Pre- and postjunctional modulation by endothelin-1 of the adrenergic neurogenic response in canine mesenteric arteries

Sympathetic and Sensory-Motor Nerves in Peripheral Small Arteries

Small arteries, which play important roles in controlling blood flow, blood pressure, and capillary pressure, are under nervous influence. Their innervation is predominantly sympathetic and sensory motor in nature, and while some arteries are densely innervated, others are only sparsely so. Innervation of small arteries is a key mechanism in regulating vascular resistance. In the second half of the previous century, the physiology and pharmacology of this innervation were very actively investigated. In the past 10-20 yr, the activity in this field was more limited. With this review we highlight what has been learned during recent years with respect to development of small arteries and their innervation, some aspects of excitation-release coupling, interaction between sympathetic and sensory-motor nerves, cross talk between endothelium and vascular nerves, and some aspects of their role in vascular inflammation and hypertension. We also highlight what remains to be investigated to further increase our understanding of this fundamental aspect of vascular physiology.

Lack of prejunctional modulation of noradrenaline release by endogenous nitric oxide in guinea pig pulmonary artery

The regulation of noradrenaline (NA) release by endogenous endothelium-derived compounds was investigated in the isolated guinea pig pulmonary artery preloaded with [3H]NA. The radioactivity uptake, the basal and electrical field stimulation (10 Hz, 2 ms, 360 shocks) evoked release of [(3)H]NA was similar in arteries with intact endothelium and after removal of the endothelium. The wide selectivity nitric oxide (NO) synthase inhibitor N-omega-nitro-L-arginine (100 microM) did not affect significantly the basal and stimulation-evoked release of [(3)H]NA in control and endothelium-denuded preparations. These results indicate that neither endogenous NO nor other compounds derived from the endothelium have substantial influence on the NA outflow from sympathetic nerves innervating the pulmonary artery.

Endothelin-1-induced elevation in blood pressure is independent of increases in sympathetic nerve activity in normotensive rats

This study was performed to determine if endothelin-1 (ET-1)-induced pressor responses in urethane-anesthetized, normotensive rats are due to increased sympathetic nerve activity. Renal sympathetic nerve activity (RSNA) was used as an index of sympathetic nerve activity. ET-1 (30- 1000 pmol/kg) or sarafotoxin (S6c, ET B receptor agonist, 10-3,000 nmol/kg) given by bolus injection produced transient decreases in mean arterial pressure (MAP) and increases in RSNA and heart rate (HR). ET-1 caused a delayed but sustained increase in MAP that was not inhibited by acute sinoaortic denervation or alpha 1 -adrenergic receptor blockade. ET-1 never caused a sustained change in HR or RSNA. A-192621 (ET B receptor antagonist, 12 mg/kg) increased MAP (10-20 mm Hg) and decreased HR and RSNA. A-192621 blocked the transient decrease in MAP and increase in RSNA and HR caused by ET-1 and S6c. In A-192621-treated rats, ET-1, but not S6c, caused a sustained increase in MAP and decrease in HR and RSNA. After A-192621 treatment, ET-1 infusion caused a sustained elevation in MAP; HR and RSNA decreased only after the highest ET-1 dose. These results indicate that the initial increase in RSNA after ET-1 or S6c is secondary to ET B receptor-mediated vasodilation. Increased RSNA does not contribute to ET-1-induced pressor responses; these responses are likely due to vasoconstriction in normotensive, anesthetized rats. Finally, baroreceptor reflexes function after ET-1 or S6c treatment.

Inhibition by adrenomedullin of amine release from adrenergic nerves in dog mesenteric arteries

Adrenomedullin and calcitonin gene-related peptide (CGRP) inhibited the pressor response to transmural electrical stimulation in perfused isolated canine mesenteric arteries. The response was abolished by treatment with either prazosin or tetrodotoxin. Adrenomedullin-(22-52), an adrenomedullin receptor antagonist, reduced the inhibitory effect of adrenomedullin (10(-10) to 10(-8) mol/l), but did not alter the action of CGRP. CGRP-(8-37), a CGRP(1) receptor antagonist, did not affect the inhibition induced by adrenomedullin, but reversed the CGRP-induced inhibition. In helical strips of the arteries, adrenomedullin (up to 10(-8) mol/l) did not influence the contraction induced by noradrenaline, whereas CGRP attenuated the response. Adrenomedullin decreased the release of noradrenaline from adrenergic nerves elicited by transmural electrical stimulation, but CGRP had no effect. Adrenomedullin-(22-52) reversed the decrease in noradrenaline release induced by adrenomedullin. The adrenomedullin-induced relaxation of vascular strips precontracted with prostaglandin F(2alpha) was suppressed by CGRP-(8-37) but was unaffected by adrenomedullin-(22-52). These findings suggest that adrenomedullin impairs noradrenaline release from adrenergic nerves by acting on adrenomedullin receptors located in the nerve terminals, whereas arterial relaxation caused by adrenomedullin and CGRP is due to activation of CGRP(1) receptors in vascular smooth muscle.

Endothelin alters the reactivity of vasa vasorum: mechanisms and implications for conduit vessel physiology and pathophysiology

1 The walls of certain large blood vessels are nourished by the vasa vasorum, a network of microvessels that penetrate the adventitia and media of the vessel wall. The purpose of this study was to characterize endothelin-1 (ET-1)-mediated contraction of vasa and to investigate whether threshold concentrations of ET-1 alters the sensitivity to constrictors. Arterial vasa were dissected from the walls of porcine thoracic aorta and mounted in a tension myograph. 2 ET-1 and ETB-selective agonist, sarafotoxin 6c (S6c), produced concentration-dependent contraction. ETA receptor antagonist, BQ123 (10 microM), caused a biphasic rightward shift of ET-1 response curves. ETB receptor antagonist, BQ788 (1 microM), produced a rightward shift of response curves to ET-1 and S6c of 5- and 80 fold respectively. 3 ET-1 responses were abolished in Ca2+-free PSS but unaffected by selective depletion of intracellular Ca2+ stores. Nifedipine (10 microM), an L-type Ca2+ channel blocker, attenuated ET-1 responses by 44%. Inhibition of receptor-operated Ca2+ channels or non-selective cation entry using SKF 96365 (30 microM) and Ni2+ (1 mM) respectively, attenuated ET-1 contractions by 60%. 4 ET-1 (1-3 nM) enhanced responses to noradrenaline (NA) (4 fold) but not to thromboxane A2-mimetic, whilst K+ (10-20 mM) sensitized vasa to both types of constrictor. 5 Therefore, ET-1-induced contraction of isolated vasa is mediated by ETA and ETB receptors and involves Ca2+ influx through L-type and non-L-type Ca2+ channels. Furthermore elevation of basal tone of vasa vasorum alters the profile of contractile reactivity. These results suggest that ET-1 may be an important regulator of vasa vasorum reactivity.

Mechanisms underlying constrictor and dilator responses to perivascular nerve stimulation in canine lingual arteries

In isolated canine lingual arteries denuded of the endothelium, transmural electrical stimulation (2-20 Hz) produced a frequency-related contraction which was not significantly influenced by prazosin but which was reversed to a relaxation by alpha,beta-methylene ATP. The responses were abolished by tetrodotoxin. The stimulation-induced relaxation was abolished by treatment with NG-nitro-L-arginine (L-NA, 10(-6) M) and restored by the addition of L-arginine. Neurogenic relaxation resistant to L-NA was not observed after electrical stimulation, even though the pulse width and stimulus intensity were raised. Under treatment with prazosin, alpha,beta-methylene ATP and indomethacin, the arterial strips responded to nicotine (10(-4) M) with a marked relaxation that was abolished by hexamethonium. The relaxation was significantly inhibited but not abolished by L-NA (10(-5) M), and raising the concentration of the inhibitor to 10(-4) M, did not produce additional inhibition. In the strips treated with L-NA, the nicotine-induced relaxation was abolished or markedly reduced under desensitization with vasoactive intestinal peptide (VIP) or calcitonin gene-related peptide (CGRP) and by treatment with high concentrations of beraprost, a stable analog of prostaglandin I2, but was unaffected by CGRP or VIP receptor antagonists. Relaxant responses to a low concentration of nicotine (5 x 10(-6) M) were abolished by L-NA and restored by L-arginine. Histochemical study demonstrated many nerve fibers and bundles containing NADPH diaphorase in the adventitia of the arteries. It is concluded that the neurogenic arterial contraction is induced mainly by ATP via stimulation of P2X purinoceptors, and that the relaxation induced by electrical stimulation or a low concentration of nicotine is mediated by nitric oxide (NO) released from perivascular nerves. In high concentrations, nicotine elicits marked relaxations possibly due to the liberation of NO from the nerve and also vasodilator substances that increase the content of cyclic AMP in the tissue. CGRP and VIP are unlikely to be involved.

Inhibition by adrenomedullin of the adrenergic neurogenic response in canine mesenteric arteries

Adrenomedullin (AM) inhibited the pressor action caused by transmural electrical stimulation in perfused isolated canine mesenteric arteries. The inhibitory potency of AM was greater than that of calcitonin gene-related peptide (CGRP) or proadrenomedullin NH2-terminal 20 peptide (PAMP). [8-37]CGRP did not affect the inhibitory action of AM, but suppressed the CGRP-induced inhibition. It may be concluded that AM has an ability to inhibit adrenergic neuronal transmission without the mediation of CGRP1 receptors in the peripheral vasculature, and this inhibition partly participates in the potent hypotensive action of AM.