ABSTRACT
Skeletal muscle hemodynamics, including that in jaw muscles, is an important in their functions and is modulated by aging. Marked blood flow increases mediated by parasympathetic vasodilation may be important for blood flow in the masseter muscle (MBF); however, the relationship between parasympathetic vasodilation and aging is unclear. We examined the effect of aging on parasympathetic vasodilation evoked by trigeminal afferent inputs and their mechanisms by investigating the MBF during stimulation of the lingual nerve (LN) in young and old urethane-anesthetized and vago-sympathectomized rats. Electrical stimulation of the central cut end of the LN elicited intensity- and frequency-dependent increases in MBF in young rats, while these increases were significantly reduced in old rats. Increases in the MBF evoked by LN stimulation in the young rats were greatly reduced by hexamethonium and atropine administration. Increases in MBF in young rats were produced by exogenous acetylcholine in a dose-dependent manner, whereas acetylcholine did not influence the MBF in old rats. Significant levels of muscarinic acetylcholine receptor type 1 (MR1) and type 3 (MR3) mRNA were observed in the masseter muscle in young rats, but not in old rats. Our results indicate that cholinergic parasympathetic reflex vasodilation evoked by trigeminal afferent inputs to the masseter muscle is reduced by aging and that this reduction may be mediated by suppression of the expression of MR1 and MR3 in the masseter muscle with age.
Subject(s)
Aging/physiology , Arteries/innervation , Cholinergic Fibers/physiology , Masseter Muscle/blood supply , Parasympathetic Nervous System/physiology , Reflex , Trigeminal Nerve/physiology , Vasodilation , Acetylcholine/metabolism , Age Factors , Aging/metabolism , Animals , Cholinergic Fibers/metabolism , Electric Stimulation , Male , Masseter Muscle/metabolism , Parasympathetic Nervous System/metabolism , Rats, Wistar , Receptor, Muscarinic M1/metabolism , Receptor, Muscarinic M3/metabolism , Regional Blood Flow , Sympathectomy , Trigeminal Nerve/metabolism , VagotomyABSTRACT
BACKGROUND: The effects of chronic alcohol intake on skeletal muscle are clinically observed as muscle cramps with decrease in the amount of muscle. It was clarified by expired gas analysis that acute alcohol load affects disturbed energy metabolism of skeletal muscle. We studied abnormal energy metabolism of skeletal muscles in alcoholic liver diseases using expired gas analysis. METHODS: Subjects of the study were five inpatients with alcoholic liver disease (fatty liver: one case, hepatic fibrosis: one case, liver cirrhosis: three case). Expired gas analysis during exercise was performed using AEROMONITOR. Minute ventilation, oxygen consumption and carbon dioxide output were monitored, and anaerobic threshold (AT) and respiratory compensation point (RCP) were calculated. RESULTS: The anaerobic threshold, which is the limit of the aerobic exercise, was significantly reduced in patients with alcoholic disease (p < 0.01). The respiratory compensation point, which is the limit of the metabolic compensation of intracellular lactic acidosis, was decreased (p < 0.01). CONCLUSIONS: The results of expired gas analysis during exercise indicate that the aerobic energy metabolism of skeletal muscle had been disturbed in alcoholic liver disease. The reduced RCP suggests that the lactate metabolism in skeletal muscle is also disturbed in alcoholic liver disease. Expired gas analysis during exercise allows determination of the amount of exercise required to treat liver diseases through analysis of AT.
