Passive Lengthening Research Articles

Ultrastructural basis of acute left ventricular failure from severe acute aortic stenosis in the rabbit

The haemodynamic and morphological data of experimental left ventricular failure due to acute aortic constriction in the rabbit have been studied. A progressive decrease of contractility is preceded by an initial transitory increase in contractility. The sarcomere length/filling pressure curve demonstrates that after constriction of the aorta a decrease in passive extensibility of sarcomeres occurs despite the fact that the ventricular volume is significantly increased in animals with aortic stenosis. Variation in passive lengthening of myofibres, myofibrillar degeneration including fragmentation of Z lines and mitochondrial alterations are the most important morphological changes observed.

Experimental cardiac hypertrophy: A quantitative ultrastructural study in the compensatory stage

An ultrastructural study of the rabbit myocardium with experimental advanced left ventricular hypertrophy was undertaken to determine the volumetric density, surface density and surface-to-volume ratio of the contractile material, mitochondria and T-system and to describe changes in the ultrastructure of the myocardium in this condition. Biometric data demonstrated a significant increase in the contractile mass which maintained its normal space arrangement. The mitochondria had a normal structure but biometric investigations confirmed a statistically significant decrease in the relative volume and the mitochondria/myofibril ratio. The T-system was dilated and seemed to have adapted itself to a larger contractile mass mainly by swelling. Finally, the structure of the sarcomere was analysed on the basis of the length/passive filling pressure curve. This curve showed that the passive lengthening of sarcomeres in the hypertrophic myocardium was less than in the normal heart.

The effect of changing temperature upon the time course of active and of passive lengthening of rabbit smooth muscle.

The effect of changing temperature upon the time course of active and of passive lengthening of rabbit smooth muscle.

Current Topics and Events

THE announcement of the award - of the Nobel prize for medicine for 1922 to Prof. A. V. Hill and Prof. Otto Meyerhof, and for 1923 to Dr. Banting and Prof. Macleod, is gratifying to British research in medical science. The Toronto workers who discovered insulin share with workers at home a common inheritance of scientific tradition; their work has attracted much notice and is well known. The division of last year's prize between Prof. Hill and the professor of physiology at Kiel emphasises the friendly co-operation which has marked their work on muscular contraction since the investigations of Fletcher and Hopkins in 1908. Sir Walter Fletcher, now secretary of the Medical Research Council, was Prof. Hill's tutor at Cambridge and urged him to take up physiology. Work on muscle at that time awaited the elaboration of a new technique of investigation. It was Langley who suggested the line of approach which has since proved so productive in the hands of A. V. Hill, whose modification of the thermopile made possible the investigation of the total heat produced in a muscular contraction, of the time-relations of the heat-production, either “initial” or “recovery,” and of the thermal changes associated with the passive lengthening or shortening of the muscle. Oxygen is not used in the primary break-down processes of rest or activity, but only in what, strictly speaking, may be called the recovery processes. Prof. Hill has shown that but for the body's ability to meet its oxygen liabilities in arrears, it would not be possible to make more than the most moderate muscular effort. The muscle “goes into debt” for oxygen on the security of the lactic acid liberated in activity. Mechanical response is probably due to the production of lactic acid during contraction, its sudden appearance changing the electrical and colloidal state of protein interfaces in the muscle. Prof. Hill and his collaborators then passed to the consideration of the efficiency and speed of the recovery process, to the use of the “oxygen debt” as an indicator of the absolute amount of lactic acid present in the body at the end of exercise and to other problems of muscular exertion in man. Meyerhof continued in the use of the calorimetrical and chemical methods, his account of the role of lactic acid in contraction running parallel to A. V. Hill's. Muscle problems apart, Meyerhof, following Hopkins, has done notable work on the mechanism of oxidation; while A. V. Hill's work on blood-gases and on nervous excitation is also very widely known.