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Biomedical subjects

B Ljung

Publications and source records attributed to B Ljung.

At least 55 records · Page 3Linked to original sources
PubMed1977

Oxygen consumption and contractile force during vibrations of cat soleus muscle.

The influence of longitudinal vibrations (50 Hz, 0.4 mm) on isometric twitch force development (4 Hz), blood flow and oxygen consumption was studied in the acutely denervated soleus muscle of the anesthetized cat. It was found that the sinusoidal vibrations reduced the twitch amplitude by 60 per cent whereas oxygen consumption and blood flow were lowered by 15 per cent only. Similar reduction in twitch force was also obtained by lowering the nerve stimulation intensity (4 Hz). This was associated with a diminution in oxygen consumption, the degree of which was linearly related to the attenuation of active force, i.e. the number of activated motor units. The results are in agreement with previous observations as to the mechanical effect of vibrations on active force in smooth and striated muscle. They demonstrate that vibrations prevent the contractile response with maintained high oxygen consumption which adds further support to the hypothesis forwarded by Joyce et al. (1969) that vibrations cause increased rate of detachment of actin-myosin cross-links. In addition it appears possible that vibrations to some extent prevent formation of such cross-links.

Animals↗
PubMed1977

Contractility, muscle mass and agonist sensitivity of isolated portal veins from normo- and hypertensive rats.

Properties of the longitudinal smooth muscle of portal veins from normotensive Wistar rats, adult (NCR) and young (NCRy); spontaneously hypertensive Okamoto rats, adult (SHR) and young (SHRy); and adult Wistar rats with renal hypertension (RHR) were studied in vitro and histologically. Some aortic strips from SHR and SHRy were compared with controls. In response to noradrenaline (NA) and acetylcholine (ACh) greater maximum force was developed by veins from all hypertensive groups than by those from control rats. Cross-sectional area of the longitudinal muscle of veins from SHR but nor SHRy nor RHR was greater than control. Maximum stress in response to agonists was greater in both SHR and RHR than NCR. ED50-values for NA and ACh were lower in portal veins from SHR than NCR but not from RHR nor SHRy compared to controls. Denervation did not abolish any of the differences between SHR and NCR. Aortic strips from SHR developed less maximum force to NA and ED50 was greater than those from NCR, i.e. opposite to the findings in portal veins. Low levels of external Ca2+ reveal altered calcium handling in veins from SHR compared to controls. It is concluded that portal veins from hypertensive rats are functionally different from those of normotensive rats and differ in SHR compared to RHR. It is suggested that the altered functional properties of portal vein, but not of aorta, in several respects resemble those of arterial resistance vessels. The implications of these findings are discussed in terms of mechanisms of hypertension in these animal models.

Acetylcholine↗
PubMed1976

Postnatal ontogenic development of the adrenergic innervation pattern in the rat portal vein. A histochemical study.

The postnatal development of the adrenergic innervation pattern in the rat portal vein has been studied with the histochemical fluorescence method of Hillarp and Falck. Stretch preparations and transverse freeze-dried sections of intact portal veins were studied from rats during the first 5 weeks of life and from adult rats. Orientation of undifferentiated smooth muscle cells into two layers was observed at 4 days of age. Dominance of the thick outer longitudinal muscle layer was apparent at two weeks of age. A terminal adrenergic nerve plexus with some varicosities was restricted outside the media at the end of the first week. Ingrowth of penetrating non-terminal adrenergic nerve fibers through the longitudinal muscle layer occurred during the second week of age when the main terminal nerve plexus was developing between the two muscle layers. After 3 weeks of age the adult pattern of a two-dimensional adrenergic plexus between the muscle was established. In the adult rat pharmacological treatment with nialamide and noradrenaline revealed the thin, penetrating non-terminal adrenergic nerve fibers in the longitudinal muscle layer which were poorly visible otherwise. The present observations strongly indicate that the main adrenergic plexus between the two muscle layers emanates directly from the outer axonal plexus. These findings are discussed regarding possible trophic interactions between ingrowing sympathetic adrenergic vasomotor nerves and maturing vascular smooth muscle.

Animals↗
PubMed1976

The influence of copper on the in vitro motility of the human Fallopian tube.

Experiments were designed to examine whether one contraceptive action of the copper intrauterine contraceptive devices (Cu-IUD's) could be associated with an influence on the smooth muscle activity of the Fallopian tube. Sections of the isthmic portion of human oviducts were removed during operation. Preparations from the circular muscle layer were mounted for isometric recording of contractile activity. Subsequently, spontaneous rhythmic contractions appeared within one to five minutes after the preparation procedure was completed. Transmural nerve stimulation or addition of norepinephrine or prostaglandin F2alpha to the Tris buffer medium caused an increase in tone and frequency. Addition of CuCl2 caused a concentration-dependent increase in frequency and a concomitant decrease in amplitude. High concentrations of CuCl2 produced a marked initial increase in frequency, but the rhythmic activity was soon abolished. Metallic copper in the incubation medium caused the same qualitative effects on the smooth muscle preparation as CuCl2. Influences of copper on contractions of rat portal vein preparations were studied in the same way, and similar effects were found. The copper concentration of the secretion in the Fallopian tube was measured by atomic absorption in seven patients wearing CU-IUD's until operation. The levels found were of the same order of magnitude as the concentration of free copper ions which in vitro caused effects on the smooth muscle. It is concluded that copper can affect smooth muscle activity. An influence of copper on the motility of the human oviduct has to be considered as a possible factor contributing to the contraceptive action of the Cu-IUD.

Adult↗
PubMed1976

Anti-hypertensive effect of metoprolol in spontaneously hypertensive rats.

1. Oral and intravenous administration of metoprolol to adult spontaneously hypertensive rats (SHR) with established hypertension lowered arterial blood pressure within 4 days of treatment. 2. Steady state plasma concentrations of metoprolol were similar to those of patients during anti-hypertensive treatment with this drug. 3. The neuroeffector function of portal veins of SHR treated orally for 14 days or intravenously for 4 days was not impaired when studied in vitro. This is in contrast to previous findings after long-term treatment. 4. It is concluded that the anti-hypertensive effect of metoprolol in SHR in many respects resembles that observed in patients. It is suggested that impairment of vasomotor nerve control may contribute to the anti-hypertensive effect of beta-adrenoreceptor antagonists.

Animals↗
PubMed1976

Haemodynamic effects of beta-adrenorecptor blockers in hypertension.

The haemodynamic effect pattern of beta-blockers in hypertension is discussed. The time curve of the antihypertensive effect differs from that of cardiac beta-blockade. The antihypertensive effect is characterized by a slower onset at the start of treatment and a more gradual disappearance when therapy is withdrawn. It appears that the crucial effect of beta-blockers in hypertension is a gradually developing reduction in total peripheral vascular resistance. The mechanism of this apparent vasodilator action is unknown. Various possible factors involved are mentioned. One is a reduced efficiency of transmitter release from the peripheral adrenergic neuron. Such an action may contribute to the antihypertensive effect, as judged by results of animal experiments described.

Adrenergic beta-Antagonists↗
PubMed1976

Vibration-induced changes in vascular tone.

Longitudinal mechanical vibrations in sonic range (10-100 Hz) and of moderate amplitude (50-500) considerably reduce the contractile force of smooth muscle as well as striated muscle. Experiments elucidating the mechanism behind this effect are described. The inhibition of the contractile force is probably due to a direct interference with the action of the contractile proteins. Vibrations are supposed to increase the rate with which the interfilamentary crosslinks are broken. Thereby the number of established crosslinks is reduced and thus the force. Finally a hypothesis concerning the possible role fo this phenomenon in the pathogenesis of vibration induced Raynaud syndrome is forwarded.

Animals↗
PubMed1975

Postnatal ontogenetic development of neurogenic and myogenic control in the rat portal vein.

The postnatal ontogenetic development of neuro-effector control in vascular smooth muscle of the single-unit type has been studied in the rat portal vein. Contractile activity was recorded isometrically in isolated preparations from rats 2-38 days of age and in adults rats. Spontaneous activity, characteristic of the adult portal vein, appeared abruptly during the third postnatal week. Whereas, induced responses to noradernaline (NA) and acetylcholine (Ach) appeared early during the first week and responses to transmural nerve stimulation occurred at the end of the first week. The appearance of spontaneous activity was accompanied by significant increases in sensitivity to NA (log ED50) and to transmural nerve stimulation (frequency giving half maximum response), but not to Ach. Also, maximum responses for NA and nerve stimulation relative to Ach responses tended to increase during the first three weeks. It is concluded that the development of a mechanism supporting myogenic propagation as revealed by highly synchronized spontaneous contractions is an important factor for promoting the effectiveness of sympathicoadrenergic control in this type of vascular smooth muscle.

Acetylcholine↗
PubMed1975

Levels of cyclic AMP and electrical events during inhibition of contractile activity in vascular smooth muscle.

The possible relationship between changes in electrical and mechanical activity and in tissue levels of cyclic AMP (cAMP) during relaxation of the myogenical active rat portal vein has been elucidated in response to different inhibitory stimuli. Isoproterenol, 10(-5) M, caused an initial pronounced inhibition of spike discharge and contractions followed by a partial recover over the 15 min exposure period. This inhibitory response was associated with doubling of tissue cAMP after 1 min and a less pronounced increase in later measurements (5 and 15 min). Papaverine, 10(-4)M, caused, in contrast, an inhibition of electrical and mechanical activity which developed gradually over the entire 15 min exposure period. The levels of cAMP at 1,5 and 15 min all exceeded the corresponding values obtained with isoproterenol. The two drugs in combination gave a biphasic inhibitory response associated with a sustained large increase in the level of cAMP. These drug induced inhibitions were thus accompanied by increased levels of cAMP, but the different time courses of the electromechanical responses could not be rlated to corresponding variations in the content of cAMP. Hyperosmolality (+150 mM sucrose) and mechanical vibration (100 Hz) elicited differentiated inhibitions of smooth muscle activity without changes in tissue cAMP. The mechanical effects elicited by isoproterenol, papaverine and hyperosmolality were accompanied by approximately parallel changes in electrical spike discharge. It is concluded that increased levels of cAMP are not indispensible for vascular smooth muscle relaxation, and that the magnitude of pharmacologically induced inhibitions are not always closely related to the total tissue content of the nucleotide.

Animals↗
PubMed1975

Vasomotor nerve control of isolated arteries and veins.

In order to compare neuro-effector function in different blood vessels, frequency-response relationships were determined for the following preparations: 1)Isolated rings of the proximal saphenous, distal saphenous and ear arteries, the parietal branch of the internal iliac vein and the small saphenous vein from the rabbit, 2) spiral strips of the rabbit pulmonary artery and 3) longitudinal preparations of the rat portal vein. In each rabbit tissue only one low (less than or equal to 4 Hz) and one high (larger than or equal to 8 Hz) transmural nerve stimulation frequency was applied until steady state responses were obtained and these were expressed as a percentage of a maximum response to exogenous noradrenaline (NA) applied in each experiment. The general shape of the frequency-response curves was similar, but differences in steepness and amplitude of the maximum neurogenic response relative to exogenous NA were found. The steepness of the frequency-response relationships of the veins tended to be greater than those of the arteries. It appears that factors such as close neuro-muscular contacts, presence of terminal nerve fibres within the media and the operation of mechanisms for myogenic propagation of activity contribute to the effectiveness of neurogenic vascular control as revealed by frequency-response curves. In vivo, geometrical factors can greatly augment the hemodynamic significance of the observed differences.

Animals↗
PubMed1975

n the mechanism of inhibitory action of vibrations as studied in a molluscan catch muscle and in vertebrate vascular smooth muscle.

In previous studies longitudinal vibrations have been found to reduce active force development in smooth muscle, possibly due to a direct action on the contractile mechanism. In the present experiments the inhibitory effect of vibrations on isometric tension was studied in isolated preparations of the rat portal vein, the rabbit thoracic aorta and the anterior byssus retractor muscle (ABRM) of the Mytilus edulis. The results demonstrate that vibrations of appropriate frequency and amplitude caused prompt inhibition of contractile tension and that complete recovery of active force normally occurred after cessation of vibration in vertebrate smooth muscle as well as during the phasic contraction of ABRM. However, in the "catch" of the ABRM there was no regain in force following the vibration induced inhibition. The contractile proteins are considered to be a locked state during the catch situation. Thus, this contracted state seems to be released by vibrations. It is therefore concluded that vibrations do interfere with the interrelationship between the myofilaments. This conclusion supports the previously forwarded hypothesis that vibrations act by increasing the rate of detachment of actin-myosin crosslinks in vertebrate smooth muscle.

Acetylcholine↗
PubMed1975

Vibration-induced inhibition of vascular smooth muscle contraction.

Vascular smooth muscle is known to be exposed to an oscillating strain under physiological and patho-physiological conditions as well as in different occupational and environmental situations. The effect of vibrations of smooth muscle seems to be largly unknown. In the present experiments on isolated preparations of the rat portal vein and the rabbit thoracic aorta, imposed sinusoidal changes in length were found to cause prompt reduction in active force, the extent of which was dependent on amplitude (1-10% of tissue length, peak to peak, i.e. approximately plus or minus 50-500 mum) and frequency of vibration (1-400 Hz) as well as on the prevailing level of active and passive forces. Vibration caused only small and inconsistant reductions of passive force of vascular smooth muscle. The results are in accordance with the hypothesis that vibrations exert a direct action on the contractile process by causing an increased rate of detachment of actin-myosin cross-links. It is suggested that, in vivo, vibrations may affect the diameter of conduit arteries locally in the case of turbulent blood flow as seen in post-stenotic dilation and arterio-venous anastomosis. Possibly, even the normal pulse pressure oscillations may sometimes tend to inhibit the smooth muscle activity in such arteries and thereby influence their diameters.

Animals↗