Growth differentiation factor 15 (GDF15) and semaglutide inhibit food intake and body weight through largely distinct, additive mechanisms

AIMS

To evaluate whether the potent hypophagic and weight-suppressive effects of growth differentiation factor-15 (GDF15) and semaglutide combined would be a more efficacious antiobesity treatment than either treatment alone by examining whether the neural and behavioural mechanisms contributing to their anorectic effects were common or disparate.

MATERIALS/METHODS

Three mechanisms were investigated to determine how GDF15 and semaglutide induce anorexia: the potentiation of the intake suppression by gastrointestinal satiation signals; the reduction in motivation to feed; and the induction of visceral malaise. We then compared the effects of short-term, combined GDF15 and semaglutide treatment on weight loss to the individual treatments. Rat pharmaco-behavioural experiments assessed whether GDF15 or semaglutide added to the satiating effects of orally gavaged food and exogenous cholecystokinin (CCK). A progressive ratio operant paradigm was used to examine whether GDF15 or semaglutide reduced feeding motivation. Pica behaviour (ie, kaolin intake) and conditioned affective food aversion testing were used to evaluate visceral malaise. Additionally, fibre photometry studies were conducted in agouti-related protein (AgRP)-Cre mice to examine whether GDF15 or semaglutide, alone or in combination with CCK, modulate calcium signalling in hypothalamic AgRP neurons.

RESULTS

Semaglutide reduced food intake by amplifying the feeding-inhibitory effect of CCK or ingested food, inhibited the activity of AgRP neurons when combined with CCK, reduced feeding motivation and induced malaise. GDF15 induced visceral malaise but, strikingly, did not affect feeding motivation, the satiating effect of ingested food or CCK signal processing. Combined GDF15 and semaglutide treatment produced greater food intake and body weight suppression than did either treatment alone, without enhancing malaise.

CONCLUSIONS

GDF15 and semaglutide reduce food intake and body weight through largely distinct processes that produce greater weight loss and feeding suppression when combined.

The CCR5Delta32 allele is associated with reduced liver inflammation in hepatitis C virus infection

CCR5Delta32 is a deletion mutation in the chemokine receptor CCR5. Liver inflammatory activity was found to be significantly reduced (P = 0.005) in Jewish Israeli patients infected with the hepatitis C virus (HCV) carrying the CCR5Delta32 allele. The CCR5Delta32 allele does not alter susceptibility to HCV infection; however, it may play a role in the progression and outcome of the disease.

Vitamin D reduces renal NaPi-2 in PTH-infused rats: complexity of vitamin D action on renal P(i) handling

Acute administration of dihydroxycholecalciferol [1,25(OH)(2)D(3)] blunts phosphaturia and increases urinary cAMP excretion in parathyroid hormone (PTH)-infused parathyroidectomized (PTX) rats. Because chronic administration of 1,25(OH)(2)D(3) enhances the phosphaturic response to exogenous parathyroid hormone despite blunting of urinary cAMP excretion, we have examined the expression of the renal cortex type II Na-P(i) cotransporter (NaPi-2) mRNA and protein in 1) chronic PTX Sabra rats, 2) PTX rats receiving a physiological dose of 1,25(OH)-2-D(3), 3) PTX rats receiving 35 ng/h of PTH, and 4) rats receiving both PTH and 1,25(OH)(2)D(3), for 7 days via osmotic minipumps. Our results confirm that there is increased phosphaturia in the PTH+1,25(OH)(2)D(3)-infused animals despite blunting of urinary cAMP excretion, a reduced filtered load of phosphate, and lack of a phosphaturic effect by 1,25(OH)(2)D(3) alone. Both PTH and 1,25(OH)(2)D(3) significantly reduced expression of renal cortex NaPi-2 mRNA and NaPi-2 protein, and the administration of PTH together with 1,25(OH)(2)D(3) had additive effects in further decreasing NaPi-2 mRNA and NaPi-2 protein levels. Expression of two other epithelial transporters, type 1 Na-sulfate and type 1 Na-glucose cotransporters, were not different between the groups, suggesting specificity of the effects of PTH and 1,25(OH)(2)D(3) on phosphate transport. The effect of chronic administration of 1,25(OH)(2)D(3) has not been noted previously, and the cellular mechanisms and signaling processes that mediate the decrease in NaPi-2 remain to be determined.

Regulation of ROMK and channel-inducing factor (CHIF) in acute renal failure due to ischemic reperfusion injury

BACKGROUND

Acute renal failure caused by ischemia followed by reperfusion is often associated with severe hyperkalemia. The present study was undertaken to characterize the effects of renal ischemia and reperfusion on plasma potassium (K) and on the gene expression of channel-inducing factor (CHIF), a putative K channel regulator, and of ROMK, the distal nephron secretory K channel.

METHODS

The following groups of rats were studied: (1) sham operated (sham); (2) after one hour of ischemia by bilateral renal artery clamping (I), and after one hour of ischemia; (3) one hour of reperfusion (I-R 1 h); (4) 24 hours of reperfusion (I-R 24 h); (5) 48 hours of reperfusion (I-R 48 h); and (6) 72 hours reperfusion (I-R 72 h). The expression of CHIF and ROMK was examined by Northern blot hybridization in renal cortex, medulla, and papilla and in the colon. The abundance of ROMK protein was determined in the renal cortex and medulla by immunoblotting.

RESULTS

Maximal plasma creatinine and potassium levels after ischemia and reperfusion were 470 +/- 16 micromol/L, P < 0.0001 versus sham, and 9.65 +/- 0.33 mmol/L, P < 0.0001 versus sham, respectively. The expression of CHIF was significantly down-regulated in the medulla and papilla, with a maximal decrease of 80% at 48 to 72 hours. In contrast, a most significant increase in CHIF mRNA expression (250% of baseline) was noted in the colon after 24 to 48 hours of reperfusion. ROMK expression was reduced in the cortex and was completely abolished in the medulla at 48 to 72 hours of reperfusion. Ischemia and reperfusion injury significantly decreased ROMK protein abundance to 10% of control in the medullary fractions.

CONCLUSIONS

These results suggest that down-regulation of renal CHIF and ROMK may contribute at least partly to the hyperkalemia of acute renal failure after ischemia and reperfusion, while CHIF up-regulation in the colon may act as a compensatory mechanism of maintaining K balance via increased K secretion.

Late-onset downregulation of NaPi-2 in experimental Fanconi syndrome

The pathogenesis of renal phosphate (Pi) leak in Fanconi syndrome is unknown. Disorders of apical membrane transporters, leaky apical membrane, depleted cellular Pi and ATP, and impaired sodium (Na) pumps have been proposed as underlying defects. The present study examined the role of type II Na-Pi cotransport system (NaPi-2) in experimental Fanconi syndrome in rats. Following a single injection of maleic acid (MA), 75 mg/kg body weight i.p., rats were sacrificed after 90 min, 4 h, and 24 h. Renal cortical expression of NaPi-2 mRNA was determined by Northern blotting, and brush border membrane (BBM) NaPi-2 protein by Western blotting. Increased urinary excretion of phosphate was demonstrated as soon as 90 min after MA injection, and was sustained at 4 and 24 h, NaPi-2 mRNA expression and NaPi-2 protein were not decreased after 90 min. NaPi-2 mRNA decreased after 4 h, while NaPi-2 protein decreased only at 24 h. Hence, the immediate phosphaturia in experimental Fanconi syndrome may be independent of NaPi-2 downregulation, possibly resulting from energy depletion or membrane dysfunction. The decrease in NaPi-2 mRNA expression and the subsequent NaPi-2 protein decrease may account for the second-phase phosphaturia.

Evaluating the effectiveness of student assistance programs in Pennsylvania

This article presents data from an evaluation of the Pennsylvania Student Assistance Program (SAP). Focusing on both program process and effectiveness, the evaluation was conducted to determine the overall efficacy of SAPs in Pennsylvania and, more specifically, how SAP is currently being implemented. Five data collection strategies were employed: statewide surveys of SAP team members and county administrators, focus groups, site visits, and the Pennsylvania Department of Education SAP Database. A total of 1204 individual team members from 154 school buildings completed the team member survey. Fifty-three county administrators completed the county administrator survey. Focus groups were comprised of SAP coordinators, school board personnel and community agency staff. Site visits were conducted at five schools. The findings of the evaluation indicate that SAP in Pennsylvania is being implemented as designed. Recommended is the development of benchmarks and indicators that focus on the best SAP practices and the extent to which various indicators of the effectiveness of SAP are occurring at appropriate levels.

1,25-Dihydroxyvitamin D3-induced calcium efflux from calvaria is mediated by protein kinase C

1,25-dihydroxyvitamin D3 (1,25(OH)2D3) is an important regulator of bone metabolism involved in both formation and resorption. Traditionally it was assumed that vitamin D receptors are intracellular. Recent data indicate that vitamin D may also act through a membrane receptor, specifically raising intracellular calcium and inositol 1,4,5 triphosphate. The present study was undertaken to explore further the mechanism(s) of vitamin D-induced bone resorption in cultured bone. 1,25(OH)2D3 induced a dose-dependent increase of calcium efflux from cultured bone. This increase was completely obliterated by inhibition of protein kinase C (PKC) with either staurosporine or calphostin C. In cultured rat calvariae, 1,25(OH)2D3 also induced a dose-dependent translocation of PKC from cytosol to membrane. The activation of PKC by 1, 25(OH)2D3 occurred following a 30-s incubation, peaked at 1 minute, and disappeared by 5 minutes. 1,25(OH)2D3 did not increase cAMP production in similarly cultured calvaria. These results suggest that the action of 1,25(OH)2D3 on calcium flux from cultured bone is mediated, in part, via activation of PKC.

Regulation of the ROMK potassium channel in the kidney

ROMK is a gene encoding inwardly rectifying adenosine triphosphate regulated K+ channels. Alternative splicing of ROMK exons yields several different transcripts, ROMK 1-3, that are differentially expressed along the nephron. Cloned ROMK channels expressed in Xenopus oocytes exhibit properties similar to those of the native low-conductance K+ secretory channels in cortical collecting duct and medullary thick ascending limb, as manifested by use of the patch-clamp technique. These similarities between the cloned and native channels suggest that ROMK represents the low-conductance secretory K+ channels in the kidney. We studied the role of dietary K+ and aldosterone in the regulation of ROMK mRNA expression in the rat kidney. K+ deficiency downregulated ROMK mRNA in cortex and medulla. Adrenalectomy markedly downregulated cortical ROMK, while it increased it in the medulla. In adrenalectomized rats K+ deficiency decreased ROMK mRNA in cortex and medulla similarly to intact rats. Na-K-ATPase subunits alpha1 and beta1 were regulated in parallel to the regulation of ROMK. In the medulla ROMK mRNA correlated highly with serum K+ and with the alpha1 and beta1 subunits of Na-K-ATPase. These results show that cortical ROMK expression is regulated by aldosterone and K+, while the medullary ROMK mRNA is regulated by serum K+, irrespective of aldosterone.

Role of down-regulated CHIF mRNA in the pathophysiology of hyperkalemia of acute tubular necrosis

Acute tubular necrosis (ATN) is associated with hyperkalemia. We have shown that the medulla is the main site of impaired sodium (Na+)/potassium (K+) pump activity in ATN. CHIF, a gene that evokes K+ conductance in oocytes, is regulated in the colon by aldosterone and in the kidney by K+ intake. It is assumed that CHIF has a role in K+ homeostasis. To characterize the impaired K+ handling in ATN, the effect of impaired renal function on CHIF mRNA expression in the kidney and colon was studied. Three groups of rats with glycerol-induced ATN were studied: (1) control group, (2) moderate-ATN group, and (3) severe-ATN group. Serum creatinine levels in the control group were 45+/-2.1 micromol/L; in the moderate-ATN group, 224.8+/-16.9 micromol/L; and in the severe-ATN group, 376.5+/-15.9 micromol/L. In the group with severe ATN, significant hyperkalemia (P < 0.001 v control group) was noted. The expression of CHIF mRNA in relative units (percentage of control) in the moderate-ATN group, in the medulla, papilla, and colon, was 16.3%+/-5.6% (P < 0.001), 94.2%+/-9.3% (P=not significant ), and 165.9%+/-11.1% (P < 0.001); and in the severe-ATN group was 11.1%+/-6.4% (P < 0.001), 73.7%+/-4% (P < 0.001), and 310.8%+/-27.3% (P < 0.001), respectively. These results show that (1) in both moderate and severe ATN, CHIF mRNA is dramatically reduced in the medulla, (2) in severe ATN, CHIF mRNA expression decreases in the papilla, and (3) CHIF mRNA is upregulated in direct relationship to the severity of ATN and to the levels of aldosterone in the colon. These results suggest that the hyperkalemia that occurs in severe ATN stems at least in part from the downregulation of CHIF mRNA in the kidney medulla and papilla. The compensatory increase in colonic CHIF mRNA is not sufficient to maintain normal serum K+ levels.

The ontogeny of the expression of K+ channel-like gene (CHIF) in the rat kidney papilla

Recently, an IsK-like potassium (K+) channel corticosteroid-induced gene (CHIF) was cloned. A high-K+ diet enhances, while a low-K+ diet decreases the expression of this gene. The major expression of CHIF in the adult rat kidney is in the papilla, where it is constitutive, in contrast to its inducibility by corticosteroids and a low-salt diet in the rat colon. In order to further understand the ontogeny of K+ clearance, we studied the presence of CHIF in the kidney papilla in different stages of rat development. Total RNA from rat kidney papillae of 1- to 3-day pre-labor unborn offspring, 2- to 3-day-old newborns, 10-day-old, 6-week-old, and 43-week-old rats underwent northern hybridization for CHIF and the alpha-subunit of the Na+-K+-ATPase mRNA. Minor expression of CHIF mRNA was found in fetal and newborn rat papillae, while older rats showed an age-related increase in gene expression. The expression of the alpha-sub unit of the Na+-K+-ATPase was not age related. We conclude that CHIF is present in the rat kidney papilla and the expression is related to age. The relative deficiency of CHIF in the newborn may be one of the factors responsible for the reduced K+ clearance in is period.

Differential regulation of ROMK expression in kidney cortex and medulla by aldosterone and potassium

This study explores the role of K+ and aldosterone in the regulation of mRNA of the ATP-sensitive, inwardly rectifying K+ channel, ROMK, in the rat kidney. K+ deficiency downregulated ROMK mRNA in cortex to 47.1 +/- 5.1% of control (P < 0.001) and in medulla to 56.1 +/- 3. 4% (P < 0.001). High-K+ diet slightly increased ROMK mRNA in medulla to 122 +/- 9% (P < 0.05 vs. control). Adrenalectomy (Adx) downregulated cortical ROMK mRNA to 30.7 +/- 6.8% (P < 0.001 vs. control), and increased it in medulla to 138 +/- 12.9% (P < 0.02 vs. control). In Adx rats, K+ deficiency decreased ROMK mRNA in cortex and medulla similar to intact rats. The alpha1- and beta1-Na-K-ATPase subunits were regulated in parallel to that of ROMK. In medulla, ROMK mRNA correlated with serum K+ concentration at R = 0.9406 (n = 6, P < 0.001) and alpha1-Na-K-ATPase mRNA at R = 0.9756 (n = 6, P < 0.001). ROMK2 also correlated with serum K+ concentration (R = 0.895; n = 6, P < 0.01). These results show that cortical ROMK expression is regulated by aldosterone and K+, whereas the medullary ROMK mRNA is regulated by serum K+.

Evidence for interference of vitamin D with PTH/PTHrP receptor expression in opossum kidney cells

Vitamin D counters the phosphaturic action of parathyroid hormone (PTH) in rats in vivo. The present study was undertaken to examine this interaction using monolayers of Opossum kidney (OK) cells. 32P uptake, cAMP generation, PTH/PTHrP receptor mRNA expression and intracellular Ca2+ [Ca2+]i were measured in (1) control cells, (2) cells exposed to PTH, (3) cells pretreated with 1, 25-dihydroxyvitamin D3 [1,25(OH)2D3], and (4) 1,25(OH)2D3-pretreated cells exposed to PTH. 32P uptakes were in (1) 5.00+/-0.20 (mean +/-SE), in (2) 2.30+/-0.14 (P<0.001 versus group 1), in (3) 4.80+/-0. 24 (P NS versus group 1) and in (4) 3.70+/-0.20 (P<0.001 versus group 2) nmol Pi/(mg.prot 10 mm). cAMP levels were in (1) 10+/-3, in (2) 210+/-8, in (3) 12+/-4, and in (4) 122+/-12 pmol cAMP/mg protein (P<0.001 versus group 2). PTH/PTHrP receptor mRNA expression was in relative units: (1) 100+/-0, (2) 99.5+/-6.2, (3) 68.7+/-2.6 (P<0.001 versus group 1), and (4) 34.8+/-3.3 (P<0.001 versus group 1). In groups 2 and 4 PTH induced equal transient increments in [Ca2+]i. These experiments demonstrate that the effect of vitamin D on phosphate transport is associated with a commensurate diminution in PTH/PTHrP receptor gene expression and PTH-induced cAMP formation but not with Ca2+ transients. Vitamin D per se does not affect 32P uptake or cAMP generation while it slightly decreased PTH/PTHrP receptor gene expression. These observations demonstrate that: (1) 1. 25(OH)2D3 directly antagonizes the effects of PTH on 32P uptake in OK cells, (2) this effect is mediated via inhibition of PTH-induced activation of AC/cAMP system, (3) the diminution in PTH-induced cAMP formation may stem at least in part from a decrease in the expression of PTH/PTHrP receptor mRNA.

Glycerol-induced acute renal failure attenuates subsequent HgCl2-associated nephrotoxicity: correlation of renal function and morphology

Glycerol induced acute renal failure (ARF) is known to attenuate subsequent mercuric chloride nephrotoxicity. This protection was evaluated in rats. Glycerol induced varying degrees of renal insufficiency. After 14 days, when serum creatinine (SCr) creatinine clearance (CCr) and fractional excretion of sodium (FENa) had returned to baseline, injection of mercuric chloride caused significantly milder renal insufficiency in recovered rats than in controls (SCr 356 +/- 46 vs. 475 +/- 19 mumol/L; CCr 0.12 +/- 0.02 vs. 0.02 +/- 0.02 mL/min, p < .05; and mortality 0 vs. 45%, respectively, p < .01). A striking finding was that the degree of renal insufficiency induced by mercuric chloride correlated inversely with the degree of renal insufficiency previously induced by glycerol (r = -0.496, p < .05 for SCr and CCr), but there was no correlation with other measures of previous renal function such as urine volume, sodium excretion, or FENa. Glycerol induced ARF also attenuated the renal toxicity of mercuric chloride injected 4 days after glycerol, before full recovery of renal function. The decrements in renal function after the two insults were also inversely related (r = -0.76, p < .01). A third renal insult with a second mercuric chloride injection after three weeks was still attenuated. However, after the third insult, there was no longer an inverse or any statistical relationship with previous measurements of renal function. Histopathology revealed a good correlation between peak Scr after glycerol, and percentage of tubules undergoing re-generation 14 days later (r = 0.97, p < .01). There was an inverse correlation between Scr after mercuric chloride (administered 14 days after glycerol) and percentage of tubular regeneration seen two days later (r = -0.79, p < .05). The correlations of SCr and CCr with regeneration was greater than the correlations with tubular necrosis, suggesting that the regenerative process is involved in the protection from repeated renal insults. In conclusion, glycerol-induced ARF attenuates subsequent mercuric chloride renal insult. The attenuation correlates directly with the initial glycerol-induced damage, so that the more severe the initial renal insufficiency, the milder the renal insufficiency following subsequent mercuric chloride. This protection can be seen as early as 4 days and also 14 days after previous renal insult. The degree of renal tubular regeneration correlates well with the protection seen, and probably plays a role in acquired renal resistance to repeated insults.

Differential regulation of CHIF mRNA by potassium intake and aldosterone

The channel-inducing factor (CHIF) is an epithelial-specific transmembrane protein, which is induced by aldosterone in distal colon (but not in kidney) and can evoke K+ conductance in Xenopus oocytes. The current study examined the possibility that CHIF participates in maintaining K+ balance by assessing its regulation during variations in K+ intake. In adrenal-intact rats, high-K+ diet stimulated, whereas K+ deficiency downregulated, CHIF mRNA both in kidney and colon. The downregulation of CHIF observed in rats fed a low-K+ diet for different periods of time closely correlated with a decrease in plasma K+ but also with changes in aldosterone levels. To differentiate between the two, modulation of CHIF has been studied in adrenalectomized rats with and without corticosteroid supplementation. These experiments have demonstrated that a low-K+ intake suppresses CHIF mRNA, irrespective of aldosterone level. On the other hand, the upregulation evoked by a high-K+ load is apparent only in adrenal-intact rats. This is despite the fact that infusing rats with aldosterone and corticosterone does not increase the expression of this mRNA in kidney. These findings may suggest a role for CHIF in preserving K+ balance.

Parathyroid hormone-induced calcium efflux from cultured bone is mediated by protein kinase C translocation

Activation of adenylate cyclase is believed to be the major intracellular mediator of bone resorption induced by parathyroid hormone (PTH), prostaglandins, and various bone resorbing cytokines. Studies have demonstrated a dissociation between PTH-induced bone resorption and adenosine 3',5'-cyclic monophosphate (cAMP) formation, as well as suggested a role of protein kinase C (PKC) in mediating in part the actions of PTH. We therefore investigated the relative contribution of the adenylate cyclase or PKC signal transduction pathways in mediating the PTH-induced net calcium release from cultured neonatal calvariae, an in vitro model of bone resorption. PTH (10(-11) to 10(-7) M) caused a dose-dependent increase in calcium efflux from cultured bone and activated both cAMP and PKC. To determine the role of each of these second messengers in mediating PTH-induced calcium release from bone, calvariae were preincubated with either the adenylate cyclase inhibitor SQ-22536 (10(-5) to 10(-4) M) or the PKC inhibitor staurosporine (10(-7) M) before coincubation with PTH. Compared with control, PTH caused a significant calcium efflux, whereas preincubation with SQ-22536 had no effect on basal calcium efflux and partially inhibited the calcium efflux caused by PTH. In contrast preincubation with staurosporine completely obliterated the PTH-induced calcium efflux. PTH is a potent stimulator of calcium release and activates both the cAMP and PKC signal transduction pathways in cultured bone. Inhibition of PTH-stimulated PKC activity completely abolished the PTH-induced calcium efflux from calvariae, whereas PTH-induced calcium efflux persisted despite adenylate cyclase inhibition. Thus the bone resorbing effect of PTH appears to be dependent predominantly on activation of PKC.

Aldosterone induction and epithelial distribution of CHIF

CHIF is a recently cloned, corticosteroid-induced gene which evokes K+ channel activity in oocytes (B. Attali, H. Latter, N. Rachamim, and H. Garty. Proc. Natl. Acad. Sci. USA 92: 6092-6096, 1995). To further characterize the possible role of this gene in epithelial ion transport, we have studied its epithelial distribution and hormonal induction. Northern hybridizations indicate that the zonal distribution of CHIF mRNA in kidney is: papilla >>medulla>> cortex. High levels of CHIF were also detected in a primary culture from inner medullary collecting duct (IMCD). Perfusing rats with < 20 nM aldosterone through osmotic minipumps evoked a 22.4 +/- 1.9-fold increase in colonic CHIF. A significant increase was observed 3 h after administrating the corticosteroid, but maximal response was detected only after a 72-h incubation. This response appears to be mineralocorticoid specific; perfusing or injecting rats with maximal doses of dexamethasone did not evoke a further increase in CHIF mRNA. In contrast, high levels of CHIF are expressed in kidney papilla and IMCD primary culture, irrespective of corticosteroid treatment. Thus, like the apical Na+ channel and the H(+)-K(+)-adenosinetriphosphatase, CHIF is mineralocorticoid induced in the colon but constitutively expressed in kidney.

Aldosterone-induced increase in the abundance of Na+ channel subunits

The highly selective, amilorideblockable Na+ channel is a major target to the natriferic action of the mineralocorticoid aldosterone. This rat epithelial Na+ channel (rENaC) has been recently cloned from colon and is composed of three homologous subunits denoted alpha-, beta-, and gamma-rENaC (C. M. Canessa, L. Schild, G. Buell, B. Thorens, L. Gautschi, J.-D. Horisberger, and B. C. Rossier. Nature Lond. 367: 463-467, 1994). We have tested the effects of corticosteroids on the abundance of mRNA coding for each subunit in kidney cortex and distal colon. Chronic treatment of rats with aldosterone or dexamethasone evoked in kidney cortex a small induction of alpha-rENaC and no change in beta- and gamma-rENaC. In distal colon, however, beta- and gamma-rENaC were strongly induced by either aldosterone or dexamethasone, whereas alpha-rENaC was constitutively expressed. Most of the aldosterone-induced increase in beta- and gamma-rENaC mRNA took place during 3-24 h after plasma aldosterone was elevated. A similar differential induction of rENaC subunits in kidney and colon was also evoked by a Na(+)-free diet. The effects of salt deprivation were reversed by resalinating rats with a half time of < 2 h, suggesting a high turnover rate of at least beta- and gamma-rENaC. The data are consistent with the possibility that induction of channel subunits contributes to the chronic but not the acute response to aldosterone in the colon. Such a mechanism is not likely to play a major role in cortical collecting ducts.

Dexamethasone enhances expression of mitochondrial oxidative phosphorylation genes in rat distal colon

Dexamethasone and aldosterone are major activators of Na+ reabsorption in tight epithelia. The genes whose expression mediates the steroid actions are mostly unknown. To identify such genes, we performed differential screening of a rat colon cDNA library with total 32P-labeled cDNA probes reverse transcribed from steroid-stimulated and steroid-depleted poly(A)+ RNA. Several cDNAs whose corresponding mRNA is enhanced two- to threefold after dexamethasone injection were identified. Partial sequencing indicated that four of them code for subunits of cytochrome-c oxidase and 16S mitochondrial mRNA. The dexamethasone-induced increase in mitochondrial RNA abundance could not be mimicked by a low-salt diet, found to increase plasma aldosterone from 1.0 +/- 0.1 to 12.8 +/- 1.4 nM. Induction of mitochondrial genes by adrenal steroids may serve to prevent limitation of transport by the ATP supply to the Na(+)-K+ pump under conditions of maximal stimulation of Na+ transport.

22-Oxacalcitriol does not interfere with parathyroid hormone-induced phosphaturia or cyclic-AMP excretion

The vitamin D analogue, 22-oxacalcitriol [22-oxa-1,25(OH)2 vitamin D3], has pleiotropic effects similar to or greater than calcitriol but has markedly fewer calcemic and phosphatemic effects. To test the hypothesis that the lesser phosphatemic effect of 22-oxacalcitriol is due, at least in part, to a lack of interference with the phosphaturic effect of parathyroid hormone, acute clearance experiments were performed in parathyroidectomized rats receiving continuous 1-34 parathyroid hormone (PTH) infusion together with 22-oxacalcitriol (200 pmol.100 g body weight-1.min-1) or vehicle. In contrast to the previously reported inhibitory effect of calcitriol on PTH-induced phosphaturia, fractional excretion of phosphorus increased similarly in both groups, from 0.05 +/- 0.01 to 0.26 +/- 0.02 (p < 0.01) in the vehicle-infused animals and from 0.04 +/- 0.01 to 0.24 +/- 0.02 (p < 0.01) in the 22-oxacalcitriol-treated rats (p between groups not significant [n.s.]). Urinary cyclic AMP excretion also increased similarly, from 45.5 +/- 5.2 to 101.6 +/- 21.6 (p < 0.01) and from 45.4 +/- 5.6 to 102.6 +/- 16.7 pmol/min (p < 0.01), respectively (p between groups n.s.). In search for a nongenomic mechanism that might account for the disparate effects of 22-oxacalcitriol and calcitriol, OK cells, which are reminiscent of the mammalian proximal tubule cell, were stimulated with calcitriol and 22-oxacalcitriol and free intracellular calcium concentration was determined. At high concentrations, calcitriol caused a dose-dependent increase in [Ca2+]i; 22-oxacalcitriol had no effect on [Ca2+]i at any concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of myo-inositol supplementation on the development of renal pathological changes in the Cohen diabetic (type 2) rat

A lower concentration of intracellular myo-inositol has been implicated in the development of diabetic nephropathy. This was based on short-term studies showing that early administration of aldose reductase inhibitors or myo-inositol supplementation reduces increased glomerular filtration rate and partly reduces increased urinary albumin excretion in streptozotocin diabetic rats. We studied the effect of long-term (4 months) administration of 1% myo-inositol supplement to the Cohen diabetic (type 2) rat on the development of nephropathy and renal Na(+)-K(+)-ATPase. This treatment reduced the increased renal Na(+)-K(+)-ATPase activity but had no effect on blood glucose levels, body weight, increased kidney weight, or creatinine clearance and did not prevent or reduce the development of renal glomerular pathology. There was no correlation between the level of Na(+)-K(+)-ATPase activity and the degree of nephropathy. It is possible that the renal pathological changes are due to metabolic and humoral factors resulting from hyperglycaemia, other than myo-inositol depletion. The fact that myo-inositol treatment had no effect on the development of renal pathological changes but was shown to have a beneficial effect on restoring impaired conduction velocity and on the disruption of structural elements in the nerve indicates that the effect of the biological changes ensuing from hyperglycaemia vary in different tissues depending on local conditions.

Renal tubular Na(+)-K(+)-ATPase in diabetes mellitus: relationship to metabolic abnormality

This study was undertaken to evaluate the effect of long-term diabetes on Na(+)-K(+)-ATPase in isolated nephron segments in five groups of rats: 1) controls of 7 wk duration (7 WD), 2) diabetes mellitus (DM) of 7 WD, 3) DM of 7 WD treated with insulin replacement, 4) DM rats of 25 WD, and 5) control rats of 25 WD. The blood glucose (BG) values in the first three groups were 123 +/- 9, 450 +/- 25, and 302 +/- 30 mg/dl; the glomerular filtration rate (GFR) was 1.34 +/- 0.08, 1.80 +/- 0.10, and 1.77 +/- 0.08 ml/min; and urinary sodium excretion was 0.94 +/- 0.05, 1.76 +/- 0.10, and 1.40 +/- 0.07 mu eq/min. Na(+)-K(+)-ATPase in group 2 increased in all segments studied (P < 0.001, group 1 vs. 2 for all). In group 3, Na(+)-K(+)-ATPase normalized in proximal convoluted (PC), proximal straight (PS), and distal convoluted (DC) tubules (P < 0.001, group 2 vs. group 3 for all), whereas in the outer medullary thick ascending limb (OMTAL) the correction was partial and in the CTAL and CCD there was no correction. In group 4 BG was 420 +/- 20 mg/100 ml compared with 123 +/- 9 in group 5 (P < 0.001), and GFR was 1.19 +/- 0.11 ml/min vs. 1.15 +/- 0.11 in group 5 (P = not significant).(ABSTRACT TRUNCATED AT 250 WORDS)

Indomethacin and sodium retention in the rat: role of inhibition of prostaglandin E2 synthesis

1. To further explore the Na(+)-retaining effect of indomethacin along the whole length of the nephron, the Na(+)-K(+)-ATPase activity of isolated tubules from indomethacin-pretreated rats was compared with that of tubules isolated from intact rats and exposed directly to prostaglandin E2. 2. Indomethacin increased Na(+)-K(+)-ATPase activity in the proximal convoluted tubule (+24%, P < 0.001 versus control), proximal straight tubule (+75%, P < 0.001 versus control), medullary thick ascending limb (+68%, P < 0.001 versus control), cortical thick ascending limb (+7%, not significant) and cortical collecting duct (+18%, P < 0.025 versus control). In contrast, in the distal convoluted tubule indomethacin decreased Na(+)-K(+)-ATPase activity by -42% (P < 0.001 versus control). 3. Indomethacin also strongly increased Na(+)-K(+)-ATPase activity in the cortical collecting duct of adrenalectomized rats. 4. In isolated tubules from control rats, prostaglandin E2 reduced Na(+)-K(+)-ATPase activity in the proximal convoluted tubule (-33%, P < 0.05), proximal straight tubule (-60%, P < 0.001), medullary thick ascending limb (-43%, P < 0.001), cortical thick ascending limb (-25%, P < 0.001) and cortical collecting duct (-45%, P < 0.001) and in the distal convoluted tubule, prostaglandin E2 increased Na(+)-K(+)-ATPase activity (+32%, P < 0.05). 5. That these changes in Na(+)-K(+)-ATPase activity in indomethacin-pretreated rats and prostaglandin E2-treated controls are similar in magnitude but occur in opposite directions suggests that the response to indomethacin is mediated by inhibition of prostaglandin E2 synthesis in the nephron. In the cortical collecting duct the effect of indomethacin is aldosterone-independent.

Na,K-ATPase in isolated nephron segments in rats with experimental heart failure

To characterize renal transport of Na+ in heart failure, urinary Na+ excretion (UNaV), aldosterone levels, and Na,K-ATPase activity in isolated nephron segments were determined in three groups: control rats, rats with heart failure and moderate sodium retention, and rats with heart failure and severe sodium retention. Heart failure was induced by a fistula between the aorta and vena cava. For the control group, UNaV was 0.66 +/- 0.04 (mean +/- SEM) mueq/min, and aldosterone was 18.4 +/- 3.5 ng%. Na,K-ATPase activity (in 10(-11) mol/mm/min) was 28.4 +/- 1.1 in the proximal convoluted tubule, 23.3 +/- 1.0 in the proximal straight tubule, 37.4 +/- 1.9 in the medullary thick ascending limb, 40.2 +/- 1.9 in the cortical thick ascending limb, 43.2 +/- 2.2 in the distal convoluted tubule, and 20.5 +/- 0.9 in the cortical collecting duct. For the group with moderate heart failure, UNaV was 0.35 +/- 0.02 (p less than 0.001 versus control), and aldosterone was 15.9 +/- 4.4 (p = NS versus control). Na,K-ATPase activity was unchanged in the proximal convoluted tubule, proximal straight tubule, medullary thick ascending limb, and cortical collecting duct, but it increased in the cortical thick ascending limb to 57.7 +/- 3.1 (p less than 0.001 versus control) and decreased in the distal convoluted tubule to 35.3 +/- 1.2 (p less than 0.005 versus control). For the group with severe heart failure, UNaV was 0.029 +/- 0.016 (p less than 0.001 versus control), and aldosterone was 186.0 +/- 14.8 (p less than 0.001 versus control).(ABSTRACT TRUNCATED AT 250 WORDS)

Opposite effects of diabetes on nephrotoxic and ischemic acute tubular necrosis

The effect of streptozotocin-induced diabetes mellitus on two different models of acute tubular necrosis (ATN), was studied: (i) the nephrotoxic model of HgCl2-induced ATN and (ii) the ischemic model of renal artery clamping for 60 min. Induction of ATN with HgCl2 in normal rats decreased CrCl from 0.67 +/- 0.05 to 0.1 +/- 0.019 ml/min (P less than 0.001) after 24 hr, and it deteriorated further to 0.03 +/- 0.013 ml/min after 48 hr; whereas, in the diabetic rats, HgCl2 decreased CrCl from 0.98 +/- 0.11 only to 0.31 +/- 0.037 ml/min (P less than 0.0001), but CrCl recovered to 0.50 +/- 0.08 ml/min after 48 hr. Bilateral clamping of renal arteries for 60 min in control and diabetic rats extremely decreased CrCl in both groups. Twenty-four hours after clamping, two of nine rats from the diabetic group died, whereas none from the control group died. Forty-eight hours after clamping, all nine rats from the diabetic group died, whereas only two rats from the control group died, and in the four surviving rats CrCl recovered slightly. Our study shows that streptozotocin-induced diabetes could not confer a general protection against ATN. It was protective against a nephrotoxic insult but aggravated the ischemic insult. An attempt to reconcile these discrepant effects is made in the Discussion.

Reduced Na-K-ATPase in distal nephron in glycerol-induced acute tubular necrosis

To further characterize changes in tubular Na-K-ATPase in acute tubular necrosis (ATN), segmental analysis was performed in rat nephrons. Na-K-ATPase was assayed in the following segments: proximal convolution (PC), proximal straight (PS), outer medullary thick ascending limb (MTAL), cortical thick ascending limb (CTAL), distal convolution (DC) and cortical collecting duct (CCD) in three groups of rats: 1.) intact; 2.) moderate non-oliguric ATN; and 3.) severe oliguric ATN. GFR and CNa/GFR X 100 were in group 1 0.80 +/- 0.05 ml/min and 0.68 +/- 0.06, in group 2 0.14 +/- 0.02 and 1.46 +/- 0.35, and in group 3 0.04 +/- 0.01 and 0.46 +/- 0.15, respectively. Na-K-ATPase in PC and PS were similar in all three groups. Na-K-ATPase levels were in MTAL: in group 1 37 +/- 2 X 10(-11) mol/mm/min, in group 2 20 +/- 1 X 10(-11), P less than 0.001 versus group 1, and in group 3 24 +/- 2 X 10(-11), P less than 0.001 versus group 1. In CTAL Na-K-ATPase levels were: in group 1 40 +/- 2 X 10(-11), in group 2 33 +/- 1 X 10(-11), P less than 0.001 versus group 1, and in group 3 27 +/- 2 X 10(-11), P less than 0.001 versus groups 1 and 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal sodium handling and stimulation of medullary Na-K-ATPase during blockade of prostaglandin synthesis

The effect of suppression of prostaglandin synthesis on renal sodium handling and microsomal Na-K ATPase was studied in control and indomethacin treated intact rats maintained on a normal sodium diet (series A) and chronically salt loaded (series B). Indomethacin administration resulted in a decreased GFR and a significantly depressed urinary excretion and an increased fractional reabsorption of sodium in animals fed the normal sodium diet or chronically salt loaded. In rats maintained on a normal Na diet, the activity of the renal medullary Na-K ATPase after indomethacin was 206.3 +/- 6.4 ug Pi/mg protein, i.e. significantly higher as compared with the enzyme activity in the medullary renal fraction from control animals in which it averaged 148 +/- 7.79 ug Pi/mg protein (p less than 0.001). While after chronic salt load a similar increment in the activity of renal medullary Na-K ATPase was observed, no additional stimulation was elicited by subsequent indomethacin administration. The addition of exogenous PGE2, 0.1 mM to microsomal fractions obtained from kidneys of normal rats, was associated with a moderate suppression of the medullary Na-K-ATPase activity, from a basal level of 170 +/- 16 to 151.3 +/- 13 umol Pi/mg protein/hr (p less than 0.005). In isolated segments of medullary thick ascending limb of Henle's loop (MTAL) addition of PGE2 to the incubation medium resulted in a significant inhibition of Na-K ATPase from 37.2 +/- 2 to 21.25 +/- 1.17 x 10(-11) mol/mm/min (p less than 0.0001). These findings suggest that the increased renal Na reabsorption after inhibition of PG synthesis might be related, at least partly, to stimulation of medullary Na-K ATPase. In parallel, the reported natriuretic effect of prostaglandins might imply a direct inhibitory effect of these mediators on renal Na-K ATPase.

Effect of indomethacin in vivo and PGE2 in vitro on MTAL Na-K-ATPase of the rat kidney

We have previously shown that prostaglandin synthesis inhibition in rats which reduces urinary excretion of PGE2 and sodium, is associated with increased Na-K-ATPase activity in renal medulla. To further characterize this interaction studies were performed in isolated segments of medullary thick ascending limb of Henle's loop (MTAL) in rats. The effect of pretreatment with indomethacin in vivo and incubation with PGE2 in vitro on MTAL Na-K-ATPase activity was studied. Pretreatment of rats with indomethacin increased Na-K-ATPase of the MTAL from 37.2 +/- 2.0 x 10(-11) mol/mm/min in controls to 62.7 +/- 2.2 (p less than 0.001) while Mg-ATPase was only slightly decreased. Incubation of MTAL Na-K-ATPase from indomethacin pretreated rats with increasing concentration of PGE2 in vitro dose dependently inhibited MTAL Na-K-ATPase activity with no effect on Mg-ATPase. Baseline Na-K-ATPase was 62.7 +/- 2.2 in MTAL from indomethacin pretreated rats and decreased to 36.9 +/- 1.4 (p less than 0.001) with 1 microM of PGE2, to 26.5 +/- 2.3 (p less than 0.001) with 10 microM PGE2 and to 22.0 +/- 1.0 (p less than 0.001) with 100 microM PGE2. 100 microM PGE2 in the incubation medium inhibited MTAL Na-K-ATPase of intact rats from 37.2 +/- 2 to 21.3 +/- 1.2 (p less than 0.001) and completely abolished the indomethacin induced increase in MTAL Na-K-ATPase. The results of this study show stimulation of MTAL Na-K-ATPase by pretreatment with indomethacin in vivo and, direct inhibition of MTAL Na-K-ATPase by PGE2 in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

Glycerol-induced acute renal failure in the rat: the protective effect of unilateral nephrectomy

Studies were performed to evaluate the effect of unilateral nephrectomy on glycerol-induced acute renal failure in the rat. Normal rats were subjected to either sham uninephrectomy (n = 43) or right uninephrectomy (n = 53). The functional compensation of the remaining kidney was followed after 1 and 2 weeks. Fourteen days after the operation, acute renal failure was induced by injection of 50% glycerol solution to both groups. Uninephrectomised rats developed a lesser degree of renal failure compared to sham-operated rats. Forty-eight hours after glycerol injection, PCr of uninephrectomised rats was 260 +/- 22 mumol/l compared with 338 +/- 26 in sham-operated rats (P less than 0.0125) and CCr in uninephrectomised rats was greater (0.10 +/- 0.01 ml/min vs 0.07 +/- 0.01; P less than 0.025) in sham rats. Uninephrectomised rats had significantly greater recovery of CCr compared to sham rats at 24 h (20.1% +/- 2.3 vs 13.1% +/- 2.2, P less than 0.025) and at 48 h (32.1% +/- 3.3 vs 19.2% +/- 3.3, P less than 0.005) after glycerol injection. FENa was significantly less in uninephrectomised rats: 0.96 +/- 0.16% vs 2.25 +/- 0.05% (P less than 0.025) in sham rats 24 h post glycerol. Urinary excretion of K+ was greater in rats following uninephrectomy compared to sham rats both after 24 h and 48 h post glycerol (P less than 0.01), accompanied by lower plasma potassium (P less than 0.05). A correlation coefficient (r) of 0.793 was observed between urinary potassium excretion rate and percentage recovery of CCr.(ABSTRACT TRUNCATED AT 250 WORDS)

The in vivo and in vitro effect of calmodulin antagonists on the renal actions of 25(OH) vitamin D3 in the rat

Previous work from this laboratory has demonstrated that 25(OH) vitamin D3 [25(OH)D3] acutely suppresses the phosphaturic action of parathyroid hormone (PTH) and interferes with the PTH-induced activation of adenylate cyclase (AC). Calmodulin inhibitors block vitamin D-induced Ca2+ transport in the gut and phosphorus uptake in renal BBMV's. We have examined whether calmodulin antagonists affect the renal action of 25(OH)D3. Acute clearance experiments were performed in PTH-infused parathyroidectomized rats receiving 25(OH)D3 after pretreatment with trifluoperazine (TFP) or promethazine (P). In vitro PTH-induced activation of renal AC was also studied in membrane preparations from pretreated rats in the presence of 25(OH)D3. 25(OH)D3 reduced the PTH-stimulated increase in fractional excretion of phosphorus (CP/CIn) from 0.292 +/- 0.024 to 0.195 +/- 0.018 (p less than 0.005) and urinary cAMP from 149.3 +/- 20.3 to 78.1 +/- 10.4 pmol/min (p less than 0.01) and also blunted AC activation in vitro. TFP but not P abolished the effects of 25(OH)D3 both in vivo and in vitro. R 24571 also abolished the in vitro effect of 25(OH)D3. Thus, (1) TFP abolishes both the antiphosphaturic and the AC/cAMP-related actions of 25(OH)D3, (2) P does not have these effects, and (3) R 24571 abolishes the in vitro effect of 25(OH)D3. These results suggest that the antiphosphaturic effect of 25(OH)D3 acting via the AC/cAMP system may be calmodulin dependent.

Inhibition of thick ascending limb Na+-K+-ATPase activity in salt-loaded rats by furosemide

To evaluate the role of increased thick ascending limb Na+-K+-ATPase activity in rats undergoing hypertonic salt loading, the following groups of rats were studied: 1) control rats, 2) rats receiving an oral hypertonic Na load for 7 days, and 3) rats receiving the same oral Na load as in group 2 plus a daily injection of 10 mg/100 g of furosemide ip for 7 days. Salt loading (group 2) was associated with increased glomerular filtration rate (GFR) and hence an increased filtered load of sodium. Plasma aldosterone levels were markedly decreased. Na+-K+-ATPase was unchanged in the proximal tubule [convoluted (PC) and straight (PS)], increased in the thick ascending limb of Henle's loop [outer medullary (OMTAL) and cortical (CTAL)] and decreased in the distal nephron [distal convoluted tubule (DCT) and cortical collecting duct (CCD)]. The renal corticomedullary gradient of solutes was markedly increased in the salt-loaded group. Salt loading plus furosemide for 7 days (group 3) was associated with severe dehydration and hypernatremia. GFR as well as plasma aldosterone levels were unchanged compared with control. Na+-K+-ATPase was significantly increased in the proximal tubule (PC and PS), markedly decreased in the thick ascending limb of Henle's loop (OMTAL and CTAL), increased in the DCT and unchanged in the CCD. The increase in the corticomedullary gradient caused by salt loading per se was abolished by treatment of salt-loaded rats with furosemide. These results indicate that treatment with furosemide prevents the preservation of water balance and of normal body fluid tonicity in rats undergoing hypertonic Na loading.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced glomerular filtration and Na+-K+-ATPase with furosemide administration

To evaluate the effect of furosemide on kidney function, glomerular filtration rate (GFR), urinary Na excretion (UNaV), Na reabsorption (NAR), and Na+-K+-ATPase in isolated nephron segments were measured in 1) rats treated with furosemide 10 mg X 100 g-1 X 24 h-1 ip for 7 days, and 2) rats receiving an oral Na load for 12 days. In furosemide-treated rats, GFR rose from 0.61 +/- 0.03 (mean +/- SD) to 0.83 +/- 0.06 ml/min (P less than 0.01), UNaV rose from 904 +/- 71 to 1,402 +/- 85 mueq/day (P less than 0.001), and net NAR rose from 87.5 +/- 3.7 to 116.7 +/- 9.0 mueq/min (P less than 0.01). Na+-K+-ATPase remained unchanged in the proximal convoluted tubule (PCT), proximal straight tubule (PST), cortical thick ascending limb of Henle's loop (cTALH), and medullary thick ascending limb of Henle's loop (mTALH), but was increased in the distal convoluted tubule (DCT) and in cortical collecting duct (CCD) from 48.5 +/- 1.2 to 75.3 +/- 0.7 (P less than 0.001) and from 18.6 +/- 0.7 to 27.1 +/- 2.7 (P less than 0.02) X 10(-11) mol X mm-1 X min-1, respectively. In Na-loaded rats GFR rose from 0.61 +/- 0.04 to 0.86 +/- 0.03 ml/min (P less than 0.001), UNaV rose from 1,064 +/- 118 to 18,532 +/- 2,045 mueq/day (P less than 0.001), net NAR from 88.1 +/- 3.0 to 107.8 +/- 3.9 mueq/min and Na-K-ATPase in the mTALH rose from 40.3 +/- 1.4 to 56.2 +/- 2.11 (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of bicarbonate and phosphate on renal phosphate leak in experimental Fanconi syndrome

The role of acidosis in the renal phosphate leak in Fanconi syndrome (FS) was studied in maleate-induced FS in rats. Clearance studies were performed in the following groups: 1) intact rats served as control, 2) rats with maleate-induced FS, 3) rats with FS receiving intravenous bicarbonate (HCO3-), 4) intact rats receiving intravenous 0.03 N HCl (inducing acidosis similar to that of Group 2), 5) rats with FS receiving intravenous phosphate buffer and NaCl, and 6) rats with FS receiving intravenous phosphate buffer and bicarbonate similar to Group 3. In Group 2 serum pH and fractional excretion of phosphate (CP/GFR) averaged 7.31 +/- 0.08 (mean +/- SE) and 1.00 +/- 0.06, respectively, and differed significantly from Group 1, in which the corresponding values were 7.41 +/- 0.01 and 0.12 +/- 0.02, respectively. In Group 3, intravenous HCO3- corrected pH to 7.43 +/- 0.01 and reduced CP/GFR to 0.33 +/- 0.05, both results were different from the corresponding rates in Group 2 (P less than 0.0005). In Group 4, intravenous HCl reduced serum pH to 7.31 +/- 0.02 (P not significant as compared with Group 2) and increased CP/GFR to 0.186 +/- 0.030, the latter was higher than CP/GFR in control rats (P less than 0.01) but was lower than that in HCO3- -treated FS rats. In Group 5 serum pH was 7.31 +/- 0.021, similar to Group 2. CP/GFR was 0.84 +/- 0.031, significantly lower than in Group 2 (P less than 0.05). In Group 6 serum pH was 7.43 +/- 0.013 and CP/GFR was 0.86 +/- 0.044.(ABSTRACT TRUNCATED AT 250 WORDS)

24,25(OH)2D3 enhances the calcemic effect of 1,25(OH)2D3 in PTX rats

The effect of 24,25(OH)2D3 on 1,25(OH)2D3-induced hypercalcemia was studied in parathyroidectomized (PTX) rats for 10 days. Serum (S) and urinary Ca excretion (UCaV) were measured in (a) control rats, (b) rats receiving a daily sc injection of 54 ng 1,25(OH)2D3, (c) rats receiving 24,25(OH)2D3 in the same dose and same manner, and (d) rats receiving 1,25(OH)2D3 + 24,25(OH)2D3. Our results show that (i) 24,25(OH)2D3 alone does not increase SCa2+ in PTX rats, (ii) combined administration of 1,25(OH)2D3 + 24,25(OH)2D3 enhances the hypercalcemic response to 1,25(OH)2D3 without a parallel increase in UCaV, (iii) combined administration of 1,25(OH)2D3 + 24,25(OH)2D3 reduces the rise in urinary excretion of Ca2+ compared with that of rats receiving 1,25(OH)2D3 alone for 10 days, and (iv) these alterations are independent of parathyroid hormone.

Sodium handling by the Sabra hypertension prone (SBH) and resistant (SBN) rats

The acute and chronic renal handling of salt was evaluated in age matched Sabra hypertension-prone (SBH) and hypertension-resistant (SBN) rats. Acute oral (4 ml/100 g) and intravenous (3.3 ml/100 g) isotonic saline loading in unanesthetized normotensive animals maintained on normal diet elicited a significantly lesser diuretic and natriuretic response in SBH than in SBN. Intermittent studies in metabolic cages in rats aged 5 to 21 weeks showed that both strains consumed similar amounts of salt but that SBH excreted significantly less urinary sodium than SBN (F = 40, p less than 0.001). Twenty four hour clearance studies showed a similar filtered sodium load in the two strains but a lower total and fractional sodium excretion in SBH, suggesting increased tubular reabsorption. Under conditions of water diuresis, free water clearance was similar in the two strains, suggesting the site for disparate tubular sodium handling to be distal to the thick medullary ascending limb of the loop of Henle. Acute oral saline loading and long term studies in metabolic cages in rats prepared with deoxycorticosterone-acetate (doca) and salt showed no significant differences in sodium excretion between hypertensive SBH and normotensive SBN. These findings indicate disparate renal sodium handling between SBH and SBN rats, already apparent before the onset of hypertension, which dissipates during doca-salt treatment.

Enhanced renal tubular ouabain-sensitive ATPase in streptozotocin diabetes mellitus

The effect of streptozotocin-induced diabetes mellitus on rat renal ouabain-sensitive ATPase in six distinct nephron segments was studied. Twenty-four hours after administration of streptozotocin, blood glucose increased threefold (P less than 0.001), and glucosuria was evident. Aldosterone levels increased almost twofold (P less than 0.001). Ouabain-sensitive ATPase increased in the proximal segments PC (proximal convoluted tubule) and PS (proximal straight tubule) by 43 and 62%, respectively, (P less than 0.001) and CD (cortical collecting duct) ouabain-sensitive ATPase increased 77% (P less than 0.001). Ouabain-sensitive ATPase in the cortical (CTAL) and medullary (MTAL) thick ascending limbs of Henle's loop and in the DC (distal convoluted tubule) remained unchanged after 24 h of streptozotocin administration. Eight days after streptozotocin administration, when glomerular filtration rate (GFR) was already markedly elevated, ouabain-sensitive ATPase remained increased in the PC, PS, and CD but was significantly less compared with the activity after 24 h (P less than 0.05), whereas in the CTAL and MTAL a marked increase in ouabain-sensitive ATPase occurred by 54% in the CTAL and 65% in the MTAL (P less than 0.001). Aldosterone levels remained elevated compared with control but less than after 24 h. Pretreatment with deoxycorticosterone acetate abolished the increase in ouabain-sensitive ATPase in the CD. These findings show that streptozotocin-induced diabetes mellitus in the rat is associated with a substantial increase in ouabain-sensitive ATPase activity along most of the nephron. This increase in enzyme activity may represent a mechanism of physiological adaptation of the nephron to maintain electrolyte homeostasis in diabetes in face of the increased GFR and osmotic diuresis.

24,25(OH)2D3 enhances the calcemic effect of 1,25(OH)2D3

The effect of 24,25(OH)2D3 on 1,25(OH)2D3-induced hypercalcemia was studied in normal rats. Serum (S) levels and urinary excretion of Ca2+ (UCaV) were measured in (a) control rats, (b) rats receiving a daily sc injection of 54 ng 1,25(OH)2D3, (c) rats receiving 24,25(OH)2D3 in the same dose and same manner, and (d) rats receiving 1,25(OH)2D3 + 24,25(OH)2D3. The animals were housed in metabolic cages and 24-hr urine specimens were collected. After 24 hr SCa2+ increased similarly with 1,25(OH)2D3 and with 1,25(OH)2D3 + 24,25(OH)2D3, while 24,25(OH)2D3 alone did not change SCa2+. UCaV after 24 hr increased significantly less (P less than 0.025) with 1,25(OH)2D3 + 24,25(OH)2D3 than with 1,25(OH)2D3 alone. After 5 days of 1,25(OH)2D3, SCa2+ rose from 5.1 +/- 0.15 to 6.29 +/- 0.08 whereas 1,25(OH)2D3 + 24,25(OH)2D3 effected a greater increase in SCa2+ up to 6.63 +/- 0.09 (P less than 0.01). 24,25(OH)2D3 alone did not change SCa2+. UCaV after 5 days of treatment rose similarly with 1,25(OH)2D3 and with 1,25(OH)2D3 + 24,25(OH)2D3. After 10 days of 1,25(OH)2D3 SCa2+ was 6.17 +/- 0.15 meq/liter while with the combination SCa2+ rose to 6.74 +/- 0.2 (P less than 0.025). 24,25(OH)2D3 alone did not change SCa2+. These results show that (a) 24,25(OH)2D3 alone does not alter SCa2+ in normal rats, (b) combined administration of 1,25(OH)2D3 + 24,25(OH)2D3 enhances the hypercalcemic response to 1,25(OH)2D3 without a parallel increase in UCaV, and (c) it is suggested that the effect of 24,25(OH)2D3 on serum Ca2+ level, at least partly, may result from its hypocalciuric effect.

The effect of acute saline volume expansion on renal Na-K-ATPase

To examine the role of Na-K-ATPase in the natriuresis that occurs after acute extracellular volume expansion, we performed acute clearance experiments and in vitro analysis of renal microsomal ATPase activity in rats receiving intravenous 0.9% sodium chloride (0.1 ml/100 g bw/min). Despite increased absolute reabsorption of filtered sodium (196 +/- 8.1 vs. 165 +/- 11.4 uEq/min, p less than 0.05), renal medullary microsomal Na-K-ATPase activity was decreased from 134 +/- 5.9 to 110 +/- 6.3 pmol Pi/mg protein/hour (p less than 0.02). No changes occurred in cortical or papillary regions and Mg-ATPase was unaffected. Similar results were obtained after adding 4 mEq/l potassium chloride to the infusion to prevent any fall in serum K+. These data suggest that a considerable percentage of sodium reabsorption is suppressed in acutely volume expanded animals and it is proposed that this is mediated by inhibition of medullary Na-K-ATPase.

Water handling by the sabra hypertension prone (SBH) and resistant (SBN) rats

The renal handling of water by SBH and SBN rats was evaluated under basal conditions and following various intervention procedures. During 17 weeks of unrestricted water intake, SBH rats drank less water and excreted less urine with a higher osmolality than SBN. The differences in urine volume and osmolality persisted during 2 weeks of paired water intake. Acute water loading elicited comparable dilution of the urine in the two strains. Water deprivation for 48 h resulted in a marked rise in urine osmolality, which tended to be higher in SBN. Administration of exogenous vasopressin in water loaded animals caused a similar rise in urine osmolality. Papillary solute and urea content was higher in SBH than in SBN, but comparable in water loaded animals. The results show that although SBH differ from SBN rats in the handling of water under basal conditions, their renal diluting and concentrating capacity is comparable at extreme conditions. GFR and RBF were equal in both strains. The data suggest that SBH rats have increased renal water reabsorption as compared to SBN, which may be mediated by ADH, PG or other mechanisms. This characteristic may be related to their propensity to develop hypertension.

The effect of acutely reduced plasma osmolality on acute renal failure in rats

The present study was designed to evaluate the effect of acute fall in plasma osmolality in three models of acute tubular necrosis in rats: (a) glycerol, (b) arterial clamping and (c) mercuric chloride. Plasma osmolality was reduced by a water loading during a mild anaesthesia from 305 +/- 7 to 270 +/- 12 mosmol/kg of water (P less than 0.01). In the ischaemic models of acute tubular necrosis (glycerol and arterial clamping), during the first 24 h in rats with reduced plasma osmolality, the respective creatinine clearance rates (CCR), 0.04 +/- 0.02 and 0.06 +/- 0.04 ml/min, were strikingly lower than those in rats with normal osmolality, 0.21 +/- 0.03 and 0.26 +/- 0.06 ml/min (P less than 0.001) respectively. The control CCR were 0.65 +/- 0.07 and 0.62 +/- 0.07 ml/min respectively. During the second day after induction of ischaemic (glycerol and arterial clamping) acute tubular necrosis, rats with reduced plasma osmolality exhibited a similar worsening in CCR as on the first day, when compared with that in rats with normal osmolality. In rats with acute tubular necrosis induced with mercuric chloride reduction in plasma osmolality did not aggravate the severity of renal failure. These results show that acute fall in plasma osmolality worsens the renal failure in the ischaemic but not in the nephrotoxic models of acute tubular necrosis.

Parallel changes in red blood cell and renal Na-K-ATPase activity in adrenal and electrolyte disorders in the rat

To compare the activity of Na-K-ATPase in the red blood cells (RBCs) and in renal tissue in disorders of Na+ metabolism, the following groups of rats were studied: 1) control, intact rats, 2) adrenalectomized (ADX) rats, 3) intact rats treated with DOCA, 4) ADX DOCA-treated rats, 5) intact salt-loaded rats, 6) ADX salt-loaded rats, 7) intact dexamethasone-treated rats (DEXA), and 8) ADX DEXA-treated rats. After adrenalectomy (group 2) serum Na+ decreased and serum K+ increased. Renal Na-K-ATPase in cortex, medulla and papilla of the control group was 44 +/- 2.7 mumol Pi/mg prot/h, 128.2 +/- 5.9 and 44 +/- 3.2 respectively and in group 2 the enzyme activity was 32.5 +/- 2.0 (P less than 0.005), 81.7 +/- 4.5 (P less than 0.001) and 23.6 +/- 1.9 (P less than 0.001) respectively. RBCs Na-K-ATPase of control animals was 2.82 +/- 0.19 mumol Pi/mg prot/h, while in group 2 the activity was 1.43 +/- 0.24 (P less than 0.001). DOCA treatment of ADX rats (group 4) normalized serum electrolytes and Na-K-ATPase activity in the renal cortex and papilla and in the RBCs. In the renal medulla the correction by DOCA was only partial. Salt loading of ADX rats (group 6) normalized serum electrolytes and Na-K-ATPase activity in the renal medulla and RBCs. Salt loading of normal rats increased RBC Na-K-ATPase to 3.72 +/- 0.36 (P less than 0.02) and medullary Na-K-ATPase to 185.6 +/- 9.8 (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Na-K-ATPase in isolated rabbit tubules after unilateral nephrectomy and Na+ loading

Na-K-ATPase activity was studied in tubule segments from the cortex and medulla of rabbit kidneys under normal conditions, after unilateral nephrectomy, and after chronic salt loading. After unilateral nephrectomy kidney weight increased by 37% and Na-K-ATPase activity rose significantly in all nephron segments by 36-200% (P less than 0.01). Oral salt loading for 2 wk with 0.5% NaCl caused an increase in GFR and in absolute sodium excretion as well as reabsorption; plasma aldosterone decreased by 44% (P less than 0.005). In the proximal segments (PCT, CPST, OMPST, and TDL) there were no marked changes in Na-K-ATPase activity, whereas along the whole length of the ascending limb of Henle's loop (iMTAL, MTAL, and CTAL) there was a significant rise in the enzymatic activity of 30-200% (P less than 0.02). In the distal segments (DCT, CCD, and OMCD) there was a marked decrease of 50-60% (P less than 0.005) in Na-K-ATPase activity after the salt loading. We conclude that unilateral nephrectomy caused a general increase in Na-K-ATPase activity along the whole length of the nephron, and salt loading caused a selective increase in enzyme activity along the ascending limb of Henle's loop and decrease in the distal segments.

Renal refractoriness to PTH in experimental Fanconi syndrome: evidence for intact adenylate cyclase activation

Previous studies demonstrated renal refractoriness to parathyroid hormone (PTH) in maleate-induced Fanconi syndrome (FS) in rats. In membrane fraction of renal cortex of parathyroidectomized (PTX) rats with FS, PTH increased adenylate cyclase (AC) activity from a basal value of 7.4 +/- 0.6 (mean +/- SE) to 16.8 +/- 3.5 pmoles cAMP/mg prot/min (P less than 0.01), similar stimulation by PTH was observed in control incubation with normal kidneys. In membrane fraction of renal cortex of PTX rats incubated with maleate, PTH increased AC from 5.7 +/- 0.42 to 10.7 +/- 1.08 (P less than 0.01) similar to control incubation without maleate. In cortical slices from PTX rates with FS incubated in vitro, PTH increased cAMP content only from 4.0 +/- 0.21 to 5.27 +/- 0.27 pmole cAMP/mg prot (P less than 0.005), while in slices from the control group the increment by PTH was from 3.9 +/- 0.43 to 10.7 +/- 0.93 pmoles cAMP/mg prot (P less than 0.001). For the difference in the increment between the control and FS group, P less than 0.001. In cortical tissue of PTX rats with FS, PTH injection failed to increase cAMP content: basal value 7.4 +/- 0.8 and with PTH 9.2 +/- 0.8 pmole cAMP/mg prot (P NS), as compared with controls: basal value 9.5 +/- 0.5 and with PTH 23.8 +/- 1.6 (P less than 0.001). ATP content of cortical slices fell from a control value of 2.3 +/- 0.18 in PTX rats to 1.0 +/- 0.14 nmol/mg prot in PTX rats with FS.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental aspects of sugar transport by isolated dog renal cortical tubules

alpha-Methyl-D-glucoside (AMG) uptake was examined in isolated renal cortical tubules from newborn, 3-month-old, and adult dogs. All three age groups demonstrated active sugar transport. The initial rate of AMG uptake was similar in the 3-month-old and adult tubules which was twice that of the newborn. At steady-state, the adult and newborn tubules had achieved a similar intracellular AMG concentration which was 45% greater than that of the 3-month-old. Determination of the flux constants of these uptake patterns revealed that there was an age-dependent increase in both the net flux and the fractional influx rate constant. However, the 3-month-old had the highest fractional efflux rate constant and the newborn the lowest value with the adult in between. Kinetic analysis of AMG uptake showed a single saturable transport system for each age group. The newborn and adult had similar Km values but the 3-month-old had a value that was 60% higher. The 3-month-old tubules had the highest Vmax and the newborn tubules the lowest with the adult value in between. AMG uptake by tubules from each age group demonstrated a similar pattern of inhibition in a low sodium buffer and by glucose and phlorizin. This indicated that, aside from kinetic changes with maturation, the saturable transport system for AMG is similar in each age group.

The effect of streptozotocin-induced diabetes mellitus on urinary excretion of sodium and renal Na+-K+-ATPase activity

Renal sodium handling and microsomal Na+-K+-ATPase activity in kidney cortex, medulla and papilla of rats with streptozotocin-induced diabetes mellitus (DM) was studied. During 7 days following the administration of streptozotocin GFR, urinary excretion, filtered load and tubular reabsorption of Na+ averaged (mean +/- SE) 1.18 +/- 0.016 ml/min, 1.74 +/- 0.14, 177.3 +/- 8.9 and 175.6 +/- 8.9 mEq/min respectively in experimental rats as compared to corresponding rates of 0.85 +/- 0.04 (P less than 0.001), 0.85 +/- 0.03 (P less than 0.001), 129.8 +/- 5.8 (P less than 0.001) and 129 +/- 5.8 (P less than 0.001) respectively in the control rats. The activity of microsomal Na-K-ATPase in the kidney cortex, medulla and papilla of the control group was (mean +/- SE) 44.7 +/- 1.7, 150 +/- 7.5 and 37.4 +/- 3.6 (mumoles Pi/mg prot/h) respectively. 24 h after DM induction Na-K-ATPase activity in the cortex rose to 59.3 +/- 2.4 (P less than 0.001) and remained high after 3 and 7 days. Medullary Na-K-ATPase activity was unchanged 24 h after streptozotocin administration but was markedly increased to 260 +/- 9 (P less than 0.001) after 3 days and remained high after 7 days. These findings show that streptozotocin-induced DM in rats causes a substantial increase in GFR which is associated with a net increase in filtered and reabsorbed load of Na+ and natriuresis. These alterations are accompanied by a marked increase in Na-K-ATPase activity in renal medulla and in the cortex.

Blockade of the renal tubular effects of vitamin D by cycloheximide in the rat

To further characterize the mechanisms by which 25(OH) vitamin D3 (25(OH)D3) and 1.25(OH)2 vitamin D3 (1,25(OH)2D3) suppress the phosphaturic action of parathyroid hormone (PTH) we have studied the effects of cycloheximide (cyclohex), a protein synthesis inhibitor, on the interaction between PTH and vitamin D metabolites in parathyroidectomized (PTX) rats, both in vivo and in vitro experiments. In clearance studies PTX PTH-infused rats were pretreated with cyclohex 2 h before the administration of vitamin D. In control, PTX PTH-infused rats not pretreated with cyclohex, the administration of 25(OH)D3 and 1,25(OH)2D3 was associated with a fall in fractional excretion of phosphate (CP/CIN) from 0.30 +/- 0.05 to 0.16 +/- 0.02 and from 0.31 +/- 0.05 to 0.13 +/- 0.01 (P less than 0.005) respectively. Cyclohex-pretreated PTX PTH-infused rats failed to respond to both 25(OH)D3 and 1,25(OH)2D3, and CP/CIN, which rose after PTH, remained 0.32 +/- 0.05 and 0.29 +/- 0.03 respectively. In vitro, both 25(OH)D3 and 1,25(OH)2D3 inhibited the PTH-induced activation of adenylate cyclase in the renal isolated membrane fractions. Pretreatment with cyclohex abolished this effect of vitamin D metabolites. These results show that cyclohex blocks the antiphosphaturic effects of both 25(OH)D3 and 1,25(OH)2D3 but does not alter the response to PTH. These findings are consistent with the possibility that the acute renal action of vitamin D depends on de novo synthesis of protein.

Renal effect of vitamin D metabolites: evidence for the essential role of the 25(OH) group

The effects of 1 alpha (OH)vitamin D3 [1 alpha (OH)D3] and 24,25(OH)2vitamin D3 [24,25(OH)2D3] on the phosphaturic action of parathyroid hormone (PTH) were studied in two groups of parathyroidectomized (PTX) rats. In group 1, PTX PTH-infused rats received intravenous 1 alpha (OH)D3, and in group 2, PTX PTH-infused rats received intravenous 24,25(OH)2D3. PTX PTH-infused rats served as controls. The effects of both vitamin D metabolites on renal PTH-activated adenylate cyclase (AC) were studied in vitro. In group 1, PTH increased fractional excretion of phosphate (CP/CIn) from 0.045 +/- 0.012 (+/- SE) to 0.263 +/- 0.011 (P less than 0.005). 1 alpha (OH)D3 failed to influence this response. In group 2, PTH increased CP/CIn from 0.055 +/- 0.008 to 0.289 +/- 0.027 (P less than 0.005). 24,25(OH)2D3 reduced the PTH-induced rise in CP/CIn from 0.289 +/- 0.027 to 0.192 +/- 0.021 (P less than 0.01) and decreased the urinary excretion of adenosine 3',5'-cyclic monophosphate. In vitro, 24,25(OH)2D3 blunted the PTH-activated AC, whereas 1 alpha (OH)D3 had no effect. These results show that 24,25(OH)D3, similar to two other 25(OH) metabolites of vitamin D-25(OH)vitamin D3 and 1,25(OH)2vitamin D3-suppresses the phosphaturic action of PTH, whereas 1 alpha(OH)D3, which is devoid of a 25(OH) group, lacks this effect. This suggests that a 25(OH) group is a prerequisite for the antiphosphaturic effect of vitamin D, whereas the 1 alpha (OH) group is not essential for this action.