Age-Related Changes in Tetanic Contraction of Ventricular Myocardium

Driscoll, David J.; Michael, Lloyd H.

doi:10.1159/000457152

Cited by 3 publications

(2 citation statements)

References 16 publications

(24 reference statements)

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“…They were decapitated, and the two SM muscles were collected. The weight and length of each muscle were obtained, and the cross-sectional area was calculated (Driscoll and Michael, 1984).…”

Section: Methodsmentioning

confidence: 99%

Microtrauma to Rat Superficial Masseter Muscles Following Lengthening Contractions

Hutchins¹,

Skjonsby²

1990

J Dent Res

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Repetitive lengthening contractions have been predicted as a mechanism causing injury, pain, and delayed soreness in the hyperactive masticatory muscle. This mechanism was examined by the mechanical lengthening of the contracted superficial masseter (SM) muscle in anesthetized rats. Repetitive stimulation of the left SM to tetanic tension was followed by mechanical lengthening, which stressed contracted muscle. The contralateral muscle was passively lengthened repetitively. Contractile tension in response to a varying frequency of stimulation was measured in pre- and post-lengthened SM muscles. A selective loss of force at all frequencies up to 100 Hz occurred in the muscles subjected to lengthening contractions. Low-frequency fatigue did not occur in SM muscles passively lengthened. All animals recovered without loss of weight or dehydration. They were killed at 24 or 72 h post-lengthening. The SM muscles were collected, and no significant differences were found in mean weight, length, or cross-sectional area when the right and left SM muscles were compared at 24 or 72 h. Two observers independently examined histological secretions of SM muscles and graded the localized inflammatory sites on a scale of 1-4. A non-parametric statistical test was used so that the inflammatory scale for each muscle could be ranked. There were significantly more injured sites in SM muscles subjected to lengthening contractions, compared with the lengthened (but relaxed) SM muscles. The SM muscles of anesthetized rats were internally injured by repetitive lengthening contractions, and they exhibited low-frequency fatigue. These findings support the hypothesis that repetitive lengthening contractions in the masticatory muscle could be a mechanism for the pain and dysfunction of masticatory muscles in humans with certain parafunctional habits.

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“…They were decapitated, and the two SM muscles were collected. The weight and length of each muscle were obtained, and the cross-sectional area was calculated (Driscoll and Michael, 1984).…”

Section: Methodsmentioning

confidence: 99%

Microtrauma to Rat Superficial Masseter Muscles Following Lengthening Contractions

Hutchins¹,

Skjonsby²

1990

J Dent Res

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“…Milrinone is a phosphodiesterase in hibitor, which increases cyclic AMP [23], and produces an increased transsarcolemmal flux of calcium [24], Thus, in the immature heart, this drug offers the theoretical advan tage of bypassing the ß-receptor and of not needing a mature sarcoplasmic reticulum in order to increase intracellular calcium. Dris coll and Michael [25] evaluated the effects of another phosphodiesterase inhibitor (caf feine). They produced a greater increase in…”

Section: Myocardial Oxygen Consumption and Efficiencymentioning

confidence: 99%

Milrinone Effects in the Isolated Immature Rabbit Heart

et al. 1988

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Milrinone, a new positive inotropic agent, was evaluated and compared to isoproterenol in an immature isolated isovolumic rabbit heart model. Three age groups were studied; newborns (0-6 days), juveniles (4-6 weeks old) and adults (5-7 months old). Heart rate did not change significantly with milrinone or isoproterenol in adults or juveniles, but increased in newborns from 144 ± 1 to 162 ± (SEM) 6 beats/min at peak milrinone effect. Milrinone had a greater effect on the contractility (maximum positive dP/dt) of the mature hearts, with newborns increasing to 134 ± 6% of baseline, juveniles to 154 ± 8%and adults to 216 ± 15%. Results were similar for isoproterenol, although the positive inotropic effect occurred over a wider dosage range for this drug. No additive effects of the two drugs were noted. We conclude, that although milrinone is a positive inotropic drug in all age groups studied, the response of the newborn heart is quantitatively much weaker than that of the adult.

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