DEVELOPMENTAL CHANGES AND HETEROGENEITY OF LACTIC AND MALIC DEHYDROGENASES OF HUMAN SKELETAL MUSCLES AND OTHER ORGANS

The effects of thyroid status on some properties of rat fast-twitch muscle

The effects of different thyroid states on some histochemical and biochemical properties of fast-twitch muscle were studied using rat extensor digitorum longus (EDL) muscle. This muscle was found to be much less responsive to thyroidal influence than the slow-twitch soleus muscle. In EDL muscles of hypothyroid rats, fast leads to slow conversions were observed in fibre type composition, myosin ATPase activity and light chain pattern, and in the subunit composition of lactate dehydrogenase, while the only significant slow leads to fast conversion observed in thyrotoxicosis was a decrease in the proportion of slow-oxidative fibres. Denervation of the hypothyroid muscle produced the highest degree of fast leads to slow transformation. These findings support the view that denervation and dysthyreosis alter gene expression in muscle by independent mechanisms.

Diaphragmatic blood flow and energy expenditure in the dog. Effects of inspiratory airflow resistance and hypercapnia

To investigate the mechanisms which enable the diaphragm to preserve ventilation when the work of breathing is elevated, we measured diaphragmatic blood flow (Q di) and oxygen consumption (VO2 di) in lightly anesthetized dogs. The animals were studied when they breathed quietly, when they inhaled 5% CO2 in 21% or 14% O2, or when they inhaled these gas mixtures through moderate to severe inspiratory resistances. Q di was determined from the integrated diaphragmatic arteriovenous difference of krypton-85, by the Kety-Schmidt technique. VO2 di was calculated as the product of Q di and the diaphragmatic arteriovenous oxygen difference ([A-V]O2 di). Alteration in these parameters consequent to augmentation of ventilatory effort were compared with concomitant alterations in diaphragmatic electrical activity (EMG di) and an inspiratory pleural pressure-time index (PPTI). Addition of inspiratory resistances combined with inhalation of CO2 usually increased Q di and consistently increased VO2 di, EMG di, and PPTI, the maximum increases being approximately 400-1,600% above control levels. In individual animals, as inspiratory resistance was increased, VO2 di, EMG di, and PPTI rose in direct proportion to each other. In the group as a whole, during resistance breathing the oxygen requirements of the diaphragm were met by a combination of increased [A-V]O2 di and Q di. Unlike other skeletal muscles, oxygen extraction tended to plateau at peak loads, whereas blood flow continued to rise as PPTI and VO2 di increased. We conclude that augmentation of perfusion permits the diaphragm to sustain high levels of contractile effort when the work of breathing is increased.

The modification of some biochemical properties of muscle by cross-innervation

Crossing of the nerves leading to muscles with different contraction characteristics leads to biochemical changes related to the modification of the functional properties. Such changes affect the calcium-transporting activity of isolated sarcotubular vesicles, and the amount and isozyme composition of lactic dehydrogenase.

Lactate dehydrogenase isozyme patterns in human skeletal muscle. I. Variation of isozyme pattern in the adult

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Lactate dehydrogenase isoenzyme patterns in human skeletal muscle. II. Changes of isozyme pattern in ontogeny

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The determination of lactate dehydrogenase isoenzymes in normal human muscle and other tissues

1. A technique has been developed, based on preferential inhibition by urea, for determining the amounts and proportions of the M and H sub-units of lactate dehydrogenase (referred to as LDH-M and LDH-H respectively) in human tissues, including muscle. 2. There was good agreement between the results obtained with urea inhibition and those obtained with starch-gel electrophoresis. 3. With increasing age there was a significant decrease in the total amount of lactate dehydrogenase and the amount of LDH-M in skeletal muscle. This could not be accounted for by the replacement of functioning muscle tissue by fibrous connective tissue. 4. The proportion of LDH-M was less in certain muscles (e.g. soleus and extra-ocular) than in other muscles (e.g. gastrocnemius and rectus abdominis). 5. The proportions of LDH-M and LDH-H did not differ significantly in different superficial limb muscles and were not significantly affected by either age or sex. 6. Specimens of muscle from 86 different individuals (all Europeans) have been subjected to electrophoresis, but no variants of lactate dehydrogenase isoenzymes have been found.

The cardiomyopathy of progressive muscular dystrophy

A prospective study was undertaken in order to examine the histories, physical signs, phonocardiograms, electrocardiograms, vectorcardiograms, X-rays, serum enzymes, pulmonary ventilatory findings, and hemodynamics in a group of 55 patients selected solely on the basis of one of the major types of progressive muscular dystrophy (table 9). The classification included: (1) the classic Duchenne type, (2) the limb girdle type, (3) the facioscapulohumeral type, and (4) a group of patients in whom clinical distinction between benign Duchenne dystrophy and limb girdle dystrophy with pseudohypertrophy could not be made. No patient had recognized heart disease prior to selection. Follow-up periods ranged from a few months to 5 years. The pertinent literature was extensively reviewed.

In all groups clinical evidence of heart disease had to be interpreted in the context of the influence of the somatic musculoskeletal defects on "cardiac" symptoms, cardiovascular physical signs, and radiological appearance of the heart. On the other hand, convincing evidence of intrinsic heart disease-subtle to overt-was found in each of the major categories of progressive muscular dystrophy. Detection of cardiomyopathy was simplest and most frequent in the classic Duchenne group because of the highly characteristic features of the scalar electrocardiogram which might direct attention to the systemic myopathy prior to its clinical recognition. However, the presence of heart disease in patients with forms of dystrophy other than the classic Duchenne deserves particular emphasis. Evidence of cardiomyopathy in these latter forms varied from subtle quadruple gallop rhythms in the limb girdle and facioscapulohumeral groups to cardiomyopathic death in the benign Duchenne and limb girdle-pseudohypertrophic group.

Currently available information on the heart in muscular dystrophy has as a rule depended upon retrospective studies, upon reviews of published reports of incompletely classified cases, upon discussions of individual cardiovascular features, or upon observations of individual types of dystrophy. The present prospective study was undertaken to obviate some of these shortcomings. Comprehensive assessment of a large and carefully classified group of dystrophic subjects has provided additional information regarding the clinical spectrum of dystrophic cardiomyopathy.

Electrophoretic characterization of human dehydrogenases

Several isoenzymes of lactate, malate, and isocitrate dehydrogenases have been demonstrated in human skeletal muscle, heart, and liver. Single zones of activity were shown for glucose-6-phosphate and glutamate dehydrogenases. A zone possessing a marked reducing capacity towards nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide phosphate was visualized in the absence of any substrate, using the tetrazolium-coupled histochemical method. This zone represents the so-called "nothing dehydrogenase".