title: Microvascular dilation evoked by chemical stimulation of C-fibers in rats.
abstract: Activation of pulmonary C-fibers can reflexively decrease heart rate, blood pressure, and peripheral vascular resistance. However, the effects of these afferents on microvascular tone remain incompletely understood. In this study, we examined the effects of these afferents on microvascular tone in a striated muscle vascular bed. The right cremaster muscle in pentobarbital-anesthetized rats with intact circulation and innervation was suspended in a tissue bath, and diameters of small arterioles were measured by intravital video microscopy. Stimulation of pulmonary C-fibers by injecting capsaicin (5 μg/kg) or phenylbiguanide (20 μg/kg) into the right atrium dilated small arterioles and decreased blood pressure and heart rate. The effects persisted when the cervical vagus nerves were cooled to 5 to 7°C (blocking myelinated fibers), but were prevented by cooling to 0°C (blocking C-fibers and myelinated fibers), by cutting the genital femoral nerve (GFN) supplying the cremaster to block the nerve supply to the muscle, or by adding 6-hydroxydopamine to the bathing medium to selectively block sympathetic effects by depleting norepinephrine from adrenergic nerve terminals. Our results show that stimulation of pulmonary C-fibers reflexively dilates small arterioles in striated muscle by a mechanism that could involve withdrawal of sympathetic adrenergic tone. In conclusion, pulmonary C-fibers can exert an inhibitory influence on neural tone of the microcirculation at an important site where microvascular resistance and tissue blood flow are regulated.
authors.affiliation: Department of Physiology and Biophysics, School of Medicine, University of Louisville, Louisville, Kentucky; Department of Pediatrics, School of Medicine, University of Louisville, Louisville, Kentucky; andrew.roberts@louisville.edu.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Roberts
authors.affiliation: Department of Physiology and Biophysics, School of Medicine, University of Louisville, Louisville, Kentucky; Department of Medicine, School of Medicine, University of Louisville, Louisville, Kentucky; and Robley Rex Veterans Administration Medical Center, Louisville, Kentucky.
authors.forename: Jerry
authors.initials: J
authors.lastname: Yu
authors.affiliation: Department of Physiology and Biophysics, School of Medicine, University of Louisville, Louisville, Kentucky;
authors.forename: Irving G
authors.initials: IG
authors.lastname: Joshua
mesh_terms: D000818:Animals; D001645:Biguanides / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects* / Q000502:physiology; D002211:Capsaicin / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects* / Q000502:physiology; D008297:Male; D018482:Muscle, Skeletal / Q000098:blood supply* / Q000187:drug effects / Q000502:physiology; D036421:Nerve Fibers, Unmyelinated / Q000187:drug effects* / Q000502:physiology; D009431:Neural Conduction / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013268:Stimulation, Chemical; D014664:Vasodilation / Q000187:drug effects* / Q000502:physiology
chemical_list: D001645:Biguanides; D002211:Capsaicin; C008846:phenyl biguanide
keywords: arterioles; microcirculation; pulmonary C-fibers; pulmonary chemoreflex; vagal afferents