ISSN:0009-7330    

出版商:OVID    

年代:1974

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

The uptake of3H-l-norepinephrine was examined in isolated perfused rat lungs, and the mechanism of uptake was compared with that previously found for 5-hydroxytryptamine. Most of the norepinephrine taken up by the lungs was rapidly deaminated and O-methylated, and the metabolic products were subsequently returned to the perfusate. The presence of iproniazid and tropolone markedly inhibited this metabolism; because the metabolites were released from the lungs more rapidly than was norepinephrine itself, these inhibitors appeared to increase the rate of uptake of the amine. The uptake of norepinephrine was a saturable, temperature-dependent process with aKmof 1.11 × 10−6M and aVmaxmeasured during metabolic inhibition of 2.78 × 10−9moles/g min−1. Uptake was inhibited by cocaine, imipramine, ouabain, and potassium-free medium as well as by decreasing the sodium concentration or increasing the potassium concentration of the medium. Although normetanephrine reduced the uptake of norepinephrine, metaraminol had no effect. Autoradiography indicated that norepinephrine was taken up into endothelial and smooth muscle cells, but the mechanism of the uptake appeared to combine features characteristic of both extraneuronal and neuronal uptake. The mechanism of uptake of norepinephrine by the lungs is compatible with a sodium-dependent, carrier-mediated transport, but several differences appear to exist between the transport and the site of uptake of norepinephrine and 5-hydroxytryptamine.

ISSN:0009-7330    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

The vasoactive properties of hypoxia, elevated extracellular potassium concentration ([K]o), and hyperosmolarity were studied in helical strip preparations of small coronary and deep femoral arteries (260–700 μm, o.d.) equilibrated in a physiological salt solution with an oxygen tension (Po2) of 100 mm Hg, [K]oof 3.18 mM, and an osmolarity of 304 milliosmoles/liter. Increasing [K]o(2–6 mM) or osmolarity (30–50 milliosmoles/liter) produced relaxation of resting tension in 50% of the coronary strips but had no effect on resting tension in deep femoral strips. Sustained increments in [K]oor osmolarity produced concentration-dependent, transient relaxation of aganist-induced contractile tension in both coronary and deep femoral arterial strips: a potassium increment of 4 mM produced 40% relaxation with 100% recovery within 5–6 minutes, an osmotic increment of 30 milliosmoles/liter caused 20–40% relaxation with 100% recovery within 15–60 minutes, and simultaneous potassium (4 mM) and osmotic (30 milliosmoles/liter) increments produced 85–95% relaxation with 100% recovery within 10–15 minutes. Decreasing Po2from 100 mm Hg to 10 mm Hg resulted in a sustained 35–40% fall in agonist-induced contractile tension. Although a nonspecific additive interaction was observed during a simultaneous change to high [K]o, hyperosmolarity, and hypoxia, for any given level of vascular tone hypoxia had little or no effect on the degree or the duration of the tension relaxation-recovery sequence produced by elevated [K]o, hyperosmolarity, or both. Therefore, it is proposed that hypoxia is the only one of these three factors that, by a direct interaction with vascular smooth muscle cells, can contribute to sustained vasodilation of small arteries in rabbit cardiac or skeletal muscle.

ISSN:0009-7330    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

The formation of cholesteryl ester in aortic tissue was studied using subcellular fractions from normal and atherosclerotic rabbit and rhesus monkey aortas. The properties of two enzyme systems capable of esterifying 1-14C-oleic acid into cholesteryl ester in vitro were investigated, and increased activity was demonstrated for both systems as a result of cholesterol feeding. Microsomal preparations were used to study the ATP, CoA-dependent esterification which involves two enzymes, fatty acyl CoA synthetase and fatty acyl CoA: cholesterol acyltransferase. The properties of both enzymes were investigated, and an increase of about fourfold in activity of the acryltransfrease was demonstrated in aortic microsomes as a result of cholesterol feeding for 3–6 months. Esterification of oleic acid into cholesteryl ester by aortic high-speed supernatant fractions at an acidic pH was also observed; the enzyme system involved did not require cofactors, and its activity greatly increased as a result of cholesterol feeding. Similar increases in the activity of both esterifying enzyme systems were found when normal and atherosclerotic rhesus monkey aortic fractions were compared.p-Chlorophenoxyisobutyrate (CPIB) and 2-methyl-2-[p-(1, 2, 3, 4-tetrahydro-l-naphthyl)-phenoxy]propionic acid (TPIA) produced inhibition of both cholesterol-esterifying enzyme systems. TPIA was a more effective inhibitor than CPIB on both enzyme systems by at least an order of magnitude. These studies suggest that increased intracellular synthesis of cholesteryl ester by aortic tissue may contribute to its accumulation in atherosclerosis.

ISSN:0009-7330    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

With electromagnetic flow transducers and pneumatic cuff occluders on the circumflex branch of the left coronary artery in conscious and in anesthetized dogs, we examined the effects of both a temporary reduction in postocclusion hyperemia and one- and two-cardiac cycle occlusions of the artery on the size and the duration of the hyperemic response. After release of 8-second occlusions, flow was prevented from rising to more than 10–20% above the preocclusion value for the expected duration of the hyperemia. Peripheral coronary arterial pressure measurements established that this maneuver produced a pressure gradient. Temporary restriction of arterial inflow markedly reduced the percent repayment of the flow deficit from 618 ± 34± to 213 ± 17% (mean ± SE) and moderately prolonged the duration of the response from 95 ± 4 seconds to 129 ± 5 seconds (P< 0.0005 for both). In conscious dogs, the mean percent repayment after a one-cycle (0.7-second) occlusion was 227%. Much larger and longer-lasting responses were obtained with one-cycle (0.4-second) occlusions in anesthetized dogs in which heart rate and blood pressure were considerably higher. Since restricting arterial inflow resulted in a large reduction in reactive hyperemia with only a small increase in its duration, local mechanisms acting in the interstitial space and possibly in the vascular smooth muscle may be relatively more important for the hyperemia that occurs after short occlusions than is the myocardial release of freely diffusible metabolites that are removed by the blood stream. The results with one- and two-cycle occlusions suggest that myogenic responses contribute to the hyperemia, since it is unlikely that such brief occlusions produce myocardial hypoxia under resting conditions.

ISSN:0009-7330    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Canine plasma lipoproteins were fractionated into four distinct classes by ultracentrifugation combined with Geon-Pevikon block electrophoresis and characterized with respect to physical and chemical properties. The distribution of plasma lipids and lipoproteins was quite unlike that in man, the dog having approximately five to six times as much high density as lower density lipoproteins. Despite the marked difference in distribution, human lipoprotein equivalents were present. Very low density lipoproteins (VLDL) isolated at density less than 1.006 g/ml were triglyceride-rich particles ranging in size from 260 to 900 Å in diameter. The density range from 1.006 to 1.063 g/ml contained two classes of lipoproteins: one closely resembled aolow density lipoprotein (LDL) with β mobility and a particle size of approximately 200 Å and the other (called HDL1) was closely related to the high density lipoproteins with respect to immunochemical reactivity, electrophoretic mobility, and apoprotein content. The HDL1particles ranged in size from 100 to 350 Å in diameter and appeared to be unlike any of the commonly described human lipoproteins. High density lipoproteins called HDL2isolated in the density range from 1.087 to 1.21 g/ml were protein-rich particles ranging in size from 55 to 85 Å. The apolipoprotein patterns of VLDL, LDL, and HDL2on polyacrylamide gel electrophoresis were similar to those of the corresponding lipoproteins of man.

ISSN:0009-7330    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Characterization of the hyperlipoproteinemia induced by feeding high-cholesterol diets to hypothyroid dogs was undertaken in an attempt to identify a lipoprotein pattern or a specific lipoprotein responsible for the atherosclerosis associated with such hyperlipoproteinemia. Various degrees of hyperlipidemia and atherosclerosis were produced during the diet, which was imposed for 3 months to more than a year. Dogs referred to as hyporesponders did not develop significant atherosclerosis despite plasma cholesterol levels ranging from two to five times normal or up to 750 mg/100 ml. This nonatherogenic hyperlipidemia was characterized by an increase in the LDL (low density lipoprotein) and HDLcclasses (HDLcrefers to a broad spectrum of cholesterol-enriched particles which resemble high density lipoproteins). Dogs referred to as hyperresponders developed significant and often complicated atherosclerosis. Their plasma cholesterol levels were in excess of 750 mg/100 ml, and most of the increased cholesterol was present in lipoproteins with density less than 1.006 g/ml. Several classes of lipoproteins were isolated by ultracentrifugation and purified by Geon-Pevikon block electrophoresis. These lipoproteins were characterized with respect to chemical composition, electrophoretic mobility, immunochemical reactivity, electron microscopic size after negative staining, and apoprotein content as determined by polyacrylamide gel electrophoresis. We concluded that the atherogenic hyperlipidemia of the hyperresponders was characterized by an increase in the amount of cholesterol-rich HDLcas in the hyporesponders but was distinguished by the appearance of a spectrum of cholesterol-rich lipoproteins in the fraction with a density less than 1.006 g/ml. One of these cholesterol-rich lipoproteins had the properties of β very low density lipoproteins, and the others had those of HDLc. We suggest that the spectrum of lipoproteins with density less than 1.006 g/ml represents “remnants” that accumulate because of defective catabolism of lipoproteins synthesized to carry excess of dietary cholesterol.

ISSN:0009-7330    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Studies were performed to substantiate the hypothesis that a physiological change, apart from the rise in blood pressure, occurs in two-kidney hypertensive rats. Both the slow development of hypertension following renal arterial constriction versus its rapid reversal following removal of the constriction and the early increase in plasma renin activity which subsides in the chronic hypertensive phase suggest such a progressive change. We studied the development of hypertension following initial renal arterial constriction (clipping) and after reclipping in rats that had been relieved of two-kidney hypertension by unclipping for 2 or 21 days. Full hypertensive blood pressure levels were established within 1–2 hours after reclipping in 2-day unclipped rats, but similar levels were not reached in either of the other two groups for at least 1 week. These changes in response to renal arterial constriction were paralleled by differences in responsiveness to hog renin and angiotensin infusions. Plasma renin activity 1 hour after clipping or reclipping was adequate to account for the observed blood pressure increases in all groups. These data suggest that (1) a physiological change resulting in increased vasoresponsiveness to renin and angiotensin occurs concomitantly with the development of two-kidney hypertension and (2) this type of hypertension is dependent on both renin and increased sensitivity to angiotensin. Moreover, we suggest that study of recently unelipped, normotensive rats may help to uncover the causes for the angiotensin sensitivity change.

ISSN:0009-7330    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

The frequency-response curve of isolated canine arterial segments at transmural pressures between 140 and 40 mm Hg showed an initial constant-amplitude portion over the lower frequency range followed by one or two major amplitude peaks (resonances) at higher frequencies. At lower transmural pressures, the response was more damped and resonances were infrequent. The amplitude of the flat portion of the curve increased as transmural pressure was decreased, and thus the dynamic modulus of elasticity calculated at 10 Hz decreased. The static modulus behaved in a similar fashion, but it was always lower than the dynamic modulus. The resonances shifted to lower frequencies as transmural pressure was decreased, and thus the dynamic modulus of elasticity calcuwall stiffness. Two series of five arteries each were examined; in one series the arteries were mounted with a fixed 50% longitudinal elongation and in the other series they were mounted with variable, mean 85%, longitudinal elongations. The difference between the two series suggests that increasing longitudinal elongation markedly increases the frequency shift induced by transmural pressure of one of the resonances and may result in coincidence of the two resonances at a given transmural pressure which varies from artery to artery.

ISSN:0009-7330    

出版商:OVID    

年代:1974

数据来源: OVID