Phenoxybenzamine Research Articles

Interaction of BK Ca channel modulators with adrenergic agonists in the rat aorta is influenced by receptor reserve

Our main objective was to study the interaction of BK Ca channel modulators with adrenergic agonists UK 14304 and noradrenaline (NA), acting on α 1-adrenoceptors, in the rat aorta and how this is affected by receptor reserve. NA and UK 14304 evoked concentration-dependent contractions of the rat aorta. UK 14304 was a partial agonist relative to NA in this preparation. The BK Ca channel blocker tetraethylammonium (TEA, 1 mM) and opener NS 1619 (3×10 −5 M) modulated NA- and UK 14304-induced contractions, and were more effective on UK 14304-induced contractions. TEA (1 mM) increased the maximum response to NA and UK 14304 by about 13% and 300%, respectively, while NS 1619 (3×10 −5 M) reduced the maximum response to UK 14304 by about 81% compared to 31% for noradrenaline. The effect of TEA on the noradrenaline concentration–response curve was increased after treatment of the aorta with phenoxybenzamine (PBZ), an irreversible α 1-adrenoceptor antagonist, to reduce receptor reserve. We concluded that the interaction of BK Ca channel modulators with α 1-adrenergic agonists in the rat aorta was influenced by receptor reserve.

A 3D cardiovascular model for brachytherapy planning based on biplane angiography and intravascular ultrasound

Background: Phenoxybenzamine (PBZ) is a nonselective, irreversible alpha-adrenergic receptor antagonist that is approved for the treatment of diaphoresis and hypertension associated with pheochromocytoma. It may also be useful in several chronic conditions whose pathogenesis is mediated or affected by alpha-adrenergic stimulation, such as lower urinary tract symptoms associated with benign prostatic hyperplasia (BPH) and neurogenic bladder (eg, secondary to myelomeningocele and in sphincter dyssynergia and autonomic dysreflexia); in an adjunctive role after urogenital surgery or brachytherapy by relieving symptoms associated with increased alpha-adrenergic tone; and in the treatment of complex regional pain syndrome (CRPS) and prostatitis. However, carcinogenic concerns may have limited its potential application.Objective: The purpose of this article is to reassess the usefulness and contemporary application of PBZ for the control of urinary tract symptoms associated with BPH and neurogenic bladder, after urogenital surgery and brachytherapy, and in certain other conditions (eg, CRPS, prostatitis).Methods: A search of literature published from 1966 to 2002 was performed on MEDLINE using the search terms phenoxybenzamine, alpha-adrenergic blockers, benign prostatic hyperplasia, neurogenic bladder, urinary retention, and complex regional pain syndrome.Results: Despite concerns about possible carcinogenicity, no reports of drug-related tumors have been made since PBZ's introduction in 1953. Investigators have used PBZ in off-label trials to alleviate symptoms of a variety of conditions that cause urinary retention. In adult male patients with retention due to inguinal hernioplasty and female patients with retention caused by vaginal repair, as well as in pediatric patients with myelomeningocele, treatment with PBZ improved bladder function and, in the patients with myelomeningocele, was associated with reduced incidence of urinary tract infection. Larger trials of PBZ in men with BPH produced significant urinary symptom relief (P < 0.05 in 2 studies). Moreover, studies suggest that PBZ may be useful in alleviating pain due to trauma and CRPS. The most common adverse events appear to be dizziness, impotence and ejaculatory dysfunction, and nasal stuffiness.Conclusions: No drug-related tumors in humans have been reported after ∼50 years of clinical experience with PBZ. Clinical trials have demonstrated that it can relieve symptoms in patients with BPH and other urologic and pain-related conditions.

Calcium/Calmodulin-Dependent Signaling for Prepenetration Development inColletotrichum gloeosporioides

ABSTRACT Colletotrichum gloeosporioides forms a specialized infection structure, an appressorium, for host infection. Contacting hard surface induces appressorium formation in C. gloeosporioides, whereas hydrophobicity of the contact surface does not affect this infection-related differentiation. To determine if the calcium/calmodulin-dependent signaling system is involved in prepenetration morphogenesis in C. gloeosporioides pathogenic on red pepper, effects of calcium chelator (EGTA), phospholipase C inhibitor (neomycin), intracellular calcium modulators (TMB-8 and methoxy verampamil), and calmodulin antagonists (chloroproma-zine, phenoxy benzamine, and W-7) were tested on conidial germination and appressorium formation. Exogenous addition of Ca(2+), regardless of concentration, augmented conidial germination, while appressorial differentiation decreased at higher concentrations. Inhibition of appressorium formation by EGTA was partly restored by the addition of calcium ionophore A23187 or CaCl(2). Calcium channel blockers and calmodulin antagonists specifically reduced appressorium formation at micromolar levels. These results suggest that biochemical processes controlled by the calcium/calmodulin signaling system are involved in the induction of prepenetration morphogenesis in C. gloeosporioides pathogenic on red pepper.

Improved survival of patients undergoing palliation of hypoplastic left heart syndrome: lessons learned from 115 consecutive patients

Outcome of stage 1 palliation (S1P) for hypoplastic left heart syndrome (HLHS) has improved coincident with application of treatment strategies including continuous superior vena cava oximetry (SvO2), phenoxybenzamine (POB), strategies to minimize the duration of deep hypothermic circulatory arrest (DHCA) and efforts to ameliorate the inflammatory response to cardiopulmonary bypass (CPB) using aprotinin and modified ultrafiltration. Analysis of a consecutive series of 115 patients undergoing S1P was done to identify the risk factors for mortality and the impact of new treatment strategies. For the current era, July 1996 to October 2001, hospital survival was 93% (75/81) compared with 53% (18/34) for the time period, January 1992 to June 1996, P<0.001. Survival to stage 2 palliation (S2P) was also significantly improved in the current era, 81% (66/81) versus 44% (15/34), P<0.01. Anti-inflammatory treatment strategies demonstrated improved survival by univariate analysis (P<0.001). Multivariate analysis identified continuous SvO2 monitoring as a factor favoring S1P survival (P=0.02) and use of POB as a factor favoring survival to S2P (P=0.003). In the current era shorter duration of DHCA was associated with improved survival to S2P (P=0.02). Improved survival following S1P can be achieved with strategies that allow for early identification of decreased systemic output and the use of afterload reduction to stabilize systemic vascular resistance and therefore the pulmonary to systemic flow ratio. Strategies to ameliorate the inflammatory response to CPB may decrease the degree and duration of postoperative support. Strategies to minimize duration of DHCA may improve intermediate survival and merit additional studies.

Neurotransmitter release in an arterial preparation and the action of alpha-adrenoceptor antagonists.

1 This study examined the potentiating effects of competitive antagonists of the adrenergic alpha2 receptors and of phenoxybenzamine (POB) an irreversible antagonist, on the stimulation-induced efflux of [3H]-noradrenaline in arterial tissue of rabbit. This was done to determine if the lack of concordance of efflux potentiation by antagonists with the expectations of presynaptic negative feedback theory can be attributed to increasingly successful competition from rising perineuronal transmitter concentrations, when stimulation parameters are increased, in the presence of a fixed concentration of competitive antagonist. 2 Tissues were stimulated with a fixed pulse number and frequency, to rule out confounding factors, and major alterations in the concentration of released transmitter were achieved through variations in the pulse duration. 3 Rauwolscine potentiated transmitter release less at the longest, rather than at the shortest pulse duration, and showed a potentiation of release that was indifferent to the quantities of released transmitter. This was also seen with POB although it binds covalently to the presynaptic receptor. 4 Noradrenaline inhibited stimulation-induced transmitter release confirming the presence of presynaptic alpha inhibitory sites. 5 Yohimbine potentiated transmitter release the same as did rauwolscine and POB, and protected the relevant sites against POB potentiation, confirming site identity. The combination of POB and rauwolscine had no greater effect than did either alone certifying that they acted similarly and that maximally effective concentrations of each were used. 6 Consequently, noradrenaline breakthrough of presynaptic receptor blockade does not explain the non-conforming observations made with competitive antagonists in tests of presynaptic theory.

Improved Survival of Patients Undergoing Palliation of Hypoplastic Left Heart Syndrome: Lessons Learned From 115 Consecutive Patients

Background Outcome of stage 1 palliation (S1P) for hypoplastic left heart syndrome (HLHS) has improved coincident with application of treatment strategies including continuous superior vena cava oximetry (SvO 2 ), phenoxybenzamine (POB), strategies to minimize the duration of deep hypothermic circulatory arrest (DHCA) and efforts to ameliorate the inflammatory response to cardiopulmonary bypass (CPB) using aprotinin and modified ultrafiltration. Methods and Results Analysis of a consecutive series of 115 patients undergoing S1P was done to identify the risk factors for mortality and the impact of new treatment strategies. For the current era, July 1996 to October 2001, hospital survival was 93% (75/81) compared with 53% (18/34) for the time period, January 1992 to June 1996, P &lt;0.001. Survival to stage 2 palliation (S2P) was also significantly improved in the current era, 81% (66/81) versus 44% (15/34), P &lt;0.01. Anti-inflammatory treatment strategies demonstrated improved survival by univariate analysis ( P &lt;0.001). Multivariate analysis identified continuous SvO 2 monitoring as a factor favoring S1P survival ( P =0.02) and use of POB as a factor favoring survival to S2P ( P =0.003). In the current era shorter duration of DHCA was associated with improved survival to S2P ( P =0.02). Conclusions–Improved survival following S1P can be achieved with strategies that allow for early identification of decreased systemic output and the use of afterload reduction to stabilize systemic vascular resistance and therefore the pulmonary to systemic flow ratio. Strategies to ameliorate the inflammatory response to CPB may decrease the degree and duration of postoperative support. Strategies to minimize duration of DHCA may improve intermediate survival and merit additional studies.

Expression and pharmacological profile of the human organic cation transporters hOCT1, hOCT2 and hOCT3.

1. Organic cation transporters (OCTs) are involved in the elimination of monoamines and cationic xenobiotics. To examine whether some cell lines express several different OCTs, we investigated seven human cell lines for the mRNA expression pattern of the human (h) transporters hOCT1, hOCT2 and hOCT3. hOCT1 mRNA was found in all cell lines, six additionally expressed hOCT3 and only two cell lines contained all three hOCTs. 2. Among the three OCTs only for the OCT3 (also designated as 'uptake(2)' or 'extraneuronal monoamine transporter') 'selective' inhibitors are described in the literature. The affinities of the OCT3 inhibitors for the other two OCTs are largely unknown. Therefore, we compared the potencies of eight compounds as inhibitors of hOCT-mediated uptake of the organic cation [(3)H]-1-methyl-4-phenylpyridinium ([(3)H]-MPP(+)) in human embryonic kidney 293 (HEK293) cells stably expressing hOCT1, hOCT2 or hOCT3. Decynium-22 inhibited hOCT3 with 10 fold higher potency than hOCT1 and hOCT2. Corticosterone was about 100 fold more potent as inhibitor of hOCT3 than of hOCT1 or hOCT2, and O-methylisoprenaline (OMI) inhibited almost exclusively hOCT3. Progesterone and beta-Oestradiol preferentially inhibited hOCT3 and hOCT1, whereas prazosin was a potent inhibitor of hOCT1 and hOCT3. Phenoxybenzamine (PbA) inhibited with about equal apparent potency all three hOCTs, whereas the PbA derivative SKF550 ((9-fluorenyl)-N-methyl-beta-chloroethylamine) preferentially inhibited hOCT3 and hOCT2. 3. PbA reversibly inhibited hOCT1 and irreversibly hOCT2 and hOCT3; SKF550 also irreversibly inhibited hOCT3 but hOCT2 in a reversible manner. 4. These compounds enable a functional discrimination of the three hOCTs: hOCT1 is selectively inhibited by prazosin, reversibly inhibited by PbA and it is not sensitive to inhibition by SKF550 and OMI; hOCT2 is reversibly inhibited by SKF550, irreversibly by PbA and not by prazosin, beta-oestradiol and OMI, whereas hOCT3 is selectively inhibited by corticosterone, OMI and decynium22.

A modern rationale for the use of phenoxybenzamine in urinary tract disorders and other conditions

Background: Phenoxybenzamine (PBZ) is a nonselective, irreversible alpha-adrenergic receptor antagonist that is approved for the treatment of diaphoresis and hypertension associated with pheochromocytoma. It may also be useful in several chronic conditions whose pathogenesis is mediated or affected by alpha-adrenergic stimulation, such as lower urinary tract symptoms associated with benign prostatic hyperplasia (BPH) and neurogenic bladder (eg, secondary to myelomeningocele and in sphincter dyssynergia and autonomic dysreflexia); in an adjunctive role after urogenital surgery or brachytherapy by relieving symptoms associated with increased alpha-adrenergic tone; and in the treatment of complex regional pain syndrome (CRPS) and prostatitis. However, carcinogenic concerns may have limited its potential application.Objective: The purpose of this article is to reassess the usefulness and contemporary application of PBZ for the control of urinary tract symptoms associated with BPH and neurogenic bladder, after urogenital surgery and brachytherapy, and in certain other conditions (eg, CRPS, prostatitis).Methods: A search of literature published from 1966 to 2002 was performed on MEDLINE using the search terms phenoxybenzamine, alpha-adrenergic blockers, benign prostatic hyperplasia, neurogenic bladder, urinary retention, and complex regional pain syndrome.Results: Despite concerns about possible carcinogenicity, no reports of drug-related tumors have been made since PBZ's introduction in 1953. Investigators have used PBZ in off-label trials to alleviate symptoms of a variety of conditions that cause urinary retention. In adult male patients with retention due to inguinal hernioplasty and female patients with retention caused by vaginal repair, as well as in pediatric patients with myelomeningocele, treatment with PBZ improved bladder function and, in the patients with myelomeningocele, was associated with reduced incidence of urinary tract infection. Larger trials of PBZ in men with BPH produced significant urinary symptom relief (P < 0.05 in 2 studies). Moreover, studies suggest that PBZ may be useful in alleviating pain due to trauma and CRPS. The most common adverse events appear to be dizziness, impotence and ejaculatory dysfunction, and nasal stuffiness.Conclusions: No drug-related tumors in humans have been reported after ∼50 years of clinical experience with PBZ. Clinical trials have demonstrated that it can relieve symptoms in patients with BPH and other urologic and pain-related conditions.

Brief pretreatment of radial artery conduits with phenoxybenzamine prevents vasoconstriction long term

Background. Radial artery bypass conduits are prone to early vasospasm or “string sign” with use of vasopressor therapy intraoperatively and postoperatively, causing increased resistance in coronary artery grafts. Current intraoperative treatment with papaverine fails to provide sustained inhibition of vasoconstriction. We tested the hypothesis that a 30-minute pretreatment of radial artery segments with the α-adrenergic antagonist phenoxybenzamine (PB) or the putative protein phosphatase 2,3-butadione monoxime (BDM) attenuates vasoconstriction induced by the vasopressors phenylephrine or norepinephrine for as long as 48 hours compared with papaverine. Methods. Canine radial arteries were harvested, incubated in control buffer or solutions of papaverine 10 −6 M, BDM 10 −6 M or phenoxybenzamine 10 −6 M for 30 minutes, washed, and stored in drug-free culture medium for 2, 24, or 48 hours. After storage, constriction was induced by norepinephrine at incremental concentrations ranging from 0.7 to 3.5 μmol/L or by phenylephrine (0.300 to 1.5 μmol/L) with or without the inhibitors, and the degree of vasoconstriction was quantified in organ chambers. Responses to norepinephrine or phenylephrine were compared to constriction with receptor-independent potassium chloride KC1 (30 mmol/L). Results. Maximum responses to phenylephrine and norepinephrine were comparable at 2, 24, and 48 hours after harvest in the control group (phenylephrine: 67% ± 4%, 62% ± 6%, 65% ± 6% of KC1 response; norepinephrine: 75% ± 4%, 62% ± 1%, 58% ± 7%, respectively). Papaverine failed to attenuate constriction to phenylephrine and norepinephrine 2, 24, or 48 hours posttreatment. Pretreatment with BDM did not reduce vasoconstriction responses to phenylephrine or norepinephrine 2 hours after incubation but did reduce constriction responses thereafter. In contrast, phenoxybenzamine completely attenuated constriction to both phenylephrine (19% ± 8%, 1% ± 4%, −12% ± 4%) and norepinephrine (7.1% ± 1%, −5% ± 5%, −20% ± 5%) at 2, 24, and 48 hours posttreatment, respectively. Phenoxybenzamine did not alter endothelial function relative to controls at any time point. Conclusions. Thirty-minute pretreatment of RA conduits with 10 −6 M phenoxybenzamine completely inhibits vasoconstriction to phenylephrine and norepinephrine for as long as 48 hours. Soaking radial artery grafts briefly in phenoxybenzamine solution before implantation may be effective in preventing postoperative vasospasm caused by two common α-adrenergic agonists used in postoperative hemodynamic management.

Phenoxybenzamine Binding Reveals the Helical Orientation of the Third Transmembrane Domain of Adrenergic Receptors

Phenoxybenzamine (PB), a classical alpha-adrenergic antagonist, binds irreversibly to the alpha-adrenergic receptors (ARs). Amino acid sequence alignments and the predicted helical arrangement of the seven transmembrane (TM) domains suggested an accessible cysteine residue in transmembrane 3 of the alpha(2)-ARs, in position C(3.36) (in subtypes A, B, and C corresponding to amino acid residue numbers 117/96/135, respectively), as a possible site for the PB interaction. Irreversible binding of PB to recombinant human alpha(2)-ARs (90 nm, 30 min) reduced the ligand binding capacity of alpha(2A)-, alpha(2B)-, and alpha(2C)-AR by 81, 96, and 77%. When the TM3 cysteine, Cys(117), of alpha(2A)-AR was mutated to valine (alpha(2A)-C117V), the receptor became resistant to PB (inactivation, 10%). The beta(2)-AR contains a valine in this position (V(3.36); position number 117) and a cysteine in the preceding position (Cys(116)) and was not inactivated by PB (10 microm, 30 min) (inactivation 26%). The helical orientation of TM3 was tested by exchanging the amino acids at positions 116 and 117 of the alpha(2A)-AR and beta(2)-AR. The alpha(2A)-F116C/C117V mutant was resistant to PB (inactivation, 7%), whereas beta(2)-V117C was irreversibly inactivated (inactivation, 93%), confirming that position 3.36 is exposed to receptor ligands, and position 3.35 is not exposed in the binding pocket.

Doxazosin Inhibits MCP-1 Directed Migration of Human Monocytes

P65 Monocyte chemotactic protein 1 (MCP-1) - directed transendothelial migration of monocytes plays a key role in the early development of atherosclerosis. Migration requires degradation of extracellular matrices, a process that involves matrix metalloproteinases (MMP) and tissue inhibitors of MMPs (TIMP). Recent studies suggest that the alpha1-adrenergic receptor (alpha1-AR) antagonist doxazosin (Dox) might have antiatherosclerotic effects by inhibiting proliferation and migration of vascular cells. The purpose of the present study was to determine the effects of Dox on MCP-1 directed monocyte migration, MMP-9 and TIMP-1 regulation, and to identify signalling pathways mediating these processes. MCP-1 (50ng/ml) stimulated migration of human peripheral blood monocytes (HPBM) by 2.8 +/-0.7 fold and of THP-1 human monocytes by 7 +/- 2.7 - fold (both p&lt;0.05 vs. unstimulated cells). Dox inhibited MCP-1 induced migration in a dose dependent manner, with a maximal reduction at 10μM of 50.8 +/- 1.9% in HPBM and 73.5 +/- 3.2 % in THP-1 cells (both p&lt;0.01 vs. MCP-1 alone). Dox blocked migration even after pretreatment with phenoxybenzamine (PBA), an irreversible alpha1-AR antagonist (THP-1 cells: PBA 1μM + Dox 10μM: 76 +/- 11.6% inhibition, p&lt;0.01 vs. MCP-1 alone), suggesting that the antimigratory activity of Dox is mediated through a novel mechanism unrelated to its blocking the alpha1-AR. Pretreatment of monocytes with SB203580 (10μM), a p38 MAPK inhibitor, also attenuated MCP-1 directed migration ( HPBM: 55.3 +/- 0.3% inhibtion; THP-1 cells: 55.4 +/- 13.9% inhibition, both p&lt; 0.05 vs. MCP-1 alone), indicating that activation of this pathway is required for migration towards MCP-1 by these cells. Dox (10μM) inhibited MMP-9 activity by 62% +/- 3.15% (p&lt;0.05) measured by ELISA, whereas MMP-9 protein levels were not affected. Dox also increased phorbol 12-myristate 13-acetate (PMA) induced TIMP-1 expression, which may account for its inhibition of MMP activity. The present study demonstrates a potential novel antiatherosclerotic action of Dox by blocking MCP-1 directed-monocyte migration, mediated, in part, through an inhibtion of MMP-9 activity and upregulation of TIMP-1 production.

Efficacy of muscarinic stimulation and mode of excitation-contraction coupling in bovine trachealis muscle

We have compared the efficacy of cromakalim and nifedipine to inhibit acetylcholine (ACh) and pilocarpine-induced tonic contractions in control preparations and in tissues where a fraction of the muscarinic receptor population had been removed by alkylation with phenoxybenzamine (PBZ). Both agonists induced contractions by stimulating pharmacologically similar receptors, probably of the M 3 muscarinic subtype. The receptor reserve was larger, and the coupling between stimulation and contraction (E-C coupling) more efficient when ACh was the stimulating agonist. For stimulations that produced equal levels of muscle response, cromakalim was more efficacious in inhibiting contractions induced by pilocarpine. The efficacy of cromakalim in relaxing contractions induced by ACh increased when the number of functional receptors decreased. Cromakalim and nifedipine decreased the efficiency of E-C coupling for ACh and pilocarpine. Cromakalim efficacy decreased in a sigmoid manner when stimulating concentrations of ACh (and receptor occupancy) increased, and there was an inverse relationship between receptor occupancy by ACh and cromakalim efficacy. In the presence of TEA, a K + channel blocker, nifedipine almost completely inhibited contractions induced by the M 3 muscarinic agonist bethanechol. These data indicate that in bovine tracheal smooth muscle, electro-mechanical coupling is an inherent part of muscarinic E-C coupling, but its functional expression is dependent upon the efficacy of stimulation. The data also suggest that the M 3 receptor is coupled to a cellular pathway linked with the activation of K + channels that exerts a potent functional antagonism against activation of voltage-dependent Ca 2+ entry.

Effect of papaya latex extract on gravid and non-gravid rat uterine preparations in vitro

In search of uterotonic principles, papaya ( Carica papaya, Caricaceae) latex extract (PLE) was tested on rat uterine preparations in vitro at various stages of the estrous cycle and gestation periods. Rat uterine contractile activity was remarkably increased by different doses of PLE in proestrus and estrus stages compared to metestrus and diestrus stages of the estrous cycles. The maximum contractile activity of the uterus was observed at the later stages of pregnancy which correspond with the peak level of estrogen in the plasma. A direct dose-dependent spasmodic action with increased frequency and amplitude was observed with PLE in all non-gravid uterine preparations. Pretreatment of the tissue with phenoxybenzamine (PB) non-competitively blocked the effect of PLE. Blocking of the 5-HT receptors with methysergide partially blocked the excitatory response to PLE. Pretreating the tissue with Indomethacin, a cyclo-oxygenase inhibitor, had no effect on the response to PLE. The release of PLE induced mast cell degranulation and subsequent release of heparin, biogenic amines or prostaglandins (PGs) was ruled out by pretreating the tissue with sodium cromoglycate, a mast cell stabilizer. Pure papain induced uterine contractions were not sustained for a longer period and at higher concentrations the receptor proteins were affected by the enzymatic action of papain. From this study it is evident that the crude papaya latex contain a uterotonic principle which might be a combination of enzymes, alkaloids and other substances which can evoke sustained contraction of the uterus acting mainly on the alpha adrenergic receptor population of the uterus at different stages.

Alpha1-adrenoceptor antagonist effect of (+/-)-dobutamine in rat isolated gastric artery preparation.

(+/-)-Dobutamine at concentrations < or =10(-5) M did not evoke contractions of rat gastric artery segments. However, when the tissues were contracted with methoxamine, (+/-)-dobutamine evoked concentration-dependent relaxation. The relaxant responses were not significantly affected by propranolol. In the same preparation, propranolol competitively antagonized isoprenaline-induced relaxation with a -log K(B) value of 7.90+/-0.26. (+/-)-Dobutamine did not relax arterial ring segments precontracted with vasopressin (10(-7) M). (+/-)-Dobutamine antagonized noradrenaline-induced contractions of the gastric artery segments. The pA2 value was 6.93+/-0.20, and the slope of the Schild regression line was 1.22+/-0.14. This value (slope) was not significantly different from 1, indicating competitive antagonism. Pretreatment of gastric artery segments with dobutamine before phenoxybenzamine (PBZ) protected against inactivation of alpha1-adrenoceptors by PBZ. The dose ratio of prazosin (3x10(-9) M) and (+/-)-dobutamine (10(-5) M) in combination was close to the expected sum of their individual dose ratios minus 1, indicating interaction with a common site. It was therefore concluded that (+/-)-dobutamine evoked relaxation of rat gastric artery segments by an action not involving beta-adrenoceptor activation but by blocking alpha1-adrenoceptors.

Contact dermatitis caused by phenoxybenzamine hydrochloride

Contact dermatitis caused by phenoxybenzamine hydrochloride

Calcium-contraction relationship in rat mesenteric arterial smooth muscle. Effects of exogenous and neurogenic noradrenaline.

We evaluated the relationship between intracellular calcium concentration ([Ca2+]i) and vasoconstriction during the presence of exogenous noradrenaline (NA) and sympathetic nerve stimulation. An imaging technique was used to determine calcium/tension relationships in isolated rat mesenteric resistance arteries that had been mounted for recording of isometric tension development and loaded with Fura-2/AM. Experiments were performed after depletion of vasodilator neuropeptides and in the continuous presence of 1 microM propranolol, 3 microM indomethacin, and 30 microM nitro-l-arginine. NA (10 microM) was shown first to induce a further increase in tension, but not [Ca2+]i, during the contraction induced by 125 mM K+. Subsequently, calcium/tension relationships were determined during stimulation with graded increases in extracellular [K+] (5. 9-125 mM K+), cumulative administration of NA (0.2-10 microM) and electrical field stimulation of perivascular nerves (EFS, 1-16 Hz). A basal calcium/tension relationship without the calcium-sensitizing property of NA was constructed using a cumulative concentration/response curve of 5.9-125 mM K+ in arteries after prior exposure to the irreversible alpha-adrenoceptor antagonist phenoxybenzamine (POB). K+ series before and during alpha-blockade were also studied using the combination of the alpha1-antagonist prazosin and alpha2-antagonist yohimbine yielding comparable results as with POB. Calcium/tension curves obtained in the presence of NA, K+ and during EFS all were shifted to the left compared with the basal condition and all showed a similar slope indicating that neurogenically released NA is equally capable of inducing calcium sensitization in smooth muscle of mesenteric resistance arteries as exogenously applied NA. In the presence of exogenous and endogenous NA we not only observed an elevated contractile response for a given increase in [Ca2+]i, but also an attenuated rise in [Ca2+]i for a given intensity of stimulation. This suggests that the agonist-induced calcium-sensitization is accompanied by a reduction of the rise in [Ca2+]i.

THE EFFECTS OF PHENOXYBENZAMINE ON IMMEDIATE-EARLY GENE EXPRESSION AFTER HYPOTHERMIC CIRCULATORY ARREST

Introduction. Cardiopulmonary bypass (CPB) and hypothermic circulatory arrest (HCA) can cause significant neurologic complications in infants, including seizures, developmental delays, choreoathetosis, and diminished intelligence. Brain injury is multifactorial, but the pathophysiology is due to diminished substrate supply to neurons and the excessive release of excitatory amino acids within the brain. [1,2] Our institution routinely uses the long-acting alpha-blocker, phenoxybenzamine (PB), in all neonates and infants receiving blood primes. This study evaluated the effects of PB on postoperative metabolic acidosis and the expression of the ischemia/stress-associated immediate-early gene, c-fos, in neurons of neonatal lambs subjected to CPB and HCA. Methods. Neonatal lambs (4-6 kg) anesthetized with isoflurane were cannulated for CPB via the right atrium and ascending aorta. Group A (n=12) received saline vehicle and Group B (n=6) received PB, 1 mg/kg iv, prior to CPB. The animals were cooled to 16[degree sign]C and subjected to 90 or 120 mins of HCA. CPB was resumed, the animals were rewarmed to 38[degree sign]C, and weaned from CPB. Arterial blood gas samples were obtained before and after CPB. One hour after terminating CPB, the brains were perfusion-fixed, removed, and analyzed for Fos-related proteins using immunohistochemistry techniques. Neurons positive for intranuclear Fos were identified and quantitated within the subregions of the hippocampal formation, the area of the brain most vulnerable to ischemic injury after CPB and HCA. Results. All animals survived the CPB and HCA. Cooling times and mean blood pressure on bypass were the same in both groups. Pump flows on CPB were significantly higher (p < 0.01) at 20[degree sign]C in PB-treated animals averaging 200 ml/kg compared to 75 ml/kg in vehicle-treated animals. PB treated animals had significantly less (p < 0.05) metabolic acidosis than Group A animals 15 min after weaning from CPB: base excess -2.5 +/- 2 vs. -7.2 +/- 3, respectively. Fos related proteins were expressed in neurons throughout the hippocampal formation after 90 and 120 min of HCA in Group A. PB significantly reduced Fos protein expression in CA1 and CA3 neurons after 90 and 120 min HCA. Discussion. PB facilitated higher flows at the same mean blood pressure on CPB at all temperatures. PB-treated animals had significantly less metabolic acidosis following CPB and HCA and decreased expression of immediate-early genes associated with cellular stress. We speculate that PB increases blood flow in the cerebral microcirculation maintaining substrate supply more effectively during hypothermic CPB and enhances the restoration of cerebral blood flow after HCA.

Infarct size-reducing effect of ischemic preconditioning is related to alpha1b-adrenoceptors but not to alpha1a-adrenoceptors in rabbits.

In rabbits and rats, both stimulation of alpha-adrenoceptors and ischemic preconditioning (PC) reduce infarct size. Activation of alpha1b-adrenoceptors play an important role in the PC effect on ventricular function in rats. However, the alpha1-adrenoceptors have not been reported to be related to the PC effect in rabbits, because the infarct size-reducing effect of PC is not blocked by the nonselective alpha-adrenoceptor antagonist, phenoxybenzamine (POB) or by the alpha1-adrenoceptor antagonist, BE2254. However, we speculated that alpha1b-adrenoceptors but not alpha1a-adrenoceptors may be related to the infarct size-reducing effect of PC in rabbit hearts. Thus we examined in rabbits whether the alpha1b-adrenoceptor blocker chloroethylclonidine (CEC), the alpha1a-adrenoceptor blocker 5-methylurapidil (5-MU), the selective alpha1-adrenoceptor antagonist bunazosin (BN), and the nonselective apha-adrenoceptor antagonist phenoxybenzamine (POB) can block the PC effect on infarct size. Eighty-eight anesthetized open-chest Japanese white male rabbits were subjected to 30-min coronary occlusion and 48-h reperfusion. In five PC groups, the rabbits were subjected to a single 5-min occlusion and 5-min reperfusion before 30-min sustained ischemia. In the PC groups, those with CEC (3 mg/kg, n = 10), 5-MU (3 mg/kg, n = 10), BN (0.3 mg/kg, n = 10), POB (4 mg/kg, n = 10), or placebo saline (n = 10) were pretreated before PC. In the non-PC groups, those with CEC (3 mg/kg, n = 7), 5-MU (3 mg/kg, n = 7), BN (0.3 mg/kg, n = 7), POB (4 mg/kg, n = 7), or placebo saline (n = 10) were pretreated before 30-min sustained ischemia. After a 48-h reperfusion, the infarct size was measured histologically and expressed as a percentage of the area at risk. PC caused a marked reduction of infarct size as compared with the non-PC control (10 +/- 3% vs. 42 +/- 2%; p < 0.05). The PC effect was completely blocked by CEC (36 +/- 2%) and by BN (42 +/- 4%) but not by 5-MU (14 +/- 1%) or POB (13 +/- 2%). None of the drugs by itself affected the infarct size. Stimulation of alpha1b-adrenoceptors but not of alpha1a-adrenoceptors during PC plays an important role in the PC effect on infarct size. This may explain the previous confusion concerning the PC blocking effect of various alpha1-blockers.

Stability of phenoxybenzamine hydrochloride in various vehicles

The stability of phenoxybenzamine hydrochloride in various oral liquids was studied. Phenoxybenzamine hydrochloride powder or capsules were combined with various vehicles to prepare 10-mL formulations with a drug concentration of 2 mg/mL and a 20-mL stock solution containing 10 mg/mL. All formulations were prepared in triplicate and stored at 4 degrees C. A 1.0-mL sample of each of the 2-mg/mL formulations was withdrawn on days 0, 1, 2, 3, and 4, and samples of selected formulations were taken on days 7 and 10. Samples of the stock solution were withdrawn on days 0, 2, 4, 7, 10, 14, and 30. All samples were analyzed by high-performance liquid chromatography. Phenoxybenzamine hydrochloride 2 mg/mL was stable for a longer time in 1% propylene glycol, 0.15% citric acid, and water than in a similar vehicle in which syrup was used in place of water. The concentrations of the drug in both the 10-mg/mL stock solution and stock solutions diluted to 2 mg/mL were > 90% of the initial drug concentration for 30 days. Phenoxybenzamine hydrochloride 2 mg/mL in 1% propylene glycol and 0.15% citric acid in distilled water was stable for 7 days at 4 degrees C. A stock solution of phenoxybenzamine hydrochloride 10 mg/mL in propylene glycol was stable for 30 days at 4 degrees C and, after dilution with 66.7% sucrose in distilled water to a concentration of 2 mg/mL, for up to one hour at 4 degrees C.

The effect of blockade of κ-opioid receptors in the medial preoptic area on the luteinizing hormone surge in the proestrous rat

The present study examined whether blockade of κ-opioid receptors in the medial preoptic area (MPOA) prior to the critical period on the afternoon of proestrus could prematurely evoke an ovulatory luteinizing hormone (LH) surge, and if so, whether norepinephrine (NE) is involved in mediating this response. In the first experiment, push–pull perfusion of the MPOA with nor-binaltorphimine (nor-BNI), a specific κ-opioid receptor antagonist, was done in rats between 10.30 and 13.50 h on proestrus. To determine whether any resulting ovulation was due to a nor-BNI-induced increase in LH release, rats were injected with pentobarbital at 13.55 h to block the afternoon LH surge. In 7 of 10 rats, nor-BNI in the MPOA produced a large increase in LH release beginning between 12.30 and 13.30 h, and 5 of 7 ovulated. During MPOA perfusion with cerebrospinal fluid in our normal colony between 14.00 and 17.00 h, surges of LH release began in the majority of rats between 15.30 and 16.30 h. Thus blockade of MPOA κ-opioid receptors advanced the LH surge by 3 h. The next experiment examined the effect of NE synthesis inhibition with bis(4-methyl-1-homopiperazinylthiocarbonyl) disulfide (FLA-63), or α-adrenergic receptor blockade with phenoxybenzamine (PBZ), on the nor-BNI-induced LH response. In 5 of 6 vehicle-treated rats, blockade of MPOA κ-opioid receptors elicited a large increase in LH release and all 5 ovulated. In contrast, only 3 of 8 rats pretreated with FLA-63 had a large increase in LH release and ovulated, and PBZ prevented the nor-BNI-induced LH increase and ovulation in 4 of 4 rats. PBZ also prevented the afternoon LH surge and ovulation in 4 of 4 rats in our normal colony. Finally, HPLC measurement of NE levels in MPOA push–pull perfusate indicated no increase in NE release during the nor-BNI-induced or normal afternoon LH surges. These results indicate that antagonism of κ-opioid receptors in the MPOA can prematurely evoke an ovulatory LH surge prior to the critical period on the afternoon of proestrus. Furthermore, the nor-BNI-induced as well as the normal afternoon LH surges are dependent on the proper functioning of central noradrenergic neurons, but do not involve increased NE release within the MPOA.