Sensitization of group III muscle afferents to static contraction by arachidonic acid.
The afferent arm of the reflex are responsible for the pressor response to static contraction is comprised of group III and IV fibers. The nature of the contraction-induced stimulus activating these fibers remains unclear. Evidence suggests that most group III afferents are sensitive to mechanical stimuli, whereas most group IV afferents are sensitive to metabolic stimuli. Recently, in anesthetized cats, stimulation of group III mechanoreceptors has been shown to have a role in the reflex pressor response to static contraction. In skin, the sensitivity of thin fiber mechanoreceptors to distortion of their receptive fields has been shown to be increased by both cyclooxygenase and lipoxygenase products of arachidonic acid metabolism. Therefore, in barbiturate-anesthetized cats we recorded the responses of group III muscle afferents to static contraction before and after arachidonic acid (1-2 mg ia) and/or indomethacin (5 mg/kg iv). Arachidonic acid increased the responses of group III afferents (n = 11) to contraction by 265% (from 0.17 +/- 0.07 to 0.62 +/- 0.24 impulses/s; P less than 0.025). Indomethacin decreased the responses of group III afferents (n = 9) to contraction by 61% (from 1.00 +/- 0.37 to 0.39 +/- 0.16 impulses/s; P less than 0.025). Arachidonic acid given after indomethacin increased the responses of two of four group III afferents to contraction. We conclude that both cyclooxygenase and lipoxygenase products of arachidonic acid metabolism sensitize group III muscle afferents to static contraction.
Rotto
D M
DM
Department of Internal Medicine, University of California, Davis 95616.
Schultz
H D
HD
Longhurst
J C
JC
Kaufman
M P
MP
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000344:Afferent Pathways / Q000187:drug effects / Q000502:physiology; D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000494:pharmacology*; D002415:Cats; D004558:Electric Stimulation; D007213:Indomethacin / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology; D009469:Neuromuscular Junction / Q000187:drug effects* / Q000502:physiology; D012018:Reflex / Q000187:drug effects / Q000502:physiology
D001095:Arachidonic Acids; D016718:Arachidonic Acid; D007213:Indomethacin