Inhaled corticosteroids increase interleukin-10 but reduce macrophage inflammatory protein-1alpha, granulocyte-macrophage colony-stimulating factor, and interferon-gamma release from alveolar macrophages in asthma

We determined the effect of inhaled corticosteroid, budesonide, on the release of the anti-inflammatory cytokine, interleukin-10 (IL-10), and of pro-inflammatory cytokines, macrophage inflammatory protein-1alpha (MIP-1alpha), interferon-gamma (IFN-gamma), and granulocyte-macrophage colony-stimulating factor (GM-CSF), from blood monocytes and alveolar macrophages of mild asthmatic subjects in a double-blind, cross-over, placebo-controlled study. Budesonide reduced bronchial hyperresponsiveness and improved baseline FEV1. Alveolar macrophages were obtained by bronchoalveolar lavage performed at the end of each treatment phase. IL-10 from blood monocytes was not altered, but both IL-10 mRNA and protein expression from alveolar macrophages stimulated by lipopolysaccharide and IL-1beta were increased after corticosteroid therapy. By contrast, alveolar macrophages released significantly less MIP-1alpha, IFN-gamma, and GM-CSF after steroid treatment. In comparison to alveolar macrophages from normal nonasthmatic volunteers, those from asthmatic patients released more MIP-1alpha, IFN-gamma, and GM-CSF but lower amounts of IL-10 particularly at baseline and after IL-1beta stimulation. The ability of steroids to inhibit pro-inflammatory cytokines but to enhance the anti-inflammatory cytokine such as IL-10 may contribute to their beneficial actions in asthma. Asthma is characterized by alveolar macrophages exhibiting both an enhanced capacity to release pro-inflammatory cytokines and a reduced capacity to produce IL-10.

Renal dopamine receptors in health and hypertension

During the past decade, it has become evident that dopamine plays an important role in the regulation of renal function and blood pressure. Dopamine exerts its actions via a class of cell-surface receptors coupled to G-proteins that belong to the rhodopsin family. Dopamine receptors have been classified into two families based on pharmacologic and molecular cloning studies. In mammals, two D1-like receptors that have been cloned, the D1 and D5 receptors (known as D1A and D1B, respectively, in rodents), are linked to stimulation of adenylyl cyclase. Three D2-like receptors that have been cloned (D2, D3, and D4) are linked to inhibition of adenylyl cyclase and Ca2+ channels and stimulation of K+ channels. All the mammalian dopamine receptors, initially cloned from the brain, have been found to be expressed outside the central nervous system, in such sites as the adrenal gland, blood vessels, carotid body, intestines, heart, parathyroid gland, and the kidney and urinary tract. Dopamine receptor subtypes are differentially expressed along the nephron, where they regulate renal hemodynamics and electrolyte and water transport, as well as renin secretion. The ability of renal proximal tubules to produce dopamine and the presence of receptors in these tubules suggest that dopamine can act in an autocrine or paracrine fashion; this action becomes most evident during extracellular fluid volume expansion. This renal autocrine/paracrine function is lost in essential hypertension and in some animal models of genetic hypertension; disruption of the D1 or D3 receptor produces hypertension in mice. In humans with essential hypertension, renal dopamine production in response to sodium loading is often impaired and may contribute to the hypertension. The molecular basis for the dopaminergic dysfunction in hypertension is not known, but may involve an abnormal post-translational modification of the dopamine receptor.

Role of the D1A dopamine receptor in the pathogenesis of genetic hypertension

Since dopamine produced by the kidney is an intrarenal regulator of sodium transport, an abnormality of the dopaminergic system may be important in the pathogenesis of hypertension. In the spontaneously hypertensive rat (SHR), in spite of normal renal production of dopamine and receptor density, there is defective transduction of the D1 receptor signal in renal proximal tubules, resulting in decreased inhibition of sodium transport (Na+/H+ exchanger [NHE] and Na+/K+ATPase activity) by dopamine. To determine if impaired D1 receptor regulation of NHE in proximal tubules is related to hypertension, studies were performed in a F2 generation from female Wistar Kyoto (WKY) and male SHR crosses. A D1 agonist, SKF 81297, inhibited (37.6 +/- 4.7%) NHE activity in brush border membranes of normotensive F2s (systolic blood pressure < 140 mm Hg, n = 7) but not in hypertensive F2s (n = 21). Furthermore, a D1 agonist, SKF 38393, when infused into the renal artery, dose dependently increased sodium excretion in normotensive F2s (n = 3) without altering renal blood flow but was inactive in hypertensive F2s (n = 21). Since the major D1 receptor gene expressed in renal proximal tubules is the D1A subtype, we determined the importance of this gene in the control of blood pressure in mice lacking functional D1A receptors. Systolic blood pressure was greater in homozygous (n = 6) and heterozygous (n = 5) mice compared to normal sex matched litter mate controls (n = 12); moreover, the mice lacking one or both D1A alleles developed diastolic hypertension. The cosegregation with hypertension of an impaired D1 receptor regulation of renal sodium transport and the development of elevated systolic and diastolic pressure in mice lacking one or both D1A alleles suggest a causal relationship of the D1A receptor gene with hypertension.

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.

Disruption of the dopamine D3 receptor gene produces renin-dependent hypertension

Since dopamine receptors are important in the regulation of renal and cardiovascular function, we studied the cardiovascular consequences of the disruption of the D3 receptor, a member of the family of D2-like receptors, expressed in renal proximal tubules and juxtaglomerular cells. Systolic and diastolic blood pressures were higher (approximately 20 mmHg) in heterozygous and homozygous than in wild-type mice. An acute saline load increased urine flow rate and sodium excretion to a similar extent in wild-type and heterozygous mice but the increase was attenuated in homozygous mice. Renal renin activity was much greater in homozygous than in wild-type mice; values for heterozygous mice were intermediate. Blockade of angiotensin II subtype-1 receptors decreased systolic blood pressure for a longer duration in mutant than in wild-type mice. Thus, disruption of the D3 receptor increases renal renin production and produces renal sodium retention and renin-dependent hypertension.

Dopamine-1 receptor coupling defect in renal proximal tubule cells in hypertension

The ability of the dopamine-1 (D1)-like receptor to stimulate adenylyl cyclase (AC) and phospholipase C (PLC), inhibit sodium transport in the renal proximal tubule (RPT), and produce natriuresis is attenuated in several rat models of hypertension. Since the inhibitory effect of D1-like receptors on RPT sodium transport is also reduced in some patients with essential hypertension, we measured D1-like receptor coupling to AC and PLC in cultures of human RPT cells from normotensive (NT) and hypertensive (HT) subjects. Basal cAMP concentrations were the same in NT (n=6) and HT (n=4). However, the D1-like receptor agonist fenoldopam increased cAMP production to a greater extent in NT (maximum response=67+/-1%) than in HT (maximum response=17+/-5%), with a potency ratio of 105. Dopamine also increased cAMP production to a greater extent in NT (32+/-3%) than in HT (14+/-3%). The fenoldopam-mediated increase in cAMP production was blocked by SCH23390 (a D1-like receptor antagonist) and by antisense D1 oligonucleotides in both HT and NT, indicating action at the D1 receptor. The stimulatory effects of forskolin and parathyroid hormone-related protein of cAMP accumulation were not statistically different in NT and HT, indicating receptor specificity and an intact G-protein/AC pathway. The fenoldopam-stimulated PLC activity was not impaired in HT, and the primary sequence and expression of the D1 receptor were the same in NT and HT. However, D1 receptor serine phosphorylation in the basal state was greater in HT than in NT and was not responsive to fenoldopam stimulation in HT. These studies demonstrate the expression of D1 receptors in human RPT cells in culture. The uncoupling of the D1 receptor in both rats (previously described) and humans (described here) suggests that this mechanism may be involved in the pathogenesis of hypertension; the uncoupling may be due to ligand-independent phosphorylation of the D1 receptor in hypertension.

Combinations of variations in multiple genes are associated with hypertension

The genetic analysis of hypertension has revealed complex and inconsistent results, making it difficult to draw clear conclusions regarding the impact of specific genes on blood pressure regulation in diverse human populations. Some of the confusion from previous studies is probably due to undetected gene-gene interactions. Instead of focusing on the effects of single genes on hypertension, we examined the effects of interactions of alleles at 4 candidate loci. Three of the loci are in the renin-angiotensin-system, angiotensinogen, ACE, and angiotensin II type 1 receptor, and they have been associated with hypertension in at least 1 previous study. The fourth locus studied is a previously undescribed locus, named FJ. In total, 7 polymorphic sites at these loci were analyzed for their association with hypertension in 51 normotensive and 126 hypertensive age-matched individuals. There were no significant differences between the 2 phenotypic classes with respect to either allele or genotype frequencies. However, when we tested for nonallelic associations (linkage disequilibrium), we found that of the 120 multilocus comparisons, 16 deviated significantly from random in the hypertensive class, but there were no significant deviations in the normotensive group. These findings suggest that genetic interactions between multiple loci rather than variants of a single gene underlie the genetic basis of hypertension in our study subjects. We hypothesize that such interactions may account for the inconsistent findings in previous studies because, unlike our study, prior studies almost always examined single-locus effects and did not consider the effects of variation at other potentially interacting loci.

Attenuated renal response to dopaminergic drugs in spontaneously hypertensive rats

Activation of renal dopamine-1 receptors decreases sodium transport. However, the spontaneously hypertensive rat retains sodium despite increased renal dopamine concentration. We tested the hypothesis that the abnormal sodium handling in spontaneously hypertensive rats (Okamoto-Aoki strain) is related to a decreased dopaminergic response by studying the effects of the intrarenal infusion of the dopamine-1 agonist SKF-38393 and the dopamine-1 antagonist SCH-23390 in hypertensive and in normotensive Wistar-Kyoto rats. Rats (9-16 weeks old) were studied with renal nerves intact under pentobarbital anesthesia (n = 5-6 in each group). Specificity of dopamine-1 effects of SKF-38393 was verified because its natriuretic effect was blocked in a dose-related manner by the dopamine-1 antagonist SCH-23390 (n = 5). Intrarenal but resulted in a dose-related natriuresis and diuresis in normotensive but not in hypertensive rats. Intrarenal arterial infusion of the dopamine-1 antagonist SCH-23390 alone induced an antinatriuresis, without affecting glomerular filtration rate, in normotensive but not in hypertensive rats. Addition of the dopamine-2 antagonist YM-09151 to the dopamine-1 antagonist infusion did not enhance the effect of the dopamine-1 antagonist. The lack of response to the dopamine-1 agonist or antagonist in hypertensive rats was not due to differences in renal dopamine-1 receptor density (1.3 +/- 0.3 pmol/mg protein for spontaneously hypertensive rats, n = 4; 1 +/- 0.2 for Wistar-Kyoto rats, n = 4) or affinity; distribution determined by autoradiography was also similar. The abnormal renal sodium handling in 9-16-week-old spontaneously hypertensive rats is in part due to decreased response distal to the dopamine-1 receptor.

Familial nephrosis, nerve deafness, and hypoparathyroidism

Two male siblings with nephrotic syndrome, nerve deafness, and hypoparathyroidism are described. Each child, one at five years of age and the other at eight years, died in renal failure. At autopsy the parathyroid glands were absent in one child and hypoplastic in the other one. Two twin male siblings presented with similar findings and died at the age of three years. At autopsy their parathyroid glands were fibrotic, and glomerular basement membranes were thickened. This may be the first recorded association of familial nephrosis, nerve deafness, and hypoparathyroidism. The mode of transmission is compatible with autosomal recessive inheritance.

Dopamine receptor subtypes in renal brush border and basolateral membranes

Dopamine (DA) modulates renal tubular sodium transport by actions at both brush border (BBM) and basolateral membranes (BLM). DA receptors have been demonstrated in proximal tubule but the subtype of DA receptor in either BBM or BLM has not been determined. DA-1 receptors were quantitated by the specific binding of 125I-SCH 23982, a DA-1 antagonist (defined by 20 microM SCH 23390, a DA-1 antagonist) and DA-2 receptors by the specific binding of 3H-methyl-spiroperidol or 3H-spiroperidol (defined by 30 microM trifluperidol, a predominantly DA-2 antagonist). The specific binding of 125I-SCH 23982 and 3H-methyl-spiroperidol or 3H-spiroperidol were saturable with time and ligand concentration and reversible. Analysis of Rosenthal plots by non-linear regression revealed a high affinity site and a very low affinity site for both BLM and BBM. Maximum receptor density was similar in BBM and BLM. Competition experiments with 125I-SCH 23982 revealed high and low affinity binding sites in both BBM and BLM. The high affinity site was characteristic of a DA-1 receptor. Competition experiments with 3H-spiroperidol were also suggestive of DA-2 receptors. DA-1 but not DA-2 drugs increased adenylate cyclase and phospholipase-C activities in both BBM and BLM. However, their effects were greater in BLM than BBM. We conclude that DA-1 and DA-2 receptors are present in both BBM and BLM in canine kidney. Renal DA-1 receptors are linked to stimulation of both adenylate cyclase and phospholipase-C activity.

Microsphere measurement of intrarenal circulation of the dog

Distribution of cortical blood flow was measured in the dog by a technique based on radionuclide-labeled microspheres. Initially it was necessary to test possible pitfalls of this technique. Completeness of trapping in the kidney, the effect on renal function, and the notion that microsphere distribution reflects blood flow distribution in the kidney cortex were studied. Renal vein blood contained less than 0.2% of the microspheres (16.8µ diameter) found in the renal artery after an aortic injection. No impairment of C PAH (control 167±4; postinjection 179±31 ml/min), C In (control 39.3%6; postinjection 37.6±2 ml/min), and T m glucose (control 90.8±13; postinjection 102±24) was found using doses adequate to measure renal blood flow (5 mg/injection x 4 injections). After 4 injections of 50 mg each significant impairment of renal function was observed. Intrarenal blood flow distribution was determined during hemorrhagic hypotension. 169 Yb-labeled microspheres were injected into the root of the aorta before, and 85 Sr-labeled microspheres after, acute hemorrhage. Radioactivity was measured in the outer two thirds and inner one third of kidney slices. Tissue blood flow was calculated and expressed as the ratio of outer cortex to inner cortex counts. Renal blood flow was redistributed to the inner cortex after hemorrhage (ratio before, 3.00; after 1.30, P < 0.01). Finally, the results of this technique were compared to a widely used method of measuring intrarenal blood flow distribution, 133 Xe washout. The first component of the washout technique correlated fairly well with total cortical flow but it was not possible to match the second component with any single anatomical area of the kidney. Limitations of the 133 Xe washout are discussed.

Dopamine(1) receptor, G(salpha), and Na(+)-H(+) exchanger interactions in the kidney in hypertension

The ability of dopamine(1) (D(1)) receptors to inhibit luminal Na(+)-H(+) exchanger (NHE) activity in renal proximal tubules and induce a natriuresis is impaired in spontaneously hypertensive rats (SHR). However, it is not clear whether the defect is at the level of the D(1) receptor, G(salpha), or effector proteins. The coupling of the D(1) receptor to G(salpha) and NHE3 was studied in renal brush border membranes (BBM), devoid of cytoplasmic second messengers. D(1) receptor, G(salpha), and NHE3 expressions were similar in SHR and their normotensive controls, Wistar-Kyoto rats (WKY). Guanosine-5'-O:-(3-thiotriphosphate) (GTPgammaS) decreased NHE activity and increased NHE3 linked with G(salpha) similarly in WKY and SHR, indicating normal G(salpha) and NHE3 regulation in SHR. However, D(1) agonists increased NHE3 linked with G(salpha) in WKY but not in SHR, and the inhibitory effects of D(1) agonists on NHE activity were less in SHR than in WKY. Moreover, GTPgammaS enhanced the inhibitory effect of D(1) agonist on NHE activity in WKY but not in SHR, suggesting an uncoupling of the D(1) receptor from G(salpha)/NHE3 in SHR. Similar results were obtained with the use of immortalized renal proximal tubule cells from WKY and SHR. We conclude that the defective D(1) receptor function in renal proximal tubules in SHR is proximal to G(salpha)/effectors and presumably at the receptor level. The mechanism(s) responsible for the uncoupling of the D(1) receptor from G proteins remains to be determined. Because the primary structure of the D(1) receptor is not different between normotensive and hypertensive rats, differences in D(1) receptor posttranslational modification are possible.

Dopamine receptor signaling defects in spontaneous hypertension

Dopamine produced by renal proximal tubules acts as an intrarenal natriuretic factor by direct tubular action; this paracrine effect is influenced by the state of sodium balance. Up to 60% of sodium excretion with volume (2%-10%) expansion may be mediated by D1-like receptors. The renal paracrine effect of dopamine is impaired in genetic hypertension; this is due to defects in renal dopamine production or transduction of the dopamine signal. The Dahl salt sensitive rat and the spontaneously hypertensive rat (SHR), which have normal renal dopamine production and expression of dopamine receptors, have a defect in the coupling of a D1-like receptor to G-protein/effector enzyme complex. A consequence of the defective D1-like receptor/effector enzyme coupling in SHR is a decreased ability of D1 agonists to inhibit Na+/H+ exchange and Na+/K+-ATPase activity. The defect is 1) genetic, since it precedes the onset of and cosegregates with the hypertension; 2) receptor specific, since it is not shared by other humoral agents; and 3) confined to the renal proximal tubule. Two of the cloned dopamine receptors in mammals are D1-like (D1A and D1B). The D1A receptor gene is expressed to a greater extent in renal proximal tubules than the D1B receptor gene. The D1-like receptor is important in the pathogenesis of hypertension. Chronic blockade of dopamine receptors accelerates the development of hypertension in normotensive and hypertensive rats. Moreover, disruption of the D1A receptor gene in mice increases systolic blood pressure and results in diastolic hypertension. The abnormal D1-like receptor in SHR may be the D1A receptor; its uncoupling from the G-protein/effector enzyme complex in renal proximal tubules of SHR may be due to mistargeting. The mechanism for this "mistargeting" of the D1A receptor is not due to a mutation in the primary sequence and remains to be determined.

Drug Repurposing: An Effective Tool in Modern Drug Discovery

Drug repurposing is using an existing drug for a new treatment that was not indicated before. It has received immense attention during the COVID-19 pandemic emergency. Drug repurposing has become the need of time to fasten the drug discovery process and find quicker solutions to the over-exerted healthcare scenario and drug needs. Drug repurposing involves identifying the drug, evaluating its efficiency using preclinical models, and proceeding to phase II clinical trials. Identification of the drug candidate can be made through computational and experimental approaches. This approach usually utilizes public databases for drugs. Data from primary and translational research, clinical trials, anecdotal reports regarding off-label uses, and other published human data information available are included. Using artificial intelligence algorithms and other bioinformatics tools, investigators systematically try to identify the interaction between drugs and protein targets. It can be combined with genetic data, clinical analysis, structure (molecular docking), pathways, signatures, targets, phenotypes, binding assays, and artificial intelligence to get an optimum outcome in repurposing. This article describes the strategies involved in drug repurposing and enlists a series of repurposed drugs and their indications.

Dopamine inhibits Na(+)-H+ exchanger activity in renal BBMV by stimulation of adenylate cyclase

To determine a renal tubular mechanism for the natriuretic effect of dopamine (DA) and DA-1 agonists, we measured Na(+)-H+ exchange activity (amiloride sensitive) in rat renal cortical brush-border membrane vesicles (BBMV). Renal cortical tissues were preincubated with ligands before BBMV preparation to study Na(+)-H+ exchange activity in the absence of the added ligands that may compete for ion binding sites of the exchanger. DA and DA-1 agonist-inhibited Na(+)-H+ exchange activity was concentration and time dependent. The inhibitory effect was not due to increased permeability, collapse of the proton gradient, or change in vesicle size and did not extend to Na(+)-glucose symport. DA-2 agonists had no effect, whereas alpha-adrenergic agonists increased Na(+)-H+ exchange activity. Kinetic analysis revealed that the DA-1 agonist inhibited Na(+)-H+ exchange activity by a noncompetitive process. 2',5'-Dideoxyadenosine inhibited adenylate cyclase activity and reversed the inhibitory effect of DA-1 agonist on the exchanger. H4, an isoquinoline sulfonamide, which inhibits protein kinase A, also reversed the inhibitory effect of DA-1 agonist on the exchanger. Thus the DA-1 agonist-mediated inhibition of Na(+)-H+ exchange activity in BBMV is a receptor-mediated adenylate cyclase-linked process.

Impaired renal D(1)-like and D(2)-like dopamine receptor interaction in the spontaneously hypertensive rat

D(1)-like (D(1), D(5)) and D(2)-like (D(2), D(3), D(4)) dopamine receptors interact in the kidney to produce a natriuresis and a diuresis. Disruption of D(1) or D(3) receptors in mice results in hypertension that is caused, in part, by a decreased ability to excrete an acute saline load. We studied D(1)-like and D(2)-like receptor interaction in anesthetized spontaneously hypertensive rats (SHR) by the intrarenal infusion of Z-1046 (a novel dopamine receptor agonist with rank order potency of D(3)> or =D(4)>D(2)>D(5)>D(1)). Z-1046 increased glomerular filtration rate (GFR), urine flow, and sodium excretion in normotensive Wistar-Kyoto rats but not in SHRs. The lack of responsiveness to Z-1046 in SHRs was not an epiphenomenon, because intrarenal cholecystokinin infusion increased GFR, urine flow, and sodium excretion to a similar extent in the two rat strains. We conclude that renal D(1)-like and D(2)-like receptor interaction is impaired in SHRs. The impaired D(1)-like and D(2)-like receptor interaction in SHRs is not caused by alterations in the coding sequence of the D(3) receptor, the D(2)-like receptor expressed in rat renal tubules that has been shown to be involved in sodium transport. Because the diuretic and natriuretic effects of D(1)-like receptors are, in part, caused by an interaction with D(2)-like receptors, it is possible that the decreased Z-1046 action in SHRs is secondary to the renal D(1)-like receptor dysfunction in this rat strain.

Degradation of porstaglandin F2alpha in the human pulmonary circulation

Degradation of prostaglandins (PGs) during passage through the human pulmonary circulation was investigated by measuring the transpulmonary plasma PGF2 alpha difference during continuous intravenous infusion of PGF2 alpha (5-10 mug/min). Seven patients with cardiological disorders and two patients with extensive pulmonary abnormalities were investigated during diagnostic cardiac catheterization. PGF2 alpha levels were measured by radioimmunoassay. The seven cardiac patients were found to have transpulmonary PGF2 alpha differences of 47-88%, indicating metabolism of the PG in the lungs. A patient with extensive bronchiectasis had an apparently normal transpulmonary PGF2alpha difference despite gross abnormalities in routine lung function tests. A patient with primary pulmonary arterial hypertension showed no metabolism of PGF2alpha in the pulmonary circulation. The results show that PG degradation is an aspect of normal lung function and suggest that it becomes imparied when extensive pulmonary vascular damage exists.

Dopamine D1A receptor regulation of phospholipase C isoform

In LTK- cells stably transfected with rat D1A receptor cDNA, fenoldopam, a D1 agonist, increased phosphatidylinositol 4, 5-bisphosphate hydrolysis in a time-dependent manner. In the cytosol, phospholipase C (PLC) activity increased (50 +/- 7%) in 30 s, returned to basal level at 4 h, and decreased below basal values by 24 h; in the membrane, PLC activity also increased (36 +/- 13%) in 30 s, returned to basal level at 10 min, and decreased below basal value at 4 and 24 h. Fenoldopam also increased PLC-gamma protein in a time-dependent manner. The latter was blocked by the D1 antagonist SKF83742 and by a D1A antisense oligodeoxynucleotide, indicating involvement of the D1A receptor. The fenoldopam-induced increase in PLC-gamma and activity was mediated by protein kinase A (PKA) since it was blocked by the PKA antagonist Rp-8-CTP-adenosine cyclic 3':5'-monophosphorothioate (Rp-8-CTP-cAMP-S) and mimicked by direct stimulation of adenylyl cyclase with forskolin or by a PKA agonist, Sp-cAMP-S. Protein kinase C (PKC) was also involved, since the fenoldopam-induced increase in PLC-gamma protein was blocked by two different PKC inhibitors, calphostin C and chelerythrine; calphostin C also blocked the fenoldopam-induced increase in PLC activity. In addition, forskolin and a PKA agonist, Sp-8-CTP-cAMP-S, increased PKC activity, and direct stimulation of PKC with phorbol 12-myristate 13-acetate increased PLC-gamma protein and activity, effects that were blocked by calphostin C. We suggest that the D1A-mediated stimulation of PLC occurs as a result of PKA activation. PKA then stimulates PLC-gamma in cytosol and membrane via activation of PKC.

Differential expression of adenylyl cyclases in the rat nephron

BACKGROUND

Adenylyl cyclases (ACs) are a family of enzymes that catalyze the formation of the second-messenger cyclic adenosine 3',5'-monophosphate (cAMP). At least nine isoforms of AC have been cloned. These isoforms differ in their tissue distribution and basal activity. AC isoforms also differ in their capacity to be stimulated or inhibited by G protein alpha(i), alpha(s) and beta/gamma subunits, protein kinase C, and intracellular calcium. The distribution of ACs in the kidney is only partially known, although it is known that ACs play important roles in kidney signal transduction. Several receptors are known to couple to AC, but their linkage to individual AC isoforms in the kidney is not known.

METHODS

This study investigated the tissue distribution of AC isoforms along the nephron of Wistar-Kyoto rats using reverse transcription-polymerase chain reaction (RT-PCR), immunohistochemistry, and immunoblotting.

RESULTS

While AC VI and IX mRNA were found in all nephron segments, there was no expression of AC VIII mRNA. ACs II through V and VII mRNA were variably found in specific nephron segments. mRNA for AC isoforms II, III, VI, VII, and IX were expressed in renal proximal tubules. All of the AC isoforms studied, except VIII, were found in glomeruli. Immunoblotting and immunohistochemistry confirmed the mRNA results. AC isoforms II, III, IV, and IX were expressed in luminal rather than in basolateral membranes. However, immunohistochemical studies were not feasible for the other isoforms that could be expressed in basolateral membranes.

CONCLUSION

Knowledge of the distribution of ACs may help establish the linkage between receptors and specific AC isoforms and define their functions.

Adrenergic and endothelin B receptor-dependent hypertension in dopamine receptor type-2 knockout mice

Polymorphism of the dopamine receptor type-2 (D(2)) gene is associated with essential hypertension. To assess whether D(2) receptors participate in regulation of blood pressure (BP), we studied mice in which the D(2) receptor was disrupted. In anesthetized mice, systolic and diastolic BPs (in millimeters of mercury) were higher in D(2) homozygous and heterozygous mutant mice than in D(2)+/+ littermates. BP after alpha-adrenergic blockade decreased to a greater extent in D(2)-/- mice than in D(2)+/+ mice. Epinephrine excretion was greater in D(2)-/- mice than in D(2)+/+ mice, and acute adrenalectomy decreased BP to a similar level in D(2)-/- and D(2)+/+ mice. An endothelin B (ET[B]) receptor blocker for both ET(B1) and ET(B2) receptors decreased, whereas a selective ET(B1) blocker increased, BP in D(2)-/- mice but not D(2)+/+ mice. ET(B) receptor expression was greater in D(2)-/- mice than in D(2)+/+ mice. In contrast, blockade of ET(A) and V(1) vasopressin receptors had no effect on BP in either D(2)-/- or D(2)+/+ mice. The hypotensive effect of an AT(1) antagonist was also similar in D(2)-/- and D(2)+/+ mice. Basal Na(+),K(+)-ATPase activities in renal cortex and medulla were higher in D(2)+/+ mice than in D(2)-/- mice. Urine flow and sodium excretion were higher in D(2)-/- mice than in D(2)+/+ mice before and after acute saline loading. Thus, complete loss of the D(2) receptor results in hypertension that is not due to impairment of sodium excretion. Instead, enhanced vascular reactivity in the D(2) mutant mice may be caused by increased sympathetic and ET(B) receptor activities.

Regulation of NHE3 activity by G protein subunits in renal brush-border membranes

NHE3 activity is regulated by phosphorylation/dephosphorylation processes and membrane recycling in intact cells. However, the Na(+)/H(+) exchanger (NHE) can also be regulated by G proteins independent of cytoplasmic second messengers, but the G protein subunits involved in this regulation are not known. Therefore, we studied G protein subunit regulation of NHE3 activity in renal brush-border membrane vesicles (BBMV) in a system devoid of cytoplasmic components and second messengers. Basal NHE3 activity was not regulated by G(s)alpha or G(i)alpha, because antibodies to these G proteins by themselves were without effect. The inhibitory effect of D(1)-like agonists on NHE3 activity was mediated, in part, by G(s)alpha, because it was partially reversed by anti-G(s)alpha antibodies. Moreover, the amount of G(s)alpha that coimmunoprecipitated with NHE3 was increased by fenoldopam in both brush-border membranes and renal proximal tubule cells. Furthermore, guanosine 5'-O-(3-thiotriphosphate) but not guanosine 5'-O-(2-thiodiphosphate), the inactive analog of GDP, increased the amount of G(s)alpha that coimmunoprecipitated with NHE3. The alpha(2)-adrenergic agonist, UK-14304 or pertussis toxin (PTX) alone had no effect on NHE3 activity, but UK-14304 and PTX treatment attenuated the D(1)-like receptor-mediated NHE3 inhibition. The ability of UK-14304 to attenuate the D(1)-like agonist effect was not due to G(i)alpha, because the attenuation was not blocked by anti-G(i)alpha antibodies or by PTX. Anti-Gbeta(common) antibodies, by themselves, slightly inhibited NHE3 activity but had little effect on D(1)-like receptor-mediated NHE3 inhibition. However, anti-Gbeta(common) antibodies reversed the effects of UK-14304 and PTX on D(1)-like agonist-mediated NHE3 inhibition. These studies provide concrete evidence of a direct regulatory role for G(s)alpha, independent of second messengers, in the D(1)-like-mediated inhibition of NHE3 activity in rat renal BBMV. In addition, beta/gamma dimers of heterotrimeric G proteins appear to have a stimulatory effect on NHE3 activity in BBMV.

Dopamine D1 receptor and protein kinase C isoforms in spontaneously hypertensive rats

-Dopamine, via D1-like receptors, stimulates the activity of both protein kinase A (PKA) and protein kinase C (PKC), which results in inhibition of renal sodium transport. Since D1-like receptors differentially regulate sodium transport in normotensive and hypertensive rats, they may also differentially regulate PKC expression in these rat strains. Thus, 2 different D1-like agonists (fenoldopam or SKF 38393) were infused into the renal artery of anesthetized normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) (n=5 to 6/drug/strain). Ten or 60 minutes after starting the D1-like agonist infusion, both the infused kidney and the noninfused kidney that served as control were prepared for analysis. The D1-like agonists produced a greater diuresis and natriuresis and inhibited Na+,K+-ATPase activity in proximal tubule (PT) and medullary thick ascending limb (mTAL) to a greater extent in WKY (Delta20+/-1%) than in SHR (Delta7+/-1%, P<0.001). D1-like agonists had no effect on PKC-alpha or PKC-lambda expression in either membrane or cytosol but increased PKC-theta expression in PT in both WKY and SHR at 10 minutes but not at 60 minutes. However, membranous PKC-delta expression in PT and mTAL decreased in WKY but increased in SHR with either 10 or 60 minutes of D1-like agonist infusion. D1-like agonists also decreased membranous PKC-zeta expression in PT and mTAL in WKY but increased it in PT but not in mTAL in SHR. We conclude that there is differential regulation of PKC isoform expression by D1-like agonists that inhibits membranous PKC-delta and PKC-zeta in WKY but stimulates them in SHR; this effect in SHR is similar to the stimulatory effect of norepinephrine and angiotensin II and may be a mechanism for their differential effects on sodium transport.

D1 dopamine receptor hyperphosphorylation in renal proximal tubules in hypertension

A defect in the coupling of the D(1) receptor (D(1)R) to its G protein/effector complex in renal proximal tubules plays a role in the pathogenesis of spontaneous hypertension. As there is no mutation of the D(1)R gene in the spontaneously hypertensive rat (SHR), we tested the hypothesis that the coupling defect is associated with constitutive desensitization/phosphorylation of the D(1)R. The following experiments were performed: (1) Cell culture and membrane preparations from rat kidneys and immortalized rat renal proximal tubule cells (RPTCs); (2) immunoprecipitation and immunoblotting; (3) cyclic adenosine 3',5' monophosphate and adenylyl cyclase assays; (4) immunofluorescence and confocal microscopy; (5) biotinylation of cell surface proteins; and (6) in vitro enzyme dephosphorylation. Basal serine-phosphorylated D(1)Rs in renal proximal tubules, brush border membranes, and membranes from immortalized RPTCs were greater in SHRs (21.0+/-1.5 density units, DU) than in normotensive rats (7.4+/-2.9 DU). The increased basal serine phosphorylation of D(1)Rs in SHRs was accompanied by decreased expression of D(1)R at the cell surface, and decreased ability of a D(1)-like receptor agonist (fenoldopam) to stimulate cyclic adenosine 3',5' monophosphate (cAMP) production. Increasing protein phosphatase 2A activity with protamine enhanced the ability of fenoldopam to stimulate cAMP accumulation (17+/-4%) and alter D(1)R cell surface expression in intact cells from SHRs. Alkaline phosphatase treatment of RPTC membranes decreased D(1)R phosphorylation and enhanced fenoldopam stimulation of adenylyl cyclase activity (26+/-6%) in SHRs. Uncoupling of the D(1)R from its G protein/effector complex in renal proximal tubules in SHRs is caused, in part, by increased D(1)R serine phosphorylation.

Autoregulation of renal blood flow in the puppy

The ability of the immature kidney to autoregulate blood flow was investigated. Renal blood flow was measured by electromagnetic flowmeter. In six puppies, selective blockade of the intrarenal effects of angiotensin II (AII) by [1-sarcosine, 8-alanine]angiotensin II (anti-AII) administered into the renal artery did not change renal blood flow. During selective renal AII blockade, intravenous AII raised perfusion pressure from 76 +/- 2 to 100 +/- 6 mmHg. Renal blood flow increased from 1.59 +/- 0.29 to 1.98 +/- 0.59 ml/g kidney per min, but returned to control levels within 40 s in spite of persistent arterial pressure elevation. In another group of seven puppies, renal blood flow remained constant despite reduction of renal perfusion pressure by aortic constriction to 60 mmHg. In two of these seven puppies intrarenal anti-AII did not abolish autoregulation. Autoregulation of renal blood flow occurs in the puppy and is not influenced by inhibition of angiotensin. The renin-angiotensin system does not appear to be involved in the normal regulation of renal blood flow in the puppy.