Failure of stimulated skeletal muscle mainly contributed by passive force: an in vivo rabbit model

OBJECTIVE: To evaluate the role of active and passive muscle forces in the failure mechanism of stimulated muscle. DESIGN: An in vivo rabbit model. BACKGROUND: Eccentric contractions can result in a greater incidence of muscle injury. However, the relative role of the active and passive muscle force in the failure mechanism of the activated muscle is not well elucidated. METHODS: After anaesthesia, New Zealand white rabbits were fixed in a frame on a materials testing machine. The triceps surae muscle-tendon units were passively stretched to rupture with our without continuous nerve stimulation. The force and muscle length were simultaneously recorded. Active muscle force, passive muscle force, and ratio of the active to passive muscle were calculated and depicted against strain. RESULTS: The results showed that the mean maximal passive force of triceps surae muscle was 293.1 N at a strain of 38%. The mean peak active muscle force was 21.5 N at a strain of 21%. The ratio of active to passive muscle force reached its peak first, followed by the active muscle force, and then the passive muscle force. The ratio of active to passive muscle force at the peak total force was only 3.3%. CONCLUSIONS: The stimulated muscle can exert its maximal response at extreme physiological extension. Injury of the stimulated muscle is caused mainly by passive muscle force.     

The 'market' for medical and health information in transition: the case of the Hong Kong Hospital Authority libraries

The last few years have been a period of transition not only for hospitals and their governance but also for post-graduate medical education in Hong Kong. Both trends have a direct impact on the information market place. This article starts by studying the provision of medical and health-related information in Hong Kong. The two university medical and dental libraries, together with the hospital and health sciences libraries in government hospitals and the Department of Health, house the major collections on medicine and health care. The demand for medical and health care information is increasingly felt with the takeover of 39 hospitals by the statutory Hong Kong Hospital Authority in 1991. The major problems and issues in planning for library information services are the historically uneven development of libraries, discrepancies in funding, the changes in organizational and management structure, and the competition with higher development priorities within the organization. In view of current technology and the availability of rich external resources, the adopted strategies tend towards the formation of 10 library service networks, development of integrated library information systems on the Health Authority-wide area network, and the devolution of management responsibilities. The future challenges in store for the information professional are examined.     

Comparison of nifedipine and metoprolol on collateral coronary blood flow in a swine model of chronic coronary obstruction and acute ischaemia during isoflurane anaesthesia

Purpose

This study compared the effects of nifedipine and metoprolol on collateral-dependent myocardial blood flow in a swine model of chronic coronary obstruction and acute ischaemia during isoflurane anaesthesia.

Methods

Collateral coronary circulation was induced in 15 three-week-old piglets by banding of the proximal left anterior descending coronary artery (LAD). After 8–10 wk, the distal LAD was ligcted and the open-chest pigs were randomized to receive infusions of either saline, nifedipine (5 μg·kg^?1 · min^?1) or metoprolol (10 μg · kg^?1 · min^?1) for 30 min during isoflurane anaesthesia (2%). Transient ischaemia was induced by 30 secocclusion of the left circumflex artery. Arterial blood pressures, heart rate and regional myocardial blood flow (radio-labelled microspheres technique) were measured at the end of drug infusion (baseline) and one minute after transient ischaemia.

Results

No differences in the blood flow to the collateral-dependent (CD) myocardium or haemodynamic variables were observed at baseline among the three groups. Following transient ischaemia, in the nifedipine but not in the metoprolol group, blood flow to the CD myocardium was reduced by 28 ± 24% in the epicardium (P< 0.05) and 56 ± 20% in the endocardium (P< 0.01), resulting from intercoronary and transmural steal. This was associated with a moderate increase (10%, P< 0.05) in the heart rate in the nifedipine group.

Conclusions

In a swine model of chronic coronary obstruction and acute ischaemia during isoflurane anaesthesia, the collateral coronary blood flow was maintained in the presence of metoprolol, but reduced in the presence of nifedipine following transient ischaemia due to intercoronary and transmural steal.     

Inhibition of growth of B16 murine malignant melanoma by exogenous interferon

We previously reported that polyinosinic-polycytidylic acid, a potent interferon inducer, inhibits the growth of B16 malignant melanoma in the C57BL/6 mouse. Two experiments were done to evaluate the effectiveness of interferon in tumor inhibition in vivo. In the first, mice were implanted with melanoma and divided into four groups, according to treatment: interferon preparation; interferon control preparation ("breakthrough fraction"); phosphate-buffered saline control; and murine serum albumin control. Daily, each mouse was given i.p. injections of 200,000 NIH reference units (hereafter called units) of interferon or of one of the control substances. The second experiment was similar to the first, except that bovine serum albumin was an additional control. In both experiments, the average tumor volume in interferon-treated mice was statistically significantly smaller than that of each control group. Mouse interferon preparations also inhibited the multiplication of B16 malignant melanoma cells in culture. This inhibition was statistically significant from interferon levels as low as 5 to as high as 5000 units/ml. The degree of inhibition markedly increased from 5 up to 500 units, the inhibition reaching its maximum at this concentration. The inhibitory effect of interferon was abrogated by anti-murine interferon serum produced in a rabbit. These findings suggest that the in vivo inhibition of the growth of B16 melanoma demonstrated with polyinosinicpolycytidylic acid and with exogenous interferon probably results, at least in part, from a direct effect of interferon on the tumor cells themselves.     

Mutagenic, transforming and promoting effect of pickled vegetables from Linxian county, China

A recent epidemiological survey in China showed that there is a regional distribution of esophageal cancer and a correlation between mortality for this cancer and environmental factors, especially the consumption of pickled vegetables. A series of experimental studies with pickled vegetable extract were done using different in vitro biological systems. The results showed that pickled vegetable extract induced 6-thioguanine-resistant mutants in V79 cells and increased sister chromatid exchanges in the same cells and in Syrian hamster embryo cells. Pickled vegetables extract induced transformed foci in Syrian hamster embryo cells and in 3-methylcholanthrene initiated C3H/10T1/2 cells. The mutagenic, transforming and promoting activities of pickled vegetable extract seen in vitro conform with in vivo results and provide evidence for the presence of a mutagen and/or a carcinogen in pickled vegetable extract. A possible role of pickled vegetables consumption in the etiology of esophageal cancer is discussed.     

Studies on the luminescence of channels in rats and its law of changes with "syndromes" and treatment of acupuncture and moxibustion.

We previously reported the discovery of 14 channels in the human body, which possessed the biophysical property of high emission of light. In this study we found the same property on the Ren and Du channels in healthy rats. Additionally, we discovered that the luminance of the related channels in rat models with different "syndromes" varied greatly. For instance, a markedly low luminance appeared on the Du channel in animals with experimental syndrome of Yang deficiency induced by hydrocortisone; while in animals with experimental syndrome of blood deficiency caused by bleeding, an apparently low luminance occurred on the Ren channel. The intensity of the emitted light on Du and Ren channels increased after acupuncture treatment, but not significantly. This phenomenon conforms to the theory in traditional Chinese medicine that the Du channel is the "sea of Yang channels", while the Ren channel is the "sea of Yin channels".     

Initial results of laser angioplasty under angioscopic guidance for salvage of an ischemic lower limb: preliminary report

From March to July 1989, nine patients at risk for peripheral artery disease underwent intraoperative Nd:YAG laser angioplasty using angioscopy at the Veterans General Hospital (Taipei, Taiwan, Republic of China). Following the laser angioplasty, balloon dilatation was performed in all cases. Eight men and one woman at an average age of 68 were included in the study (range: 58 to 78 years old). Ischemic symptoms included five patients with disabling claudication, four with pain at rest and one with gangrene on the toes. Eight of the nine patients had complete occlusions ranging from 2 to 19 cm in length. Two patients had high degree multiple segmental stenosis of the superficial femoral artery from 1 to 2 cm in length. Initial clinical success (indicated by relief of symptoms and increase in Doppler ankle pressure and index) and improvement in the angiographic luminal diameter was noted in 9 of 10 occluded vessels (90%) that underwent Nd:YAG laser treatment which was delivered at 10 to 12 watts through laser probes. Prelaser intraluminal diameter increased from 0.05 +/- 0.07 to 0.53 +/- 0.07 mm, Doppler ankle pressure index rose from 0.51 +/- 0.12 to 0.81 +/- 0.12, Doppler ankle pressure increased from 62.44 +/- 16.10 to 104 +/- 21.21 mmHg and the amplitude of pulse volume recorder at ankle level rose from 5.77 +/- 2.80 to 12.11 +/- 2.77 mm as compared with prelaser therapy (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Scintigraphy and distribution of labeled antibodies in rats with tumors

Radioiodinated antitumor (Ab-gamma globulins), non-tumor-specific Ab, and R¹³¹ISA were used for imaging radiation-induced intestinal tumors in rats. Each agent detected tumors larger than 2 g, but labeled Ab were most efficient in detecting smaller tumors. Tissue distribution studies showed that while purified Ab localized specifically in tumors, unpurified Ab concentrated in the tumor by a mechanism not considered immunological. Localization was variable and the concentration of antitumor Ab reached useful levels only in a small number of cases. The use of high specific activity purified Ab unexpectedly decreased the concentrations of label observed in the tumors when compared with the use of the same activity of low specific activity purified Ab. These results indicated the presence of circulating tumor antigens which were capable of binding the injected Ab. Subsequently, these findings have been substantiated. Thus the animal-to-animal variability could be explained on the basis of differing degrees of interaction of injected Ab with circulating tumor antigens. The usefulness of labeled purified or monospecific antitumor antibodies for tumor imaging and therapy would thus be influenced by the extent of such interactions.This work was presented in part at the Twentieth Annual Meeting of the Radiation Research Society, Portland, Oregon, May, 1972.     

Antileukemic activity of substituted ureidothiazoles, ureidothiadiazoles, and related compounds.

A number of ureidothiazole and ureidothiadiazole derivatives related to ethyl 4-[[(2-thiazolylamino)carbonyl]-amino]benzoate were prepared and evaluated against the leukemia P-388 tumor system in mice. Preliminary structure-activity relationship study revealed that, among other considerations, active compounds of this series contain either an "isothioureido" [N-C(S-)=N-] or an "isothiosemicarbazono" [N-C(S-)=N-N=] structural unit.