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At least 253 records · Page 14Linked to original sources
PubMed1988

Cardioprotective action of alpha-blocking agents, phentolamine and bunazosin, on hypoxic and reoxygenated myocardium.

The present study was undertaken to determine whether alpha-blocking agents, phentolamine and bunazosin, may exert a cardioprotective effect on hypoxic and subsequently reoxygenated hearts. For this purpose, rabbit hearts were perfused for 20 min under hypoxic conditions, followed by a 45 min-reoxygenation. Agents were administered between the 8th and 20th min of hypoxic perfusion. Hypoxic perfusion for 8 min resulted in a decline of cardiac contractile force and myocardial high-energy phosphates and a loss of adenine nucleotide metabolites from the heart, whereas a rise in resting tension was not observed. Neither increase in perfusion pressure, release of creatine kinase from hearts nor increase in tissue calcium was observed. At 20 min-hypoxia, significant changes in resting tension and perfusion pressure of the heart and release of creatine kinase from the heart were observed. Cardiac contractile force after 45 min of reoxygenation was less than 10% of the initial value. Treatment with 83 microM phentolamine or 46 microM of bunazosin resulted in a significant suppression of hypoxia-induced increase in tissue calcium, release of creatine kinase and adenine nucleotide metabolites and rise in perfusion pressure and resting tension. Treatment with either phentolamine or bunazosin resulted in appreciable recovery of cardiac contractile force. Reoxygenation-induced release of creatine kinase was also suppressed significantly. Two possible mechanisms for the protective effect of this treatment are considered; 1) preservation of ATP metabolites which may be utilized as substrates for a salvage synthesis of ATP during reoxygenation and 2) prevention of a nonselective transmembrane flux of cellular constituents due to changes in cell membrane permeability.

Adenosine Triphosphate↗
PubMed1989

Phentolamine for enhanced visualization of distal arteries in lower extremity arteriography.

To augment visualization of the distal arteries, phentolamine was administered to 83 patients (164 limbs) undergoing lower extremity arteriography. Arterial visualization was graded into three classes and skin temperatures were recorded. Phentolamine provided very good visualization of the distal arterial bed in 95% of limbs. A strong correlation was observed between the temperature rise of the feet and the class of arterial visualization. No side effects were recorded. The use of phentolamine in lower extremity arteriography is recommended.

Angiography↗
PubMed1971

Effect of flow-stop on noradrenaline release from normal spleens and spleens treated with cocaine, phentolamine or phenoxybenzamine.

1. Cat spleens were perfused with Krebs-bicarbonate solution, using a constant-flow pump at a rate of about 7 ml/min at 33-35 degrees C. Noradrenaline (NA) overflow by nerve stimulation at 10 Hz for 20 s was determined with or without flow-stop before and after treatment with cocaine, phentolamine or phenoxybenzamine. In order to determine the effect of flow-stop on overflow, the arterial and the venous flows were occluded by clamping the inflow and outflow tubes during the period of stimulation plus 30, 60 or 120 seconds.2. Without flow-stop, NA output was 0.93+/-0.25 ng/stimulus, which was significantly increased after cocaine (123+/-6.6%), phentolamine (415+/-93%) and phenoxybenzamine (578+/-107%). Phentolamine and phenoxybenzamine were much more effective than cocaine in enhancing overflow.3. Before treatment with drugs, flow-stops of 30, 60 and 120 s reduced NA outputs to 70+/-6.6, 27.5+/-2 and 7%, respectively, of the control outputs without flow-stop. None of the drugs significantly influenced the percentage reductions in NA outputs during a 30 s flow-stop. However, the percentage outputs after cocaine or phenoxybenzamine treatment during a 60 s flow-stop significantly increased to 45+/-2.5% and 57+/-6%, respectively, as compared to the percentage output of 27.5+/-2% from untreated spleens during a corresponding flow-stop period. During flow-stop, there was no appreciable metabolism of the released transmitter.4. Diffusion of the released transmitter from the site of liberation plays only a minor role in the removal of the released NA.5. It is suggested that the NA released by nerve stimulation acts on the presynaptic alpha sites to inhibit its own release by a negative feedback mechanism. Adrenoceptor blocking agents enhance the NA overflow from spleen because they remove this autoinhibition by blocking the presynaptic alpha sites.

Animals↗
PubMedDate not supplied

[Effect of phentolamine on the electroencephalogram and pulse activity of the cortical neurons].

In tests with vigilant immobilized and also urethan anesthetized rabbits the influence of intravenous injection of phentolamine (3--10 mg/kg) on the EEG waves parameters was studied. It is shown that within 45 to 75 minutes following introduction of phentolamine there is observed either shortening or elimination of the EEG activation reaction in response to stimulation of the sciatic nerve. The blocking effect of the intravenous administration of phentolamine is noted also by following dynamic changes in the discharge activity of single neurons.

Animals↗
PubMed1981

The effect of preload on the dissociation constant of phentolamine in isolated rabbit thoracic aorta.

The affinity of phentolamine for the alpha-adrenergic receptor of isolated rabbit thoracic aorta was determined under two different preload conditions. In one condition, strips or rings or aorta were preloaded with a 1/4 g weight; in the other condition, with a 10 g weight. To measure affinity, dose-response curves were first obtained for agonist alone and then for agonist in the presence of various concentrations of phentolamine, a reversible alpha-adrenergic antagonist. From these curves, equieffective agonist concentrations were selected and Schild plots constructed to determine the dissociation constant (1/affinity). It was found that values of the dissociation constant, KB, for phentolamine were independent of the agonist used (norepinephrine or phenylephrine) to obtain the dose-response curves. KB was, however, a function of preload conditions. In all cases, IB at 1/4 g was greater than KB at 10 g preload. The magnitude of this difference in affinity with preload though, was less then previously obtained for agonists in the same preparation. The implications of this finding are discussed in terms of the effect of preload on receptor conformation and possible differences between agonist and antagonist binding.

Animals↗
PubMed1981

Effect of denervation and phentolamine on the thermogenic action of noradrenaline in rat skeletal muscle.

Vascularly isolated skeletal muscle of the cold-acclimated (CA) rat was perfused with blood in situ or in vitro and the effect of denervation and an alpha-adrenolytic agent (phentolamine) on its oxygen consumption was studied in the resting state and after administering noradrenaline (NA). The resting metabolism of muscle in situ rose by 28% after denervation. The infusion of NA further raised the oxygen consumption of acutely denervated muscle perfused in situ of in vitro by 43%. The thermogenic effect of NA on muscle denervated two hours before the experiment was only transitory. Phentolamine raised the oxygen consumption of the innervated muscle in situ by 42%; the infusion of NA did not stimulate metabolism any further. Phentolamine reduced the vascular resistance of resting muscle, but did not inhibit the vasoconstriction during the infusion of NA. The results show that the thermogenic effect of infused NA in perfused muscle is inhibited not by acute denervation, but by a vasoconstriction, which cannot be prevented by the administration of an alpha-adrenolytic agent.

Animals↗
PubMed1984

Influence of phentolamine and propranolol on the length of tonus and clonus in pentylenetetrazol-induced seizures in dogs.

The goal of this study was to test the hypothesis that phentolamine and propranolol premedication would affect tonus differently than clonus in pentylenetetrazol (PTZ)-induced tonic-clonic seizures in dogs. Tonic-clonic seizures were induced with IV infusion of PTZ, given as an initial 300-mg bolus and then 100-mg boluses every 10 S until a seizure began. Premedication with phentolamine (2 mg/kg of body weight) significantly shortened clonus (P less than 0.05), whereas propranolol (1 mg/kg) significantly lengthened clonus (P less than 0.05). Neither phentolamine nor propranolol significantly altered the length of tonus or the dose of PTZ required to induce seizures (P greater than 0.05). This indicates that tonus and clonus may have different neural mechanisms and that adrenergic receptors may be involved in the neural mechanisms of clonus.

Animals↗
PubMed1981

Control of hypertension during cardiopulmonary bypass with urapidil and phentolamine.

The vasodilating effect of 6-(3-[4-(o-methoxy-phenyl)-piperazin-1-yl]-propylamino)-1,3-dimethyluracil (urapidil, Ebrantil) and phentolamine was investigated during extracorporeal circulation in patients undergoing coronary artery bypass (CABG) operations. To compare the vasodilating effect, 10 patients received 2 times 25 mg urapidil, and another 10 patients 2 times 5 mg phentolamine when mean arterial blood pressure (MAP) exceeded 100 mgHg. Both drugs caused a significant (p less than 0.01) decrease in mean arterial blood pressure and total peripheral resistance (TPR), using constant flow (Qecc). Central venous pressure (CVP), measured in the inferior vena cava, showed no significant change, while a marked volume loss (delta V) in the oxygenator was observed. There was no significant difference in the measured cardiovascular parameters in the two groups of patients. The peripheral vasodilating effect of urapidil, expressed in mg was found 5 times weaker than that of phentolamine. Urapidil was found effective in the treatment of hypertension during extracorporeal circulation.

Aged↗
PubMed1980

Central actions of norepinephrine, phentolamine and 6-hydroxydopamine in spontaneously hypertensive rats.

The effects of norepinephrine HCl, isoproterenol HCl, phentolamine and 6-hydroxydopamine HCl on mean arterial blood pressure (MABP), heart rate (HR), and pulmonary respiration were examined in 67 urethane-anesthetized, spontaneously hypertensive rats (SHR) with carotid arterial and femoral venous catheters and stereotaxically positioned intracerebral cannulae. Norepinephrine produced significant pressor responses when it was instilled into the posterior hypothalamic region and/or the pars magnocellularis region of the ventral medial thalamus. Central pretreatment with either phentolamine mesylate or phentolamine HCl, 30 min before central administration of norepinephrine, blocked the norepinephrine-induced pressor responses. Central administration of 6-hydroxydopamine HCl in the hypothalamic-thalamic region of the diencephalon produced significant depressor responses within 60 min. Neither norepinephrine nor isoprotereol produced their centrally-induced pressor and depressor responses when they were instilled centrally into the reticular formation. The results suggest that receptors that respond to norepinephrine are located in the posterior hypothalamic-ventral medial thalamic region of the diencephalon. The results also suggest that cells located in these areas send projection fibers either directly or indirectly to the vasomotor center located in the brain stem.

Animals↗
PubMed1994

[Influence of thoracic spinal subarachnoid microinjection of phentolamine on the effect of electroacupuncture].

The influence of thoracic spinal subarachnoid microinjection of Phentolamine (Phen, 200ug/20ul) on the effect of electroacupuncture (EA) at Neiguan (PC 6) was observed in 42 urethan-chloralose anesthetized rabbits. Results showed that: 1) EA of Neiguan (PC 6) could significantly promote recovery of elevated ST-segments and T-waves of electrocardiogram induced by acute myocardial ischemia (AMI). 2) subarachnoid microinjection of phentolamine had no marked influence on recovery of ST-segments and T-waves, but impeded recovery of blood pressure of post-AMI; and 3) subarachnoid microinjection of phentolamine could significantly weaken or eliminate the effect of EA of Neiguan (PC 6) in accelerating recovery of ST-segments and T-waves of post-AMI. It denotes that alpha-receptors of intra-thoracic spinal cord participate in the action of EA of Neiguan (PC 6) in improving AMI, and the upper thoracic segment of the spinal cord is one of the links for connecting Neiguan and the heart.

Animals↗
PubMed1994

[Periodical blood pressure variation during cardiopulmonary bypass--effects of cervicothoracic epidural anesthesia and phentolamine].

We studied the effects of cervicothoracic epidural anesthesia or intravenous phentolamine on periodical blood pressure variation during cardiopulmonary bypass in 12 adult patients undergoing open heart surgery under fentanyl anesthesia. Spontaneous periodical fluctuation of the blood pressure was analyzed by means of autoregressive power spectrum method. Amplitudes of the low frequency (0.02-0.15 Hz) component of the blood pressure variation amplitudes were calculated. The amplitudes decreased significantly 10 minutes after cervicothoracic epidural block with 15 ml of 2% lidocaine solution (P < 0.05), and after infusion of 0.4 mg.kg-1 of phentolamine (P < 0.05). Since amplitudes of the blood pressure variation were reduced by adequate epidural block or phentolamine, they are likely to reflect sympathetic vasomotor activity.

Adult↗
PubMed1976

Comparative anti-hypertensive effects of labetalol and the combination of oxprenolol and phentolamine.

1 The interaction of phentolamine with the beta-adrenoreceptor-blocking drug, oxprenolol, was studied in a controlled trial. 2 The combination was generally well tolerated. 3 Oxprenolol alone produced modest but significant reductions in supine, standing and post-exercise blood pressures. Small reductions were observed only with sustained phentolamine administration. 4 The combined effect of the two drugs seemed to be addictive only at the lower level of oxyprenolol dosage. 5 Labetalol produced significantly greater reductions in supine and standing blood pressure than combined oxprenolol-phentolamine. At a daily dose of 400 mg, postural hypotension was not observed, although transient symptoms were frequent.

Adult↗
PubMed1976

The anti-hypertensive efficacy of combined alpha- and beta-adrenoreceptor blockade with phentolamine-oxprenolol or with labetalol (AH 5158).

1. The interaction of phentolamine with the beta-receptor blocker oxprenolol was studied in a controlled trial. 2. The combination was generally well tolerated. 3. Oxprenolol alone produced modest but significant reductions in supine, standing and post-exercise blood pressures. Small reductions were seen only with sustained phentolamine administration. 4. The combined effect of the two drugs appeared to be additive only at the lower doses of oxprenolol. 5. Labetalol produced significantly greater reductions in supine and standing blood pressure than combined oxprenolol-phentolamine. At a daily dose of 400 mg, postural hypotension was not seen, though transient symptoms were frequent.

Adult↗
PubMed1996

Prostaglandin E1 with phentolamine for the treatment of erectile dysfunction.

AIM OF THE STUDY: to evaluate the feasibility of a self-injection programme for impotence with a combination of 10 micrograms prostaglandine E1 (PGE1) and 0.5 mg phentolamine. METHOD: follow-up at outpatients department with history taking, physical examination and questionnaires of 58 patients using this combination. Many patients could compare this drug combination with previously used drugs for intracavernous use. RESULTS: 42 patients started regular use. After a follow-up of 14 months, 26 are still on the programme. Drug related problems encountered: 10 patients reported insufficient erectile response, five patients have had priapism, four patients experienced severe pain, one patient developed fibrosis. CONCLUSION: the combination of PGE1 and phentolamine is very effective. The complication rate is comparable with those reported from PGE1 alone and from papaverine with phentolamine.

Adrenergic alpha-Antagonists↗
PubMed1977

[Treatment of heart failure with phentolamine (Regitin)].

Vasodilative treatment of severe heart failure with infusions of phentolamine leads to ventricular unloading and in many cases brings about a dramatic improvement of the patient's condition. Phentolamine is the only one of the vasodilators so far used in the treatment of heart failure that has a positively inotropic effect. In contrast to sodium nitroprusside and nitroglycerin, it also increases stroke volume at normal filling pressures. Although vasodilative therapy has resulted in a notable decline in the mortality from severe heart failure among hospitalized patients, the long-term prognosis after discharge remains poor. One of the chief reasons is that there has hitherto been no effective orally administrable drug suitable for protracted therapy. Initial clinical studies with a newly developed slow-release formulation of phentolamine have shown that the preparation produces remarkably good effects in patients with chronic heart failure: systolic pressure rises, the amplitude of the blood pressure is augmented and there is an increase in urinary excretion accompanied with a corresponding reduction in weight. In practically all cases, there is a distinct decrease in the size of the heart and in pulmonary congestion.

Chronic Disease↗
PubMed2002

Studies on glycogen autophagy: effects of phorbol myristate acetate, ionophore A23187, or phentolamine.

The effects of agents that could manipulate the lysosomal calcium such as phorbol myristate acetate, ionophore A23187, and phentolamine on the lysosomal glycogen degradation were studied by electron microscopy, morphometric analysis, and biochemical assays in newborn rat hepatocytes. Phorbol myristate acetate, which promotes the input of calcium to lysosomes, increased the total volume of autophagic vacuoles and the activity of lysosomal glycogen-hydrolyzing acid alpha 1,4 glucosidase and decreased the fractional volume of undigested glycogen inside the autophagic vacuoles and also decreased the activity of acid mannose 6-phosphatase. Ionophore A23187, which releases lysosomal calcium, produced opposite results in these enzyme activities. Phentolamine, an alpha-adrenergic blocking agent which interferes with the generation of phosphoinositides and may activate the lysosomal calcium uptake pump, increased the total volume of autophagic vacuoles and the activity of lysosomal glycogen-hydrolyzing acid glucosidase and decreased the fractional volume of undigested glycogen inside the autophagic vacuoles. The results of this study constitute evidence that changes in lysosomal calcium may influence certain aspects of autophagy, including the degradation of glycogen inside the autophagic vacuoles. They also support our previous postulate [Kalamidas and Kotoulas (2000a,b) Histol Histopathol 15:29-35, 1011-1018] that stimulation of autophagic mechanisms in newborn rat hepatocytes may be associated with acid mannose 6-phosphatase activity-deficient lysosomes.

Animals↗
PubMed1981

Effect of hydrocortisone, reserpine, propranolol and phentolamine on in vivo uptake of exogenous amines by adrenal chromaffin cells.

An autoradiographic study was performed on the effects of hydrocortisone, reserpine, propranolol and phentolamine on the uptake of tritiated amines by adrenal medullary cells of the mouse. Oral feeding of hydrocortisone ahd no significant effect on the normal uptake pattern of dopamine, noradrenaline or adrenaline by medullary cells of different type (A cells or NA cells) or location (marginal or central), although the overall amounts taken up were markedly reduced. Handling the animals led to similar reductions in the uptake of all three amines and was thus clearly shown to be the important factor in this effect. Reserpine reduced the uptake of [3H] noradrenaline to 25% of the control value although the relative distribution remained unchanged. Propranolol and phentolamine had no observed effect on [3H] noradrenaline uptake. These results are discussed in the light of the previously reported action of ACTH in reversing the effects of hypophysectomy on medullary amine uptake (Hirano and Kobayashi 1978), and it is concluded that ACTH must exert this effect directly on the adrenal medulla rather than through the secretion of adrenal corticosteroids. It is also suggested that reserpine acts, as in neurons, by blocking amine uptake into intracellular granules rather than by blocking uptake into the cell itself.

Adrenal Medulla↗
PubMed1991

Effect of phentolamine on the relationship between O2 consumption and delivery in sheep.

The oxygen flux challenge test (OFT) has recently been used in critically ill patients as a dynamic test for assessment of the response in oxygen consumption (VO2) to an increase in O2 delivery (QO2). Such a test may indicate whether a patient demonstrates delivery-dependent VO2. However, the increase in whole body VO2 following an increase of QO2 might be due to the agents used for the OFT. In this study, we examined the possibility of obtaining false positive OFT with an alpha-adrenergic antagonist. Five normothermic thiopentone-anaesthetised and mechanically-ventilated (inspired O2 fraction, 0.3; expired CO2 fraction, 0.045-0.055) adult sheep (25-31 kg) were investigated. The QO2 was increased in a stepwise fashion from 200 to 850 ml.min-1 by vasodilatation with intravenous infusion of phentolamine. The VO2 was calculated at each step from the product of arteriovenous. O2 content difference (CO2, a-v) and cardiac output (Qc), the latter being continuously measured with a transit-time ultrasonic flow probe placed around the main pulmonary artery. The VO2 (y) was linearly related to QO2 (x), y = 0.034 (SD 0.024) x + 29.3 (SD 3.9). The relationship between Qc (y) and CO2, a-v (x) was y = 4.6x(-1.12) (n = 69; r2 = 0.75; P = NS compared to the expected relationship for isoconsumption conditions, i.e. where Qc = VO2.(CO2, a-v)(-1). Our data suggested that under stable conditions, an infusion of phentolamine did not sufficiently alter the relationship between Qc and CO2, a-v to invalidate its use for OFT in normal sheep.

Animals↗