Phosphorus-31 NMR magnetization-transfer measurements of ATP turnover during steady-state isometric muscle contraction in the rat hind limb in vivo

The purposes of this study were to create a three-dimensional representation of strain during isometric contraction in vivo and to interpret it with respect to the muscle fiber direction. Diffusion tensor MRI was used to measure the muscle fiber direction of the tibialis anterior (TA) muscle of seven healthy volunteers. Spatial-tagging MRI was used to measure linear strains in six directions during separate 50% maximal isometric contractions of the TA. The strain tensor (E) was computed in the TA's deep and superficial compartments and compared with the respective diffusion tensors. Diagonalization of E revealed a planar strain pattern, with one nonzero negative strain (εN) and one nonzero positive strain (εP); both strains were larger in magnitude ( P < 0.05) in the deep compartment [εN = −40.4 ± 4.3%, εP = 35.1 ± 3.5% (means ± SE)] than in the superficial compartment (εN = −24.3 ± 3.9%, εP = 6.3 ± 4.9%). The principal shortening direction deviated from the fiber direction by 24.0 ± 1.3° and 39.8 ± 6.1° in the deep and superficial compartments, respectively ( P < 0.05, deep vs. superficial). The deviation of the shortening direction from the fiber direction was due primarily to the lower angle of elevation of the shortening direction over the axial plane than that of the fiber direction. It is concluded that three-dimensional analyses of strain interpreted with respect to the fiber architecture are necessary to characterize skeletal muscle contraction in vivo. The deviation of the principal shortening direction from the fiber direction may relate to intramuscle variations in fiber length and pennation angle.

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Rostral ventrolateral medullary opioid receptor activation modulates pressor response to muscle contraction

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1998.274.1.h139 ◽

1998 ◽

Vol 274 (1) ◽

pp. H139-H146 ◽

Cited By ~ 8

Author(s):

Daryl Caringi ◽

David J. Mokler ◽

David M. Koester ◽

Ahmmed Ally

Keyword(s):

Muscle Contraction ◽

Nerve Stimulation ◽

Tibial Nerve ◽

Pressor Response ◽

Cardiovascular Responses ◽

Receptor Activation ◽

Ventrolateral Medulla ◽

Tibial Nerve Stimulation ◽

Isometric Muscle Contraction ◽

Isometric Muscle

The effects of an opioid agonist, [d-Ala2]methionine enkephalinamide (DAME), administered into the rostral ventrolateral medulla (rVLM) or caudal ventrolateral medulla (cVLM) on cardiovascular responses to isometric muscle contraction were determined in anesthetized rats. A 30-s contraction evoked by tibial nerve stimulation increased mean arterial pressure (MAP) and heart rate (HR) by 34 ± 6 mmHg and 40 ± 7 beats/min, respectively, with a developed tension of 322 ± 30 g, after bilateral insertion of microdialysis probes into the rVLM. Thirty-minute dialysis of DAME (10 and 100 μM) attenuated the contraction-evoked cardiovascular changes dose dependently (10 μM: MAP = 25 ± 4 mmHg, HR = 27 ± 3 beats/min, tension = 333 ± 25 g; 100 μM: MAP = 14 ± 4 mmHg, HR = 16 ± 5 beats/min, tension = 330 ± 34 g). Preadministration of an opioid antagonist, naloxone (100 μM), augmented contraction-evoked MAP and HR responses and blocked effects of 100 μM DAME. Microdialysis of DAME into the cVLM produced no changes in the pressor response to contraction. At end of each experiment, tibial nerve stimulation after neuromuscular blockade evoked no MAP or HR change. Results demonstrate that opioid receptor activation within the rVLM modulates cardiovascular responses to isometric muscle contraction.

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