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H Attramadal

Publications and source records attributed to H Attramadal.

At least 37 records · Page 2Linked to original sources
PubMed1998

ET-receptor antagonism, myocardial gene expression, and ventricular remodeling during CHF in rats.

Both myocardial and plasma endothelin-1 (ET-1) are elevated in congestive heart failure (CHF). However, the role played by endogenous ET-1 in the progression of CHF remains unknown. The aim of the present study was to investigate and correlate myocardial gene expression programs and left ventricular (LV) remodeling during chronic ET-receptor antagonism in CHF rats. After ligation of the left coronary artery, rats were randomized to oral treatment with a nonselective ET-receptor antagonist (bosentan, 100 mg . kg-1 . day-1, n = 11) or vehicle (saline, n = 13) for 15 days, starting 24 h after induction of myocardial infarction. Bosentan substantially attenuated LV dilatation during postinfarction failure as evaluated by echocardiography. Furthermore, bosentan decreased LV systolic and end-diastolic pressures and increased fractional shortening. Myocardial expression of preproET-1 mRNA and a fetal gene program characteristic of myocardial hypertrophy were increased in the CHF rats and were not affected by bosentan. Consistently, right ventricular-to-body weight ratios, diameters of cardiomyocytes, and echocardiographic analysis demonstrated a sustained hypertrophic response and a normalized relative wall thickness after intervention with bosentan. Thus the modest reduction of preload and afterload provided by bosentan substantially attenuates LV dilatation, causing improved pressure-volume relationships. However, the compensatory hypertrophic response was not altered by ET-receptor antagonism. Therefore, ET-1 does not appear to play a crucial role in the mechanisms of myocardial hypertrophy during the early phase of postinfarction failure.

Angiotensinogen↗
PubMed1997

Increased cardiac expression of endothelin-1 mRNA in ischemic heart failure in rats.

OBJECTIVES: Plasma endothelin (ET) concentrations are increased in heart failure. The aims of the present study were to investigate to what extent cardiac ET mRNA expression is induced in ischemic heart failure and whether there may be compensatory downregulation of myocardial mRNA levels for the ETA and ETB receptor subtypes. METHODS: In rats with ischemic heart failure (left ventricular end-diastolic pressure > 15 mmHg) due to left coronary artery ligation. Northern blot analyses were performed on mRNA isolated from cardiac tissues. RESULTS: A substantial upregulation was revealed in all chambers of the failing hearts. Up to 27-fold upregulation (mean 10.6 +/- 4.0, P = 0.002) of left ventricular ET-1 mRNA levels was measured 1 week after myocardial infarction, whereas only a modest upregulation was detected after 6 weeks (mean 2.7 +/- 0.5, P < 0.05). Ribonuclease protection assay revealed 2.8 +/- 0.4-fold higher levels of ET-1 mRNA in the left ventricular area subjected to myocardial infarction compared to the non-infarcted tissue after 1 week. Left ventricular ET-1 mRNA correlated significantly with left ventricular end-diastolic pressure after 1 week (r2 = 0.86, P = 0.007). The ETA and ETB receptor mRNA levels tended to increase 1 week after myocardial infarction although these changes were not statistically significant. CONCLUSIONS: Cardiac ET-1 mRNA levels are increased in ischemic heart failure and correlate significantly with left ventricular end-diastolic pressure 1 week after myocardial infarction. The increase in cardiac ET-1 mRNA is not accompanied by a decrease in ET receptor mRNA.

Animals↗
PubMed1997

Transient, isopeptide-specific induction of myocardial endothelin-1 mRNA in congestive heart failure in rats.

Increased myocardial expression of preproendothelin-1 (ppET-1) mRNA has been associated with congestive heart failure (CHF) in rats. However, the time course and isoform pattern of ppET mRNA induction and the cellular localization of ET in failing hearts are unknown. Thus our aim was to investigate myocardial ppET mRNA expression in CHF rats during the first 6 wk after induction of myocardial infarction. Furthermore, performing immunohistochemical analysis, we also investigated the origin and localization of immunoreactive endothelin (ET) in different regions of the failing heart. Ribonuclease protection assays revealed a marked increase in ppET-1 mRNA levels in rat myocardial tissues during CHF. The induction of ppET-1 mRNA was isopeptide specific and transient. The most substantial upregulation was observed in the infarcted area, where maximal expression of ppET-1 mRNA was observed after 7 days (25-fold increase, P < 0.05). However, a marked and statistically significant induction of ppET-1 mRNA was also observed in the nonischemic myocardium. Immunohistochemical analysis revealed ET-1-like immunoreactivity in cardiomyocytes, vascular endothelial cells, macrophages, and proliferating fibroblasts. Thus immunohistochemistry revealed the structural basis for the dramatic upregulation of the myocardial ET system in the infarcted region, suggesting a role for ET in the healing process after myocardial infarction. However, the global upregulation of ppET-1 mRNA in the heart also suggests an autocrine/paracrine regulatory mechanism in the nonischemic myocardium during CHF.

Animals↗
PubMed1995

Modulation of gonadotropic and purinergic responsiveness by islet activating protein in sertoli cells from immature rats.

In the present study we have examined the effects of islet activating protein (IAP) on the regulatory effects of FSH, glucagon and (-)N6-(R)-phenyl-isopropyladenosine (PIA), an adenosine A1 receptor agonist, on the formation of cAMP and estradiol-17 beta (E2) in Sertoli cell cultures isolated from immature (19-day-old) rats. FSH (NIH-FSH-S-15) (1.25 micrograms/ml) caused a more than 10-fold stimulation of the level of both cAMP and E2 in the spent media from Sertoli cell cultures during an 18 h incubation. Both responses were reduced by 80% in the presence of PIA (10(-6) M). When the cultures were preincubated for 24 h with increasing concentration of IAP, the inhibitory effects of PIA were counteracted in a concentration-dependent manner. Moreover, preincubation with IAP (> 20 ng/ml) caused a significant stimulation of FSH-stimulated cAMP production even in the absence of PIA. PIA inhibited FSH-stimulated cAMP production in a concentration dependent manner. However, when the cells were preincubated with IAP (100 ng/ml) for 24 h, the inhibitory effects of PIA were completely abolished, and PIA now actually caused a slight stimulation of cAMP production. Both FSH and glucagon stimulated cAMP production in a concentration-dependent manner. Preincubation with IAP (100 ng/ml for 24 h) resulted in an increase in maximal stimulation of cAMP production for both FSH and glucagon. When adenylyl cyclase (AC) activity was measured directly in isolated membrane particles from Sertoli cells cultured in the presence of IAP (100 ng/ml) for 24 h, both basal and FSH-stimulated AC activity were significantly higher than in membrane particles from control cells. These results provide a further characterization of the functional Gi component coupled to the AC complex in cultured rat Sertoli cells, mediating the inhibitory effects of adenosine and possibly other endogenous substances on cAMP production.

Adenosine↗
PubMed1993

Beta-adrenergic receptor kinase-2 and beta-arrestin-2 as mediators of odorant-induced desensitization.

beta-Adrenergic receptor kinase (beta ARK) and beta-arrestin function in the homologous or agonist-activated desensitization of G protein-coupled receptors. The isoforms beta ARK-2 and beta-arrestin-2 are highly enriched in and localized to the dendritic knobs and cilia of the olfactory receptor neurons where the initial events of olfactory signal transduction occur. Odorants induce a rapid and transient elevation of adenosine 3',5'-monophosphate (cAMP), which activates a nonspecific cation channel and produces membrane depolarization. Preincubation of rat olfactory cilia with antibodies raised against beta ARK-2 and beta-arrestin-2 increased the odorant-induced elevation of cAMP and attenuated desensitization. These results suggest that beta ARK-2 and beta-arrestin-2 mediate agonist-dependent desensitization in olfaction.

Animals↗
PubMed1993

Beta-adrenoceptor mediated responses and subtypes of beta-adrenoceptors in cultured rat Sertoli cells.

Membrane particles from Sertoli cell cultures were examined for subtypes of beta-adrenoceptors with a radioligand binding technique using [125I]iodocyanopindolol and a beta 1-selective antagonist (Sandoz 204 545) or a beta 2-selective antagonist (ICI 118 551). Biphasic competition curves and modified Eddie-Hofstee plots revealed a relative distribution of approx. 80% beta 1-adrenoceptors and 20% beta 2-adrenoceptors. Only 45% of the adrenoceptor mediated stimulation of adenylyl cyclase activity was associated with beta 1-adrenoceptors, whereas the remaining 55% was mediated via beta 2-adrenoceptors. The subtype selective antagonists inhibited isoproterenol stimulated aromatization of testosterone to estradiol-17 beta in a concentration-dependent manner. Complete inhibition of beta 1-adrenoceptors resulted in a 45% reduction of estradiol-17 beta formation, whereas similar inhibition of beta 2-adrenoceptors resulted in only a 35% reduction. It is concluded that cAMP-dependent effects of beta-adrenergic agonists in Sertoli cells are mediated by activation of both beta 1- and beta 2-adrenoceptors. The discrepancy between the relative number of beta 1- and beta 2-adrenoceptors and their relative contribution to cAMP production and aromatization indicates that beta 2-adrenoceptors in Sertoli cells are more tightly coupled to the adenylyl cyclase system than beta 1-adrenoceptors. Furthermore, complete inhibition of either beta 1- or beta 2-adrenoceptors by subtype selective antagonists, demonstrates a substantial fraction of spareness between agonist activation of the adenylyl cyclase complex and aromatization.

Adenylyl Cyclases↗
PubMed1992

Beta-arrestin2, a novel member of the arrestin/beta-arrestin gene family.

Homologous or agonist-specific desensitization of beta 2-adrenergic receptors (beta 2AR) is mediated by the beta-adrenergic receptor kinase (beta ARK) which specifically phosphorylates the agonist-occupied form of the receptor. However, the capacity of beta ARK-phosphorylated beta 2AR to stimulate Gs in a reconstituted system is only minimally impaired. Recently, a protein termed beta-arrestin, was cloned from a bovine brain cDNA library and found to quench phosphorylated beta 2AR-coupling to Gs. Utilizing a low stringency hybridization technique to screen a rat brain cDNA library, we have now isolated cDNA clones representing two distinct beta-arrestin-like genes. One of the cDNAs is the rat homolog of bovine beta-arrestin (beta-arrestin1). In addition, we have isolated a cDNA clone encoding a novel, beta-arrestin-related protein which we have termed beta-arrestin2. Overall, beta-arrestin2 exhibits 78% amino acid identity with beta-arrestin1. The primary structure of these proteins delineates a family of proteins that regulates receptor coupling to G proteins. The capacity of purified beta-arrestin1, beta-arrestin2, and arrestin to inhibit the coupling of phosphorylated receptors to their respective G proteins were assessed in a reconstituted beta 2AR-Gs system and in a reconstituted rhodopsin-GT system. beta-Arrestin2 was equipotent to beta-arrestin1 and specifically inhibited beta 2AR function. Conversely, arrestin inhibited rhodopsin coupling to GT, whereas beta-arrestin1 and beta-arrestin2 were at least 20-fold less potent in this system. beta-Arrestin1 and beta-arrestin2 are predominantly localized in neuronal tissues and in the spleen. However, low mRNA levels can be detected in most peripheral tissues. In the central nervous system, beta-arrestin2 appears to be even more abundant than beta-arrestin1. Immunohistochemical analysis of the tissue distribution of beta-arrestin1 and beta-arrestin2 in rat brain shows extensive, but heterogenous, neuronal labeling of the two proteins. They are found in several neuronal pathways suggesting that they have relatively broad receptor specificity regulating many G protein-coupled receptors. Furthermore, immunoelectron microscopy shows that the beta-arrestins are appropriately situated at postsynaptic sites to act in concert with beta ARK to regulate G protein-coupled neurotransmitter receptors.

Amino Acid Sequence↗
PubMed1991

Different mechanisms are involved in cAMP-mediated induction of mRNAs for subunits of cAMP-dependent protein kinases.

The present study addresses possible mechanisms through which cAMP mediates its effects on mRNA levels for the subunits of protein kinase A (PKA) and the cellular protooncogene, c-fos. Messenger RNAs for the PKA subunits (RI alpha, RII alpha, RII beta, and C alpha) were regulated by cAMP with similar kinetics in Sertoli cells. However, effects of cAMP on the PKA mRNAs were slow compared to a well characterized cAMP responsive gene, c-fos. The magnitude of stimulation was dramatically different between the various PKA subunits, in that RII beta mRNA increased more than 50-fold while the mRNAs for the other subunits were induced only two to four times. Separation of nuclear and cytoplasmic RNA demonstrated that mRNAs for PKA subunits were stimulated to the same extent in these two cellular compartments. The more rapid induction of c-fos mRNA by cAMP, compared to the mRNA for RII beta, was also seen at the level of transcription. Maximal transcription rate for c-fos, RI alpha, and C alpha were observed after 30 min, whereas that for RII beta was increasing during the 2-h period examined. Transcriptional activation of the RI alpha gene also appeared faster than that for RII beta. When Sertoli cells were incubated with 8-(4-chlorophenylthio) cAMP and cycloheximide, a potent inhibitor of protein synthesis, we observed a super-induction of the mRNAs for c-fos (10-fold) and RI alpha (2-fold).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Mechanisms of glucagon-induced homologous and heterologous desensitization of adenylate cyclase in membranes and whole Sertoli cells of the rat.

In the present work the molecular mechanisms of glucagon-induced desensitization of adenylate cyclase in cultured Sertoli cells have been studied in both whole cells and in a cell-free system. 1) Pretreatment of both whole Sertoli cells and membranes with glucagon induces a time- and dose-dependent desensitization of adenylate cyclase response that is primarily homologous and similar in the two systems. The component of heterologous desensitization, estimated by the reduced responsiveness to other hormones and NaF, accounted for only 12-20% loss of glucagon-responsive adenylate cyclase activity (P less than 0.01). 2) Glucagon-induced desensitization is ATP-dependent. Half maximal desensitization was achieved between 0.1 and 0.2 mM of ATP. 3) The typical time lag in the maximal activation of adenylate cyclase by GMPP(NH)P in the absence of hormone reappeared upon desensitization in spite of the presence of glucagon. The lag, however, was eliminated by FSH, showing that the homologous desensitization is due to a receptor-specific alteration. 4) The heterologous component of glucagon-induced desensitization is largely cAMP/protein kinase dependent. cAMP/protein kinase-induced desensitization was heterologous and caused approximately 30% loss of both hormonal and fluoride-stimulated enzyme activity. 5) Glucagon-induced desensitization is not due to altered activity of Ni since it proceeded equally well in membranes of cells pretreated with pertussis toxin (100 ng/ml) which eliminates Ni-mediated effects. It is concluded that glucagon induces both homologous and heterologous desensitization of the Sertoli cell adenylate cyclase. The locus of homologous desensitization appears to be at the level of the receptor and most probably involves a cAMP-independent phosphorylation reaction, whereas the heterologous desensitization appears to be cAMP-mediated and at least involves impaired functional activity of the Ns component.

Adenosine Triphosphate↗
PubMed1986

Hormonal activation of the adenylyl cyclases of the rat and human prostate gland.

The rat ventral prostate and the human hyperplastic prostate contain adenylyl cyclases which can be activated by a variety of neurotransmittors, including vasoactive intestinal peptide (VIP), beta 2 adrenergic agonists, and dopamine. In both species the response to VIP was predominantly localized to the epithelial fraction. In the human tissue activation of the enzyme could also be achieved with prostaglandin E1 (PGE1) and an alpha 2 adrenergic agonist both associated with the stromal compartment. Castration in the rat caused a marked reduction in the basal activity of the enzyme and the maximal level of the hormone-stimulated response per cell (per mg DNA), but had only minor effects on the pattern of activation when expressed per mg membrane protein. Androgen treatment (dihydrotestosterone propionate, 2.5 mg/day) prevented the castration effects. Estrogen treatment (estradiol benzoate, 125 micrograms/day) could not prevent the castrational changes but maintained enzyme activity at a level above that of the castrate. There were no major qualitative differences in the pattern of activation of the cyclase between the different lobes of the rat prostate and the seminal vesicle.

Adenylyl Cyclases↗
PubMed1986

A transplantable rat Leydig cell tumor--3. Isoproterenol and prostaglandin E1 (PGE1) responsive adenylyl cyclase (AC). Regulatory effects of nucleotides and magnesium.

The activity of the membrane bound adenylyl cyclase (AC), the effects of nucleotides, Mg2+-cations and its responsiveness to isoproterenol and prostaglandin E1 (PGE1) were examined in a transplantable rat Leydig cell tumor (H-540). Both isoproterenol and PGE1 caused activation of the AC in Leydig cell tumors. The degree of activation by PGE1 (4-5-fold) was approximately twice that of isoproterenol (2-3-fold). The addition of both AC agonists simultaneously was not additive indicating that they activate AC of the same cell. Increasing concentrations of ATP (0.025-2.0 X 10 mM) caused a concentration dependent increase in both the basal and hormone stimulated AC activity, and the activation by isoproterenol and PGE1 (relative response) revealed a slight but significant increase with increasing ATP concentrations. Lineweaver-Burke analysis of these data indicated an apparent Km for ATP (Mg X ATP) of 0.16 mM. Free magnesium did not influence the apparent Km of the AC for ATP. Increasing concentrations of free Mg2+ (0.24-13.2 mM) also caused a concentration dependent increasing activation of AC activity up to a concentration of approx 6 mM in excess of Mg2+-binding ingredients. Higher concentrations of free Mg2+ (13.1 mM) caused a small but significant decrease in both basal and agonist stimulated AC activity. In contrast to other reports, activation by isoproterenol and PGE1 was in general not influenced by the concentration of Mg2+. Both GTP and GMP-P(NH)P stimulated basal and hormone stimulated AC activity (Kact 1 microM), but with different kinetics. In the presence of GTP, AC activity was almost constant for 90 min. In the presence of GMP-P(NH)P, AC activity was much higher, but constant AC activity occurred after a certain lag time (7-10 min), which was reduced by PGE1 and isoproterenol. In conclusion, cAMP production in Leydig cell tumors is stimulated by both PGE1 and isoproterenol. The AC activity and activation by these agonists are regulated by Mg2+ and nucleotides in a slightly different manner from most other cells. The association between AC activation and stimulation of steroid production by Leydig cell tumors remains to be investigated.

Adenosine Triphosphate↗
PubMed1986

Changes in germ cell adenylate cyclase and protein carboxyl methylase activities in rat testicular tissue during bilateral cryptorchidism and after orchidopexy.

Soluble Mn2+-dependent adenylate cyclase and protein carboxyl methylase are two enzymes that are primarily localized in haploid germ cels of rat testicular tissue, and both enzymes exhibit an increase in activity in association with sexual maturation. Experimental cryptorchidism (surgery at 17 days of age) in immature rats prevented the age-dependent increase in the activity of these two testicular enzymes. After orchidopexy at 34 days of age the activities of these two enzymes increased to normal control values in association with testicular growth. These observations show that biochemical markers such as soluble Mn2+-dependent adenylate cyclase and protein carboxyl methylase can be used to follow germ cell differentiation.

Adenylyl Cyclases↗
PubMed1985

Glucagon-stimulated cyclic AMP production and formation of estradiol in Sertoli cell cultures from immature rats.

Addition of glucagon to the incubation medium of cultured Sertoli cells isolated from immature (19-day-old) rats resulted in a time- and concentration-dependent stimulation of cAMP accumulation measured both in the cells and in the medium. Maximal intracellular levels of cAMP were reached after 30 min, after which the levels decreased. In the medium cAMP levels reached a plateau after 6 h. The magnitude and kinetics of the responses were comparable to those observed with FSH in the same culture preparations. 1-Methyl-3-isobutylxanthine (MIX), a phosphodiesterase inhibitor, greatly potentiated the magnitude of the effects of glucagon and FSH. Glucagon stimulated adenylate cyclase activity in isolated membrane preparations from similar cultures, and the concentration causing half-maximal stimulation (EC50) was approximately 300 ng/ml. Glucagon also stimulated aromatization in cultured Sertoli cells to the same extent as FSH. It is concluded that cultured Sertoli cells isolated from immature rats contain receptors for glucagon, coupled to adenylate cyclase, and that glucagon also stimulates aromatization of testosterone to estradiol.

Adenylyl Cyclases↗
PubMed1985

Studies on the mechanism of follicle-stimulating hormone-induced desensitization of Sertoli cell adenylyl cyclase in vitro.

When Sertoli cells were cultured in the presence of follicle-stimulating hormone (FSH), a time-and concentration-dependent desensitization of FSH-responsive adenylyl cyclase (AC) was observed. Maximal desensitization (80%) was attained after 6-9 h of incubation with FSH (10 micrograms/ml; NIH-FSH-S12). During 24 h of incubation the concentration of FSH causing a half-maximal desensitization was about 100 ng/ml. Removal of the hormone from the culture medium was associated with a gradual reappearance of the FSH response. Follicle-stimulating hormone-induced desensitization of Sertoli cell AC was specific for homologous hormone, since AC activation by isoproterenol was unaffected. Furthermore, AC activity of control and FSH-desensitized cells was equally activated by GTP and fluoride, showing that the interaction of the guanyl nucleotide regulatory (N) component with the catalytic subunit is not affected during FSH-induced desensitization. A loss in specific FSH binding was detected after 9 and 24 h of exposure to FSH, but not at shorter times of incubation. Desensitization of Sertoli cell AC to both FSH and isoproterenol stimulation could also be achieved by dibutyryl cyclic AMP (dbcAMP); however, a 30-40% desensitization required a high nucleotide concentration (1 mM) and a long incubation time (24 h). These results show that desensitization of Sertoli cell AC by FSH is associated with normal function of the N component, and precedes any significant loss in specific FSH binding sites. Furthermore, exogenous addition of dbcAMP (1 mM) did not cause the same effects on Sertoli cell AC as did FSH.

Adenylyl Cyclases↗
PubMed1984

A transplantable rat Leydig cell tumor--2. Adenylyl cyclase activation by prostaglandin E1, isoproterenol and glucagon.

The responsiveness of the membrane bound adenylyl cyclase (AC) system to various hormones and hormone analogues in a transplantable rat Leydig cell tumor (H-540) has been investigated and compared with that of interstitial tissue from normal adult rats. The results can be summarized as follows: The AC of the Leydig cell tumors was stimulated by isoproterenol, epinephrine, norepinephrine, dopamine, glucagon, PGE1, PGF2 alpha and LH/hCG. The AC of the Leydig cell tumors exhibited a much greater response to PGE1 than the AC in normal interstitial tissue (5-fold and 2-fold stimulation, respectively). The AC of the Leydig cell tumours also revealed a somewhat higher response to isoproterenol than the AC of interstitial tissue (2.5-fold and 2-fold, respectively). Adenylyl cyclase in both tissues were equally stimulated by glucagon (2-fold). The LH response in the Leydig cell tumors was only half of that found in normal Leydig cells. This study indicates, that in spite of the fact that tumor Leydig cells respond to LH and produce testosterone, the response pattern of the AC is different from that of normal Leydig cells.

Adenylyl Cyclases↗
PubMed1984

Beta-adrenergic regulation of Sertoli cell adenylyl cyclase: desensitization by homologous hormone.

Incubation of Sertoli cell-enriched cultures with D,L-isoproterenol caused a time- and concentration-dependent, homologous desensitization of isoproterenol-responsive adenyl cyclase, whereas the response to FSH was unaffected. Half-maximal desensitization was achieved within 1 h of preincubation, after which a more gradual loss of response was observed. Preincubation of Sertoli cells for 24 h with increasing concentrations of D,L-isoproterenol demonstrated that the concentration required to obtain half-maximal densensitization was approximately 10-fold lower than the Km for activation of adenylyl cyclase. The function of the guanine nucleotide regulatory component (N-component) of the adenylyl cyclase complex in hormonally desensitized Sertoli cells, as evaluated by activation of adenylyl cyclase by GTP, GMPP(NH)P, fluoride and Mg2+, was not affected by the hormone pretreatment. Preincubation of Sertoli cells with a high concentration of dbcAMP (10(-3) M) for 24 h was associated with a 45% reduction in adenylyl cyclase activation by both FSH and isoproterenol. Also in this case fluoride- and GTP-stimulated adenylyl cyclase activities were normal. However, the effects of dibutyryl cyclic AMP occurred much more slowly than agonist-induced desensitization, indicating that cAMP may not be the primary mediator of homologous desensitization of Sertoli cell adenylyl cyclase by isoproterenol.

Adenylyl Cyclases↗