Dopamine-induced recruitment of dopamine D1 receptors to the plasma membrane

The recruitment of G protein-coupled receptors from the cytoplasm to the plasma membrane generally is believed to be a constitutive process. We show here by the use of both confocal microscopy and subcellular fractionation that, for at least one such receptor, this recruitment is regulated and not constitutive. Cells from a proximal tubular-like cell line, LLCPK1 cells, were incubated with either a D1 agonist, a dopamine precursor, or an inhibitor of dopamine metabolism to increase dopamine availability in the cell. Each of the three procedures led to a rapid translocation of dopamine D1 receptors from the cytosol to the plasma membrane.

Detection of dopamine receptor D1A subtype-specific mRNA in rat kidney by in situ amplification

In recent years, both molecular biological and immunohistochemical techniques, utilizing receptor subtype-specific probes and antibodies to cloned central nervous system dopamine receptors, have revealed their presence in a number of peripheral organs and tissues. Molecular techniques have been hindered by the low abundance of receptor mRNA in these sites, and reverse transcription-polymerase chain reaction (RT-PCR) has been utilized to address this problem. However, RT-PCR is most often employed on either isolated mRNA or microdissected tissue samples, thereby limiting interpretation of whole tissue distribution. The present paper describes the use of a novel self-sustained sequence replication system (3SR) to amplify a target mRNA sequence in situ within the tissue or cell of interest that is then detected with the use of an internal labeled probe, using standard nonisotopic in situ hybridization. Specifically, D1A receptor mRNA was amplified and detected in kidney sections of Wistar-Kyoto rats (WKY). The amplified D1A receptor mRNA was localized to renal arterioles, juxtaglomerular apparatus, and both proximal and distal tubules. mRNA was colocalized to regions shown also to contain D1A receptor protein. D1A receptor mRNA was predominantly localized in the cortex. Specificity of D1A receptor mRNA detection was confirmed by appropriate localization in rat brain sections known to express D1A receptor mRNA. In addition, we confirmed the presence of renal D1A receptor mRNA by RT-PCR. We conclude that D1A receptor mRNA is expressed in a site-specific manner in the WKY kidney. The use of 3SR in situ permits elucidation of site specific mRNA localization in a manner not reported previously.

Zis: a developmentally regulated gene expressed in juxtaglomerular cells

Renal juxtaglomerular (JG) cells are specialized myoepithelioid cells located in the afferent arteriole at the entrance to the glomerulus. Their main function and distinctive feature is the synthesis and release of renin, the key hormone-enzyme of the renin-angiotensin system that regulates arterial blood pressure. Despite their relevance to health and disease, not much is known about factors that confer and/or maintain JG cell identity. To identify genes uniquely expressed in JG cells, we used a cell culture model and RNA differential display. JG cells cultured for 2 days express renin and renin mRNA, but after 10 days in culture they no longer contain or release renin and renin mRNA is reduced 700-fold. We report one cDNA differentially expressed in the 2-day JG cell culture that detects a 2.6-kb mRNA expressed at higher levels in newborn than adult kidney. Screening a 2-day culture JG cell cDNA library yielded clones representing differentially spliced transcripts. These cDNAs encode one unique protein (Zis) containing zinc fingers and domains characteristic of splicing factors and RNA binding proteins. Northern blot analysis confirmed Zis mRNA expression in differentiated JG cells, and identified an additional unique 1.5-kb transcript. The Zis transcripts are developmentally regulated in kidney and a number of other organs. The features of the Zis protein and its organ distribution suggest a possible role in regulation of transcription and/or splicing, both important steps for controlling developmentally expressed genes.

Expression of the subtype 2 angiotensin (AT2) receptor protein in rat kidney

In situ hybridization studies have suggested that the subtype 2 angiotensin (AT2) receptor gene is expressed in fetal and newborn rat kidney but is undetectable in the adult animals. In the present study, we investigated the expression of AT2 receptor protein in the fetal (days 14 and 19 of fetal life), newborn (day 1 postpartum), and adult (4-week-old and 3-month-old) rat kidney. Polyclonal anti-peptide antiserum was raised against the amino terminus of the native AT2 receptor. The selectivity of the antiserum was validated by recognition of the AT2 receptor in a stably transfected COS-7 cell line by Western blot and immunocytochemical analysis. As a positive control, the AT2 receptor signal was detected strongly in the adrenal gland. Positive immunohistochemical staining was observed in the mesenchymal cells and ureteric buds of the 14-day fetal kidney and in the glomeruli, tubules, and vessels in the 19-day fetal and newborn kidney. Glomeruli expressing the AT2 receptor were localized mainly in the outer layer of the renal cortex. In the young (4-week-old) and mature (3-month-old) adult rat on normal sodium intake, renal AT2 receptor immunoreactivity was present in glomeruli but substantially diminished compared with that of newborn rats. In both young and mature adult rats, dietary sodium depletion increased the renal AT2 receptor signal, mainly in the glomeruli and interstitial cells. Preimmune and preadsorption controls were negative. Western blot analysis detected a single 44-kD band in the fetal and newborn rat kidney and in the young and mature adult rat kidney. Dietary sodium depletion increased the density of the AT2 receptor band in mature adult rat kidneys. These data provide evidence that the AT2 receptor protein is expressed in the fetal and newborn rat kidney, diminishes in adult life, and is reexpressed in the adult in response to sodium depletion.

Biomechanical coupling in renin-releasing cells

The renin-angiotensin system is a major regulatory system controlling extracellular fluid volume and blood pressure. The rate-limiting enzyme in this hormonal cascade is renin, which is synthesized and secreted into the circulation by renal juxtaglomerular (JG) cells. The renal baroreceptor is a key physiologic regulator of renin secretion, whereby a change in renal perfusion pressure is sensed by these cells and results in a change in renin release. However, the mechanism, direct or indirect, underlying pressure transduction is unknown. We studied the direct application of mechanical stretch to rat JG cells and human renin-expressing (CaLu-6) cells on the release of renin. JG cells released a low level of baseline renin, comprising < 5% of their total renin content. By contrast, renin secretion from CaLu-6 cells comprised approximately 30% of cellular stores, yet was also stimulated twofold by 10 microM forskolin (P </= 0.001). In JG cells, mechanical stretch inhibited basal renin release by 42% (P < 0.01) and forskolin-stimulated renin release by 25% (P < 0.05). In CaLu-6 cells, stretch inhibited basal- and forskolin-stimulated renin release by 30 and 26%, respectively (both P < 0.01). Northern blot analysis demonstrated a stretch-induced reduction in baseline renin mRNA accumulation of 26% (P < 0.05) in JG and 46% (P < 0.05) in CaLu-6 cells. The data demonstrate that mechanical stretch in renin-releasing cells inhibits basal and stimulated renin release accompanied by a decrease in renin mRNA accumulation. Further studies will be necessary to characterize the intracellular events mediating biomechanical coupling in renin-expressing cells and the relationship of this signaling pathway to the in vivo baroreceptor control of renin secretion.

The subtype 2 angiotensin receptor regulates renal prostaglandin F2 alpha formation in conscious rats

The angiotensin AT1 receptor mediates renal prostaglandin (PG) E2 production through stimulation of phospholipase A2. Blockade of the AT2 receptor potentiates the angiotensin II-induced increase in PGE2 levels. In the kidney, PGE2 is converted to PGF2 alpha mainly by the enzyme PGE 9-ketoreductase. We hypothesized that the conversion of PGE2 to PGF2 alpha is inhibited by AT2 receptor blockade, resulting in the observed increase in PGE2 levels. Using a microdialysis technique, we monitored changes in renal interstitial fluid PGE2 and PGF2 alpha in response to 5 days of sodium depletion alone or a combination of sodium depletion and intravenous infusion of the AT1 receptor blocker losartan or the AT2 receptor blocker PD-123319 in conscious rats. We utilized the PGF2 alpha-to-PGE2 ratio as an indirect measure of the rate of renal PGF2 alpha formation. Sodium depletion increased PGE2, PGF2 alpha, and the PGF2 alpha-to-PGE2 ratio. During sodium depletion, losartan decreased PGE2 and PGF2 alpha and did not change the PGF2 alpha-to-PGE2 ratio. In contrast, PD-123319 increased PGE2, decreased PGF2 alpha, and decreased the PGF2 alpha-to-PGE2 ratio. These data demonstrate that activation of the renin-angiotensin system during sodium depletion physiologically increases renal conversion of PGE2 to PGF2 alpha. The increase in renal production of PGF2 alpha is mediated through stimulation of the angiotensin AT2 receptor.

Localization of the dopamine D1 receptor protein in the human heart and kidney

The dopamine D1 receptor has recently been identified in the rat heart and kidney. In the present study, using Western blot analysis and light microscopic immunohistochemistry, we examined D1 receptor protein expression in the human kidney and heart. Antipeptide polyclonal rabbit antiserum was raised against the third extracellular domain of the native receptor and affinity-purified using a protein-A column. Selectivity of the antiserum was validated by recognition of the D1 receptor expressed in stably transfected LTK- cells and Sf-9 cells. The immunohistochemical staining for D1 receptor protein was distributed throughout the atrium and ventricular myocardium and in the coronary vessels. In the kidney, positive immunoreactive signal was detected in the proximal and distal tubules, the collecting ducts, and the large intrarenal vasculature, whereas staining was absent in the juxtaglomerular (JG) cells and the glomeruli. D1 receptor antiserum preadsorbed against the immunizing peptide did not produce significant staining. In Western blot analysis, a single 55-kD band was detected for the D1 receptor in membranes from the D1 receptor transfected Sf-9 cells but not in nontransfected cells. In the heart and kidney, we detected a 55-kD band as well as an additional 40-kD band, which may reflect partial degradation of the receptor protein. These results provide the first evidence for the localization of the dopamine D1 receptor protein in the human heart and kidney. The similar distribution of this subtype receptor in the human heart and kidney to that in the rat supports the possible (patho)physiological significance of the peripheral dopamine system in humans.

The subtype 2 (AT2) angiotensin receptor mediates renal production of nitric oxide in conscious rats

The angiotensin AT2 receptor modulates renal production of cyclic guanosine 3',5'-monophosphate (cGMP; J. Clin. Invest. 1996. 97:1978-1982). In the present study, we hypothesized that angiotensin II (Ang II) acts at the AT2 receptor to stimulate renal production of nitric oxide leading to the previously observed increase in cGMP. Using a microdialysis technique, we monitored changes in renal interstitial fluid (RIF) cGMP in response to intravenous infusion of the AT2 receptor antagonist PD 123319 (PD), the AT1 receptor antagonist Losartan, the nitric oxide synthase (NOS) inhibitor nitro--arginine-methyl-ester (-NAME), the specific neural NOS inhibitor 7-nitroindazole (7-NI), or Ang II individually or combined in conscious rats during low or normal sodium balance. Sodium depletion significantly increased RIF cGMP. During sodium depletion, both PD and -NAME caused a similar decrease in RIF cGMP. Combined administration of PD and -NAME decreased RIF cGMP to levels observed with PD or -NAME alone or during normal sodium intake. During normal sodium intake, Ang II caused a twofold increase in RIF cGMP. Neither PD nor -NAME, individually or combined, changed RIF cGMP. Combined administration of Ang II and either PD or -NAME produced a significant decrease in RIF cGMP compared with that induced by Ang II alone. Combined administration of Ang II, PD, and -NAME blocked the increase in RIF cGMP produced by Ang II alone. During sodium depletion, 7-NI decreased RIF cGMP, but the reduction of cGMP in response to PD alone or PD combined with 7-NI was greater than with 7-NI alone. During normal sodium intake, 7-NI blocked the Ang II-induced increase in RIF cGMP. PD alone or combined with 7-NI produced a greater inhibition of cGMP than did 7-NI alone. During sodium depletion, 7-NI (partially) and -NAME (completely) inhibited RIF cGMP responses to -arginine. These data demonstrate that activation of the renin- angiotensin system during sodium depletion increases renal nitric oxide production through stimulation by Ang II at the angiotensin AT2 receptor. This response is partially mediated by neural NOS, but other NOS isoforms also contribute to nitric oxide production by this pathway.

Dopamine D1A receptors and renin release in rat juxtaglomerular cells

Two dopamine D1-like receptors have been cloned from mammals, the D1 and D5 receptors, also known as D1A and D1B receptors, respectively, in rodents. Although D1-like receptors are known to stimulate renin release, the receptor subtype mediating this action has not been determined. We investigated D1 receptor subtype expression in rat juxtaglomerular cells obtained after enzymatic dispersion of kidney cortex and differential centrifugation. Juxtaglomerular cells in primary culture were immunocytochemically 85% to 95% renin positive. These cells expressed the D1A but not the D1B receptor (mRNA and protein). D1-like receptor function was demonstrated by a concentration-dependent stimulation of cAMP production by dopamine (n = 5-9 per group). Fenoldopam, a D1-like receptor agonist, also caused a concentration-dependent increase in cAMP production and renin secretion that was blocked by the selective D1-like receptor antagonist SCH23390 (n = 4-13 per group). Although the D1 ligands do not distinguish between the cloned D1-like receptors, the actions of fenoldopam were due to occupancy of the D1A receptor: (1) the D1B receptor, the only other mammalian D1-like receptor, is not expressed in juxtaglomerular cells; (2) antisense but not sense D1A oligonucleotides completely blocked the stimulatory effect of fenoldopam on cAMP production and renin secretion. We conclude that there is selective dopamine receptor gene expression in juxtaglomerular cells; the dopamine receptor subtype linked to the stimulation of cAMP and renin secretion in juxtaglomerular cells is the D1A subtype.

Oxygen regulates vascular endothelial growth factor-mediated vasculogenesis and tubulogenesis

To determine whether low oxygen is a stimulus for endothelial cell differentiation and vascular development in the kidney, we examined the effect of low oxygen on rat metanephric organ culture, a model known to recapitulate nephrogenesis in the absence of vessels. After 6 days in culture in standard (20% O2) or low oxygen (1-3% O2) conditions, metanephric kidney growth and morphology were assessed by DNA measurement, and light and electron microscopy. DNA content was higher in 3% O2-treated explants (2.5 +/- 0.17 microgram/kidney, n = 9) than in 20% O2 explants (1.5 +/- 0.09 microgram/kidney, n = 9), P < 0.05. Low oxygen induced proliferation of tubular epithelial cells, resulting in enhanced number of tubules of similar size. Endothelial cells forming capillaries were localized in 3% O2 explants by light and electron microscopy and by immunocytochemistry using endothelial cell markers. Flt-1, Flk-1, and ACE-containing cells were detected in 3% O2-treated explants, whereas 20% O2 explants were virtually negative. VEGF mRNA levels were 10-fold higher in 3% O2-treated explants than in 20% O2-treated explants. Addition of anti-VEGF antibodies to 3% O2-treated explants prevented low oxygen-induced growth and endothelial cell differentiation and proliferation. Our data indicate that low oxygen stimulates growth by cell proliferation and induces tubulogenesis, endothelial cell differentiation, and vasculogenesis in metanephric kidneys in culture. Upregulation of VEGF expression by low oxygen and prevention of low oxygen-induced tubulogenesis and vasculogenesis by anti-VEGF antibodies indicate that these changes were mediated by VEGF. These data suggest that low oxygen is the stimulus to initiate renal vascularization.

Defining the cost of educating undergraduate medical students at the University of Virginia

PURPOSE

To develop a model for calculating the cost of a four-year undergraduate medical education at the University of Virginia School of Medicine (UVA) in 1994-95.

METHOD

All data were based on faculty contact hours (FCHs), the primary driver of cost. (An FCH was an hour during which a faculty member was actively teaching.) First- and second-year data were derived from a published curriculum schedule. Third-year data were derived from hours spent in each clerkship and a series of calculations to assess direct teaching time in each clerkship accurately. Fourth-year data were modeled on an artificial but typical program consisting of the required clerkship in neurology, a two-day course in advanced cardiac life support, and seven elective blocks; electives were chosen based on relative overall popularity. The number of full-time-equivalent (FTE) faculty required was calculated. The salary costs of UVA full-time faculty were calculated. Other total direct costs, including the costs of support and administrative services as well as the costs of the educational contributions of housestaff and contract faculty, were calculated. The overall cost, including direct and indirect costs, was calculated. An average of 139 students per year was assumed.

RESULTS

The total number of FCHs was just under 100,000. The number of FTE faculty required was 223. UVA faculty salary and fringe benefits totaled $29,400,000. The costs of support and administrative services totaled $4,100,000; the costs of housestaff and contract faculty totaled $2,300,000. The overall educational costs totaled $49,600,000.

CONCLUSION

The overall cost of a four-year medical education at UVA was $357,000 per student. Although the process of calculating this cost was complex and, at times, based on assumptions open to debate, the model developed can be applied to any medical education setting.

Localization of dopamine D1A receptor protein and messenger ribonucleic acid in rat adrenal cortex

Pharmacological, physiological, and autoradiographic studies have suggested the presence of dopamine receptors in the adrenal gland. Dopaminergic ligands have been shown to modulate adrenocortical aldosterone biosynthesis and secretion as well as adrenomedullary catecholamine production and release. Using a combination of light microscopic immunochemistry and in situ amplification and hybridization, the present study sought to determine the site-specific expression of the recently cloned D1A receptor subtype in rat adrenal gland. Light microscopic immunohistochemistry was conducted using polyclonal antisera raised to the putative rat D1A receptor. Immunoreactive product was detected using an avidin-biotin immunoperoxidase method. D1A receptor messenger RNA (mRNA) was detected using a transcription-based isothermal in situ amplification and hybridization approach using receptor-specific mRNA oligonucleotide probes. The amplified product was localized using an alkaline phosphatase 4-nitro blue tetrazolium chloride/5-bromo-4-chloro-3-indolyl-phosphate technique. This combined experimental approach, using both receptor subtype-selective antibodies and oligonucleotide probes, allows for the site-specific localization of the D1A receptor subtype, which would otherwise not be possible with the pharmacological methods currently available. The D1A receptor protein and mRNA were expressed solely in the zona glomerulosa of the rat adrenal gland, with no signal evident in any of the other cortical layers or in the medulla. Such a distribution raises the possibility that the D1A receptor subtype could modulate, at least in part, some of the known effects of dopamine on aldosterone secretion.

Preferential release of renal dopamine into the tubule lumen: effect of chronic sodium loading

Dopamine (DA), produced by the renal proximal tubule, has been demonstrated as an intrarenal paracrine hormone mediating diuresis and natriuresis. The precise mechanism by which DA exerts its cell-to-cell action is not fully understood. In the present study, renal interstitial (RIF) DA (by in vivo microdialysis) and urinary DA excretion (UDAV) were compared in anesthetized rats on either normal (0.28% NaCl, NS) or high (4.0% NaCl, HS) sodium balance (n = 9 in each group). Urine flow (UV) and sodium excretion (UNaV) in HS were greater than in NS rats (UV 7.2 +/- 0.6 vs 3.8 +/- 0.3 microliters/min, P < 0.01; UNaV 497 +/- 66 vs 265 +/- 27 nmol/min, P < 0.01). In rats on both NS and HS balance, UDAV was significantly higher than RIF DA (420 +/- 37 vs 3.68 +/- 0.49 pg/min in the NS rat; 601 +/- 68 vs 1.25 +/- 0.36 pg/min in the HS rat, both P < 0.01). UDAV was increased in HS compared with NS rats (601 +/- 68 vs 420 +/- 37 pg/min, P < 0.05). In contrast, RIF DA was significantly lower in HS than NS rats (1.25 +/- 0.36 vs 3.68 +/- 0.49 pg/min, P < 0.01). In conclusion, chronic sodium loading increased renal DA production and release predominantly into the tubular lumen rather than the peritubular interstitial space of the kidney. These results indicate that DA originating from proximal tubule cells has a direct tubule action in the control of sodium excretion.

Intrarenal dopamine production and distribution in the rat. Physiological control of sodium excretion

Dopamine (DA), produced by the renal proximal tubule, has been demonstrated as an intrarenal paracrine hormone mediating diuresis and natriuresis. The precise mechanism by which DA exerts its cell-to-cell action is not fully understood. In the present study, renal interstitial fluid (RIF) DA (by in vivo microdialysis) and urinary DA excretion (UDAV) were compared in anesthetized rats on either normal (0.28% NaCI, NS) or high (4.0% NaCI, HS) sodium balance and in response to acute gamma-L-glutamyl-L-dopa (gludopa) administration. Urine flow (UV) and sodium excretion (UNaV) in HS were greater than in NS rats. UDAV was increased in HS compared with NS rats. RIF DA was significantly lower in HS than NS rats. Gludopa at 3, 5, and 7.5 nmol/kg (IV bolus) produced a larger increase in UDAV than RIF DA. Only the highest dose of gludopa (7.5 nmol/kg), which resulted in a 7.3-fold increase in UDAV and 1.7-fold increase in RIF DA, was associated with significant diuresis and natriuresis. Cortical and medullary blood flow remained unchanged after gludopa (7.5 nmol/kg) administration, while angiotensin II (100 ng.kg-1.min-1) induced significant reduction in cortical and medullary blood flow. Prior bilateral renal denervation did not have a significant effect on basal DA levels (RIF DA and UDAV) or gludopa-induced DA production or natriuresis and diuresis. These data demonstrated that both chronic sodium loading and acute gludopa administration stimulated renal DA production and release predominantly into the tubule lumen, where DA had a direct tubule action in the control of UNaV. Renal DA production and its renal effects were not significantly regulated by renal sympathetic nerve activity.

Differential human renal tubular responses to dopamine type 1 receptor stimulation are determined by blood pressure status

We performed the present studies to determine whether a proximal renal tubular dopamine D1-like receptor defect exists in human essential hypertension. Twenty-four subjects were studied (13 normotensive and 11 hypertensive) in a randomized, double-blind, vehicle-controlled study using fenoldopam, a selective D1-like receptor agonist. Subjects were studied in sodium metabolic balance at 300 mEq/d, after which the salt sensitivity of their blood pressure was determined. Fenoldopam at peak doses of 0.1 to 0.2 microgram/kg per minute decreased mean arterial pressure in hypertensive subjects but did not change mean pressure in normotensive subjects. Fenoldopam increased renal plasma flow to a greater extent in hypertensive than normotensive subjects. Fenoldopam increased both urinary and fractional sodium excretions in the hypertensive and normotensive groups. In normotensive but not hypertensive subjects, fenoldopam increased the fractional excretion of lithium and distal sodium delivery. In contrast, both distal fractional sodium reabsorption and sodium-potassium exchange fell significantly in hypertensive subjects. We conclude that human essential hypertension is associated with a reduction in the proximal tubular response to D1-like receptor stimulation compared with normotensive subjects. Hypertensive subjects appear to have a compensatory upregulation of renal vascular and distal tubular D1-like receptor function that offsets the proximal tubular defect, resulting in an enhanced natriuretic response to D1-like receptor stimulation.

Dopamine D3 receptors in rat juxtaglomerular cells

D2-like receptors in the kidney have been suggested to be important in the regulation of renin release but the D2-like subtype(s) expressed in juxtaglomerular (JG) cells is not known. Therefore, we determined which of the D2-like family of dopamine receptors is located in primary cultures of rat juxtaglomerular (JG) cells. Reverse transcriptase-polymerase chain reaction (RT-PCR) identified D3 and D4 but not D2Long mRNA in JG cells (n = 3). D3 receptor function was demonstrated by a concentration-dependent inhibition of forskolin-stimulated cAMP production by LY-171555 (a non-selective D2-like receptor agonist) and PD-128593 (a partially selective D3 agonist) (n = 3-7/group). The stimulatory action of LY-171555 and PD-128593 we blocked by the non-selective D2-like antagonist YM-09151. We conclude that D3 and D4 dopamine receptor subtypes are expressed in JG cells; the receptor subtype linked to the inhibition of cAMP in JG cells remains to be established.

Renin-angiotensin system modulates renal bradykinin production

Previous studies have shown that sodium depletion is associated with an increase in renal kallikrein-kinin system activity. This system may play an important role in counterbalancing the renal effects of the renin-angiotensin system. In this study, we examined whether the renal renin-angiotensin system participates in the regulation of renal bradykinin (BK) levels during sodium depletion. We measured changes in renal excretory and hemodynamic function, renal interstitial fluid (RIF) BK, and RIF and urinary guanosine 3',5'-cyclic monophosphate (cGMP) and prostaglandin E2 (PGE2) in conscious uninephrectomized dogs (n = 5) in sodium metabolic balance (10 meq/day) in response to intrarenal arterial administration of the renin inhibitor ACRIP (0.2 microgram.kg-1.min-1) or angiotensin II AT1-receptor blocker losartan (100 ng.kg-1.min-1). ACRIP and losartan increased urine flow rate from 0.75 +/- 0.06 to 1.6 +/- 0.03 and 1.5 +/- 0.05 ml/min, respectively (each P < 0.001), and urine sodium excretion from 5.4 +/- 0.7 to 18.3 +/- 1.3 and 15.9 +/- 1.2 meq/min, respectively (each P < 0.001). Glomerular filtration rate and renal plasma flow increased only during losartan administration (P < 0.05). ACRIP decreased RIF BK by 48%, from 33.1 +/- 3.8 to 17.4 +/- 4.1 pg/min (P < 0.01). ACRIP decreased RIF cGMP by 38%, from 0.69 +/- 0.08 to 0.43 +/- 0.1 pmol/min (P < 0.01); urinary cGMP by 16%, from 0.63 +/- 0.05 to 0.53 +/- 0.02 pmol/min (P < 0.05); and RIF PGE2 by 46%, from 10.5 +/- 1.1 to 5.7 +/- 1.1 pg/min (P < 0.01). Urinary PGE2 was unchanged by ACRIP. Losartan decreased RIF PGE2 by 71%, from 10.8 +/- 0.6 to 3.1 +/- 0.6 pg/min (P < 0.01) but failed to change RIF BK, RIF cGMP, urinary cGMP, or urinary PGE2. These data suggest that the renin-angiotensin system tonically stimulates renal BK production and cGMP formation via a non-AT1 angiotensin receptor and renal PGE2 production via the AT1 receptor.

Academic medicine meets managed care: a high-impact collision

The managed care revolution is sweeping the country as a result of intense marketing on the part of managed care organizations and the widespread belief that price-sensitive managed care systems will control health costs. Although few believe that managed care alone can adequately stem the growth of nation health care spending, competition based on price has emerged as a powerful force in the health care sector. Academic health center (AHCs) stand to suffer with this new managed care regime because their special missions of teaching, research, and highly specialized clinical care make them more expensive than nonacademic hospitals and place them at a noncompetitive disadvantage. The traditional focus of the acute care hospital with individual departmentally designed programs will be narrow. Major changes will be required on the part of AHCs if they are to survive and preserve patient volume, maintain the integrity of medical education, advance scientific research, and provide highly specialized care. AHCs will have to make unprecedented adjustments in virtually every phase of their operations, particularly in the areas of clinical decision making and speedy patient-related information flow. A premium will be placed on multidisciplinary, inclusive medical services that can assume total health care risks for large populations. New ways of educating students in ambulatory settings with an emphasis on outcomes and population-based health will be needed along with the traditional responsibility of pursuing new approaches to the diagnosis, treatment, and prevention of disease. The extent to which managed care will ultimately alter the traditional role of AHCs in the American health care system is unclear, but successful adaptation in the short term will require them to respond broadly, flexibly, and in a timely fashion to the anticipated health care scene.

The subtype-2 (AT2) angiotensin receptor regulates renal cyclic guanosine 3', 5'-monophosphate and AT1 receptor-mediated prostaglandin E2 production in conscious rats

The renal effects of angiotensin II(AII) are attributed to AT1 receptors. In contrast, the function of renal AT2 receptors in unknown. Using a microdialysis technique, we monitored changes in renal interstitial fluid (RIF) prostaglandin E2 (PGE2) and cyclic guanosine 3', 5'-monophosphate (cGMP) in response to dietary sodium (Na) depletion alone, or Na depletion or normal Na diet combined with the AT1 receptor blocker, Losartan, the AT2 receptor blocker, PD 123319 (PD), or angiotensin II, individually or combined in conscious rats. Na depletion significantly increased PGE2 and cGMP. During Na depletion, Losartan decreased PGE2 and did not change cGMP. In contrast, PD significantly increased PGE2 and decreased cGMP. Combined administration of Losartan and PD decreased PGE2 and cGMP. During normal Na diet, RIF PGE2 and cGMP increased in response to angiotensin II. Neither Losartan nor PD, individually or combined, changed RIF PGE2 or cGMP. Combined administration of angiotensin II and Losartan or PD produced a significant decrease in response of PGE2 and cGMP to angiotensin II, respectively. These data demonstrate that activation of the reninangiotensin system during Na depletion increases renal interstitial PGE2 and cGMP. The AT1 receptor mediates renal production of PGE2. The AT2 receptor mediates cGMP. AT2 blockade potentiates angiotensin-induced PGE2 production at the AT1 receptor.

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.

Expression of the subtype 1A dopamine receptor in the rat heart

The subtype 1A dopamine receptor (D1A) has recently been detected in the rat kidney. In the present study using light microscopic immunohistochemistry, electron microscopic immunocytochemistry, and in situ amplification of mRNA, we demonstrate the D1A receptor in Sprague-Dawley and Wistar Kyoto rat hearts. For immunohistochemistry and immunocytochemistry, anti-peptide polyclonal antibodies were directed toward amino acid sequences of the third extracellular and intracellular domains of the native receptor. Selectivity was validated by recognition of the D1A receptor expressed in stably transfected LTK- cells. D1A receptor mRNA was detected with a novel transcription-based isothermal in situ amplification system as well as with reverse transcription-polymerase chain reaction. D1A receptor protein was distributed throughout the atrium and ventricular myocardium. Preimmune and preabsorption controls were negative. Electron microscopic immunocytochemistry using the protein A gold method demonstrated the D1A receptor along the cellular membranes of coronary smooth muscle cells and ventricular myocytes and in the myosin thick filaments and M-lines. D1A receptor mRNA was present in coronary vessels and myocardium in amplified but not in unamplified sections. Western blot analysis showed specific D1A bands in transfected LTK- cells and the atrium but not in nontransfected LTK- cells and the ventricle. The selective D1-like receptor agonist SKF38393 stimulated adenylyl cyclase in ventricular myocardial plasma membranes in a dose-related fashion, and the response was abolished by the selective D1-like receptor antagonist SCH23390. These results demonstrate that the D1A receptor gene and protein are expressed in normal rat heart. The physiological and pathophysiological roles and predominant cell signaling mechanism or mechanisms of this receptor remain to be determined.

Localization of dopamine D1A receptor protein in rat kidneys

The dopamine D1A receptor subtype was identified in rat kidney with both light microscopic immunohistochemistry and electron microscopic immunocytochemistry. Antipeptide polyclonal antisera were directed to both extracellular and intracellular regions of the native receptor. The use of such receptor-subtype-selective antibodies allows for the identification of specific dopamine receptor subtype clones that are not distinguished by current pharmacological or receptor-ligand binding technology. Selectivity of the antipeptide antisera was validated by their ability to recognize native receptor protein expressed in permanently transfected mouse LTK- cells. In the rat kidney, D1A receptor protein was localized to the juxtaglomerular apparatus (JGA), proximal tubule, distal tubule, cortical collecting duct, and renal vasculature. In the JGA, the receptor was predominantly located in the arteriolar smooth muscle layer within cytoplasmic granules previously shown to contain renin. In the proximal tubules, staining was localized both on the brush-border and basolateral membranes. The D1A receptor, which is present in the central nervous system, is now identified in the rat kidney at those sites previously labeled as DA1 receptor sites on the basis of pharmacological binding studies. These results suggest that at least some of the renal dopamine DA1 receptors correspond structurally to the central dopamine D1A receptor.

Renal interstitial fluid angiotensin. Modulation by anesthesia, epinephrine, sodium depletion, and renin inhibition

Using a microdialysis technique, we monitored changes in right and left renal interstitial fluid angiotensins in anesthetized and conscious dogs (both n = 5) in response to right renal interstitial epinephrine (0.2 mg/kg per minute) administration. Renal interstitial and plasma angiotensin levels also were monitored in conscious dogs (n = 4) in response to dietary sodium deprivation (10 mmol/d) for 5 consecutive days. Changes in renal interstitial and plasma angiotensins in response to interstitial administration of a specific renin inhibitor, ACRIP (0.5 micrograms/kg per minute for 20 minutes), were monitored on day 5 of sodium depletion. At basal levels, there were no significant differences between the right and left renal interstitial immunoreactive angiotensin levels in anesthetized dogs. Renal interstitial epinephrine administration caused a significant increase in renal interstitial immunoreactive angiotensin concentrations in both anesthetized and conscious dogs (P < .01). However, anesthetized dogs had significantly higher renal interstitial immunoreactive angiotensin levels basally and in response to epinephrine than conscious dogs (P < .05). Renal interstitial immunoreactive angiotensin concentrations increased significantly and progressively during exposure to a low sodium diet from 3.9 +/- 1 nmol on day 1 to 740 +/- 332 nmol on day 5 (P < .01). Renal interstitial immunoreactive angiotensin decreased significantly to 124 +/- 37 nmol (P < .01) in response to intrarenal renin inhibition at the end of day 5 of sodium depletion. Plasma immunoreactive angiotensin increased significantly (P < .01) in response to sodium depletion, and no change occurred during intrarenal renin inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine D2 receptor gene expression and binding sites in adrenal medulla and pheochromocytoma

To determine whether dopamine D2 receptors are present in normal and neoplastic chromaffin tissues, 10 pheochromocytomas and 5 human adrenal glands were studied. Dopamine D2 receptor messenger ribonucleic acid corresponding to a single band of approximately 2.5 kilobases was detected in both pheochromocytoma and human adrenal gland by Northern blot analysis. D2 receptor messenger ribonucleic acid levels determined by dot blot analysis were 3.1-fold lower in human adrenal medullas than in pheochromocytomas (P < 0.001). Simultaneous Scatchard analysis of [3H]spiperone binding experiments demonstrated the presence of two different binding sites in membrane preparations from bovine adrenal medullas [R1: Kd = 0.14 nmol/L; binding capacity (Bmax) = 6.2 fmol/mg protein: R2: Kd = 16 nmol/L; Bmax = 223 fmol/mg protein]. Similarly, two binding sites were present in membrane preparations from pheochromocytomas (R1: Kd = 0.39 nmol/L; R2: Kd = 61 nmol/L]. Binding capacities were greatly variable among pheochromocytomas (R1: Bmax = 12.0-372.5 fmol/mg protein; R2: Bmax = 1,000-11,586 fmol/mg protein). The relative potencies of different compounds to displace [3H]spiperone were spiperone > domperidone > (+)-butaclamol > quinpirole > SCH 23390 in bovine adrenal medulla, and spiperone >> domperidone > quinpirole > (+)-butaclamol > SCH 23390 in pheochromocytoma. We conclude that dopamine D2 receptors are synthesized in human adrenal medulla and pheochromocytoma tissues.

Angiotensin II type 1 receptor: role in renal growth and gene expression during normal development

To determine whether angiotensin II (ANG II) modulates renal growth and renin and angiotensin type 1 (AT1) gene expression via AT1 during development, weanling rats were given ANG II antagonist losartan (DuP 753) for 3 wk. Body weight (g), kidney weight (g), and kidney weight-to-body weight ratio were lower in losartan-treated rats (162 +/- 7, 1.6 +/- 0.06, and 9.5 +/- 0.1 x 10(-3)) than in control rats (184 +/- 5, 1.8 +/- 0.07, and 10.1 +/- 0.1 x 10(-3); P < 0.05). Renal DNA content (mg/kidney) was lower in losartan-treated (2.4 +/- 0.17) than in control rats (3.3 +/- 0.31; P < 0.05), whereas protein-to-DNA and RNA-to-DNA ratios were similar in losartan-treated and control rats. Renin mRNA levels were sevenfold higher in losartan-treated than in control rats, as determined by quantitative standardized dot blot analysis. In addition, blockade of AT1 with losartan induced recruitment of renin-synthesizing and renin-containing cells in the renal vasculature, as determined by immunocytochemistry and in situ hybridization. To establish whether AT1 blockade has a direct effect on renin gene expression, freshly isolated renin-producing cells were exposed in vitro to losartan (10(-6) M) or culture media (control). Losartan induced a twofold increase in steady-state renin mRNA levels above control (P < 0.05). Intrarenal AT1 mRNA levels were not altered by losartan given either in vivo or in vitro to freshly dispersed cells. To define whether immature renin-secreting cells are responsive to ANG II, renin release was determined by reverse hemolytic plaque assay.(ABSTRACT TRUNCATED AT 250 WORDS)

Neonatal ureteral obstruction stimulates recruitment of renin-secreting renal cortical cells

Unilateral ureteral obstruction (UUO) in the neonate increases ipsilateral renal renin gene expression, an effect which is mediated by renal nerves. To determine whether neonatal UUO alters the number of renal cortical cells secreting renin and whether this change is modulated by renal nerve activity, newborn Sprague-Dawley rats were subjected to left UUO, right uninephrectomy, or sham operation and studied four weeks thereafter. To evaluate the importance of renal nerves in this response, an additional group of animals underwent chemical sympathectomy with guanethidine. Ureteral obstruction was associated with marked reduction in renal mass in the obstructed kidney and contralateral compensatory hypertrophy, changes which were not altered by sympathectomy. Renin messenger RNA and renal renin content were elevated in the obstructed kidney. The number of cells secreting renin, measured by the reverse hemolytic plaque assay, was markedly increased in the obstructed kidney (45 +/- 18 plaques/slide vs. 11 +/- 1 plaques/slide in sham animals), but not in the opposite kidney or following uninephrectomy. This effect was not significantly altered by sympathectomy. There was no change in the amount of renin secreted per cell or in the secretory response to Ca++. These results show that UUO results in recruitment of cells not previously secreting renin by a mechanism independent of renal nerve activity. This recruitment occurs without alteration of the quantity of renin secreted per cell or in the normal regulatory effect of Ca++ on renin secretion. An increase in the number of renin-secreting cells may contribute to the activation of the renin-angiotensin system, and thus to the vasoconstriction observed following ureteral obstruction.

Role of angiotensin II in renal vasoconstriction with acute hypoxemia and hypercapnic acidosis in conscious dogs

To evaluate the role of renin-angiotensin in the renal vasoconstriction with combined acute hypoxemia and hypercapnic acidosis preceded by acute hypoxemia, we studied eight conscious mongrel uninephrectomized dogs with chronic renal catheters and controlled sodium intake (80 mEq/24 h x 4 days). The animals were studied during combined acute hypoxemia and hypercapnic acidosis (PaO2 34 +/- 1 mm Hg, PaCo2 57 +/- 1 mm Hg, pH 7.20 +/- 0.01) preceded by 80 min of acute hypoxemia (PaO2 34 +/- 1 mm Hg) during: (a) intrarenal infusion of vehicle (n = 8); or (b) intrarenal administration of the angiotensin II antagonist [Sar1,Ala8]-AII, 70 ng kg-1 min-1 (n = 8). The combination of acute hypoxemia and hypercapnic acidosis resulted in diminished effective renal plasma flow and increased renal vascular resistance during intrarenal vehicle infusion. Intrarenal [Sar1,Ala8]-AII did not abolish the renal vasoconstriction in the initial 20 min of this combined blood gas derangement but resulted in a more prompt return of the renal vascular variables toward control levels with continuation of the blood gas derangement for an additional 20 min, suggesting a role for angiotensin in renal vasoconstriction. These observations suggest that while renin-angiotensin may not mediate the initial renal vasoconstriction in the first 20 min of combined acute hypoxemia and hypercapnic acidosis, in uninephrectomized conscious dogs, it attenuates the spontaneous recovery of renal hemodynamic variables to baseline as the blood gas derangement continues.

Evaluating faculty clinical excellence in the academic health sciences center

Although excellence in the clinical care of patients is the cornerstone of medicine, academic health sciences centers have increasingly given more weight to research and correspondingly less emphasis to patient care. To better recognize and reward clinical excellence, it is first necessary to effectively evaluate physicians' performances in patient care. In addition to addressing the value of faculty clinical excellence in the academic setting, the authors discuss different approaches to clinical assessment, theoretical and practical problems in assessing the performances of clinical faculty, and a system of evaluation being initiated at the University of Virginia School of Medicine. This system of evaluation combines--in annual individual reviews--a limited amount of objective assessment data with subjective evaluations from several sources. The objective data include board certification and recertification, analysis of outcomes data, and documentation of scholarly activity. The subjective evaluations include letters of recognition and appreciation from faculty colleagues and written observations from department chairs, housestaff, students, and nurses. The system has been accepted by department chairs, members of the Promotion and Tenure Committee, and the general faculty. In implementing this new system, periodic review of the pace and direction of change will be crucial to track progress and provide feedback for further modification.

Localization of angiotensin peptide-forming enzymes of 3T3-F442A adipocytes

We have demonstrated that angiotensinogen is synthesized by 3T3-F442A cells and is hydrolyzed to angiotensins I and II (ANG I and II) by this model adipocyte system. This study was designed to determine whether ANG I is generated by renin or some other enzyme and where the formation of ANG I and/or II occurs in 3T3-F442A cells. Renin mRNA was not detected by Northern blot analysis of poly(A)(+)-selected RNA from cultures of fully differentiated adipocytes nor by the more sensitive polymerase chain reaction, implying that renin is not synthesized in this model adipocyte system. Hydrolysis of angiotensinogen to ANG I and II was demonstrated to be associated with the cell but not the media. Inhibitors, including EDTA, aimed at inactivating enzymes belonging to the serine, acid, or aspartyl proteases, and metalloproteases were ineffective in preventing the formation of either ANG I or II. Therefore the model adipocyte 3T3-F442A cell system forms ANG I and II in the absence of renin and angiotensin-converting enzyme. The unidentified enzymes responsible for peptide formation are associated with the cell itself.

Distribution and content of renin and renin mRNA in remnant kidney of adult rat

To determine whether kidney hypertrophy secondary to reduction of renal mass affects the intrarenal distribution and concentration of renin mRNA and its protein, adult male Sprague-Dawley rats were studied 4 wk after sham operation (Sham, n = 10), uninephrectomy (UNX, n = 14), or five-sixths nephrectomy (5/6 NX, n = 12). Left kidney weight-to-body weight ratio (x10(3)) was higher in 5/6 NX (6.6 +/- 0.2) than in UNX (4.5 +/- 0.2) or Sham (3.8 +/- 0.1) groups (P < 0.001). The percentage of juxtaglomerular apparatuses (%JGA) containing renin was lower in 5/6 NX (32 +/- 5) than in UNX (56 +/- 2, P < 0.001) or Sham (50 +/- 1, P < 0.05) groups. Renal renin mRNA concentrations (pg renin mRNA/microgram total RNA) detected by radiodensitometric renin mRNA dot-blot assay were lower in 5/6 NX (1.8 +/- 0.3) than in UNX (13.2 +/- 1) or Sham (14.2 +/- 1.1, P < 0.001). In situ hybridization histochemistry demonstrated that in all groups of rats renin mRNA was confined to the JGA. However, the hybridization signals (grains/JGA) were less intense in 5/6 NX (211 +/- 24) than in UNX (486 +/- 35) or Sham (541 +/- 40) groups (P < 0.001). Renal renin concentration (ng angiotensin I.mg protein-1.h-1) tended to be lower in 5/6 NX (20 +/- 15) than in UNX (44 +/- 7.8) or Sham (60.8 +/- 10) groups. In addition, plasma renin activity (ng.ml-1.h-1) was lower in 5/6 NX (3.8 +/- 0.6) than in UNX (8.8 +/- 1.8, P < 0.05) or Sham (14.3 +/- 2, P < 0.001) groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of angiotensin converting enzyme inhibition, sodium depletion, calcium, isoproterenol, and angiotensin II on renin secretion by individual renocortical cells

Angiotensin-converting enzyme inhibition with enalapril increases the number of glomeruli with juxtaglomerular cells and the number of cells in the afferent arteriole that express the renin gene and contain renin. However, renin release from these newly recruited renin-containing cells has not been demonstrated. Sodium depletion also has been shown to increase renal renin messenger RNA levels. The aim of these studies was to determine whether increases in renin secretion are a result of altered numbers of cells synthesizing/releasing renin or a change in the amount of renin release per cell, or both. Adult Wistar-Kyoto rats were treated with enalapril or sodium depleted and single cell renin secretion of enzymatically dispersed renal cortical cells was examined by reverse hemolytic plaque assay. Enalapril treatment increased the number of renin secreting cells by approximately 10-fold (P < 0.05). The newly recruited renin-secreting cells were not responsive to changes in extracellular calcium concentration or the presence of isoproterenol. At physiological (2.5 mM) extracellular calcium concentration, the amount of renin secreted per cell was approximately 2-fold greater (P < 0.05) when cells from enalapril-treated rats were compared to controls and sodium depletion increased both the number of renin-secreting cells and the amount of renin secreted by approximately 35% (P < 0.05). Angiotensin II (AII) inhibited the number of cells secreting renin in cortical cells prepared from enalapril-treated and control rats. In conclusion, angiotensin converting enzyme inhibition increased renin secretion predominantly by recruitment of additional renin-secreting cells and, to a lesser extent, by augmentation of the amount of renin released per cell. In contrast, sodium depletion increased renin secretion equally by both mechanisms. Newly recruited renin-secreting cells were not regulated by the extracellular calcium concentration or beta-adrenergic stimulation. Angiotensin II inhibited renin secretion directly by decreasing the number of individual cells releasing renin through a process which was independent of the extracellular calcium concentration.

Colocalization and release of angiotensin and renin in renal cortical cells

Angiotensin is generated within the kidney, but the precise loci for the formation of angiotensin I (ANG I) and angiotensin II (ANG II) have not been demonstrated. We performed electron microscopy immunocytochemistry in kidney sections of 10-day-old (newborn) and adult Wistar-Kyoto (WKY) rats using specific antibodies to renin, ANG I, ANG II, and angiotensinogen (AO). Renin, ANG I, ANG II, and AO were present in juxtaglomerular (JG) cells. Renin was largely confined to cytoplasmic granules; ANG I and ANG II were colocalized to these granules but also were present in the cytoplasm; AO was distributed throughout the cytoplasm. AO also was present in a renal cortical distribution in proximal tubular cells. Northern blot analysis demonstrated AO mRNA in total kidney and liver but not in renal microvessels. Using the reverse hemolytic plaque assay, we demonstrated release of ANG I and renin from individual renocortical cells of adult WKY rats. Under control conditions, the number of releasing cells was 11 +/- 1 for ANG I and 10 +/- 1 for renin. Addition of rat renin inhibitor (RI) (1 x 10(-5) M), which inhibited renin activity in the medium from 37 to 9 pg ANG I.ml-1.h-1, did not alter ANG I plaque number. Addition of rat AO increased ANG I plaque number to 17 +/- 2 (P less than 0.05). Incubation with both RI and AO prevented the increase in ANG I plaque number obtained with AO alone. Enalapril treatment (7 days; n = 5) increased the number of plaque-forming cells to 22 +/- 2 for ANG I (P less than 0.0005) and to 39 +/- 7 for renin (P less than 0.001). The results suggest an intracellular location for AO and angiotensin and release of renin and ANG I by renal cortical cells and suggest that released angiotensin is produced intracellularly and that secretion of ANG I is augmented by converting enzyme inhibition.

Intrarenal DA2 dopamine receptor stimulation in the conscious dog

DA2 dopamine receptors are present in renal blood vessels and glomeruli. Stimulation of DA1 dopamine receptors leads to renal vasodilation, diuresis, and natriuresis, but a functional role for renal DA2 receptors is largely unknown. We investigated the possible role of DA2 receptors in the control of renal function by intrarenal infusion of a highly specific DA2 agonist, LY 171555 (LY), in conscious uninephrectomized dogs (n = 5) in metabolic balance at sodium intake of 40 meq/day. The infusion of LY at 0.5 pmol.kg-1.min-1 did not change the urinary sodium excretion or renal hemodynamic function. A significant dose-dependent antidiuresis (F = 8.1, P less than 0.0001) and antinatriuresis (F = 93.3, P less than 0.0001) and a decrease in filtration fraction (F = 2.3, P less than 0.02) occurred as the LY dose was increased from 1.0 to 10.0 pmol.kg-1.min-1. There were no changes in systemic plasma renin activity, plasma aldosterone concentration, or mean arterial pressure during intrarenal LY administration. These data suggest that intrarenal DA2 receptor stimulation with LY decreases renal sodium excretion in part by hemodynamic mechanisms. Renal dopamine may act at vascular and/or glomerular DA2 receptors to modulate renal function.

Nitric oxide alters renal function and guanosine 3',5'-cyclic monophosphate

Endothelium-derived relaxing factor (EDRF) activates soluble guanylate cyclase, resulting in an increase in vascular smooth muscle guanosine 3',5'-cyclic monophosphate (cGMP) levels, which correlates with its relaxing effect. Using a microdialysis technique, we investigated changes in right and left renal interstitial fluid cGMP levels in response to right intrarenal administration of an EDRF inhibitor, NG-monomethyl-L-arginine (L-NMMA). Studies were conducted in anesthetized dogs (n = 5) in metabolic balance at a sodium intake of 40 meq/day. Urine was collected directly from the right and left ureters individually. Changes in the right and left urinary cGMP excretion and renal function in response to cumulative doses of L-NMMA were studied. In the right kidney, 20-100 micrograms/kg/min L-NMMA caused 1) a dose-dependent decrease in renal interstitial fluid and urinary cGMP levels (p less than 0.0001 and p less than 0.001, respectively), 2) antinatriuresis (p less than 0.01), 3) antidiuresis (p less than 0.01), 4) a decrease in renal blood flow (p less than 0.01) and glomerular filtration rate (p less than 0.01), and 5) a decrease in fractional sodium excretion (p less than 0.01). No changes in left renal interstitial fluid and urinary cGMP levels or excretory and hemodynamic function were observed during right intrarenal administration of L-NMMA at 20 and 60 micrograms/kg/min.(ABSTRACT TRUNCATED AT 250 WORDS)

Temporal pattern of renin and aldosterone secretion in men: effects of sodium balance

To investigate the pulsatile nature of basal and stimulated renin and aldosterone secretion, we sampled blood for plasma renin activity (PRA) and plasma aldosterone concentration at 10-min intervals for 24 h in nine normal supine human male subjects after equilibration in high- and low-sodium balance states. We evaluated serial hormonal measures by a quantitative waveform-independent deconvolution technique designed to compute the number, amplitude, and mass of underlying secretory bursts and simultaneously to estimate the presence and extent of basal secretion. For both PRA and aldosterone: 1) burstlike release accounted for greater than or equal to 60% of total secretion and tonic release for less than 40%; 2) there was an 80- to 85-min interpulse interval unchanged by sodium intake; 3) sodium restriction engendered an increase in plasma hormone concentrations by increasing the amount and maximal rate of hormone secreted per burst; 4) low dietary sodium also induced increases in basal hormone secretory rates, suggesting that there may be two regulatory processes driving renin and aldosterone secretion; and 5) PRA was significantly coupled to plasma aldosterone concentration by a 0-, 10-, or 20-min aldosterone lag time in both high- and low-sodium balance. We conclude that both renin and aldosterone are released via a predominantly burstlike mode of secretion; PRA and plasma aldosterone concentrations are positively coupled by a short time lag (0-20 min); and sodium restriction achieves an increase in mean PRA and plasma aldosterone concentration by selective amplitude enhancement of individual hormone secretory bursts and by increased tonic (interburst) basal secretory rates.

Expression of alpha-smooth muscle actin in the developing kidney vasculature

To determine whether alpha-smooth muscle (alpha-SM) isoactin is expressed in the maturing kidney as well as the changes associated with maturation, we processed for immunocytochemistry kidney sections from Wistar-Kyoto rats at various prenatal (15, 17, 19, and 20 days) and postnatal (2, 5, 10, 15, and 90 days) ages using a monoclonal anti-alpha-SM actin antibody. At 15 days of gestation, only a few mesenchymal cells contained alpha-SM actin. However, other fetal vasculature structures (heart, aorta, peripheral blood vessels) expressed alpha-SM actin. Vascular localization was first observed at 17 days of gestation in larger corticomedullary vessels. As maturation progressed, actin expression accompanied the outward growth and branching of the kidney vasculature. During fetal life (17 days), alpha-SM actin also was expressed within juxtamedullary glomeruli. As the centrifugal maturation of nephrons proceeded, intraglomerular expression extended to outer cortical glomeruli. After 10 days of postnatal life, once glomerular development was completed, intraglomerular expression was no longer present. Peritubular capillaries expressed alpha-SM actin during early (fetal and neonatal) development, but not in the adult kidney. We conclude that 1) expression of alpha-SM actin in the developing kidney is delayed with respect to other vascular beds, 2) expression of alpha-SM actin follows the centrifugal pattern of nephrovascular development, and 3) glomerular and peritubular capillary expression of alpha-SM actin is a transient developmental phenomenon associated with active glomerulogenesis and capillary growth.

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.

Spatial association of renin-containing cells and nerve fibers in developing rat kidney

The development of renin-containing cells and nerve fibers was studied in Sprague-Dawley rat kidneys during the last third of gestation and the first 15 days of postnatal life. Kidney tissue sections were stained for nerve fibers or double stained employing an anti-rat renin polyclonal antibody and a monoclonal antibody (TUJ1) directed against a neuron-specific class III beta-tubulin isotype. Renin-containing cells and nerve fibers were detected at 17 days of gestation, in close spatial relationship along the main branches of the renal artery. During fetal life, renin-containing cells and nerve fibers were spatially associated along arcuate and interlobular arteries, renin-containing cells being also present throughout the entire length of afferent arterioles supplying juxtamedullary glomeruli. During postnatal life the distribution of renin-containing cells progressively shifted to a restricted juxtaglomerular position in afferent arterioles. Simultaneously, density and organization of nerve fibers increased with age along the arterial vascular tree. Our results suggest that innervation of renin-containing cells is present in fetal life and follows the centrifugal pattern of renin distribution and nephrovascular development.

Role of intrarenal angiotensin II and alpha-adrenoceptors in renal vasoconstriction with acute hypoxemia and hypercapnic acidosis in conscious dogs

To evaluate our previous observation of renal vasoconstriction during combined acute hypoxemia and hypercapnic acidosis preceded by acute hypoxemia, we studied 13 conscious mongrel uninephrectomized dogs with chronic renal catheters and controlled sodium intake (80 meq/day for 4 days). Five dogs were studied during combined acute hypoxemia (PaO2, 37 +/- 1 mm Hg) and hypercapnic acidosis (PaCO2, 59 +/- 1 mm Hg; pH 7.20 +/- 0.01). Each dog was studied during infusion of 1) the intrarenal vehicle (n = 5), 2) the intrarenal alpha 1-antagonist prazosin (0.2 micrograms.kg-1.min-1, n = 5), 3) intrarenal [Sar1,Ala8]angiotensin II (70 ng.kg-1.min-1, n = 5), and 4) intrarenal prazosin and [Sar1,Ala8]angiotensin II (n = 4). Immediate induction of combined hypoxemia and hypercapnic acidosis after control measurements during intrarenal vehicle infusion resulted in a decrease in effective renal plasma flow and glomerular filtration rate, increase in renal vascular resistance, and decrease in filtered sodium load in the first 20 minutes of the blood gas derangement. Intrarenal administration of [Sar1,Ala8]angiotensin II failed to reverse the effects of the combined blood gas derangement on renal function. In contrast, intrarenal prazosin administration either alone or in combination with [Sar1,Ala8]angiotensin II abrogated the increase in renal vascular resistance, decrease in glomerular filtration rate, and fall in filtered sodium load. These studies identify a major role for alpha 1-adrenoceptors in the renal vasoconstriction during combined hypoxemia and hypercapnic acidosis.

Inhibition of ANP clearance receptors and endopeptidase 24.11 in maturing rats

Systemic clearance of atrial natriuretic peptide (ANP) decreases during postnatal development. To determine the relative contribution of ANP clearance (C) receptors and neutral endopeptidase 24.11 (NEP; EC 3.4.24.11) in regulation of plasma ANP concentration ([ANP]) during maturation, 18- to 60-day-old male Sprague-Dawley rats were anesthetized and infused with rat ANP (35 ng.kg-1.min-1). Infusion of the NEP inhibitor phosphoramidon increased [ANP] and urine guanosine 3',5'-cyclic monophosphate (cGMP) excretion in both weanling and adult rats. Infusion of C-ANP, an analogue that binds C receptors selectively, resulted in a greater rise in [ANP] in preweaned than in adult rats, suggesting a maturational decrease in function of C receptors. Despite the increase in [ANP], however, urine flow, cGMP, and sodium excretion failed to increase in preweaned compared with adult rats. Combined infusion of phosphoramidon and C-ANP resulted in a marked increase in [ANP] and cGMP excretion in weanling and adult rats. These results indicate that both C receptors and NEP modulate plasma [ANP] in the physiological range and that each pathway compensates when the other is inhibited. Age-related differences in the renal response to ANP clearance inhibitors may have important physiological implications in the regulation of sodium balance during development.

Renal nerves modulate renin gene expression in the developing rat kidney with ureteral obstruction

Chronic unilateral ureteral obstruction (UUO) in newborn rats activates renin gene expression in the obstructed kidney, and increases renin distribution along afferent glomerular arterioles in both kidneys. To investigate the role of the renal nerves in this response, 2-d-old Sprague-Dawley rats were subjected to UUO or sham operation. Chemical sympathectomy was performed by injection of guanethidine, whereas, control groups received saline vehicle. At 4-5 wk, renal renin distribution was determined by immunocytochemistry, and renin mRNA levels were determined by Northern blot hybridization. Compared to the saline-treated rats with UUO, renin remained localized to the juxtaglomerular region in both kidneys of rats with UUO receiving guanethidine (P less than 0.05). Moreover, renin mRNA levels were eightfold lower in obstructed kidneys of rats receiving guanethidine than in those receiving saline. Additional groups of rats with UUO were subjected to unilateral mechanical renal denervation: renin gene expression in the obstructed kidney was suppressed by ipsilateral but not by contralateral renal denervation. These findings indicate that either chemical or mechanical denervation suppressed the increase in renin gene expression of the neonatal kidney with ipsilateral UUO. We conclude that the renal sympathetic nerves modulate renin gene expression in the developing kidney with chronic UUO.

Physiological modulation of renal function by the renal dopaminergic system

1. The renal dopaminergic system is a potentially important regulator of sodium homeostasis and kidney function. 2. We have presented evidence that dopamine acts as a paracrine substance at DA-1 and DA-2 receptors in the physiological control of renal function. 3. Much more information is required regarding basic cellular mechanisms and the functional regulation of the system so that the role of renal dopamine can be placed clearly in context with other established hormonal regulatory systems.

Angiotensin II regulates renin gene expression

We investigated the effect of angiotensin II (ANG II) and enalapril on accumulation of renin messenger RNA (mRNA) and on renal renin distribution (immunohistochemical analysis). Adult Wistar-Kyoto rats received enalapril (0.2 mg/ml) in distilled drinking water for 8 or 12 days. On day 5 of enalapril treatment, an osmotic minipump was implanted in the peritoneum that caused sustained release of ANG II (200 ng.kg-1.min-1) or vehicle (bovine serum albumin) for 3 or 7 days. Control rats received water for 8 or 12 days and osmotic minipump implantation (containing vehicle solution) on the 5th day. Renin mRNA was identified by hybridization with a 32P-labeled full-length complementary DNA and was detected by autoradiography. Enalapril treatment increased renal renin mRNA specific activity (renin mRNA/total RNA). Subsequent infusion of angiotensin II for 3 or 7 days decreased renal renin mRNA specific activity. In addition, renin immunostaining increased along the afferent arteriole after enalapril treatment; however, enalapril-induced spread of renin immunostaining was not inhibited by ANG II. Thus ANG II attenuates the accumulation of renin mRNA stimulated by enalapril treatment without alteration of renal renin distribution. The lack of effect of ANG II on renal renin distribution may be due to the length of turnover time for stored protein. These findings suggest the shortloop negative feedback of ANG II on renin reflects inhibition of renin synthesis by ANG II. Therefore, we propose that ANG II exerts a direct inhibitory effect on renin by regulation of renin gene expression in renal vasculature.

Evidence that dopamine-2 mechanisms control renal function

Dopamine is synthesized by the kidney, and dopamine-2 (DA2) receptors are present in the renal glomerulus. However, no role for DA2 receptors in the kidney has been defined. We investigated the possible role of DA2 receptors in control of renal function by intrarenal infusion of a highly specific DA2 antagonist YM-09151 (YM), in conscious uninephrectomized dogs (n = 5) in metabolic balance at Na intake 40 meq/day. YM infused at 0.01 pmol.kg-1.min-1 did not cause any changes in urinary flow rate or Na excretion. Administration of YM (infusions from 0.1 to 10.0 pmol.kg-1.min-1) caused a significant dose-dependent diuresis (F = 20.3; P less than 0.001) and natriuresis (F = 35.2; P less than 0.0001) and an increase in glomerular filtration rate (F = 45.4; P less than 0.0001), renal plasma flow (F = 209.3; P less than 0.0001), and filtration fraction (F = 11.2; P less than 0.0001). No significant changes in plasma renin activity, plasma aldosterone concentration, or mean arterial blood pressure occurred with any of the doses of YM infused into the renal artery. Coinfusion of LY-171555, a specific DA2 agonist, at a dose that itself did not affect renal function, completely abrogated the renal hemodynamic and excretory changes induced by YM. The data suggest that dopamine produced intrarenally may act at renal vascular and/or glomerular DA2 receptors to control renal function.

Molecular biology of the renal renin-angiotensin system

This paper describes an interrelated series of studies designed to examine molecular and cellular aspects of renin expression and release within the kidney. Using immunocytochemical techniques, Northern blot analysis, in situ hybridization, measurement of renin activity, and the reverse hemolytic plaque assay, it has been possible to demonstrate that the intrarenal distribution of renin, renin gene expressing cells and the number of renin secretory cells vary during diverse physiologic and pathologic conditions. Overall, these studies demonstrate that the renal preglomerular vasculature has the plasticity and capacity to elicit a recruitment of renin containing and/or renin gene expressing cells.

Role of vasopressin in renal vascular changes with hypoxemia and hypercapnic acidosis in conscious dogs

To evaluate the role of vasopressin in the renal changes during combined acute hypoxemia and acute hypercapnic acidosis, eight conscious female mongrel dogs prepared with controlled sodium intake at 80 meq/24 h for 4 days were studied in one of the following six protocols: acute hypoxemia (80 min, arterial PO2 34 +/- 1 mmHg) followed by combined acute hypoxemia and hypercapnic acidosis (40 min, arterial PO2 35 +/- 1 mmHg, arterial PCO2 58 +/- 1 mmHg, pH = 7.20 +/- 0.01) during 1) intrarenal vehicle at 0.5 ml/min (N = 8); or 2) intrarenal infusion of vasopressin V1-receptor antagonist [d(CH2)5Tyr(Me)]AVP at 5 ng.kg-1.min-1 (N = 5); and with normal gas exchange during 3) intrarenal vasopressin at 0.05 mU.kg-1.min-1 (N = 8); 4) simultaneous infusion of intrarenal vasopressin and [d(CH2)5Tyr(Me)]AVP, 5 ng.kg-1.min-1 (N = 4); 5) intrarenal [d(CH2)5Tyr(Me)]AVP, 5 ng.kg-1.min-1 (N =4); and 6) intrarenal vehicle at 0.5 ml/min (N = 7). Intrarenal infusion of a subpressor dose of vasopressin resulted in a transient decrease in glomerular filtration rate and effective renal plasma flow over the first 20 min of infusion, suggesting that vasopressin induced nonsustained vasoconstriction of the renal vasculature. Intrarenal administration of [d(CH2)5Tyr-(Me)]AVP failed to block the fall in glomerular filtration rate or effective renal plasma flow when renal arterial blood vasopressin levels were elevated by intrarenal administration of exogenous vasopressin or by elevated systemic arterial endogenous circulating vasopressin during combined acute hypoxemia and hypercapnic acidosis. These data suggest that vasopressin (V1-receptor stimulation) does not play an important role in the renal vasoconstriction during combined acute hypoxemia and hypercapnic acidosis in conscious dogs.

Recruitment of renin gene-expressing cells in adult rat kidneys

To define whether angiotensin I-converting enzyme (ACE) inhibition affects the distribution of renin gene-expressing cells within the kidney, a control group of adult male Wistar-Kyoto rats (C, n = 7) was compared with a group of rats treated with enalapril (E, n = 6) for 5 days. Renin mRNA distribution was assessed using in situ hybridization to a 35S-labeled 28 mer oligonucleotide complementary to rat renin mRNA. Whereas in control rats renin mRNA was confined to a juxtaglomerular location, in enalapril-treated rats, renin mRNA extended proximally along the length of the afferent arteriole. The percent of visible afferent arteriolar length containing renin mRNA was higher in enalapril-treated (71.7 +/- 2.8%) than in control (49.6 +/- 2.1%) rats (P less than 0.0001). These findings were accompanied by an increase in the percent of juxtaglomerular apparatuses (JGAs) containing renin mRNA (71 +/- 2.2 vs. 49 +/- 2.9%; E vs. C, P less than 0.0001). Also, the intensity of the JGA hybridization signals was higher in enalapril-treated (757 +/- 59 grains/JGA) than in control (167 +/- 11 grains/JGA) rats (P less than 0.00001). We conclude that the increased kidney renin gene expression elicited by ACE inhibition is the result of an increase in renin mRNA content per JGA, an increase in the number of JGAs expressing the renin gene, and a recruitment of renin gene-expressing cells along the afferent arteriole.