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Biomedical subjects

F M Abboud

Publications and source records attributed to F M Abboud.

At least 109 records · Page 6Linked to original sources
PubMed1984

The sympathetic nervous system in hypertension.

Sympathetic drive can contribute not only to the acute adjustment to circulatory stresses but also to sustained elevation in vascular resistance and arterial pressure. In hypertensive animals and humans excessive sympathetic activity coupled with a possible genetic factor may result in defects in electrogenic ion transport of vascular muscle or in excessive vascular hypertrophy. Increased sympathetic activity and release of the neurotransmitter may occur as a result of defects of the efferent, afferent or central components of the sympathetic system. Several studies in various animal models and in humans are described to support the notion that the mosaic concept in hypertension may be embodied in a dual theory that includes a vascular muscle defect coupled with excessive sympathetic drive both of which may be of genetic or acquired origin. Almost regardless of the cause of hypertension, interruption of sympathetic efferent activity lowers arterial pressure.

Afferent Pathways↗
PubMed1984

Vasopressin and oxytocin in the neural control of the circulation.

Catecholamine innervation originating in dorsal medial and ventral lateral medulla terminates on parvocellular and magnocellular subnuclei, respectively, of the paraventricular nucleus of the hypothalamus. In turn, parvocellular pathways terminate in brain stem and spinal cord, whereas magnocellular pathways terminate in median eminence and posterior pituitary. Consistent with the neuroanatomy, we find that baroreceptor regulation of neuroendocrine (plasma vasopressin) and autonomic (blood pressure) functions can be dissociated. Further, studies indicate that sympathetic vasomotor pathways are activated by injections of vasopressin and oxytocin into the nucleus tractus solitarii and vasopressin into the lateral cerebral ventricles. Also, parasympathetic pathways to the heart and baroreflex function are activated and augmented, respectively, by i.v. administered vasopressin. These results are consistent with at least three central sites of action and suggest a complex role of vasopressin (and possibly oxytocin) in the central neural regulation of the heart and circulation.

Afferent Pathways↗
PubMed1983

Effects of calcium channel blockers on isolated carotid baroreceptors and baroreflex.

Our study determined the effects of the calcium antagonists, nifedipine and verapamil, on the carotid sinus baroreceptors and baroreflex. The left carotid sinus region in dogs was vascularly isolated and filled with oxygenated physiological salt solution. Steady-state multiunit activity was recorded from the carotid sinus nerve for sinus pressures of 50-200 mmHg after bathing the carotid sinus region in a solution containing no drug, 10 micrograms/ml nifedipine (n = 6), or 5 micrograms/ml verapamil (n = 5). The slopes of the curves relating carotid sinus nerve activity (% of maximum control) to carotid sinus pressure were control, 0.81 +/- 0.06; nifedipine, 1.29 +/- 0.14; and verapamil, 0.48 +/- 0.06%/mmHg, indicating that nifedipine increased and verapamil decreased the sensitivity of the carotid sinus baroreceptors. Additional studies with bilateral carotid sinus isolation (carotid sinus nerves intact) indicated that nifedipine enhanced and verapamil attenuated carotid baroreflex control of renal sympathetic nerve activity. Pressure-volume curves generated in the isolated carotid sinus showed that effects on smooth muscle do not account for the opposing effects of the two Ca2+ antagonists. Omitting Ca2+ from the physiological solution resulted in increased carotid sinus nerve activity, an effect blocked by verapamil but not nifedipine. Verapamil, but not nifedipine, inhibited veratrine-induced (Na+-dependent) excitation of carotid baroreceptors. Thus the excitatory effects of nifedipine on the carotid sinus baroreceptors are dependent on Ca2+ mechanisms, whereas the inhibitory effects of verapamil may be due mainly to interference with the inward Na+ current.

Animals↗
PubMed1983

Hemodynamic sequelae of regression of experimental atherosclerosis.

Regression of experimental atherosclerosis is characterized by decreased intimal thickness and luminal enlargement, but intimal fibrosis becomes more dense. We tested the hypothesis that fibrosis of arteries during regression might limit vasodilator capacity and restrict hemodynamic improvement despite luminal improvement. We studied limb, coronary, and cerebral hemodynamics in 11 normal cynomolgus monkeys, 10 monkeys given an atherogenic diet for 20 mo and 8 monkeys given a regression diet for an additional 18 mo. The atherogenic diet induced lesions of moderate severity (50-60% stenosis); owing to characteristic vessel growth during the atherogenic period, luminal size did not decrease correspondingly. Regression monkeys showed typical changes of regression with luminal enlargement but increased fibrosis. The iliac artery was perfused at constant blood flow and maximal vasodilatation was produced with papaverine. Blood flow was measured with microspheres during maximal vasodilatation in the coronary bed (adenosine) and cerebral bed (hypercapnia). In normal monkeys, minimal vascular resistances were 1.95 +/- 0.19 mm Hg/ml/min X 100 g (mean +/- SE) (limb), 0.13 +/- 0.01 (coronary), and 0.44 +/- 0.02 (cerebral). In atherosclerotic monkeys minimal resistance increased (P less than 0.05) 108, 62, and 166% in the limb, coronary, and cerebral beds, respectively. In regression monkeys, minimal resistance increased from values found in atherosclerotic animals in the limb (+22%), decreased inconsistently in the coronary bed (-19%), and decreased significantly in the cerebral bed (-44%, P less than 0.05). Thus morphologic regression was accompanied by significant hemodynamic improvement during maximal dilatation only in cerebral vessels. We conclude that increases in luminal size during regression of atherosclerotic lesions may not be associated with increases in vasodilator capacity, as intimal fibrosis may limit physiologically important hemodynamic improvement.

Animals↗
PubMed1982

Baroreflex regulation of renal nerve activity during volume expansion.

Volume expansion could inhibit renal nerve activity by stimulating cardiopulmonary baroreflexes or by increasing arterial pressure (i.e., stimulating the sinoaortic baroreflexes). Our study assessed the relative roles of these two reflexes in the renal nerve activity responses to volume expansion (15 ml/kg 6% dextran in normal saline). With cardiopulmonary and arterial baroreflexes intact, volume expansion resulted in increases in arterial pressure and pulmonary artery wedge pressure and in decreases in renal nerve activity. After sinoaortic denervation, volume expansion resulted in similar decreases in renal nerve activity for similar increases in pulmonary artery wedge pressure. In contrast, after selective vagotomy (sinoaortic baroreflexes intact) volume expansion resulted in increases in arterial pressure and pulmonary artery wedge pressure, but reductions in renal nerve activity were markedly attenuated. After sinoaortic denervation and vagotomy, volume expansion did not result in significant changes in renal nerve activity. We conclude that decreases in renal nerve activity during volume expansion are mediated mainly by cardiopulmonary receptors with afferent vagal fibers. Sinoaortic baroreceptors appear to play a minor role in mediating these responses.

Animals↗
PubMed1982

Sensitization of vagal cardiopulmonary baroreflex by chronic digoxin.

It has been recently reported that intracoronary acetylstrophanthidin injection acutely sensitizes the cardiac baroreflex (vagal afferents). We wondered whether chronic administration of digoxin also augmented the gain of this reflex. We treated seven dogs with digoxin intravenously (40 micrograms/kg loading dose followed by 15 micrograms.kg-1.day-1) for 7 days; eight additional dogs received vehicle for 7 days. With the dogs under chloralose anesthesia, we assessed the changes in renal nerve activity that resulted from stimulation of cardiopulmonary receptors with volume expansion (15 ml/kg of 6% dextran in saline) in digoxin- and vehicle-treated groups under control conditions, after sinoaortic denervation (SAD), and after SAD plus vagotomy. Under control conditions volume expansion resulted in decreases of renal nerve activity of 13.5 +/- 3.5%/mmHg increase in pulmonary artery wedge pressure in digoxin-treated dogs. This tended to be greater than the response of sham-treated dogs (-9.5 +/- 1.5%/mmHg increase). After SAD, renal nerve activity decreased 19 +/- 5%/mmHg increase in pulmonary artery wedge pressure in the digoxin group compared with only 8 +/- 1%/mmHg increase in the vehicle group. These responses were significantly different. The plasma digoxin level in the digoxin-treated group was in the therapeutic range (1.9 +/- 0.4 ng/ml). Vagotomy abolished the responses to volume expansion in both groups. Thus chronic digoxin treatment resulting in therapeutic plasma levels of digoxin sensitizes vagal afferents mediating the cardiopulmonary baroreflex influence on renal nerve activity.

Animals↗
PubMed1982

Differential baroreflex control of heart rate and vascular resistance in rabbits. Relative role of carotid, aortic, and cardiopulmonary baroreceptors.

We assessed the relative roles of aortic (ABR), carotid sinus (CBR), and vagal cardiopulmonary baroreceptors in the reflex control of heart rate and vascular resistance during changes in arterial blood pressure. Injections of phenylephrine (PE) and nitroglycerin (NG) were given intravenously to anesthetized rabbits (chloralose-urethane). Reflex, heart rate responses were impaired significantly by denervation (X) of either CBR or ABR. In contrast, reflex vascular responses in the hindlimb (perfused at constant blood flow) were preserved except for a slight impairment of reflex vasoconstriction after ABRX. Vagotomy with intact CBR and ABR impaired only the reflex bradycardia. After vagotomy, neither CBRX nor ABRX altered significantly the reflex heart rate or vascular responses except, again, for an impairment of reflex vasoconstriction after ABRX. Combined CBRX and ABRX eliminated all reflex responses except for a small bradycardia and a biphasic change in perfusion pressure (constrictor-dilator) during PE. Vagotomy eliminated the bradycardia and the dilator phase; the constrictor phase persisted and was abolished by lumbar sympathectomy. The results indicate that (1) reflex control of heart rate may be impaired when reflex control of hindlimb resistance is preserved; thus reflex changes in heart rate may not be used as a reliable index of the integrity of arterial baroreceptor control of the total circulation; (2) one set of arterial baroreceptors does not compensate for the absence of the other with respect to activation of vagal neurons; in contrast, one set of baroreceptors compensates fully for the absence of the other with respect to inhibition of sympathetic neurons; (3) cardiopulmonary and other baroreceptors contribute minimally to reflex responses only during large PE-induced increases in arterial pressure.

Afferent Pathways↗
PubMed1980

Sensitization of cardiac receptors (vagal afferents) by intracoronary acetylstrophanthidin.

The purpose of this study was to determine if sensitization of cardiac receptors with acetylstrophanthidin augments the inhibition of renal nerve activity resulting from expansion of the blood volume or from coronary artery occlusion. Ten chloralose-anesthetized dogs with sinoaortic baroreceptor denervation were subjected to volume expansion with dextran in saline. Under control conditions, volume expansion resulted in decreases in renal nerve activity (% or control) that were inversely related to left atrial pressure (-13.0%/mmHg left atrial pressure). After intracoronary acetylstrophanthidin, volume expansion resulted in a significantly greater suppression of renal nerve activity (-20.6%/mmHg). Occlusion of the circumflex coronary artery in 19 dogs with carotid baroreceptor denervation resulted in a 29 +/- 5% (SE) reduction in renal nerve activity. After intracoronary acetylstrophanthidin, circumflex occlusion resulted in a significantly greater decrease in renal nerve activity (45 +/- 4%). Vagotomy abolished the decreases in renal nerve activity, which resulted from volume expansion and from circumflex coronary occlusion. These data show that volume expansion and coronary occlusion reflexly decrease renal nerve activity via cardiac afferent vagal endings. These reflex inhibitory influences are augmented after intracoronary acetylstrophanthidin. The results are consistent with the view that intracoronary acetylstrophanthidin sensitizes cardiac afferent vagal endings.

Afferent Pathways↗
PubMed1980

Dickinson W. Richards Lecture: Circulatory adjustments to hypoxia.

Circulatory adjustments during hypoxia act to redistribute blood flow and maintain arterial pressure. Redistribution of blood flow is accomplished by a local effect of hypoxia, which produces dilatation in coronary and cerebral vessels, and the chemoreceptor reflex, which produces vasoconstriction in skeletal muscle and the splanchnic bed and dilatation in coronary vessels. Arterial pressure is maintained primarily by the chemoreceptor reflex. If the chemoreceptor reflex fails to maintain arterial pressure, hypoxia and hypotension together activate the central pressor response. Compensatory mechanisms usually are sufficient to maintain homeostasis during hypoxia. However, when a hypotensive stress is superimposed during hypoxia, compensatory mechanisms may fail to maintain arterial pressure. Thus, systemic hypoxia interferes with autonomic cardiovascular adjustments.

Animals↗
PubMed1980

Interaction of cardiopulmonary and somatic reflexes in humans.

Activation of cardiopulmonary receptors with vagal afferents results predominantly in reflex inhibition of efferent sympathetic activity, whereas activation of somatic receptors reflexly increases sympathetic activity to the heart and circulation. Previous studies in experimental animals indicate that there is an important interaction between these excitatory and inhibitory reflexes in the control of the renal circulation. The purpose of this study was to determine whether there is a similar interaction between somatic and cardiopulmonary reflexes in humans. The activity of the cardiopulmonary receptors was altered (reduced) with lower body negative pressure (-5 mm Hg), which causes a decrease in cardiac filling pressure and a small reflex increase in forearm vascular resistance without accompanying changes in arterial pressure. Activation of somatic receptors by isometric handgrip for 2 min at 10 and 20% of maximum voluntary contraction resulted in reflex vasoconstriction in the nonexercising arm. Lower body negative pressure at -5 mm Hg produced a threefold augmentation in the forearm vasoconstrictor response to isometric handgrip in the nonexercising arm. This increase in resistance was significantly greater (P < 0.05) than the algebraic sum of the increases in resistance resulting from lower body suction alone plus isometric handgrip alone. Furthermore, it occurred despite a greater rise in arterial pressure, which would be expected to decrease forearm vascular resistance through activation of arterial baroreceptors and through passive dilatation of forearm vessels. Thus, removal of the inhibitory influence of cardiopulmonary receptors by pooling blood in the lower extremities enhances the somatic reflex. These data suggest an interaction between cardiopulmonary and somatic reflexes in the control of forearm vascular resistance in man.

Adult↗
PubMed1979

Carotid and cardiopulmonary baroreceptor control of splanchnic and forearm vascular resistance during venous pooling in man.

1. This study evaluated the contribution of carotid and cardiopulmonary baroreceptors to reflex splanchnic and forearm vascular adjustments during venous pooling in man. We compared (a) responses to lower body suction which produces venous pooling with (b) responses to lower body suction plus simultaneous application of neck suction. The rationale was that simultaneous application of neck suction, which stretches carotid baroreceptors, would minimize the contribution of carotid baroreceptors to circulatory adjustments produced by lower body suction.2. Lower body suction at 40 mmHg decreased central venous pressure and arterial pulse pressure and increased forearm vascular resistance (plethysmography), splanchnic vascular resistance (indocyanine green dye clearance), and heart rate. Simultaneous application of neck suction prevented the tachycardia and most of the splanchnic vasoconstriction during lower body suction, but did not significantly attenuate the forearm vasoconstriction.3. The major findings in this study are first, that the splanchnic vasoconstrictor response during venous pooling is mediated primarily through carotid baroreceptors, and secondly, that carotid and cardiopulmonary baroreceptors produce strikingly contrasting and non-uniform regional vascular responses during venous pooling. Cardiopulmonary baroreceptors exert the predominant influence on forearm vascular resistance, but appear to have only a minor influence on splanchnic vascular resistance. Carotid baroreceptors produce most of the splanchnic vasoconstriction during venous pooling. but have a minor role in the forearm vasoconstriction.

Abdomen↗
PubMed1979

Effect of central venous pressure on arterial baroreflex control of heart rate.

There is considerable evidence that the level of afferent cardiopulmonary receptor activity modulates sinus node responses to arterial baroreflex stimulation in experimental animals. We tested the hypothesis that this reflex interaction occurs also in man by measuring sinus node responses to arterial baroreceptor stimulation with phenylephrine injection or neck suction, before and during changes of central venous pressure provoked by lower body negative pressure or leg and lower trunk elevation. Variations of central venous pressure between 1.1 and 9.0 mmHg did not influence arterial baroreflex mediated bradycardia. Baroreflex sinus node responses were augmented by intravenous propranolol, but the level of responses after propranolol was comparable during the control state, lower body negative pressure, and leg and trunk elevation. Sinus node responses to very brief baroreceptor stimuli applied during the transitions of central venous pressure also were comparable in the three states. We conclude that physiological variations of central venous pressure do not influence sinus node responses to arterial baroreceptor stimulation in man.

Adult↗