Neuroendocrine and substrate responses to altered brain 5-HT activity during prolonged exercise to fatigue.
Pharmacological manipulation of brain serotonergic [5-hydroxytryptamine (5-HT)] activity affects run time to exhaustion in the rat. These effects may be mediated by neurochemical, hormonal, or substrate mechanisms. Groups of rats were decapitated during rest, after 1 h of treadmill running (20 m/min, 5% grade), and at exhaustion. Immediately before exercise rats were injected intraperitoneally with 1 mg/kg of quipazine dimaleate (QD; a 5-HT agonist), 1.5 mg/kg of LY 53857 (LY; a 5-HT antagonist), or the vehicle (V; 0.9% saline). LY increased and QD decreased time to exhaustion (approximately 28 and 32%, respectively; P < 0.05). At fatigue, QD animals had greater plasma glucose, liver glycogen, and muscle glycogen concentrations but lower plasma free fatty acid concentration than did V and LY animals (P < 0.05). In general, plasma corticosterone and catecholamine levels during exercise in QD and LY rats were similar to those in V rats. Brain 5-HT and 5-hydroxyindole-3-acetic acid concentrations were higher at 1 h of exercise than at rest (P < 0.05), and the latter increased even further at fatigue in the midbrain and striatum (P < 0.05). Brain dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were higher at 1 h of exercise (P < 0.05) but were similar to resting levels at fatigue. QD appeared to block the increase in DA and DOPAC at 1 h of exercise, and LY prevented the decrease in DA and DOPAC at fatigue (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Bailey
S P
SP
Department of Exercise Science, School of Public Health, University of South Carolina, Columbia 29208.
Davis
J M
JM
Ahlborn
E N
EN
D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism; D004873:Ergolines / Q000494:pharmacology; D005221:Fatigue / Q000378:metabolism; D005230:Fatty Acids, Nonesterified / Q000097:blood; D006003:Glycogen / Q000378:metabolism; D008297:Male; D005082:Physical Exertion / Q000187:drug effects / Q000502:physiology*; D011814:Quipazine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012701:Serotonin / Q000378:metabolism*; D012702:Serotonin Antagonists / Q000494:pharmacology
D001786:Blood Glucose; D004873:Ergolines; D005230:Fatty Acids, Nonesterified; D012702:Serotonin Antagonists; D015102:3,4-Dihydroxyphenylacetic Acid; D012701:Serotonin; D011814:Quipazine; D006003:Glycogen; C032663:LY 53857; D004298:Dopamine