Clinical and histological correlations of decline in renal function in diabetic patients with proteinuria.

In 47 patients with diabetic nephropathy (29 type I, 18 type II) renal function and blood pressure (BP) (treated with or without an angiotensin-converting enzyme [ACE] inhibitor, enalapril [10 mg], in 38 hypertensive patients) were followed over 4 years. A percutaneous renal biopsy was performed in all patients initially and repeated in a representative 19 patients with treated hypertension after 4 years. Mean glomerular volume (MGV), interstitial fibrosis (IF), capillary volume, and sclerosed glomeruli (GS) were measured histomorphometrically. Mean fall in creatinine clearance (CCr) was 11.8% after 4 years with no difference between treatment groups or type of diabetes. BP both initially and during treatment correlated with initial and final serum creatinine and CCr (P < 0.01). There were no histomorphometric differences between type I and type II patients or hypertension treatment groups. Initial IF correlated with initial and final serum creatinine and CCr (P < 0.05) in all patients and type I patients alone, MGV correlated inversely with CCr in type I patients (P < 0.05). After 4 years, IF (24.8 vs. 30.0%, P < 0.01) and GS (26 vs. 37%, P < 0.05) increased significantly, and increase in IF correlated with fall in CCr (P < 0.01). Proteinuria and HbA1 did not correlate with indexes of function or structure. In this longitudinal study of patients with diabetic nephropathy, there was a close relation between BP and renal function but no difference between treatment with enalapril and other hypertensive agents. The correlations between renal function and histology at entry and after 4 years suggest that IF is a co-determinant of renal function in diabetic nephropathy.

A clinical-histological study of individuals with diabetes mellitus and proteinuria.

Coexistent renal pathology with diabetic glomerulosclerosis was found in 38 of 136 (28%) consecutive renal biopsies performed primarily for proteinuria in individuals with diabetes mellitus. The histological lesions found were glomerulonephritis (14), focal tubulointerstitial disease (23), and amyloidosis (1). Significant microscopic haematuria was present in 66% of all patients and did not help to distinguish non-diabetic disease. The severity of diffuse diabetic glomerular disease was independently associated with duration of diabetes, raised plasma creatinine, the presence of hypertension, clinical retinopathy and neuropathy, but not with type of diabetes, degree of proteinuria or glycosylated haemoglobin at the time of biopsy. Diffuse interstitial fibrosis was related to the severity of glomerular disease and, if severe, also with a significantly (p less than 0.01) higher plasma creatinine. Coexisting renal disease was found to be associated with a significantly higher plasma creatinine (p less than 0.01) independent of the severity of diabetic glomerulopathy. Coexistent pathology is a not uncommon finding in renal biopsies from diabetic patients with proteinuria. These lesions and their underlying causes may not only influence the renal function and natural history of renal disease in diabetic individuals, but may also determine the response of proteinuria to therapy.

Lack of effect of gliclazide on platelet aggregation in insulin-treated and non-insulin-treated diabetes: a two-year controlled study.

Previous studies have suggested that the sulphonylurea hypoglycaemic agent gliclazide has specific effects in inhibiting platelet aggregation, and other haemorrheological effects that could be beneficial in preventing diabetic microangiopathy. A double-blind trial of the effect of gliclazide on platelet aggregatory responses was performed in 51 diabetic patients. Insulin- and non-insulin-treated diabetics were assessed during an initial 12-month placebo period, and in a subsequent 24-month active period after randomisation into placebo and gliclazide groups in insulin-treated patients or to glibenclamide and gliclazide groups in non-insulin-treated patients. Platelet-rich plasma was obtained from patients at intervals of at least 6 months during the trial. Circulating platelet aggregates were estimated, platelet aggregation was studied in response to three concentrations of adrenaline, ADP and collagen and thromboxane B2 produced by platelets exposed to collagen was measured. No significant effect of gliclazide was demonstrated on any parameter of platelet function evaluated.

A role for calmodulin in renal production of 1,25-dihydroxyvitamin D3.

The conversion of circulating 25-hydroxyvitamin D3 (25OHD3) to its active metabolite 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] in the renal tubule mitochondrion by the enzyme 25OHD3-1 alpha-hydroxylase is closely regulated in vivo according to the physiological need for calcium and phosphorus. The mechanism by which this regulation is achieved at the cellular level has not been clarified, although a number of lines of evidence suggest that calcium ions (Ca2+) are involved. This study was designed to determine whether calmodulin, the ubiquitous cell protein that binds and mediates many of the regulatory functions of Ca2+, plays a role in the regulation of renal vitamin D metabolism. The calmodulin antagonists trifluoperazine (TFP), Janssen R24571, and the naphthalene sulfonamides W5 and W7 inhibited conversion of 25OHD3 to 1,25-(OH)2D3 by isolated renal tubules from vitamin D-deficient chicks in a dose-dependent manner (ED50: TFP, 12 mumol/liter; R24571, 10 mumol/liter; W7, 30 mumol/liter; W5, 75 mumol/liter). TFP did not inhibit production of the alternative metabolite 24,25-(OH)2D3 by chick renal tubules. In a similar manner, TFP, W7, and W5 inhibited conversion of 25OHD3 to 1,25-(OH)2D3 by isolated energized chick renal mitochondria, with no detrimental effect on mitochondrial respiratory indices. Bovine brain calmodulin in a concentration of 1 X 10(-7) mol/liter enhanced 1,25-(OH)2D3 production by isolated chick renal mitochondria in Ca2+ -containing medium, but not in the absence of Ca2+. Preincubating mitochondria with anticalmodulin antiserum resulted in decreased conversion of 25OHD3 to 1,25-(OH)2D3, an effect that was prevented by exogenous calmodulin. These data support the notion of a role for calmodulin in the Ca2+ -mediated control of renal 1 alpha-hydroxylase activity.

A role for the cytoskeleton in renal vitamin D metabolism.

Conversion of circulating 25-hydroxyvitamin D3 (25(OH)D3) to its active metabolite 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) occurs in the renal tubule mitochondrion. Recent reports have implicated the cytoskeleton in certain other steroid metabolizing cells as a mediator of a rate-limiting mitochondrial transport step. Whilst the activity of the renal converting enzyme, a typical steroid hydroxylase, is known to be regulated closely by a number of well studied factors, no information is available to indicate whether an analogous transport step is relevant to the regulation of vitamin D metabolism. Cytochalasin B and vinblastine were used as chemical antagonists of the microfilamentous and microtubular elements of the cytoskeleton. Both agents inhibited the conversion of 25(OH)D3 to 1,25(OH)2D3 by isolated vitamin D-deficient chick renal tubules in a dose-dependent manner. At the concentrations required to inhibit 25(OH)D3-1 alpha-hydroxylase activity in whole cells, these agents inhibited neither isolated mitochondrial 1,25(OH)2D3 production, nor 24,25(OH)2D3 synthesis by vitamin D-replete tubules. The cytoskeletal antagonists were found to increase the content of labelled 1,25(OH)2D3 and 25(OH)D3 in a mitochondrial fraction prepared by Percoll fractionation of tubule cells pre-exposed to the antagonists and labelled 25(OH)D3 substrate. The data suggest that disruption of the cytoskeleton may result in inhibition of transport of newly synthesised 1,25(OH)2D3 out of the mitochondrion and through the cell, and accumulating 1,25(OH)2D3 may oppose its further synthesis. This is consistent with a transport process mediated by the cytoskeleton being involved in the regulation of renal vitamin D metabolism.

Opposing actions of methylxanthines and dibutyryl cyclic AMP on 1,25 dihydroxyvitamin D3 production and calcium fluxes in isolated chick renal tubules.

In contrast to dibutyryl cyclic AMP, the methylxanthine phosphodiesterase inhibitors theophylline and caffeine were found to inhibit the conversion of 25 hydroxyvitamin D3 to 1,25 dihydroxyvitamin D3 in isolated renal tubules from vitamin D deficient chicks. This inhibition occurred at concentrations of methylxanthines which were shown to increase renal tubule cyclic AMP levels. No effect of theophylline or caffeine on 25 hydroxyvitamin D3 metabolism in isolated chick renal mitochondria was detected. Because of a demonstrated inhibitory action of calcium (10 and 20 mumol/l) on renal mitochondrial conversion of 25 hydroxyvitamin D3 to 1,25 dihydroxyvitamin D3, the effect of theophylline and dibutyryl cyclic AMP on cellular calcium-45 efflux and total renal tubule calcium content was estimated. Theophylline 10 mmol/l was found to inhibit renal tubular calcium efflux and to increase total cellular calcium content, while dibutyryl cyclic AMP 1 mmol/l had the reverse effect on both parameters. Divergent actions of the methylxanthines and dibutyryl cyclic AMP on the formation of 1,25 dihydroxyvitamin D3 and renal tubule calcium efflux and content support the hypothesis that intracellular calcium is an important regulator of renal vitamin D metabolism. The results indicate that observed actions of methylxanthines cannot always be ascribed to cyclic AMP accumulation.

Biphasic action of prostaglandin E2 on conversion of 25-hydroxyvitamin D3 to 1,25-dihydroxyvitamin D3 in chick renal tubules.

The effect of PGE2 on the conversion of 25-hydroxyvitamin D3 (25 OH D3) to 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) by isolated renal tubules from vitamin D deficient chicks was studied under a variety of experimental conditions. In the absence of added vitamin D metabolites, PGE2 (2 x 10(-6)M) caused an immediate inhibition of formation of 1,25-(OH)2D3, followed by a delayed stimulation, apparent after 15 h exposure to PGE2. Pretreatment of the tubules with 1,25-(OH)-2D3 prevented the immediate inhibitory action of PGE2, and allowed the stimulation to be apparent after 4 h exposure to PGE2. The cyclic nucleotide phosphodiesterase inhibitor 3-isobutyl-1-methyl xanthine (IBMX) significantly stimulated the formation of 1,25-(OH)-2D3. PGE2 significantly inhibited 1,25-(OH)2D3 formation in tubules which had been stimulated by IBMX. PGE2 stimulated the adenylate cyclase activity in a crude particulate fraction from the chick kidney, and raised cyclic adenosine 3', 5'-monophosphate (cyclic AMP) levels in the renal tubules. It is concluded that PGE2 can either stimulate or inhibit 1,25-(OH)2D3 formation in chick renal tubules. The stimulatory effect may be partly due to elevation of cyclic AMP. The mechanism of the inhibitory effect requires further investigation.

Chesapeake bay anoxia: origin, development, and significance.

Anoxia occurs annually in deeper waters of the central portion of the Chesapeake Bay and presently extends from Baltimore to the mouth of the Potomac estuary. This condition, which encompasses some 5 billion cubic meters of water and lasts from May to September, is the result of increased stratification of the water column in early spring, with consequent curtailment of reoxygenation of the bottom waters across the halocline, and benthic decay of organic detritus accumulated from plankton blooms of the previous summer and fall. The Chesapeake Bay anoxia appears to have had significant ecological effects on many marine species, including several of economic importance.