Sympathetic transmission in small mesenteric arteries from the rat: influence of impulse pattern

Abstract

We have previously studied the transmitters involved in, and the calcium dependency of, the neurogenic response to continuous, regular nerve stimulation in small mesenteric arteries from the rat. We have now studied responses to irregular nerve stimulation in these respects. Small mesenteric arteries from rat were mounted into a myograph and the intramural sympathetic nerves were activated by field stimulation. Irregular nerve stimulation was patterned after recorded activity in human cutaneous nerves. The response to irregular stimulation was reduced by only approximately 50% in the presence of the alpha 1-adrenoceptor antagonist prazosin. In particular, responses to low-frequency stimulation were resistant to prazosin. When the extracellular calcium concentration was reduced from 2.5 to 1.0 mM, approximately 50% of the response to irregular nerve stimulation remained. Responses to low-frequency stimulation were particularly reduced. Thus in these arteries the neurogenic response is caused by noradrenaline and a, perhaps purinergic, co-transmitter. The co-transmitter is important for the response to low-frequency stimulation and for the initial part of the contraction caused by high-frequency stimulation. Reducing the calcium concentration affects more strongly the response to low-frequency nerve stimulation.

ATP and norepinephrine contributions to sympathetic vasoconstriction of tail artery are altered in streptozotocin-diabetic rats

“…Responses to electrical stimulation in the presence of suramin in all nondiabetic groups were markedly reduced (Figs. 2B and 3A), and this reduction was more marked at lower impulse numbers (50 -75% reduction in response to 1 impulse) compared with that at higher impulse numbers (15-25% reduction in response to 100 impulses; P Ͻ 0.05, 1 vs. 100 impulses nondiabetic injected tissue, Wilcoxon signedrank), which accords with previous work (5,23). The three nondiabetic groups yielded similar inhibition profiles, whereas the diabetic group profile of inhibition was clearly different, being uniform across the range of impulse numbers (difference between groups, P Ͻ 0.001, two-way ANOVA), independent of the length of pulse train used (65-68% reduction; Fig.…”

“…Norepinephrine is usually coreleased with other neurotransmitters, particularly ATP and neuropeptide Y (NPY) in rat tail and mesenteric arteries, each having a synergistic effect on each other (5,22,23). Furthermore, the role of each cotransmitter varies with nerve impulse patterns: norepinephrine contributes to more to sustained trains of impulses, and ATP mediates responses to smaller numbers of impulses (5,22,23).…”

Purinergic Signaling and Blood Vessels in Health and Disease

“…An important implication is that the purinergic component of sympathetic neurotransmission may have been underestimated in experimental studies in which the pressure has been kept relatively low. Low-and high-frequency stimulation of sympathetic nerves in rat mesenteric arteries favors the purinergic and noradrenergic components respectively (Sjöblom-Widfeldt and Nilsson, 1990;Lamont and Wier, 2002). Nerve-evoked P2X 1 receptormediated contractions dominated in rat small and medium sized mesenteric arteries, whereas the noradrenergic component dominated in large (first order) mesenteric arteries (Gitterman and Evans, 2001).…”

Prenatal Hypoxia Leads to Increased Muscle Sympathetic Nerve Activity, Sympathetic Hyperinnervation, Premature Blunting of Neuropeptide Y Signaling, and Hypertension in Adult Life

“…36,37 The greater sympathetic nerve density revealed in tibial arteries of Y-CHU might be expected to further augment the number of impulses reaching arterial smooth muscle. And yet, baseline FVR was not different between Y-N and Y-CHU rats.…”