Biomedical subjects

J Tremblay

Publications and source records attributed to J Tremblay.

At least 73 records · Page 4Linked to original sources

PubMed1997

Smooth muscle apoptosis during vascular regression in spontaneously hypertensive rats.

We previously reported that apoptosis is increased in smooth muscle cells cultured from the aorta of spontaneously hypertensive rats versus normotensive controls. As an initial in vivo exploration, we now examined smooth muscle cell apoptosis regulation during the regression of vascular hypertrophy in the thoracic aorta media of spontaneously hypertensive rats receiving the antihypertensive drug enalapril (30 mg.kg-1.d-1), losartan (30 mg.kg-1.d-1), nifedipine (35 mg.kg-1.d-1), hydralazine (40 mg.kg-1.d-1), propranolol (50 mg.kg-1.d-1), or hydrochlorothiazide (75 mg.kg-1.d-1) for 1 to 4 weeks starting at 10 to 11 weeks of age. Three criteria were used to evaluate smooth muscle cell apoptosis: (1) oligonucleosomal fragmentation of the extracted aortic DNA, (2) reduction in aortic DNA content, and (3) depletion of smooth muscle cells in the arterial media. Arterial DNA synthesis was evaluated by [3H]thymidine incorporation in vivo. After 4 weeks of treatment, systolic blood pressure was reduced significantly by > 42% with losartan, enalapril, and hydralazine, and by 23% with nifedipine, versus control values of 220 +/- 5 mm Hg. However these agents affected vascular growth and apoptosis differently. Losartan, enalapril, and nifedipine stimulated smooth muscle cell apoptosis threefold to fivefold before there was a significant reduction in DNA synthesis (> 25%), vascular mass (> 19%), or vascular DNA content (> 38%), and these treatments markedly reduced (by 38% to 50%) medial cell number as measured at 4 weeks by the three-dimensional disector method. Losartan and nifedipine stimulated smooth muscle cell apoptosis before reducing blood pressure. In contrast, hydralazine did not affect vascular mass, apoptosis, or DNA synthesis, although blood pressure was lowered. Propranolol or hydrochlorothiazide failed to affect hypertension or vascular growth. Thus, smooth muscle cell apoptosis represents a novel therapeutic target for the control of hypertensive vessel remodeling in response to therapeutic agents.

Animals↗

PubMed1997

Abnormal adrenal and vascular responses to vasopressin mediated by a V1-vasopressin receptor in a patient with adrenocorticotropin-independent macronodular adrenal hyperplasia, Cushing's syndrome, and orthostatic hypotension.

The elucidation of gastric inhibitory polypeptide-dependent Cushing's syndrome suggested that ectopic expression or increased responsiveness of other adrenal hormone receptors may underlie ACTH-independent macronodular adrenal hyperplasia (AIMAH) or adrenocortical tumors. We studied a 36-yr-old woman with Cushing's syndrome, AIMAH, and orthostatic hypotension. During upright posture, cortisol and aldosterone were stimulated despite suppression of ACTH and renin. Arginine vasopressin (AVP, 10 U im), under dexamethasone suppression, increased plasma cortisol (3.4-fold), aldosterone (67-fold), and androgens in this patient but not in controls. ACTH 1-24, but not desmopressin acetate, angiotensin II, isoproterenol, or other hormones stimulated steroidogenesis in vivo. Plasma AVP was undetectable initially and increased suboptimally during posture tests after bilateral adrenalectomy. AVP stimulated cortisol production more in dispersed cells from the AIMAH than from a normal adult adrenal (424 vs. 135% at 10 nmol/L). Adrenal V1-AVP receptor presence and mediation of response were shown by RT-PCR and by binding and [Ca+2]i studies. Post adrenalectomy, orthostatic hypotension persisted; a prolonged vasoconstrictive response to AVP was found in vitro in the patient's sc small arteries. We propose that altered adrenal and vascular responses of the V1-AVP receptor-effector pathway underlie this new syndrome.

Adrenal Glands↗

PubMed1997

Regulation of the natriuretic peptide system in rat uterus during the estrous cycle.

Uterine natriuretic peptides may be involved in the alterations that occur in the uterus during the estrous cycle through its role in hydromineral balance. The following studies were performed to determine whether uterine natriuretic peptides and receptors follow a cyclic pattern during the estrous cycle. The results obtained show that atrial natriuretic peptide (ANP) content in rat uterine tissue was low in proestrus (8.5 +/- 2.6 pg/g) and significantly increased (P < 0.001) in estrus (71.5 +/- 16.6 pg/g), metestrus (82.6 +/- 19.7 pg/g) and diestrus (91.0 +/- 19.4 pg/g), whereas plasma ANP was not altered during the cycle. Similarly, measurement of uterine ANP mRNA by reverse transcribed polymerase chain reaction (RT-PCR) indicated lowest levels of ANP mRNA at proestrus. Measurement of C-type natriuretic peptide (CNP) by a specific and sensitive radioimmunoassay revealed that uterine CNP also varies with the estrous cycle. Uterine CNP was low in diestrus (143.2 +/- 22.4 pg/mg protein) as compared with proestrus, estrus and metestrus (305.3 +/- 51.5, 267.5 +/- 44.9, 291 +/- 41.2 pg/mg protein respectively, P < 0.05). Autoradiography performed on uterine tissue slices localized natriuretic peptide receptors to myometrial smooth muscle layers and to endometrial uterine glands. High binding of 125I-ANP was observed in proestrus and estrus with 60-75% decreases during metestrus and diestrus. Binding of 125I-tyr0CNP to uterine slices was also high during proestrus, but declined by 35% at estrus, metestrus and diestrus. The alterations in the receptors were also observed at the level of synthesis. RT-PCR detection of guanylyl cyclase A (GC-A) receptor mRNA and guanylyl cyclase B (GC-B) mRNA showed high signals at proestrus but 4- and 2-fold reductions respectively at metestrus and diestrus. In conclusion, variations in uterine ANP and CNP and their receptors during the rat estrous cycle imply the involvement of the natriuretic peptides in uterine hydromineral balance and myometrial motor activity.

Animals↗

PubMed1997

The peripheral action of clonidine analog ST-91: involvement of atrial natriuretic factor.

It is generally thought that the cardiovascular and renal effects of clonidine, an alpha-2 adrenergic agonist, are mediated by central mechanisms. Our previous work has shown that diuresis and natriuresis caused by central administration of clonidine are mediated by an enhanced release of atrial natriuretic factor (ANF). Because clonidine has been shown to have peripheral actions the objective of the present study was to determine whether ANF is also involved in these actions. Studies were performed with use of a structural clonidine analog, ST-91, which does not cross the blood-brain barrier, Intravenous injection of various doses (0-250 micrograms/rat) of ST-91 into conscious, normally hydrated female Sprague-Dawley rats (200-250 g) produced dose-related increases in urinary output, which were accompanied by significant increases in urinary sodium, potassium and cGMP excretion. Compared with saline, the highest dose of ST-91 (250 micrograms/rat) during the first hour of treatment significantly (P < .001, n = 18) enhanced urinary output (0.2 +/- 0.1 vs. 3.0 +/- 1.1 ml/h) and excretion of sodium (28 +/- 4 vs. 345 +/- 50 mumol/h), potassium (10 +/- 4 vs. 165 +/- 37 mumol/h) and cGMP (191 +/- 29 vs. 1340 +/- 322 pmol/h), the biological marker of ANF. These renal responses were associated with increased plasma ANF (59 +/- 7 vs. 810 +/- 28 pg/ml, P < .001, n = 12), measured 10 min after ST-91 (250 micrograms/rat), which remained elevated for at least 1 h (P < .01, n = 6). The enhanced renal responses that were induced by 10 micrograms ST-91 were partially, yet significantly inhibited by yohimbine (50 micrograms), an alpha-2 antagonist. On the other hand, efaroxan (500 micrograms), an l1 imidazoline receptor antagonist, showed a stronger inhibitory effect, whereas naloxone (0.8 mg) had no effect. Pretreatment of rats with anti-ANF reduced the diuretic and natriuretic effects of ST-91. These results indicate that the renal effects of ST-91 are mediated by imidazoline as well as by alpha-2 adrenergic receptors, but not by opioid receptors. Furthermore, the renal effects evoked by ST-91 are mediated by ANF.

Adrenergic alpha-2 Receptor Agonists↗

PubMed1996

Apoptosis in pressure overload-induced heart hypertrophy in the rat.

Pressure overload induces cardiac growth in the rat, which implies the hypertrophy of cardiac muscle cells and proliferation of nonmuscle cells. The cardiac cell loss observed in parallel has generally been attributed to necrosis. Using an in situ assay, we demonstrated a phase of apoptosis or programmed cell death during the first 7 d after pressure overload with a peak at day 4 while cardiac growth continued for over 30 d. The increase in apoptosis was confirmed by quantification of 180-1500-bp DNA oligonucleosomes with agarose gel electrophoresis and in situ labeling via 3'-terminal deoxynucleotidyl transferase assay. While some apoptosis was observed in the basal state in nonmuscle cells, pressure overload induced apoptosis mainly in cardiomyocytes. These data suggest that cardiac hypertrophy is initiated by a wave of apoptosis of cardiomyocytes. Thus, apoptosis may be involved in the pathogenesis of heart remodeling.

Adaptation, Physiological↗

PubMed1996

Apoptosis in vascular smooth muscle cells: role of cell shrinkage.

Cell volume decrease is known to be one of the earliest steps of apoptosis in immune system cells. In this study, we compared the kinetics of apoptosis and cell volume adjustment in cultured vascular smooth muscle cells (VSMC) from the aorta of normotensive Brown-Norway (BN.1x) as well as spontaneously hypertensive (SHR) rats and in Mardin-Darby canine kidney (MDCK) cells. The transfer of VSMC to serum-deprived medium led to a transient cell volume decrease and to increased apoptosis. Both the cell volume decrease and apoptosis displayed faster kinetics in SHR than in BN.1x VSMC. Increased tonicity of serum-deprived medium by the addition of 200 mM mannitol augmented apoptosis in VSMC by 2.5- to 3-fold. In contrast to VSMC, neither apoptosis nor the cell volume of MDCK cells was affected by serum deprivation. Apoptosis in MDCK cells was also insensitive to tonicity of serum-deprived medium. There results demonstrate an initial volume decrease in VSMC undergoing apoptosis and suggest that this phenomenon is involved in triggering the apoptotic process.

Animals↗

PubMed1996

Natriuretic peptide system in the rat submaxillary gland.

Natriuretic peptides and their receptors were characterized in rat submaxillary glands (SGs). Reverse phase-high performance liquid chromatography (HPLC) of rat SGs extracts revealed the presence of the 28-amino-acid (AA) circulating peptide ANP (Ser99-Tyr126) and the 126-AA prohormone (Asn1-Tyr126). The presence of ANP prohormone indicated that SGs are a site of ANP synthesis. Indeed, ANP mRNAs were demonstrated. ANP mRNA was 10 times lower than in the lung and only about 7 times lower than in the hypothalamus. ANP content in SG was determined as 30 +/- 8 ng/mg of protein (n = 7). In addition the presence of another member of the natriuretic peptide family, C-type natriuretic peptide (CNP), was found in SG. The CNP level of 293 +/- 38 pg/mg protein was significantly higher than in the lungs (44 +/- 6 pg/mg protein, P < 0.001, n = 5), but about 15 times lower than in hypothalamus (4.5 +/- 0.6 ng/mg protein, P < 0.001, n = 6). Both guanylyl cyclase and clearance receptors were expressed in SG. The presence of natriuretic peptide transcripts and their receptors suggests a role in rat SG functions.

Animals↗

PubMed1996

Bumetanide-sensitive ion fluxes in vascular smooth muscle cells: lack of functional Na+, K+, 2 Cl- cotransport.

To examine the involvement of Na+,K+,2Cl- cotransport in monovalent ion fluxes in vascular smooth muscle cells (VSMC), we compared the effect of bumetanide on 86Rb, 36Cl and 22Na uptake by quiescent cultures of VSMC from rat aorta. Under basal conditions, the values of bumetanide-sensitive (BS) inward and outward 86Rb fluxes were not different. Bumetanide decreased basal 86Rb uptake by 70-75% with a Ki of approximately 0.2-0.3 microM. At concentrations ranging up to 1 microM, bumetanide did not affect 36Cl influx and reduced it by 20-30% in the range from 3 to 100 microM. In contrast to 86Rb and 36Cl influx, bumetanide did not inhibit 22Na uptake by VSMC. BS 86Rb uptake was completely abolished in Na(+)- or Cl(-)-free media. In contrast to 86Rb, basal BS 36Cl influx was not affected by Nao+ and Ko+. Hyperosmotic and isosmotic shrinkage of VSMC increased 86Rb and 36Cl influx to the same extent. Shrinkage-induced increments of 86Rb and 36Cl uptake were completely abolished by bumetanide with a Ki or approximately 0.3 microM. Shrinkage did not induce BS 86Rb and 36Cl influx in (Na+ or Cl-)- and (Na+ or K+)-depleted media, respectively. In the presence of an inhibitor of Na+/H+ exchange (EIPA), neither hyperosmotic nor isosmotic shrinkage activated 22Na influx. Bumetanide (1 microM) did not modify basal VSMC volume and intracellular content of sodium, potassium and chloride but abolished the regulatory volume increase in isosmotically-shrunken VSMC. These data demonstrate the absence of the functional Na+,K+,2Cl- cotransporter in VSMC and suggest that in these cells basal and shrinkage-induced BS K+ influx is mediated by (Nao+ + Clo-)-dependent K+/K+ exchange and Nao(+)-dependent K+,Cl- cotransport, respectively.

Animals↗

PubMed1996

Cell volume in vascular smooth muscle is regulated by bumetanide-sensitive ion transport.

Vascular smooth muscle cells (VSMC) exhibit shrinkage-induced bumetanide-inhibited 86Rb influx and ethylisopropylamiloride (EIPA)-inhibited 22Na influx. In this study, we examined the role of these transport pathways in volume adjustment of VSMC after isosmotic and hyperosmotic shrinkage. Cell volume was assessed by measurement of [14C]urea distribution. An initial 18-20% cell volume decrease in isosmotically shrunken VSMC was followed by a regulatory volume increase (RVI). RVI was completely abolished by bumetanide but not by EIPA. No RVI was noted in hyperosmotically shrunken VSMC. The initial rate of bumetanide-inhibited 86Rb influx was two- to threefold higher in isosmotically shrunken VSMC than with hyperosmotic shrinkage. Hyperosmotic shrinkage of VSMC was accompanied by a three- to fourfold increase in the rate of bumetanide-inhibited 86Rb efflux, whereas isosmotic shrinkage augmented this component by only 20-30%. In contrast to bumetanide-inhibited 86Rb influx, isosmotic shrinkage slightly increased the rate of EIPA-sensitive 22Na influx. Hyperosmotic shrinkage led to transient activation of EIPA-inhibited 22Na influx, which was completely abolished in 15 min. Activation of adenosine 3',5'-cyclic monophosphate (cAMP) signaling with isoproterenol arborized VSMC and decreased their volume by approximately 15%. A similar volume decrease was seen in VSMC treated with the microfilament-disrupting compound, cytochalasin B. The isoproterenol-induced cell volume decrease was prolonged by the addition of bumetanide. Unlike isoproterenol, agents that raise intracellular Ca2+ (A-23187 and angiotensin II) did not modify VSMC volume. Thus our data demonstrate involvement of cAMP signaling in the regulating of VSMC volume and a key role of bumetanide-inhibited ion transport in the RVI after isosmotically induced shrinkage.

Animals↗

PubMed1996

Alteration of lung atrial natriuretic peptide receptors in genetic cardiomyopathy.

These studies were designed to characterize the atrial natriuretic peptide (ANF) receptor subtypes [guanylyl cyclase natriuretic peptide receptors (NPR-A, NPR-B) and NPR-C] in lungs of normal hamsters and to evaluate alterations in receptor kinetics in genetic cardiomyopathy (CMO), a model of human congestive heart failure. Lung membranes were obtained from normal and CMO 200-to 230-day-old hamsters. Cross-linking and competitive binding receptor assays using 125I-labeled human ANF showed that lung membranes exhibit NPR, mainly guanylyl cyclase NPR-A and clearance NPR-C receptors. Stimulation of guanylyl cyclase by ANF and C-type natriuretic peptide (CNP) confirmed the presence of NPR-A and NPR-B. The maximum binding capacity of total ANF binding sites (442 +/- 68 vs. 271 +/- 57 fmol/mg protein, P < 0.05) was reduced, but dissociation constant (0.26 +/- 0.04 vs. 0.41 +/- 0.08 nM) was not altered in CMO animals. Similar reductions were observed in the binding sites for brain natriuretic peptide (BNP; 438 +/- 83 vs. 236 +/- 53 fmol/mg protein) and CNP (321 +/- 80 vs. 165 +/- 56 fmol/mg protein, P < 0.05) which may reflect a decline in NPR-A and NPR-B and/or NPR-C. Acid wash improved binding of 125I-labeled rat ANF to lung membranes of both normal and CMO hamsters, but the tendency towards reduced binding in CMO hamsters did not reach statistical significance, implying that downregulation may not have been due only to prior occupancy of the receptors. Transcripts of NPR-A, NPR-B, and NPR-C receptors in hamster lungs were detected by quantitative polymerase chain reaction. Compared with normal controls, the CMO hamster lung NPR-A mRNA was reduced by 50%, but NPR-B mRNA and NPR-C mRNA were not altered. Moreover, CMO hamster lungs showed less activation of guanylyl cyclase by ANF. These studies demonstrate that lung NPR are downregulated in hamster CMO.

Animals↗

PubMed1996

cAMP signaling inhibits dihydropyridine-sensitive Ca2+ influx in vascular smooth muscle cells.

This study examines the role of the cAMP signaling pathway in the regulation of 45Ca influx in cultured vascular smooth muscle cells from the rat aorta. K+o-induced depolarization of smooth muscle cells increased the rate of 45Ca uptake by twofold to threefold. This effect was completely abolished by the dihydropyridine derivatives nifedipine and nicardipine, with a Ki of 3 and 10 nmol/L, respectively. Activators of cAMP signaling (isoproterenol, forskolin, cholera toxin) increased cAMP content by 50- to 100-fold and decreased voltage-dependent 45Ca uptake by 50% to 70%. Neither the dihydropyridines nor the cAMP activators affected basal 45Ca influx. Direct addition of the protein kinase inhibitor H-89 to the incubation medium in the 1- to 10-micromol/L range did not alter basal 45Ca uptake but completely abolished voltage-dependent Ca2+ transport. Preincubation of cells for 1 hour with 10 micromol/L H-89 did not modify basal and depolarization-induced 45Ca uptake in H-89-free medium but prevented forskolin-induced inhibition of voltage-dependent Ca2+ influx. The addition of cytoskeleton-active compounds reduced voltage-dependent Ca2+ transport and completely abolished its regulation by cAMP. Activation of cAMP signaling decreased the volume of smooth muscle cells by 12% to 15%. The same cell volume diminution in hyperosmotic medium did not alter voltage-dependent 45Ca uptake. Thus, data obtained in this study show that in contrast to cardiac and skeletal myocytes, in vascular smooth muscle cells, 45Ca influx, putatively due to L-type channels, is inhibited by cAMP. This regulatory pathway appears to be mediated via protein kinase A activation and cytoskeleton reorganization.

Animals↗

PubMed1996

Apoptosis and vascular wall remodeling in hypertension.

Vascular structure plays a key role in the pathogenesis of hypertension. Because it is less readily reversible than protein accumulation, DNA accumulation in the arterial wall may be considered as a record of past episodes of vascular growth, contributing to the persistence of the vascular disease. Apoptosis, a ubiquitous and highly regulated form of programmed cell death that is involved in tissue morphogenesis and homeostasis as the essential counterpart of cell replication, is potentially involved in the regulation of vascular structure, via the deletion of cells in the vessel wall. We discuss how the current knowledge on apoptosis may provide insights into the pathogenesis of vascular wall remodeling, with an emphasis on the biology of vascular smooth muscle cells. Evidence suggests that heightened cell replication rates are often associated with increased apoptosis, as for smooth muscle cells in genetic hypertension or in arterial repair after injury. However, apoptotic cell death may also be regulated independently of cell growth. The triggering of apoptosis depends on a balance of environmental cues that are not specific to apoptosis. However, there is a common set of key biochemical events mediating apoptosis (i.e., committing the cell to die), thus providing a basis for the design of novel pharmacological strategies specifically targeting apoptotic cell death. The identification of biochemical markers of apoptosis and other methodological advances will ultimately help in understanding the role of apoptotic cell death in vascular remodeling and hypertensive end-organ damage.

Animals↗

PubMed1996

HSP27 locus cosegregates with left ventricular mass independently of blood pressure.

Left ventricular hypertrophy remains a significant clinical problem and a predictor of fatal outcome in hypertension. Blood pressure per se and environmental modifiers including stress affect cardiac mass. Heat shock proteins are involved in the stress response as well as in the regulation of cardiac growth and cytoprotection. The present study evaluates heat shock protein 27 as a locus marker or candidate gene of cardiac hypertrophy in hypertension. The spontaneously hypertensive rat allele of heat shock protein 27 was associated with about a 6% increase in relative left ventricular weight (P = .0112) in 30 recombinant inbred strains from crosses of Brown Norway and spontaneously hypertensive rats. In 336 F2 crosses of spontaneously hypertensive and Wistar-Kyoto rats, the hypertensive allele was dominant and cosegregated with a similar 6% increase in the ratio of left ventricular weight to body weight (P = .0058) in rats fed a normal salt diet, but its contribution to left ventricular weight decreased in rats kept on a high salt diet. The contribution of the heat shock protein 27 allele was independent of blood pressure. We suggest that heat shock protein 27 represents a candidate gene/locus marker of cardiac hypertrophy in hypertension.

Alleles↗

PubMed1996

The time window of apoptosis: a new component in the therapeutic strategy for cardiovascular remodeling.

APOPTOSIS AND EXPERIMENTAL HYPERTROPHY: Apoptosis (programmed cell death) is a physiological counterpart of cell replication with shared as well as specific pathways. Our initial studies have demonstrated increased apoptosis in the heart, kidney and brain of spontaneously hypertensive rats (SHR) and mice, persisting in cultured vascular smooth muscle cells. In these target organs of hypertension, programmed cell death paralleled the well known hypertrophy/hyperplasia. We also observed that the two processes can be dissociated in time, as in experimental hypertrophy of the heart induced by pressure overload. In this context, only a short-lived apoptotic window precedes the overt development of cardiac hypertrophy. EFFECTS IN HYPERTENSION: We now propose that a more prolonged apoptotic window is present in hypertension. Apoptosis seems to be significantly reduced during the first weeks of life in SHR, possibly contributing to the early cardiac hyperplasia. However, increased apoptosis is clearly evident thereafter throughout the development of hypertension and fades below the levels observed in normotensive animals after the age of 24 weeks. ANTIHYPERTENSIVE THERAPY AND APOPTOSIS: In addition to the apoptotic windows that suggest a dynamic regulation of this process in disease states, antihypertensive therapy with angiotensin converting enzyme inhibitors, angiotensin II receptor antagonists and calcium channel blockers can also modify the contribution of apoptosis, independently of the blood pressure fall. We propose that the presence of apoptotic windows and the involvement of this biological process as a primary or secondary event in cardiovascular remodeling should be taken into account when designing innovative therapeutic approaches.

Animals↗

PubMed1995

Comparative study of DNA adducts levels in white sucker fish (Catostomus commersoni) from the basin of the St. Lawrence River (Canada).

The levels of DNA adducts in the hepatic tissue of the white sucker fish species Catostomus commersoni were determined by 32P-postlabelling. The fish were caught at four sites: two sites near the city of Windsor (Québec, Canada) on the St. François River, a downstream tributary of the St. Lawrence River, and two sites in the St. Lawrence River itself, near the city of Montréal (Québec, Canada). The latter sites are known to be contaminated by many pollutants including polycyclic aromatic hydrocarbons. Total adduct levels in all fish ranged from 25.1-178.0 adducts per 10(9) nucleotides. White sucker from the selected sites of the St. Lawrence River had a significantly higher mean level of DNA adducts than those of the St. François River (129.4 vs 56.8, respectively). These results suggest that the effluents of many heavy industries (e.g. from a Soderberg aluminium plant) flowing in the St. Lawrence River are more likely to produce genotoxic damage to fish than those released in one of its tributary, and mainly associated to the activities of a small town and a nearby pulp and paper mill.

Animals↗

PubMed1995

Altered beta-adrenergic regulation of Na-K-Cl cotransport in cultured smooth muscle cells from the aorta of spontaneously hypertensive rats. Role of the cytoskeleton network.

To verify the hypothesis of Na-K-Cl cotransport (COTR) involvement in ion transport abnormalities as revealed in vascular smooth muscle cells (VSMC) of spontaneously hypertensive rats (SHR), we compared the rate of ouabain-insensitive, bumetanide-inhibited 86Rb influx in quiescent and growing cultures of VSMC from the aorta of SHR and normotensive (BN.lx) rats and its regulation by the cAMP signaling system. Basal COTR was not altered in quiescent cells from SHR but was decreased by 30% to 40% (P < .02) in growing SHR VSMC as compared to BN.lx rats. In quiescent BN.lx VSMC, isoproterenol inhibited COTR by 50% and induced cell shape transition of > 90% of cells, resulting in the appearance of rounded VSMC with arborized cytoplasms. In contrast, isoproterenol elicited cell shape transition in only 50% of quiescent SHR VSMC and did not modify COTR. In growing cells, it decreased COTR by 85% to 95% and altered cell morphology in > 95% of VSMC without differences between SHR and BN.lx rats. Neither inhibitors of protein kinase A (H-89 and KT-5720) nor an inhibitor of phosphoprotein phosphatase (okadaic acid) affected cell shape transition and COTR suppression in isoproterenol-treated VSMC. The COTR suppression and cytoplasm arborization was also demonstrated by the addition of cytochalasin B, a disintegrator of microfilament bundles, and staurosporine, an inhibitor of protein kinase C. The effects of these compounds on COTR and SHR and BN.lx VSMC morphology were not different. The calmodulin antagonist R24571 decreased COTR by 60% to 70% in quiescent BN.lx VSMC and did not modify this carrier in SHR VSMC.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Agonists↗

PubMed1995

Localization of mRNA coding for the three subtypes of atrial natriuretic factor (ANF) receptors in rat anterior pituitary gland cells.

Atrial Natriuretic Factor (ANF) action is mediated by highly selective and specific receptors. Three subtypes have been characterized and cloned: ANF receptor-A, -B and -C. These subtypes are all expressed in the anterior pituitary of the rat. In the present study, the mRNA for each subtype was detected by in situ hybridization. The amounts of ANFR-A and -B mRNA were found to be similar, and to be twice that of ANFR-C mRNA. At the ultrastructural level, the three types of ANFR mRNA were expressed in three anterior pituitary cell types, namely lactotrophs, corticotrophs, and gonadotrophs, identified by their hormonal content. No signal was revealed in somatotrophs or thyrotrophs. The different forms of mRNA were similar in terms of subcellular localization: in the cytoplasmic matrix and the nuclear euchromatin. These data indicate that the anterior pituitary is an important target tissue for ANF action.

Animals↗

PubMed1995

Alternative splicing of natriuretic peptide A and B receptor transcripts in the rat brain.

1. In the present study we searched for variants of alternative splicing of guanylyl cyclase A and B mRNA in rats in vivo. 2. Guanylyl cyclase A2 and guanylyl cyclase B2 isoforms of guanylyl cyclase produced by alternative splicing leading to the deletion of exon 9 of both transcripts were quantified in several rat organs. 3. Only one alternative splicing was found in the regulatory domain, encoded by exons 8-15. 4. Quantification of the guanylyl cyclase B2 isoform in different rat organs and in cultured aortic smooth muscle cells showed that this alternative splicing was tissue-specific and occurred predominantly in the central nervous system where the alternatively spliced variant represented more than 50% of the guanylyl cyclase B mRNA. 5. The same alternative splicing existed for guanylyl cyclase A mRNA but at very low levels in the organs studied. 6. Alternative splicing of guanylyl cyclase B exon 9 in the brain may play an important role in signal transduction, since the expressed protein possesses a constitutionally active guanylyl cyclase acting independently of C-type natriuretic peptide regulation.

Alternative Splicing↗