A fourth-year elective course in alternative medicine.
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Attitude of Health Personnel↗
Biomedical subjects
W B Jeffries
Publications and source records attributed to W B Jeffries.
Functional calcitonin gene-related peptide subtype 2 receptors in porcine coronary arteries are identified as calcitonin gene-related peptide subtype 1 receptors by radioligand binding and reverse transcription-polymerase chain reaction.
Calcitonin gene-related peptide (CGRP) receptors are classified into CGRP subtype 1 (CGRP(1)) and CGRP subtype 2 (CGRP(2)) based on the affinity of the antagonist, human alpha (halpha)-CGRP(8-37). halpha-CGRP(8-37) antagonizes CGRP(1) receptor-mediated responses with high affinity (K(B) < 100 nM) and antagonizes CGRP(2) receptor-mediated responses with low affinity (K(B) > 1 microM). CGRP(2) receptors have been previously reported to mediate relaxation of large porcine coronary arteries because this action is antagonized with low affinity by halpha-CGRP(8-37). In the present study, we used reverse transcription-polymerase chain reaction, radioligand binding, and values from our previously reported isolated tissue experiments to compare the CGRP receptor in porcine coronary arteries with the porcine CGRP(1) receptor stably expressed in human embryonic kidney (HEK) 293 cells. We identified calcitonin receptor-like receptor and receptor activity modifying protein 1 mRNA in coronary arteries. We also found that the ligand binding characteristics of the CGRP receptor in coronary arteries and the cloned CGRP(1) receptor were highly similar. K(I) values for halpha-CGRP(8-37) were 6.6 and 5.7 nM in porcine coronary arteries and the cloned CGRP(1) receptor, respectively. The affinities (K(B)) of halpha-CGRP(8-37) and five other antagonists were 22- to 707-fold lower in functional experiments measuring relaxation of coronary arteries than in radioligand binding experiments. Despite this difference in absolute affinity values, there was a high correlation of the rank order of affinity for the antagonists determined by the two methods. Thus halpha-CGRP(8-37) antagonizes CGRP-induced relaxation of porcine coronary arteries with low affinity at the CGRP(1) receptor. Taken together, these data do not support the existence of the CGRP(2) receptor.
Animals↗
Kinetics of alkylation of cloned rat alpha1-adrenoceptor subtypes by chloroethylclonidine.
We quantified and compared the rates at which chloroethylclonidine (CEC) inactivated cloned rat alpha1A, alpha1B-, and alpha1D-adrenoceptors. Membranes from cells transfected with one of the three cloned alpha1-adrenoceptors were incubated for various intervals with 100 microM chloroethylclonidine at 10 degrees C, 25 degrees C or 37 degrees C. The fraction of receptors alkylated by chloroethylclonidine was determined by [3H]prazosin binding. Chloroethylclonidine fully inactivated each alpha1-adrenoceptor subtype via a first order reaction. Alkylation by chloroethylclonidine was markedly slower for the alpha1A-adrenoceptor vs. the other two subtypes (rate constants in 10(-3) min(-1) at 10 degrees C: 0.99 +/- 0.01 (alpha1A), 7.26 +/- 0.15 (alpha1B), and 7.01 +/- 0.12 (alpha1D)). Despite differences in rate, activation energies for alkylation were similar among subtypes. suggesting a similar binding sites for chloroethylclonidine. Computer simulations of kinetic data in mixed receptor populations and experiments with membranes from rat brain showed that nonlinear curve fitting could distinguish relative proportions of alpha1A-adrenoceptor vs. the other two subtypes. We conclude that measurement of the rate of alkylation by chloroethylclonidine, rather than the total amount of alkylation, is most useful in distinguishing the relative proportion of alpha1A-adrenoceptor in tissues.
Adrenergic alpha-Antagonists↗
Molecular cloning, expression and characterization of cDNA encoding a mouse alpha1a-adrenoceptor.
1. In this study, we have cloned, expressed, and characterized an alpha1a-adrenoceptor gene from the mouse. We designed oligonucleotide PCR primers complementary to regions of the rat alpha1a-adrenoceptor sequence and amplified cDNA fragments from total RNA of mouse cerebral cortex, liver and kidney by reverse transcription-polymerase chain reaction (RT PCR). 2. Both the nucleotide and deduced peptide sequences of the cDNA showed high sequence identity with those of cloned alpha1a-adrenoceptors from other species. The cDNA clone had an open reading frame of 1398 nucleotides encoding a 466 amino acid peptide which had 97%, 92% and 90% identity with the deduced amino acid sequences of the rat, human and bovine alpha1a-adrenoceptor, respectively. 3. The amplified mouse cDNA was inserted into a mammalian expression vector pcDNA3.1(+) and expressed in COS-1 cells. The pharmacological properties of the mouse cDNA clone were examined in radioligand binding studies and functional assays. The expressed mouse protein had a high affinity for [3H]-prazosin (Kd = 0.48 nM) and pattern of affinity for antagonists in competition studies that is similar to that of the rat alpha1a-adrenoceptor. Chloroethylclonidine (CEC) could slowly alkylate the expressed protein, with a rate similar to that of the rat alpha1a-adrenoceptor. 4. The expressed receptors were able to mediate noradrenaline (NA) stimulation of the production of inositol phosphates in COS-1 cells, consistent with coupling to phospholipase C. This response to NA could be reversed by pretreatment of the transfected cells with prazosin. 5. Based on the above evidence, we concluded that the cloned cDNA is that of the mouse alpha1a-adrenoceptor.
Adrenergic alpha-Antagonists↗
Regulation of cAMP production in initial and terminal inner medullary collecting ducts.
BACKGROUND: The inner medullary collecting duct (IMCD) is composed of at least two functionally and morphologically distinct segments, the initial (IMCDi) and the terminal (IMCDt) portions. However, most studies of receptor signaling have been performed on cells obtained from the entire inner medulla. The purpose of this study was to determine whether the patterns of receptor-activated cAMP accumulation were different between these segments. METHODS: We measured cAMP accumulation stimulated by vasopressin and isoproterenol, and the effect of epinephrine in freshly dissected IMCDi and IMCDt segments cultured and IMCDi and IMCDt cells in primary culture. RESULTS: The maximum response to vasopressin was twofold higher in fresh IMCDt verus IMCDi (P < 0.05), however, it increased in cultured IMCDi by 40% verus fresh cells with no change in the response in fresh verus cultured IMCDt. The maximum response to isoproterenol was small in fresh cells but increased by five- and sixfold, respectively, in cultured IMCDi and IMCDt cells. alpha 2-Adrenoceptor stimulation almost completely inhibited both vasopressin and isoproterenol-stimulated cAMP accumulations in fresh IMCDi and IMCDt cells, but only partially inhibited either accumulation by 34 to 49% in cultured cells. CONCLUSIONS: (1) IMCDi and IMCDt cells are both subject to vasopressin and alpha 2- and beta-adrenergic regulation of adenylyl cyclase activity; (2) the relative influence of beta-adrenergic, alpha 2-adrenergic and V2 receptors to affect cAMP accumulation is altered in primary culture versus freshly dissected IMCD segments, suggesting that caution must be exercised in the extrapolation of data from cultured IMCD cells to in vivo models.
Adrenergic alpha-Agonists↗
Distribution of alpha1-adrenergic receptor mRNA species in rat heart.
Radioligand binding studies have detected alpha1A- and alpha1B-adrenergic receptors (AR) in rat heart, but the ligands available for these studies lack the sensitivity and specificity needed to map possible differences in alpha1-AR subtype expression. We therefore used competitive reverse transcriptase-polymerase chain reaction (RT-PCR) techniques to measure steady-state amounts of alpha1-AR messenger RNA (mRNA) subtypes in tissue dissected from several regions of rat heart. We detected mRNA for alpha1A-, alpha1B-, and alpha1D-AR in each region. Irrespective of the alphaAR subtype, the total number of alpha1-AR transcripts has the following regional rank order: left ventricular papillary muscle > left ventricle > left atrium > apex > right ventricle > ventricular septum > right atria. Among the regions, the fractional contribution of alpha1A-, alpha1B-, and alpha1D-AR mRNA to the total amount of alpha1-AR displays considerable variability. The alpha1B-AR mRNA accounts for >50% of the total alpha1-AR mRNA in all regions except the ventricular septum. There are also significant percentages of alpha1A-AR in each region, especially in the papillary muscle (48%) and ventricular septum (48%). The alpha1D-AR mRNA transcripts are found in comparatively low numbers; their highest levels (18% of total) were found in the right ventricle. These differences in alpha1-AR mRNA expression may contribute to the observed regional differences in myocardial responses to alpha1-AR agonists and antagonists.
Animals↗
Selective inhibition of alpha1B-adrenergic receptor expression and function using a phosphorothioate antisense oligodeoxynucleotide.
To investigate alpha1B-adrenoceptor function, we developed a phosphorothioate antisense oligodeoxynucleotide (AO) to inhibit the expression of the alpha1B-adrenoceptor subtype in DDT1 MF2 cells. We measured the cellular uptake of the AO and its effect on alpha1B-adrenoceptor mRNA expression, protein density, and coupling to phospholipase C. Cells treated with either a control oligodeoxynucleotide (CO) or medium alone served as control groups. Confocal microscopy demonstrated that DDT1 MF2 cells internalized carboxyfluorescein-labeled (FAM) AO within 30 min. Analysis of cellular lysates showed that approximately 50% of the intracellular FAM-AO was present as an intact 18-mer for up to 48 hr. Incubation of cells with AO for 48 hr decreased alpha1B-adrenoceptor density ([3H]prazosin Bmax) versus control groups by 12% (1 microM AO) and 72% (10 microM AO). In time course experiments, AO (10 microM) reduced alpha1B-adrenoceptor density by 28, 64, and 68% versus controls after 24, 48, and 72 hr of exposure, respectively. alpha1B-Adrenoceptor mRNA concentration (measured by RT-PCR) was reduced by 25% in cells treated for 48 hr with 10 microM AO versus controls. AO pretreatment (10 microM, 48 hr) reduced the maximum response to agonist-stimulated [3H]inositol phosphate accumulation. The maximal response of the full agonist norepinephrine was reduced by 30% after AO treatment, and by 73% for the partial agonist naphazoline. In contrast, AO did not affect histamine-stimulated total [3H]inositol phosphate accumulation. Thus, AO effectively reduced alpha1B-adrenoceptor subtype expression and function in vitro, suggesting a potential to selectively inhibit alpha1B-adrenoceptor function in vivo.
Adrenergic alpha-1 Receptor Antagonists↗
Effect of epinephrine on cAMP accumulation in cultured rat inner medullary collecting duct cells.
In a previous study we have reported the existence of alpha2- and beta-adrenoceptors in cultured rat inner medullary collecting duct (IMCD) cells. In this report, we examined the effect of epinephrine on intracellular adenosine 3',5'-cyclic monophosphate (cAMP) accumulation and evaluated whether alpha2-adrenoceptors interact with beta-receptors, vasopressin receptors, and prostaglandin (PG) E2 receptors by measuring cAMP generation. Epinephrine stimulated cAMP accumulation in a dose-dependent manner [half-maximal effective concentration (EC50) = 300 nM]. Rauwolscine (10 microM) enhanced epinephrine effects, shifting the dose-response curve for epinephrine to the left (EC50 = 120 nM); however, beta-antagonists inhibited epinephrine-induced cAMP accumulation. Epinephrine (10 microM) inhibited cAMP accumulation maximally induced by isoproterenol (10 microM); this effect was reversed by rauwolscine (10 microM). Epinephrine inhibited vasopressin (100 nM)-induced cAMP accumulation but failed to inhibit PGE2 (10 microM)-induced cAMP accumulation. We conclude that epinephrine acts as an alpha2- and beta-adrenoceptor agonist and that alpha2-adrenoceptors interact with beta-adrenoceptors and vasopressin receptors but not with PGE2 receptors on cAMP accumulation. This suggests that alpha2-adrenoceptors play a physiological role via interaction with different hormone receptors.
Adrenergic Agonists↗
Radioligand binding using 125I-labeled peptides.
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Animals↗
Analysis of data from "cold saturation" radioligand binding experiments.
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Animals↗
The beta 1- and beta 2-adrenoceptor subtypes in cultured rat inner medullary collecting duct cells.
We investigated beta-adrenoceptor subtype(s) expressed in cultured rat inner medullary collecting duct (IMCD) cells. In radioligand binding assay, [125I]iodocyanopindolol bound to IMCD cell membranes, representing a single class of binding sites (dissociation constant = 96.1 pM, maximum binding capacity = 18.2 fmol/mg protein, n = 8). In competition studies, ICI-89406 (beta 1-antagonist) and ICI-118551 (beta 2-antagonist) bound with high affinity, fitting a two-site model. Isoproterenol increased intracellular adenosine 3',5'-cyclic monophosphate (cAMP) accumulation (half-maximal effective concentration = 200 nM). Propranolol completely inhibited isoproterenol-induced cAMP accumulation [half-maximal inhibitory concentration (IC50) = 270 nM]. ICI-89406 and ICI-118551 inhibited cAMP accumulation by 50% (IC50 = 1.5 microM and 1.7 microM, respectively). The combined addition of ICI-89406 and ICI-118551 resulted in a curve indistinguishable from that of propranolol. The beta 1- and beta 2-adrenoceptor mRNAs have been demonstrated using reverse transcription-polymerase chain reaction. In initial and terminal IMCD cells, propranolol (3 microM) inhibited isoproterenol-stimulated cAMP accumulation by 80%, whereas ICI-89406 (3 microM) and ICI-118551 (3 microM) resulted in only partial inhibition (50%). We conclude that both beta 1- and beta 2-adrenoceptors are expressed in initial and terminal IMCD cells in primary culture.
Adrenergic beta-Agonists↗
Quantification of steady state expression of mRNA for alpha-1 adrenergic receptor subtypes using reverse transcription and a competitive polymerase chain reaction.
Three distinct alpha-1 adrenergic receptor subtypes (alpha-1a, alpha-1b and alpha-1d) have been identified through molecular cloning. Expression of alpha-1 adrenergic receptor mRNA has been detected in several tissues, but previous studies with Northern blot analysis or RNase protection assays have provided only semiquantitative information. Furthermore, the mRNA distribution of these subtypes in many rat tissues is unknown. In the present study, we quantified alpha-1a, alpha-1b and alpha-1d adrenergic receptor mRNA in 19 adult rat tissues through the use of reverse transcription (RT) and a competitive polymerase chain reaction (PCR). This procedure used internal cRNA standards as competitive templates that contained sequences complementary to the primers for alpha-1a, alpha-1b and alpha-1d adrenergic receptors and that differed in molecular size from the native sequences. Total RNA was harvested from 19 freshly dissected organs of the rat. The PCR products were labeled by inclusion of alpha-32P-dCTP in the PCR. After electrophoresis, ratios of competing to native radio-labeled products were used to interpolate the amount of native RNA originally present in each sample. The results revealed that the relative abundance of alpha-1a adrenergic receptor mRNA among various tissues was as follows: vas deferens > colon > or = stomach > or = cerebral cortex > heart > or = small intestine > or = testis > prostate. The relative rank order of alpha-1b adrenergic receptor mRNA expression was heart > or = cerebral cortex > liver, whereas that of alpha-1d adrenergic receptor mRNA was vas deferens > cerebral cortex > or = aorta > adrenal gland.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Endothelium, vasopressin receptors, and resistance to DOCA-salt hypertension.
Mesenteric artery rings from Wistar and Wistar-Furth rats subcutaneously treated with deoxycorticosterone acetate (DOCA) and 1% NaCl drinking water were used to measure endothelial modulation of contractile sensitivity and vasopressin receptor function and affinity. DOCA-salt hypertension reduced contractile sensitivity to arginine vasopressin (AVP) and did not affect contractile sensitivity to norepinephrine in arteries from Wistar rats. Endothelial removal caused a threefold increase in contractile sensitivity to AVP and norepinephrine in DOCA-salt hypertensive Wistar rats. In Wistar-Furth rats, DOCA-salt treatment did not affect contractile sensitivity to AVP, lysine vasopressin, oxytocin, and norepinephrine or the affinity of the vasopressin receptor for agonists or antagonists. Removal of endothelium did not affect vasopressin contractile sensitivity but caused a 15-fold increase in contractile sensitivity to norepinephrine in untreated or DOCA-salt-treated Wistar-Furth rats. These data show that reduced vasopressin receptor function and increased endothelial function that compensate for increased contractile sensitivity in arteries from DOCA-salt hypertensive Wistar rats are not the cause of resistance of DOCA-salt-treated Wistar-Furth rats to the development of enhanced contractile sensitivity and hypertension.
Animals↗
Binding and functional characterization of alpha-2 adrenergic receptor subtypes on pig vascular endothelium.
Alpha-2 adrenergic receptor subtypes were characterized in membranes of pig vascular endothelium using [3H]rauwolscine. Alpha-2 adrenergic receptor subtypes that mediate endothelium-dependent vascular relaxation were studied in vitro by using ring segments of pig epicardial coronary arteries. Specific [3H]rauwolscine binding in endothelial membranes was saturable and to a single class of high-affinity sites with a mean KD of 0.217 +/- 0.05 nM and Bmax of 156 +/- 28 fmol/mg of protein. Nonlinear regression analysis indicated that competition binding curves for drugs that distinguish the alpha-2A adrenergic receptor subtype from the alpha-2C adrenergic receptor subtype fit best to two-site binding models. Kl values for drugs in binding to endothelial alpha-2 adrenergic receptors correlated well with their Kl values for alpha-2A (r = .98) and alpha-2C (r = .97) adrenergic receptor subtypes identified in other tissues. Vascular endothelium contained 23% alpha-2A and 77% alpha-2C adrenergic receptors. In the presence of indomethacin, the rank order of potency for agonists that cause endothelium-dependent vascular relaxation was p-iodoclonidine > clonidine > UK-14,304 > guanabenz > epinephrine > norepinephrine. KB values for antagonist inhibition of epinephrine-induced, endothelium-dependent vascular relaxation correlated best with Kl values for antagonist binding at the alpha-2A adrenergic receptor subtype. These results suggest that the alpha-2A and alpha-2C adrenergic receptor subtypes are present on pig vascular endothelium and that the alpha-2A adrenergic receptor subtype mediates indomethacin-insensitive, endothelium-dependent relaxation of pig epicardial coronary arteries.
Adrenergic alpha-Antagonists↗
Heterogeneous expression of alpha 1-adrenoceptor subtypes among rat nephron segments.
alpha 1-Adrenoceptor subtypes mediate many of the actions of the renal nerve, but their locations along the nephron are unknown. We investigated the distribution of alpha 1-adrenoceptor subtype mRNA and protein in rat proximal tubules and medullary thick ascending limbs (MTAL) using reverse transcription combined with polymerase chain reaction (PCR) and radioligand binding methods. Complementary primers were designed to span cDNA sequences in each of the third intracellular loops of the rat alpha 1B- and alpha 1D-adrenoceptors. Expression of the mRNA of alpha 1B- and alpha 1D-adrenoceptors was first detected in total RNA from whole rat kidney, and the PCR product identity was confirmed by sequencing. Endogenous expression of alpha 1B- and/or alpha 1D-adrenoceptor mRNA was then investigated in microdissected segments of the rat proximal convoluted tubule (S2 segments) and the MTAL. mRNA was reverse-transcribed directly from permeabilized microdissected segments and the resulting cDNA was subjected to PCR with the alpha 1-adrenoceptor primers. In proximal convoluted tubules, amplification of both alpha 1B- and alpha 1D-adrenoceptor mRNA was observed. In MTAL segments, only alpha 1D-adrenoceptor mRNA was detected. We also measured receptor protein using [3H]prazosin in saturation and competition binding experiments. Proximal tubular membranes contained 3.3-fold more alpha 1-adrenoceptor than did MTAL membranes (163 +/- 21 versus 49 +/- 3 fmol/mg of protein). When the alkylating agent chloroethylclonidine (CEC) (10 microM, 10 min) was used to define alpha 1-adrenoceptor subtypes, proximal tubules were found to contain primarily CEC-insensitive (alpha 1A) sites (68 +/- 4%) and MTAL primarily CEC-sensitive sites (75 +/- 3%). Most [3H]prazosin binding sites (72 +/- 2%) in MTAL segments were also sensitive to the alkylating agent SZL-49, consistent with their identification as alpha 1D-adrenoceptors. In competition studies with the antagonists WB4101, 5-methylurapidil, and (+)-niguldipine, both high and low affinity sites were observed in proximal tubules. WB4101 interacted with only one site in MTAL membranes, intermediate in affinity between those sites found in proximal tubules. We conclude that reverse transcription-PCR is a useful method for demonstrating the expression of alpha 1-adrenoceptor subtypes in small amounts of tissue. Results from our experiments suggest that alpha 1A-, alpha 1B-, and alpha 1D-adrenoceptors are all expressed in proximal tubules and that alpha 1D-adrenoceptors are the primary alpha 1-adrenoceptor subtype expressed in MTAL. The distinct anatomical distribution of each of these adrenoceptor subtypes suggests that they serve different functions in the kidney.
Animals↗
Reduced contractile sensitivity and vasopressin receptor affinity in DOCA-salt hypertension.
The affinity of vascular vasopressin receptors was studied to determine its role in altered vascular contractile sensitivity in deoxycorticosterone acetate (DOCA)-salt hypertension. Ring segments of rat mesenteric arteries were used to study vascular vasopressin receptors. Male Wistar rats were given subcutaneous injections of DOCA and 1% NaCl in the drinking water. Mesenteric arteries from hypertensive rats had a reduced contractile sensitivity to arginine vasopressin (AVP) and lysine vasopressin (LVP). The order of potency of vasopressin receptor agonists (AVP greater than LVP greater than oxytocin) was the same in arteries from hypertensive compared with normotensive animals. The affinity of the vasopressin receptor antagonist [deamino-Pen1,O-Me-Tyr2,Arg8] vasopressin, and the affinities of the vasopressin receptor agonists AVP and LVP were not altered during developing DOCA-salt hypertension. There was no change in contractile sensitivity to norepinephrine and KCl in arteries from hypertensive rats. The reduced vasopressin contractile sensitivity is not due to a change in vasopressin receptor affinity but may be a compensatory response to elevated blood pressure. These data suggest that increased vascular sensitivity does not contribute to elevated blood pressure during the developing stage of DOCA-salt hypertension.
Angiotensin Receptor Antagonists↗
DOCA-enhanced sites of vasopressin-stimulated cAMP formation in rat cortical collecting tubule.
In deoxycorticosterone acetate (DOCA)-NaCl hypertension, the effects of vasopressin (VP) in the cortical collecting tubule (CCT) are exaggerated. These include both the biochemical effect of VP-stimulated adenosine 3',5'-cyclic monophosphate (cAMP) formation in the CCT and physiological effects of VP-mediated sodium and water retention. In this study, we examined the mechanism of enhanced VP-stimulated cAMP formation in the CCT. We compared cAMP formation in response to activators (following in parentheses) of the VP receptor (VP), of the stimulatory guanine nucleotide binding (Gs) protein [guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S); F-], and of the catalytic subunit of adenylyl cyclase (forskolin, Mn2+) between control and DOCA-NaCl-treated rats. The effects of VP and forskolin were enhanced in CCT of DOCA-NaCl-treated animals by 201 and 139%, respectively, compared with control animals. Other activators, Mn2+ (150%), F- (142%), and GTP gamma S (156%), also caused augmented cAMP formation in the CCT of DOCA-NaCl-treated rats. The DOCA-NaCl-induced increment in cAMP response to VP remained after pretreatment of the rats with pertussis toxin (171 and 169% increase in response in DOCA-NaCl and control rats, respectively), suggesting that altered inhibitory guanine nucleotide binding (Gi) protein function is not the mechanism for the altered response to VP in the CCT. Further evidence that Gi function is intact in DOCA-NaCl animals is that epinephrine (via alpha 2-adrenoceptor stimulation) inhibited VP-stimulated cAMP accumulation to a similar degree in DOCA-NaCl and control rats (86 and 76%, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Enhanced release of endothelium-derived relaxing factor in mineralocorticoid hypertension.
Ring segments of superior mesenteric arteries studied in vitro were used to determine the role of the vascular endothelium in regulating vascular contractile and relaxant sensitivity in deoxycorticosterone acetate (DOCA)-salt hypertension. Wistar rats were given DOCA (20 mg/kg s.c. twice per week) and 1% NaCl drinking water for 5 weeks. In ring segments containing endothelium, there was a decrease in contractile sensitivity to arginine vasopressin, no change in contractile sensitivity to norepinephrine and KCl, and no change in relaxant sensitivity to acetylcholine or isoproterenol in arteries from hypertensive rats compared with normotensive controls. Removal of the vascular endothelium by rubbing had no effect on the contractile response to arginine vasopressin and KCl or the relaxant response to isoproterenol in control arteries. In arteries without endothelium, DOCA-salt hypertension caused a threefold increase in contractile sensitivity for arginine vasopressin, norepinephrine, and KCl; a 50% reduction in maximal relaxation to isoproterenol; and a threefold decrease in relaxant sensitivity to sodium nitroprusside. Indomethacin (10 microM) had no effect on contraction or relaxation. However, N-monomethyl L-arginine unmasked altered contractile sensitivity to norepinephrine in arteries from DOCA-salt hypertensive rats. These data show that the endothelium compensates for increased contractile and reduced relaxant responses of vascular muscle in DOCA-salt hypertension by increasing the release of endothelium-derived relaxing factor. These data suggest that altered vascular responsiveness is masked by the endothelium, thus preventing these alterations from contributing to increased peripheral resistance during the development of DOCA-salt hypertension.
Animals↗