Biomedical subjects

T Inagami

Publications and source records attributed to T Inagami.

At least 163 records · Page 9Linked to original sources

PubMed1993

Peptide growth factors markedly decrease the ligand binding of angiotensin II type 2 receptor in rat cultured vascular smooth muscle cells.

Of two major isoforms of angiotensin II receptors, AT1 and AT2, biological roles of AT2 remain unclear. Using vascular smooth muscle cells, we investigated the regulation of expression of AT2 by growth factors in comparison with that of AT1. The cultured rat aorta smooth muscle cells had detectable AT2 binding sites, which were reduced significantly by treatment with platelet derived growth factor-BB. On the other hand, AT1 binding sites were increased under the same conditions. Other growth factors, such as epidermal growth factor and endothelin-1, also suppressed AT2 receptors to varying extents. A negative correlation between DNA synthesis promoted by these growth factors and the binding capacity of AT2 sites was observed. This study indicated that the expression of AT2 is downregulated in cultured vascular smooth muscle cells by growth factors in contrast to that of AT1, which was slightly upregulated.

Analysis of Variance↗

PubMed1993

Neurotransmitter release from lysophosphatidic acid stimulated PC12 cells: involvement of lysophosphatidic acid receptors.

The significance of phospholipase D in metabolic regulation is being recognized. The products of phospholipase D action are phosphatidic acid and lysophosphatidic acid (LPA). Whether these lipid products exert their effect through plasma membrane receptor-mediated mechanism is not yet clear. In the present study we have shown the presence of specific receptors for LPA in plasma membranes of PC12 pheochromocytoma cells. LPA evoked a transient rise in [Ca2+]i concomitant with formation of IP3. LPA also stimulated dopamine release from PC12 cells. These results indicate that LPA stimulates catecholamine release via specific LPA receptors presumably by activating the IP3 mediated Ca2+ release.

Animals↗

PubMed1993

Isolation of an endogenous Na-pump specific inhibitor from normal pig urine: characterization and comparison with the inhibitor purified from bovine adrenal glands.

An endogenous Na-pump specific inhibitor has been purified to homogeneity from normal pig urine using Amberlite XAD-2 adsorption chromatography followed by five steps of reverse phase HPLC. Although most of the dose response curves for this purified Na-pump inhibitor, designated uroxin, in the various assay systems paralleled those of authentic ouabain and the specific Na-pump inhibitor previously purified from bovine adrenal glands (designated adrexin C), the cross-reactivity curve with anti-ouabain antibodies did not. The retention times of uroxin on various types of reverse phase HPLC columns were also different from those of plant-derived cardiotonic steroids and adrexin C. The cross-reaction curve of adrexin C was superimposable with that of ouabain, and adrexin C coeluted with ouabain from all of the HPLC columns tested. The results from physical and chemical characterization of both purified inhibitors suggest that uroxin is a novel Na-pump inhibitor which is structurally different from any of the known cardiotonic steroids or other substances previously reported to exhibit Na-pump inhibitory activity. The results also indicate that adrexin C is indistinguishable from ouabain. These results suggest that there are at least two different types of endogenous Na+,K(+)-ATPase inhibitors in the mammalian body.

Adrenal Glands↗

PubMed1993

Differing signal transductions elicited by three isoforms of platelet-derived growth factor in vascular smooth muscle cells.

The differing signal transductions elicited by three isoforms of platelet-derived growth factor (PDGF) were studied in cultured rat vascular smooth muscle cells (VSMC), which show different mitogenic responses to the three PDGF isoforms. PDGF-BB elicited a variety of cellular signals, including the phosphorylation on tyrosine of phospholipase C-gamma 1 (PLC-gamma 1) and the PDGF receptor, formation of inositol 1,4,5-trisphosphate and diacylglycerol, degradation of phosphoinositides (phosphatidylinositol, phosphatidylinositol 4-phosphate, and phosphatidylinositol 4,5-bisphosphate) and elevation of intracellular calcium ([Ca2+]i). However, PDGF-AB failed to show some of these signals, although it stimulated [3H]thymidine incorporation to almost the same extent as PDGF-BB. Importantly, phosphorylation on tyrosine of the PLC-gamma 1 was far less (< 6.25%) in the case of PDGF-AB than that of PDGF-BB when assessed by immunoblotting. On the other hand, calcium ion entry from the extracellular medium was comparable in PDGF-AB- and PDGF-BB- stimulated VSMC. PDGF-AA, which did not stimulate [3H]thymidine incorporation, failed to show any of these effects with the exception of diacylglycerol formation. These observations suggest that the three PDGF isoforms stimulate different signal transduction pathways and that calcium ion entry, but not tyrosine phosphorylation of PLC-gamma 1, is essential for PDGF-induced mitogenesis in VSMC.

Animals↗

PubMed1993

Cellular localization of angiotensin type 1 receptor and angiotensinogen mRNAs in the subfornical organ of the rat brain.

The cellular localization of angiotensin type 1 receptor (AT 1) and angiotensinogen mRNA expression in the subfornical organ (SFO) of the rat brain has been studied by means of non-radioactive in situ hybridization combined with immunocytochemistry for glial fibrillary acidic protein (GFAP) and Neutral red staining. The AT 1 receptor mRNA expression is shown to be within putative nerve cells without any association with the glial fibrillary acidic protein (GFAP)-immunoreactive (IR) cells. In contrast the angiotensinogen cRNA expression is associated predominantly with GFAP-IR cells. The results demonstrate that a neuronal AT 1 receptor mediates the actions of circulating angiotensin II on the SFO and that the angiotensinogen mRNA is predominantly expressed in the SFO astroglial cells.

Angiotensin I↗

PubMed1993

Isolation and characterization of an endogenous Na+,K(+)-ATPase-specific inhibitor from pig urine.

A Na+,K(+)-ATPase inhibitor was purified from 88.6 l pig urine with a yield of approximately 10 micrograms. It inhibits the ouabain-sensitive uptake of 86Rb into human erythrocytes and the specific binding of ouabain to Na+,K(+)-ATPase. It also exhibits cross-reactivity to anti-ouabain serum. The purification procedure consisted of adsorption chromatography on an Amberlite XAD-2 column, preparative scale C18 low-pressure liquid chromatography (LPLC), and five steps of HPLC with five different types of reverse-phase columns. The dose dependence of the purified substance for the inhibition of ouabain-sensitive Na+,K(+)-ATPase activity and 86Rb uptake into human erythrocytes, and for the ouabain-displacing activity, paralleled those of ouabain, spanning two orders of magnitude in concentration range. However, the curve obtained from the cross-immunoreactivity with anti-ouabain serum did not parallel that of ouabain. The inhibitory potencies of the purified substance against the Na(+)-pump and ouabain-binding were diminished with increasing K+ concentration, exhibiting characteristics typical of cardiac glycosides. This substance had no effect on Ca(2+)-ATPase activity in human erythrocyte plasma membrane and skeletal-muscle sarcoplasmic reticulum, nor on Mg(2+)-ATPase activity. Acid treatment with 6 M HCl at 115 degrees C for less than 1 min destroyed approximately 82% of the inhibitory activity of the purified substance against Na(+)-pump activity. Alkaline treatment with 0.2 M NaOH at 23 degrees C for 2 h and heat treatment at 150 degrees C for 30 min partially destroyed the inhibitory activity. Boiling for 10 min and digestion by various enzymes did not affect the activity. Molecular mass was estimated to be 620 Da by gel-filtration column chromatography. Preliminary MS analysis suggested that the purified substance has a molecular mass of 625 Da. An 1H-NMR study revealed that this substance does not contain a tertiary methyl group. The results suggest that the purified Na+,K(+)-ATPase inhibitor is not a peptide and is distinct from any of the known cardiotonic steroids or various substances previously reported to exhibit Na+,K(+)-ATPase inhibitory activity. Thus, the purified substance may be a novel endogenous regulator of Na+,K(+)-ATPase.

Animals↗

PubMed1993

Atrial natriuretic factor stimulates phosphorylation of a 52-kDa calmodulin-binding protein in vascular smooth muscle cells.

The effect of atrial natriuretic factor (ANF) on the phosphorylation of the calmodulin-binding protein in vascular smooth muscle cells was investigated. Several phosphorylated calmodulin-binding proteins ranging in molecular weight from 205,000 to 50,000 were detected. Among them, we have found that the phosphorylation of a 52-kDa protein present mainly in the cytosolic fraction is stimulated by ANF and that the elevation of the phosphorylation is both time- and dose-dependent. Furthermore, the stimulation was mimicked by 8-bromo-cyclic GMP but not by 8-bromo-cyclic AMP. Endothelin induced significant inhibition of the phosphorylation. These results indicate that 52-kDa protein phosphorylation may be responsible for the regulation of vascular smooth muscle tone.

Animals↗

PubMed1993

Intrarenal localization of angiotensin II type 1 receptor mRNA in the rat.

We examined intrarenal localization of angiotensin II type 1 receptor (AT1) mRNA in kidneys of normal adult male Munich Wistar rats using the methods of reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization. For RT-PCR, we used a rat AT1 subtype A (AT1A)-specific oligonucleotide primer pair. To semi-quantitatively assess the expression level of AT1 mRNA among several regions of kidney, AT1 cDNA was coamplified with beta-actin cDNA. When compared to the level in the adrenal gland (expressed as 100%), the level of AT1 mRNA was markedly higher in glomeruli (273 +/- 69%), followed in intensity by the renal papilla (151 +/- 57%), renal cortex (139 +/- 19%), and renal medulla (114 +/- 35%). In situ hybridization studies, using a 479 bp nucleotide fragment from AT1A-coding exon as a probe, also revealed a glomerular preponderant pattern of AT1 mRNA localization. Thus, within the glomerulus, AT1 mRNA localized in mesangial areas, predominantly at the vascular pole. In the vascular components of the juxtaglomerular apparatus (JGA), namely the terminal portion of the afferent arteriole (that is, immunohistochemically renin-positive site) and extraglomerular mesangial cells, the latter showed AT1 mRNA localization in the non-manipulated kidney, while AT1 mRNA was undetectable in the arteriole outside the JGA. The kidneys of rats treated with an angiotensin I converting enzyme inhibitor (ACEI) showed extension of the AT1 mRNA localization on the afferent arteriole toward the interlobular artery.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗

PubMed1993

Cellular expression of angiotensin type-1 receptor mRNA in the kidney.

Angiotensin II has multiple renal effects that are important in the regulation of renal hemodynamics and electrolyte secretion, and binding sites for angiotensin II have been demonstrated in different cells of the kidney. In the present study the cellular localization of mRNA for the angiotensin type 1 (AT1) subtype of the angiotensin II receptor was studied in adult rat kidney using a cRNA probe and in situ hybridization. Strong labeling was demonstrated in tubule cells of the inner and outer stripe of the outer medulla. In emulsion-dipped sections, counter-stained with hematoxylin-eosin, labeling was identified in segment S3 of proximal tubules and in the thick ascending limb of loop of Henle (mTAL). The results suggest expression of AT1-receptor mRNA with a distinct compartmentalization within the nephron.

Animals↗

PubMed1993

Intravenous adenosine suppresses cardiac release of endothelin after myocardial ischaemia and reperfusion.

OBJECTIVE: Intravenous adenosine decreases infarct size in experimental models of myocardial ischaemia/reperfusion. Ischaemia/reperfusion is associated with a significant increase in cardiac release of endothelin. The effect of cardioprotective doses of adenosine on endothelin release was explored in dogs undergoing 90 min coronary occlusion and 210 min reperfusion. METHODS: Dogs were assigned to intravenous adenosine in a dose of 0.15 mg.kg-1.min-1 (n = 12) or control (n = 11) during the first 150 min reperfusion. Serial endothelin levels were obtained from the coronary sinus and aortic blood and measured by radioimmunoassay. RESULTS: Adenosine significantly reduced infarct size expressed as a percent of the risk region (28.8 6% v 14.4 2%; p = 0.03). A similar increase in aortic and coronary sinus blood endothelin was observed in both groups during temporary occlusion. A significant transcardiac increase in endothelin levels was present in the control group 60 min after reperfusion whereas no increase occurred in the adenosine treated group [control 5.6(SEM 1.9) v adenosine -0.2(1.4) pg.ml-1; p = 0.02]. Similarly, intravenous adenosine tended to prevent the increase in myocardial endothelin production seen in control animals during the early reperfusion period [control 280(146) v adenosine -57(55) pg.min-1; p = 0.05]. Endocardial blood flow in the ischaemic zone 210 min after reperfusion was significantly higher in the adenosine group, at 0.60(0.02) v 0.38(0.02) ml.min-1.g-1; p < 0.05. A significant correlation between endothelin levels, endocardial flow and infarct size was observed in the control group 3 h after reperfusion: r = 0.73, p = 0.02; r = 0.62, p = 0.03 respectively. This relationship was absent in animals treated with adenosine. CONCLUSIONS: Intravenous adenosine suppresses the release of endothelin from the previously ischaemic myocardium during the early reperfusion period. This effect may in part contribute to the improvement by adenosine in postischaemic microcirculatory flow resulting in attenuation of the "no reflow" phenomenon.

Adenosine↗

PubMed1993

Molecular genetics of the SA-gene: cosegregation with hypertension and mapping to rat chromosome 1.

OBJECTIVES: The SA-gene shows markedly higher levels of expression in the kidneys of spontaneously hypertensive rats (SHR) than in their non-hypertensive reference strain, the Wistar-Kyoto (WKY) rat. Based on the important role of the kidney in blood pressure regulation, the possibility has been raised that this gene, the translational product of which remains unknown, may participate in the pathogenesis of primary hypertension. The present study was conducted to test this hypothesis and to ascertain the chromosomal localization of the SA-gene. DESIGN: A cosegregation study was performed using an F2 intercross between stroke-prone SHR (SHRSP) and WKY rats, and a previously described restriction fragment length polymorphism of the SA-gene for characterization of genotype. Mapping of the SA-gene was accomplished by screening a somatic cell-hybrid panel and by linkage group analysis. RESULTS: A statistically significant difference in systolic blood pressure was found after sodium loading, but not under basal conditions between groups of rats defined by zygosity at the SA locus, consistent with a hypertensive effect of the SHRSP allele. No effect of SA genotype on diastolic blood pressure was observed. The SA-gene was localized on rat chromosome 1. CONCLUSIONS: This study establishes the SA locus on chromosome 1 as a region in which a gene or genes contributing to blood pressure regulation in this model are localized, and provides further evidence for a possible role of the SA-gene in the pathogenesis of hypertension.

Animals↗

PubMed1993

Chromosomal assignment of human and rat hypertension candidate genes: type 1 angiotensin II receptor genes and the SA gene.

OBJECTIVE: The chromosomal location of candidate genes for a disease, especially if the disease is multifactorial, is an important datum. The objective of the present study was to determine the chromosomal location of candidate hypertensinogenic genes, both in humans and in the rat, a species widely used for animal models of human hypertension. The type 1 angiotensin II receptor (AT1) genes are obvious hypertension candidate genes, whereas the SA gene has recently been shown to cosegregate with hypertension in the rat. DESIGN: The chromosomal location of the relevant genes was determined using somatic cell hybrids segregating either human chromosomes or rat chromosomes. The presence of the human or rat genes was determined by the Southern blot method, using rat probes. RESULTS: A single AT1 gene (AT1) was detected in the human genome, and was assigned to chromosome 3, whereas two non-syntenic genes were detected in the rat genome, corresponding to the previously identified A and B subtypes. They were assigned to the rat chromosome 17 (At1a) and 2 (AT1b). The Sa gene was assigned to human chromosome 16 and rat chromosome 1, disclosing a new synteny group retained on rat chromosome 1 and human chromosome 16. CONCLUSIONS: These chromosomal assignments should be useful for linkage analyses of genes controlling blood pressure. The genes that we studied, and the chromosomes that we identified, deserve special attention in such linkage analyses.

Angiotensin II↗

PubMed1993

Central cardiovascular effects of joining peptide in genetically hypertensive rats.

Joining peptide (JP) is one of the major products of proopiomelanocortin (POMC). The biological function of this peptide has not been clarified despite its relative abundance in the pituitary and the hypothalamus. Recently we demonstrated that JP, which was isolated from bovine posterior pituitary, possesses Na pump inhibitor activity. The purpose of this study is to explore the physiological relevance of JP in cardiovascular regulation. For these investigations, we used the synthetic peptides bovine JP (bJP) and COOH-terminally amidated rat JP (rJP), since JP is known to have sequence variability among species. Intracisternal administration of both bJP and rJP in urethan-anesthetized rats evoked similar hypertensive and tachycardia effects. The effects of both peptides were markedly greater in the spontaneously hypertensive rats (SHR) compared with the normotensive Wistar Kyoto rats (WKY). Intravenous bolus injections of rJP at the same doses were without effect. Autoradiography, using 125I-labeled [0Tyr]-rJP as a ligand, revealed specific binding sites for rJP in the dorsal medulla in areas corresponding to the nucleus tractus solitarii (NTS) (extending from approximately 0.4 mm caudal to 1.8 mm rostral to the obex). Microinjections of rJP into the caudal part of the NTS of anesthetized SHR produced dose-related pressor and tachycardic responses. The pressor and tachycardic responses were also observed at the rostral part of the NTS, whereas the injections into the intermediate part of the NTS evoked depressor and bradycardic responses in SHR. These results suggest that at doses tested, the site of JP action resides in the central nervous system, and that JP is a potent neuropeptide in medullary sites known to be pivotal in central cardiovascular regulation. The effect of JP is especially prominent in the genetically hypertensive rat.

Analysis of Variance↗

PubMed1993

Cloning of a rabbit kidney cortex AT1 angiotensin II receptor that is present in proximal tubule epithelium.

The rabbit proximal tubule (PT) has been widely utilized to study the direct effects of angiotensin II (ANG II) on PT function. The purpose of the present study was to characterize the binding properties of PT ANG II receptors, using nonpeptide antagonists, and to clone a rabbit PT ANG II receptor. In rat and rabbit kidney cortical brush-border and basolateral membranes, specific binding of 125I-ANG II was inhibited by the AT1 ANG II-receptor antagonist DuP 753, but not by the AT2 antagonist PD 123319. Using a rabbit kidney cortex cDNA library, we isolated cDNA encoding an ANG II receptor, with an open-reading frame sharing a high degree of sequence homology to previously cloned AT1 ANG II receptors. In transfected COS-1 cells, this rabbit ANG II receptor had properties of the AT1 class. Northern analysis revealed high levels of mRNA expression for this receptor in rabbit kidney cortex and adrenal gland. Within the kidney, message was detected in primary cultures of rabbit PT cells, as well as in freshly isolated rabbit PT segments. Message was also present in cells of the mouse PT line, MCT, and in rat glomerular mesangial cells. Utilizing polymerase chain reaction (PCR) with primers derived from the 1st and 4th transmembrane domains of the rat AT1A ANG II receptor, a 279-bp DNA fragment was amplified from reverse-transcribed RNA from rabbit PT cells. This DNA encoded an amino acid sequence identical to that encoded by the rabbit kidney cDNA clone in the corresponding region and differed by a single base substitution. Southern analysis of rabbit genomic DNA restriction digests with the rabbit ANG II receptor probe revealed hybridization to a single band in each lane. These results indicate that an AT1 ANG II receptor is present in the PT and that a single gene codes for the AT1 receptor in rabbit. The clone isolated in the present study should provide a useful tool with which to study the regulation of the PT renin-angiotensin system.

Amino Acid Sequence↗

PubMed1993

Direct visualization of renin-cell distribution in preglomerular vascular trees dissected from rat kidney.

Three methods to visualize directly the distribution of granulated renin-positive cells in vascular trees microdissected from rat kidney were developed. Kidneys were removed from anesthesized rats, hemisectioned, macerated in HCl, and soaked in distilled water for 24-48 h. Cortical preglomerular vascular trees consisting of arcuate and cortical radial arteries and afferent arterioles were microdissected with the aid of a stereomicroscope. Granulated cells can be visualized in three ways. First, under transmitted or incident light observation, granulated cells are readily distinguished from the surrounding smooth muscle cells, because of marked differences in the refractive properties of these two cell types. Second, quinacrine, a fluorescent, intravital stain selective for dense-core granules, can be administered (2 mg/kg iv) to the rat 1 h before nephrectomy. When illuminated with 440-nm light, granulated cells fluorescence strongly at 510 nm. Third, specific immunostaining for renin can be obtained with a polyclonal anti-rat renin antibody and avidin-biotin immunoperoxidase staining in vascular trees subjected to cell permeabilization with Triton. These new techniques permit the direct visualization of the distribution of granulated renin-positive cells in preglomerular vessels under conditions in which the vascular architecture is largely preserved.

Animals↗

PubMed1993

Molecular forms of atrial natriuretic factor in normal and failing human myocardium.

BACKGROUND: Atrial natriuretic factor (ANF) is produced by myocardial tissue, and the plasma ANF concentration is known to be elevated in congestive heart failure (CHF). Data from animal models indicate that myocardial concentrations of ANF are depleted in CHF, and this has given rise to the hypothesis that CHF is characterized by depletion of stored ANF. To date, the molecular forms of ANF and their concentrations in atrial and ventricular myocardium remain poorly characterized in the normal and the failing human heart. METHODS AND RESULTS: We measured ANF concentrations in fresh tissue from failing human hearts explanted at the time of cardiac transplantation and from organ donors whose normal hearts could not be used for transplantation. We determined total ANF and alpha, beta, and gamma ANF concentrations in the right and left atrial appendages, atrial free walls, and ventricles. In normal hearts, ANF concentration in the atrial appendages was 40-fold higher than ANF in the rest of the atrial free wall and in the ventricles. In the failing hearts, atrial appendage ANF concentrations increased 5- to 10-fold, and atrial free wall ANF concentrations increased 200-fold. Analysis of molecular forms of ANF demonstrated significant increases in the gamma and beta forms in the left atrial appendage of failing hearts. alpha, beta, and gamma ANF forms were also significantly increased in right and left atrial free wall tissue from failing hearts. In addition, failing hearts were characterized by absolute and relative increases in the precursor form gamma ANF. CONCLUSIONS: These data from fresh tissues suggest that cardiac ANF stores are not decreased in severe CHF in humans; rather, chronic CHF is characterized by marked increases in atrial ANF tissue concentrations, particularly the beta and gamma ANF forms. These findings are consistent with intracellular accumulation of precursor ANF forms in severe chronic human CHF.

Adolescent↗

PubMed1993

Regulation of vascular angiotensin release.

To investigate the regulatory mechanism of the vascular renin-angiotensin system, we perfused isolated rat hind legs with plasma-free buffer and quantified angiotensin peptides in the perfusate. Angiotensin release from hind legs was increased in rats pretreated with losartan (DuP 753) and rats fed a low sodium diet with subsequent furosemide and was decreased in nephrectomized rats and rats given dexamethasone, ethynylestradiol, and triiodothyronine. Using these models, we have attempted to identify which step or component of angiotensin metabolism determines angiotensin release level. Changes caused by these manipulations in plasma renin concentration and basal angiotensin release from hind legs were almost parallel, whereas plasma angiotensinogen concentration and the angiotensin release changed in opposite directions. Infusion of renin in hind legs caused a marked increase in angiotensin release and continued even 1 hour after cessation of renin infusion. Infusion of angiotensinogen did not alter the angiotensin release. Angiotensin clearance and angiotensin I conversion were not affected by either nephrectomy or losartan pretreatment. Aortic renin messenger RNA level was extremely low and not increased by nephrectomy or losartan pretreatment, although kidney renin messenger RNA level was increased by losartan pretreatment. These results provide evidence that plasma renin of kidney origin is the major source of vascular functional renin and plays the determining role in the regulation of vascular angiotensin release. Plasma-derived or locally produced angiotensinogen, locally produced renin, converting enzyme, and angiotensin clearance are not considered to be the primary determinant in the regulation of vascular angiotensin release in these acute and subacute experimental models.

Angiotensin I↗

PubMed1993

Endothelin as a neuropeptide. Cardiovascular effects in the brainstem of normotensive rats.

The relevance of endothelin in central cardiovascular function was studied in urethane-anesthetized Sprague-Dawley rats. Blood pressure (BP) was monitored intra-arterially, and cerebrospinal fluid (CSF) was collected through an intracisternal catheter for radioimmunoassay of endothelin-1 (ET-1). Endothelin levels in the CSF were significantly higher (39 +/- 3 pg/ml) than in plasma (10 +/- 3 pg/ml, n = 11). ET-1 in CSF or plasma was not affected by systemic infusion of saline, but its levels significantly decreased when a sustained increase in BP was elicited with phenylephrine (14 +/- 7 pg/ml in the CSF and 6 +/- 4 pg/ml in plasma, n = 5). In sinoaortic-denervated animals, phenylephrine failed to reduce CSF endothelin levels. In different experiments, intracisternal administration of ET-1 (10 pmol) evoked an initial decrease in BP and heart rate (HR), followed by pronounced hypertension, bradycardia, and, in 70% of the animals, death from cardiorespiratory failure. Intracisternal administration of endothelin-3 (ET-3, 80 pmol, n = 11) evoked only a modest hypotensive and bradycardic response without cardiorespiratory impairment. Microinjection of ET-1 (0.5, 1, 2, 4, and 6 pmol/60 nl) into the nucleus of the solitary tract or area postrema produced a decrease in BP and HR. On the other hand, injection of low concentrations of ET-3 into the nucleus of the solitary tract increased BP and HR (at 2 pmol, 17 +/- 3 mm Hg, 14 +/- 6 beats per minute, n = 7), whereas ET-3 in the area postrema produced a prominent dose-related decrease in BP and HR. In the rostroventrolateral medulla, the lowest doses of ET-1 first modestly increased BP and renal sympathetic nerve activity. These effects were followed by hypotension, bradycardia, increase in respiratory frequency, and further enhancement of sympathetic nerve traffic. In 29% of the animals, these effects were followed by cardiorespiratory arrest. The specificity of the cardiovascular response to endothelin was demonstrated by the inhibitory effects of the receptor antagonist BQ-123. These results demonstrate that endothelin has specific cardiovascular effects in the brainstem of the rat and support a role for endothelin in cardiovascular regulation.

Animals↗