Pharmacological properties of α1-adrenoceptor-mediated vasoconstrictions in dog and monkey lingual arteries: Evidence for subtypes of α1-adrenoceptors

The following is the abstract of the article discussed in the subsequent letter:

Sublingual and intestinal mucosal blood flow and Pco2 were studied in a canine model of endotoxin-induced circulatory shock and resuscitation. Sublingual Pco2 (Ps[Formula: see text]) was measured by using a novel fluorescent optrode-based technique and compared with lingual measurements obtained by using a Stowe-Severinghaus electrode [lingual Pco2 (Pl[Formula: see text])]. Endotoxin caused parallel changes in cardiac output, and in portal, intestinal mucosal, and sublingual blood flow (Q̇s). Different blood flow patterns were observed during resuscitation: intestinal mucosal blood flow returned to near baseline levels postfluid resuscitation and decreased by 21% after vasopressor resuscitation, whereas Q̇s rose to twice that of the preshock level and was maintained throughout the resuscitation period. Electrochemical and fluorescent Pco2 measurements showed similar changes throughout the experiments. The shock-induced increases in Ps[Formula: see text] and Pl[Formula: see text] were nearly reversed after fluid resuscitation, despite persistent systemic arterial hypotension. Vasopressor administration induced a rebound of Ps[Formula: see text] and Pl[Formula: see text] to shock levels, despite higher cardiac output and Q̇s, possibly due to blood flow redistribution and shunting. Changes in Pl[Formula: see text] and Ps[Formula: see text] paralleled gastric and intestinal Pco2 changes during shock but not during resuscitation. We found that the lingual, splanchnic, and systemic circulations follow a similar pattern of blood flow variations in response to endotoxin shock, although discrepancies were observed during resuscitation. Restoration of systemic, splanchnic, and lingual perfusion can be accompanied by persistent tissue hypercarbia, mainly lingual and intestinal, more so when a vasopressor agent is used to normalize systemic hemodynamic variables.

Existence of alpha-adrenoceptor subtypes in isolated human gastroepiploic and omental arteries

Establishing the existence of alpha-adrenoceptor subtypes in isolated human gastroepiploic and omental arteries was the goal of the present study. Functional vascular reactivity of selective alpha(1)- and alpha(2)-adrenoceptor agonists and antagonists was studied, using a cannula inserting technique. Intraluminal administration of norepinephrine (NE), phenylephrine (PE) or BHT-933 caused a vasoconstrictive response in a dose-related manner. The relative potencies of the 3 agonists were almost the same in both arteries. NE-induced vasoconstrictions were significantly antagonized by either prazosin or rauwolscine. PE-induced responses were strongly inhibited by prazosin. BHT-933-induced constrictions were inhibited by rauwolscine. These results indicate that both alpha(1)- and alpha(2)-adrenoceptors exist in the human gastroepiploic and omental arteries.

The functional alpha-adrenoceptor in dog caudal vesical arteries is mainly an alpha1A subtype

1 The present study attempted to pharmacologically characterize the subtypes of alpha-adrenoceptors mediating the vasoconstriction in the isolated and perfused canine vesical artery. 2 Noradrenaline (NA) and phenylephrine (PE, an alpha1-adrenoceptor agonist) induced a dose-dependent vasoconstriction, whereas xylazine (an alpha2-agonist) did not induce any clear vascular constrictor response. 3 Prazosin at 0.01 microM and rauwolscine at 0.1 microM failed to affect the NA-induced vasoconstriction. Prazosin at 0.1 microM antagonized the vasoconstrictor responses to NA, with pKB value of 7.8. 4 WB 4101 at 0.01-0.1 microM dose-dependently inhibited the responses to NA, with a pKB value of 8.9. The vasoconstrictor responses to NA were not significantly affected by chloroethylclonidine (10-30 microM) or BMY 7378 (0.1 microM). 5 The present results indicate that the canine vesical arteries dominantly contain alpha1-adrenoceptors but have no alpha2-adrenoceptors, and the functional subtype of alpha1-adrenoceptor is characterized as an alpha1A-adrenoceptor subtype.

Existence of alpha(1A)- and alpha(1B)-adrenoceptor subtypes in canine mandibular alveolar arteries

1. The present study attempted to pharmacologically characterize the alpha-adrenoceptor subtypes mediating vasoconstriction in canine isolated and perfused mandibular alveolar artery (MAA). 2. Noradrenaline (NA) and phenylephrine (PE) induced a strong vasoconstriction in a dose-dependent manner. The PE-induced vascular constriction was significantly inhibited by treatment with prazosin. Xylazine evoked a moderate vascular constriction and the xylazine-induced response was suppressed by rauwolscine. The NA-induced response was partially inhibited by rauwolscine and the remaining response to NA was abolished by subsequent administration of prazosin. 3. Treatment of MAA with WB4101 produced a dose-dependent inhibition of NA-induced vasoconstriction. Pretreatment of tissues with 10 micromol/L chloroethylclonidine produced a slight and statistically significant inhibition of NA-induced responses. BMY 7378, a selective alpha(1D)-adrenoceptor antagonist, failed to significantly affect vasoconstrictor responses to NA. 4. The present results suggests that: (i) both alpha(1)- and alpha(2)-adrenoceptors are involved in vasoconstrictor responses in the canine MAA; and (ii) the alpha(1)-adrenoceptors involved in the vasoconstrictor responses in the MAA are characterized as mainly of the alpha(1A)- and partially of the alpha(1B)-adrenoceptor subtype.

Bradykinin-induced vascular responses in dog isolated lingual artery

1. Kinin-induced vascular responses were studied and kinin receptor subtypes were characterized in canine isolated and preconstricted lingual arteries. 2. A low dose of bradykinin (BK; < 3 x 10(-14) mol) induced only vasodilation, while a higher dose of BK (> 3 x 10(-13) mol) frequently induced a biphasic response: a transient constriction followed by dilation. 3. The BK-induced vasodilation was mostly endothelium dependent but was also partly endothelium independent because although the dilation response was greatly reduced after removal of the endothelium, it was not completely abolished. 4. The dilation response to BK was significantly inhibited by the B2 kinin receptor antagonist HOE 140 and was partly reduced by indomethacin (10 mumol/L) (P < 0.05). 5. Bradykinin-induced vasoconstriction was enhanced in endothelium-denuded preparations. The constriction was significantly inhibited by HOE 140 (10(-10) mol/L). The BK-induced responses were not affected by the B1 kinin receptor antagonist des-Arg9-[Leu8]-BK (3 x 10(-11) mol/L). 6. The B1 kinin receptor agonist des-Arg9-BK (> 10(-12) mol/L) produced vasodilation in 60% of endothelium-intact preparations. In 20% of the endothelium-intact preparations des-Arg9-BK produced a biphasic response: weak vasoconstriction followed by weak vasodilation. The des-Arg9-BK-induced dilation and constriction were significantly inhibited by des-Arg9-[Leu8]-BK (3 x 10(-11) mol/L), but were not affected by HOE 140 (10(-10) mol/L). 7. In conclusion, it appears that both B1 and B2 kinin receptors are present in the dog lingual artery. Both receptor subtypes mediate either vasodilation or vasoconstriction and BK-induced vasodilation is mostly endothelium dependent, although it may also be partially prostaglandin dependent.

Mechanisms for histamine H1 receptor-mediated vasodilation in isolated canine lingual arteries

Histamine and selective histamine receptor subtype agonists' effects on isolated and perfused canine lingual arteries were investigated with the cannula insertion method. In preparations preconstricted with phenylephrine, histamine and a selective histamine H1 receptor agonist, 2-pyridylethylamine induced a biphasic vascular response in a dose-related manner, i.e., vasoconstriction followed by vasodilatation. The biphasic responses to histamine and 2-pyridylethylamine were inhibited by diphenhydramine, a selective histamine H1 receptor antagonist, but were not influenced by cimetidine, a selective histamine H2 receptor antagonist. Dimaprit, a selective histamine H2 receptor agonist, induced only a slight vasoconstriction which was not modified by cimetidine. Dimaprit never induced vasodilation even at a large dose. A histamine H3 receptor agonist, R-alpha-methylhistamine, did not produce any significant vascular responses. Moreover, histamine-induced vasodilation was in part inhibited by removal of the endothelium, and the vasodilation remaining was abolished by H1 blockade. Thus, it is concluded that in canine lingual arteries there are abundant histamine H1 receptors which mediate both vasoconstriction and vasodilation, and that the histamine-induced vasodilation is in part due to endothelium-dependent mechanisms.

Possible involvement of muscarinic M1 and M3 receptor subtypes mediating vasodilation in isolated, perfused canine lingual arteries

1. Using the cannula insertion method, muscarinic receptor subtypes were analysed in isolated, perfused canine lingual arteries preconstricted with phenylephrine. 2. Both acetylcholine and McN-A-343 induced a profound vasodilation in a dose-related manner. Acetylcholine-induced dilations were approximately 1000-times more potent than McN-A-343-induced dilation. 3. Acetylcholine-induced dilations were abolished after removal of the endothelium by intraluminal treatment with 1 mg saponin. 4. Acetylcholine-induced dilations were markedly inhibited by an M1/M3 receptor antagonist, 4-DAMP. Moreover, they were slightly, but significantly, inhibited by an M1 antagonist, pirenzepine, but never influenced by an M2 antagonist, AF-DX 116. Mc-N-A-343-induced vasodilations were inhibited by both 4-DAMP or pirenzepine. 5. These results suggest that there are abundant functional M3 and a few M1 receptors in the canine lingual artery that mediate vasodilation and that this vasodilation is dependent on the presence of an intact endothelium.

Dominant antagonistic action of alpha 2-adrenoceptor agonists on alpha 1-agonist-induced vasoconstriction

The action of clonidine and xylazine to suppress constrictor responses to norepinephrine (NE) and phenylephrine was analysed in isolated, perfused dog and monkey lingual arteries. In both kinds of arteries, alpha 1-adrenoceptor agonists, NE and phenylephrine induced strong vasoconstrictor responses, whereas alpha 2-adrenoceptor agonists, clonidine and xylazine, produced only a slight but long-lasting increase in perfusion pressure. Pretreatment with bolus injections of 300 micrograms clonidine or 1000 micrograms xylazine caused a significant inhibition of vasoconstrictor responses to NE and phenylephrine and shifted the dose-responses curves to the right. Clonidine induced a more potent inhibition than did xylazine. However, neither clonidine nor xylazine pretreatment inhibited 5-HT- and KCl-induced vasoconstriction. In preparations preconstricted with phenylephrine, clonidine and xylazine induced vasodilatation dose relatedly, but in preparations preconstricted with prostaglandin F2 alpha (PGF2 alpha), clonidine and xylazine never induced vasodilatation but only vasoconstriction. The vasoconstrictor effect of clonidine was readily blocked by bunazosin (an alpha 1-adrenoceptor antagonist), but was not affected by midaglizole (an alpha 2-antagonist). It was now demonstrated that alpha 2-agonists act as partial agonists on alpha 1-adrenoceptors when added alone but antagonized alpha 1 activation by alpha 1-agonists, suggesting that alpha 2-agonists have a high affinity for alpha 1-adrenoceptors in isolated lingual arteries.