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J A Faulkner

Publications and source records attributed to J A Faulkner.

At least 91 records · Page 5Linked to original sources
PubMed1988

Intramuscular substrate depletion and fatigability of soleus grafts in rats.

We investigated the relationship between oxidative capacity, substrate depletion, and fatigability of muscle grafts in situ. Isometric contractile properties and fatigability were measured in stabilized grafts and control muscles from age-matched rats. Intramuscular glycogen and triglyceride concentrations were measured before and after the fatigue protocol. Even though stabilized soleus grafts have a reduced oxidative capacity compared with control soleus muscles, no difference was observed between groups in terms of resistance to fatigue. Glycogen concentrations did not decrease significantly during the fatigue protocol in either group. Compared with control muscles, the triglyceride concentration in the grafts was significantly higher before the fatigue protocol and it decreased significantly more following the fatigue protocol.

Animals↗
PubMed1988

Total and regional blood flows in vascularized skeletal muscle grafts in rabbits.

The transplantation of whole skeletal muscles is a common clinical procedure. Although atypical blood flows have been reported in small free muscle grafts, the blood flow of large neurovascular-intact (NVI) and neurovascular-anastomosed (NVA) grafts have not been measured. Because the maximum specific force (N/cm2) of NVI and NVA grafts is 65% that of control muscles, we hypothesized that total and regional blood flows (ml.min-1.100g-1) of NVI and NVA grafts at rest and during twitch contractions are significantly lower than lower flows of control muscles. In rabbits, blood flows of control rectus femoris (RFM) muscles and NVI and NVA grafts of RFM muscles were measured by the radioactive-microsphere technique. In control muscles, blood flow increased linearly from 6.8 +/- 1 ml.min-1.100 g-1 at rest to 64.4 +/- 7 ml.min-1. 100 g-1 at a stimulation frequency of 3 Hz with no further increase at 4 Hz. Total blood flows in grafts were not different from the control RFM muscle values, except for a higher resting flow in NVA grafts and a lower flow at 3 Hz in NVI grafts. Minor variations in regional flows were observed. We conclude that the operative procedures of grafting and repair of blood vessels affect the vascular bed of muscles minimally, and the deficits observed in grafts do not arise from inadequate perfusion.

Animals↗
PubMed1987

The response of arterioles in skeletal muscle grafts to vasoactive agents.

Arteriolar responses to the vasodilator adenosine and to the vasoconstrictor norepinephrine (NE) were examined in small bundles of extensor digitorum longus muscle grafted onto the cheek pouches of hamsters. Responses of arterioles to topically applied adenosine or NE were measured from 30 to 180 days after grafting and compared with the response of arterioles in control cheek pouches. Verapamil and potassium chloride (KCl) were applied to 120- and 180-day grafts to determine the response of arterioles to vasoactive agents not mediated by receptors. Arterioles in grafted muscle did not respond to adenosine until 60 days. The response increased with time but was significantly less than the control value even after 180 days. Arterioles in grafts did not respond to NE until 90 days. At both 90 and 120 days the degree of constriction in response to NE was not uniform along the length of a given arteriole (punctate response). By 180 days, the response of a given arteriole to NE was uniform but significantly less than the control value. In 120- and 180-day grafts the responses of arterioles to verapamil and KCl were similar to the responses of arterioles to adenosine and NE, respectively. We conclude that the diminished response of arterioles in small EDL muscle grafts to vasoactive agents may be caused by either a structural or a functional impairment in the smooth muscle layer of arterioles.

Adenosine Diphosphate↗
PubMed1987

Microcirculatory adaptation to skeletal muscle transplantation.

A standard whole muscle graft, in which all neural and vascular connections with the host tissue are severed, reinnervates and revascularizes spontaneously. The extent to which a standard graft regains structure and function depends largely on the degree and timing of revascularization. Whether the endothelial cells that form the first capillary tubes in a whole muscle graft originate inside or outside of the graft is unknown. Blood vessel growth into a graft proceeds in a centripetal fashion and precedes muscle fiber regeneration. Abnormalities have been observed in the structure of capillaries and of the larger vessels in stable muscle grafts. The ability of the vascular bed in large standard grafts to regulate blood flow in response to twitch contractions is impaired, as is the ability of arterioles in small grafts to respond following topical application of norepinephrine and adenosine. The dysfunction of arterioles in standard grafts may be related to structural abnormalities. Blood flow at rest and in response to twitch contractions in stable grafts in which nerves and blood vessels are left intact is not different from control muscles. The following should be investigated to provide further insights into the revascularization process in regenerating skeletal muscle and the structure and function of the microcirculation in stable muscle grafts: the origin of mitotic endothelial and smooth muscle cells; the stimulus for blood vessel growth; the overall architecture and organization of the vascular bed; the presence or absence of adrenergic innervation of blood vessels; and the development of receptors involved in blood flow regulation in muscle grafts.

Animals↗
PubMed1987

Plasticity of skeletal muscle: regenerating fibers adapt more rapidly than surviving fibers.

The properties of mammalian skeletal muscle demonstrate a high degree of structural and functional plasticity as evidenced by their adaptability to an atypical site after cross-transplantation and to atypical innervation after cross-innervation. We tested the hypothesis that, regardless of fiber type, skeletal muscles composed of regenerating fibers adapt more readily than muscles composed of surviving fibers when placed in an atypical site with atypical innervation. Fast muscles of rats were autografted into the site of slow muscles or vice versa with the donor muscle innervated by the motor nerve to the recipient site. Surviving fibers in donor muscles were obtained by grafting with vasculature intact (vascularized muscle graft), and regenerating fibers were obtained by grafting with vasculature severed (free muscle graft). Our hypothesis was supported because 60 days after grafting, transposed muscles with surviving fibers demonstrated only a slight change from the contractile properties and fiber typing of donor muscles, whereas transplanted muscles with regenerating fibers demonstrated almost complete change to those of the muscle formerly in the atypical site.

Animals↗
PubMed1986

Architecture, composition, and contractile properties of rat soleus muscle grafts.

Skeletal muscle grafts have a deficit in tension development compared with control muscles, even after accounting for reduced mass and total muscle cross-sectional area. Our purpose was to determine relationships among the architecture, tissue composition, and contractile properties of rat soleus muscle grafts. Data were compared with control soleus muscles obtained from littermates. Female Wistar rats were anesthetized with pentobarbital sodium for grafting of soleus muscles with nerve implant and for dissection of muscles 56 days after grafting. Compared with control values, the maximum specific tension (N/cm2) of grafts was 76%, the interstitial (inulin) space was 135%, and the connective tissue protein concentration was 177%. For grafts, total muscle length and fiber length were 91 and 123% of control values, respectively. The extrapolated shortening velocity at zero load (fiber lengths/s) for grafts was not different from the control value. The deficit in specific tension of grafts is explained by a greater concentration of noncontractile tissue components. Changes in muscle architecture and composition following grafting had little affect on contraction dynamics.

Animals↗
PubMed1986

Characteristics of motor units in muscles of rats grafted with nerves intact.

Extensor digitorum longus (EDL) muscles of rats were grafted with the nerves intact. Sixty days after grafting, single motor units were isolated and characterized in terms of fatigability and morphology. The distribution of fatigue indexes for motor units in control muscles revealed two main peaks, whereas in grafts no clear peaks were observed, fatigue indexes being distributed more evenly over the entire range. This difference in the distribution of fatigue indexes of motor units may explain the increased resistance to fatigue observed for whole grafts compared with whole EDL muscles. An inverse linear relationship was found between maximum tetanic tensions and the fatigue indexes of motor units from control and grafted EDL muscles. The distribution of fiber areas for single motor units was broader in grafts than in control EDL muscles, but the mean innervation ratio was not different. In approximately 20% of the units mapped in grafts, fibers were clustered tightly within a small portion of the total cross section, suggesting axonal sprouting during regeneration.

Animals↗
PubMed1986

Muscle grafts overloaded by ablation of synergistic muscles.

We hypothesized that the mass and maximum tetanic tension (Po) of nerve-intact grafts overloaded by ablation of synergistic muscles would be greater than that of standard nerve-intact grafts or of control soleus muscles. Soleus muscles were grafted orthotopically and bilaterally in 35 female rats. Control soleus muscles were obtained from 30 age-matched cohorts. Twenty-eight days following grafting, gastrocnemius muscles were ablated bilaterally in half of the animals. Comparisons were made between 28 and 112 days following grafting. By 112 days the wet mass of the overload nerve-intact grafts was 138% of the standard grafts and 152% of the control soleus muscles, whereas the Po was 161% and 107%, respectively. Specific tension stabilized at approximately 19 +/- 1 N/cm2 for both types of grafts, significantly lower than the value of 24 +/- 1 N/cm2 for control soleus muscles. Ablation of synergistic muscles resulted in a significant and sustained increase in mass and Po in regenerating skeletal muscle autografts. We conclude that provided the appropriate conditioning stimulus small grafts (100-200 mg) are capable of achieving the values for the mass and Po of control muscles.

Animals↗
PubMed1986

Characteristics of lengthening contractions associated with injury to skeletal muscle fibers.

Lengthening (eccentric) contractions result in injury to skeletal muscle fibers. Two hypotheses were tested through lengthening contractions of an in situ muscle preparation: the extent of injury increases with increases in the duration; and the extent of injury increases with increases in the peak force. Mice were anesthetized, and distal tendons of the extensor digitorum longus muscles were attached to a servomotor. Muscles were stimulated at 150 Hz and lengthened 20% of fiber length (Lf). Lengthening contractions were performed at 0.2, 0.5, or 1.0 Lf/s with durations of 0.5-15 min. Peak force during lengthening contractions at 1.0 Lf/s was decreased by inducing fatigue with isometric contractions, stimulating at 70-100 Hz, or 3) lengthening 10% of Lf. Injury was assessed 3 days after lengthening contractions by histological appearance and maximum force (Po) development. Injury increased with duration up to 5 min. After 5 min, fatigue appeared to prevent further injury. Results for 0.2 and 0.5 Lf/s were similar to those for 1.0 Lf/s but with less injury. A high correlation was observed between histological appearance of injury and the decrease in Po. The extent of injury was related to the peak force developed during the lengthening contractions.

Animals↗
PubMed1986

Skeletal muscle fatigue in vitro is temperature dependent.

Our purpose was to determine the effect of temperature on the fatigability of isolated soleus and extensor digitorum longus (EDL) muscles from rats during repeated isometric contractions. Muscles (70-90 mg) were studied at 20-40 degrees C in vitro. Fatigability was defined with respect to both the time and number of stimuli required to reach 50% of the force (P) developed at the onset of the fatigue test. Fatigue was studied during stimulation protocols of variable [force approximately 70% of maximum force (Po)] and constant frequency (28 Hz). Results for soleus and EDL muscles were qualitatively similar, but fatigue times were longer for soleus than for EDL muscles. During the variable-frequency protocol, development of approximately 70% of Po required an increase in stimulation frequency as temperature increased. During stimulation at these frequencies, fatigue time shortened as temperature increased. For both fatigue protocols, the relationship between temperature and the number of stimuli required to reach fatigue followed a bell-shaped curve, with maximum values at 25-30 degrees C. The temperature optimum for maximizing the number of isometric contractions to reach fatigue reflects direct effects of temperature on muscle function.

Animals↗
PubMed1986

Functional deficits in skeletal muscle grafts.

Individual skeletal muscle fibers degenerate and regenerate with minimal functional deficits. When whole skeletal muscles are grafted in rats or cats by standard grafting techniques, revascularization and reinnervation must occur spontaneously. Under these circumstances, contraction times and maximum velocities of shortening eventually return to control values, but a significant deficit is observed in maximum tetanic tension. Grafts made with anastomosis of nerves or with nerves left intact have smaller deficits in tension development than do standard grafts made without nerve repair. The measurement of contractile properties of single motor units in extensor digitorum longus (EDL) muscles and in EDL grafts in rats indicates that the decreased maximum tetanic tension of whole grafts is due to a 10-20% decrease in the maximum tetanic tension of individual motor units, whereas standard grafts also show a 40-45% decrease in the number of motor units. Compared with control values, the fatigability of 100-mg grafts in rats is decreased, whereas larger 3-g grafts in cats show an increased fatigability. The deficits observed in large grafts can be reduced, but not eliminated, by grafting with neurovascular anastomoses.

Animals↗
PubMed1985

Contractile properties of standard and nerve-intact muscle grafts in the rat.

The contractile properties of standard and nerve-intact grafts of extensor digitorum longus muscles of rats were compared in vitro. Fourteen days after grafting, the time to peak tension and the half-relaxation times of nerve-intact grafts were shorter than those of standard grafts, but both were longer than control values. By 60 days, these variables attained normal values. At every sample period, the tetanic tensions of nerve-intact grafts were higher than those of standard grafts. Even at the early sampling periods, the twitch-tetanic tension ratios of nerve-intact grafts were close to normal values, whereas those of standard grafts were higher than normal. Stabilized nerve-intact grafts had a larger mass and greater maximum tetanic tension development than standard grafts, but were more fatigable. Compared with control EDL muscles, stable nerve-intact grafts show no differences except for lessened fatigability, whereas standard grafts demonstrate significant functional deficits.

Age Factors↗
PubMed1985

Functional properties of palmaris longus muscles of rhesus monkeys transplanted as index finger flexors.

This experiment with skeletal muscle autografts in monkeys was designed to retest previous findings that transplanted skeletal muscle can regenerate to a functional degree in primates without predenervation and to test a new hypothesis that increased functional demands on regenerated muscle grafts in monkeys may result in improved functional capacity of the grafts. Rhesus monkey index flexors were replaced with free palmaris longus muscle autografts with microneural anastomoses between the graft motor nerve and the severed profundus motor nerve. One monkey was taught selective index flexion before grafting and continued with this program after grafting to test the effect of training on the graft. Mature grafts were evaluated for in vivo contractile properties and by histology and histochemistry and were compared with a group of normal Rhesus palmaris longus muscles. The results reconfirm the capacity of nonpredenervated monkey skeletal muscle grafts to regenerate and to achieve some contractile ability and suggest that training of free muscle grafts may enhance recovery of their functional and structural properties.

Animals↗
PubMed1985

Shortening velocity extrapolated to zero load and unloaded shortening velocity of whole rat skeletal muscle.

The shortening velocity at zero load (Vmax) extrapolated from velocities measured during isotonic releases was compared with unloaded shortening velocity (V0) determined by the slack test. Experiments were performed in vitro at 20 degrees C on soleus muscles from rats. The Vmax was 3.2 +/- 0.1 (mean +/- S.E. of mean, n = 10) fibre lengths/s while the V0 determined for the same muscles was 5.0 +/- 0.1 fibre lengths/s. The ratio of V0/Vmax was 1.6 +/- 0.1. Soleus muscles of the rat are heterogeneous with respect to the intrinsic shortening velocities of their fibres. The results suggest that V0 is a measure of the unloaded shortening velocity of the fastest fibres whereas Vmax is a function of the force-velocity characteristics of all the fibres within a skeletal muscle preparation.

Animals↗