ISSN:1018-1172    

DOI:10.1159/000158147

出版商:S. Karger AG    

年代:1978

数据来源: Karger

摘要:

It has been reported that the concentration of extracellular magnesium ions ([Mg++]o) can affect blood flow, blood pressure and vascular reactivity in intact mammals. The present studies, using a variety of rat and rabbit blood vessels, were undertaken to shed further light on the relationship between [Mg++]o, Ca++, tone and vascular responsiveness. [Mg++]o was found to differentially affect a variety of hormone and drug-induced contractions in isolated rat and rabbit arteries as well as isolated perfused rat mesenteric arterioles (15–20 µm i.d.). Progressive elevations in [Mg++]o above physiologic levels will dose-dependently produce progressive, increased inhibition of most contractile substances. These results are not reflections of osmolarity. Withdrawal of [Mg++]o can induce contractions of rat arteries as well as of isolated perfused rat mesenteric arterioles. Using isolated rat portal veins, withdrawal of [Mg++] results in rapid enhancement of the spontaneously evoked mechanical responses and increases in rhythmic contractility; these spontaneously evoked responses are abolished in hypermagnesemic solutions (e.g., 10 mM). The contractile responses observed upon withdrawal of [Mg++]o are dependent upon the [Ca++] and the polarity of the membrane but are not related to inhibition of Na+, K+ ATPase. With rat aortic strips, addition of CaEDTA potentiates contractions induced by Mg++ withdrawal, while EGTA promotes rapid relaxations. Rapid relaxations of contractions induced by Mg++ withdrawal in rat aorta could also be induced by Mn++, Ni++, Co++ and Cd++ but not Sr++. Addition of [Ni++] to portal veins exposed either to a Mg++-free solution, or to a solution containing Mg++, results in dose-dependent, and eventual complete, inhibition of all spontaneous mechanical events. These data suggest that [Mg++]o: (a) plays an important role in regulating membrane permeability to [Ca++]o; (b) probably occupies sites which are exchangeable with membrane-bound Ca in arterial, venous and arteriolar smooth muscle; (c) acts intracellularly as well to compete with Ca for certain divalent cation sites; and (d) may play an important role in regulating arteriolar tone and blood pressu

ISSN:1018-1172    

DOI:10.1159/000158148

出版商:S. Karger AG    

年代:1978

数据来源: Karger

摘要:

The frequency response curves (FRC) of isolated blood vessels differ from each other not only in their initial slopes, but in their maxima, and their intercept on the frequency axis. Within the physiological range, there is a linear relation between response and frequency. The FRC of most vessels with junctional innervation are similar, varying only somewhat with innervation density. Other factors found to influence the FRC are: variation in innervation distribution, in the extent of myogenic propagation, and large differences in the sensitivity of the α-adrenergic receptor. The effectiveness of the transmitter increases with frequency rise. The maximum effective radius of the transmitter released from one varicosity is only several microns. In vessels with light to moderate innervation density at low frequencies, there is probably little overlap of transmitter effect from adjacent varicosities even at the outermost layers of smooth muscle cells. There is a disparity between neurogenic response and that which might be expected from the direct action of the transmitter. It is proposed that a local limited myogenic extension of excitation may extend the local action of a quantum of transmitter

ISSN:1018-1172    

DOI:10.1159/000158149

出版商:S. Karger AG    

年代:1978

数据来源: Karger

摘要:

An in vitro preparation from the media of the pig carotid artery develops somewhat higher force/cell cross-sectional area with one-fifth the myosin content of skeletal muscle cells. The following results suggest that this performance reflects cellular properties rather than the arrangement of cells within the tissue: (1) force development at the peak of the length-force curve is independent of the length of the tissue segment in a strip of constant cross-section, and (2) average cell length is directly proportional to tissue length. We conclude that the contractile system of arterial smooth muscle cells is specialized for force generation and that the mechanical properties of the pig carotid media preparation provide valid estimates of cellular function.

ISSN:1018-1172    

DOI:10.1159/000158150

出版商:S. Karger AG    

年代:1978

数据来源: Karger

摘要:

This brief review summarizes the author’s current understanding of the circulatory changes in hypertension. Differences in four important regulatory systems are dependent on structural changes: (1) An increase in wall-to-lumen ratio of precapillary resistance vessels is responsible for an increase in vascular reactivity, or ‘structural autoregulation’. (2) A structural change primarily in the preglomerular arteriole causes a resetting of the pressure required for glomerular filtration. This serves a ‘long-tem barostatic function’. (3) Stiffening of the aorta and other pressure-sensing systems contributes to a resetting of baroreceptors bringing about a reset of the ‘short-term barostats’. (4) Left ventricular hypertrophy causes a decrease in compliance, hence tending to decrease stroke volume for a given filling pressure. Functional changes such as increased neurogenic activity may serve as important ‘trigger’ elements in spontaneously hypertensive rats and at least in one important variant of essential hypertension in the human. An example of a functional alteration in vascular smooth muscle is found in that the vascular resistance response in the spontaneously hypertensive rat in low calcium concentration (0.2 mM) is better maintained than in the normotensive control rat, but this alteration seems to be secondary in nature. An experiment is described which permits simultaneous assessment of the responses of capacitance and resistance vessels to nerve stimulation: when the splanchnic nerves are stimulated there is a simultaneous decrease in venous capacity and an increase in resistance in the liver, gastrointestinal tract and kidneys. The decrease in venous capacity is reflected in an increase in stroke volume whereas the increase in regional resistance is evidenced in an incraese in total peripheral resistance. Using this index the spontaneously hypertensive rats had a less efficient capacitance response (possibly due to the decrease in ventricular compliance) and a greater resistance response than did the normotensive control rat. Although both functional and structural changes in the cardiovascular system occur, the rapidly developed structural changes appear to be the major determinant of the differences between normal and hyperten

ISSN:1018-1172    

DOI:10.1159/000158151

出版商:S. Karger AG    

年代:1978

数据来源: Karger

摘要:

In strips of rabbit main pulmonary artery, full dose-response curves of noradrenaline for the mechanical and electrical responses of the vascular smooth muscle cells were obtained under normal conditions and after increasing and decreasing the membrane potential with strychnine and tetraethylammonium, respectively. The results suggest that the magnitude of the noradrenaline-induced contraction is related to the height of the membrane potential and not to the degree of depolarization produced by the adrenergic transmitter.

ISSN:1018-1172    

DOI:10.1159/000158152

出版商:S. Karger AG    

年代:1978

数据来源: Karger

摘要:

When cyclic nucleotide phosphodiesterase was purified from isolated smooth muscle layer of human aorta by DEAE-cellulose column chromatography, separated cyclic GMP phosphodiesterase activity was markedly stimulated in the presence of 10–20 µM of Ca2+ by a protein modulator which has similar physico-chemical properties to troponin C. Synthetic compound, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide, which produced relaxations of arteries contracted by prostaglandin F2α or KCl was found to inhibit selectively this Ca2+-dependent cyclic GMP phosphodiesterase. This compound produced inhibition of superprecipitation of myosin B system obtained form mouse skeletal muscle and also inhibited adenosine triphosphatase activity of myosin B. Our data suggest that calcium is involved through a protein modulator in cyclic nucleotide metabolism of vascular smooth muscle and that the calcium-dependent protein modulator probably participates in the regulation of contractile response of vascular smooth muscle by affecting actomyosin ATPase activ

ISSN:1018-1172    

DOI:10.1159/000158153

出版商:S. Karger AG    

年代:1978

数据来源: Karger

摘要:

Quick-release and quick-stretch experiments have been performed on preparations of smooth muscle from rat portal vein and rabbit urinary bladder. The low equivalent mass of the isotonic lever (8 mg) implied that inertial oscillations were limited to the first 5–10 msec after the load step. The high time resolution achieved in this way enabled us to separate three components in the length response to a step change in force: (1) an immediate passive elastic recoil, (2) an isotonic velocity transient lasting 50–75 msec and (3) shortening of the contractile element after its full adjustment to the new load. The maximal series elastic recoil was about 10% of the total muscle length in portal vein but only some 3% in urinary bladder. Stiffness of series elasticity increased in proportion to force and was about 3 times higher in bladder than in portal vein at any force level. Force-velocity relations for loads less than Po could be fitted to Hill’s equation; Vmax in 4 AC-stimulated portal veins was 0.53 ± 0.03 muscle lengths/sec and in 8 K+-activated bladder preparations 0.18 ± 0.01 muscle lengths/sec. Application of loads greater than Po produced rates of lengthening greater than expected from an extrapolation of Hill’s hyperbola. The nature of the transient component is discussed in the light of recent studies of force and velocity transients in skelet

ISSN:1018-1172    

DOI:10.1159/000158154

出版商:S. Karger AG    

年代:1978

数据来源: Karger

摘要:

The washout of radioisotopes was studied in aorta, femoral artery and portal mesenteric vein from controls and rats made hypertensive with injection of deoxycorticosterone (DOC) acetate. Experiments were also conducted on tonic (pulmonary artery) and phasic (portal mesenteric vein) smooth muscle from rabbits. The rate constants for the washout of 42K, 36Cl and 24Na from aorta were significantly elevated in the DOC hypertensives. Acute removal of extracellular K slowed the washout of 24Na by 50%, however, the rate constant for the DOC group remained higher than the controls. Increased turnover of 42K was also observed in the femoral artery and in a vessel (portal mesenteric vein) not exposed to the effects of high blood pressure in the rat. The rate constants for the washout of 42K, 36Cl and 24Na from phasic smooth muscle in rabbit were greater than the tonic type. Ouabain significantly slowed 24Na washout, however, the rate constant for the portal mesenteric vein remained higher than the pulmonary artery. DOC hypertension was associated with increased ion transport at several vascular sites. A similar change was observed for the phasic vascular smooth muscle from normal rabbits. A question is raised whether increased spontaneous activity of arteries reported to accompany DOC hypertension is the consequence of a membrane in transition from tonic to phasic behavior.

ISSN:1018-1172    

DOI:10.1159/000158155

出版商:S. Karger AG    

年代:1978

数据来源: Karger

摘要:

6-Hydroxydopamine (6-OHDA) increased the sensitivity of rat, rabbit and guinea pig portal veins to norepinephrine (NE), methoxamine (ME), barium (Ba++) and calcium (Ca++) but not to potassium (K+). Reserpine potentiated the responses of NE, ME and Ca++ but not Ba++ or K+ in rabbit and guinea pig veins and did not alter the sensitivity of rat veins to all agonists tested. Cocaine only potentiated the NE responses of the veins and decreased the sensitivity of rabbit and guinea pig veins to K+. 6-OHDA increased 45Ca-influx in all veins whereas reserpine increased 45Ca-influx only in rabbit and guinea pig veins. Cocaine failed to increase 45Ca-influx in all veins tested. NE, ME and K+ increased 45Ca-influx in the veins from the different animals. The agonist-induced 45Ca-influx was greater in most of the supersensitive veins than in the control veins. In veins that failed to develop supersensitivity, agonist-induced 45Ca-influx did not differ from that of the control veins. It is concluded that the development of super- and subsensitivity exhibits species variation and that the alteration in Ca++ influx would be consistent with the changes in sensitivity of the venous smooth muscle.

ISSN:1018-1172    

DOI:10.1159/000158156

出版商:S. Karger AG    

年代:1978

数据来源: Karger