRA), active renin (AR), total renin (TR), inactive renin (IR), 18-hydroxycorticosterone (18-OH-B), aldosterone (PAC), and cortisol were measured in plasma from CAPD (n = 6) and HD (n = 10) patients. Blood from CAPD patients was sampled at 8 AM after overnight recumbency and at 12 noon after four hours ambulation. Blood from HD patients was sampled immediately pre-HD (8 AM) and post-HD (12 noon) at both 8 AM and 12 noon. PRA (P less than 0.01), AR (P less than 0.01), and AR/TR (100%; P less than 0.01) were higher in CAPD than in HD. IR and TR were not different in the two groups. Plasma 18-OH-B was normal in HD but markedly elevated in CAPD. 18-OH-B was higher in CAPD than in HD at 8 AM (P less than 0.05) and at 12 noon (P less than 0.05). Plasma cortisol was not different in the two groups. We conclude that the greater degree of renin activation in CAPD versus HD contributes to the higher levels of 18-OH-B and PAC observed in CAPD patients.

Continuous ambulatory peritoneal dialysis (CAPD) entails the continuous presence of hypertonic dialysate in the peritoneal cavity. We postulated that the continuous, gradual ultrafiltration produces chronic activation of the renin-angiotensin system and the adrenal zona glomerulosa. To explore this hypothesis, we measured plasma levels of PRA, active renin (AR), total renin (TR), inactive renin (IR), 18-hydroxycorticosterone (18-OH-B), and aldosterone (PAC) under basal and stimulated conditions. At 0800 and 1200 hr after overnight recumbency, plasma levels of PRA, AR, TR, IR, and 18-OH-B were elevated above the range for sodium-replete recumbent normal subjects. PAC, however, was normal. The increase in TR was due predominantly to an increase in AR. After the combined stimulus of 4 hr ambulation and the ultrafiltration induced by a 2 L exchange, plasma levels of PRA, AR, TR, IR, and PAC were within the range for sodium-replete upright normal subjects. Plasma 18-OH-B levels, however, remained markedly elevated. Graded intravenous infusion of ACTH at rates of 0.03 to 10 ng/min demonstrated that the threshold for an ACTH-stimulated rise in plasma 18-OH-B and PAC is at least as low as that for cortisol and corticosterone. We conclude that CAPD produces activation of the renin-angiotensin system. The high circulating levels of PRA, AR, and, presumably, angiotensin II result in increased secretion of 18-OH-B by the adrenal zona glomerulosa.

Plasma levels of aldosterone decrease during hypokalemic hemodialysis. Our study was performed to determine whether the changes in plasma aldosterone level observed during hemodialysis are modulated by changes in corticosterone methyloxidase II activity. We measured plasma levels of adrenal zona glomerulosa steroids, for example, aldosterone and 18-hydroxycorticosterone (18-OH-B), immediately before and after 4 hours of hemodialysis (n = 8). Plasma levels of steroids originating from the adrenal zona fasciculata, for example, cortisol, corticosterone, 18-hydroxy-11-deoxycorticosterone, and 11-deoxycorticosterone, were also measured. Dialysance rates of 18-OH-B, aldosterone, and cortisol were calculated (n = 8). Plasma levels of both aldosterone (P less than 0.05) and 18-OH-B (p less than 0.01) decreased during hemodialysis. The 18-OH-B/aldosterone plasma concentration ratios did not change significantly during hemodialysis. No significant changes in plasma levels of fasciculata steroids were observed during hemodialysis. Dialysance rates for aldosterone and 18-OH-B were similar (P not significant). The dialysance of cortisol was 10-fold lower than that of aldosterone (P less than 0.01) and 18-OH-B (P less than 0.01). The relative constancy of the 18-OH-B/aldosterone plasma concentration ratios indicates that corticosterone methyloxidase II activity is normal in patients with end-stage renal disease who are maintained by hemodialysis.

The adrenocorticoid responses to low doses of ACTH (0.03-10 ng/min) in sodium-deplete normal subjects and end-stage renal disease patients maintained on continuous ambulator peritoneal dialysis (CAPD) were compared. All subjects were pretreated with dexamethasone. ACTH was administered by graded iv infusions in doses of 0.03, 0.3, 1.0, 3.0, and 10 ng ACTH/min. Each rate of infusion was maintained for 30 min. Plasma aldosterone, 18-hydroxycorticosterone, corticosterone, 18-hydroxy-11-deoxycorticosterone, and cortisol were measured in plasma sampled at the end of each rate of infusion in both groups. Plasma 11-deoxycorticosterone was measured in CAPD patients. The plasma steroid levels in the CAPD patients after each infusion rate were equal to or greater than the levels in normal subjects. The slopes of the cumulative increases above baseline in plasma steroid levels in the CAPD patients were equal to or greater than those in the normal subjects. In both groups, plasma corticosterone increased the most and aldosterone the least. Kinetic analyses indicated that the adrenal responses to low dose ACTH were not linear. A distinct threshold for ACTH-stimulated increase in plasma adrenocorticoid levels, if present, is very low. The responses of plasma adrenocorticoids to low dose ACTH are normal in CAPD patients.

Plasma 18-hydroxycorticosterone (18-OH-B) to aldosterone (aldo) concentration ratios reflect adrenal corticosterone methyloxidase type II activity. This ratio is determined not only by the relative secretion rates of the two steroids but also by differences in binding, distribution, and metabolism. Plasma cortisol alters the distribution of aldo between red blood cells (RBC) and plasma. We postulated that the distribution of 18-OH-B, like that of aldo, is determined by the availability of high affinity binding sites on plasma transcortin. Double equilibrium dialyses demonstrated that 18-OH-B, aldo, and cortisol compete for binding sites on transcortin. Increasing amounts of each of the three unlabeled steroids produced progressive decrements in the binding of all three labeled steroids to transcortin. The affinity of 18-OH-B (2 X 10(6) M-1) for transcortin was intermediate between those of cortisol (3 X 10(7) M-1) and aldo (0.9 X 10(6) M-1). Heat treatment of plasma decreased the binding of 18-OH-B and cortisol to transcortin by 82% and 75%, respectively. Gel filtration of plasma revealed that protein-bound [3H]18-OH-B and [14C]cortisol eluted in the same fractions. The addition of increasing quantities of unlabeled cortisol to whole blood in vitro produced similar increments in RBC to plasma concentration ratios of [3H]18-OH-B and [14C]aldo. The ratio of the percentage of circulating 18-OH-B in plasma to the percentage of circulating aldo in plasma was constant in blood containing low and high cortisol concentrations. Therefore, changes in plasma cortisol have similar effects on the distribution of 18-OH-B and aldo between RBC and plasma.