Angiotensin-(1-7) potentiates responses to bradykinin but does not change responses to angiotensin I

Angiotensin-(1-7) (Ang-(1-7)), a bioactive peptide in the renin-angiotensin system, has counterregulatory actions to angiotensin II (Ang II). However, the mechanism by which Ang-(1-7) enhances vasodepressor responses to bradykinin (BK) is not well understood. In the present study, the effects of Ang-(1-7) on responses to BK, BK analogs, angiotensin I (Ang I), and Ang II were investigated in the anesthetized rat. The infusion of Ang-(1-7) (55 pmol/min i.v.) enhanced decreases in systemic arterial pressure in response to i.v. injections of BK and the BK analogs [Hyp3, Tyr(Me)8]-bradykinin (HT-BK) and [Phe8psi (CH2-NH) Arg9]-bradykinin (PA-BK) without altering pressor responses to Ang I or II, or depressor responses to acetylcholine and sodium nitroprusside. The angiotensin-converting enzyme (ACE) inhibitor enalaprilat enhanced responses to BK and the BK analog HT-BK without altering responses to PA-BK and inhibited responses to Ang I. The potentiating effects of Ang-(1-7) and enalaprilat on responses to BK were not attenuated by the Ang-(1-7) receptor antagonist A-779. Ang-(1-7)- and ACE inhibitor-potentiated responses to BK were attenuated by the BK B2 receptor antagonist Hoe 140. The cyclooxygenase inhibitor sodium meclofenamate had no significant effect on responses to BK or Ang-(1-7)-potentiated BK responses. These results suggest that Ang-(1-7) potentiates responses to BK by a selective B2 receptor mechanism that is independent of an effect on Ang-(1-7) receptors, ACE, or cyclooxygenase product formation. These data suggest that ACE inhibitor-potentiated responses to BK are not mediated by an A-779-sensitive mechanism and are consistent with the hypothesis that enalaprilat-induced BK potentiation is due to decreased BK inactivation.

Clonidine inhibits the canine external carotid vasodilatation to capsaicin by α2A/2C-adrenoceptors

Migraine is a disorder associated with increased plasma concentrations of calcitonin gene-related peptide (CGRP). CGRP, a neuropeptide released from activated trigeminal sensory nerves, dilates cranial blood vessels and transmits vascular nociception. Moreover, several antimigraine drugs inhibit the dural neurogenic vasodilatation to trigeminal stimulation. Hence, this study investigated in anaesthetized dogs the effects of the alpha(2)-adrenoceptor agonist, clonidine, on the external carotid vasodilator responses to capsaicin, alpha-CGRP and acetylcholine. 1-min intracarotid infusions of capsaicin (10, 18, 30 and 56 microg/min), alpha-CGRP (0.1, 0.3, 1 and 3 microg/min) and acetylcholine (0.01, 0.03, 0.1 and 0.3 microg/min) produced dose-dependent increases in external carotid conductance without affecting blood pressure or heart rate. Interestingly, the carotid vasodilator responses to capsaicin, but not those to alpha-CGRP or acetylcholine, were partially inhibited after clonidine (total dose: 24.4 microg/kg, i.v.); in contrast, equivalent volumes of saline did not affect the responses to capsaicin, alpha-CGRP or acetylcholine. The inhibitory responses to clonidine were antagonized by i.v. administration of the alpha(2)-adrenoceptor antagonists rauwolscine (alpha(2A/2B/2C); 300 microg/kg), BRL44408 (alpha(2A); 1000 microg/kg) or MK912 (alpha(2C); 100 and 300 microg/kg), but not by imiloxan (alpha(2B); 1000 microg/kg). These results suggest that clonidine inhibits the external carotid vasodilator responses to capsaicin by peripheral trigeminovascular and/or central mechanisms; this inhibitory response to clonidine seems to be predominantly mediated by alpha(2A)-adrenoceptors and, to a much lesser extent, by alpha(2C)-adrenoceptors.

Donitriptan, but not sumatriptan, inhibits capsaicin-induced canine external carotid vasodilatation via 5-HT1B rather than 5-HT1D receptors

BACKGROUND AND PURPOSE

It has been suggested that during a migraine attack capsaicin-sensitive trigeminal sensory nerves release calcitonin gene-related peptide (CGRP), resulting in cranial vasodilatation and central nociception; hence, trigeminal inhibition may prevent this vasodilatation and abort migraine headache. This study investigated the effects of the agonists sumatriptan (5-HT(1B/1D) water-soluble), donitriptan (5-HT(1B/1D) lipid-soluble), PNU-142633 (5-HT(1D) water-soluble) and PNU-109291 (5-HT(1D) lipid-soluble) on vasodilator responses to capsaicin, alpha-CGRP and acetylcholine in dog external carotid artery.

EXPERIMENTAL APPROACH

59 vagosympathectomized dogs were anaesthetized with sodium pentobarbitone. Blood pressure and heart rate were recorded with a pressure transducer, connected to a cannula inserted into a femoral artery. A precalibrated flow probe was placed around the common carotid artery, with ligation of the internal carotid and occipital branches, and connected to an ultrasonic flowmeter. The thyroid artery was cannulated for infusion of agonists.

KEY RESULTS

Intracarotid infusions of capsaicin, alpha-CGRP and acetylcholine dose-dependently increased blood flow through the carotid artery. These responses remained unaffected after intravenous (i.v.) infusions of sumatriptan, PNU-142633, PNU-109291 or physiological saline; in contrast, donitriptan significantly attenuated the vasodilator responses to capsaicin, but not those to alpha-CGRP or acetylcholine. Only sumatriptan and donitriptan dose-dependently decreased the carotid blood flow. Interestingly, i.v. administration of the antagonist, SB224289 (5-HT(1B)), but not of BRL15572 (5-HT(1D)), abolished the inhibition by donitriptan.

CONCLUSIONS AND IMPLICATIONS

Our results suggest that the inhibition produced by donitriptan of capsaicin-induced external carotid vasodilatation is mainly mediated by 5-HT(1B), rather than 5-HT(1D), receptors, probably by a central mechanism.

Phenotypic modifications of vascular smooth muscle cells could be responsible for vascular hyporeactivity to contracting agent in mechanically injured rat carotid artery

Vascular smooth muscle cells (VSMCs) that accumulate in neointima after angioplastic injury show different phenotypic characteristics from those of medial layer and an impaired reactivity to contracting agents. The aim of the study was to correlate the vascular hyporesponsiveness to the changes in intracellular calcium concentration [Ca(2+)](i) and the expression of proteins necessary for its utilization in mechanically injured rat carotid arteries (IC) at 14 and 28 days after angioplastic balloon. IC showed a significant reduction (P<0.01) to PE- or KCl-induced contraction as compared to uninjured carotid (UC). Fura-2AM-loaded VSMCs isolated from IC revealed that this hyporeactivity to PE or KCl was accompanied by the impairment of the increase in [Ca(2+)](i) induced by contracting agents in both Ca(2+)-free or -containing medium. Similar results were observed following the ryanodine challenge in VSMC. Western blot analysis showed a significant (P<0.05) reduction in myosin heavy chain (MHC) and IP(3)-type III receptor expression in IC isolated at 14 days from injury compared to UC, while an improvement of these proteins expression was observed at 28 days after damage. On the other hand, in IC tissue, SERCA2 and alpha-actin expression, compared to UC was significantly higher at 14 days than at 28 days. These data indicate that vascular hyporeactivity induced by mechanical injury may be due to alterations of either [Ca(2+)](i) or contractile proteins. These modifications could be related to the changes of VSMC phenotypic characteristics, as supported by the observed modifications in MHC, SERCA2 and alpha-actin expression, proteins considered as biological markers of cellular differentiation.

5-HT1B receptors and alpha 2A/2C-adrenoceptors mediate external carotid vasoconstriction to dihydroergotamine

Dihydroergotamine produces external carotid vasoconstriction in vagosympathectomized dogs by 5-HT(1B/1D) receptors and alpha(2)-adrenoceptors. This study identified the specific subtypes involved in this response. One-minute intracarotid infusions of dihydroergotamine (5.6-10 microg/min) dose-dependently decreased external carotid blood flow without affecting blood pressure or heart rate. This response was: (1) partly blocked in dogs pretreated intravenously with the antagonists SB224289 (5-HT(1B); 2,3,6,7-tetrahydro-1'-methyl-5-[2'-methyl-4' (5-methyl-1,2,4-oxadiazol-3-yl)biphenyl-4-carbonyl]furo[2,3-f]indole-3-spiro-4'-piperidine hydrochloride), rauwolscine (alpha(2)), BRL44408 (alpha(2A); 2-[2H-(1-methyl-1,3-dihydroisoindole)methyl]-4,5-dihydroimidazole) or MK912 (alpha(2C); (2S,12bS)-1'3'-dimethylspiro(1,3,4,5',6,6',7,12b-octahydro-2Hbenzo[b]furo[2,3-a]quinazoline)-2,4'-pyrimidin-2'-one); (2) markedly blocked after SB224289 plus rauwolscine; and (3) unaffected after BRL15572 (5-HT(1D); 1-(3-chlorophenyl)-4-[3,3-diphenyl (2-(S,R) hydroxypropanyl) piperazine] hydrochloride) or imiloxan (alpha(2B)). Therefore, the above response involves 5-HT(1B) receptors and alpha(2A/2C)-adrenoceptors.

5-HT1B receptors, alpha2A/2C- and, to a lesser extent, alpha1-adrenoceptors mediate the external carotid vasoconstriction to ergotamine in vagosympathectomised dogs

It has previously been suggested that ergotamine produces external carotid vasoconstriction in vagosympathectomised dogs via 5-HT1B/1D receptors and alpha2-adrenoceptors. The present study has reanalysed this suggestion by using more selective antagonists alone and in combination. Fifty-two anaesthetised dogs were prepared for ultrasonic measurements of external carotid blood flow. The animals were divided into thirteen groups (n=4 each) receiving an i.v. bolus injection of, either physiological saline (0.3 ml/kg; control), or the antagonists SB224289 (300 microg/kg; 5-HT1B), BRL15572 (300 microg/kg; 5-HT1D), rauwolscine (300 microg/kg; alpha2), SB224289 + BRL15572 (300 microg/kg each), SB224289 + rauwolscine (300 microg/kg each), BRL15572 + rauwolscine (300 microg/kg each), rauwolscine (300 microg/kg) + prazosin (100 microg/kg; alpha1), SB224289 (300 microg/kg) + prazosin (100 microg/kg), SB224289 (300 microg/kg) + rauwolscine (300 microg/kg) + prazosin (100 microg/kg), SB224289 (300 microg/kg) + prazosin (100 microg/kg) + BRL44408 (1,000 microg/kg; alpha2A), SB224289 (300 microg/kg) + prazosin (100 microg/kg)+ imiloxan (1,000 microg/kg; alpha2B), or SB224289 (300 microg/kg) + prazosin (100 microg/kg) + MK912 (300 microg/kg; alpha2C). Each group received consecutive 1-min intracarotid infusions of ergotamine (0.56, 1, 1.8, 3.1, 5.6, 10 and 18 microg/min), following a cumulative schedule. In saline-pretreated animals, ergotamine induced dose-dependent decreases in external carotid blood flow without affecting arterial blood pressure or heart rate. These control responses were: unaffected by SB224289, BRL15572, rauwolscine or the combinations of SB224289 + BRL15572, BRL15572 + rauwolscine, rauwolscine + prazosin, SB224289 + prazosin, or SB224289 + prazosin + imiloxan; slightly blocked by SB224289 + rauwolscine; and markedly blocked by SB224289 + rauwolscine + prazosin, SB224289 + prazosin + BRL44408 or SB224289 + prazosin + MK912. Thus, the cranio-selective vasoconstriction elicited by ergotamine in dogs is predominantly mediated by 5-HT1B receptors as well as alpha2A/2C-adrenoceptor subtypes and, to a lesser extent, by alpha1-adrenoceptors.

Pharmacological profile of the vascular responses to dopamine in the canine external carotid circulation

The present study investigated the effects of dopamine on the canine external carotid circulation. One min. intracarotid artery (i.c.) infusions of dopamine (10-310 microg min.-1) produced dose-dependent decreases in the canine external carotid conductance without affecting blood pressure or heart rate. This effect was mimicked by the D1/2-like receptor agonist apomorphine (1-310 microg min-1), but not by the D2-like receptor agonist, bromocriptine (31-310 microg min.-1). In contrast, fenoldopam (1-310 microg min.-1, intracarotid), a D1-like receptor agonist, produced dose-dependent increases in external carotid conductance. The vasoconstrictor response to dopamine was abolished after intravenous administration of the antagonists, phentolamine (alpha1/2; 2000 microg kg-1) or rauwolscine (alpha2; 100 microg kg-1), but remained unaffected after prazosin (alpha1; 100 microg kg-1) or haloperidol (D2-like; 1000 microg kg-1). Interestingly, after phentolamine not only were the vasoconstrictor responses to dopamine abolished, but even a dose-dependent vasodilator component was unmasked. These vasodilator responses to dopamine remained unchanged after intravenous haloperidol or propranolol (1000 microg kg-1 each). On the other hand, the vasodilator responses to fenoldopam, which remained unchanged after intravenous saline (0.1 ml kg-1), propranolol (1000 microg kg-1) or vagosympathectomy, were abolished by the D1-like receptor antagonist, SCH-23390 (10 microg kg-1). Lastly, the responses to dopamine and fenoldopam were not significantly altered after intraperitoneal pretreatment with reserpine (5 mg kg-1; -24 hr). The above results suggest that the canine external carotid vasoconstrictor responses to dopamine: (i) are mainly mediated by alpha2-adrenoceptors; and (ii) overshadow a vasodilator component, which involves vascular D1-like receptors.

Histopathologic damage to vessels in head and neck microsurgery

PURPOSE

This study assessed the incidence of pre-existing damage in recipient arteries excised before the vessels were used for microvascular anastomoses between 1988 and 1999.

PATIENTS AND METHODS

Recipient arteries of the head and neck region from 100 patients who had undergone ablative surgery requiring microvascular tissue reconstruction were examined histologically. Past illnesses believed to be risk factors included hypertension, myocardial disease, and diabetes. Blood vessels chosen for microsurgical anastomoses were examined using histological staining, scanning electron microscopy, and immunofluorescence.

RESULTS

Of the patients undergoing microvascular surgery, 51% showed histologic vessel abnormalities. Marked thickening of the blood vessel wall and severe exfoliation of the endothelial cells were observed in most arteries. Thickening of the intima was evaluated using scanning electron microscopy (Friedman's method; Microvasc Res 3:416, 1971). Values higher than twice the ratio of wall thickness-to-lumen diameter were observed in 9 recipient arteries. Six graft failures were correlated with both technical errors and pre-existing vessel lesions.

CONCLUSIONS

This study revealed that most patients undergoing microsurgery in the head and neck region had pre-existing damage to vessels that hindered anastomoses. Pre-existing changes in the recipient arteries may cause technical difficulties and must be regarded as additional factors contributing to graft failure.

Endogenous nitric oxide synthesis differentially modulates pressure-flow and pressure-conductance relationships in the internal and external carotid artery circulations of the rat

The role of endogenous nitric oxide (NO) synthesis was investigated in the regulation of the internal (ICA) and external carotid artery (ECA) beds of ventilated, anesthetized rats in a model in which the left common carotid artery was perfused from the aorta via an extracorporeal circuit under conditions of non-pulsatile controlled flow. The territories supplied by the extracranial ICA and ECA were studied separately following occlusion of the appropriate artery. An inhibitor of nitric oxide synthesis, N(G)-monomethyl-L-arginine (L-NMMA), and the NO synthase substrate L-arginine were administered via a jugular venous catheter. NO synthesis exerted an important influence on the pressure-flow relationships of the ICA and ECA circulations as L-NMMA increased input perfusion pressure at any given flow rate. However, in the presence of NO synthesis, hydraulic conductance increased rapidly with flow in the ICA, thereby stabilizing perfusion pressures over a wide range of flow rates, whereas this phenomenon was not evident in the ECA territory. Differences between the two circulations were further emphasized by observations that L-arginine antagonized the systemic hemodynamic response to L-NMMA and its effects on the conductance of the ECA bed, whereas the effects of L-NMMA were irreversible in the ICA territory.

Self-expanding stents for carotid interventions: comparison of nitinol versus stainless-steel stents

BACKGROUND

Angioplasty and stenting are becoming increasingly accepted techniques for the treatment of carotid stenosis. However, the optimal stent for carotid intervention is not known.

METHODS

We compared the short- and intermediate-term results of carotid stenting using either nitinol or stainless-steel self-expanding stents in 178 high surgical risk patients undergoing carotid stenting at our institution. Of these 178 patients, eighty-nine received stainless-steel stents and 89 received nitinol stents. The groups were similar with respect to age, gender, diabetes, hypertension, left ventricular function, and symptom status. There were more patients with contralateral carotid occlusion in the nitinol stent group. Independent neurological evaluation was performed in all patients pre- and post-carotid stenting.

RESULTS

At 6 months, there was a similar incidence of stroke (3.3% versus 2.2%) in the stainless-steel group and nitinol stent group, respectively. There was higher 6-month mortality noted in the stainless-steel stent group, but there were no neurological deaths in either group.

CONCLUSIONS

In a single-center patient cohort with similar baseline characteristics, patients receiving nitinol stents and stainless-steel stents had similar neurological outcomes.

Pharmacological profile of the mechanisms involved in the external carotid vascular effects of the antimigraine agent isometheptene in anaesthetised dogs

The present study set out to investigate the external carotid vascular effects of isometheptene in vagosympathectomised dogs, anaesthetised with pentobarbital. One-minute intracarotid (intra-arterial; i.a.) infusions of isometheptene (10, 30, 100 and 300 microg/min) produced dose-dependent decreases in external carotid blood flow, without affecting blood pressure or heart rate. The vasoconstrictor responses to 100 microg/min and 300 microg/min of isometheptene were clearly attenuated in animals pretreated with reserpine (5,000 microg/kg). Moreover, after prazosin (an alpha1-adrenoceptor antagonist; 100 microg/kg), the responses to isometheptene remained unaltered in untreated as well as reserpine-pretreated dogs. In contrast, the responses to isometheptene were attenuated by rauwolscine (an alpha2-adrenoceptor antagonist; 300 microg/kg) in untreated animals, and were practically abolished in reserpine-pretreated dogs. Further investigation into the specific alpha2-adrenoceptor subtypes, using selective antagonists, showed that BRL44408 (alpha2A) and MK912 (alpha2C) markedly attenuated this response, while imiloxan (alpha2B) was ineffective. The involvement of 5-HT1B and 5-HT1D receptors seems highly unlikely since antagonists at 5-HT1B (SB224289) and 5-HT1D (BRL15572) receptors (both at 300 microg/kg) were ineffective. On this basis, it is concluded that isometheptene-induced canine external carotid vasoconstriction is mediated by both indirect (a tyramine-like action) and direct (acting at receptors) mechanisms, which mainly involve alphaA- and alpha2C-adrenoceptors, while the involvement of alpha1-adrenoceptors seems rather limited.

Pharmacological identification of the major subtypes of adrenoceptors involved in the canine external carotid vasoconstrictor effects of adrenaline and noradrenaline

This study investigated the potential effects of adrenaline and noradrenaline on the external carotid blood flow of vagosympathectomised dogs and the receptor mechanisms involved. One minute (1 min) intracarotid infusions of adrenaline and noradrenaline produced dose-dependent decreases in external carotid blood flow without changes in blood pressure or heart rate. These responses, which remained unaffected after saline, were: (i) mimicked by the adrenoceptor agonists, phenylephrine (alpha1) and BHT933 (6-Ethyl-5,6,7,8-tetrahydro-4H-oxazolo [4,5-d] azepin-2-amine dihydrochloride; alpha2); (ii) abolished after phentolamine (2000 microg/kg) unmasking a vasodilator component (subsequently blocked by propranolol; 1000 microg/kg); and (iii) partly blocked by rauwolscine (30 and 100 microg/kg), and subsequently abolished by prazosin (100 microg/kg). Accordingly, rauwolscine (100 and 300 microg/kg) markedly blocked the responses to BHT933 without affecting those to phenylephrine; likewise, prazosin (100 microg/kg) markedly blocked the responses to phenylephrine without affecting those to BHT933. These results show that both alpha1- and alpha2-adrenoceptors mediate vasoconstriction within the canine external carotid circulation. Moreover, after blockade of alpha1/alpha2-adrenoceptors, both adrenaline and noradrenaline exhibit a beta-adrenoceptor-mediated vasodilator component.

The role of several alpha(1)- and alpha(2)-adrenoceptor subtypes mediating vasoconstriction in the canine external carotid circulation

1. It has recently been shown that both alpha(1)- and alpha(2)-adrenoceptors mediate vasoconstriction in the canine external carotid circulation. The present study set out to identify the specific subtypes (alpha(1A), alpha(1B) and alpha(1D) as well as alpha(2A), alpha(2B) and alpha(2C)) mediating the above response. 2. Consecutive 1 min intracarotid infusions of phenylephrine (alpha(1)-adrenoceptor agonist) and BHT933 (alpha(2)-adrenoceptor agonist) produced dose-dependent decreases in external carotid blood flow, without affecting mean arterial blood pressure or heart rate. 3. The responses to phenylephrine were selectively antagonized by the antagonists, 5-methylurapidil (alpha(1A)) or BMY7378 (alpha(1D)), but not by L-765,314 (alpha(1B)), BRL44408 (alpha(2A)), imiloxan (alpha(2B)) or MK912 (alpha(2C)). In contrast, only BRL44408 or MK912 affected the responses to BHT933. 4. The above results support our contention that mainly the alpha(1A), alpha(1D), alpha(2A) and alpha(2C)-adrenoceptor subtypes mediate vasoconstriction in the canine external carotid circulation.

Unravelling the pharmacological profile of the canine external carotid vasodilator '5-HT1-like' receptors: coexistence of sympatho-inhibitory 5-HT1B and postjunctional 5-HT7 receptors

It has been suggested that the external carotid vasodilatation produced by serotonin (5-hydroxytryptamine; 5-HT) in anaesthetised dogs with intact vagosympathetic trunks is mediated by sympatho-inhibitory '5-HT1D' receptors and musculotropic '5-HT1-like' receptors. The present study has re-analysed this suggestion with regard to the classification schemes recently proposed by the NC-IUPHAR subcommittee on 5-HT receptors. In pentobarbital-anaesthetised dogs with intact vagosympathetic trunks, 1-min intracarotid (i.c.) infusions of 5-carboxamidotryptamine (5-CT; 0.01-0.3 microg/min), 5-HT (0.3-30 microg/ min), 5-methoxytryptamine (5-MeO-T; 1-100 microg/min) or sumatriptan (1-100 microg/min) dose-dependently increased the external carotid blood flow without affecting blood pressure or heart rate. The selective 5-HT1D receptor agonist, PNU-142633 (1-1000 microg/min), was essentially inactive. After mesulergine (300 microg/kg, i.v.), an antagonist at cardiovascular 5-HT7 receptors, the above responses to 5-HT, 5-CT and 5-MeO-T were blocked, whilst those to sumatriptan remained unaffected. In contrast, after the 5-HT1B/1D receptor antagonist, GR127935 (10 microg/kg, i.v.), the responses to 5-HT, 5-CT and 5-MeO-T were not affected, but those to sumatriptan were abolished. Furthermore, after the selective 5-HT1B receptor antagonist, SB224289 (300 microg/kg, i.v.), the responses to 5-HT, 5-CT and 5-MeO-T were significantly enhanced, whereas those to sumatriptan were abolished. Interestingly, the responses to all these agonists remained unmodified after the selective 5-HT1D receptor antagonist, BRL15572 (300 microg/kg, i.v.). The above results suggest that the '5-HT1-like' receptors, which mediate canine external carotid vasodilatation, display the pharmacological profile of sympatho-inhibitory 5-HT1B receptors and musculotropic 5-HT7 receptors, and confirm the existence of vasoconstrictor 5-HT1B receptors.

The canine external carotid vasoconstrictor 5-HT1 receptor: blockade by 5-HT1B (SB224289), but not by 5-HT1D (BRL15572) receptor antagonists

In vagosympathectomised dogs pre-treated intravenously (i.v.) with mesulergine (300 microg/kg), 1-min intracarotid (i.c.) infusions of 5-hydroxytryptamine (5-HT; 0.3-30 microg/min) and sumatriptan (1-30 microg/min) dose-dependently decreased external carotid blood flow, without affecting mean blood pressure or heart rate. Treatment with the selective 5-HT1B receptor antagonist SB224289 (2,3,6,7-tetrahydro-1'-methyl-5-[2'-methyl-4'(5-methyl-1,2,4-oxadiazo l-3-yl) biphenyl-4-carbonyl]furo[2,3f]indole-3-spiro-4'-piperidine hydrochloride; 30-300 microg/kg, i.v.) produced a potent, specific and dose-dependent blockade of this response, whereas the selective 5-HT1D receptor antagonist BRL15572 (1-(3-chlorophenyl)-4-[3,3-diphenyl(2-(S,R) hydroxypropanyl)piperazine]hydrochloride; 30-300 microg/kg, i.v.) was ineffective. It is concluded that mainly 5-HT1B, but not 5-HT1D receptors mediate the canine external carotid vasoconstriction by 5-HT and sumatriptan.

External carotid effects of 2-(2-aminoethyl)-quinoline (D-1997) in vagosympathectomized dogs

Serotonin (5-hydroxytryptamine; 5-HT) elicits external carotid vasoconstriction in vagosympathectomized dogs via 5-HT1B/1D receptors and a mechanism unrelated to the 5-HT1, 5-HT2, 5-HT3 and 5-HT4 types. In order to further explore the nature of this novel mechanism, the canine external carotid effects of 2-(2-aminoethyl)-quinoline (D-1997), a novel 5-HT1 receptor agonist, were analyzed and compared with those of 5-HT and sumatriptan. Intracarotid (i.c.) infusions of 5-HT, D-1997 and sumatriptan to vagosympathectomized dogs dose-dependently decreased external carotid conductance, the rank order of agonist potency being 5-HT > sumatriptan > D-1997. The effects to D-1997 were resistant to intravenous (i.v.) pretreatment with 5-HT2 and 5-HT3/5-HT4 receptor antagonists. Remarkably, the effects induced by lower (10-100 microg/min), but not higher (300-1000 microg/min), doses of D-1997 were blocked by high doses of methiothepin (1 and 3 mg/kg, i.v.), as previously shown with 5-HT. In addition, GR-127935 (1-10 microg/kg, i.v.), partially and dose-dependently antagonized D-1997-induced responses. However, the effects of D-1997 remained unaltered after blockade of alpha- and beta-adrenoceptors, muscarinic, nicotinic, histamine and dopamine receptors, or inhibition of 5-HT-uptake or cyclo-oxygenase, depletion of biogenic amines or blockade of Ca2+ channels. These results may support our previous contention that lower doses of 5-HT elicit external carotid vasoconstriction in vagosympathectomized dogs by activation of 5-HT1B/1D receptors, whilst higher doses of 5-HT stimulate a novel vasoconstrictor mechanism.

Heparinase III limits rat arterial smooth muscle cell proliferation in vitro and in vivo

Heparinase III degrades heparan sulfate proteoglycans, which are co-receptors for growth factors that stimulate arterial proliferation. We assessed the ability of locally-delivered heparinase III to limit medial vascular smooth muscle cell proliferation induced by balloon catheter injury in rat carotid arteries. Whereas vehicle-treated arteries showed 12% of smooth muscle cells proliferating after 2 days, heparinase III (0.022-5.7 mg/kg) treated arteries showed 0.8-4%. Chemically-inactivated heparinase III did not limit proliferation. In isolated rat A10 vascular smooth muscle cells, heparinase III (1 IU/ml) inhibited both PDGF-BB and bFGF mediated increases in proliferation and migration. These results suggest that heparinase III can limit proliferation by affecting heparan sulfate proteoglycan binding growth factors following arterial injury.

Inhibition of platelet-derived growth factor receptor tyrosine kinase inhibits vascular smooth muscle cell migration and proliferation

Platelet-derived growth factors (PDGFs) and their receptors (PDGFRs) have been linked to vascular smooth muscle cell (SMC) migration and proliferation leading to atherosclerosis, restenosis, and chronic allograft rejection. This study describes the effect of CGP 53716, a specific PDGFR tyrosine kinase inhibitor on SMC proliferation and migration in vitro and in neointimal formation in vivo. CGP 53716 inhibited dose dependently tyrosine phosphorylation of both the known PDGFRs: the PDGFR-alpha and PDGFR-beta. In primary rat SMC cultures, a dose-dependent inhibition of PDGF-AA and PDGF-BB induced migration, and tritiated thymidine incorporation of SMC was seen at nontoxic concentrations. After rat carotid artery ballooning injury in vivo, the migration of alpha-actin-positive cells on the luminal side of internal elastic lamina was decreased with 50 mg x kg(-1) x day(-1) of CGP 53716 from 38 +/- 10 (control group) to 4 +/- 2 (P<0.0001, Mann-Whitney U test, N=18). CGP 53716 did not inhibit the number of replicating bromodeoxyuridine (BrdU)-incorporating cells in the intima, media, or adventitia during BrdU labeling at 0-96 postoperative h, though it inhibited significantly (P<0.01) the replication of medial and intimal cells from 93 h onward. Intima/media ratio was inhibited by 40% after 14 days in the CGP 53716-treated group (P=0.028) after rat aortic denudation. The results indicate that inhibition of the PDGFR tyrosine kinase inhibits SMC migration and proliferation in vitro, SMC migration, and, to a lesser extent, proliferation after ballooning injury in vivo, confirming a causal role for activation of the PDGFR and the formation of neointimal lesions.

Pharmacological profile of the receptors that mediate external carotid vasoconstriction by 5-HT in vagosympathectomized dogs

1. 5-Hydroxytryptamine (5-HT) can produce vasodilatation or vasoconstriction of the canine external carotid bed depending upon the degree of carotid sympathetic tone. Hence, external carotid vasodilatation to 5-HT in dogs with intact sympathetic tone is primarily mediated by prejunctional 5-HT1-like receptors similar to the 5-HT1D subtype, which inhibit the carotid sympathetic outflow. The present investigation is devoted to the pharmacological analysis of the receptors mediating external carotid vasoconstriction by 5-HT in vagosympathectomized dogs. 2. Intracarotid (i.c.) infusions for 1 min of 5-HT (0.3, 1, 3, 10, 30 and 100 micrograms) resulted in dose-dependent decreases in both external carotid blood flow and the corresponding conductance; both mean arterial blood pressure and heart rate remained unchanged during the infusions of 5-HT. These responses to 5-HT were resistant to blockade by antagonists at 5-HT2 (ritanserin) and 5-HT3/5-HT4 (tropisetron) receptors, but were partly blocked by the 5-HT1-like and 5-HT2 receptor antagonist, methiothepin (0.3 mg kg-1); higher doses of methiothepin (1 and 3 mg kg-1) caused little, if any, further blockade. These methiothepin (3 mg kg-1)-resistant responses to 5-HT were not significantly antagonized by MDL 72222 (0.3 mg kg-1) or tropisetron (3 mg kg-1). 3. The external carotid vasoconstrictor effects of 5-HT were mimicked by the selective 5-HT1-like receptor agonist, sumatriptan (3, 10, 30 and 100 micrograms during 1 min, i.c.), which produced dose-dependent decreases in external carotid blood flow and the corresponding conductance; these effects of sumatriptan were dose-dependently antagonized by methiothepin (0.3, 1 and 3 mg kg-1), but not by 5-HT1D-like receptor blocking doses of metergoline (0.1 mg kg-1). 4. The above vasoconstrictor effects of 5-HT remained unaltered after administration of phentolamine, propranolol, atropine, hexamethonium, brompheniramine, cimetidine and haloperidol, thus excluding the involvement of alpha- and beta-adrenoceptors, muscarinic, nicotinic, histamine and dopamine receptors. Likewise, inhibition of either 5-HT-uptake (with fluoxetine) or cyclo-oxygenase (with indomethacin), depletion of biogenic amines (with reserpine) or blockade of calcium channels (with verapamil) did not modify the effects of 5-HT. 5. Taken together, the above results support our contention that the external carotid vasoconstrictor responses to 5-HT in vagosympathectomized dogs are mainly mediated by activation of sumatriptan-sensitive 5-HT1-like receptors. It must be emphasized, notwithstanding, that other mechanisms of 5-HT, including an interaction with a novel 5-HT receptor (sub)type and/or an indirect action that may lead to the release of a known (or even unknown) neurotransmitter substance cannot be categorically excluded.

Role of alpha1-adrenoceptors in the reduction of external carotid blood flow induced by buspirone and ipsapirone in the dog

The effects of the 5-HT1A receptor agonist with anxiolytic properties, buspirone and ipsapirone, in the external carotid bed of anaesthetized dogs were analyzed. Since these agonists produce several vascular effects via activation of both 5-HT receptors and alpha1-adrenoceptors, their effects were compared with those elicited by the 5-HT agonist, quipazine, and the alpha1-adrenoceptor agonist, methoxamine. 1-Min intracarotid (i.c.) infusions of buspirone (300 microgram/min), ipsapirone (40 microgram/min), quipazine (300 microgram/min) and methoxamine (15 microgram/min) produced consistent decreases in external carotid blood flow (ECBF); since these changes in blood flow were not accompanied by modifications in systemic blood pressure, the agonists produced parallel increases in external carotid resistance. After interruption of the sympathetic tone by bilateral cervical vagosympathectomy, the vasoconstrictor responses to all the agonists remained unaffected. The intravenous (i.v.) administration of the nonselective 5-HT1-like receptor antagonist, methiothepin (1-100 microgram/kg), potently and dose-dependently antagonized buspirone-, ipsapirone- and quipazine-induced vasoconstriction; methiothepin similarly antagonized the vasoconstrictor responses to methoxamine. Interestingly, the alpha1-adrenoceptor antagonist, prazosin (1-100 microgram/kg, i.v.), also antagonized the vasoconstrictor responses to buspirone, ipsapirone and methoxamine in a dose-dependent manner. Finally, buspirone (300 microgram/min, i.c.) and ipsapirone (40 microgram/min, i.c.) did not modify the responses to noradrenaline (10 microgram/min, i.c.) or tyramine (100 microgram/min, i.c.). It is concluded that canine external carotid vasoconstriction induced by buspirone and ipsapirone is mainly mediated by activation of alpha1-adrenoceptors located in vascular smooth muscle. These data further highlight the ability of the above anxiolytics to produce significant vascular effects under in vivo conditions.

[A comparison of the effects of serotonin, 2-(2-aminoethyl)quinoline (D-1997) and sumatriptan on the external carotid blood flow in the dog]

The quinoline derivative, 2-(2-aminoethyl)-quinoline (D-1997) has been shown to mimic the contractile effects induced by serotonin (5-hydroxytryptamine; 5-HT) in the saphenous vein and basilar artery of the dog. Inasmuch as the receptor mechanisms mediating the above effects are similar to those involved in 5-HT-induced vasoconstriction of the canine common carotid circulation, the present study was set out to analyze the haemodynamic profile of D-1997 in the canine external carotid vascular bed. The effects of D-1997 were compared with those produced by 5-HT and the antimigraine drug, sumatriptan. One-min intracarotid (i.c.) infusions of D-1997 (10, 30, 100, 300 and 1000 micrograms/min), 5-HT (0.3, 1, 3, 10, 30 and 100 micrograms/min) and sumatriptan (3, 10, 30 and 100 micrograms/min) elicited dose-dependent decreases in external carotid blood flow (ECBF); since the infusions of agonists did not modify arterial blood pressure, they produced dose-dependent increases in external carotid resistance (ECR). The vasoconstrictor responses to D-1997 and 5-HT were of short duration (up to 10 min) whilst those to sumatriptan were longer lasting (up to 40 min). In addition, the effects induced by the agonists in the external carotid bed did not affect basal resistance in the contralateral common carotid, thereby suggesting a local effect by D-1997. The rank order of agonist potency was 5-HT > sumatriptan > D-1997; however, the order of agonist efficacy, represented as the maximum response obtained with the highest dose, displayed a different pattern, namely, D-1997 > or = sumatriptan > 5-HT.(ABSTRACT TRUNCATED AT 250 WORDS)

The 5-HT1-like receptor mediating the increase in canine external carotid blood flow: close resemblance to the 5-HT1D subtype

1. It has recently been shown that the increase in external carotid blood flow induced by 5-hydroxy-tryptamine (5-HT) in the anaesthetized dog, being mimicked by 5-carboxamidotryptamine (5-CT), inhibited by methiothepin, vagosympathectomy and sympatho-inhibitory drugs, and resistant to blockade by ritanserin and MDL 72222, is mediated by stimulation of prejunctional 5-HT1-like receptors leading to an inhibitory action on carotid sympathetic nerves; these 5-HT1-like receptors are unrelated to either the 5-HT1A, 5-HT1B or 5-HT1C (now 5-HT2C) receptor subtypes. Inasmuch as 5-CT, 5-methoxytryptamine, sumatriptan and metergoline display high affinity, amongst other 5-HT binding sites, for the 5-HT1D subtype, in the present study we have used these drugs in an attempt to determine whether the above inhibitory prejunctional 5-HT1-like receptors correlate with the 5-HT1D subtype. 2. One-minute intracarotid (i.c.) infusions of 5-HT (0.3, 1, 3 and 10 micrograms), 5-CT (0.01, 0.03, 0.1 and 0.3 micrograms), 5-methoxytryptamine (1, 3, 10 and 30 micrograms) and sumatriptan (1, 3, 10, 30 and 100 micrograms) resulted in dose-dependent increases in external carotid blood flow (without changes in mean arterial blood pressure or heart rate) with the following rank order of agonist potency: 5-CT >> 5-HT > 5-methoxytryptamine > or = sumatriptan. Interestingly, sumatriptan-induced vasodilatation was followed by a more pronounced vasoconstriction. 3. The external carotid vasodilator effects of 5-HT, 5-CT, 5-methoxytryptamine and sumatriptan were dose-dependently and specifically antagonized by metergoline (10, 30 and/or 100 micrograms kg-1, i.v.). In addition, 5-methoxytryptamine- and sumatriptan-induced vasodilator effects were, respectively, markedly inhibited or abolished after vagosympathectomy, as previously shown for 5-CT and 5-HT.4. Sumatriptan showed tachyphylaxis in its vasodilator component and antagonized 5-HT-induced external carotid vasodilatation in a specific manner, suggesting that a common site of action may be involved.5. Taken together, the above results support our contention that 5-HT, 5-CT, 5-methoxytryptamine and sumatriptan produce external carotid vasodilatation in the dog by an action that might primarily involve a prejunctional inhibition on carotid sympathetic nerves; a secondary component of this vasodilator response may be postsynaptic (endothelium-dependent and/or even directly on the vasculature).Based on the rank order of agonist potency, inhibition by vagosympathectomy and blockade by metergoline, we suggest that the inhibitory prejunctional 5-HT1-like receptors mediating external carotid vasodilatation in the dog closely resemble the 5-HTID receptor subtype. The pharmacological profile of these receptors is similar (sympathetic nerves of the rat kidney and human saphenous vein, as well as porcine coronary endothelium) to other putative 5-HTID receptors mediating vascular responses.

Role of 5-HT1-like receptors in the increase in external carotid blood flow induced by 5-hydroxytryptamine in the dog

This study investigated the receptor involved in the 5-hydroxytryptamine (5-HT)-induced increase in external carotid blood flow in pentobarbital-anaesthetized dogs. One-minute intracarotid (i.c.) infusions of 5-HT (0.3, 1, 3 and 10 micrograms) and 5-carboxamidotryptamine (5-CT; 0.01, 0.03, 0.1 and 0.3 micrograms) produced dose-dependent increases in external carotid blood flow without changes in mean arterial blood pressure or heart rate. After vagosympathectomy, the above vasodilator responses to 5-HT and 5-CT were abolished and remained so even after restoration of carotid vascular tone with noradrenaline. Furthermore, the 5-HT- and 5-CT-induced increases in external carotid blood flow were not modified by the 5-HT2 receptor antagonist, ritanserin (100 micrograms/kg i.v.), nor the 5-HT3 receptor antagonist, 1 alpha H,3 alpha, 5 alpha H-tropan-3yl-3,5-dichlorobenzoate (MDL 72222; 140 micrograms/kg i.v.), but were potently and dose dependently antagonized by the mixed 5-HT1-like and 5-HT2 receptor blocker, methiothepin (3, 10 and 30 micrograms/kg i.v.). Interestingly, the 5-HT1A and 5-HT1B receptor antagonist, cyanopindolol (100, 300 and 1000 micrograms/kg i.v.), blocked the effects of 5-HT, but the block was not elicited in a dose-dependent manner, with only the response induced by 0.3 microgram/min 5-CT being significantly antagonized by the highest dose of cyanopindolol; however, this blockade was not selective. Unlike 5-HT and 5-CT, 1 min i.c. infusions of either the 5-HT1C/5-HT2 receptor agonist, 1-(2,5-dimethoxy-4-iodophenyl)-aminopropane (DOI; 30-300 micrograms), or the 5-HT3 receptor agonist, 2-methyl-5-HT (10-300 micrograms), were devoid of effects on the canine external carotid blood flow. It is concluded that the 5-HT-induced increase in external carotid blood flow is mediated by 5-HT1-like receptors probably located on carotid sympathetic nerves. These receptors, however, do not seem to correspond to either the 5-HT1A, 5-HT1B or 5-HT1C receptor subtypes.

Elastic behaviour of the carotid artery in intact spontaneously hypertensive rats

Intact spontaneously hypertensive rats (SHR) were studied to assess the effect of prolonged antihypertensive treatment on the elastic behaviour of the external carotid artery. Thirty-week-old SHR received the ACE inhibitor captopril, the arteriolar dilator hydralazine or their vehicle for 6 weeks. These rats were compared to normotensive, vehicle treated WKY rats. The internal diameter of the carotid artery was measured continuously in halothane-anaesthetized rats using an echo-tracking device, and intra-arterial pressure was also monitored continuously, on the contralateral side. Captopril- and hydralazine-treated SHR as well as normotensive controls had similar blood pressure values. No significant shift in the distensibility-pressure curves was observed among vehicle-treated SHR and WKY rats or the SHR which had received captopril or hydralazine. Histological examination of the carotid artery fixed ex vivo with paraformaldehyde showed a significant increase in cross-sectional area in vehicle-treated SHR as compared to their normotensive counterparts. These results therefore suggest that the elastic behaviour of elastic arteries is not necessarily altered by the structural changes developing in response to hypertension.

[Effect of intraventricular injection of substance P on pulmonary and carotid arterial pressure in rabbits]

In the present investigation changes of pulmonary and carotid arterial pressure in response to injection of substance P(SP) into the 4th ventricle of rabbits were studied. The results were as follows: (1) Intraventricular (ivt.) injection of SP could induce either an increase or a decrease in pulmonary arterial pressure as well as carotid arterial pressor response and bradycardia. (2) Bilateral cervical vagotomy could initiate a definite pulmonary pressor response and a marked decrease in the bradycardiac response to injection of SP in those rabbits originally showing a depressor response of pulmonary artery to SP. (3) Pretreatment by i.c.v. and i.v. phentolamine or alpha 1 blocker, prazosin, could block both the SP-induced pulmonary and carotid pressor responses. (4) alpha 2 blocker, yohimbine, or naloxone could enhance the pressor responses in the both arteries. (5) Propranolol had no effect on the pressor responses in both arteries. (6) The cardiovascular responses to SP could be blocked by the SP blocker (D-Pro2.D-Trp7.9)-SP. It is assumed that increase of SP in the brain may induce an increase in both the pulmonary and carotid arterial pressures and bradycardia by activating the SP receptors. The central mechanism responsible for the SP- induced pressor response involves the participation of adrenergic alpha 1 receptor activities, while the central adrenergic alpha 2 receptor system as well as the endorphin system exerts an inhibitory modulation on the central SP-induced pressor pathway. It appears that SP, catecholamine and opiate substance are all involved in the regulation of blood pressure by brain stem.

Vasomotor responses in the isolated perfused external and internal carotid vascular beds of the rat

1. The external (ECB) or the internal (ICB) carotid vascular beds of the rat were isolated and perfused with Krebs-Henseleit solution at constant flow (1 ml/min). Changes in perfusion pressure (PP) were recorded after cervical sympathetic stimulation and after the administration of norepinephrine (NE) and serotonin (5-HT). 2. Sympathetic stimulation induced an increase in PP (vasoconstriction) in both vascular beds, however, this effect was significantly higher in the ECB than in the ICB. 3. Exogenous NE also induced a significantly higher contractile response in the ECB. 4. Prazosin (10(-8) M) significantly inhibited the response to sympathetic stimulation and to NE both in the ECB and in the ICB, but yohimbine (10(-7) M) had no effect, suggesting that the vasoconstriction was mainly due to the activation of alpha 1-adrenoceptors. 5. 5-HT induced a contractile response both in the ECB and the ICB. In contrast with the response to NE, the contraction induced by 5-HT in the ICB was significantly higher than in the ECB. 6. Ketanserine (10(-8) M) antagonised both responses, indicating the involvement of 5-HT2 receptors. 7. The contractile effect of 5-HT in the ECB was significantly enhanced by a subthreshold sympathetic stimulation that did not modify the PP by itself. This effect was not seen in the ICB. 8. The differential perfusions of the ECB or the ICB demonstrated a different reactivity of ECB and ICB, both to sympathetic stimulation and to the administration of exogenous NE or 5-HT. 9. Furthermore, the response to 5-HT in the ECB was modulated by a subthreshold sympathetic stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Severe facial ischaemia caused by ergotism

A case of ergotamine induced severe face ischaemia mimicking acute arteritis is presented. The unique clinical picture was due to bilateral involvement of both external carotid arteries. No case of ergotism with such a localization has been previously described in the literature.

Response of canine internal carotid system to acetylcholine

The reactivity of the canine internal carotid system to acetylcholine (10(-8)-10(-4) M) was studied isometrically with 4-mm cylindrical segments from cervical and cavernous portions of the internal carotid artery and from the middle cerebral artery. Under control conditions, the cervical portion relaxed to every dose, the cavernous portion relaxed at low concentrations (10(-8)-10(-6) M) and contracted at higher concentrations (10(-5)-10(-4) M), whereas the middle cerebral artery contracted to every dose of acetylcholine. These responses were blocked by atropine (10(-6) M). Without endothelium, the cervical portion exhibited a lower relaxation, the cavernous portion contracted, and the middle cerebral artery was practically unresponsive to acetylcholine. These responses were also blocked by atropine. It suggests that the reactivity of the internal carotid system to acetylcholine 1) is endothelium dependent and 2) changes as it courses toward the brain, and this could be related to different embryological origin of the components of this arterial system.

Reproducibility of Doppler blood flow velocity waveform measurements: study on variability within and between day and during haemodynamic intervention in normal subjects

Reproducibility of Doppler blood velocity waveform measurements in external and internal carotid, middle cerebral, and brachial arteries and ascending aorta was determined in 8 normal male volunteers twice daily on three occasions each separated by two or more weeks. Measurements were made in supine and standing positions at rest and after taking glyceryl trinitrate and in the supine position after performing a standardized exercise test. The Doppler blood flow waveform indices showed a between days coefficient of variation of less than 15% both for baseline measurements and during haemodynamic change induced by exercise or glyceryl trinitrate. We conclude that Doppler blood velocity waveform measurement in different vascular beds is reproducible at baseline and when the cardiovascular system is interrupted pharmacologically or physiologically.

A possible role of the glomus cell in controlling vascular tone of the carotid labyrinth of Xenopus laevis

To clarify the physiological significance of the g-s connection (intimate apposition of the glomus cell to the smooth muscle) in the Xenopus carotid labyrinth, experiments were carried out morphologically and physiologically. Results obtained are as follows. Efferent electrical stimulation of the glossopharyngeal nerve resulted in concentrating dense-cored vesicles on the peripheral region of the glomus cell, and a decrease of vesicles as a whole. In the carotid labyrinth perfused artificially, outflow of the internal and the external carotid arteries decreased with administration of catecholamines (adrenaline, noradrenaline and dopamine). Acetylcholine reduced only the internal outflow. This response was depressed by atropine, hexamethonium and phentolamine, whereas accelerated by propranolol. Sodium cyanide reduced the internal outflow without affecting the external outflow, and its effect is depressed by phentolamine. From these results, a possibility that the glomus cell participates in controlling the blood flow in the labyrinth through the intervention of the g-s connection was discussed.

Neurogenic muscarinic vasodilation in the cat. An example of endothelial cell-independent cholinergic relaxation

Nerve-mediated and acetylcholine-induced dilator behavior of feline posterior auricular arteries was studied in vitro. We evaluated the muscarinic nature and endothelial cell-dependence of the vasodilations and attempted to determine if there are inhibitory muscarinic receptors located directly on the smooth muscle cells in this artery. Transmural nerve stimulation of arteries which were pretreated with guanethidine (5 X 10(-6)M) and constricted with prostaglandin F2 alpha (3 X 10(-6)M) caused a frequency-dependent, tetrodotoxin-sensitive relaxation of up to 50% of induced tone. Atropine (10(-7)M) blocked more than 95% of this response at all frequencies. Removal of the endothelium by rubbing the intimal surface did not affect the magnitude of the response, but prolonged it slightly. Neurogenic relaxations in rubbed preparations were atropine-sensitive, although less so than control at higher stimulation frequencies. Relaxation of this artery to the calcium ionophore A23187 was completely endothelial cell-dependent. However, exogenous acetylcholine caused dose-dependent relaxations both in control and rubbed preparations. We conclude that the posterior auricular artery is an example of a blood vessel which has muscarinic receptors located directly on its smooth muscle cells which, when activated by acetylcholine released from perivascular nerves, mediate a smooth muscle cell relaxation. This finding contrasts with models of the vascular smooth muscle cell which indicates an excitatory role for muscarinic receptors.

Influence of chronic stellectomy on reactivity to serotonin in the dog external carotid bed

The influence of chronic stellectomy on external carotid flow responses to i.a. serotonin (5HT) was determined in dogs in which both stellate ganglia had been removed 1, 2, 4 or 8 weeks previously. The effect of this maneuver on carotid and heart rate responses to i.a. and i.v. norepinephrine (NE), respectively, was also assessed for comparison. Constrictor responses to NE in the carotid were moderately increased at 2 and 4 weeks, while its positive chronotropic effects were markedly augmented throughout the observation period. Dilator responses to 5HT increased at 4 and specially at 8 weeks after stellectomy. Results obtained with NE were considered compatible with supersensitivity induced by decentralization in the carotid and by denervation in the heart. Changes in carotid responses to 5HT were interpreted as being due to a prejunctional mechanism similar to that responsible for supersensitivity to NE. Differences in the time course of development of supersensitivity to both amines were attributed to masking of 5HT dilatation by NE released by the indoleamine at the time of increased sensitivity to constriction by the catecholamine.

Redistribution of flow between canine isolated internal and external carotid arteries by vasoactive substances

A Y-shaped segment consisting of the common, internal, and external carotid arteries was isolated from the canine carotid artery. The preparation has the advantage of allowing direct comparison of responses to vasoactive substances in the internal and external carotid arteries. It was perfused at a constant rate (within the range of 10-15 ml/min) through the common carotid with either Locke's solution or arterial blood led from a support dog. Adding norepinephrine or epinephrine to the perfusate raised the perfusion pressure, increased the flow along the internal carotid branch, and decreased it in the external carotid branch in the blood-perfused experiments but not in the saline-perfused ones. In contrast, 5-hydroxytryptamine, prostaglandin F2 alpha, and ATP caused a decrease in internal carotid flow and an increase in external carotid flow, raising the perfusion pressure in both experiments. Controlled bleeding of the support dog (at the rate of 4 ml/(kg X min] produced a similar result to that produced by exogenous norepinephrine or epinephrine. These findings may suggest that a redistribution of blood flow between the larger internal and external carotid arteries can be induced by a difference of responsiveness to certain vasoactive substances between the two arteries.

[Doppler ultrasound studies of the extracranial cerebral vessels in migraine patients after ergotamine tartrate administration]

Doppler ultrasound investigations were done in 20 patients with migraine during the symptom-free interval after oral administration of 2 mg and 6 mg ergotamine tartrate. The observed changes of end-diastolic flow velocity as a measure of peripheral total resistance permit simultaneous assessment of the vasoconstrictor effect of ergotamine in the perfusion area of the internal and external carotid arteries. A dosage of 2 mg led to an exclusive increase of resistance in the external carotid artery area without significant changes in the internal carotid area. A maximal therapeutic dosage of 6 mg ergotamine tartrate did not lead to a significant increase of the vasoconstrictor effect in the external carotid circulation. In addition, a barely registrable increase of resistance in the internal carotid area could now be observed.

The feline carotid rete: vasomotor reactivity of isolated arteries

Vasomotor responses of arteries from the feline carotid rete were examined using a sensitive in vitro system. The vessel segments constricted in response to several vasoactive agents and putative neurotransmitters. Sympathomimetic agents (noradrenaline, adrenaline, oxymetazoline, phenylephrine), 5-hydroxytryptamine, histamine, angiotensin II, and prostaglandin F2 alpha all induced concentration-dependent contractile responses. The contractions induced by noradrenaline, 5-hydroxytryptamine, and histamine could be antagonized by phentolamine, methysergide, and mepyramine, respectively. Cholinomimetics (acetylcholine, carbacholine), vasoactive intestinal peptide and papaverine induced potent dilatory responses. The effect of carbacholine was shifted towards higher agonist concentrations by atropine. Dilatations, though small in magnitude, were found by application of adenosine, isoproterenol, and histamine. These results correlate well with the recent demonstration of autonomic nerves and indicate the occurrence of corresponding receptor sites in the walls of the carotid rete arteries.

[Comparative responsiveness of isolated saphenous, femoral and external carotid arteries and veins of dogs to dihydroergotamine mesylate (DEM) (author's transl)]

Changes in tension of spiral strips of saphenous, femoral and external carotid arteries and veins were measured isometrically. DEM stimulated 6 preparations in almost the same concentration ranges (pD2 values were 8.64 to 8.40). However, the dose-response curves for DEM indicted variations in responsiveness among the different arteries and veins. Compared with norepinephrine (NE) (1)( the intrinsic activity of DEM was 0.002 on saphenous arteries, 0.05 on saphenous veins, 0.03 on femoral arteries, 0.18 on femoral veins, 0.13 on external carotid arteries and 0.13 on external carotid jugular veins. Thus DEM contracted more potently the venous strips from the hind limbs. IN femoral and external carotid arteries, antagonism of serotonin by DEM or methysergide was investigated. DEM displaced the dose-contractile response curves for serotonin in a noncompetitive manner, and the antagonistic response of DEM to serotonin was about 8 times more effective in external carotid arteries (pD'2 value=6.96) than in femoral arteries (pD'2 value=6.05). Methysergide, unlike DEM, antagonized the response to serotonin in a competitive manner at low doses but in a noncompetitive manner in high doses, and was fairly equal in antagonizing response to serotonin in external carotid arteries (pA2 value=that the therapeutic value of DEM in the treatment of orthostatic hypotension is due to its selective anti-serotonin activity on the external carotid arteries.

Isolated, blood-perfused canine arteries: different vasoconstrictor responses of internal and external carotid arteries to 5-hydroxytryptamine

Canine carotid arteries were isolated, suspended in a bath and perfused under a constant flow rate with arterial blood led from a support dog. Resting perfusion pressure was set at a constant level over 50 mm Hg. Drugs were administered into the endothelial side of the artery through a cannulated tubing and the response was obtained as pressure changes. This preparation was proved to be superior to usual isolated arterial strips, since its reactivity was kept in a stable condition over 5-10 hours at 37 degrees C. Using this preparation, effects of 5-hydroxytryptamine (5-HT) on the internal and external carotid arteries were investigated in comparison with effects of norepinephrine. In the internal carotid artery, 5-HT caused a much more potent vasoconstriction than norepinephrine. On the other hand, in the external carotid artery, 5-HT caused only slight vasoconstriction, while norepinephrine produced a marked vasoconstriction.

Internal and external carotid vascular responses to vasoactive agents in the monkey

Internal and external carotid blood flows in anesthetized monkeys were measured simultaneously using electromagnetic flowmeters. Complete dose-response relationships were established for the effects of intracarotid infusion of several humoral agents implicated in migraine. Both the internal and external carotid vasculatures were constricted by serotonin and prostaglandin F2alpha and dilated by bradykinin, histamine, and acetylcholine. Noradrenalin and adrenaline constricted the external carotid vasculature but had little direct effect in the internal carotid territory. Prostaglandin E1 dilated the external carotid vasculature. Low doses of prostaglandin E1 produced dilation in the internal carotid circulation, but with higher doses there was a paradoxical abolition of this effect.

Actions of bradykinin on isolated cerebral and peripheral arteries

The addition of bradykinin (BK) caused a dose-related contraction in helical strips of canine cerebral, internal carotid, external carotid, and femoral arteries, while the peptide elicited a relaxation in canine coronary, renal, and mesenteric arteries contracted with 5+ or prostaglandin F2alpha. In contrast to canine cerebral arteries, human cerebral arteries contracted with K+ or prostaglandin relaxed with BK. Contractile responses of canine cerebral arteries to BK were not influenced by phentolamine, diphenhydramine, and methysergide, but were attenuated by aspirin and indomethacin. Contractions induced by K+ were not or only slightly inhibited by these anti-inflammatory agents. Polyphloretin phosphate failed to reduce BK-induced contractions. Relaxing effects of BK on canine coronary arterial strips were not altered by atropine, propranolol, metiamide, and aminophylline, but were inhibited by aspirin and indomethacin. Adenosine-induced relaxation was unaffected by the latter two agents. It may be concluded that adrenergic, cholinergic, histaminergic, and adenosine-related mechanisms are not involved in the genesis of BK-induced contraction and relaxation. Contractile responses of canine cerebral arteries to BK do not appear to derive from prostaglandins released, but rather from a direct action on vascular smooth muscle cells.

Cerebral arterial spasm. Part 7: In vitro effects of alpha adrenergic agents on canine arteries from six anatomical sites and six blocking agents on serotonin-induced contractions of the canine basilar artery

In vitro experiments were performed using a small volume chamber to determine the contractile activity of several adrenergic agents on arteries from six locations of the canine vascular bed. Cumulative log-dose response curves were obtained for epinephrine, norepinephrine, phenylephrine and dopamine. It was found that the basilar and internal carotid arteries responded much less to these agents than did the mesenteric, renal and femoral arteries. Six blocking agents including nitroprusside were tested to determine their effect on the response of the canine basilar artery to log-dose additions of serotonin, prostaglandin F2alpha and KC1. Another chamber was developed to study the differential effect of nitroprusside and papaverine when placed on the luminal side versus the adventitial (cerebrospinal fluid) side of the basilar artery during a sustained contraction with serotonin. A theoretical treatment of cerebral arterial spasm following a subarachnoid hemorrhage is presented.

Effect of vasodilating drugs on external carotid and pulpal blood flow in dogs: "stealing" of dental perfusion pressure

Blood flow in the external cartoid artery (ECBF) and dental pulp (PBF) was measured during arterial infusion of vasodilators (isoprenaline, papaverine, acetylcholine and bradykinin). Systemic arterial pressure (AP) and local arterial pressure of the teeth (LAP) were recorded in a femoral and the lateral nasal artery respectively. All four vasodilators were found to increase ECBF and simultaneously reduce lateral nasal arterial pressure--or in other words-to STEAL" PERFUSION PRESSURE FROM THE TEETH. AP remained practically unchanged whereas PBF was variably affected. During infusion of isoprenaline PBF decreased on average by 19% of control. Papaverine nearly doubled PBG, while bradykinin caused no consistent change. Great pulpal flow variations were often recorded during constant acetylcholine infusion rate. The variable effect of the four vasodilators on PBF could partly be explained by the fall in LAP. Calculated pulpal resistance (LAP/PBF) showed no consistent change during isoprenaline infusion, bradykinin caused a slight fall and papaverine reduced LAP/PBF by 49%. The experiments demonstrate that due to the "stealing" of dental perfusion pressure caused by vasodilation in the neighbouring tissues, the effect of vasodilators on pulpal resistance vessels cannot be estimated without knowledge of the pressure in the small arteries directly feeding the teeth.

Comparative effects of four migraine prophylactic drugs on an isolated extracranial artery

Clonidine and methysergide constrict the rabbit auricular artery by activating smooth muscle alpha-adrenoceptors. Clonidine inhibits and methysergide enhances responses to stimulation of the sympathetic nerves. Both drugs sensitise the artery to a variety of vasoconstrictor stimuli, although not to potassium chloride. This weak generalised sensitisation may depend on clonidine and methysergide themselves being vasoconstrictor since sensitisation after clonidine did not occur when vasoconstriction was abolished with phentolamine. The marked potentiation of 5-HT and tryptamine observed during clonidine perfusion may reflect a property of the tryptamines since it was observed during perfusion with histamine but not when histamine vasoconstriction was abolished with mepyramine. Cyproheptadine and pizotifen neither constrict the artery nor sensitise it to vasoconstrictor agents. They inhibit responses to nerve stimulation, alpha-adrenoceptor agonists, potassium chloride and particularly histamine. Sensitisation of blood vessels reinforced by direct vasoconstriction may contribute to the mechanism of action of clonidine and methysergide in migraine. Conversely, alterations in vascular function may be less important to the antimigraine actions of either cyproheptadine or pizotifen.

Responsiveness of isolated canine cerebral and peripheral arteries to ergotamine

Changes in tension of spiral strips from dog saphenous, external carotid and basilar arteries were monitored isometrically. Serotonin (5-HT) contracted the 3 arterial preparations in about the same concentration range. Compared with noradrenaline (NA) (100%) the efficacy of 5-HT was about 60% on saphenous, 150% on external carotid and about 500% on basilar arteries. Ergotamine (E) stimulated the 3 vascular preparations in concentrations about 100 times lower than 5-HT. Compared with NA the efficacy of E was about 20% on saphenous, 50% on external carotid and 200% on basilar arteries. Compared with 5-HT (100%) however, E had similar constrictor activities in the 3 arteries. It seemed likely therefore that 5-HT receptors are involved in the vasoconstrictor activity of E. Evidence for this was obtained in experiments in which cyproheptadine (Cy), a 5-HT antagonist, was used. For antagonism of E concentrations of Cy about 6 times higher than those required to inhibit 5-HT were necessary, whereas for antagonism of NA about 500 times higher Cy concentrations were necessary. The results suggest that on canine arterial vascular smooth muscle the constrictor activity of E is mediated mainly through serotoninergic receptor sites.

Responsiveness of isolated cerebral and peripheral arteries to serotonin, norepinephrine, and transmural electrical stimulation

Spirally cut strips of cerebral and peripheral arteries from dogs were used for comparing the vasoconstricting effect of serotonin, norepinephrine, K + , and transmural electrical stimulation. Sensitivity of cerebral (basilar, posterior cerebral, and middle cerebral) arterial strips to serotonin was markedly greater than that to norepinephrine with respect to the median effective concentration (ED 50 ) and the maximum response. Contractile responses of isolated human cerebral arteries to serotonin and norepinephrine were similar to those observed in the dog arteries. In contrast, proximal and distal strips from superior mesenteric arteries and strips from renal arteries were more sensitive to norepinephrine than they were to serotonin. Mean values of contractions caused by 5 x 10 -6 M serotonin relative to those caused by 30 mM K + in cerebral, internal carotid, external carotid, common carotid, and superior mesenteric arteries were in a descending order, whereas those for norepinephrine were in an ascending order. These studies demonstrate that a gradual transition occurs from characteristic responses seen in mesenteric arteries (high sensitivity to norepinephrine, low sensitivity to serotonin) to those seen in cerebral arteries (high sensitivity to serotonin, low sensitivity to norepinephrine). Transmural stimulation did not produce contractions of cerebral and internal carotid arteries, but contractions were produced in external carotid, common carotid, and superior mesenteric arteries. It appears that sympathetic nerves cannot play an important role in the regulation of vascular tone in large cerebral arteries.