Pharmacological analysis of the double peaked vasoconstrictor responses to periarterial electric stimulation

The hemostatic effect study of Cirsium setosum on regulating α1-ARs via mediating norepinephrine synthesis by enzyme catalysis

BACKGROUND

Cirsium setosum (CS) is the aboveground part of Cephalanoplos segetum Kitam. Although it has been used as a hemostatic treatment for thousands of years and is still in use today, the mechanism of CS on regulating ARs is still not clear.

PURPOSE

In this study, we aimed to clarify the mechanism of CS on regulating ARs.

METHODS

We developed a simple method based on UPLC/Q-TOF MS combined adrenergic receptor dual-luciferase reporter assay systems for the rapid determination of active constituents in CS. The mechanism of tyramine, the main active component for regulating ARs, was further investigated by an in vitro norepinephrine biotransformation test and in vivo vaso activity tests.

RESULTS

Two phenethylamine ARs regulators (tyramine and N-methyltyramine) in CS were characterized, and it was found that tyramine could induce vasoconstriction via regulation of α1-ARs by mediating norepinephrine synthesis.

CONCLUSION

The hemostatic effect of CS is associated with tyramine and N-methyltyramine, via regulation of α1-ARs, and the mechanism of tyramine is related to mediating norepinephrine synthesis by enzyme catalysis.

Purinergic receptors in the splanchnic circulation

There is considerable evidence that purines are vasoactive molecules involved in the regulation of blood flow. Adenosine is a well known vasodilator that also acts as a modulator of the response to other vasoactive substances. Adenosine exerts its effects by interacting with adenosine receptors. These are metabotropic G-protein coupled receptors and include four subtypes, A(1), A(2A), A(2B) and A(3). Adenosine triphosphate (ATP) is a co-transmitter in vascular neuroeffector junctions and is known to activate two distinct types of P2 receptors, P2X (ionotropic) and P2Y (metabotropic). ATP can exert either vasoconstrictive or vasorelaxant effects, depending on the P2 receptor subtype involved. Splanchnic vascular beds are of particular interest, as they receive a large fraction of the cardiac output. This review focus on purinergic receptors role in the splanchnic vasomotor control. Here, we give an overview on the distribution and diversity of effects of purinergic receptors in splanchnic vessels. Pre- and post-junctional receptormediated responses are summarized. Attention is also given to the interactions between purinergic receptors and other receptors in the splanchnic circulation.

Neurogenic double-peaked vasoconstriction of human gastroepiploic artery is mediated by both alpha1- and alpha2-adrenoceptors

1. The contribution of postjunctional P2X receptors and subtypes of alpha-adrenoceptors to vasoconstrictor responses following periarterial electrical nerve stimulation (PNS, 30 s trains of pulses at a frequency of 2, 4 or 8 Hz) was investigated in human gastroepiploic arteries. 2. The vasoconstrictor response to PNS at a stimulation of 4 or 8 Hz was a two-peaked response, whereas at a frequency of 2 Hz it appeared only as a late peak. All vasoconstrictions evoked by PNS were abolished by phentolamine, a nonselective alpha-adrenoceptor inhibitor, but not by alpha,beta-methylene ATP, a P2X receptor-desensitizing agent. 3. The early peak to PNS at 4 or 8 Hz was abolished by prazosin, an alpha1-adrenoceptor antagonist, while the late one still remained, although it was markedly inhibited. The responses remaining after prazosin were blocked by rauwolscine. The vasoconstrictor response to PNS at 2 Hz was not affected by prazosin (0.1 microM), but was abolished by rauwolscine (0.1 microM), an alpha2-adrenoceptor antagonist. 4. OPC-28326 (10 microM), a newly developed vasodilator, which preferentially exerts its antagonistic actions on the alpha2B- and alpha2C-adrenoceptors, significantly reduced the noradrenaline-induced vasoconstriction in the absence or presence of prazosin. OPC-28326 had a greater inhibitory effect on the late peak evoked by PNS than the early one. The neurogenic responses remaining after OPC-28326 were abolished by prazosin. 5. The present results suggest that sympathetic vasoconstriction of the human gastroepiploic artery is mediated by both alpha1- and alpha2-adrenoceptors postjunctionally, but not by P2X receptors. The alpha2-adrenoceptors may be preferentially activated at a low frequency of stimulation, which induces a constriction more slowly than that by alpha1-adrenoceptors. The existence of alpha2-adrenoceptors may cause an enhancement of alpha1-adrenoceptor-induced responses.

Differences in alpha 1-adrenoceptor subtype-mediated vasoconstriction by tyramine and nerve stimulation in canine splenic artery

This study was designed to clarify the alpha(1)-adrenoceptor subtypes mediating the vasoconstrictor response to tyramine in isolated and perfused canine splenic artery. It was shown that tyramine potentiated the nerve stimulation-induced second peaked vasoconstriction that was readily suppressed by prazosin treatment. A bolus injection of tyramine (0.01-0.3 micromol) caused a vasoconstriction in a dose-related manner. The tyramine-induced vasoconstriction was inhibited by WB 4101 (10 and 100 nM), an alpha(1A)-and alpha(1D)-adrenoceptor antagonist, in a concentration-related manner. Neither BMY 7378 (100 nM), a selective alpha(1D)-adrenoceptor antagonist, nor chloroethylclonidine (60 microM), an alpha(1B)- and alpha(1D)-adrenoceptor antagonist, affected the tyramine-induced response. The results indicate that the noradrenaline released by tyramine may diffuse to the extrajunctional cleft, and thus it activates the extrajunctional alpha(1A)-adrenoceptors, because nerve stimulation-evoked second peaked vasoconstrictions were markedly inhibited by chloroethylclonidine but not by WB 4101.

Purinergic and adrenergic cotransmission in canine isolated and perfused gastroepiploic arteries

1. The vasoconstrictor responses of canine gastroepiploic artery to periarterial electrical nerve stimulation (PNS; 30 s trains of pulses at a frequency of 2, 4 or 8 Hz) were observed in a frequency dependent manner. The PNS-induced vasoconstrictions were abolished by tetrodotoxin (1 micromol/L) and mostly depressed but not completely by guanethidine (10 micromol/L). 2. Vasoconstrictor responses to administered noradrenaline were antagonized significantly by prazosin (0.1 micromol/L), an alpha1-adrenoceptor antagonist, but were not significantly affected by suramin (100 micromol/L), a P2 purinoceptor antagonist, or alpha,beta-methylene ATP (1 micromol/L), a P2X receptor desensitizing agent. Exogenous ATP-induced responses were clearly depressed by suramin or alpha,beta-methylene ATP, but were not significantly affected by prazosin. 3. The vasoconstrictor responses to PNS at a low frequency (2 and 4 Hz) of stimulation were markedly inhibited by suramin (100 micromol/L) and by alpha,beta-methylene ATP (1 micromol/L). The remaining responses after suramin or alpha,beta-methylene ATP were abolished by subsequent application of prazosin (0.1 micromol/L). At a high frequency (8 Hz) of stimulation, the vascular response was not significantly inhibited by suramin or alpha,beta-methylene ATP, but it was abolished by prazosin. 4. Injection of xylazine (0.3-30 nmol/L), an alpha2-adrenoceptor agonist, did not induce any clear vasoconstriction. The exposure of tissues to rauwolscine (0.1-0.3 micromol/L), an alpha2-adrenoceptor antagonist, dose-dependently increased PNS-induced vasoconstrictions at all frequencies tested. 5. The present results indicate that ATP acts as a cotransmitter with noradrenaline and is responsible for post-junctional vasoconstrictor responses at low frequencies of sitmulation, whereas the effect of noradrenaline is dominant at high-frequency stimulation in canine gastroepiploic artery. Prejunctional alpha2-adrenoceptor autoinhibition may modulate the release of either noradrenaline or ATP from sympathetic nerve terminals.

The preferential inhibitory effect of olmesartan, a new angiotensin II type 1 antagonist, on sympathetic nerve terminals in isolated canine splenic artery

Effects of olmesartan (RNH-6270: (5-methyl-2-oxo-1,3-dioxolen-4-yl)methoxy-4-(1-hydroxy-1-methylethyl)-2-propyl[4-[2-(tetrazol-5-yl)-phenyl]phenyl]methylimidazol-5-carboxylase, an active form of olmesartan medoxomil (CS-866)) was investigated in isolated, perfused canine splenic arterial preparations. Neither exogenous noradrenaline- nor ATP-induced vasoconstrictor responses were modified by treatment with the used concentrations of olmesartan (1-100 nM). A high concentration of 10 nM angiotensin II caused a potentiation of either noradrenaline- and ATP-induced constrictions, although 1 nM angiotensin II did not induce any potentiating effects for these responses. These potentiations were inhibited by olmesartan in a concentration-related manner. Periarterial nerve electrical stimulation (PNS) readily induced a biphasic constriction consisting of an initial P2X purinoceptor-mediated vasoconstriction followed by a prolonged mainly alpha(1)-adrenoceptor-mediated response. PNS-induced 1st and 2nd peaked responses were significantly inhibited by olmesartan in a concentration-related manner. With a low concentration of 1 nM angiotensin II, which did not induce any vascular effects by itself, PNS-induced responses were markedly enhanced. The enhanced responses were inhibited by olmesartan. It is concluded that endogenous angiotensin II exerts its stimulating action on the releases of ATP and noradrenaline from the periarterial sympathetic nerve terminal, and olmesartan has an inhibitory property on angiotensin II-induced potentiation of endogenous ATP- and noradrenaline-induced responses.

Effects of reserpine on nerve stimulation-induced constrictions in canine isolated splenic artery

1. Our previous studies have demonstrated that peri-arterial electrical nerve stimulation (PNS) of the canine splenic artery induces a double-peaked vasoconstriction consisting of an initial transient, dominantly P2X purinoceptor-mediated constriction, followed by a prolonged, mainly alpha1-adrenoceptor-induced response. In the present study, we examined the effects of reserpine on PNS-induced double-peaked responses. 2. The vasoconstrictor response to tyramine was abolished after reserpine treatment, but the responses to noradrenaline (NA) and ATP were not significantly modified. 3. The PNS-induced second peak vasoconstrictor responses were markedly reduced in reserpinized vessels, whereas the first peak vasoconstrictor responses were not so strongly influenced (i.e. they were not significantly affected at 1 Hz, but were significantly affected at 4 and 10 Hz). 4. All reserpine-resistant responses were unaffected by treatment with prazosin, but were abolished by subsequent application of alpha,beta-methylene ATP. The exposure of reserpine-treated tissues to NA almost completely restored tyramine-induced vasoconstriction and the second neurogenic peak vasoconstrictor response, but failed to affect the first neurogenic response. 5. The present results indicate that ATP and NA are cotransmitters responsible for the double-peaked vasoconstrictor responses of canine splenic artery. In addition, it is suggested that PNS causes NA release not only from intragranular NA storage sites, but also from tyramine-sensitive cytoplasmic sites.

Neuroeffector mechanisms involved in the regulation of dog splenic arterial tone

It has been recognized that sympathetic neurons release several transmitters but mainly adenosine 5'-triphosphate (ATP), noradrenaline, and neuropeptide Y (NPY). Recently, we reported that periarterial nerve electrical stimulation (PNS) produced biphasic vasoconstrictions consisting of an initial transient, predominantly P2X-purinoceptor-mediated constriction followed by a prolonged, alpha(1)-adrenoceptor-mediated one in canine isolated splenic arteries. In this article, we tried to analyze the effects of several selective key drugs that influence the PNS-induced responses, and we functionally showed sympathetic transmitter releasing mechanisms by pharmacological analysis using purinergic, adrenergic, and NPYergic agonists and antagonists.

Interaction between neuropeptide Y Y1 receptors and alpha1B-adrenoceptors in the neurovascular junction of canine splenic arteries

Previous study has demonstrated that periarterial electrical nerve stimulation (30-s trains of pulses at a frequency of 1 or 4 Hz) induces a double-peaked vasoconstriction consisting of an initial transient, predominantly P2X-receptor-mediated constriction followed by a prolonged, mainly alpha(1)-adrenoceptor-mediated response in the isolated canine splenic artery. Treatment with 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione (BMY 7378, 0.1 micromol/l), a selective alpha(1D)-adrenoceptor antagonist, produced a slight but significant inhibition of the second peaked responses. A marked inhibition of second peaked responses was obtained by exposure of the tissues to chloroethylclonidine (60 micromol/l), an alpha(1B)- and alpha(1D)-adrenoeptor antagonist. Neither BMY 7378 nor chloroethylclonidine affected the first peaked vasoconstrictor responses. [Leu(31),Pro(34)]Neuropeptide Y (10-30 nmol/l), a selective neuropeptide Y Y(1) receptor agonist, enhanced the second peaked responses in the presence of BMY 7378 but failed to enhance the responses in the presence of chloroethylclonidine. The results indicate that the postjunctional alpha(1B)-adrenoceptor subtype is likely coupled to neuropeptide Y Y(1) receptors responsible for the cooperation of the sympathetic adrenergic and neuropeptide Yergic transmission in the canine splenic artery.

Effects of L-765,314, a selective and potent alpha 1B-adrenoceptor antagonist, on periarterial nerve electrical stimulation-induced double-peaked constrictor responses in isolated dog splenic arteries

The periarterial nerve electrical stimulation (PNS) at a frequency of 1 or 4 Hz (30-s trains of pulses) readily caused a double peaked vasoconstriction in the canine splenic artery. The treatment with 1 microM L-765,314, a selective and potent alpha1B-adrenoceptor antagonist, markedly inhibited the second peaked constriction, whereas it did not modify the vasoconstrictor responses to exogenous noradrenaline (0.03-1 nmol) and A61603 (1-30 pmol), a selective alpha1A-agonist. A large dose of 10 microM L-765,314 significantly blocked exogenous noradrenaline- and A61603-induced responses. It is concluded that PNS-induced responses are mediated via the postjunctional alpha1B-adrenoceptor subtype.

Antagonistic interaction between BIIE 0246, a neuropeptide Y Y2-receptor antagonist, and omega-conotoxin GVIA, a Ca2+ channel antagonist, in presynaptic transmitter releases in dog splenic arteries

Isolated dog splenic arteries were perfused with Krebs-Henseleit solution at 37 degrees C, using the cannula inserting method. Periarterial nerve electrical stimulation (10-V amplitude; 1-ms duration; 30-s trains of pulses; 1, 4 and 10 Hz) readily caused double peaked vasoconstrictions, i.e., 1st peaked response was mostly inhibited by alpha,beta-methylene ATP and the 2nd one, by prazosin. These responses were consistently inhibited by omega-conotoxin GVIA (omega-CTX), whereas they were facilitated by BIIE 0246, a neuropeptide Y (NPY) Y2-receptor antagonist. The omega-CTX-induced blocking effects of transmitter release were significantly antagonized by BIIE 0246. It is possible that the NPY Y2 receptor activity may partially be linked to presynaptic Ca2+ channels.

Neuropeptide Y inhibits double peaked vasoconstrictor responses to periarterial nerve stimulation primarily through prejunctional Y2 receptor subtype in canine splenic arteries

1 The effects of BIIE 0246, a novel and non-peptide neuropeptide Y (NPY) Y2 receptor antagonist on sympathetic vasoconstriction of the canine splenic artery were investigated. 2 The vasoconstrictor response to periarterial electrical nerve stimulation was described to be a double peaked vasoconstriction consisting of an initial transient, dominantly P2X purinoceptor-mediated constriction followed by a prolonged, mainly alpha1 adrenoceptor-induced response. 3 BIIE 0246 at a concentration of 0.1-1 microM dose-dependently potentiated double peaked constrictions at low frequencies (1 and 4 Hz), whereas at high frequency (10 Hz), it failed to affect these responses. BIIE 0246 (1 microM) also enhanced double peaked responses even in the presence of rauwolscine (0.1 microM). NPY (13-36) (1-100 nM), a selective Y2 receptor agonist reduced these two peaked responses in a dose-related manner. The vasoconstriction to noradrenaline (0.1-10 nmol) or adenosine triphosphate (0.01-1 micromol) was not significantly influenced by either 1 microM BIIE 0246 or 100 nM NPY (13-36). Exposure of tissues to 1 microM BIIE 0246 almost completely prevented the suppression of double peaked constrictions by NPY (13-36) (10 nM) or by NPY (10 nM). 4 We conclude that NPY inhibits sympathetic purinergic and adrenergic vasoconstrictions through an activation of prejunctional Y2 receptor subtype in the neurovascular junction of the canine splenic artery.

Different sensitivities to alpha1 adrenoceptor blockade on periarterial sympathetic nerve-induced constriction by low and high frequencies in canine isolated splenic arteries

The periarterial nerve electrical stimulation at 4 and 10 Hz induced a monophasic vasoconstriction of the canine splenic artery in a pulse number-related manner (1-30 pulses). The responses at 4 Hz were not significantly affected by 0.1 microM prazosin, but abolished by 1 microM alpha, beta-methylene ATP. Prazosin (0.1 microM) partially but significantly inhibited responses at 10 Hz, and the remaining responses were blocked by 1 microM alpha, beta-methylene ATP. It indicates that the monophasic vasoconstrictor response to short pulses of stimulation at a low frequency is mediated by P2X-receptors, whereas the response at a high frequency may be due to activation of not only P2X-receptors but also alpha1 adrenoceptors.

Separate modulation of neuropeptide Y1 receptor on purinergic and on adrenergic neuroeffector transmission in canine splenic artery

Our previous study demonstrated that the vasoconstrictor responses to trains of up to 10 pulses at 1 Hz of stimulation appeared to be purinergic monophasic, whereas a longer train of 30 pulses induced a biphasic vasoconstriction consisting of an initial, transient purinergic constriction followed by a prolonged adrenergic response. Neuropeptide Y (NPY) at doses of 0.01 and 0.1 microM produced a dose-dependent inhibition on the monophasic and biphasic vasoconstrictor responses to nerve stimulation. The treatment with Leu31 Pro34 neuropeptide Y (LP-NPY) (0.03 microM) did not affect the monophasic responses to short pulse trains of stimulation. However, LP-NPY markedly potentiated the second phase response to 30 pulse trains of stimulation, although it did not modify the first one. The LP-NPY-induced potentiation was abolished by BIBP 3226 (1 microM), a selective NPY Y1 receptor antagonist. The results indicate that the activation of NPY Y1 receptors may enhance the prolonged adrenergic vasoconstriction but not the transient purinergic response in the canine splenic artery.

Existence of different alpha(1)-adrenoceptor subtypes in junctional and extrajunctional neurovascular regions in canine splenic arteries

The present study attempted to characterize the alpha(1)-adrenoceptor subtypes mediating vasoconstrictor responses to administered and nerve stimulation-evoked noradrenaline (NA) release in the isolated and perfused canine splenic artery. A previous study demonstrated that periarterial electrical nerve stimulation (30 s trains of pulses at a frequency of 1, 4 or 10 Hz) induced a double peaked vasoconstriction consisting of an initial transient, predominantly P2X-purinoceptor-mediated constriction followed by a prolonged, mainly alpha(1)-adrenoceptor-mediated response in the canine splenic artery. The effects of alpha(1)-adrenoceptor subtype antagonists on neuronally-mediated second peaked vasoconstrictions were analysed. BMY 7378 (10 - 100 nM), a selective alpha(1D)-adrenoceptor antagonist produced a dose-dependent inhibition of the second peak responses at all frequencies used. BMY 7378 (100 nM) reduced these responses by approximately 30%. Exposure of tissues to chloroethylclonidine (CEC, 60 microM), a selective alpha(1B)-adrenoceptor antagonist attenuated the second peak response by approximately 60%, even in the presence of BMY 7378 (100 nM). On the other hand, WB 4101 (100 nM), a selective alpha(1A)-adrenoceptor antagonist potentiated nerve-stimulation-evoked double peaked vasoconstrictions, especially at low frequencies (1 and 4 Hz). Vasoconstrictor responses to administered NA were dose-dependently antagonized by WB 4101 (10 - 100 nM), but were not significantly affected by either BMY 7378 (10 - 100 nM) or by CEC (60 microM). The present results indicate that NA released from sympathetic nerves may junctionally exert its vasoconstrictor effect via activation of postjunctional alpha(1B)- and in part alpha(1D)-adrenoceptors, whereas exogenous NA extrajunctionally activates alpha(1A)-adrenoceptors to produce its vascular action in canine splenic arteries.

Differential effects of omega-conotoxin GVIA, tetrodotoxin and prolonged cold storage on purinergic and adrenergic transmission in isolated canine splenic artery

Double-peaked vasoconstrictions (biphases of vasoconstrictions) were readily induced in the conditions of 30 s trains of pulses at 1 Hz in the isolated, perfused canine splenic artery. P2X purinoceptors have previously been shown to be involved mainfy in the first-peaked response and alpha1-adrenoceptors mostly in the second. The treatment with 10 nM omega-conotoxin GVIA (omega-CTX) produced a parallel inhibitory effect on the first- and second-peaked vasoconstrictor responses to nerve stimulation. A submaximal concentration of tetrodotoxin (TTX) (3 nM) did not affect the first peak of constriction, but strongly inhibited the second peak, although a larger dose of TTX (30 nM) abolished either the first- or second-peaked response. On the other hand, after cold storage at 4 degrees C for 7 days, the first-peaked vasoconstriction markedly decreased, whereas the second-peaked response was not significantly modified.

IN CONCLUSION

(1) omega-CTX-sensitive calcium channels may produce a parallel modulation of purinergic and adrenergic components of sympathetic cotransmission; (2) TTX-sensitive sodium channels may have a more important role in controlling the adrenergic rather than purinergic transmission; and (3) the function of purinergic transmission of sympathetic nerve might be affected more strongly than that of adrenergic transmission in the cold-stored canine splenic artery.

Periarterial electrical nerve stimulation-induced adrenergic vasoconstriction inhibited by adrenergic alpha1B-receptor blockade but not by alpha1A-blockade

The periarterial electrical nerve stimulation at a frequency of 4 Hz (30-s trains of pulses) induced a double-peaked vasoconstriction in the canine splenic artery. The treatment with chloroethylclonidine (CEC, 60 microM) markedly inhibited the second-peaked constriction, whereas it produced an insignificant effect on the first-peaked response. The vasoconstriction to noradrenaline (NA, 1 nmol) was not significantly influenced by 60 microM CEC. On the other hand, WB 4101 (1 microM) consistently abolished the vascular response induced by NA (1 nmol), but rather potentiated the double-peaked constriction. The results indicate that neuronal NA may junctionally exert its vasoconstrictor effect via an activation of postjunctional alpha1B-receptors, whereas exogenous NA may extrajunctionally activate alpha1A-receptors for its vascular action in the canine splenic artery.

Effects of a selective neuropeptide Y Y(1) receptor antagonist BIBP 3226 on double peaked vasoconstrictor responses to periarterial nerve stimulation in canine splenic arteries

The periarterial electrical nerve stimulation (30 s trains of pulses at a frequency of 1, 4 or 10 Hz) induced a double peaked vasoconstriction consisting of an initial transient constriction (first peak) followed by a prolonged response (second peak) in the isolated, perfused canine splenic artery. At low frequencies (1 and 4 Hz), a neuropeptide Y (NPY) Y(1) receptor antagonist BIBP 3226 (0.1-1 microM) produced a dose-dependent inhibitory effect on the second peak, but did not modify the first peak. At a high frequency (10 Hz), 1 microM BIBP 3226 induced a slight, but significant inhibition on both the first and second peaked responses. At a low frequency (1 Hz), the first peak was not influenced by blockade of alpha(1)-adrenoceptors or NPY Y(1) receptors with prazosin (0.1 microM) or BIBP 3226 (1 microM), respectively, but abolished by P2X receptor desensitization with alpha,beta-methylene ATP (alphabeta-m ATP, 1 microM). At a high frequency (10 Hz), the first peak was mostly inhibited by alphabeta-m ATP and partially by prazosin and BIBP 3226. On the other hand, the second peak at a low frequency was largely decreased by BIBP 3226 and partially by prazosin and alphabeta-m ATP, whereas at a high frequency, it was largely attenuated by prazosin and partially by alphabeta-m ATP and BIBP 3226. The results suggest that at a low frequency, the firstly transient constriction of double peaked responses is mainly induced via an activation of P2X-receptors, whereas at a high frequency, it is mostly mediated by the P2X-receptors, and partially by alpha(1)-receptors and NPY Y(1)-receptors. The secondary prolonged vasoconstriction at frequencies used is predominantly mediated via both alpha(1)-receptor and NPY Y(1) receptor activations, and in part by P2X-receptors. Furthermore, an activation of NPY Y(1) receptors may play an important role in evoking the prolonged vasoconstrictor response to longer pulse trains of stimulation at a low frequency, whereas an alpha(1)-adrenoceptor activation exerts a main vasomotor effect for the prolonged response at a high frequency.

Dissociation of potentiation of Leu31 Pro34 neuropeptide Y on adrenergic and purinergic transmission in isolated canine splenic artery

The present study observed the effects of an activation of neuropeptide Y (NPY) Y1 receptors on adrenergic and purinergic components of double-peaked vasoconstrictor responses to periarterial nerve stimulation in the isolated, perfused canine splenic arteries. The results showed that 3-30 nM Leu31 Pro34 neuropeptide Y (LP-NPY) produced a dose-dependent potentiation of double-peaked vasoconstrictor responses to trains of 30-s pulses at 1, 4 or 10 Hz of stimulation. The potentiation of LP-NPY of the nerve-stimulated vasoconstrictions were completely inhibited by subsequent blockade of alpha1-adrenoceptors or Y1 receptors with 0.1 microM prazosin or with 1 microM BIBP 3226 ((R)-N2-(diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]-argininami de), respectively. The remaining responses in the presence of LP-NPY and prazosin were abolished by P2X receptor desensitization with 1 microM alpha,beta-methylene ATP. Moreover, 30 nM LP-NPY failed to modify the vasoconstrictor responses to nerve stimulation after treatment with prazosin. A subsequent administration of alpha,beta-methylene ATP completely suppressed the remaining responses after prazosin and LP-NPY. The vasoconstrictions induced by 0.003-1 nmol noradrenaline and 0.003-1 micromol ATP were slightly, but not significantly enhanced by 30 nM LP-NPY. The observations indicated that activation of postjunctional NPY Y1 receptors may have an important role in the modulation of adrenergic rather than purinergic transmission of the sympathetic co-transmission.

Effects of neuropeptide Y on double-peaked constrictor responses to periarterial nerve stimulation in isolated, perfused canine splenic arteries

The periarterial electrical nerve stimulation readily induced a double-peaked vasoconstriction in the isolated, perfused canine splenic artery. P2X-Purinoceptors have previously been shown to be involved mainly in the 1st-phase response and alpha 1-adrenoceptors, mostly in the 2nd-one. The dose used of neuropeptide Y (NPY) (0.01-0.1 microM) given into the preparation caused a slight but insignificant vasoconstriction. The treatment with NPY at concentrations of 0.01-0.1 microM produced a parallel inhibition on the 1st- and 2nd-phase responses following nerve stimulation at the frequencies used (1-10 Hz) in a dose-dependent manner. The vasoconstrictor responses to administered ATP (0.01-1 mumol) or noradrenaline (0.03-3 nmol) were slightly but not significantly potentiated by 0.1 microM NPY. The results indicate that NPY predominantly exerts a prejunctionally inhibitory modulation on the purinergic and adrenergic transmission in peripheral sympathetic nerves innervating the canine splenic artery.

Effects of omega-conotoxin GVIA and diltiazem on double peaked vasoconstrictor responses to periarterial electric nerve stimulation in isolated canine splenic artery

The actions of omega-conotoxin (omega-CTX) and diltiazem on adrenergic and purinergic components of double peaked vasoconstrictor responses to periarterial nerve stimulation have been investigated in the isolated, perfused canine splenic arterial preparation. Double peaked vasoconstrictions (biphases of vasoconstrictors) were consistently observed in the conditions of 30 s trains of pulses at 1 - 10 Hz frequencies. omega-CTX (1 - 30 nM) produced similar inhibitory effects on the first phase and second phase responses in a dose-related manner. Thirty nM omega-CTX almost completely inhibited the biphasic vasoconstrictions at any used frequencies but did not affect the vasoconstrictor responses to exogenous applied ATP (0.01 - 1 micromol) and noradrenaline (0.03 - 3 nmol). Intraluminal application of a large dose of diltiazem (3 - 10 microM) also produced a dose-dependent inhibitory effect on biphasic vasoconstrictions at any used frequencies. Three microM diltiazem exerted rather a larger inhibitory effect on the second phase than the first phase response at low frequencies (1 - 3 Hz), but a similar inhibition on first and second phasic responses at high frequencies (6 - 10 Hz). An extremely high dose of diltiazem (10 microM) almost completely inhibited the biphasic vasoconstrictor responses to nerve stimulation, and slightly inhibited the contractile responses to exogenous applied ATP (0.01 - 1 micromol) and noradrenaline (0.03 - 3 nmol). The present results indicate that omega-CTX selectively acts prejunctionally to inhibit the release of transmitters from sympathetic nerve terminals, and omega-CTX-sensitive calcium channels may produce a parallel controlling of purinergic and adrenergic components of sympathetic cotransmission. A large dose of diltiazem has inhibitory effects on both prejunctional and postjunctional sympathetic co-transmission. British Journal of Pharmacology (2000) 129, 47 - 52

Perivascular purinergic nerve-induced vasoconstrictions in canine isolated splenic arteries

We tried to induce selective perivascular purinergic nerve stimulation in isolated canine splenic arterial preparations, using the cannula insertion method. Under the conditions of periarterial electrical stimulation (ES), i.e., trains of 1, 3 and 10 pulses, 1-ms pulse duration and 10-V amplitude at 1 Hz, monophasic vasoconstriction was consistently induced. The ES-induced vasoconstriction was not influenced by prazosin in doses that completely inhibited noradrenaline-induced vasoconstrictions, but it was suppressed by alpha,beta-methylene ATP, a P2X purinoceptor desensitizer. Thus, it is indicated that a selective purinergic transmitter release is readily obtained in the isolated splenic arterial preparation.

Pharmacological analysis of vasoconstrictor responses to periarterial purinergic nerve stimulation

1. Periarterial electrical nerve stimulation at a low frequency (1 Hz) readily induced a vasoconstrictor response of the canine splenic artery in a pulse number-related manner (1-30 pulses of trains). The vasoconstrictor response to trains of up to 10 pulses at 1 Hz of stimulation appeared to be monophasic, whereas it became clearly distinguished into two phases at a longer train of 30 pulses. 2. The monophasic vasoconstrictor responses to trains of 1, 3 or 10 pulses were not modified by an alpha1-adrenoceptor blocking agent, prazosin (0.1 microM), but were completely inhibited by the P2X receptor desensitization with alpha,beta-methylene adenosine 5'-triphosphate (alpha,beta-methylene ATP; 1 microM). The 1st phase of vasoconstriction induced by a train length of 30 pulses was not influenced by the treatment with prazosin, but was abolished by alpha,beta-methylene ATP. The 2nd phase response was markedly inhibited by prazosin, and the remaining response of this phase was blocked by alpha,beta-methylene ATP. 3. Rauwolscine (0.3 microM), an alpha2-adrenoceptor antagonist, enhanced the vasoconstrictor responses to trains of 1, 3 or 10 pulses. Particularly at 10 pulses of electrical stimulation, the vasoconstrictor responses were significantly potentiated. The blockade of neuronal uptake of noradrenaline with imipramine (1 microM) did not affect the vasoconstrictor responses to trains of 1, 3 or 10 pulses. 4. It is concluded that short pulse trains of stimulation at a low frequency may selectively activate a purinergic component of sympathetic cotransmission, and the prejunctional alpha2-adrenergic feedback mechanism may tonically participate into the modulation of ATP release. Imipramine-sensitive neuronal uptake mechanism may not play an important role in regulating vascular responses to periarterial purinergic nerve stimulation.

Endothelium-released adenosine triphosphate contributes to vasoconstrictor responses to periarterial nerve stimulation in isolated, perfused canine splenic arteries

P2X-Purinoceptors and alpha1-adrenoceptors have previously been shown to be involved in double-peaked vasoconstrictor responses to periarterial electrical nerve stimulation in the isolated and perfused canine splenic artery. The present study was designed to investigate the influence of endothelium removal on vasoconstrictor responses to periarterial nerve stimulation, tyramine, noradrenaline, and adenosine triphosphate (ATP) in the isolated canine splenic artery. Intraluminal administration of saponin completely abolished the acetylcholine-induced vasodilatation and potentiated the vasoconstrictor response to KCl. Double-peaked vasoconstriction (two phases of vasoconstriction) was readily induced by periarterial electrical nerve stimulation in the canine splenic arterial preparation with or without endothelium and was consistently abolished by treatment with tetrodotoxin. Removal of endothelium slightly but significantly decreased the first-phase vasoconstrictor responses to stimulation of 1 or 10 Hz, and did not affect the second-phase. The vasoconstrictor responses to tyramine, noradrenaline, and ATP were not modified by endothelium removal. From these results, it is postulated that ATP released from endothelium, as a modulator of sympathetic nerve cotransmission, may partially contribute to the purinergic constriction component in the canine splenic artery.

Dissociation of inhibitory effects of guanethidine on adrenergic and on purinergic transmission in isolated canine splenic artery

The aim of this study was both to investigate the effects of progressive inhibition of adrenergic neurons by increasing concentrations of guanethidine (0.1-10 microM) on the double-peaked vasoconstrictor responses to electrical periarterial nerve stimulation in the isolated and perfused canine splenic artery, and to clarify whether release of noradrenaline is presynaptically separate from release of adenosine 5'-triphosphate (ATP). Double-peaked vasoconstrictions (biphases of vasoconstrictions) were consistently observed under the conditions of 30-s trains of pulses at 1-10 Hz frequencies. Guanethidine, at a lower concentration (0.1 microM) did not modify the first (1st) phase vasoconstriction at low frequencies (1-2 Hz), but markedly inhibited the second (2nd) responses. On the other hand, it slightly but significantly inhibited the double-peaked vasoconstrictor responses at high frequencies (6-10 Hz). Furthermore, a 10-fold increase of concentration of guanethidine (1 microM) almost completely inhibited the 2nd phase responses at any frequencies used but did not completely inhibit the 1st phase response. A further increased concentration of guanethidine (10 microM) failed to enhance the 1 microM guanethidine-induced inhibition. The 1 microM guanethidine-resistant 1st phase responses at any frequencies used (1-10 Hz) were sensitive to tetrodotoxin (30 nM). Treatment with 0.1 microM prazosin did not modify the 1st phase response at any frequencies used in the 1 microM guanethidine-treated preparation. The responses remaining after 1 microM guanethidine and 0.1 microM prazosin were completely suppressed by a subsequent application of 1 microM alpha,beta-methylene ATP at any frequencies used. The results indicated that guanethidine, an adrenergic neuron blocker, may exert a dominant inhibitory effect on adrenergic rather than on purinergic components of sympathetic nerve co-transmission, indicating that guanethidine-sensitive mechanisms may mainly contribute to determine noradrenaline secretion from neurosecretory vesicles rather than ATP secretion.

Adrenergic-purinergic interactions on vasoconstrictor responses to periarterial electric nerve stimulation in canine splenic arteries

1. Periarterial nerve electrical stimulation caused a double peaked vasoconstriction in isolated perfused canine splenic arterial preparations. At low frequencies (1-3 Hz), the 1st peak responses were significantly inhibited by alpha,beta-methylene ATP. On the other hand, at high frequencies (8-10 Hz), the responses were not completely inhibited by alpha,beta-methylene ATP but the remaining response was abolished by an additional treatment of prazosin. 2. Concerning the 2nd peak responses, at low frequencies (1-3 Hz), the response was mostly suppressed by alpha,beta-methylene ATP, but at high frequencies (6-10 Hz), the response was not significantly modified by it, although the remaining responses were completely blocked by prazosin. Thus, at high frequencies an adrenergic and purinergic interaction may exist presynaptically, to prevent the inhibition by alpha,beta-methylene ATP. 3. At 1 Hz, rauwolscine, an alpha2-adrenoceptor antagonist, caused a potentiation of electrical stimulation-induced responses (both 1st and 2nd peaked responses) which were inhibited by prazosin, and the remaining ones were abolished by alpha,beta-methylene ATP. On the other hand, at 10 Hz, rauwolscine did not cause any potentiation of the double peaked responses. 4. The biphasic responses at 1 Hz were strongly inhibited by exogenously applied ATP, and its inhibition was reversed in part by a P1 receptor antagonist 8-phenyltheophylline (8-PT). On the other hand, the biphasic vasoconstrictions at 10 Hz were only slightly depressed by ATP, and a subsequent administration of 8-PT produced a partial recovery of the 1st phase response but not that of the 2nd one. 5. From these results, it is concluded that (1) at low frequencies the double peaked responses are mostly mediated via P2X receptor, presynaptic P1 receptors may also modulate the release of ATP, and presynaptic alpha2-adrenergic mechanism may tonically participate in the release of noradrenaline (2) at high frequencies the responses are mostly mediated via alpha1-adrenoceptors and presynaptic P2 receptors may exert its action to inhibit the release of noradrenaline from adrenergic nerve terminals.

Effects of imipramine, an uptake inhibitor, on double-peaked constrictor responses to periarterial nerve stimulation in isolated, perfused canine splenic arteries

Using a cannula insertion method, periarterial nerve electrical stimulations were performed at 1 and 10 Hz in the isolated, perfused canine splenic artery. Electrical nerve stimulation readily caused double-peaked vasoconstrictions. The 1st-peak response at 1 Hz was not influenced by treatment with imipramine but the 2nd one was significantly enhanced by it. The 2nd-peak response was markedly blocked by prazosin. An additional treatment with alpha,beta-methylene ATP, a P2X-purinoceptor desensitizer, abolished electrical stimulation-induced vascular responses that remained. At 10 Hz, the responses to electrical stimulation were not significantly influenced by imipramine. On the other hand, the imipramine treatment inhibited the tyramine-induced vasoconstriction but potentiated the noradrenaline-induced one. ATP-induced responses were not modified by imipramine. From these results, it is concluded that 1) the 1st-peaked constriction is mainly due to a P2X-purinoceptor-dependent mechanism, 2) the 2nd one is mainly due to an alpha1-adrenoceptor-dependent mechanism, and 3) presynaptic uptake mechanisms may perform an important role in the regulation of vascular reactivity, especially at a low frequency.

Effects of prolonged cold storage on double peaked vasoconstrictor responses to periarterial nerve stimulation in isolated canine splenic arteries

1. P2X-Purinoceptors and alpha1-adrenoceptors have previously been shown to involve in the double peaked vasoconstrictor responses to periarterial electrical nerve stimulation in the isolated and perfused canine splenic artery. The present study made an attempt to investigate effects of prolonged cold storage (7 days at 4 degrees C) on vasoconstrictor responses to periarterial electrical nerve stimulation, tyramine, noradrenaline and adenosine 5'-triphosphate (ATP) in the isolated canine splenic artery. 2. The periarterial nerve stimulation (1-10 Hz) readily causes a double peaked vasoconstriction in the non-stored preparations. After cold stored for 7 days, the double peaked vasoconstriction was still recognized, although the response became significantly smaller. The first phase was decreased relatively greater than the second phase by the cold storage. 3. In the cold stored preparations, the dose-response curve for tyramine was shifted to the right in a parallel manner. Prazosin almost completely inhibited tyramine-induced vasoconstriction but alpha,beta-methylene ATP failed to influence the response to tyramine. 4. The vasoconstrictor responses to noradrenaline and ATP were not significantly modified by the prolonged cold storage. 5. From these results, it is concluded that the functions of sympathetic co-transmission of purinergic components might be influenced more than that of adrenergic components in the cold storage canine splenic artery.