Lack of autonomic contributions to tonic nitric oxide-mediated vasodilatation in unanesthetized free-moving rats.
OBJECTIVE
To clarify the controversial issue of whether autonomic influences modulate vascular nitric oxide-mediated vasodilatation or even directly contribute to production of nitric oxide (NO) via nitroxidergic fibers.


METHODS
Chronic venous and arterial catheters were implanted in Wistar-Kyoto rats (n = 65) for continuous blood pressure measurement, drug administration and blood sampling. Tonic NO-dependent vasodilatation in the conscious free-moving animal was evaluated as the pressor response to inhibition of NO synthesis by intravenous L-monomethylarginine (a 100 mg/kg intravenous bolus plus 0.5 mg/kg per min infusion for 30 min). Experiments were performed under control conditions, chemical sympathectomy by 6-hydroxy-dopamine, ganglionic blockade by hexamethonium, and surgical denervation of sino-aortic baroreceptors.


RESULTS
Baseline mean arterial pressure was 100+/-4 mmHg (mean +/- SEM) in control rats and 73+/-3, 62+/-5, and 105+/-10 mmHg in sympathectomized, ganglion-blocked, and denervated rats, respectively. The peak increase in mean arterial pressure after administration of L-monomethylarginine was 38+/-3 mmHg in control rats and 51+/-3, 50+/-6, and 63+/-10 mmHg in sympathectomized, ganglion-blocked, and denervated rats, respectively. Epinephrine and norepinephrine levels in rats of separate groups of unanesthetized control, sympathectomized and ganglion-blocked animals were measured by high-performance liquid chromatography from an arterial blood sample, the results indicating drastic reductions in levels of both catecholamines in the ganglion-blocked (but not in the sympathectomized) rats compared with those in the control rats.


CONCLUSIONS
Tonic NO-dependent vasodilatation can normally be maintained in the unanesthetized unrestrained rat irrespective of autonomic or humoral adrenergic influences.
Radaelli
A
A
Divisione de Cardioriabilitazione, Ospedale di Seregno, Desio, Italy.
Mircoli
L
L
Perlini
S
S
Bolla
G
G
Mori
I
I
Mancia
G
G
Ferrari
A U
AU
D000818:Animals; D001341:Autonomic Nervous System / Q000187:drug effects / Q000502:physiology*; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D003714:Denervation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004837:Epinephrine / Q000097:blood; D005724:Ganglia / Q000187:drug effects / Q000502:physiology; D018738:Hexamethonium / Q000494:pharmacology; D009569:Nitric Oxide / Q000096:biosynthesis / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D009638:Norepinephrine / Q000097:blood; D016627:Oxidopamine / Q000494:pharmacology; D011311:Pressoreceptors / Q000502:physiology; D051381:Rats; D011921:Rats, Inbred WKY; D013563:Sympathectomy, Chemical; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*; D014667:Vasopressins / Q000494:pharmacology; D019323:omega-N-Methylarginine / Q000494:pharmacology
D004791:Enzyme Inhibitors; D014667:Vasopressins; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D018738:Hexamethonium; D016627:Oxidopamine; D019001:Nitric Oxide Synthase; D009638:Norepinephrine; D004837:Epinephrine