Characterization of thromboxane A2 receptors in rat kidney

The renal TXA2 receptors were investigated in preparations derived from rat kidney. Perfused rat kidneys were removed and separated into cortex and medulla. Each subcellular fraction was prepared by a sucrose density gradient method for analyzing the subcellular distribution of TXA2 receptors. The membranes were obtained by 40,000 x g centrifugation for analyzing the renal distribution of TXA2 receptors. Bindings of [3H]SQ 29548, a TXA2 receptor antagonist, to these preparations were carried out using a filtration method. Furthermore, the binding of [3H]SQ 29548 to membranes from rat kidney cortex was compared with its binding to rat washed platelets. The membrane fraction had the highest density of TXA2 receptors among subcellular fractions determined. TXA2 receptors appeared in corticomedullary junction with high density. Scatchard analysis using [3H]SQ 29548 as a ligand revealed a single binding site of TXA2 receptors in membranes from rat kidney cortex, and the dissociation constant (Kd) was remarkably higher than the Kd in rat washed platelets. These findings suggest that TXA2 receptors in membranes from rat kidney cortex are different from those in rat platelets, and TXA2 receptor activation in kidney might play a role in renal function.     

The renal dopamine receptors.

Dopamine is an endogenous catecholamine that modulates many functions including behavior, movement, nerve conduction, hormone synthesis and release, blood pressure, and ion fluxes. Dopamine receptors in the brain have been classically divided into D1 and D2 subtypes, based on pharmacological data. However, molecular biology techniques have identified many more dopamine receptor subtypes. Several of the receptors cloned from the brain correspond to the classically described D1 and D2 receptors. Several D1 receptor subtypes have been cloned (D1A, D1B, and D5) and are each coupled to the stimulation of adenylyl cyclase. The D2 receptor has two isoforms, a shorter form, composed of 415 amino acids, is termed the D2short receptor. The long form, called the D2long receptor, is composed of 444 amino acids; both are coupled to the inhibition of adenylyl cyclase. The D3 and D4 receptors are closely related to, but clearly distinct from, the D2 receptor. They have not yet been linked to adenylyl cyclase activity. Outside of the central nervous system, the peripheral dopamine receptors have been classified into the DA1 and DA2 subtypes, on the basis of synaptic localization. The pharmacological properties of DA1 receptors roughly approximate those of D1 and D5 receptors, whereas those of DA2 receptors approximate those of D2 receptors. A renal dopamine receptor with some pharmacological features of the D2 receptor but not linked to adenylyl cyclase has been described in the renal cortex and inner medulla. In the inner medulla, this D2-like receptor, termed DA2k, is linked to stimulation of prostaglandin E2 production, apparently due to stimulation of phospholipase A2. Of the cloned dopamine receptors, only the mRNA of the D3 receptor has been reported in the kidney. The DA1 receptor in the kidney is associated with renal vasodilation and an increase in electrolyte excretion. The DA1-related vasodilation and inhibition of electrolyte transport is mediated by cAMP. The role of renal DA2 receptors remains to be clarified. Although DA1 and DA2 receptors may act in concert to decrease transport in the renal proximal convoluted tubule, the overall function of DA2 receptors may be actually the opposite of those noted for DA1 receptors. Dopamine has been postulated to act as an intrarenal natriuretic hormone. Moreover, an aberrant renal dopaminergic system may play a role in the pathogenesis of some forms of hypertension. A decreased renal production of dopamine and/or a defective transduction of the dopamine signal is/are present in some animal models of experimental hypertension as well as in some forms of human essential hypertension.     

Binding properties of a selective tritiated vasopressin V2 receptor antagonist, [H]-SR 121463

BACKGROUND: [3H]-SR 121463 is the first radiolabeled selective nonpeptide vasopressin V2 receptor antagonist ligand that has been reported to date. In the present work, we studied the binding properties of [3H]-SR 121463 for renal V2 receptors from animal and human origins. METHODS: Binding studies were performed with [3H]-SR 121463 in Chinese hamster ovary (CHO) cells transfected with the human V2 receptor and in various kidney preparations expressing the native V2 receptors (rat, rabbit, dog, pig, monkey, and human). Autoradiographies were performed in rat and human kidney sections. RESULTS: [3H]-SR 121463 binding to CHO cells stably transfected with the cloned human renal V2 receptor was specific, highly stable, time dependent, saturable, and reversible. A single population of high-affinity binding sites was identified (Kd = 0.94 +/- 0.34 nmol/L, Bmax = 9876 +/- 317 fmol/mg protein). Of note, [3H]-SR 121463 revealed a higher number (about 40%) of V2 sites than [3H]-AVP in the same preparation. Displacement of [3H]-SR 121463 binding by reference peptide and nonpeptide vasopressin/oxytocin compounds exhibited a typical AVP V2 profile. [3H]-SR 121463 also displayed a high affinity for native V2 receptors in several kidney preparations from rat, pig, dog, rabbit, bovine, monkey, and human. The autoradiographic experiments using rat and human kidney sections showed intense labeling in the medullopapillary region and lower intensity in the cortex, consistent with a main localization of V2 receptors on collecting tubules. CONCLUSION: [3H]-SR 121463 is a useful ligand for the specific labeling of animal and human V2 receptors and could be a suitable probe for the search and in situ localization of V2 sites.     

Study of the effects of dopamine hydrochloride on alpha 1-adrenoceptors in rat kidney

We studied the number and affinity of catecholamine receptors in SD rat kidney by radioreceptor technique. The following conclusions were obtained: 1) By using 3H-prazosin, the numbers of alpha 1-receptor (Bmax) in rat renal cortex were greater than those in rat kidney medulla. As for affinity (Kd), the significance was not recognized between the two. Bmax of the rat renal cortex to 3H-prazosin binding was 96.1 fmol/mg protein, and Kd was 0.17 nM, and for the rat renal medullar these values were 44.5 fmol/mg protein and 0.13 nM, respectively. 2) By measurement of D1-receptor using 3H-SKF38393 in the rat renal cortex in the Scatchard plot analysis, positive cooperativity was observed under the low concentration of hot ligand which was less than 1 nM. But at the concentration of hot ligand over 1 nM, the plots showed a straight line. Bmax of the rat renal cortex to 3H-SKF38393 was 2.5 pmol/mg protein and Kd was 5.3 nM. 3) Based on displacement by dopamine for 3H-prazosin binding to rat renal cortex, it was surmised that high concentration of dopamine had an affinity to alpha 1-adrenoceptors. 4) There was no change in the Kd and Bmax of alpha 1-receptor in the rat renal cortex after incubation of samples with low concentration of dopamine. However, in the case of high concentration of dopamine, a remarkable decrease of the affinity (Kd) of alpha 1-adrenoceptor was observed.     

Dopamine and new dopamine analogs: receptors and clinical applications

Division of dopamine (DA) receptors and alpha- and beta-adrenoceptors into two subtypes provides a pharmacological basis for the clinical use of DA and new DA receptor agonists in anesthesia and critical care medicine. First, differential receptor activation explains why three distinct cardiovascular and renal responses can be obtained at low, medium, and high infusion rates of DA. Low infusion rates, in which DA1 and DA2 receptors are activated, are being increasingly used to improve renal perfusion and to treat oliguric states. The medium dose range (activation of beta1-adrenoceptors) is used for treatment of heart failure. The high dose range (activation of alpha-adrenoceptors) is used for treatment of shock. Second, selective DA1 and relatively selective DA2 agonists and agonists with different combinations of DA and receptor activity other than DA have been synthesized and are being investigated for the treatment of congestive heart failure and hypertension. Some of these compounds could have advantages over DA for acute therapy. Future availability of these drugs in anesthesia and critical care settings will depend to a great extent on input from anesthesiologists concerning potential new uses and willingness to conduct clinical investigations.     

D1-like dopamine receptor activation and natriuresis by nitrocatechol COMT inhibitors

BACKGROUND: In recent years, several nitrocatechol derivatives (tolcapone, entacapone, and nitecapone) have been developed and found to be highly selective and potent inhibitors of catechol-O-methyltransferase (COMT). More recently, natriuretic properties were described for two of these compounds (entacapone and nitecapone), although this was not accompanied by enhanced urinary excretion of dopamine. We hypothesized that nitrocatechol derivatives stimulate D1-like dopamine receptors. METHODS: Adult male Wistar rats were treated with a nitrocatechol COMT inhibitor (entacapone, tolcapone, or nitecapone, 30 mg/kg, orally), and the urinary excretion of dopamine and sodium was quantitated. The interaction of nitrocatechol derivatives with D1-like receptors was evaluated by their ability to displace [3H]-Sch23390 binding from membranes of rat renal cortex and cAMP production in opossum kidney (OK) cells. RESULTS: Urinary excretion of sodium (micromol/h) was markedly increased by all three nitrocatechol derivatives: vehicle, 55.0 +/- 5.6; entacapone, 98.4 +/- 9.3; tolcapone, 97.5 +/- 9.3; and nitecapone, 120.5 +/- 12.6. Pretreatment with the selective D1 antagonist Sch 23390 (60 microg/kg) completely prevented their natriuretic effects. Nitecapone and tolcapone were equipotent (IC50s of 48 and 42 micromol/L) and more potent than entacapone and dopamine (IC50s of 107 and 279 micromol/L) in displacing [3H]-Sch23390 binding. In OK cells, all three nitrocatechol derivatives significantly increased cAMP accumulation and reduced Na(+)/H(+) exchange and Na(+),K(+)-ATPase activities, this being prevented by a blockade of D1-like receptors. CONCLUSION: Stimulation of D1-like dopamine receptors and inhibition of Na(+)/H(+) exchange and Na(+),K(+)-ATPase activities by nitrocatechol COMT inhibitors may contribute to natriuresis produced by these compounds.     

Laudanosine does not displace receptor-specific ligands from the benzodiazepinergic or muscarinic receptors

The present study was designed to investigate whether D,L-laudanosine (a breakdown product of the neuromuscular relaxant atracurium besylate) interacts with benzodiazepinergic receptors or muscarinic receptors, both of which are involved in epilepsy and other types of seizures. The ability of D,L-laudanosine (10(-10) to 5 X 10(-5) M) to displace ligands specific for these receptors from their binding sites was tested. D,L-Laudanosine failed to inhibit the binding of [3H]flunitrazepam to central benzodiazepine receptors in the cerebral cortex, the binding of [3H]PK 11195 to peripheral benzodiazepine binding sites in the cerebral cortex and kidney, the binding of [3H]Ro 5-4864 to peripheral benzodiazepine binding sites in the kidney, or the binding of [3H]quinuclidinyl benzilate to muscarinic receptors in the cerebral cortex. These results suggest that laudanosine does not exert its convulsive effect via interaction with benzodiazepinergic or muscarinic receptors.     

Effect of dopamine infusion on hemodynamics after hepatic denervation

BACKGROUND:. The effects of dopamine (DA) on systemic hemodynamics are better understood than its effects on hepatic hemodynamics, especially after liver denervation occurring during liver transplantation. Therefore, a porcine model was used to study DA's effects on hemodynamics after hepatic denervation. MATERIALS AND METHODS: Fifteen pigs underwent laparotomy for catheter and flow probe placement. The experimental group (n = 7) also underwent hepatic denervation. After 1 week, all pigs underwent DA infusion at increasing doses (3-30 mcg/kg/min) while measuring hepatic parameters [portal vein flow (PVF), hepatic artery flow (HAF), total hepatic blood flow (THBF = HAF + PVF), portal and hepatic vein pressures] and systemic parameters [heart rate (HR), mean arterial pressure (MAP)]. RESULTS: There was a significant increase in HAF from baseline to the 30 mcg/kg/min DA infusion rate (within-subjects P < 0.01), but the differences between the two groups were not significant. PVF and THBF showed large effects (increases) with denervation, but the increase in flow with DA infusion was not present after denervation. Perihepatic pressures were unchanged by denervation or DA. Heart rate differed significantly between the control and denervated animals at baseline, 3, 6, 12 (all P < 0.05), and 30 mcg/kg/min DA (P = 0.10). Control vs denervation MAP at baseline was 100 +/- 4 vs 98 +/- 4 Torr and at 30 mcg/kg/min it was 110 +/- 3 vs 101 +/- 5 mm Hg. CONCLUSIONS: Hepatic flows tended to be higher after denervation. HAF showed similar increases with DA in both control and denervation groups. Increases in PVF and THBF with DA infusion were not present after denervation. HR was significantly decreased and MAP tended to be lower after denervation. The HR and MAP response to DA was similar in both groups. Therefore, both denervation and DA infusion have an effect on systemic and hepatic hemodynamics.     

Autoradiographic localization of vasopressin and oxytocin binding sites in rat kidney

The presence of vasopressin receptors of the V1 (vascular) type and of oxytocin receptors in the rat kidney was investigated using an autoradiographical approach. Rat kidney sections were incubated with tritiated vasopressin ([3H]vasopressin, 1.5 nM) or oxytocin ([3H]oxytocin, 3 nM). The ligand selectivity of the [3H]vasopressin binding sites detected was deduced from competition experiments using one selective unlabeled ligand for V2 (antidiuretic) vasopressin receptors (1-deamino-[8-D-arginine]-vasopressin, dDAVP) and one selective unlabeled ligand for V1 receptors (des-glycineamide-[1-(beta-mercapto-beta,beta-cyclopentamethylene propionic acid]-arginine vasopressin, des(Gly(NH2)9d(CH2)5-AVP). Specific and dense [3H]vasopressin labeling was observable in the medullopapillary and cortical portions of the kidney. Specific [3H]vasopressin binding in the cortex was insensitive to the V1-selective ligand, des(Gly(NH2)9d(CH2)5-AVP, but was inhibited by dDAVP. Glomerular structures identified as such by microscopical observation of the kidney sections were specifically labeled with [3H]oxytocin and [125I]-SAR1-angiotensin II but not with [3H]vasopressin. It is concluded that V1 receptors which have been evidenced on mesangial cells in culture are not expressed in a detectable quantity on mesangial cells in situ. The specific [3H]oxytocin binding to glomeruli might reflect the presence on glomerular structures of oxytocin receptors involved in the effects of the hormone on renal hemodynamics, and possibly in some of the effects ascribed to vasopressin.     

Unilateral MPTP-induced parkinsonism in monkeys. A quantitative autoradiographic study of dopamine D1 and D2 receptors and re-uptake sites.

The cynomolgus monkeys received a unilateral intracarotid injection of the neurotoxin N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in order to induce a chronic model of hemi-parkinsonism. The procedure was well tolerated by the animals. Unilateral injection of MPTP caused rigidity and bradykinesia of the contralateral limbs, but the animals were able to eat and drink without levodopa therapy. During spontaneous motor activity, animals rotated toward the lesioned side whereas systemic apomorphine injection stimulated circling toward the normal non-lesioned side. Twelve weeks after MPTP injection, we found a marked reduction in striatal and nigral [3H]-mazindol binding on the MPTP-injected side which is indicative of a loss in both dopaminergic nerve terminals and cell bodies. The unilateral dopaminergic denervation was associated with an ipsilateral increase in striatal and a reduction in nigral [3H]-spiperone-labelled D2 dopamine receptors; these changes are consistent with the known localization of the D2 receptors on striatal dopaminergic nerve terminals and on nigral dopaminergic cell bodies. In contrast, no changes in [3H]-SCH 23390-labelled D1 dopamine receptors were observed at the level of either the striatum or the substantia nigra. This study describes a well tolerated procedure which induces a clinical and morphological hemi-parkinsonian syndrome. This animal model may be useful in the studies of new antiparkinsonian drugs, for testing the functional efficacy of brain tissue implants and in the understanding of the physiopathogenesis of levodopa-induced dyskinesias.     

Intrarenal serotonin, dopamine, and phosphate handling in remnant kidneys

BACKGROUND: Serotonin (5-HT) and dopamine (DA) are intrarenal autocrine/paracrine substances that regulate phosphate reabsorption. The present studies explored intrarenal serotonin and DA metabolism and the implications for phosphate homeostasis in rats with remnant kidneys, a model for renal failure. METHODS: The intrarenal productions of serotonin and DA were determined from measurements of renal interstitial fluid (microdialysate) and urine in rats with remnant or intact kidneys. In clearance studies, the effects of infusion of methiothepin, a serotonin receptor antagonist, or gludopa, a renal selective DA precursor, on phosphate and sodium excretion were determined in rats with a remnant or intact kidneys. RESULTS: Renal interstitial serotonin (5-HT, 3.4 +/- 0.9 pg/min) was fourfold higher than DA (0.6 +/- 0.1 pg/min) in remnant kidneys. Conversely, urinary excretion of serotonin was fourfold less than DA in rats with a remnant kidney (5-HT 0.4 +/- 0.02 vs. DA 1.5 +/- 0.1 ng/min). Infusion of methiothepin or gludopa significantly increased the fractional excretion of phosphate (FE(Pi)) in rats with a remnant kidney from 54 +/- 3 to 67 +/- 7% (P < 0.05) and from 36 +/- 10% to 51 +/- 13% (P < 0.05), respectively. CONCLUSION: We conclude that serotonin preferentially accumulates in the renal interstitium, whereas DA exits primarily via the tubular lumen. Phosphate excretion is increased by both the acute infusion of the serotonin receptor antagonist and the infusion of gludopa, suggesting that both serotonin and DA modulate phosphate excretion in rats with remnant kidneys.     

Brain D1 dopamine receptor in alloxan-induced diabetes.

Specific binding of [3H]SCH 23390 to dopamine D1 receptors in the striatum and olfactory tubercle in 14-day alloxan-induced diabetic rats was investigated. The Scatchard analysis revealed decreased D1 receptor density in the striatum (Bmax values were 548 +/- 23 fmol/mg protein for the control and 466 +/- 33 fmol/mg for the diabetic rats). No change was observed in the olfactory tubercle (Bmax; 299 +/- 27 fmol/mg for the control and 317 +/- 32 fmol/mg for the diabetic rats). Thus, specific binding of [3H]SCH 23390 to striatal and olfactory tubercle membranes showed region-specific changes of brain dopamine D1 receptors in alloxan diabetic rats.     

Identification and characterization of parathyroid hormone receptors in rat renal cortical plasma membranes using radioligand binding

Parathyroid hormone (PTH) receptors have been described in renal tissue from several species, but not in the rat. In this study, radioligand binding techniques were used to identify and characterize PTH receptors in rat kidney cortical membranes. The sulfur-free PTH analog [Nle8,18Tyr34]bovine PTH-(1-34)amide was iodinated using the iodogen method. This ligand was suitable for use in identifying PTH receptors in canine renal membranes, but not rat renal membranes. Synthetic, unsubstituted rat PTH-(1-34) was iodinated using the milder, lactoperoxidase technique and was purified by HPLC on a C8 column. [125I]rat PTH-(1-34) bound rapidly to both rat and dog renal membranes. At 22 degrees C reaction reached steady state within 20 minutes, and this level was maintained for at least 3 h. Specific binding was routinely greater than 90% for rat kidney and greater than 95% for dog kidney. Similar results were obtained at 4 degrees C with a longer time required to attain steady state (approximately 45 minutes). Binding was reversible as demonstrated by dissociation of bound ligand after either infinite dilution or displacement with excess nonradioactive PTH. Binding was saturable and of high affinity (rat kidney: Bmax = 2.3 pmol/mg protein, Kd = 3.1 nM, dog kidney: Bmax = 2.1 pmol/mg protein, Kd = 3.7 nM). Rat renal cortical adenylate cyclase activity was stimulated by rat PTH in a dose-dependent manner with an EC50 of 4 nM, a value in good agreement with the binding data. This study demonstrates the feasibility of identifying and characterizing parathyroid hormone receptors in rat renal cortical plasma membranes using radioligand binding techniques.     

Time-dependent up-regulation of endothelin-A receptors and down-regulation of endothelin-B receptors and nitric oxide synthase binding sites in the renal medulla of a rabbit model of partial bladder outlet obstruction: potential clinical relevance

OBJECTIVE: To assess the density of endothelin (ET) receptors (ET-1 is a potent vasoconstrictor peptide acting on two known receptors, ETA and ETB ) and nitric oxide synthase (NOS) binding sites in the kidney of a rabbit model of bladder outlet obstruction (BOO). MATERIALS AND METHODS: Partial BOO was created in adult New Zealand White rabbits; after 1, 3, 4 and 6 weeks of BOO, kidney sections were incubated with radioligands for ET-1, ETA, ETB receptors and with [3H]-NOARG (a ligand for NOS). Autoradiographs were generated and analysed densitometrically. Sections were also assessed by NADPH histochemistry. Plasma creatinine, urea and electrolyte levels were regularly monitored. The control and 6-week BOO kidneys were also evaluated ultrastructurally by electron microscopy. RESULTS: There was no significant change in plasma creatinine, urea and electrolyte levels. ETA and ETB receptor density was significantly greater in the medulla than in the cortex (P<0.001) in all animals. There was an up-regulation of ETA receptors (P=0.03) and down-regulation of ETB receptors (P=0.03) and NOS binding sites (P<0.001), as well as decreased NADPH staining in the medulla of 6-week partial BOO kidneys. Electron microscopy detected glomerular disruption of the obstructed kidneys. CONCLUSION: The time-dependent changes in ETA and ETB receptors, NOS binding sites and NADPH staining in the renal medulla, as well as ultrastructural changes, occur despite normal renal function. These changes appear to be an early event and may play a role in the development of renal failure. Hence, the use of ETA receptor antagonists at this early stage may prevent the development of renal failure/impairment in BOO.     

Effect of diabetes and aminoguanidine therapy on renal advanced glycation end-product binding

BACKGROUND: Advanced glycation end-products (AGEs) have been implicated in the pathogenesis of diabetic nephropathy, and aminoguanidine (AG) has been shown to decrease the accumulation of AGEs in the diabetic kidney. METHODS: This study investigates changes in AGE binding associated with diabetes in the rat kidney using in vitro and in vivo autoradiographic techniques. Male Sprague-Dawley rats were randomized into control and diabetic groups with and without AG treatment and were sacrificed after three weeks. Frozen kidney sections (20 microm) were incubated with [125I]-AGE-RNase or [125I]-AGE-BSA. To localize the AGE binding site, in vivo autoradiography was performed by injection of 15 microCi of [125I]-AGE-BSA into the abdominal aorta of the rat. RESULTS: Low-affinity binding sites specific for AGEs in the renal cortex (IC50 = 0.28 microm) were detected by in vitro autoradiography. There was a significant increase in [125I]-AGE binding in the diabetic kidney, which was prevented by AG treatment. Emulsion autoradiography revealed that binding was localized primarily to proximal tubules in the renal cortex. Renal AGE levels, as assessed by fluorescence or by radioimmunoassay, were increased after three weeks of diabetes. This increase was attenuated by AG therapy. CONCLUSIONS: AGE binding sites are present within the proximal tubules of the kidney and appear to be modulated by endogenous AGE levels. It remains to be determined if these binding sites represent receptors involved in clearance of AGEs or are linked to pathogenic pathways that lead to the development of diabetic nephropathy.     

Effect of low-dose dopamine on kidney function and vasoactive hormones in pediatric patients with advanced renal failure

Dopamine (DA) was infused in a dose of 2 micrograms/kg/min in 12 children and adolescents with chronic renal failure to test the vasodilatory reserve capacity of the kidney. Mean basal GFR and ERPF were 17.8 and 93.1 ml/min/1.73 m2, respectively. DA infusion had no significant influence on GFR but effective renal plasma flow (ERPF) increased by 14% (p less than 0.05). After DA, GFR did not correlate with ERPF. There was a significant increase in urinary sodium excretion (+22%). Sodium excretion correlated with osmotic clearance and urine flow rate with free water clearance. Plasma prolactin concentration was decreased (p less than 0.01), whereas noradrenaline, adrenaline and free dopamine increased significantly after DA. Plasma renin activity, aldosterone, arginine vasopressin and atrial natriuretic peptide levels remained unchanged. The data indicate that in pediatric patients with advanced renal failure DA fails to increase filtration capacity, whereas effective renal plasma flow and sodium excretion are stimulated. It is speculated that in this situation preglomerular and tubular renal functions regulated by dopamine receptors are better conserved than those affecting glomerular microcirculation.     

Metabolism alters the selectivity of angiotensin-(1-7) receptor ligands for angiotensin receptors

The present study examined whether metabolism of the putative angiotensin-(1-7) receptor agonist and antagonist [angiotensin-(1-7) and D-alanine(7) angiotensin-(1-7), respectively] altered their ability to interact with angiotensin AT(1), AT(2), and AT(4) receptor subtypes. Both angiotensin-(1-7) and D-alanine(7) angiotensin-(1-7) competed with low affinity for (125)I-sarcosine(1), isoleucine(8) angiotensin II binding to AT(1) and AT(2) receptors in rat liver and adrenal medulla membranes, respectively, and competed with low affinity for (125)I-angiotensin IV binding to AT(4) receptors in bovine kidney epithelial cell membranes. In vitro renal metabolism of the angiotensin-(1-7) receptor ligands (incubating peptides with rat cortical tissue homogenates) had minimal influence on low-affinity binding to AT(1) and AT(2) receptors, yet caused a significant and dramatic shift toward high-affinity binding for AT(4) receptors. Low-affinity angiotensin II binding to the AT(4) receptor was also shifted toward high-affinity binding following renal metabolism of the peptide. Conversely, angiotensins with high affinity for the AT(4) receptor (e.g., angiotensin IV) were shifted toward low-affinity binding states following peptide metabolism. Incubation of (125)I-angiotensin-(1-7) with rat cortical tissue generated the high-affinity AT(4) receptor ligand (125)I-angiotensin-(3-7), whereas the renal metabolism of (125)I-angiotensin II generated both (125)I-angiotensin-(3-7) and (125)I-angiotensin IV. These results reveal that renal metabolism of angiotensin-(1-7) receptor ligands and angiotensin II yields products that have high affinity for the AT(4) receptor and could potentially contribute to the biologic actions of the parent peptide in the kidney.     

Antagonistic effects of sulpiride--racemic and enantiomers--on renal response to low-dose dopamine infusion in normal women

In healthy women during moderate hydrosaline retention we have evaluated the antagonistic effects of sulpiride--enantiomers and racemic--on the renal action of a low-dose dopamine (DA) infusion (0.1 microgram/kg/min). The studies were performed, in hypotonic polyuria, by the clearance (C1) method in (1) hydrosaline retention (n = 23), (2) retention + dl-sulpiride (n = 8), (3) retention + d-sulpiride and (4) retention + l-sulpiride (in the latter two cases n = 7 subjects submitted to paired studies). Hydrosaline retention was induced by deoxycorticosterone acetate treatment. A common pattern of sulpiride treatment was applied. The DA renal hyperemia is abolished by l-sulpiride while it is transitorily attenuated by d-sulpiride. In both conditions 3 and 4 the increase in glomerular filtration rate, the inhibition of fractional isosmotic sodium reabsorption and the increase in urinary sodium excretion--induced by DA in condition 1--are suppressed. On the contrary, DA inhibition of fractional anisosmotic sodium reabsorption is not affected by sulpiride. The data indicate that DA renal hyperemia results from the action of DA on DA2 receptors; the DA inhibition of sodium transport by the diluting segments does not appear to be mediated by typical DA receptors.     

Autoradiographic quantification of adrenergic receptors in rat kidney

The adrenergic nervous system is active in kidney function, and the kidney has large numbers of adrenergic receptor subtypes. Because of the cellular complexity of the kidney, it is difficult to obtain direct assessments of adrenergic receptor binding characteristics over specific tissue compartments. Qualitative autoradiography allows the localization of adrenergic receptors over tissue types in the kidney, but quantitative autoradiography allows direct comparison of adrenergic receptor number over different cellular compartments. The purpose of this study was to obtain direct assessments of alpha 1, alpha 2, and beta adrenergic receptor numbers over different tissue compartments of the kidney using quantitative autoradiography. Sections of Sprague-Dawley rat kidney were incubated in several concentrations of 3H-dihydroalprenolol to label beta receptors, 3H-prazosin to label alpha 1 receptors and 3H-rauwolscine to label the alpha 2 receptors. Sections of rat heart incubated in 3H-dihydroalprenolol were included as standards. The sections were then prepared for receptor autoradiography. After processing, the grains were then quantified on an image analysis system, and binding curves constructed from the specific binding. In some animals, the proximal tubules were stained to localize the proximal convoluted tubules. Significant Scatchard analyses were obtained in the glomeruli with dihydroalprenolol (5.18 X 10(9) receptors/mm3) and with rauwolscine (2.48 X 10(9) receptors/mm3). Significant Scatchard analyses were obtained in the cortex with rauwolscine (9.47 X 10(9) receptors/mm3) and with prazosin (3.9 X 10(9)). In addition, specific binding was seen with rauwolscine and prazosin to the kidney arterioles.(ABSTRACT TRUNCATED AT 250 WORDS)