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Biomedical subjects

P Friberg

Publications and source records attributed to P Friberg.

At least 127 records · Page 7Linked to original sources
PubMed1991

Abundance and chemistry of interstellar HOCO+.

We derive HOCO+ column densities approximately 10(15) cm-2 toward the Galactic center and < or = 10(12) cm-2 for cold dark clouds from observations and an LVG model. We mapped the HOCO+ 4(04)-3(03) line toward Sgr A. The fractional abundance of HOCO+ in the Galactic center region is three orders of magnitude larger than predicted by quiescent ion-molecule chemistry and an order of magnitude larger than predicted by a MHD shock model. If HOCO+ traces interstellar CO2, the implied high abundance ([CO2] approximately [CO]) in the Galactic center may result from UV photolysis of grain mantles.

Astronomical Phenomena↗
PubMed1990

Interstellar cyanomethane.

We have made an observational study of the newly identified cyanomethane radical CH2CN and the possibly related species CH3CN with the goals of (1) elucidating the possible role of reactions of the type CnHm(+) + N in astrochemistry, and (2) providing a possible test of Bates's models of dissociative electron recombination. We find a remarkably different abundance ratio CH2CN/CH3CN in TMC-1 and Sgr B2, which we deduce is a result of the large difference in temperature of these objects. Studies of CH2CN and CH3CN in other sources, including two new detections of CH2CN, support this conclusion and are consistent with a monotonic increase in the CH2CN/CH3CN ratio with decreasing temperature over the range 10-120 K. This behavior may be explained by the destruction of CH2CN by reaction with O. If this reaction does not proceed, then CH2CN and CH3CN are concluded to form via different chemical pathways. Thus, they do not provide a test of Bates's conjectures (they do not both form from CH3CNH+). CH2CN is then likely to form via C2H4(+) + N --> CH2CNH+, thus demonstrating the viability of this important reaction in astrochemistry. The T dependence of the CH2CN/CH3CN ratio would then reflect the increasing rate of the C2H4(+) + N reaction with decreasing temperature.

Acetonitriles↗
PubMed1990

Cardiac and vascular structural adaptation in experimental hypertension.

Various colonies of the spontaneously hypertensive rat (SHR) of the same age demonstrate different forms of the left ventricle (LV) in end-diastole. SHR from breeders in Australia and Switzerland exhibit concentrically hypertrophied LV, evident from an increased wall thickness to internal radius ratio (w/ri), while SHR from a Danish colony show an unchanged w/ri ratio, indicating eccentrically hypertrophied LV. These differences may be related to changes in arterial blood pressure and/or altered cardiac filling patterns. A more favourable situation seems to prevail for the eccentrically hypertrophied SHR heart compared with the concentrically hypertrophied heart, the former demonstrating enhanced cardiac function. Thus, an LV with increased diastolic diameter, as in the eccentrically hypertrophied SHR heart, can produce an elevated stroke volume for a given degree of myocardial shortening. In renal hypertension, however, LV function was depressed, probably due to a factor, possibly released upon clipping of the renal artery, that has inherent negative inotropic properties. Here, the reduction of LV performance could be explained neither by the changed LV geometrical design nor by the altered myocardial myosin isoenzyme pattern. At low aortic pressures and hence limited coronary perfusion, LV performance is attenuated in SHR and renal hypertensive rats, most likely due to the vascular structural changes within the coronary vascular bed.

Animals↗
PubMed1990

Evidence for increased renal norepinephrine overflow during sodium restriction in humans.

To investigate the differentiated pattern of efferent sympathetic nerve activity by means of analyzing norepinephrine kinetics in response to sodium restriction, cardiorenal sympathetic activity during rest and mental stress was studied in 12 subjects (33.3 +/- 2.6 years old, SEM) exposed to a low and a normal sodium diet; 5-40 mmol and 160-200 mmol/24 hours, respectively (crossover design). Organ norepinephrine release was calculated from organ plasma flow, arteriovenous plasma concentration gradient across the organ and the organ's fractional extraction of radiolabeled norepinephrine. Body weight and urinary sodium/24 hr fell significantly and urinary potassium/24 hr and both supine and standing blood pressure remained unchanged. Total norepinephrine release to plasma and norepinephrine plasma clearance were similar in both phases (approximately 460 ng/min and 1.90 l/min, respectively). A 138% increase in renal norepinephrine overflow was observed during sodium restriction (from 112 to 267 ng/min, p less than 0.025), which was due to elevated renal vein norepinephrine (434 versus 290 pg/ml, p less than 0.01) because renal plasma flow and renal norepinephrine extraction were unaltered. Similarly, sodium restriction caused a 168% elevation of renal renin secretion (p less than 0.05). Resting cardiac norepinephrine spillover and cardiac norepinephrine reuptake were unchanged between the two salt phases. Total and cardiac norepinephrine release, supine blood pressure, and heart rate increased to about the same extent in response to mental testing regardless of salt phase. In conclusion, sodium restriction induced a differential and physiological increase in resting renal sympathetic nervous activity, leaving cardiac norepinephrine overflow unchanged. Cardiac norepinephrine uptake was normal, which further supports the concept of a true increase of efferent renal nerve activity.

Adult↗
PubMed1990

Effect of endurance exercise on cardiac secretion and renal clearance of atrial natriuretic peptide in normal humans.

Previous work from our laboratory has shown that (i) regular endurance exercise lowers blood pressure (BP), and (ii) acute exercise increases circulating levels of atrial natriuretic peptide (ANP). We hypothesised that increased ANP release may contribute to the antihypertensive effect of regular exercise. Using arterial and selective venous (coronary sinus and renal vein) catheterization and sampling, we measured cardiac secretion and renal clearance of ANP at rest in 7 normal healthy males (mean age 36 years), before and after 4 weeks of training. Body weight and haematocrit remained unchanged. Systolic BP fell by 10 mmHg with training (p = 0.008), diastolic BP fell by 6 mmHg (p = 0.006) and heart rate decreased by 9 beats/minute (p = 0.002), but central venous pressure remained unchanged. Arterial, coronary sinus and renal vein ANP concentrations did not change with training. There was no significant rise in cardiac secretion of ANP with training (sedentary: 42.6 +/- 13.2 ng/ml, trained: 47.4 +/- 17.9 ng/ml, p n.s.). Renal extraction of ANP was 72 +/- 4% before training, and unchanged (66 +/- 5%) after the exercise period. Renal clearance of ANP was also unaltered by training (514.2 +/- 48.4 ml/min before, and 508.9 +/- 74.8 ml/min after training, p n.s.). We conclude that as ANP release is not increased by training, the peptide does not account for the anti-hypertensive effect of endurance exercise. Other humoral and/or neural mechanisms possibly mediate the beneficial haemodynamic effects of training.

Adult↗
PubMed1990

Detection of formic acid in the cold, dark cloud L134N.

We report the first detection of formic acid (HCOOH) in a cold, dark interstellar cloud (L134N). The observed abundance of 3x10(-10) relative to H2 is between one and two orders of magnitude lower than that calculated by published ion molecule models of dark cloud chemistry, but is quite consistent with recent model revisions based on new reaction rates. Formic acid was not detected in the archetypical dark cloud TMC-1, and was tentatively detected in the region of massive star formation, W51.

Astronomical Phenomena↗
PubMed1989

Interstellar SiO as a tracer of high-temperature chemistry.

The J = 2-1 transition of SiO has been searched for toward both hot and cold molecular gas. SiO was not detected toward the dark clouds TMC-1, L134 N, and B335, down to column density upper limits of N < 2-4 x 10(10) cm-2. The species, however, has been observed toward all sources with a kinetic temperature greater than or equal to 30 K, with the largest column densities (N approximately 10(13)-10(17) cm-2) measured in the warmest (TK > or = 100 K) material. The abundance of SiO, relative to HCN, is found to be approximately 0.1-1 in the massive star-forming regions toward Orion and NGC 7538; toward the dark clouds, the upper limits to this ratio is less than 0.0002-0.004. A similar enhancement in the warmer regions is reflected in the SiO/H2 ratio as well. A linear relation was found between the natural log of the SiO concentration and 1/TK, suggesting that the species' formation involves a chemically specific process that contains an activation barrier of approximately 90 K. SiO was also found to be underabundant with respect to SO in cold clouds, with SiO/SO < 1/1000, versus SiO/SO > or =, measured in Orion-KL. The formation of SiO is therefore linked closely to the local gas kinetic temperature, rather than the oxygen abundance, and its synthesis is likely to involve high-temperature gas-phase reactions. The species thus may serve as an unambiguous indicator of high-temperature or "shock" chemistry.

Astronomical Phenomena↗
PubMed1989

Observations of some oxygen-containing and sulfur-containing organic molecules in cold dark clouds.

Observations of nine oxygen- and sulfur-containing organic molecules have been made toward the cold dark clouds TMC-1 and L134N. We have confirmed the presence of para-ketene (H2C2O) in TMC-1, have for the first time observed ortho-ketene, and find a total ketene column density approximately 1 x 10(13) cm-2. Thioformaldehyde (H2CS) is easily detectable in both TMC-1 and L134N, with a column density about 5 times larger in the former source (approximately 3 x 10(13) cm-2). The fractional abundance of ketene is comparable to the predictions of ion-molecule chemistry, while that of thioformaldehyde in TMC-1 is one to two orders of magnitude greater than that expected from such models at steady state. Interstellar sulfur chemistry thus continues to be poorly understood. We set upper limits for the column densities of formic acid (HCOOH), vinyl alcohol (CH2CHOH), methyl formate (HCO2CH3), formamide (NH2CHO), methyl mercaptan (CH3SH), isothiocyanic acid (HNCS), and thioketene (H2C2S) in both sources.

Astronomical Phenomena↗
PubMed1989

Cardiac secretion and renal clearance of atrial natriuretic peptide in normal man: effect of salt restriction.

1. Previous studies of endogenous atrial natriuretic peptide (ANP) in humans have examined changes in plasma levels, rather than regional secretion and clearance of the peptide. Using arterial and selective venous catheterization and sampling, and measurement of regional organ flow, we measured haemodynamics, cardiac secretion of ANP and renal clearance of ANP in six healthy volunteers at rest, on a normal sodium diet. 2. Salt restriction decreases plasma concentrations of ANP. We assessed the contribution of the heart and kidney to this decrease, by measuring cardiac secretion and renal clearance of ANP at the termination of a low salt diet. 3. Twenty-four hour urinary sodium excretion fell on the low salt diet from 163 to 29 mmol/day [standard error of the difference (SED)+/- 14, P less than 0.001]. Body weight decreased on salt restriction from 76.4 to 75.4 kg (SED +/- 0.33, P less than 0.05). Brachial mean arterial pressure fell by 6% (P less than 0.05), but right atrial pressure was unchanged. Renal vein plasma renin activity increased by 56% with sodium restriction (P less than 0.01), whereas arterial ANP concentrations fell by 39% (P less than 0.05). 4. Coronary sinus ANP levels fell from 417 to 268 pg/ml (SED +/- 74, P less than 0.05), whereas renal vein concentrations were unaltered. There was a 47% decrease in cardiac secretion of ANP in the low salt state (P less than 0.05). Net extraction of ANP across the kidney (about two-thirds) and renal clearance of ANP were unchanged on the low salt diet. Thus decreased plasma ANP with sodium restriction is due to reduced cardiac secretion.

Adult↗
PubMed1989

A survey of cyclopropenylidene (C3H2) in galactic sources.

We report the results of an initial survey in a variety of Galactic sources for cyclopropenylidene (C3H2), the first interstellar hydrocarbon ring molecule. C3H2 is found to be very widespread throughout the Galaxy. This, together with its large dipole moment and many observable transitions, makes cyclopropenylidene a promising probe for physical conditions in the interstellar medium. The ortho 1(10)-1(01) transition at 18 GHz is detected in a variety of environments, including giant molecular clouds, diffuse clouds, cold dark clouds, the spiral arm clouds in the direction of distant continuum sources, and the envelope of the carbon star IRC + 10216. The 2(20)-2(11) para line at 21.6 GHz was surveyed in many sources having strong 1(10)-1(01) emission, and, when detected, it was always seen in absorption. A more limited survey of the ortho 2(12)-1(01) transition at 85.3 GHz has been conducted. In addition, the 2(11)-2(02) line of the para species at 46.8 GHz was detected in the dark clouds TMC-1 and L134N. Maps have been made of the clouds TMC-1, L134N, W51, and Orion, confirming that the C3H2 emission is extended in these objects. The data obtained thus far suggest that C3H2 is one of the more abundant organic constituents of the dense interstellar medium.

Astronomical Phenomena↗
PubMed1989

Autonomic control of the diurnal variation in arterial blood pressure and heart rate in spontaneously hypertensive and Wistar-Kyoto rats.

The relative influences of sympathetic and parasympathetic neural modulation on mean arterial pressure (MAP) and heart rate (HR), and their respective variabilities, were studied in young spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). An on-line computerized system was used for continuous intra-arterial measurements of MAP and HR in unrestrained rats. In addition, the autonomic nervous control of MAP and HR was studied in ageing SHR and WKY. Both WKY and SHR showed diurnal rhythms with regard to MAP and HR. The MAP variability was higher in SHR than in WKY during both daytime (inactive) and night-time (active), and did not change in response to either beta 1-adrenoceptor- or cholinergic blockade. Structural vascular changes, with a resultant increase in reactivity, may explain the elevated MAP variability in SHR. HR variability was clearly reduced in SHR; this was not influenced by vagal blockade, whereas HR variability was significantly reduced in WKY. This pattern is suggested to be due to a reduced tonic vagal discharge in SHR, as part of a persistent, mild defence reaction. The initial reduction in vagal activity will in turn eliminate vagally mediated tachycardias. Furthermore, administration beta 1-blockade to SHR of different ages caused a greater fall in MAP and HR than in WKY, indicating an increased dependence upon the sympathetic nervous system in SHR with age.

Animals↗
PubMed1989

Functional and biochemical analyses of isolated rat hearts in renal and reversed renal hypertension.

The present study evaluates cardiac function, plasma renin activity (PRA) and left ventricular (LV) myosin isoenzymes in untreated two-kidney, one-clip Goldblatt hypertensive rats (2KIC) and in 2KIC treated with felodipine and metoprolol. Normotensive rats (NCR) and another group of 2KIC, in which the renal artery constriction was removed (UC-2KIC), were also investigated. Cardiac performance was assessed by means of a working heart perfusion device, allowing also for measurements of myocardial oxygen consumption. Following antihypertensive therapy and unclipping, blood pressure became close to normotensive levels. PRA remained equally elevated in treated and untreated 2KIC, but became practically normalized after unclipping. Relative LV weight in 2KIC increased 74% above that in NCR but in treated 2KIC increased by only 20%. In UC-2KIC LV hypertrophy became reversed, LV weight/body being about the same as in treated 2KIC. In treated 2KIC, coronary resistance at maximal dilatation was significantly reduced, implying prevention of hypertensive, structural coronary vascular changes, and optimal LV function was improved markedly in the lower range of perfusion pressures compared with untreated 2KIC. When, however, the hearts were challenged at a high pumping resistance (perfusion pressure), LV function was similar in untreated and treated 2KIC. Myocardial oxygen consumption for given levels of stroke work was significantly lower in treated than in untreated 2KIC. The myosin isoenzyme pattern in the LV of 2KIC was shifted, with significantly higher amounts of VM-3 than in NCR. This shift was normalized by antihypertensive therapy or by unclipping. In conclusion, antihypertensive therapy with felodipine and metoprolol prevents the development of coronary vascular and left ventricular hypertrophy in 2KIC. This may contribute to enhance cardiac performance at low aortic pressure. The lack of improvement in optimal cardiac performance (at high aortic pressure) implies that the hypertensive state per se, rather than extent of pressure elevation, cardiac hypertrophy, or changes of LV isoenzymes, determines the reduced cardiac function in renal hypertensive rats (Friberg & Nordborg 1986).

Animals↗
PubMed1989

Electrophysiological and mechanical characteristics of isolated hearts from spontaneously hypertensive (SHR) and normotensive (WKY) rats on very high- and low-sodium diets.

Electrophysiological, mechanical, dimensional and coronary flow characteristics were studied on papillary strips and on isolated hearts, from spontaneously hypertensive (SHR) and normotensive (WKY) rats respectively, which from 5 to 15 weeks of age had been on either 'low' (LNa, 0.5 mmol 100 g-1 food), control (CNa, 5) 'high' (HNa, 50) or 'very high' (vHNa, 120) sodium diets. With respect to cardiac electrophysiological characteristics, contractility, and maximal stroke volume capacity only minor, if any, differences were observed between the various Na diet groups, both in WKY and SHR. This is in accordance with our earlier findings concerning vascular smooth muscle, where a largely unchanged sensitivity and responsiveness to, for example, noradrenaline was noted. Further, only to the extent that the various Na diets had also caused changes in average blood pressure levels, adaptations of cardiac and coronary resistance vessel design were observed, in general agreement with our earlier findings in other preparations and experimental designs. The largely unaffected functional characteristics of cardiac as well as vascular effector cells, despite 240-fold long-term variations in sodium intake, are in sharp contrast to the marked changes that have been shown to affect the adrenergic nerves, as here chronic low-Na intakes cause reductions of transmitter release/impulse, and vice versa at high Na intakes. This latter type of change seems to be by far the most important functional deviation affecting cardiovascular control during long-term alterations of sodium intake, as it can markedly affect both cardiac and vascular influences on haemodynamics, even though the respective effector functions seem to be surprisingly little influenced directly.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Resistance control in hypertension.

In hypertension the small arteries undergo structural changes that increase vascular resistance, both in vivo and in vitro. The hallmark of a physiological vascular amplifier is that enhanced resistance responses must occur about the resting value. For this to happen, the average radius of the resistance vessels must be narrower than normal; increased wall thickness without narrowing does not result in this type of amplification. In primary hypertension in spontaneously hypertensive rats (SHR), the structural changes in the resistance vessels precede the elevation in blood pressure. This is consistent with the hypothesis that these changes cause hypertension. The role of the sympathetic nervous system in early vascular development is unclear, in view of the absence of regression of amplifier properties in the hindlimb vessels after extensive immunosympathectomy. However, short periods of enalapril treatment in young animals attenuate the development of hypertension and normalize hindlimb resistance properties, suggesting that the renin-angiotensin system may have a role in early vascular growth. Studies in tissue culture suggest that both systems could play a role in smooth muscle growth, in conjunction with growth factors such as platelet-derived growth factor (PDGF)-like peptides and endothelin. The early structural change that occurs in hypertension is probably a variant of normal development of the resistance vasculature, with greater secretion of 'normal' growth factors and/or enhanced responsiveness of the vascular smooth muscle.

Animals↗
PubMed1988

A new interstellar polyatomic molecule: detection of propynal in the cold cloud TMC-1.

We report the detection of the acetylene derivative propynal (HC triple bond CCHO) in the cold cloud TMC-1, with an abundance that is very close to that for the related species tricarbon monoxide (C3O). Propadienone, an isomer of propynal with the formula H2C=C=C=O, was not detected and is hence less abundant than either C3O or HC2CHO.

Aldehydes↗
PubMed1988

Identification of the interstellar cyanomethyl radical (CH2CN) in the molecular clouds TMC-1 and Sagittarius B2.

We report the astronomical identification of the cyanomethyl radical, CH2CN, the heaviest nonlinear molecular radical to be identified in interstellar clouds. The complex fine and hyperfine structures of the lowest rotational transitions at about 20.12 and 40.24 GHz are resolved in TMC-1, where the abundance appears to be about 5 x 10(-9) relative to that of H2. This is significantly greater than the observed abundance of CH3CN (methyl cyanide) in TMC-1. In Sgr B2 the hyperfine structure is blended in the higher frequency transitions at 40, 80, and 100 GHz, although the spin-rotation doubling is clearly evident. Preliminary searches in other sources indicate that the distribution of CH2CN is similar to that for such carbon chain species as HC3N or C4H.

Acetonitriles↗
PubMed1988

Diastolic characteristics and cardiac energetics of isolated hearts exposed to volume and pressure overload.

The relation between diastolic dimensions and systolic function was studied in isolated rat hearts exposed to pressure (primary hypertension) and to volume load (hyperthyroidism). The hearts were arrested in diastole and cardiac dimensions analysed. Cardiac function was determined using an anterograde working heart preparation. Both models of cardiac overload produced significant left ventricular hypertrophy, however with different design. One concentric and one eccentric form of left ventricular hypertrophy were found in the spontaneously hypertensive rat obtained from two different breeders. An even more pronounced form of eccentric left ventricular hypertrophy was seen in hyperthyroid rats. The hearts with an eccentric form of hypertrophy had a higher maximal stroke volume when perfused at a high aortic pressure than those with a concentric form. At a low aortic pressure and hence a limited coronary perfusion cardiac performance was diminished in both types of spontaneously hypertensive rats but remained normal in hyperthyroid rats. Furthermore, oxygen consumption was reduced in all hypertrophied hearts compared with non-hypertrophied hearts. These data therefore suggest (a) that hearts having an eccentric type of hypertrophy may be in a more favourable situation, delivering a higher stroke volume for a given degree of myocardial fibre shortening; and (b) that the development of coronary vascular structural changes in spontaneously hypertensive rats, thereby increasing vascular resistance, leads to a decrease in left ventricular function at a low coronary perfusion pressure, whereas no such reduction was observed in hyperthyroid hearts, probably owing to a normal vascular resistance.

Animals↗