Biomedical subjects

A W Hahn

Publications and source records attributed to A W Hahn.

At least 73 records · Page 4Linked to original sources

PubMed1991

Stimulation of autocrine platelet--derived growth factor AA-homodimer and transforming growth factor beta in vascular smooth muscle cells.

We have investigated the interrelationship between growth factors and vasoconstrictor peptides in terms of their possible paracrine/autocrine regulation of vascular smooth muscle cell differentiation/proliferation. Responses of quiescent cells from spontaneously hypertensive and Wistar-Kyoto rats to stimulation with a selected number of growth factors- and vasoconstrictor peptides were established (induction of mRNA as well as secretion of immunoreactive peptides). A single exposure of quiescent vascular smooth muscle cells to the vasoconstrictor peptides Angiotensin II and Endothelin-1 (10(-8) M each) resulted in a prolonged induction of platelet- derived growth factor A-chain and transforming growth factor beta transcripts (maximal at 5-6 hrs poststimulatory). The interrelationship between platelet- derived growth factor AA and transforming growth factor beta was investigated in experiments using the pure peptides individually for stimulation of mRNA and peptide secretion. Both growth factors enhanced their own and one anothers transcript expression. The results demonstrated that in spontaneously hypertensive rats, an established animal model of hypertension, the steady state balance of this set of growth factors may be disturbed. Defects involved may be attributable to alterations in the secretory machinery and/or amount of autocrine growth factor produced.

Angiotensin II↗

PubMed1991

Modulation of gene expression by high and low density lipoproteins in human vascular smooth muscle cells.

Low density lipoprotein and its oxidized form has been implicated in the process of arteriosclerosis which involves growth-related events in the smooth muscle cells of the arterial wall. The induction of so-called early-growth response genes e.g. c-myc and c-fos can serve as an indicator for these growth-related events. In cultured human vascular smooth muscle cells, both LDL and HDL3 were individually capable of stimulating c-myc and c-fos expression in a concentration dependent manner. However, when they were used in combination, depending on the proportion of HDL3 to LDL, c-fos but not c-myc expression was less pronounced than with the single components. In contrast to HDL3 and LDL alone, a combination of the two lipoproteins also blunted both the expression of autoinduced transforming growth factor beta transcripts and the transforming growth factor beta-induced increase of c-fos mRNA. It is concluded that a) the inhibition of transforming growth factor beta autostimulation by HDL3 plus LDL may involve reduced AP-1 activity via a reduction of c-fos expression by the lipoprotein combination and b) the ratio HDL3:LDL might influence the pathogenesis of arteriosclerosis via growth-related events in the arterial wall.

Arteries↗

PubMed1991

Angiotensin-induced growth related metabolism is activated in cultured smooth muscle cells from spontaneously hypertensive rats and Wistar-Kyoto rats.

Smooth muscle cells from spontaneously hypertensive rats (SHR) proliferate in culture faster than those isolated from sex- and age-matched Wistar-Kyoto (WKY) animals. There was no difference in the kinetics of S6 kinase activation in the two cultures, but later metabolic events associated with proliferation were stimulated earlier in SHR cells than in WKY, eg, activation of ornithine decarboxylase. Both cell types elaborated an extensive extra-cellular matrix in culture composed of a different blend of connective tissue macromolecules. Matrix material from SHR cells was more stimulatory to growth of WKY cultures than their own matrices. Angiotensin stimulated the growth and synthesis of extra-cellular matrix material in SHR more than in WKY derived vascular smooth muscle cell cultures.

Angiotensin II↗

PubMed1991

Induction of endothelin secretion by angiotensin II: effects on growth and synthetic activity of vascular smooth muscle cells.

Angiotensin II induces the synthesis and secretion of endothelin by cultured rat vascular smooth muscle cells. Previous studies demonstrate that angiotensin II also activates the synthesis of extracellular matrix-associated glycoconjugates (glycopeptides and proteoglycans) by cultured smooth muscle cells. Furthermore, in culture medium containing mitogen-depleted, plasma-derived serum (1.0%), angiotensin II stimulates the growth of rat smooth muscle cells. Therefore, the influence of endothelin-1 (ET-1) on the growth and matrix elaboration by cultured rat smooth muscle cells was studied to assess its contribution to the stimulatory activity of angiotensin II. In quiescent cultures of smooth muscle cells, no stimulation of the incorporation of [3H]thymidine into DNA by ET-1 was apparent, even at maximal doses (10(-7) M). Under the same conditions, the synthesis of extracellular matrix glycoconjugate material was not enhanced by ET-1, unlike angiotensin II. In cultures maintained in medium containing 1.0% plasma-derived serum, ET-1 was incapable of stimulating either proliferation or incorporation of [3H]thymidine into DNA whereas angiotensin II stimulated both activities. ET-1, however, did induce the expression of growth factor and thrombospondin genes in quiescent smooth muscle cultures. The data suggest that growth stimulation of smooth muscle cells by angiotensin II does not occur as a consequence of stimulated ET-1 production.

Angiotensin II↗

PubMed1991

Nonlinear algorithm for identification of a fiducial marker for various cardiac events.

We report on a nonlinear algorithm which identifies R-wave peaks on the surface electrocardiogram, consistent reference points on the left ventricular pressure waveform and the initiation of the QRS complex on the epicardial electrogram. The algorithm has been used to evaluate data from horses, ponies, dogs and humans at rest and during exercise. It permits rapid, accurate evaluation of data on a beat-by-beat basis even with noisy signals and varying waveform configurations. The algorithm facilitates the acquisition of detailed information previously difficult or impossible to obtain by more conventional methods of analysis.

Algorithms↗

PubMed1991

Low- and high-density lipoproteins as hormonal regulators of platelet, vascular endothelial and smooth muscle cell interactions: relevance to hypertension.

The major risk factors for cardiovascular disease include hypertension, hyperlipidemia, hyperinsulinemia and smoking. They promote the development of atherosclerosis and thromboembolic complications, i.e. strokes and heart attacks. There are diverse interactions between these factors, the outstanding common denominator being alterations in serum lipoproteins, mainly elevated low-density lipoprotein (LDL)-cholesterol and reduced high-density lipoprotein (HDL)-cholesterol concentrations, which results in disturbed cholesterol homeostasis (transport and metabolism) and eventually in perturbations of cellular integrity/function. In addition to their roles as cholesterol-transporting molecules, LDL and HDL directly influence inter- and intracellular communication via stimulation of pivotal signal transduction processes. The 'hormonal' effects of LDL on platelets, endothelial cells and vascular smooth muscle cells are potentially harmful, whereas the effects of HDL may be protective in as much as HDL can antagonize LDL-mediated stimulation of cells. Therapy aimed at reducing serum LDL-cholesterol levels and increasing HDL-cholesterol levels will have multifactorial beneficial effects on cardiovascular disease.

Animals↗

PubMed1991

Digital signal analysis of cardiac events in horses and ponies.

We have developed a digital signal analysis technique which can be used to evaluate various cardiac events in ponies and horses at rest and during exercise. The algorithm is designed to identify R-wave peaks on the surface electrocardiogram, consistent reference points on the left ventricular pressure waveform and the initiation of the QRS complex on the epicardial electrogram. We have used the technique to evaluate data from 10 horses and ponies at rest, during strenuous exercise and during experimentally-induced coronary artery occlusion. The technique provided rapid and accurate beat-by-beat evaluation of data, even with relatively noisy signals and under conditions in which the waveform configurations were not consistent. The benefits afforded by this technique make it especially useful for extracting information which previously was difficult or impossible to obtain using more conventional methods of analysis.

Algorithms↗

PubMed1991

Functional hermetic encapsulation of integrated circuits.

This study demonstrates a new process technology for synthesizing thin films which should be applicable to a variety of implantable devices of different substrate composition and geometries. This new technology, termed the plasma polymerization/vapor deposition (PP/VD) technology, combines the features of surface cleaning, surface treatment, and hermetic encapsulation into a series of in situ vacuum processes. This PP/VD process has produced functional hermetic encapsulating polymer films with a total thickness of 5 microns, independent of the composition, dimensions or geometry of the substrates. CMOS integrated circuits coated by this process and immersed in Ringer's solution and tested for a year, demonstrated unchanging device performance parameters characteristic of hermetically encapsulated integrated circuits.

Electric Conductivity↗

PubMed1990

Inducible endothelin mRNA expression and peptide secretion in cultured human vascular smooth muscle cells.

This study demonstrates the induction of endothelin (ET) mRNA expression and synthesis of functional ET peptide in cultured human vascular smooth muscle cells (hVSMC). Compounds eliciting such responses in hVSMC include the vasoconstrictor hormones angiotensin II and arginine-vasopressin and the growth factors transforming growth factor beta, platelet derived growth factor AA and epidermal growth factor. Induction of ET mRNA expression in hVSMC exhibited transient kinetics (peak at 3-5 hrs. and return to basal within 7 hrs.) which differed from the more sustained ET transcript induction observed for porcine endothelial cells. ET peptide (determined by both radioimmuno- and radioreceptor assays) produced by stimulated hVSMC attained levels (approximately 120-160 pg/10(6) cells/4 hrs.; concentration approximately 3 x 10(-11) M) within the biologically effective concentration range of ET. Stimulated secretion of ET from hVSMC was abolished in the presence of the protein synthesis inhibitor cycloheximide. Sep-pak C18 extracts of medium from stimulated hVSMC elicited a concentration-dependent phosphoinositide catabolic response in myo-[2-3H]-inositol-prelabelled hVSMC. Our findings invoke a role for ET which extends beyond the paracrine regulation by peptide synthesized and secreted by endothelial cells. We propose that VSMC-synthesized ET may function in an autocrine manner to regulate both tone and structural modelling of vasculature.

Angiotensin II↗

PubMed1990

Specific growth stimulation of cultured smooth muscle cells from spontaneously hypertensive rats by platelet-derived growth factor A-chain homodimer.

Cultured vascular smooth muscle cells (VSMC)1 from spontaneously hypertensive rats (SHR) possess specific cell surface receptors for both homodimeric forms of platelet-derived growth factor (PDGF-AA and PDGF-BB), in contrast to cells from normotensive Wistar Kyoto (WKY) animals, which express receptors only for the B-chain form of PDGF. Stimulation of quiescent VSMC from SHR with PDGF-AA resulted in activation of S6-kinase and induction of phosphoinositide catabolism, as well as cellular proliferation when cultures were maintained for prolonged periods with daily supplementation of the growth factor. WKY-derived VSMC showed no response to PDGF-AA, which was consistent with their lack of specific receptors for this homodimer. The responsiveness of quiescent cells from SHR and WKY to the B-chain homodimer was similar. The enhanced growth responsiveness of SHR-derived cells to fetal calf serum, as compared with cells from their normotensive counterparts, may be accounted for in part by their expression of receptors for the AA homodimer of PDGF.

Animals↗

PubMed1990

Stimulation of endothelin mRNA and secretion in rat vascular smooth muscle cells: a novel autocrine function.

Endothelin (ET), a peptide originally isolated from the supernatants of cultured endothelial cells, exerts a wide variety of biological effects in different tissues. Endothelial-cell-synthesized ET-1 has been proposed to act in a paracrine manner on adjacent smooth muscle cells (SMC) in vivo, with effects that include both vascular reactivity (vasodilation/vasoconstriction) and mitogenesis. This study, by the use of immunocytochemically characterized SMC (rVSMC) isolated from the aortas of spontaneously hypertensive rats, has investigated a possible autocrine role for ET in regulation of the vasculature. Although quiescent cultures of rVSMC apparently did not constitutively express prepro ET-1mRNA, ET-specific transcripts could be induced by a variety of growth factors (transforming growth factor beta [TGF-beta]; platelet-derived growth factor-AA homodimer [PDGF-A chain]) and vasoactive hormones (angiotensin II [Ang II], arginine-vasopressin, and ET-1 itself). The kinetics for prepro ET-1mRNA induction in rVSMC were characteristically rapid in onset and transient. Down-regulation of protein kinase C by 48 h pretreatment of rVSMC with phorbol ester markedly reduced the subsequent ability of rVSMC to express ET-1 transcripts and secrete ET-1 peptide in response to Ang II. Inducible prepro ET-1mRNA expression was accompanied by a cycloheximide-inhibitable release of ET-1 peptide into the medium of rVSMC. ET-1 peptide was determined by both radioreceptor- and radioimmunoassay. Stimulated rVSMC accumulated ET-1 (approximately 200 pg.10(6) cells-1 x 4 h-1) at levels that attained biological relevance (approximately 10(-10) M). Sep-pak C18 extracts of medium from stimulated rVSMC elicited contraction of isolated endothelium-denuded rat mesenteric resistance vessels, and this response was characteristically protracted and difficult to "wash out." Synthetic (porcine) ET-1 promoted the expression of transcripts for PDGF-A chain, TGF-beta, and thrombospondin in quiescent rVSMC. Such effects of ET-1 on gene expression may be relevant to the mitogenic potential of ET-1 on VSMC. Our findings imply a role for ET-1 in the control of vascular function via both paracrine and autocrine regulatory mechanisms. The expression of prepro ET-1mRNA and peptide biosynthesis by rVSMC may have both short-term (e.g., vasoconstriction) and long-term (e.g., structural remodeling) consequences. A sustained loop of autocrine stimulation by ET-1 in SMC could contribute toward the pathogenesis of vasospasm and/or atherosclerosis.

Animals↗

PubMed1990

Endothelin messenger RNA and receptors are differentially expressed in cultured human breast epithelial and stromal cells.

Paracrine regulation is implicit in the biosynthesis and secretion of milk in the breast. An important determinant for this regulation in vivo is proximate cellular location as exemplified by stromal and epithelial cells in breast tissue. Cultured human breast epithelial cells exhibited low constitutive expression of mRNA for endothelin which was enhanced 20-fold after prolactin stimulation. Human breast stromal cells did not express measurable levels of endothelin mRNA under similar conditions. In a similar differential manner, the stimulated release of immunoreactive endothelin into medium overlay was observed only for breast epithelial and not stromal cells. Specific cell-surface receptors for endothelin and biochemical responsiveness to the peptide were observed only in the stromal cells.

Breast↗

PubMed1990

Modulation of extracellular matrix by angiotensin II: stimulated glycoconjugate synthesis and growth in vascular smooth muscle cells.

A role for angiotensin II (Ang II) in the pathogenesis of hypertension and atherosclerosis was studied using cultured vascular smooth muscle cells from spontaneously hypertensive rats. Chronic exposure of vascular smooth muscle cells, cultured in the presence of 1% plasma-derived serum, to Ang II resulted in a dose-dependent stimulation in growth and incorporation of radiolabeled matrix precursors into extracellular matrix-associated glycoconjugate material. The hormone also stimulated the incorporation of [3H]glycine into extracellular matrix glycoproteins and proteoglycans synthesized by cultures rendered quiescent by maintenance on serum-free medium for 48 h prior to exposure to Ang II. This was negated in the presence of saralasin. In quiescent cultures, a single exposure to angiotensin induced a rapid induction of mRNA coding for the extracellular matrix glycoprotein thrombospondin. Similar results were obtained with cells maintained on medium containing 1% plasma-derived serum; however, the levels of induction were reduced by this procedure. This study demonstrated that Ang II was capable of stimulating both growth and matrix elaboration by cultured vascular smooth muscle cells. These observations are indicative of a pathophysiological role for the vasoconstrictor peptide, which may contribute significantly to the development of hypertension.

Angiotensin II↗

PubMed1990

Induction of thrombospondin expression in vascular smooth muscle cells by angiotensin II.

Vascular smooth muscle cells (VSMCs), unlike cardiac or skeletal myocytes, are capable of undergoing reversible phenotypic modulation from "contractile" to "proliferative/synthetic" cells in vivo. We have investigated the ability of angiotensin II (Ang II) to influence this process via modulation of extracellular matrix synthesis. Ang II induced a rapid (within 2 h), dose (10(-6)-10(-9) M)-dependent stimulation (14-fold) of thrombospondin (TSP) gene expression in rat VSMCs in the absence of additional factors. This was followed by an enhanced platelet-derived growth factor (PDGF) A chain and transforming growth factor-beta (TGF beta) gene expression. These effects of Ang II could be negated by the simultaneous addition of saralasin (IC50 approximately 10(-9) M for Ang II at 10(-7) M) to cells. Transcription levels for TSP were further enhanced (to 28 X control values) by 6 h, at which time the synthesis of PDGF A chain mRNA was maximal. Although exposure of cells to TSP (5 X 10(-8) M) stimulated signal transduction pathways, it did not enhance levels of either PDGFA or TGF beta transcripts. The glycoconjugate content of extracellular matrices elaborated by cells chronically exposed to Ang II was elevated compared to control cultures and there was a small increase in cell number.

Angiotensin II↗

PubMed1990

Effects of halothane and isoflurane on mean arterial blood pressure, heart rate, and respiratory rate in adult Pekin ducks.

Although the cardiovascular and respiratory effects of halothane and isoflurane have been documented in a variety of common mammalian laboratory animals, they have not been investigated in birds. In this study, the effects of halothane and isoflurane anesthesia on respiratory rate, heart rate, heart rhythm, and mean arterial pressure in adult Pekin ducks were evaluated. Both anesthetics significantly increased heart rate and depressed blood pressure and respiration. Halothane induced a more profound alteration in heart rate and respiratory rate. With the ducks under halothane anesthesia, abnormal cardiac rhythms included ventricular fibrillation, ventricular bigeminy, and multifocal ventricular rhythms. Other than cardiac tachycardia, isoflurane induced no changes in cardiac rhythm.

Anesthesia↗

PubMed1990

Digital processing of equine exercise electrocardiograms.

We have developed and used a system for recording and analyzing the electrocardiogram (ECG) of the horse during exercise. The system consists of a commercial ECG transmitter telemetering a Z lead (base-apex) ECG from an exercising horse. The received data are then remodulated at an audio frequency and stored on a audio cassette recorder. Exercise protocols of up to 10 minutes are digitized using a Macintosh II computer. For rhythm analysis, a computer program to identify the various waves of the ECG uses a modification and refinement of the integrated-squared-derivative (ISD) technique. This technique consists of frequency selective digital filtering and differentiation followed by integration of the squared derivative. The waves of the ECG are identified using adaptive thresholding of the ISD and the derivative of the ECG. Thus far, we have been able to successfully identify the Q, R, and the end of T in ECGs severely contaminated by exercise artifact. The system can place the absolute time of occurrence of the Q, R, and end of T in a text file for export to other analysis programs such as spreadsheets and statistics packages.

Algorithms↗

PubMed1989

Induction of growth-related metabolism in human vascular smooth muscle cells by low density lipoprotein.

Human vascular smooth muscle cells (hVSMC) rendered quiescent by maintenance under serum-free culture conditions for 48 h exhibited several metabolic responses, normally associated with proliferation, following exposure to low density lipoprotein (LDL). LDL induced a time- and dose- (half-maximally effective concentration, ED50 25.0 +/- 8 nM) dependent activation of S6 kinase which could be negated following pretreatment of hVSMC with 12-O-tetradecanoylphorbol-13-acetate (TPA) for 48 h. In myo-[3H]inositol-prelabeled hVSMC, LDL caused a rapid (maximum within 1 min) decrease in phosphatidylinositol 4,5-bisphosphate (35% p less than 0.001) and phosphatidylinositol 4-phosphate (20%, p less than 0.01) with a return to prestimulated levels within 5-10 min. LDL induced a concomitant increase in [3H]inositol phosphates for which the order of generation was inositol-tris greater than -bis greater than -mono phosphate and which reached threshold levels of significance (p less than 0.05) above control values within 1, 2, and 10 min, respectively. The effect of LDL on hVSMC phosphoinositide metabolism was dose-dependent (half-maximally effective concentration, ED50 32.1 +/- 5.0 nM). This concentration, like that for S6 kinase, approximates with the KD (5-21 nM) for high affinity binding of 125I-LDL to specific receptors (1.5 x 10(4) sites/cell) on hVSMC. LDL induced a rapid but transient translocation of protein kinase C from the cytosol to membranes as assessed using both immunoblotting and [3H] 4-beta-phorbol-12-13-dibutyrate-binding procedures. Exposure of quiescent hVSMC to LDL elevated intracellular pH (delta pH 0.30 +/- 0.03, p less than 0.001). Such alkalinization was prevented in the presence of Na+/K+ exchange inhibitors such as amiloride, dimethylamiloride, and ethylisopropylamiloride. In an investigation of the nuclear action of LDL, a time-dependent induction of both c-myc and c-fos was observed. Such LDL-induced expression of these nuclear proto-onco-genes was not detectable in protein kinase C down-regulated hVSMC. Nevertheless, in spite of the cascade of "growth-promotional" responses elicited by LDL in quiescent hVSMC, this lipoprotein alone (under serum-free conditions) was neither mitogenic in nuclear labeling experiments, nor could it support growth of hVSMC in culture. We demonstrate that LDL might function in a complementary/synergistic fashion with other weakly mitogenic (to VSMC) growth factors and suggest that activation of protein kinase C (vis à vis intrinsic tyrosine kinase characteristic of other growth factor receptors) may be crucial to the signal transduction pathway for LDL.

Arterioles↗

PubMed1989

A miniaturized ultrasonic flowmeter and telemetry transmitter for chronic animal blood flow measurements.

An ultrasonic blood flowmeter telemetry system, using only two integrated circuits and one transistor, has been designed for chronic unanesthetized animal studies. Standard components and construction techniques are utilized. The CW Doppler system employs LZT piezoelectric 10 MHZ transmitting and receiving crystals held in a lightweight polystyrene arterial transducer. The audio frequency, FM Doppler signal modulates an FM oscillator-transmitter to produce an FM/FM radio frequency carrier which is transmitted to an FM receiver at a remote location. The transmitted Doppler audio flow signal is demodulated at the receiver by a zero crossing detector. Power consumption is 48 mw. The 12.4 cc package volume can be further reduced for animal implantation.

Animals↗