Transmitter characteristics of small mesenteric arteries from the rat.
We have studied the neurogenic response of small mesenteric arteries from the rat to evaluate the involvement of possible co-transmitters under various modes of stimulation. Segments of small branches of the mesenteric artery were mounted in a myograph and the intramural nerves were activated with transmural electrical stimulation. A single stimulation of the nerves caused a contraction that was reduced by only 20% in the presence of adrenergic blocking agents (prazosin or phenoxybenzamine), whereas the steady-state response to continuous nerve stimulation of high frequency was reduced by 90-95%. In contrast, all responses to applied noradrenaline in doses up to at least 1 mM were eliminated by phenoxybenzamine treatment. The stable ATP analogue, alpha,beta-methylene ATP, reduced the response to a single nerve stimulation by 70%, but reduced the contraction caused by continuous high-frequency nerve stimulation by only 10%. None of these agents affected the response to applied neuropeptide Y (NPY). The response of relaxed vessels to nerve stimulation was totally blocked by the combination of an adrenoceptor-blocking agent and alpha,beta-methylene ATP, although even in this situation a further neurogenic response could be revealed in vessels precontracted with vasopressin. Responses to either single stimuli or brief burst stimulations were potentiated after high-frequency stimulation. Both the adrenergic and non-adrenergic components were enhanced to roughly the same extent. Also the potentiated response was eliminated by the combined application of prazosin and alpha,beta-methylene ATP. The non-adrenergic transmitter in the sympathetic nerves of small arteries thus appears to be the dominant transmitter during low-frequency nerve stimulation, causing rapid but phasic activation. Noradrenaline is the most important transmitter for higher frequencies, exerting slower but sustained contractions. The post-stimulatory potentiation affects both the adrenergic and the non-adrenergic part of the neurogenic response.
Sjöblom-Widfeldt
N
N
Department of Physiology, University of Gothenburg, Sweden.
Gustafsson
H
H
Nilsson
H
H
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004558:Electric Stimulation; D066298:In Vitro Techniques; D008297:Male; D008638:Mesenteric Arteries / Q000294:innervation / Q000502:physiology; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000294:innervation / Q000502:physiology*; D009469:Neuromuscular Junction / Q000502:physiology*; D009478:Neuropeptide Y / Q000494:pharmacology*; D009638:Norepinephrine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D009435:Synaptic Transmission / Q000187:drug effects*
D000317:Adrenergic alpha-Antagonists; D009478:Neuropeptide Y; D000255:Adenosine Triphosphate; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; D009638:Norepinephrine