Biomedical subjects

K M Baker

Publications and source records attributed to K M Baker.

At least 55 records · Page 3Linked to original sources

PubMed1995

Identification and activation of autocrine renin-angiotensin system in adult ventricular myocytes.

To date, the demonstration that the molecular components of the renin-angiotensin system (RAS) are present in adult ventricular myocytes is lacking. In addition, whether the RAS is upregulated under conditions of overload and myocyte hypertrophy in vivo remains to be determined. By employing an in vivo model of ischemic cardiomyopathy in rats, we document that adult myocytes express genes for renin, angiotensinogen, angiotensin-converting enzyme (ACE), and angiotensin II (ANG II) receptors. Moreover, renin, ACE, and ANG II receptor mRNAs increased in stressed myocytes undergoing cellular hypertrophy. At the protein level, the percentage of myocytes containing renin, ANG I, and ANG II was significantly increased in the overloaded heart. The number of binding sites for ANG II per myocyte also markedly increased under this setting. These results provide direct evidence of the existence of a myocyte RAS, which may be activated in pathological states of the heart to support myocyte growth and contractile function.

Angiotensinogen↗

PubMed1995

Sensitive bioassay for the detection and quantification of angiotensin II in tissue culture medium.

We have developed a sensitive, high-throughput bioassay to quantify angiotensin II in culture medium. Using Chinese hamster ovary cells that stably express a transfected angiotensin II receptor as target cells, we demonstrated that an agonist-stimulated myelin basic protein kinase response can be used as a basis of quantitative bioassay for angiotensin II. The assay permits detection of as little as 10 pg of angiotensin II in 1 mL of medium and offers an excellent alternative to HPLC and radioimmunoassay. This approach may also be applicable for quantification of other peptide hormones or growth factors produced by cell cultures.

Angiotensin II↗

PubMed1995

Molecular signalling mechanisms controlling growth and function of cardiac fibroblasts.

Cardiac fibroblasts appear to be important in producing and maintaining the extracellular matrix (ECM) of the heart. The abnormal proliferation of cardiac fibroblasts and deposition of the ECM protein, collagen, associated with hypertension and myocardial infarction, may adversely affect the performance of the heart. Several groups of factors affect collagen gene expression and/or growth of cardiac fibroblasts. Angiotensin II, aldosterone and endothelins play a central role in the remodeling of the ECM in hypertension, and decrease collagenase activity and/or increase collagen synthesis in cultured cells. Regulatory peptides that are generally elevated at sites of injury, such as TGF-beta 1 and PDGF, increase collagen synthesis and/or stimulate mitogenesis. Mechanical stretch enhances collagen expression and cell proliferation, responses which could in part be due to integrin activation. Cytokines may stimulate or inhibit cell growth, the latter through prostaglandin formation. Angiotensin II is a principal determinant in vivo of cardiac fibroplasia and synthesis of the ECM proteins, collagen and fibronectin. Cardiac fibroblasts possess G-protein-coupled AT1 receptors for angiotensin II that couple to activation of multiple signalling pathways, including: phospholipase C-beta, with the subsequent release of Ca2+ from intracellular stores and activation of protein kinase C, mitogen-activated protein kinases, tyrosine kinases, phospholipase D, phosphatidic acid formation, and the STAT family of transcription factors. Cardiac fibroblasts respond to angiotensin II with hyperplastic/hypertrophic growth, and increased expression of collagen, fibronectin, and integrins. The mechanisms by which the AT1 receptor activates multiple signalling pathways are not known, although the receptor might interact at some level with both integrins and cytokine receptors. Different signalling pathways of the AT1 receptor may subserve different cellular responses, such as mitogenesis, ECM synthesis, or an inflammatory/stress response. Crosstalk among the signalling pathways of the AT1 receptor, and those of G-protein, cytokine, and growth-factor receptors, may determine the ultimate response of the cell.

Angiotensin II↗

PubMed1994

Angiotensin II induces phosphatidic acid formation in neonatal rat cardiac fibroblasts: evaluation of the roles of phospholipases C and D.

Phosphatidic acid has been proposed to contribute to the mitogenic actions of various growth factors. In 32P-labeled neonatal rat cardiac fibroblasts, 100 nM [Sar1]angiotensin II was shown to rapidly induce formation of 32P-phosphatidic acid. Levels peaked at 5 min (1.5-fold above control), but were partially sustained over 2 h. Phospholipase D contributed in part to phosphatidic acid formation, as 32P- or 3H-phosphatidylethanol was produced when cells labeled with [32P]H3PO4 or 1-O-[1,2- 3H]hexadecyl-2-lyso-sn-glycero-3-phosphocholine were stimulated in the presence of 1% ethanol. [Sar1]angiotensin II-induced phospholipase D activity was transient and mainly mediated through protein kinase C (PKC), since PKC downregulation reduced phosphatidylethanol formation by 68%. Residual activity may have been due to increased intracellular Ca2+, as ionomycin also activated phospholipase D in PKC-depleted cells. Phospholipase D did not fully account for [Sar1]angiotensin II-induced phosphatidic acid: 1) compared to PMA, a potent activator of phospholipase D, [Sar1]angiotensin II produced more phosphatidic acid relative to phosphatidylethanol, and 2) PKC downregulation did not affect [Sar1]angiotensin II-induced phosphatidic acid formation. The diacylglycerol kinase inhibitor R59949 depressed [Sar1]angiotensin II-induced phosphatidic acid formation by only 21%, indicating that activation of a phospholipase C and diacylglycerol kinase also can not account for the bulk of phosphatidic acid. Thus, additional pathways not involving phospholipases C and D, such as de novo synthesis, may contribute to [Sar1]angiotensin II-induced phosphatidic acid in these cells. Finally, as previously shown for [Sar1]angiotensin II, phosphatidic acid stimulated mitogen activated protein (MAP) kinase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗

PubMed1994

Angiotensin II stimulates sis-inducing factor-like DNA binding activity. Evidence that the AT1A receptor activates transcription factor-Stat91 and/or a related protein.

Recent studies on cytokine and growth factor stimulated signal transduction have defined a direct pathway (Stat91) linking cell surface receptors to target genes in the nucleus. The Stat91 pathway regulated c-fos gene transcription involves activation by tyrosine phosphorylation of the DNA binding factor SIF (sis-inducing factor) in the cytoplasm, its nuclear translocation, and interaction with the regulatory element SIE (sis-inducing element). SIF is a complex of proteins containing members of the STAT family of transcription factors. We determined whether angiotensin II (AII), which acts as a growth factor in many cell types, could activate the Stat91 pathway. We used neonatal rat cardiac fibroblasts expressing G-protein linked AII receptors and CHO-K1 cells expressing stably transfected angiotensin type 1A (AT1A) receptors to address this question. Angiotensin II induced SIF-like activity in both cell types, with initial induction at 15-30 min, maximal around 2-3 h, and undetectable at 6 h. Cytoplasmic and nuclear fractions from cells exposed to AII contained DNA binding activity to SIE. The SIF activity was insensitive to protein synthesis inhibitors and sensitive to the tyrosine kinase inhibitor genistein. Stat91 or a related protein was identified as a component of the AII-induced SIF complex and increased levels of this tyrosine-phosphorylated protein were found in nuclear extracts of cells treated with AII. This is the first evidence that a seven transmembrane, G-protein-coupled receptor, namely AT1A, activates the Stat91-nuclear signaling pathway.

Angiotensin II↗

PubMed1994

Angiotensin II-induced protein tyrosine phosphorylation in neonatal rat cardiac fibroblasts.

Angiotensin II has been demonstrated to act as a growth factor in rat cardiac fibroblasts. However, the signaling events that lead to fibroblast cell growth in response to angiotensin II remain to be elucidated. This study was designed to determine whether angiotensin II stimulated tyrosine phosphorylation of proteins in cardiac fibroblasts. Immunoblot analysis demonstrated rapid tyrosine phosphorylation of distinct substrates of 125, 95, 46-60, and 44 kDa in response to 10 nM angiotensin II. Tyrosine phosphorylation was maximal at 5 min and persisted for at least 180 min. Additional tyrosine-phosphorylated proteins of 185, 145, and 85 kDa were detected in response to 10 ng/ml platelet-derived growth factor BB. A cluster of 75-80-kDa proteins were phosphorylated in response to angiotensin II, phorbol ester, and platelet-derived growth factor. Angiotensin II-induced tyrosine phosphorylation was unaffected by phorbol ester-sensitive protein kinase C down-regulation and could be partially blocked by pertussis toxin pretreatment. Angiotensin II stimulation resulted in increased cytosolic tyrosine kinase activity which was recovered by immunoprecipitation. Immunoblot analysis demonstrated tyrosine phosphorylation of p44MAPK, and, in addition, we demonstrated for the first time tyrosine phosphorylation of p125FAK, p46SHC, and p56SHC in response to angiotensin II. The finding that angiotensin II and platelet-derived growth factor stimulated tyrosine phosphorylation of p46SHC and p56SHC suggested that this protein may serve as a common tyrosine kinase substrate in the mitogenic signaling cascade induced by G-protein-coupled receptors and growth factors and is consistent with the hypothesis that angiotensin II-induced tyrosine phosphorylation is involved in mitogenic signaling pathways in neonatal rat cardiac fibroblasts.

Adaptor Proteins, Signal Transducing↗

PubMed1994

An improved method for absolute quantification of mRNA using multiplex polymerase chain reaction: determination of renin and angiotensinogen mRNA levels in various tissues.

We have developed a multiplex, competitive, reverse-transcriptase polymerase chain reaction (RT-PCR) method which measures absolute levels of renin, angiotensinogen, and the housekeeping transcript elongation factor-1 alpha (EF-1 alpha) mRNA. Sample RNA was simultaneously titrated with serial dilutions of renin, angiotensinogen, and EF-1 alpha competitor RNAs which flanked the endogenous concentrations of target transcripts. The samples were coreverse transcribed in the presence of random primers and resulting first-strand cDNA was coamplified for 10-15 cycles with [32P]-dCTP and primers for renin angiotensinogen, after which EF-1 alpha primers were added. Amplified DNA was separated by electrophoresis on polyacrylamide gel and radioactivity in the bands was quantified by direct radioanalytical scanning. Three conditions were necessary to obtain absolute quantification of renin and angiotensinogen mRNA levels: (a) exogenous competitor RNA was used to control for tube-to-tube variability in the efficiencies of reverse transcription and amplification; (b) Sample RNA was titrated with flanking concentrations of competitor RNA to correct for intraassay differences in the efficiency of amplification due to concentration differences between competitor and target templates; and (c) a housekeeping transcript EF-1 alpha was used to control for tube-to-tube differences in RNA loading and/or degradation. We show that the multiplex RT-PCR method is precise and accurate over approximately three logs of transcript concentration and sensitive to less than 5 and 0.5 fg for renin and angiotensinogen mRNA, respectively. This method will be useful for absolute quantification of target mRNAs, especially when the amount of sample RNA is limited or unknown and/or the gene expression is low.

Angiotensinogen↗

PubMed1994

Involvement of protein kianse C and Ca2+ in angiotensin II-induced mitogenesis of cardiac fibroblasts.

Angiotensin (ANG) II has been previously shown to stimulate proliferation of neonatal rat cardiac fibroblasts via AT1 receptors. Here we conducted studies to assess involvement in this process of two second messengers linked to AT1 receptors, protein kinase C (PKC) and Ca2+. Several findings argue against a dominant role for PKC in ANG II-induced mitogenesis: 1) [Sar1]ANG II, which produced a modest, transient increase in PKC activity, was equally effective in inducing thymidine incorporation into DNA in PKC-depleted cells, whereas the effect of platelet-derived growth factor (PDGF)-BB on thymidine incorporation was reduced to the level observed with [Sar1]ANG II; 2) phorbol 12-myristate 13-acetate (PMA), a potent PKC stimulator, was ineffective in stimulating thymidine incorporation; and 3) PKC downregulation or the highly specific PKC inhibitor, compound 3, eliminated PMA-induced mitogen-activated protein (MAP) kinase activity but did not affect comparable increases induced by [Sar1]ANG II or PDGF-BB. Increased intracellular Ca2+ may be sufficient to account for [Sar1]ANG II-induced MAP kinase activity because ionomycin also increased MAP kinase activity and chelation of intracellular Ca2+ eliminated [Sar1]ANG II-induced activity in PKC-depleted fibroblasts. However, Ca2+ chelation did not prevent [Sar1]ANG II-induced MAP kinase activity in non-PKC-depleted fibroblasts. Thus ANG II can activate MAP kinase in cardiac fibroblasts by either Ca(2+)- or PKC-dependent pathways, and whereas the full effect of PDGF-BB on thymidine incorporation and cell proliferation requires a phorbol ester-sensitive PKC, the hyperplastic growth effect of ANG II does not.

Angiotensin II↗

PubMed1993

Alpha-adrenergic receptor agonists stimulate ribosome formation in hearts from enalapril-treated piglets.

Hearts from untreated or enalapril-treated piglets were used to measure rates of ribosome formation and total protein synthesis during perfusion as modified Langendorff preparations. Pretreatment of newborn piglets with enalapril maleate (5 mg, once daily for 3 days) resulted in a decreased rate of growth of the left ventricle. Addition of 1 microM angiotensin II to the perfusate had no effect on in vitro ribosome formation or protein synthesis in either the right or left ventricle of hearts from untreated or enalapril-treated piglets. Angiotensin II receptor number or affinity in the left ventricle was not decreased by enalapril treatment. In contrast, addition of combinations of 1 microM norepinephrine and 1 microM propranolol or 1 microM phenylephrine and 1 microM propranolol to the perfusate restored the rate of ribosome formation in the left ventricle of hearts from enalapril-treated piglets to that observed in the left ventricle of hearts from untreated piglets. Prazosin (100 nM) blocked the stimulatory effect of either norepinephrine or phenylephrine on ribosome formation in the left ventricle. Binding of [3H] prazosin to membranes from the left ventricle was unaltered by pretreatment of the piglet with enalapril maleate. Pretreatment of piglets with prazosin (1 mg, twice daily for 3 days) resulted in a small but significant decrease in mean arterial pressure as well as the rate of left ventricular growth. Pretreatment of piglets with hydralazine (10 mg, twice daily for 3 days) significantly reduced mean arterial pressure but did not alter left ventricular growth. These results support a role for alpha 1-adrenergic receptor stimulation in the regulation of neonatal cardiac growth.

Adrenergic alpha-Agonists↗

PubMed1993

Angiotensin II is mitogenic in neonatal rat cardiac fibroblasts.

Angiotensin II has been reported to be a hormonal stimulus of cardiac growth, a response that may involve myocyte hypertrophy as well as growth of nonmyocytes. This study was designed to determine whether neonatal rat cardiac fibroblasts have an angiotensin II receptor that is coupled with hypertrophic and/or proliferative growth. Competitive radioligand binding studies showed that cardiac fibroblasts have a single class of high-affinity (IC50, 1.0 nM) angiotensin II binding sites (Bmax, 778 fmol/mg protein) that are sensitive to the competitive nonpeptide AT1 receptor antagonist losartan (IC50, 13 nM). Other angiotensin peptides competed for [125I]angiotensin II binding in the following rank order: angiotensin II > angiotensin III > angiotensin I > > [des-Asp1-des-Arg2]angiotensin II. A nonhydrolyzable analogue of guanosine triphosphate increased the dissociation rate of bound [125I]angiotensin II and decreased hormone binding to the receptor at equilibrium. The angiotensin II receptor was coupled with increases in intracellular calcium. Incorporation of precursors into protein, DNA, and RNA in response to angiotensin II was determined. In serum-deprived cultures, a 24-hour exposure to 1 microM [Sar1]angiotensin II increased rates of phenylalanine, thymidine, and uridine incorporation by 58%, 103%, and 118%, respectively. These increases were blocked by the noncompetitive AT1 receptor antagonist EXP3174. After 48 hours, [Sar1]angiotensin II increased total protein and DNA of cardiac fibroblasts by 23% and 15%, respectively, with no change in the protein/DNA ratio. [Sar1]Angiotensin II increased cell number by 138% after a 24-hour exposure, without affecting cell area. In summary, cardiac fibroblasts have G protein-linked AT1 receptors that are coupled with proliferative growth. These results suggest that angiotensin II-induced cardiac hypertrophy is, in part, secondary to stimulated increases in nonmyocyte cellular growth.

Angiotensin II↗

PubMed1992

Angiotensin II stimulation of left ventricular hypertrophy in adult rat heart. Mediation by the AT1 receptor.

Angiotensin II (AII) has been reported to have direct hypertrophic actions in mammalian and avian myocardium. In this study we determined whether AII had receptor-mediated effects on stimulating cardiac hypertrophy independent of mechanical stimuli (increased cardiac afterload) in adult rats. Angiotensin II was infused into Sprague-Dawley rats for 7 and 14 days. Following this infusion, left ventricular mass indexed to body weight (LV/BW) increased 18.6 and 17.3%, respectively, compared with control (saline infused) rats. Administration of the nonpeptide AII receptor antagonist Dup 753 prevented the increase in left ventricular hypertrophy. Blockade of converting enzyme with enalapril maleate and treatment with a vasodilator had no effect on the AII-induced hypertrophy. In this animal model, the cardiac hypertrophy appeared to be independent of cardiac afterload, because normalization of blood pressure with hydralazine did not prevent the AII-induced hypertrophy. These in vivo studies indicate that AII-induced cardiac hypertrophy is mediated through AT1 angiotensin receptors.

Angiotensin II↗

PubMed1992

Cardiac actions of angiotensin II: Role of an intracardiac renin-angiotensin system.

The renin-angiotensin system has a varied role in the regulation of cardiac function, ranging from early receptor-mediated effects such as second messenger generation, to more delayed responses such as protein synthesis and cell growth. Clinically, the importance of the RAS in cardiovascular disease is becoming increasingly evident with the use of ACE inhibitors in treating various pathological processes. With evidence for the existence of a local RAS in the heart, the molecular and biochemical regulation of this system requires investigation. Much additional work needs to be directed toward elucidating the mechanisms by which the AII-receptor couples to cardiac growth, how the local RAS is regulated, and the nature of controls that modulate cardiac production and actions of this peptide. Increased understanding of the mechanisms by which AII actions are affected in cardiac tissue will likely lead to enhanced therapeutic modalities for the treatment of pathological cardiovascular conditions in which the RAS plays an integral role.

Angiotensin II↗

PubMed1992

Metabolic response to a high-fat diet in neonatal and adult rat muscle.

Neonatal rats were exposed to a high-fat low-carbohydrate diet to determine how substrate availability might affect the metabolic phenotype of muscle. Mixed-fiber homogenates of extensor digitorum longus, soleus, and diaphragm muscles were assayed for beta-hydroxyacyl-CoA dehydrogenase (beta-OAC), succinate dehydrogenase, malate dehydrogenase, lactate dehydrogenase, phosphofructokinase (PFK), adenylokinase, and creatine kinase. The three muscles showed significant increases in enzyme activity for fatty acid oxidation (beta-OAC) in weaned neonatal rats maintained on the high-fat diet compared with normal weaned controls. This effect persisted for 6 wk of the diet. The other consistent metabolic change was a decrease in PFK. Adult animals subjected to the same diet had similar increases in fatty acid oxidation and a fall in PFK after 1 wk, with most of these changes persisting for the 4 wk of the diet. Examination of individual fibers revealed enzyme changes in fibers of all types, but with the largest effect in type IIb fibers. The data indicate that both adult and neonatal muscles are similarly capable of adjusting their energy metabolism in response to dietary factors.

Aging↗

PubMed1992

Intracardiac detection of angiotensinogen and renin: a localized renin-angiotensin system in neonatal rat heart.

There is increasing evidence that the renin-angiotensin system (RAS) modulates cardiovascular function through both blood-borne and tissue-derived components. The existence of a local RAS has been proposed in the heart based on biochemical and molecular biological studies that identify angiotensinogen and renin. We conducted the present study to determine the chamber localization of angiotensinogen and renin mRNA in neonatal rat heart and whether these components could be identified in cultured cardiomyocytes and fibroblasts obtained from neonatal rat heart. Experiments using polymerase chain reaction (PCR) indicated that whole hearts obtained from neonatal rats contained both angiotensinogen and renin mRNA. With the use of radiolabeled cDNA probes and in situ hybridization, angiotensinogen and renin transcripts were localized both in the atria and ventricles of neonatal rat hearts. Relative signal strengths for angiotensinogen were highest in the left and right ventricles. In contrast, renin signal strength was overall much lower and preferentially localized in the left ventricle. To investigate the cellular source of angiotensinogen and renin, cultured neonatal heart cardiomyocytes and ventricular fibroblasts were screened for angiotensinogen and renin messenger RNA and protein using PCR and indirect immunofluorescent staining, respectively. These experiments demonstrated that both cell types produce transcripts and the respective translation products for angiotensinogen and renin. These data suggest that the site of angiotensin II synthesis can occur at the level of the individual cardiomyocyte and fibroblast, where it may serve to directly and/or indirectly regulate cardiac rate, force, growth, and development in the neonate.

Angiotensinogen↗

PubMed1992

Detection of angiotensin I and II in cultured rat cardiac myocytes and fibroblasts.

Angiotensin II (ANG II) is a stimulus for positive chronotropic and inotropic effects, protein synthesis, and hypertrophic growth in cardiac tissue. These short- and long-term effects of ANG II are mediated through specific plasma membrane receptors. Indirect evidence suggests that ANG II synthesized in the myocardium may be important in regulating cardiac function. The cell types in the myocardium that produce components of the renin-angiotensin system have not been determined. In this study, we evaluated whether cultured cardiomyocytes and fibroblasts obtained from ventricles of neonatal rat hearts were capable of synthesizing ANG I and II. Both cardiomyocytes and fibroblasts were found to have immunofluorescent staining for ANG I, ANG II, and angiotensin-converting enzyme (ACE). The amounts of ANG I and II in cell extracts and conditioned media obtained from cardiomyocytes and fibroblasts were quantified by radioimmunoassay. The amounts of ANG I and II detected in cardiomyocyte cultures (1.48 x 10(6) cells/dish) were 32.2 +/- 16.2 (n = 4) and 6.2 +/- 2.9 (n = 4) ng/10(6) cells, respectively. The amounts of ANG I and II detected in the media conditioned by a 48-h exposure to cardiomyocytes were 5.2 +/- 1.2 (n = 3) and 2.1 +/- 1.2 (n = 3) ng/10(6) cells, respectively. The amounts of ANG I and II detected in fibroblast cultures (5.38 x 10(6) cells/dish) were 34.8 +/- 4.9 (n = 4) and 8.0 +/- 3.5 (n = 4) ng/10(6) cells, respectively. The amounts of ANG I and II obtained from media conditioned by a 48-h exposure to fibroblasts were 4.7 +/- 0.6 (n = 4) and 3.3 +/- 2.1 (n = 4) ng/10(6) cells, respectively. The identity of the radioimmunoassayable materials as ANG I and II peptides was confirmed in cardiomyocytes using an in vitro bioassay based on displacement of 125I-ANG II from receptor binding sites in cardiac membranes prepared from neonatal pig heart. Identification of ANG I and II and ACE in vitro in cultures of cardiac myocytes and fibroblasts supports the hypothesis that there is an intracardiac renin-angiotensin system that produces these peptides.

Angiotensin I↗

PubMed1992

Angiotensin-II-binding sites on hepatocyte nuclei.

Angiotensin-II (Ang II) stimulates gene expression and cell growth in several cell types. Studies that have shown localization of Ang II to nuclei of myocytes and hepatic nuclear Ang II binding suggest that these actions may be mediated by nuclear receptors. We characterized Ang II binding to rat liver nuclei, which were free of plasma membrane based on enzyme analysis and electron microscopy. At 18 C, specific binding of 0.1-0.3 nM [125I]Ang II to nuclei and nuclear envelopes reached equilibrium by 2 h. Unlabeled Ang II inhibited [125I]Ang II binding to nuclei with an IC50 of 1.4 +/- 0.2 nM (+/- SE; n = 6). In half of the nuclear preparations, a lower affinity site (IC50, 50.4 +/- 23.6 nM), which accounted for 7-32% of specific Ang II binding, was detected by Scatchard analysis. Results similar to these were obtained with nuclear envelopes. Other Ang peptides competed for binding in the rank order: Ang III (IC50, 2.1 nM) greater than Ang I (IC50, 33) greater than [Des-Phe8]Ang II (IC50, 362) greater than [Des-Asp1-Des-Arg2]Ang II (IC50, 736). Losartan (DuP 753), an AT1 receptor antagonist, inhibited binding (IC50, 10.9 +/- 0.9 nM), whereas the AT2 receptor antagonist PD123177 did not. The pH optimum for binding to nuclear envelopes was 7, with binding more sensitive to low (5 and 6) than high (8 and 9) pH. Nonhydrolyzable GTP analogs accelerated displacement of bound [125I]Ang II by 10(-5) M Ang II. Differences were noted in pH sensitivity, time course, binding affinity for Ang I, II, and III, and rate of dissociation between nuclei or nuclear envelopes and plasma membrane Ang II binding. These results suggest that nuclear envelopes have a G-protein-coupled Ang II-binding site, which belongs to the AT1 class of Ang II receptors, with properties different from the plasma membrane receptor.

Angiotensin II↗

PubMed1991

Angiotensin II and left ventricular growth in newborn pig heart.

The left ventricle of the neonatal pig heart is a model of rapid physiological cardiac growth that is dependent upon accelerated ribosome formation and increased RNA content. The goals of the present study were to investigate the role of angiotensin II in this rapid growth. Hearts from 3 d old control piglets or piglets that were treated with enalapril maleate, an angiotensin converting enzyme inhibitor, or DuP 753, an angiotensin II receptor antagonist, were used for measurements of left ventricular mass, RNA, DNA and protein. Hearts from enalapril-treated pigs also were used for measurements of rates of ribosome formation and total protein synthesis during perfusion as modified Langendorff preparations. Treatment of piglets with enalapril maleate resulted in decreased left ventricle/body wt ratio, RNA content, total RNA and total protein in the left ventricle. These parameters were unaffected in the right ventricle. In vitro perfusion of hearts from enalapril-treated piglets revealed decreased ribosome formation and total protein synthesis in the left ventricle. Piglets treated with DuP 753 had decreased left ventricle/body wt ratio as well as decreased RNA content, total RNA and RNA/DNA ratio in the left ventricle. These results suggest that angiotensin II may be required for rapid growth of neonatal pig hearts.

Angiotensin II↗

PubMed1991

Control of growth in the neonatal pig heart.

The newborn heart is an excellent model in which to study cardiac growth because the neonatal period is a normal situation in which the left ventricle (LV) grows rapidly and the right ventricle grows slowly. Accelerated LV growth is in response to mechanical, neural, and endocrine changes at birth. Faster growth of the LV is accounted for by greater capacity for protein synthesis, as evidenced by greater RNA content. At 18 h of life, ribosomes are formed in preference to total heart protein, but at 48 h of life, faster rates of both ribosome formation and total protein synthesis are observed. In the LV of hearts from 2-day-old pigs, these rates are insensitive to the addition of glucagon, 1-methyl-3-isobutylxanthine, or a combination of norepinephrine and propranolol. These observations could result because of maximal growth stimulation already present in the LV of the newborn heart. To restrain LV growth in the neonatal period, we treated pigs with enalapril maleate, an angiotensin II-converting enzyme inhibitor. Enalapril blocked growth of the LV as well as the increase in RNA content. When hearts from enalapril-treated pigs were perfused in vitro, rates of protein synthesis and ribosome formation in the LV were lower. These studies suggest that angiotensin II is an important factor accounting for rapid growth of the neonatal heart in response to pressure overload at birth.

1-Methyl-3-isobutylxanthine↗