Tissue blood flow and localization of arteriovenous anastomoses in pigs with microspheres of four different sizes

Chain-Like Structures of Biogenic and Nonbiogenic Magnetic Nanoparticles in Vascular Tissues

In this paper, slices of organs from various organisms (animals, plants, fungi) were investigated by using atomic force microscopy and magnetic force microscopy to identify common features of localization of both biogenic and nonbiogenic magnetic nanoparticles. It was revealed that both biogenic and nonbiogenic magnetic nanoparticles are localized in the form of chains of separate nanoparticles or chains of conglomerates of nanoparticles in the walls of the capillaries of animals and the walls of the conducting tissue of plants and fungi. Both biogenic and nonbiogenic magnetic nanoparticles are embedded as a part of the transport system in multicellular organisms. In connection with this, a new idea of the function of biogenic magnetic nanoparticles is discussed, that the chains of biogenic magnetic nanoparticles and chains of conglomerates of biogenic magnetic nanoparticles represent ferrimagnetic organelles of a specific purpose. Besides, magnetic dipole-dipole interaction of biogenic magnetic nanoparticles with magnetically labeled drugs or contrast agents for magnetic resonance imaging should be considered when designing the drug delivery and other medical systems because biogenic magnetic nanoparticles in capillary walls will serve as the trapping centers for the artificial magnetic nanoparticles. The aggregates of both artificial and biogenic magnetic nanoparticles can be formed, contributing to the risk of vascular occlusion. Bioelectromagnetics. 43:119-143, 2022. © 2021 Bioelectromagnetics Society.

A conceptual model for changes in finger photoplethysmograph signals caused by hand posture and isothermic regulation

OBJECTIVE

To observe changes in baseline and pulsatile light absorbance (photoplethysmograph, PPG) in the finger-tip, by raising the hand above the horizontal plane in recumbent subjects. We applied current knowledge of the circulation to the finger-tip, particularly arteriovenous anastomoses (AVAs), and the physiology of the venous circulation.

APPROACH

We studied healthy young volunteers in a quiet thermoneutral environment. A finger plethysmograph on the non-dominant hand recorded transmission of red and infra-red light, and the values were converted into absorbance to allow comparisons within and between subjects. Breathing movements were recorded unobtrusively to assess any effect on absorbance and the pulse amplitude of the signals. All body movements were passive: the study arm was elevated in a trough to about 40° above the horizontal plane. The following conditions were studied, each for 15 minutes, using the last 10 minutes for analysis: recumbent, study arm elevated, study arm horizontal, and both legs elevated by 40°.

MAIN RESULTS

There was a substantial time-related effect, and considerable variation between subjects. Arm elevation reduced red light absorbance and increased the range of amplitudes of the PPG waveform: only in subjects with large absorbances, did waveform amplitude increase. The other main effect was that spontaneous, thermoregulatory decreases in absorbance were associated with decreases in waveform amplitude.

SIGNIFICANCE

Finger-tip vessels distend with blood when AVAs open. The vessels pulsate more strongly if venous collapse allows the vessels to become more compliant. The postcapillary circulation is likely to be an important source of pulsation.

Conventional hemodynamic resuscitation may fail to optimize tissue perfusion: an observational study on the effects of dobutamine, enoximone, and norepinephrine in patients with acute myocardial infarction complicated by cardiogenic shock

AIM

To investigate the effects of inotropic agents on parameters of tissue perfusion in patients with cardiogenic shock.

METHODS AND RESULTS

Thirty patients with cardiogenic shock were included. Patients received dobutamine, enoximone, or norepinephrine. We performed hemodynamic measurements at baseline and after titration of the inotropic agent until cardiac index (CI) ≥ 2.5 L.min-1.m(-2) or mixed-venous oxygen saturation (SvO2) ≥ 70% (dobutamine or enoximone), and mean arterial pressure (MAP) ≥ 70 mmHg (norepinephrine). As parameters of tissue perfusion, we measured central-peripheral temperature gradient (delta-T) and sublingual perfused capillary density (PCD). All patients reached predefined therapeutic targets. The inotropes did not significantly change delta-T. Dobutamine did not change PCD. Enoximone increased PCD (9.1 [8.9-10.2] vs. 11.4 [8.4-13.9] mm.mm(-2); p<0.05), and norepinephrine tended to decrease PCD (9.8 [8.5-11.9] vs. 8.8 [8.2-9.6] mm.mm-2, p = 0.08). Fifteen patients (50%) died within 30 days after admission. Patients who had low final PCD (≤ 10.3 mm.mm-2; 64%) were more likely to die than patients who had preserved PCD (>10.3 mm.mm(-2); mortality 72% vs. 17%, p = 0.003).

CONCLUSION

This study demonstrates the effects of commonly used inotropic agents on parameters of tissue perfusion in patients with cardiogenic shock. Despite hemodynamic optimization, tissue perfusion was not sufficiently restored in most patients. In these patients, mortality was high. Interventions directed at improving microcirculation may eventually help bridging the gap between improved hemodynamics and dismal patient outcome in cardiogenic shock.

Are the precapillary sphincters and metarterioles universal components of the microcirculation? An historical review

The microcirculation is a major topic in current physiology textbooks and is frequently explained with schematics including the precapillary sphincters and metarterioles. We re-evaluated the validity and applicability of the concepts precapillary sphincters and metarterioles by reviewing the historical context in which they were developed in physiology textbooks. The studies by Zweifach up until the 1950s revealed the unique features of the mesenteric microcirculation, illustrated with impressive schematics of the microcirculation with metarterioles and precapillary sphincters. Fulton, Guyton and other authors introduced or mimicked these schematics in their physiology textbooks as representative of the microcirculation in general. However, morphological and physiological studies have revealed that the microcirculation in the other organs and tissues contains no metarterioles or precapillary sphincters. The metarterioles and precapillary sphincters were not universal components of the microcirculation in general, but unique features of the mesenteric microcirculation.

Chemical mediators of migraine: preclinical and clinical observations

Migraine is a neurovascular disorder, and although the pathophysiology of migraine has not been fully delineated, much has been learned in the past 50 years. This knowledge has been accompanied by significant advancements in the way migraine is viewed as a disease process and in the development therapeutic options. In this review, we will focus on 4 mediators (nitric oxide, histamine, serotonin, and calcitonin gene-related peptide) which have significantly advanced our understanding of migraine as a disease entity. For each mediator we begin by reviewing the preclinical data linking it to migraine pathophysiology, first focusing on the vascular mechanisms, then the neuronal mechanisms. The preclinical data are then followed by a review of the clinical data which support each mediator's role in migraine and highlights the pharmacological agents which target these mediators for migraine therapy.

The relevance of preclinical research models for the development of antimigraine drugs: focus on 5-HT(1B/1D) and CGRP receptors

Migraine is a complex neurovascular syndrome, causing a unilateral pulsating headache with accompanying symptoms. The past four decades have contributed immensely to our present understanding of migraine pathophysiology and have led to the introduction of specific antimigraine therapies, much to the relief of migraineurs. Pathophysiological factors culminating into migraine headaches have not yet been completely deciphered and, thus, pose an additional challenge for preclinical research in the absence of any direct experimental marker. Migraine provocation experiments in humans use a head-score to evaluate migraine, as articulated by the volunteer, which cannot be applied to laboratory animals. Therefore, basic research focuses on different symptoms and putative mechanisms, one at a time or in combination, to validate the hypotheses. Studies in several species, utilizing different preclinical approaches, have significantly contributed to the two antimigraine principles in therapeutics, namely: 5-HT(1B/1D) receptor agonists (known as triptans) and CGRP receptor antagonists (known as gepants). This review will analyze the preclinical experimental models currently known for the development of these therapeutic principles, which are mainly based on the vascular and/or neurogenic theories of migraine pathogenesis. These include models based on the involvement of cranial vasodilatation and/or the trigeminovascular system in migraine. Clearly, the preclinical strategies should involve both approaches, while incorporating the newer ideas/techniques in order to get better insights into migraine pathophysiology.

Animal models of headache: from bedside to bench and back to bedside

In recent years bench-based studies have greatly enhanced our understanding of headache pathophysiology, while facilitating the development of new headache medicines. At present, established animal models of headache utilize activation of pain-producing cranial structures, which for a complex syndrome, such as migraine, leaves many dimensions of the syndrome unstudied. The focus on modeling the central nociceptive mechanisms and the complexity of sensory phenomena that accompany migraine may offer new approaches for the development of new therapeutics. Given the complexity of the primary headaches, multiple approaches and techniques need to be employed. As an example, recently a model for trigeminal autonomic cephalalgias has been tested successfully, while by contrast, a satisfactory model of tension-type headache has been elusive. Moreover, although useful in many regards, migraine models are yet to provide a more complete picture of the disorder.

Low-frequency changes in finger volume in patients after surgery, related to respiration and venous pressure

BACKGROUND AND OBJECTIVE

In patients after surgery, we observed large-amplitude low-frequency changes in digital plethysmograph measurements when DC coupling of the signal was used. We set out to assess factors that might contribute to these events and in particular to test the possibility that low-frequency signals could be used to assess respiratory disturbances.

METHODS

We recorded values in 23 patients who had undergone gynaecological surgery. We measured nasal flow, abdominal pressure (by urinary catheter), venous pressure in the hand, and DC-coupled optical transmission plethysmography. Signals were replayed and analysed to assess the incidence of specific patterns of events.

RESULTS

Most patients received morphine for postoperative analgesia. Respiratory irregularity and expiratory muscle action were very frequent. Increases in abdominal pressure during expiration caused increases in venous pressure and pulsation. In 12 out of 23 patients, a characteristic response consistent with vasoconstriction was noted after increases in breath size, and, in seven patients, very-low-frequency (0.2-0.7 Hz) oscillations of finger volume were present that appeared unrelated to respiratory events. Patients who did not receive morphine had very different plethysmograph patterns, with significantly smaller pulse amplitude.

CONCLUSION

Low-frequency changes in finger volume can be simply obtained and provide considerable information about peripheral circulatory dynamics. Diverse patterns can be recognized, but the range of responses suggests that current techniques cannot be used alone to assess cardiorespiratory status. However, a combination of plethysmography with respiratory measurements shows characteristic events.

AT(2) receptor-mediated vasodilation in the heart: effect of myocardial infarction

To investigate the functional consequences of postinfarct cardiac angiotensin (ANG) type 2 (AT(2)) receptor upregulation, rats underwent coronary artery ligation or sham operation and were infused with ANG II 3-4 wk later, when scar formation is complete. ANG II increased mean arterial pressure (MAP) more modestly in infarcted animals than in sham animals. The AT(1) receptor antagonist irbesartan, but not the AT(2) receptor antagonist PD123319, decreased MAP and antagonized the ANG II-mediated systemic hemodynamic effects. Myocardial (MVC) but not renal vascular conductance (RVC) was diminished in infarcted versus sham rats. ANG II did not affect MVC and reduced RVC in all rats. MVC was unaffected by irbesartan and PD123319 in all animals. However, with PD123319, ANG II reduced MVC in sham but not infarcted animals, and, with irbesartan, ANG II increased MVC in infarcted but not sham animals. Irbesartan increased RVC and antagonized the ANG II-mediated renal effects in all animals. RVC, at baseline or with ANG II, was not affected by PD123319 in infarcted and sham animals. In conclusion, coronary but not renal AT(2) receptor stimulation results in vasodilation, and this effect is enhanced in infarcted rats.

Continuous positive pressure ventilation during epidural blockade--effects on cardiac output distribution

BACKGROUND

It has been shown that when cardiac output (CO) decreases during continuous positive pressure ventilation (CPPV), its regional distribution adapts with a favouring of vital organs. Does epidural blockade modify this adaptation?

METHODS

Regional blood flows were assessed by the microsphere technique (15 microm) in 17 anaesthetised pigs during spontaneous breathing and CPPV with 8 cm H2O end-expiratory pressure (CPPV8) before and after epidural blockade. The block was induced at either the Th6-7 (Thep) or the L6-S1 (Lep) level with 1 ml of lidocaine 40 mg x ml(-1).

RESULTS

When Lep was combined with CPPV8, mean arterial pressure and CO decreased significantly, and they decreased even more when combined with Thep. In contrast, the relative perfusion of the central nervous system, heart and kidneys remained stable during the four conditions studied. The adrenal perfusion during CPPV8 was obviated by epidural blockade. The absolute and relative perfusion of the skeletal muscle decreased during epidural blockade. The administered doses of epidural lidocaine did not affect blood flow in the spinal cord.

CONCLUSIONS

The locally mediated nutritive vasoregulation of vital organs outweighed the sympathetic blockade induced by epidural blockade. During Thep blockade the animals were less capable of responding to the haemodynamic changes induced by CPPV8, probably due to the blockade of the cardiac part of the sympathetic nervous system.

Tissue perfusion in relation to cardiac output during continuous positive-pressure ventilation and administration of propranolol or verapamil

BACKGROUND

Our objective was to determine whether administration of propranolol or verapamil modifies the hemodynamic adaptation to continuous positive-pressure ventilation (CPPV), in particular the regional distribution of cardiac output (CO).

METHODS

General hemodynamics and regional blood flows assessed by microsphere technique (15 microns) were recorded in 16 anesthetized pigs during spontaneous breathing (SB) and CPPV with 8 cm H2O end-expiratory pressure (CPPV8) before and after intravenous administration of propanolol (0.3 mg.kg-1 followed by 0.15 mg.kg-1.h-1, n = 8) or verapamil (0.1 mg.kg-1 followed by 0.3 mg.kg-1.h-1, n = 8).

RESULTS

CPPV8 depressed CO by 25% without shifts in its relative distribution with the exception of a noteworthy increase in adrenal perfusion. Propranolol increased arterial blood pressure, and due to a fall in heart rate, CO dropped by 25%. The kidneys and, to a lesser extent, the splanchic region and central nervous system received increased fractions of the remaining CO at the expense of skeletal muscle flow. Similar patterns were seen during SB and CPPV8 such that the combination of propranolol and CPPV8 depressed CO by 50%. The circulatory effects of verapamil were less evident but myocardial perfusion tended to increase.

CONCLUSIONS

The combination of propranolol or verapamil with CPPV does not result in any specific hemodynamic interaction in anesthetized pigs, except that the combined effect of propranolol and CPPV may severely reduce CO.

A physiologically based pharmacokinetic model incorporating dispersion principles to describe solute distribution in the perfused rat hindlimb preparation

A physiologically based pharmacokinetic model incorporating dispersion principles has been developed to describe outflow data from the isolated perfused rat hindlimb preparation, for the three reference markers 14C-sucrose, 14C-urea, and 3H-water and three 14C-labeled 5-n-alkyl-5-ethyl barbiturates; the methyl, butyl, and nonyl homologues. Also 51Cr-RBC and 125I-albumin were studied. The model consists of four parallel components representing each of the tissues comprising the hindlimb: skeletal muscle, skin, bone, and adipose. Attempts to simplify the model by using the principle of tissue lumping were made by examining the tissue equilibration rate constant k tau for each of respective tissues for each compound. It was found that simplification was only possible in the case of 3H-water data. The model took into account a possible shunting component in the skin tissue and incomplete mass but not volumetric recovery from the system. The dispersion model characterizes the relative spreading of solute on transit through a tissue bed by a dimension-less parameter DN. The estimated dispersion numbers (DN) obtained were in the region of 2.7-4.72, 8.39-15.54, 0.61-2.74, and 6.02-14.0 for skeletal muscle, skin, bone, and adipose, respectively, and were independent of the compound studied. These values are much larger than the range reported in the literature for hepatic outflow data, DN = 0.2-0.5, and suggest a greater heterogeneity of vascular flow in the different component tissues of the rat hindlimb.

Assessment of peripheral vascular effects of antimigraine drugs in humans

The vascular beds of the forearm and finger can be used to study the peripheral effects of antimigraine drugs under normal and pathologic circumstances. We have investigated the novel antimigraine drug sumatriptan, a selective agonist for 5HT1 receptors. Its antimigraine effect may be attributed, at least in part, to constriction of cranial arteriovenous anastomoses (AVAs). In assessing the peripheral vascular effects of sumatriptan we used a forearm and finger blood flow model. Forearm blood flow (FBF) is mainly determined by resistance vessels, whereas finger blood flow (FiBF) mainly involves skin vessels, which contain many AVAs. Changes in FBF and FiBF can be assessed using venous occlusion plethysmography. Changes in AVA flow are determined by measuring the patency of the vascular beds of the forearm and hand to well-defined radiolabelled microspheres, which are injected into the brachial artery. We report the effects of sumatriptan on FBF, FiBF and AVA flow when administered into the brachial artery of healthy volunteers, and discuss the peripheral vascular effects of therapeutic doses of sumatriptan when given subcutaneously in migraine patients during and between attacks.

The effect of nitric oxide donors on haemodynamics and blood flow distribution in the porcine carotid circulation

1. The role of nitric (NO) in the regulation of capillary and arteriovenous anastomotic blood flow was evaluated in the carotid circulation of the pig. For this purpose, the effect of intracarotid (i.c.) infusions of saline and two NO donors, nitroprusside sodium (NPR) and S-nitroso-N-acetylpenicillamine (SNAP) in concentrations of 3-100 micrograms min-1 was studied on systemic haemodynamics and carotid blood flow and its distribution in anaesthetized pigs with low arteriovenous anastomotic blood flow, by use of the radioactive microsphere method. 2. Apart from heart rate, which increased after both NPR and SNAP, no major changes in systemic haemodynamic variables were observed. In contrast to saline, both NPR and SNAP increased common carotid blood flow, vascular conductance and vascular pulsations dose-dependently. 3. The distribution of the carotid artery blood flow over capillary and arteriovenous anastomotic fraction remained stable after saline infusions. Both NPR and SNAP enhanced total capillary blood flow and conductance. In contrast to NPR, arteriovenous anastomotic blood flow and conductance were increased by SNAP. 4. At the tissue level, capillary blood flow increases following NPR or SNAP were reflected by an increase in both extracerebral and dural blood flow without changes in total brain blood flow. 5. These results indicate that both NO donors cause arteriolar dilatation together with enhanced vascular pulsations in the carotid circulation of the pig. Probably by way of a 'steal' phenomenon, this pronounced arteriolar dilatation limits the effect of NO donors on arteriovenous anastomoses. 6. The results of the present investigation support the contention that dilatation of intra- and extra cranial arteries and arteriovenous anastomoses leads to increased vascular pulsations, which (rather than increased blood flow) could, at least in part, be responsible for the headache caused by nitro vasodilators.

Inhibition of nitric oxide biosynthesis and carotid arteriovenous anastomotic shunting in the pig

1. The role of nitric oxide (NO) biosynthesis in the regulation of blood flow through arteriovenous anastomoses was evaluated in the carotid circulation of the anaesthetized pig. For this purpose, the effect of intracarotid (i.c.) administration of the NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME: 0.1, 0.3 and 1.0 mg kg-1; n = 6) or saline (n = 6) was studied on the distribution of common carotid blood flow, using the radioactive microsphere method. 2. Apart from the highest dose, L-NAME caused no major changes in the systemic haemodynamic variables. Both cardiac output and systemic vascular conductance were reduced by L-NAME (1 mg kg-1), being reversed partly by L-arginine (100 mg kg-1, i.c.). In both groups, L-arginine slightly reduced mean arterial blood pressure. 3. Total common carotid artery blood flow as well as its distribution over the capillary and arteriovenous anastomotic fraction remained stable after saline injection. In contrast, L-NAME caused a dose-dependent decline in common carotid artery blood flow and conductance and this decline was confined entirely to its arteriovenous anastomotic part. 4. Subsequent intracarotid injection of L-arginine (100 mg kg-1) reversed the reduction in total carotid conductance almost completely and that in the arteriovenous anastomotic region partially. Additionally, L-arginine increased capillary conductance significantly in the L-NAME--as well as the saline-treated animals. 5. These results indicate that the L-arginine-NO pathway contributes little to the regulation of tissue perfusion in the porcine carotid circulation. In contrast, NO seems to play an important role in shunting arterial blood through arteriovenous anastomoses in the anaesthetized pig.

Effects of tertatolol, a beta-adrenoceptor antagonist with agonist affinity at 5-HT1A receptors, in an animal model of migraine: comparison with propranolol and pindolol

Constriction of carotid arteriovenous anastomoses is a common property of several antimigraine drugs. The present study concerns the effects of tertatolol (0.1, 0.3, 1 and 3 mg/kg i.v.), a novel beta-adrenoceptor antagonist with an agonist action on 5-HT1A receptors, on systemic haemodynamics and carotid blood flow distribution in the anaesthetized pig. Two other beta-adrenoceptor antagonists, one (propranolol) with and one (pindolol) without antimigraine actions, were compared (doses: 0.03, 0.1, 0.3 and 1 mg/kg i.v.) with tertatolol in this animal experimental model of migraine. While the beta-adrenoceptor antagonist with partial agonist action, pindolol, increased heart rate and cardiac output, propranolol and tertatolol decreased these variables moderately. Mean arterial blood pressure also decreased with the two highest doses of propranolol and with the highest dose of tertatolol. The calculated total peripheral conductance decreased with the first three doses of tertatolol. Carotid haemodynamic variables were not affected by pindolol, except for some increase in the nutrient fraction after the highest dose. Propranolol and especially tertatolol decreased both total carotid blood flow and arteriovenous anastomotic blood flow without affecting the nutrient fraction. In the case of tertatolol, blood flow decreases were accompanied by similar decreases in vascular conductance, indicating active arteriovenous anastomotic constriction. It is therefore suggested that tertatolol may prove effective in the treatment of migraine.

Lack of effect of the antimigraine drugs, sumatriptan, ergotamine and dihydroergotamine on arteriovenous anastomotic shunting in the dura mater of the pig

1. In anaesthetized animals, the antimigraine drugs, sumatriptan, ergotamine and dihydroergotamine, reduce carotid arteriovenous anastomotic shunting. Within the carotid vascular bed arteriovenous anastomoses are located, amongst other places in the dura mater, which is a putative site of the pain during a migraine attack. 2. In this investigation, we have localized and measured the arteriovenous shunting within the carotid vascular bed of the pig by using simultaneous intracarotid injections of radiolabelled microspheres of three different sizes (10, 15 and 50 microns), which provides an index of blood flow via arteriovenous anastomoses larger than approximately 14, 27 and 90 microns diameter, respectively. The effects of sumatriptan (0.3 mg kg-1), ergotamine (0.02 mg kg-1), dihydroergotamine (0.1 mg kg-1) and saline were studied by repeating the injections of 15 and 50 microns spheres after the treatments. 3. There was no difference in shunting or entrapment between the 10 and 15 microns microsphere, indicating the absence of arteriovenous anastomoses with a diameter between 14 and 27 microns. 4. Arteriovenous anastomoses with a diameter between 27 and 90 microns, as indicated by the difference in blood flow measured by 15 and 50 microns spheres, were located in the dura mater, ears, skin, fat and, to a lesser extent, in the skeletal muscles and eyes. 5. Sumatriptan, ergotamine and dihydroergotamine reduced the overall flow in the smaller arteriovenous anastomoses (diameter between 27 and 90 microns), and even more in larger shunts (wider than 90 microns). 6. Locally, blood flow in the smaller arteriovenous shunts was reduced in the skin and fat, but not in the dura mater, ears, eyes and muscles.It is not possible to determine in which tissues blood flow in the larger arteriovenous anastomoses was reduced.7. Tissue blood flow measured with 15 gm microspheres remained unchanged after the three antimigraine drugs, implying a lack of effect on capillary flow.8. It is concluded that in the anaesthetized pigs the only evident effect of these antimigraine drugs on carotid haemodynamics is a decrease in blood flow in both smaller and larger arteriovenous anastomoses;the smaller arteriovenous anastomoses were affected in the skin and fat, but not in other tissues.

Comparative effects of the antimigraine drugs sumatriptan and ergotamine on the distribution of cardiac output in anaesthetized pigs

The haemodynamic effects of sumatriptan, a 5-HT1-like receptor agonist, and ergotamine, an agonist at alpha-adrenergic, dopamine as well as 5-HT receptors, were compared using intracardiac injection of radioactive microspheres of different sizes in anaesthetized pigs. Ergotamine (0.02 mg.kg-1) and sumatriptan (0.3 mg.kg-1) decreased systemic vascular conductance and cardiac output. Only ergotamine raised arterial blood pressure. Both sumatriptan and ergotamine decreased arteriovenous anastomotic, but not capillary, blood flow in the head and body skin. Arteriovenous and capillary blood flow in the dura mater and nasal mucosa and capillary blood flow in the brain, kidneys, adrenals, intestine, heart, spleen and muscle remained unchanged. However, kidney conductance was decreased by both drugs, spleen conductance by sumatriptan and heart, liver and adrenal conductances were decreased by ergotamine. Thus, both sumatriptan and ergotamine constricted arteriovenous anastomoses in the skin, but not in the dura mater or nasal mucosa. Ergotamine constricted the vasculature more than sumatriptan, although both drugs may differentially decrease vascular conductances in some organs.

Restoration of venous outflow by simultaneous creation of an arteriovenous shunt and pedicle flap using a rat model of foot replantation

Replantation of amputated rat feet utilizing an efferent arteriovenous shunt constructed between the distal posterior tibial artery and the proximal posterior tibial vein, in the absence of all other venous drainage, provides an alternative pathway to the normal venous drainage in a replanted rat foot. However, this substitute venous drainage was insufficient to prevent progressive ischemia and necrosis of some or all of a replanted rat foot. When a cutaneous pedicle flap supplemented the arteriovenous shunt, venous drainage was much improved, tissue hypoxia and edema began to subside on the third day, severe tissue necrosis was prevented, and seven of eight feet replanted by this technique survived. These observations may be useful in replantation in humans when veins in the amputated part are too small to be used or so damaged that they cannot be repaired or reconstructed by a vein graft, but arteries can still provide a means of returning blood from the amputated part. Constructing an alternative pathway to the normal venous drainage pattern may allow severely damaged parts to survive after replantation.

The effect of venous flow alterations upon patency of rat femoral vein anastomoses

The rat femoral vein has become a standard model for laboratory training in microvascular anastomotic technique as well as for research investigations into factors affecting venous patency. This study examined the short-term patency (1 and 7 days) of rat vein anastomoses. The influences upon patency of epigastric flap creation and distal femoral vessel ligation (epigastric flow only) were explored. In a separate experiment, blood flow from the femoral vein was determined through catheter collection of venous efflux; the influences of island epigastric flap creation and distal femoral ligation on flow rates were explored. It was found that 82% of basic femoral vein anastomoses were patent at one day, while 100% of anastomoses associated with an epigastric flap and ligated/transected distal femoral vessel circulation (creating a low-tension anastomosis) were patent (P less than 0.01). With distal femoral vessel ligation and no transection (normal tension at the repair), anastomoses were patent in 90% of the veins when an epigastric flap was also raised, and in 60% when a flap was not created. When a flap was raised without disturbing the distal femoral circulation, vein patency was 75% at one day. When the vein anastomosis was performed with distal femoral vein ligation, the patency rate was 50%. All veins patent at 1 day were also patent at 7 days post-op; 96% of veins clotted at 1 day were found to be patent at 7 days. The venous efflux was not found to vary significantly when an epigastric flap was raised.(ABSTRACT TRUNCATED AT 250 WORDS)

Arteriovenous shunting is not associated with venous congestion in bone. Knee tamponade studied with 15-microns and 50-microns microspheres in immature dogs

Blood flow in the hind-limb bones of 8 immature labrador dogs with unilateral knee joint tamponade at 75 percent of the mean arterial pressure was measured with 15-microns and 50-microns microspheres to determine whether or not arteriovenous shunting occurs in bone with venous congestion caused by increased outflow resistance. The intraosseous pressure was 43 percent of the mean arterial pressure in the experimental distal femoral epiphysis versus 14 percent in the control knee (P less than 0.001). No pressure changes were found in the distal femoral metaphysis. Regional blood flow with 15-microns microspheres decreased centrally in the distal femoral epiphysis and increased centrally in the proximal tibial epiphysis. Metaphyseal blood flow was largely unchanged. A net shift in the preferred embolization site of 50-microns microspheres relative to that of 15-microns microspheres from central to peripheral regions occurred within both juxtaarticular epiphyses, indicating arteriolar vasodilation, but the relation between the uptake of the two microsphere sizes was unchanged when the epiphyses and other bony flow compartments were viewed in toto. The result speaks against the hypothesis of arteriovenous shunting in intraosseous hypertension.

Pharmacology of antimigraine drugs

The drugs used in migraine therapy can be divided into two groups: agents that abort an established migraine attack and agents used prophylactically to reduce the number of migraine attacks. Both groups have drugs that are specific for migrainous headaches and that are non-specific, and are used to treat the accompanying headache (analgesics), vomiting (anti-emetics), anxiety (sedatives and anxiolytics), or depression (antidepressants). The main drugs with specific action on migraine include ergot alkaloids (ergotamine, dihydroergotamine), agonists (sumatriptan) or partial agonists (methysergide) at a specific subtype of 5-HT1-like receptors, beta-adrenoceptor antagonists (propranolol, metoprolol), calcium antagonists (flunarizine) and anti-inflammatory agents (indomethacin). The pharmacological basis of therapeutic action of several of these drugs is not well understood. In the case of the ergot alkaloids and 5-HT1-like receptor agonists, however, it is likely that the antimigraine effect is related to the potent and rather selective constriction of the large arteries and arteriovenous anastomoses in the scalp and dural regions. In addition, these drugs inhibit plasma extravasation into the dura in response to trigeminal ganglion stimulation, but it is possible that this effect is related to the selective vasoconstriction in the extracerebral vascular bed. The selectivity of the pharmacological effects of these antimigraine drugs (constriction of the extracerebral arteries and arteriovenous anastomoses, poor penetration into the central nervous system and the absence of an antinociceptive effect even after intrathecal administration) strongly suggests that excessive dilatation in the extracerebral cranial vasculature, probably initiated by a neuronal event, is an integral part of the pathophysiology of migraine.

Haemodynamic profile of the potassium channel activator EMD 52692 in anaesthetized pigs

1. The systemic and regional haemodynamic effects of the potassium channel activator EMD 52692 or its solvent were investigated after intravenous and after intracoronary administration in anaesthetized pigs. 2. Consecutive intravenous 10 min infusions of EMD 52692 (0.15, 0.30, 0.60, 1.20 micrograms kg-1 min-1; n = 7) dose-dependently decreased mean arterial blood pressure by up to 50%. This was entirely due to peripheral vasodilatation, since cardiac output did not change. Heart rate increased by up to 50%, while left ventricular end diastolic pressure decreased dose-dependently from 6 +/- 1 mmHg to 3 +/- 1 mmHg (P less than 0.05), and stroke volume decreased from 30 +/- 2 ml to 21 +/- 2 ml (P less than 0.05). Left ventricular dP/dtmax was not affected. 3. Although cardiac output did not change, EMD 52692 caused a redistribution of blood flow from the arteriovenous anastomoses to the capillary channels. Blood flow to the adrenals, small intestine, stomach, bladder, spleen and brain increased, while renal blood flow decreased and blood flow to several muscle groups and skin were not altered. Vascular conductance was increased dose-dependently in all organs, except for the kidneys, where after the initial increase, vascular conductance returned to baseline with the highest dose. Particularly striking were the effects on the vasculature of the brain. With the highest dose of EMD 52692 blood flow more than doubled, while vascular conductance increased four fold. 4. Transmural myocardial blood flow increased slightly, which was entirely due to an increase in subepicardial blood flow. Myocardial O2-consumption and segment length shortening were not significantly affected. 5. After consecutive 10 min intracoronary infusions (0.0095, 0.019, 0.0375 and 0.075 microgram kg-1 min-1; n = 7) into the left anterior descending coronary artery (LADCA), mean arterial blood pressure was maintained with the lowest two doses, but decreased by up to 15% with the higher doses, whereas heart rate increased by up to 24%. Blood flow to the LADCA-perfused myocardium doubled with the highest dose, the subepicardium benefitting the most. Coronary venous O2-saturation increased dose-dependently from 23 +/- 2% to 60 +/- 4%, while myocardial O2-consumption of the LADCA-perfused myocardium was not affected by the drug. 6. It is concluded that EMD 52692 is a potent vasodilator, with particularly pronounced effects on vasculature of the brain. Its selectivity for vascular smooth muscle cells exceeds that for the myocytes, since with doses that are much higher than those of potential clinical interest no negative inotropic effects were observed. The compound primarily dilates arteries but some venodilatation may also occur.

Microvascular hemodynamics in experimental arthritis: disparity between the distribution of microspheres and plasma flow in bone

The microcirculation in normal and arthritic juxtaarticular bone was studied in 16 young dogs with carragheenan-induced arthritis of one knee. The regional blood flow was determined by the tissue uptake of intracardially injected 15-microns 141Ce-labeled microspheres, and the microvascular plasma volume was determined by the distribution space of circulating 125I-fibrinogen. Disparities between the distribution of plasma flow and microspheres, introduced by plasma skimming or nonentrapment of spheres in the intraosseous circulation, were estimated by 59Fe-transferrin, a third intravascular tracer, injected as a bolus intracardially and trapped peripherally after 15 sec by prompt circulatory arrest. The tissue uptake of the plasma flow tracer was compared to that of microspheres by the ratio between observed and expected activity of 59Fe-transferrin, the expected activity being calculated from the microsphere distribution. The transferrin and microsphere uptake agreed well in patella, marginal epiphyseal bone, and cortical bone, whereas observed activity of transferrin was twice the expected in central epiphyseal bone, three times higher in marrow, and up to eightfold higher in metaphyses adjacent to growth plates. This discrepancy was significantly greater in arthritic bone when the metaphyses were examined in toto. The microsphere method thus appears to underestimate blood flow to cancellous bone and marrow due to uneven distribution of plasma and formed elements from profound plasma skimming and perhaps also by AV shunting.

Nimodipine has no effect on the cerebral circulation in conscious pigs, despite an increase in cardiac output

1. We studied the effects of four doses of nimodipine (0.5, 1, 2 and 4 micrograms kg-1 min-1) on systemic haemodynamics and on regional vascular beds, in particular the cerebral circulation, in conscious pigs. 2. Nimodipine caused dose-dependent, probably reflex-mediated, increases in heart rate (42% with the highest dose) and cardiac output (54%), while arterial blood pressure was only minimally affected. Left ventricular end-diastolic pressure and systemic vascular resistance decreased dose-dependently (35-40% at the highest dose) while stroke volume remained unchanged. 3. Total brain blood flow was not affected by the drug. Furthermore, we could not demonstrate any regional cerebral differences, as blood flows to both cerebral hemispheres as well as the diencephalon, cerebellum and brain stem remained unchanged. 4. Blood flow to the kidneys, liver, small intestine and skin also did not change. Nimodipine caused dose-dependent increases in blood flow to the stomach (95%), myocardium (97%) and adrenal glands (102%), while blood flow to skeletal muscles (267%) increased most. 5. It is concluded that in the conscious pig, nimodipine is an arterial vasodilator which shows some selectivity for the skeletal muscle vasculature but does not increase total or regional cerebral blood flow.

The central and regional cardiovascular responses to intravenous and intracoronary administration of the phenyldihydropyridine elgodipine in anaesthetized pigs

1. The central and regional cardiovascular responses to intravenous (0.3, 1.0, 3.0 and 10.0 micrograms kg-1 min-1) and intracoronary (0.3, 0.9, 3.0 and 4.5 micrograms kg-1 min-1) infusions of elgodipine, a phenyldihydropyridine, and its solvent were studied in anaesthetized pigs. 2. Elgodipine (i.v.) caused dose-dependent decreases in arterial blood pressure (up to 44%) and systemic vascular resistance (up to 48%), whereas heart rate, LV dP/dtmax, left ventricular filling pressure, cardiac output and segment length shortening did not change. The absence of a negative inotropic effect with the employed doses was confirmed by the intracoronary infusions; with the lowest dose (0.3 micrograms kg-1 min-1) both LV dP/dtmax and segment length shortening decreased by less than 10%. With 0.9 micrograms kg-1 min-1 (intracoronary) the negative inotropic properties of the drug became apparent as LV dP/dtmax and segment length shortening decreased by 20% and 33%, respectively, whereas heart rate and left ventricular filling pressure were not affected. 3. Transmural myocardial blood flow did not change during intravenous infusion of elgodipine, as vasodilatation, more pronounced in the subepicardial than in the subendocardial layers, compensated for the decrease in arterial perfusion pressure. The intracoronary infusions revealed that the decrease in normalized subendocardial/subepicardial blood flow ratio was not secondary to the fall in arterial blood pressure. 4. Myocardial oxygen consumption decreased during both the i.v. and the intracoronary administration of elgodipine. With the i.v. administration the decrease was secondary to the hypotensive action of the drug, whereas with the intracoronary administration the negative inotropic properties played the dominant role. 5. Elgodipine (i.v.), although not affecting total cardiac output, caused a redistribution in favour of the nutritional blood flow at the expense of the arteriovenous anastomotic (AVA) blood flow. Up to an infusion rate of 3.0upg kg - I min- 1 the decrease in AVA-flow was due to a fall in arterial blood pressure, but at the highest infusion rate both the decrease in arterial perfusion pressure and an increase in their resistance contributed to a further decrease in AVA blood flow. 6. The skeletal muscles benefited most from the elgodipine(i.v.)-induced increase in nutritional blood flow, but vasodilatation was not uniform for all muscle groups. Up to an infusion rate of 3 yg kg - ' min- 1 the vasodilatation in the renal vascular bed was more pronounced in the inner than in the outer cortex, but, at 0 pyg kg-1 min-, vascular resistances of both cortical layers returned to baseline values. In all regions of the brain, blood flow was maintained until the highest infusion rate was given. With 10 yg kg- I min - ' only flow to the vital parts of the brain (diencephalon and brain stem) was maintained. Blood flows to the skin and various abdominal organs were well maintained up to 3 pg kg'- min - 1 but, at the highest dose, a decrease was observed in blood flow to the adrenals and spleen. Vascular resistances of all these organs and tissues decreased dose-dependently. 7. The potent systemic and coronary vasodilator actions of elgodipine during i.v. administration, which were not accompanied by negative inotropic and positive chronotropic properties or decreases in the perfusion of vital organs, warrant further study as this compound could be useful in the treatment of essential hypertension, myocardial ischaemia and, possibly, moderate chronic heart failure.

Recombinant human transforming growth factor-beta 1 (rhTGF-beta 1) enhances healing and strength of granulation skin wounds

A new animal model to study secondary intention wound healing and the effects of topically applied rhTGF-beta 1 was developed. A time course study was performed of full thickness 6 mm punch wounds placed on the backs of anesthetized pigs and treated once with either 3% methylcellulose or rhTGF-beta 1 in 3% methylcellulose or left untreated. Wounds receiving rhTGF-beta 1 had enhanced tensile strength at days 4 and 7 compared to controls. Studies of the response on days 4 and 7 to graded doses of rhTGF-beta 1 showed that a dose of 250 or 2500 ng rhTGF-beta 1 gave a similar enhanced wound strength, while 25 ng rhTGF-beta 1 had no effect. Blood flow to treated granulating wounds as measured by 141Ce microspheres indicate an increase in flow in wounds treated with 250, 500 or 2500 ng rhTGF-beta 1 compared to controls. These results indicate a possible use for rhTGF-beta 1 in enhancing wound healing clinically.

Characterization of 5-hydroxytryptamine receptors in the cranial vasculature

The availability of selective compounds has made it possible to subdivide 5-hydroxytryptamine (5-HT) receptors into three distinct types, called 5-HT1-like, 5-HT2 and 5-HT3. The selective agonists at the three receptor types are, respectively, 5-carboxamidotryptamine, alpha-methyl-5-HT and 2-methyl-5-HT. While no selective antagonists are yet available for the 5-HT1-like receptors, some compounds, including ketanserin and MDL 72222, selectively antagonize 5-HT2 and 5-HT3 receptors respectively. Depending upon experimental conditions, 5-HT causes a constriction or dilatation of cerebral and extracerebral cranial vessels. Vascular contraction by 5-HT seems to be mediated primarily via 5-HT2 receptors (located mainly on large conducting vessels), though in several instances (for example, dog and human basilar arteries and porcine arteriovenous anastomoses; AVAs) 5-HT1-like receptors are involved in addition to or in place of 5-HT2 receptors. In the rabbit ear and external carotid arteries 5-HT may act directly on alpha-adrenoceptors. Arteriolar dilatation, leading to increased capillary ("nutrient") blood flow, occurs via 5-HT1-like receptors. However, the 5-HT1-like receptors on the arterioles and AVAs appear to be similar but not identical. Since a reduction of plasma 5-HT and opening of AVAs have been implicated in the pathophysiology of migraine, compounds acting on 5-HT1-like receptors to close the shunt vessels can be expected to have therapeutic activity in migraine.

Analysis of H2 clearance curves used to measure blood flow in rat sciatic nerve

1. By use of the H2 clearance technique, blood flow was measured in the sciatic nerve of healthy, anaesthetized Sprague-Dawley rats at rest, during inferior vena cava occlusion and during 5-hydroxytryptamine infusion. The purpose was to clarify the mechanisms underlying the biexponential curves which are commonly obtained using this technique. 2. An analysis of the frequency distribution of rate constants of 270 nerve and thirty-three arterial samples indicated that H2 clearance rates cluster below 20 ml min-1 100 g-1 and between 70 and 100 ml min-1 100 g-1. This suggests that at least two compartments are present. 3. The contribution of diffusion was studied by recording H2 clearance immediately following circulatory arrest. Slow clearance rates (median = 2.4 ml min-1 100 g-1) were observed, indicating that diffusion is not likely to contribute significantly to nutritive flow under most situations. 4. The contribution of arteriovenous shunts to H2 clearance was assessed by determining H2 clearance during inferior vena cava occlusion and the infusion of 5-hydroxytryptamine. Both manoeuvres caused abolition of, or a significant reduction in the weight of, the fast component which indicates that this compartment is closely related to arteriovenous shunts in nerve. 5. By use of a multi-compartmental model, it was shown that H2 clearance should follow a multi-exponential course, where the weights of the components reflect the relative volumes of each compartment and the exponents represent the relative flow (i.e. flow per unit volume) in each compartment. 6. By use of other mathematical models, estimates were made for the clearance rates attributable to polarographic oxidation of H2 at the tip of the microelectrode (0.2 ml min-1 100 g-1) and to diffusion to air (2 ml min-1 100 g-1). The latter estimate is very close to the measured value of 2.4 ml min-1 100 g-1. 7. These findings indicate that it is possible to separately assess nutritive and non-nutritive flow by application of biexponential analysis to H2 clearance curves. The data suggest that the fast component of a H2 clearance curve is closely associated with arteriovenous shunts, while the slower component is likely to represent capillary flow. Processes such as diffusion to air or oxidation of H2 by the electrode are very slow and therefore are unlikely to distort the assessment of blood flow by using this technique.

Reduction of cephalic arteriovenous shunting by ergotamine is not mediated by 5-HT1-like or 5-HT2 receptors

1. The potent, antimigraine drug ergotamine has affinity for both 5-HT1 and 5-HT2 binding sites and constricts arteriovenous anastomoses. Since 5-HT also constricts arteriovenous anastomoses (mainly via 5-HT1-like receptors), this study investigates the involvement of 5-HT receptors in the ergotamine-induced reduction of arteriovenous shunting in the carotid circulation of the cat and pig. 2. In the cat, ergotamine (3, 10 and 30 micrograms kg-1, i.v.) reduced carotid blood flow, predominantly by a reduction in arteriovenous anastomotic blood flow. Pretreatment with ketanserin (0.5 mg kg-1, i.v.) or methiothepin (1 mg kg-1, i.v.) did not antagonize the effects of ergotamine. 3. In the pig, ergotamine (2.5, 5, 10 and 20 micrograms kg-1, i.v.) also reduced carotid blood flow and arteriovenous shunting, which was not affected by pretreatment with methiothepin (1 mg kg-1, i.v.). 4. These results suggest that the reduction by ergotamine in the shunting of carotid arterial blood via cephalic arteriovenous anastomoses is not mediated by 5-HT1-like or 5-HT2 receptors.

Effects of isradipine and other calcium antagonists on arteriovenous-shunt flow in anesthetized rabbits and cats

The effects of vasodilators on arteriovenous (AV)-shunt flow was investigated in anesthetized cats and rabbits, using the tracer microsphere method. In cats, the calcium antagonist isradipine reduced AV-shunt flow; verapamil showed a similar tendency and nicardipine was without effect. Dihydralazine strongly increased, but nitroglycerin and dipyridamole decreased AV-shunt flow. In rabbits, the effects of isradipine and verapamil were similar to those seen in cats. Sodium nitroprusside had no effect, whereas prazosin, minoxidil, and the potassium-channel activator cromakalim increased AV-shunt flow. The contrasting effects of drugs sharing the same mechanism of action suggest that target-tissue selectivity is more important than the mechanism of action. An increase of AV-shunt flow is unlikely to be beneficial but could be associated with a number of undesirable side effects. It might negatively affect migraine sufferers and, if AV-shunt dilatation shows no tolerance development, it represents an unnecessary hemodynamic burden for the heart.

Enhancement of vasoconstrictor and attenuation of vasodilator effects of 5-hydroxytryptamine by the calcium channel blockers nimodipine and nifedipine in the pig

As calcium (Ca2+) channel blockers are effective against the vasoconstrictor responses to 5-hydroxytryptamine (5-HT) in vitro, and a favourable response is claimed for these drugs in migraine prophylaxis, we studied the interaction between nimodipine or nifedipine, and 5-HT for effects on carotid haemodynamics in the anaesthetized pig. Intracarotid infusions of nimodipine (0.25 microgram X kg-1 X min-1), nifedipine (0.75 microgram X kg-1 X min-1) or 5-HT (2.0 micrograms X kg-1 X min-1) caused a redistribution of carotid blood flow in favour of the nutrient (capillary) fraction at the expense of the non-nutrient (arteriovenous anastomoses; AVA) fraction. Compared to those of 5-HT, the effects of the Ca2+ channel blockers on cranial AVAs were much weaker and the increase in the capillary fraction was observed mainly in the skeletal muscles, rather than in the skin and ears as with 5-HT. When 5-HT was infused in the presence of nimodipine or nifedipine, the amine-induced vasoconstrictor responses in the total carotid vascular bed and its AVA fraction were either not attenuated or were increased while the vasodilator responses were reduced. We conclude that: in contrast to what was found in vitro, the 5-HT-induced vasoconstriction in vivo, involving either '5-HT1-like' (AVAs) or 5-HT2 (arterioles) receptors, was not antagonized by nimodipine or nifedipine; the attenuation of the 5-HT-induced dermal vasodilatation by the two Ca2+ channel blockers is most likely to be the result of a 'steal' due to the profound vasodilatation in the skeletal muscle region; and the comparatively mild reduction in AVA conductance caused by the Ca2+ channel blockers may be one of the reasons for their inability to abort acute attacks of migraine. The increase in nutrient blood flow is of potential benefit, but whether this property of the Ca2+ channel blockers is linked to their usefulness in migraine prophylaxis remains to be ascertained.

Nimodipine-induced changes in the distribution of carotid blood flow and cardiac output in pentobarbitone-anaesthetized pigs

In view of the claimed effectiveness of nimodipine in migraine and its possible selectivity for cerebral vessels, we investigated the effects of nimodipine in anaesthetized pigs on the fractionation of carotid arterial blood flow into non-nutrient (arteriovenous anastomoses; AVAs) and nutrient (capillary) parts, and on regional tissue blood flows and vascular conductances. Intracarotid infusions of nimodipine (0.05-1.25 microgram kg-1 min-1) redistributed carotid blood flow in favour of its nutrient compartment, particularly to the skeletal muscles and tongue. Vascular conductance in the non-nutrient (AVAs) compartment decreased (40%), most likely, as a result of 'steal' following profound (5.5 fold) arteriolar dilatation. Intravenous infusions of nimodipine (0.05-6.25 micrograms kg-1 min-1) caused hypotension, bradycardia, a decrease in conduction in the non-nutrient fraction, and an increase in conduction in the nutrient fraction (mostly in the skeletal muscles, but also in the gastrointestinal tract, cerebral hemispheres, heart and adrenals). Probably due to the hypotensive effect, only skeletal muscle blood flow increased. The nimodipine-induced increase in vascular conductance in the skeletal muscles showed regional variation; the effect was most pronounced in the cheek muscles, followed by the muscles of the chest, abdominal, trunk and gluteal regions. We conclude that: AVA flow seems to represent a 'reserve' perfusion which can be readily diverted to tissues in the case of increased metabolism and/or vasodilatation, though the overall response to nimodipine of carotid blood flow distribution qualitatively resembles that to some antimigraine drugs, the relevance of such acute effects in the prophylactic usefulness of nimodipine in migraine remains to be ascertained, and nimodipine lacks a selective cerebral vasodilator action in the anaesthetized pig.

Effects of MDL 72222 and methiothepin on carotid vascular responses to 5-hydroxytryptamine in the pig: evidence for the presence of "5-hydroxytryptamine1-like" receptors

The present study concerns the effects of MDL 72222 (0.5 mg X kg-1, i.v.), a 5-hydroxytryptamine3 (5-HT3) receptor antagonist, and methiothepin (1.0 mg X kg-1, i.v.), an antagonist of both 5-HT2 and "5-HT1-like" receptors, on the responses to local infusions of 5-HT (2.0 micrograms X kg-1 X min-1) on the total common carotid artery blood flow and its complete distribution in anaesthetized pigs. As reported earlier, more than 80% of the carotid blood bypassed the capillary circulation via cranial arteriovenous anastomoses, while approximately 15% and 2% was distributed to the extracerebral structures and brain, respectively. The total carotid blood flow did not change or was moderately reduced by 5-HT, but the amine consistently caused a 85% reduction in arteriovenous anastomotic blood flow and a 5-fold increase in blood flow to the extracerebral tissues, mainly the skin and ears. The colour of the skin and ears changed to bright pink. Complete recovery from the effects of 5-HT was observed once the infusion was stopped. MDL 72222 and methiothepin did not themselves affect carotid haemodynamics. The responses to 5-HT were not modified by MDL 72222 except that the reduction of the total carotid blood flow by 5-HT was augmented. In contrast, methiothepin almost completely abolished both the reduction of arteriovenous anastomotic blood flow and the increase in tissue blood flow following 5-HT-infusion. The colour of the skin and ears also did not become pink.(ABSTRACT TRUNCATED AT 250 WORDS)

5-Carboxamide tryptamine, a compound with high affinity for 5-hydroxytryptamine1 binding sites, dilates arterioles and constricts arteriovenous anastomoses

The effects of 5-carboxamide tryptamine, which activates non-5-hydroxytryptamine2-'atypical' receptors for 5-hydroxytryptamine (5-HT) in the dog saphenous vein, was studied on the complete distribution of cardiac output and common carotid blood flow in anaesthetized pigs. The drug was infused for 10 min at the rate of 0.025, 0.1 and 0.4 micrograms kg-1 min-1 either intravenously (cardiac output distribution) or intra-arterially (carotid distribution). 5-Carboxamide tryptamine decreased arterial blood pressure due to a reduction of cardiac output. This reduction was confined to its arteriovenous anastomotic component; the component used for the tissue perfusion (nutrient part) in fact increased. Similar changes were observed in the carotid blood flow distribution. Vasodilation was observed in several tissues, but the skin, ears and stomach responded most prominently. The effects of 5-carboxamide tryptamine on the carotid distribution were not significantly modified by cyproheptadine (1 mg kg-1). It is concluded that, like 5-HT, 5-carboxamide tryptamine constricts arteriovenous anastomoses and dilates arterioles by activating non-5-HT2-'atypical' receptors. These 'atypical' 5-HT receptors appear to be of the 5-HT1 type since both 5-carboxamide tryptamine and BEA 1654, a new piperazine derivative, produced similar vascular effects in the carotid bed of the pig and also showed a high and selective affinity for the 5-HT1 binding sites.

N-(3-acetylaminophenyl)piperazine hydrochloride (BEA 1654), a putative 5-HT1 agonist, causes constriction of arteriovenous anastomoses and dilatation of arterioles

Using 3H-ligands and radioactive microspheres we studied the binding characteristics and the effects on the distribution of carotid arterial blood flow of n-(3-acetylaminophenyl)piperazine hydrochloride (BEA 1654). The compound had a Ki value of 32 nM (5-HT: 8 nM) on 5-HT1 but no or very weak affinity for 5-HT2, alpha 1- and alpha 2-adrenoceptor sites in rat cerebral cortex homogenates. Intracarotid infusions of BEA 1654 (0.1-1.0 mg X kg-1 X min-1) were nearly equieffective in untreated and treated (phentolamine plus ketanserin) pigs in redistributing carotid arterial blood towards the nutrient compartment (particularly the skin and ears) at the expense of shunting via arteriovenous anastomoses (AVAs). In view of the high and selective affinity of BEA 1654 to 5-HT1 binding sites, the similarity of pharmacological responses between 5-HT and BEA 1654, and the ineffectiveness of antagonists of 5-HT2 and alpha-adrenergic receptors to block the AVA constriction and arteriolar dilatation caused by both 5-HT and BEA 1654, we conclude that these effects are mediated by 5-HT1 receptors. The vast difference between the ratios of Ki values for 5-HT1 binding sites and of the pharmacologically effective doses of BEA 1654 and 5-HT suggests that either BEA 1654 may be a partial agonist of 5-HT1 receptors or, while the drug binds with both subsets of 5-HT1 receptors, it is only one type which mediates the pharmacological response.