P14.62 Overall survival from glioblastoma: partial resection versus biopsy

BACKGROUND

Maximal safe resection is standard of care in patients with glioblastoma. Partial resection or biopsy are alternative surgical approaches when macroscopic complete resection is unachievable. Survival benefit from partial resection remains uncertain. We aimed to evaluate overall survival from glioblastoma in patients having undergone partial resection compared to biopsy.

MATERIAL AND METHODS

We retrospectively identified all patients with histologically confirmed glioblastoma having undergone partial resection or biopsy in Western Norway between 1.1.2007 and 31.12.2014. Clinical characteristics and radiology reports were extracted from electronic medical records. Categorical data were compared by chi square test or Fishers exact test, and continuous data by non-parametric tests. Kaplan Meier method and log rank test were used for survival analyses.

RESULTS

We identified 158 patients diagnosed with glioblastoma and having undergone biopsy or partial resection. Biopsy was performed in 52 patients (32.9%) and partial resection in 106 patients (67.1%). Median age (range) was 62.5 (18.1–82.3) in the biopsy group and 62.2 (27.9–85.1) in the partial resection group (p=0.90). Median Charlson comorbidity score was four in both groups. Multifocality was observed in 46.2% of patients in the biopsy group, compared to 27.4% of patients in the partial resection group (p=0.02). Deep-seated tumour localisation was also more frequent in the biopsy group than in the partial resection group, seen in 17.3% vs 5.7% of the patients (p=0.04). There was no difference in chemoradiotherapy (CRT) treatment between the groups. CRT according to the Stupp protocol, less intensive CRT and best supportive care was performed in 36.5%, 50.0% and 13.5% of patients in the biopsy group, compared to 45.3%, 49.1% and 5.7% in the partial resection group (p=0.20). Median overall survival in the biopsy group was 8.1 months (95% CI 5.2–11.1) compared to 11.1 months (95% CI 9.4–12.8) in the partial resection group (p=0.19). Median survival in the biopsy group was 13.8 months (95% CI 10.1–17.5), 6.5 months (95% CI 3.6–9.4), and 3.5 months (95% CI 0.0–7.7) for patients receiving CRT according to Stupp protocol, less-intensive CRT and best supportive care, respectively (p<0.001). The corresponding numbers in the partial resection group were 15.1 months (95% CI 13.2–16.9), 9.1 months (95% CI 7.5–10.6), and 1.5 month (95% CI 0.0–4.7) (p<0.001).

CONCLUSION

Median overall survival was slightly longer in patients having undergone partial resection compared to biopsy, however not statistically significant. Prospective studies are needed to evaluate the survival benefit from partial resection.

Wake-up stroke-Amendable for thrombolysis-like stroke with known onset time?

Patients suffering an acute ischemic stroke can be treated with intravenous thrombolysis in the absence of contraindications. A known onset time is a prerequisite as treatment, according to guidelines, has to be started within 4.5 hours. In patients awakening with a stroke, the last time they were seen without a neurological deficit is assumed to be the time of onset. Thus, despite of lack of contraindications on initial brain imaging, these patients are largely excluded from therapy. This review discusses the underlying pathophysiological, clinical, and radiological evidence surrounding wake-up stroke and its consequences for making treatment decisions.

Radiological imaging in acute ischaemic stroke

Patients who suffer acute ischaemic stroke can be treated with thrombolysis if therapy is initiated early. Radiological evaluation of the intracranial tissue before such therapy can be given is mandatory. In this review current radiological diagnostic strategies are discussed for this patient group. Beyond non-enhanced computed tomography (CT), the standard imaging method for many years, more sophisticated CT stroke protocols including CT angiography and CT perfusion have been developed, and additionally an increasing number of patients are examined with magnetic resonance imaging as the first imaging method used. Advantages and challenges of the different methods are discussed.

Acute ischemic stroke--from symptom recognition to thrombolysis

OBJECTIVES

The understanding of stroke has changed in the recent years from rehabilitation to an emergency approach. We review existing data from symptom recognition to thrombolysis and identify challenges in the different phases of patient treatment.

RESULTS

Implementation of treatment in dedicated stroke units with a multidisciplinary team exclusively treating stroke patients has led to significant reduction of stroke morbidity and mortality. Yet, first the introduction of treatment with intravenous rtPA (IVT) has led to the 'time is brain' concept where stroke is conceived as an emergency. As neuronal death in stroke is time dependent, all effort should be laid on immediate symptom recognition, rapid transport to the nearest hospital with a stroke treatment facility and diagnosis and treatment as soon as possible. The main cause of prehospital delay is that patients do not recognize that they suffered a stroke or out of other reasons do not call the Emergency Medical Services immediately. Educational stroke awareness campaigns may have an impact in increasing the number of patients eligible for rtPA treatment and can decrease the prehospital times if they are directed both to the public and to the medical divisions treating stroke. Stroke transport times can be shortened by the use of helicopter and a stroke mobile--an ambulance equipped with a CT scanner--may be helpful to decrease time from onset to treatment start in the future. Yet, IVT has several limitations such as a narrow time window and a weak effect in ischemic strokes caused by large vessel occlusions. In these cases, interventional procedures and the concept of bridging therapy, a combined approach of IVT and intraarterial thrombolysis or mechanical thrombectomy, might improve recanalization rates and patient outcome.

CONCLUSIONS

As neuronal death in stroke patients occurs in a time-dependent fashion, all effort should be made to decrease time from symptom onset to treatment start with rtPA: major challenges are stroke recognition in the public, transport times to hospital and an efficient stroke triage in the hospital.

Ischemic stroke--novel therapeutic strategies

OBJECTIVES

Treatment of acute, ischemic stroke has changed markedly during the last two decades. We review existing data for optimizing modern stroke care.

RESULTS

Implementation of stroke units, giving systematic treatment and observation to stroke patients, has lead to a significant reduction in death and dependency. Introduction of intravenous rt-PA (IVT) within 3 h for selected stroke patients and recent extension of the time window to 4.5 h improved the outcome even further. Still, one must consider that IVT has several limitations, such as a narrow time window and several contraindications, and the effect is modest, particularly in strokes with a large vessel occlusion. Recanalization of the occluded vessel is a major predictor for good outcome and should be set as a goal. Intra-arterial rt-PA (IAT) and the concept of bridging therapy (IVT prior to IAT or thrombectomy with a mechanical device) may improve recanalization rates and outcome. Randomized controlled trials (RCT) are available for IAT, but not for thrombectomy with devices, and we mostly have retrospective non-controlled data. The Merci- and Penumbra system are the most studied devices, for which recent studies report acceptable safety and efficacy.

CONCLUSIONS

Sufficiently powered RCTs to evaluate the effect of thrombectomy with mechanical devices are warranted, but as the natural course of a large vessel stroke carries a devastating prognosis, a proactive recanalization approach is justified based on today's knowledge.

Renal transplant failure due to urologic complications: Comparison of static fluid with contrast-enhanced magnetic resonance urography

PURPOSE

Postrenal reasons of renal transplant failure can be assessed by magnetic resonance urography. This study was designed to retrospectively compare the diagnostic accuracy of static fluid (T2-)MRU compared to contrast enhanced (CE-)MRU in patients with renal transplant failure.

MATERIAL AND METHODS

Thirty-five consecutive patients (14 female, 21 men; mean age 48.6 years) with renal transplant failure and sonographically detected hydronephrosis were examined both with T2-MRU as well as CE-MRU resulting in 39 MRU examinations. MRU was performed both using T2-weighted HASTE-sequence (T2-MRU) as well as Gadolinium-enhanced 3D-FLASH-sequence (CE-MRU) on a 1.5-T clinical MRI scanner (Magnetom Vision, Siemens Medical Solutions). Subjective image quality of resulting maximum intensity projection was assessed in consensus by two readers blinded to the final diagnosis, using a five point scale. MRU findings were correlated to sonography, operative results or clinical follow up.

RESULTS

CE-MRU yielded a sensitivity of 85.7% (T2-MRU 76.2%), and a specificity of 83.3% (T2-MRU: 73.7%), however statistical significance was not reached. The subjective image quality was significantly better in CE-MRU.

CONCLUSIONS

Only concerning subjective image quality CE-MRU proved superior to T2-MRU. Yet, there was no significant difference in diagnostic accuracy between T2- and CE-MRU. Thinking of incipient nephrogenic systemic fibrosis, T2-MRU can be used as reliable alternative in patients with decreased renal transplant function due to urological complications.

Assessment of three different software systems in the evaluation of dynamic MRI of the breast

OBJECTIVE

The aim was to compare the diagnostic performance and handling of dynamic contrast-enhanced MRI of the breast with two commercial software solutions ("CADstream" and "3TP") and one self-developed software system ("Mammatool").

MATERIALS AND METHODS

Identical data sets of dynamic breast MRI from 21 patients were evaluated retrospectively with all three software systems. The exams were classified according to the BI-RADS classification. The number of lesions in the parametric mapping was compared to histology or follow-up of more than 2 years. In addition, 25 quality criteria were judged by 3 independent investigators with a score from 0 to 5. Statistical analysis was performed to document the quality ranking of the different software systems.

RESULTS

There were 9 invasive carcinomas, one pure DCIS, one papilloma, one radial scar, three histologically proven changes due to mastopathy, one adenosis and two fibroadenomas. Additionally two patients with enhancing parenchyma followed with MRI for more than 3 years and one scar after breast conserving therapy were included. All malignant lesions were classified as BI-RADS 4 or 5 using all software systems and showed significant enhancement in the parametric mapping. "CADstream" showed the best score on subjective quality criteria. "3TP" showed the lowest number of false-positive results. "Mammatool" produced the lowest number of benign tissues indicated with parametric overlay.

CONCLUSION

All three software programs tested were adequate for sensitive and efficient assessment of dynamic MRI of the breast. Improvements in specificity may be achievable.

Structure-based design of potent, amidine-derived inhibitors of factor Xa: evaluation of selectivity, anticoagulant activity, and antithrombotic activity

To enhance the potency of 1,2-dibenzamidobenzene-derived inhibitors of factor Xa (fXa), an amidine substituent was incorporated on one of the benzoyl side chains to interact with Asp189 in the S1 specificity pocket. Lead molecule 1 was docked into the active site of fXa to facilitate inhibitor design. Subsequently, iterative SAR studies and molecular modeling led to a 1000-fold increase in fXa affinity and a refined model of the new inhibitors in the fXa active site. Strong support for the computational model was achieved through the acquisition of an X-ray crystal structure using thrombin as a surrogate protein. The amidines in this series show high levels of selectivity for the inhibition of fXa relative to other trypsin-like serine proteases. Furthermore, the fXa affinity of compounds in this series (K(ass) = 50-500 x 10(6) L/mol) translates effectively into both anticoagulant activity in vitro and antithrombotic activity in vivo.

Antithrombotic efficacy in the guinea pig of a derivative of human protein C with enhanced activation by thrombin

Conversion by alpha-thrombin of the zymogen human protein C (HPC) to activated protein C (aPC) is an important physiologic feedback control mechanism for the coagulation cascade. Although activation of HPC by thrombomodulin-bound thrombin is relatively rapid, activation by free thrombin occurs at a significantly slower rate. Previously, we generated a "hyper-activatable" derivative of HPC (FLIN-Q3) with an increased activation rate by free alpha-thrombin in vitro. In this study, the antithrombotic efficacy of FLIN-Q3 was compared with both native zymogen and aPC in an arteriovenous shunt model of thrombosis in the guinea pig. Recombinant proteins were infused 15 minutes before and throughout a 15-minute period while blood was circulated from carotid to jugular through tubing that enclosed a thread on which fibrin was deposited. Parallel dose-dependent antithrombotic responses were observed. Under these non-steady-state conditions, the calculated infusion doses associated with a 50% reduction of thrombus mass were 2.7, 24, and 250 mg/kg/h for aPC, FLIN-Q3, and HPC, respectively. Thrombus weight correlated inversely with plasma concentration of aPC, measured amidolytically, from either direct infusion of aPC or that generated from the zymogens in the animal, and similarly correlated inversely with anticoagulant activity measured by whole blood aPTT. Neither zymogen form showed significant aPC activity before shunt circulation, suggesting a requirement for exposure to thrombin. After the infusion was discontinued for 15 minutes, a second period of thrombus formation in the shunt demonstrated the ability of zymogen forms of PC, unlike aPC, to provide "on-demand" anticoagulant responses to repeated thrombotic stimuli. Thus, a "hyper-activatable" PC molecule such as FLIN-Q3 may represent a superior form of anticoagulant therapy than either the native zymogen or aPC.

A family of arginal thrombin inhibitors related to efegatran

Three new tripeptide arginal thrombin inhibitors were shown to have potent anticoagulant and antithrombotic activity: D-MePhg-Pro-Arg-H (LY287045), D-1-Tiq-Pro-Arg-H (LY294291), and D-MePhe-Pro-Arg-H (Efegatran). Efegatran and the related arginals differ mechanistically from old and from new anticoagulant agents. As illustrated with x-ray diffraction analysis of crystals of the LY294291 complex with human thrombin, the family of arginals binds thrombin with the P3, P2, and P1 residues interacting with the putative S3, S2, and S1 fibrinogen-binding sites. A hemi-acetal bond at Ser 195 was shown to contribute to the tight-binding reversible competitive thrombin inhibition properties observed with the arginal family. Tight-binding Kass values from thrombin inhibition studies correlated with thrombin clottin inhibition potency. The thrombin time (TT) assay was prolonged twofold with 33 nM Efegatran, which demonstrated an apparent Kass value of 0.8 x 10(8) L/mol (for comparison, 17 nM hirudin was required to prolong the TT assay two-fold). There are empirical anticoagulant selectivity differences between Efegatran and hirudin, manifested by large activated partial thromboplastin time (aPTT)/TT effect ratios (30 to 55) found with the arginals, as compared to the small aPTT/TT effect ratio (2 to 3) found with hirudin. The underlying anticoagulant mechanism differences between the arginals and hirudin appear to be confined to the aPTT pathway and, therefore, might involve different effects toward thrombin feedback activation of factor VIII. The arginals did not substantially inhibit other coagulation factor serine proteases. Antithrombotic effects of Efegatran and the arginal family occur at low infusion doses in dogs and appear to correlate with effects on TT without requiring perturbation of the aPTT. Selectivity properties regarding the fibrinolytic enzymes were shown to be important for successful use of the arginals in vivo as adjunctive agents during tissue plasminogen activator (t-PA) thrombolysis. The data suggest that LY287045, LY294291, and Efegatran should be expected to be useful as antithrombotic adjuncts to thrombolytic therapy with t-PA, urokinase, or streptokinase and should be expected to spare endogenous fibrinolysis. Efegatran has been evaluated in phase I clinical studies and is currently under clinical investigation in phase II protocols as a new cardiovascular anticoagulant.

Comparative 5-HT2-receptor antagonist activity of amesergide and its active metabolite 4-hydroxyamesergide in rats and rabbits

Amesergide is an orally active ergoline amide, 5-HT2-receptor antagonist with a long duration of action. Since a major metabolite of amesergide is 4-hydroxyamesergide, we questioned whether the formation of this metabolite might contribute to the pharmacological activity and long duration of action observed after oral administration of amesergide. 4-Hydroxyamesergide was a potent 5-HT2-receptor antagonist with an affinity equal to or greater than amesergide under in-vitro conditions as measured by blockade of vascular 5-HT2 receptors, and 5-hydroxytryptamine (5-HT)-amplified ADP-induced rabbit platelet aggregation. Furthermore, 4-hydroxyamesergide, like amesergide, inhibited the pressor response to 5-HT after its intravenous administration to rats and was about 3-fold more potent than amesergide in this regard. 4-Hydroxyamesergide was also a potent inhibitor of vascular 5-HT2 receptors after oral administration to rats. After oral administration, 4-hydroxyamesergide had a similar or slightly greater duration of activity than the parent molecule. 4-Hydroxyamesergide, again like amesergide, also blocked central 5-HT2 receptors after its in-vivo administration to rats as measured by its ability to inhibit quipazine-induced increases in serum corticosterone. Thus, the formation of 4-hydroxyamesergide after oral administration of amesergide to animals and man may contribute to the potency and long duration of action of amesergide as a 5-HT2-receptor antagonist.

Preclinical studies on LY237733, a potent and selective serotonergic antagonist

8B-N-cyclohexyl-6-methyl-1(1-methylethyl)ergoline-8-carboxamide (LY237733) is an ergoline with potent and highly selective 5-hydroxytryptamine (5-HT) antagonist activity. The in vitro radioligand displacement studies showed that LY237733 has a preferential affinity for 5-HT1c and 5-HT2 receptors compared to other monoaminergic receptors. This characteristic is shared with other previously described ergoline 5-HT antagonists, such as LY53857 and sergolexole. In parallel ligand displacement assays, LY237733 had a similar potency to sergolexole. LY237733 was equipotent to sergolexole, but slightly less potent than LY53857 in the antagonism of 5-HT-induced elevation in blood pressure and quipazine-induced elevation in corticosterone levels, which are considered to be measures of 5-HT2 and possibly 5-HT1c antagonist activity. LY237733 failed to antagonize pergolide or 8-hydroxy-2-(di-n-propylamino)tetralin-induced elevations in serum corticosterone levels, indicating selectivity for the 5-HT1c/2 receptor, relative to 5-HT1a and D2 dopaminergic receptors. The only in vivo response that could be detected after administration of LY237733 alone in doses less than 1 mg/kg was the amplification of male rat sexual behavior. LY237733 was 10 to 100 times more potent than LY53857 or sergolexole in augmenting sexual responses of male rats with different levels of sexual response capacity. LY237733 has a much longer serum half-life than sergolexole. These studies have provided the pre-clinical rationale to evaluate the effects of this compound in the treatment of sexual disorders such as psychogenic erectile dysfunction, and other therapeutic indications for a 5-HT2 antagonist, including depression, anxiety, schizophrenia and migraine.

Rat model of arterial thrombosis induced by ferric chloride

The purposes of these studies were to produce a small animal model of arterial thrombosis for study of novel antithrombotic agents, to validate a simple temperature index of occlusive thrombosis, and to describe the composition of the thrombus. Small thermocouple transducers were fabricated from readily available materials. A thermocouple was inserted under a carotid artery of the anesthetized rat and vessel temperature was recorded continuously. Arterial injury was induced by FeCl3 solution applied topically to the artery above the thermocouple. To validate the relationship between thrombotic occlusion and vessel temperature, blood flow velocity, proximal to the injury, and temperature were recorded simultaneously. Temperature decreased rapidly when velocity averaged 24 +/- 12 percent of control and velocity did not differ from zero within 20 sec. In normal vessels, average flow velocity did not decrease significantly from control until a fixed stenosis decreased diameter by 78 percent. Average time to occlusion (TTO), signaled by the abrupt temperature inflection, ranged from 56 +/- 4 min to 14 +/- 1 min after 10 and 65 percent FeCl3 application respectively. Vessel segments were fixed at various times after FeCl3 exposure and examined by scanning electron microscopy. Endothelial damage was observed and was associated with thrombus composed of activated platelets, fibrin strands and entrapped erythrocytes. The results demonstrate that FeCl3 dose-dependently induced formation of an occlusive mixed thrombus that was indexed by monitoring the time between FeCl3 application and a rapid temperature decrease in the carotid artery of the rat.

Preclinical pharmacology of a new serotonergic receptor antagonist, LY281067

The preclinical pharmacologic activity of LY281067 shows it to be a potent and highly selective serotonergic (5-HT2) receptor antagonist. Based upon binding studies with 5-HT2 receptors in brain cortical membranes and block of 5-HT-induced contractions in the rat jugular vein, LY281067 showed high affinity at 5-HT2 receptors with a dissociation constant of approximately 1 nM. Furthermore, LY281067 was a highly selective 5-HT2 receptor antagonist without appreciably binding to 5-HT1, D1 or D2 receptors or interacting with histamine (H1), cholinergic, beta adrenergic or alpha-1 adrenergic receptors in smooth muscle. LY281067 had modest affinity at alpha-2 receptors with a dissociation constant of approximately 100 nM. Oral bioavailability of LY281067 in spontaneously hypertensive rats was excellent with an oral to i.v. dose ratio approximating 4, based upon blockade of pressor responses to 5-HT as an in vivo estimate of 5-HT2 receptor antagonist activity. Furthermore, LY281067 blocked quipazine-induced increase in serum corticosterone concentration, an increase thought to be mediated by activation of central 5-HT receptors. After oral administration to rats, LY281067 antagonized vascular 5-HT2 receptors with a relatively long duration of action (greater than 6 hr), an observation likely to be related to plasma concentrations of both the parent and an active metabolite. Lastly, LY281067 was relatively nontoxic, possessing a therapeutic index of approximately 1000 after oral administration to rats. In summary, LY281067 is a potent and highly selective, orally active 5-HT2 receptor antagonist with a relatively long duration and wide margin of therapeutic safety.

Effect of meta-chlorophenylpiperazine (mCPP), a central serotonin agonist and vascular serotonin receptor antagonist, on blood pressure in SHR

mCPP (meta-chlorophenylpiperazine) has agonist activity at some central serotonin receptors and antagonist activity at peripheral vascular 5HT2 receptors, both effects that have been postulated to lower blood pressure. mCPP (10 and 30 mg/kg, i.p. 1 hr after administration) increased serotonin and decreased 5-hydroxy-indolacetic acid (5-HIAA) brain concentrations and elevated serum corticosterone and prolactin, indications of central serotonergic agonist activities. The same doses of mCPP also antagonized vascular 5HT2 receptors as measured by blockade of pressor responses to serotonin in pithed rats. Although mCPP could be demonstrated to activate central serotonergic receptors and block peripheral vascular 5HT2 receptors, mCPP (10 and 30 mg/kg, i.p.) produced little effect on blood pressure in either the anesthetized or conscious spontaneously hypertensive rat (SHR) up to 1 hr after intraperitoneal administration. The findings are consistent with initial studies in normotensive humans that have not demonstrated a reduction in blood pressure clinically after mCPP in doses that produce elevations in serum cortisol and prolactin levels.

Body fluid volumes in rats with mestranol-induced hypertension

Because estrogens have been reported to produce sodium retention, this study investigated the possibility that hypertension in rats resulting from the ingestion of an estrogen used as an oral contraceptive could be due to increases in body fluid volumes. Female rats were given feed containing mestranol for 1, 3, and 6 mo; control rats were given the feed without mestranol. The mestranol-treated rats had higher arterial pressures than the controls only after 6 mo of treatment. Plasma volume, extracellular fluid volume, and total body water were measured in each rat by the distribution volumes of radioiodinated serum albumin, 35SO4, and tritiated water, respectively. Values for blood volume, interstitial fluid volume, and intracellular fluid volume were derived from these measurements. These body fluid volumes, expressed per 100 g of body weight, were not different between the mestranol-treated rats and their controls at any of the three treatment times. Due to differences in body weight and lean body mass between the mestranol-treated and the control rats, these volumes also were expressed per 100 g of lean body mass. Again, no differences were observed between the mestranol-treated rats and the control rats for any of these body fluid compartments at any of the treatment times. These studies, therefore, were unable to provide evidence that increases in body fluid volumes contributed to the elevated arterial pressure in this rat model of oral contraceptive hypertension.

Antagonism of a peripheral vascular but not an apparently central serotonergic response by xylamidine and BW 501C67

Xylamidine and BW501C67 (alpha-anilino-N-2-m-chlorophenoxypropylacetamidine), serotonin antagonists that have been reported not to cross the blood-brain barrier, were compared to other serotonin antagonists: mianserin, ketanserin, metergoline and LY 53857. All six compounds were potent inhibitors of the binding of tritiated spiperone to 5HT2 receptors in rat frontal cortex membranes in vitro and were less potent inhibitors of the binding of tritiated serotonin to 5HT1 receptors in rat brain membranes. All were potent antagonists of the 5HT2 receptor-mediated contractile response to serotonin in the rat jugular vein in vitro. At doses of 0.1 and 0.3 mg/kg i.p., xylamidine and BW501C67 antagonized the pressor response to intravenously injected serotonin in pithed rats. In contrast, neither xylamidine nor BW501C67 at doses of 1 or 3 mg/kg i.p. antagonized the elevation of serum corticosterone concentration by quipazine in rats, although the other compounds antagonized this effect with ED50 values between 0.03 and 0.9 mg/kg. These data corroborate the previously reported antiserotonin activity of xylamidine and BW501C67. Since xylamidine and BW501C67 were potent antagonists of a peripheral serotonergic response in vivo, their inability to antagonize the elevation of serum corticosterone concentration by quipazine suggests that this effect results from activation of central serotonin receptors.

Pharmacological activity of the isomers of LY53857, potent and selective 5-HT2 receptor antagonists

LY53857 is an ergoline derivative that is a potent and selective antagonist at 5-HT2 receptors. The present study investigated the activities of the diastereomers of LY53857. The SS- and RR-isomers and the meso mixture of isomers of LY53857 all showed affinity for 5-HT2 receptors approximately 100-fold higher than for 5-HT1 receptors based on radiolabeled ligand binding studies in rat cortical membranes. Based on these binding data, the meso mixture of isomers was one-half as potent as the other two isomers. Consistent with the binding data, the SS- and RR-isomers and the meso mixture of isomers all showed high affinity as antagonists of 5-HT2 receptors in the rat jugular vein, with the meso mixture of isomers being slightly less potent than the other two isomers. Affinity of the isomers at alpha-1 and alpha-2 receptors was low. Approximately 100,000- and 2000-fold higher concentrations were required for antagonism of alpha-1 and alpha-2 receptors, respectively, relative to 5-HT2 receptors. A similar profile of selectivity was demonstrated for each of the isomers studied. These in vitro data were consistent with in vivo data showing the high i.v. and p.o. potency of all the isomers to antagonize the pressor response to i.v. administration of serotonin in pithed spontaneously hypertensive rats. As seen in vitro, the meso mixture of isomers was slightly less potent than the SS- and RR-isomers after p.o. administration in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

Renin-angiotensin mechanisms in oral contraceptive hypertension in conscious rats

Rats were placed on powdered chow containing either no additives (controls), mestranol (a synthetic estrogen), norethynodrel (a synthetic progestin), or both mestranol and norethynodrel. After 6 mo on these diets, catheters were placed in the carotid artery and jugular vein of each rat. An arterial blood sample was obtained for plasma renin activity (PRA), plasma renin concentration (PRC), and plasma renin substrate concentration (PRS). Mean arterial pressure was measured in each rat. The angiotensin II (ANG II) antagonist, [Sar1-Ile8]ANG II, was infused intravenously for 30 min while blood pressure was recorded. Rats treated with mestranol and/or norethynodrel had PRA and PRC values that were not different from the control rats; however, mestranol-treated rats and rats treated with mestranol plus norethynodrel had PRS values that were substantially (P less than 0.01) higher than the controls. Arterial pressures in rats treated with mestranol and with mestranol plus norethynodrel were significantly (P less than 0.01) elevated when compared with the controls and with the rats treated with norethynodrel alone. Infusion of the ANG II antagonist failed to alter arterial pressure in any of the groups of rats. These results indicated that, in the steroid combination found in the oral contraceptive Enovid, it is the estrogenic component that results in hypertension in this rat model. Also this study found no evidence that ANG II plays a role in maintaining the elevated arterial pressure following long-term treatment with mestranol in rats.

LY53857, a selective and potent serotonergic (5-HT2) receptor antagonist, does not lower blood pressure in the spontaneously hypertensive rat

LY53857 was a potent antagonist of vascular contraction to serotonin, which is mediated by serotonergic (5-HT2) receptors, with a dissociation constant in vitro of 5.4 X 10(-11) M. Unlike several other serotonin antagonists, LY53857 showed minimal affinity for vascular alpha adrenergic receptors (dissociation constant of 1.4 X 10(-5) M). Thus, LY53857 was a highly potent and selective antagonist at 5-HT2 receptors. In vivo activity paralleled the in vitro observations. In pithed spontaneously hypertensive rats (SHR), LY53857 at 0.1 and 3.0 mg/kg i.p. produced a 22-and 480-fold shift, respectively, in the pressor response to serotonin whereas LY53857 at 10 mg/kg did not alter the pressor response to the alpha receptor agonist, methoxamine. Furthermore, LY53857 administered peripherally also inhibited central serotonin receptors, as evidenced by blockade of the serum corticosterone increase produced by the central actions of the serotonin agonist, quipazine, and by antagonism of tryptamine-induced convulsions in rats. LY53857 in doses that blocked the pressor response to serotonin and that blocked central serotonin receptors did not lower mean arterial blood pressure in the SHR. Thus, the lack of effectiveness of LY53857 to lower blood pressure in the SHR indicates that blockade of both central and vascular serotonin receptors is not a sufficient mechanism to lower blood pressure in this model of hypertension.

Evidence that blood pressure reduction by serotonin antagonists is related to alpha receptor blockade in spontaneously hypertensive rats

In vitro affinity for vascular 5HT2 and alpha receptors was determined for several compounds (spiperone, ketanserin, mianserin, trazodone, mepiprazole, benzoctamine, m-trifluoro-methylphenylpiperazine, m-chlorophenylpiperazine, and 1-(1-naphthyl)piperazine) known to interact with serotonin receptors. All compounds competitively inhibited 5HT2 and alpha receptors with differing degrees of selectively. Based on these observations, ketanserin, benzoctamine, and 1(1-naphthyl)piperazine were evaluated as antihypertensive agents in spontaneously hypertensive rats (SHR). Of these compounds, 1-(1-naphthyl)piperazine was a highly selective 5HT2 receptor antagonist with a ratio of 5HT2 to alpha receptor affinity of greater than 2000. The ratio of 5HT2 to alpha receptor affinity for ketanserin and benzoctamine was 63 and 16, respectively. However, the order of affinity toward 5HT2 receptors was ketanserin greater than 1-(1-naphthyl)piperazine greater than benzoctamine whereas the order of affinity toward alpha receptors was ketanserin greater than benzoctamine greater than 1-(1-naphthyl)piperazine. A similar order of potency toward both 5HT2 and alpha receptors was found in pithed SHR based on antagonism of the pressor response to serotonin and methoxamine, respectively. In the SHR, maximum blood pressure reduction at a dose of 10 mg/kg i.p. was approximately 65 and 30 mm Hg for ketanserin and benzoctamine, respectively; 1-(1-naphthyl)piperazine did not affect blood pressure. Thus, blood pressure reduction more closely paralleled the in vitro and in vivo potency of these agents toward vascular alpha rather than 5HT2 receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Humoral factor in pressor hyperresponsiveness in renal prehypertensive rabbits

Prehypertensive rabbits with renal artery stenosis of 3 days' duration (one-kidney, one clip) are known to have increased pressor responses to norepinephrine and vasopressin; this pressor hyperresponsiveness is restored to normal by the angiotensin II (AII) antagonist, [ Sar1, Ile8 ] AII, even though plasma renin activity (PRA) and plasma AII concentrations are not elevated. In the present study, the cross-circulation of blood between conscious one-kidney, 3-day renal artery stenosis rabbits and conscious normal rabbits resulted in the transfer of pressor hyperresponsiveness to the normal rabbits, although both groups of rabbits had normal values for PRA. A similar cross-circulation of blood between one-kidney rabbits without renal artery stenosis and normal rabbits did not alter the pressor responsiveness of the normal rabbits to norepinephrine. It was concluded that a circulating humoral factor is involved in mediating pressor hyperresponsiveness in 3-day renal artery stenosis rabbits. To evaluate the interrelationship between AII and the hormonal hyperresponsiveness factor, an additional experiment was performed in which blood was cross-circulated between one-kidney, 3-day renal artery stenosis rabbits and normal rabbits, with the normal rabbits receiving [ Sar1, Ile8 ] AII immediately following cross-circulation. Administration of this AII antagonist to the normal rabbits prevented them from showing pressor hyperresponsiveness following the cross-circulation of blood. It is concluded that in this prehypertensive renal artery stenosis model the humoral hyperresponsiveness factor exerts its effect through AII mechanisms, rather than AII acting to increase the release or secretion of the hyperresponsiveness factor.

Fluid volumes and pressor responsiveness in two-kidney rabbits with renal artery stenosis

This study examined body fluid volumes, the pressor responses to norepinephrine (NE), and the cardiovascular responses to NE before and during infusion of an angiotensin II (ANG II) antagonist in two-kidney rabbits with unilateral renal artery stenosis (RAS) of 3 and 30 day duration. Three separate experiments were performed. In the first experiment, plasma volume, extracellular fluid volume, and total body water were measured by the distribution volumes of radioiodinated serum albumin, 35SO4, and tritiated water, respectively. No differences were seen for any of these volumes between the 3- or 30-day RAS rabbits and their controls. In the second experiment, pressor responses to infusions of several doses of NE were examined; rabbits with 3- and 30-day RAS had exaggerated pressor responses to all doses of NE when compared with the control rabbits. In the third experiment, infusion of NE at 800 ng.min-1.kg body wt-1 resulted in more pronounced increases in mean arterial pressure and total peripheral resistance (TPR) in the 3- and 30-day RAS rabbits than in the controls; after infusion of [Sar1-Ile8] ANG II the increases in mean arterial pressure and TPR during NE infusion were blunted and were of the same magnitude as in the control group. In all experiments the 30-day RAS rabbits were hypertensive, whereas the 3-day RAS rabbits were normotensive; also, plasma renin activity (PRA) values were normal in both the 3- and 30-day RAS groups. These studies demonstrated that increases in body fluid volumes are not necessary for pressor and vascular hyperresponsiveness probably is mediated by ANG II, despite normal PRA values.

Pressor responses to vasopressin in rabbits with 3-day renal artery stenosis

One-kidney rabbits were subjected to renal artery stenosis, and acute experiments were performed 3 days later on conscious animals; one-kidney rabbits without renal artery stenosis served as controls. Rabbits with 3-day renal artery stenosis were normotensive and had normal values for plasma renin activity. Intravenous infusion of arginine vasopressin at 5 mU.min-1.kg body wt-1 for 5 min resulted in a significantly (P less than 0.01) greater increase in mean arterial pressure and total peripheral resistance (TPR) in the renal artery stenosis rabbits than in the controls. Infusion of the angiotensin II (AII) competitive antagonist, [Sar1, Ile8]AII, before the vasopressin infusion abolished the hyperresponsiveness to vasopressin in the renal artery stenosis rabbits and resulted in changes in mean arterial pressure and TPR that were approximately of the same magnitude as the controls. Infusion of [SAr1, Ile8]AII before vasopressin infusion in control rabbits did not alter the cardiovascular responses to vasopressin. Because previous studies have shown that 3-day renal artery stenosis rabbits have exaggerated pressor responses to norepinephrine and that this hyperresponsiveness to norepinephrine is blocked by [Sar1, Ile8]-AII, the present study with vasopressin provided evidence that the increased responsiveness in this model is not specific for a single pressor agent. These studies also demonstrated that AII plays an important role in mediating the exaggerated pressor responses to vasopressin in this prehypertensive model.

Absence of an antihypertensive effect of 12 hour infusions of an angiotensin antagonist in chronic renal hypertensive rabbits

The effect of a continuous 12-hour infusion of a saline solution of the angiotensin II antagonist, [Sar1, Ile8] angiotensin II, on mean arterial pressure was studied in 11 conscious New Zealand white rabbits with hypertension induced by renal artery stenosis and contralateral nephrectomy, and in 11 normotensive control rabbits. Also, the effect on mean arterial pressure of infusing saline alone for 12 hours was examined in 4 hypertensive rabbits and in 8 normotensive controls. There were no significant differences in the changes in mean arterial pressure among the 4 groups of rabbits at any hourly period during these infusions. These studies were unable to provide evidence that angiotensin II is involved in maintaining the elevated arterial pressure in this hypertensive animal model.

Recovery rate of the cardiovascular system in rabbits following short-term halothane anesthesia

Mean arterial pressure, cardiac output and heart rate were determined in eight male New Zealand white rabbits while conscious and after being anesthetized with halothane plus nitrous oxide for 15 minutes. Delivery of the anesthetic agent was stopped and the measurement repeated at 15, 30, 60 and 210 minutes. In a separate experiment blood samples were obtained for plasma renin activity in six rabbits before anesthesia, after 15 minutes of halothane plus nitrous oxide administration, and again 210 minutes after cessation of the anesthesia. Later, this experiment was repeated with the same rabbits except that they were allowed to breathe room air instead of the anesthesia. The halothane anesthesia resulted in decreased mean arterial pressure and cardiac output, but these returned to the preanesthetic levels by 15 minutes after stopping the anesthesia. Heart rate increased during halothane administration, and although it tended to return toward control levels after cessation of the halothane, heart rate was still elevated 210 minutes later. Halothane plus nitrous oxide produced an increase in plasma renin activity, which then subsided to normal by 210 minutes following anesthesia; breathing room air did not result in increases in plasma renin activity. These studies revealed that although short-term anesthesia with halothane plus nitrous oxide resulted in cardiovascular changes in rabbits, after cessation of the anesthetic agent the cardiovascular system quickly returned to normal.

Reflex suppression of renin secretion during distention of cardiopulmonary receptors in dogs

We studied the effect of brief periods of left atrial-pulmonary vein distention on the rate of renin secretion in sodium-restricted dogs anesthetized with chloralose and breathing spontaneously. Series 1 consisted of 32 trials in seven dogs with intact renal nerves and intact vagi. Renin secretion, calculated as the product of renal venous minus arterial renin activity (radioimmunoassay) times renal plasma flow (electromagnetic flowmeter), was depressed to 56% of control during atrial distention despite no change in arterial pressure, central venous pressure, or renal blood flow. Series 2 consisted of 58 trials in 12 dogs which had undergone unilateral renal denervation several days prior to the studies. Simultaneous, bilateral determinations indicated that renin secretion from the innervated kidney was depressed to 58% of control during atrial distention; secretion from the denervated kidney was unchanged. Series 3 consisted of 30 trials in six dogs with bilateral cervical vagotomy. Atrial distention evoked no changes in renin secretion. We conclude that left atrial distention reflexly reduces the rates of renin secretion via vagal afferent and renal sympathetic efferent pathways.