Multicenter assessment of CSF-phosphorylated tau for the prediction of conversion of MCI.

BACKGROUND: The measurement of hyperphosphorylated tau (p-tau) in CSF has been proposed as a biomarker candidate for the prediction of Alzheimer disease (AD) in patients with mild cognitive impairment (MCI). However, a standard quantitative criterion of p-tau has not been evaluated. OBJECTIVE: To assess in a multicenter study the predictive accuracy of an a priori defined criterion of tau phosphorylated at threonine 231 (p-tau(231)) for the prediction of conversion from MCI to AD during a short-term observation interval. METHODS: The study included 43 MCI converters, 45 stable MCI (average follow-up interval = 1.5 years), and 57 healthy controls (at baseline only). Subjects were recruited at four international expert sites in a retrospective study design. Cox regression models stratified according to center were used to predict conversion status. Bootstrapped 95% CIs of classification accuracy were computed. RESULTS: Levels of p-tau(231) were a significant predictor of conversion (B = 0.026, p = 0.001), independent of age, gender, Mini-Mental State Examination, and ApoE genotype. For an a priori-defined cutoff point (27.32 pg/mL), sensitivity ranged between 66.7 and 100% and specificity between 66.7 and 77.8% among centers. The bootstrapped mean percentage of correctly classified cases was 79.95% (95% CI = 79.9 to 80.00%). Post hoc defined cutoff values yielded a mean bootstrapped classification accuracy of 80.45% (95% CI = 80.24 to 80.76%). CONCLUSIONS: An a priori defined cutoff value of p-tau(231) yields relatively stable results across centers, suggesting a good feasibility of a standard criterion of p-tau(231) for the prediction of Alzheimer disease.

MRI and CSF studies in the early diagnosis of Alzheimer's disease.

The main goal of our studies has been to use MRI, FDG-PET, and CSF biomarkers to identify in cognitively normal elderly (NL) subjects and in patients with mild cognitive impairment (MCI), the earliest clinically detectable evidence for brain changes due to Alzheimer's disease (AD). A second goal has been to describe the cross-sectional and longitudinal interrelationships amongst anatomical, CSF and cognition measures in these patient groups. It is now well known that MRI-determined hippocampal atrophy predicts the conversion from MCI to AD. In our summarized studies, we show that the conversion of NL subjects to MCI can also be predicted by reduced entorhinal cortex (EC) glucose metabolism, and by the rate of medial temporal lobe atrophy as determined by a semi-automated regional boundary shift analysis (BSA-R). However, whilst atrophy rates are predictive under research conditions, they are not specific for AD and cannot be used as primary evidence for AD. Consequently, we will also review our effort to improve the diagnostic specificity by evaluating the use of CSF biomarkers and to evaluate their performance in combination with neuroimaging. Neuropathology studies of normal ageing and MCI identify the hippocampal formation as an early locus of neuronal damage, tau protein pathology, elevated isoprostane levels, and deposition of amyloid beta 1-42 (Abeta42). Many CSF studies of MCI and AD report elevated T-tau levels (a marker of neuronal damage) and reduced Abeta42 levels (possibly due to increased plaque sequestration). However, CSF T-tau and Abeta42 level elevations may not be specific to AD. Elevated isoprostane levels are also reported in AD and MCI but these too are not specific for AD. Importantly, it has been recently observed that CSF levels of P-tau, tau hyperphosphorylated at threonine 231 (P-tau231) are uniquely elevated in AD and elevations found in MCI are useful in predicting the conversion to AD. In our current MCI studies, we are examining the hypothesis that elevations in P-tau231 are accurate and specific indicators of AD-related changes in brain and cognition. In cross-section and longitudinally, our results show that evaluations of the P-tau231 level are highly correlated with reductions in the MRI hippocampal volume and by using CSF and MRI measures together one improves the separation of NL and MCI. The data suggests that by combining MRI and CSF measures, an early (sensitive) and more specific diagnosis of AD is at hand. Numerous studies show that neither T-tau nor P-tauX (X refers to all hyper-phosphorylation site assays) levels are sensitive to the longitudinal progression of AD. The explanation for the failure to observe longitudinal changes is not known. One possibility is that brain-derived proteins are diluted in the CSF compartment. We recently used MRI to estimate ventricular CSF volume and demonstrated that an MRI-based adjustment for CSF volume dilution enables detection of a diagnostically useful longitudinal P-tau231 elevation. Curiously, our most recent data show that the CSF isoprostane level does show significant longitudinal elevations in MCI in the absence of dilution correction. In summary, we conclude that the combined use of MRI and CSF incrementally contributes to the early diagnosis of AD and to monitor the course of AD. The interim results also suggest that a panel of CSF biomarkers can provide measures both sensitive to longitudinal change as well as measures that lend specificity to the AD diagnosis.

Longitudinal cerebrospinal fluid tau load increases in mild cognitive impairment.

Cross-sectional cerebrospinal fluid (CSF) levels of tau and amyloid (A) beta (beta) are of diagnostic importance for Alzheimer's disease (AD) and mild cognitive impairment (MCI). However, most longitudinal studies of tau fail to demonstrate progression. Because predominantly brain-derived proteins such as tau, have higher ventricle to lumbar ratios, we hypothesized that adjusting for the ventricular enlargement of AD would correct for the dilution of tau, and improve detection of longitudinal change. Abeta which is not exclusively brain derived, shows a ratio <1, and no benefit was expected from adjustment. In a 1 year longitudinal study of eight MCI and ten controls, we examined CSF levels of hyperphosphorylated (P) tau231, Abeta40, and Abeta42. In cross-section, MCI patients showed elevated Ptau231 and Abeta40 levels, and greater ventricular volumes. Longitudinally, only after adjusting for the ventricular volume and only for Ptau231, were increases seen in MCI. Further studies are warranted on mechanisms of tau clearance and on using imaging to interpret CSF studies.

CSF tau protein phosphorylated at threonine 231 correlates with cognitive decline in MCI subjects.

In this longitudinal study of 77 patients with mild cognitive impairment (MCI), the authors analyzed whether levels of tau protein phosphorylated at threonine 231 (p-tau(231)) in CSF correlate with progression of cognitive decline. High CSF p-tau(231) levels at baseline, but not total tau protein levels, correlated with cognitive decline and conversion from MCI to AD. Independently, old age and APOE-epsilon 4 carrier status were predictive as well. Our data indicate that an increased p-tau(231) level is a potential risk factor for cognitive decline in patients with MCI.

Detection of tau phosphorylated at threonine 231 in cerebrospinal fluid of Alzheimer's disease patients.

A new sandwich ELISA is described which shows specificity for tau phosphorylated at threonine 231 and preferentially reacts with Alzheimer's disease (AD) brain extracts relative to other dementias. This assay was used to analyze 58 antemortem cerebrospinal fluid samples. Twenty-three of 27 AD samples (85% sensitivity) yielded signals greater than the cutoff, while only one of 31 non-AD samples (97% specificity) were greater. This indicates that detection of phosphotau in cerebrospinal fluid with this sandwich ELISA could prove useful in the diagnosis of AD.

Cardiovascular activity of A-74283, a 5-hydroxytryptamine 1A agent, in the spontaneously hypertensive rat.

A-74283, (+,-)trans-2-(4-(3a,4,4a,6a,7,7a-hexahydro-4,7-etheno-1 H cyclobut [f] isoindol-1,3-dionyl)-butyl)-9-methoxy-2,2,2a,4,5,9b-hexahydr o-1 H-benz[e]isoindol HC1, was studied in receptor binding assays and in the spontaneously hypertensive rat (SHR). In radioligand binding to rat cortex, A-74283 had high affinity (equipotent to 8-OH-DPAT) and high selectivity for 5HT1A receptors compared to 5HT1B sites. In conscious SHR, A-74283 lowered mean arterial pressure (MAP) in a dose-related fashion with a prolonged effect after oral administration of higher doses, but heart rate (HR) was not changed. In anesthetized SHR, i.v. administration of A-74283 decreased MAP and total peripheral resistance, but not cardiac output. Pretreatment of conscious SHR with the selective 5TH1A receptor antagonists spiroxatrine or BMY 7378 reduced the hypotensive effect of A-74283 significantly, but pretreatment with adrenergic antagonists phenoxybenzamine or idazoxan or the 5HT2 receptor blocker ketanserin did not alter the effect of A-74283. Intracisternal administration of A-74283 also decreased MAP; however, A-74283 had no effect on blood pressure in pithed SHR in which blood pressure was supported with vasopressin, in contrast to nitroprusside. These data demonstrate that A-74283 exerts a potent hypotensive effect in SHR via systemic vasodilation originating from a central 5HT1A receptor mechanism. A-74283 may be useful for studying 5HT1A receptors and cardiovascular function.

Effects of the putative antidepressant, ABT 200, on the clearance of exogenous norepinephrine in rat cerebellum.

ABT 200 [(RR,SS)-3-phenyl-1-[1',2',3',4'-tetrahydro-5',6'-methylenedioxy- 1'-naphthalenyl-methyl]-pyrrolidine methanesulfonate] is a potent alpha 2-adrenoceptor antagonist (Ki = 1.2 nM) with modest norepinephrine uptake-blocking activity (IC50 = 841 nM) that is currently under clinical evaluation as an antidepressant. The effects of ABT 200, nomifensine (an inhibitor of catecholamine uptake), and rauwolscine (a selective alpha 2-adrenoceptor antagonist) on the clearance of exogenous norepinephrine in the cerebellum of urethane-anesthetized rats was investigated using a vivo electrochemistry. Chronoamperometric recordings were continuously made at 5 Hz using Nafion-coated, single carbon fiber electrodes. When a calibrated amount of norepinephrine was pressure-ejected at 5-min intervals from a micropipette adjacent (290-330 microM) to the electrode, transient and reproducible norepinephrine signals were detected. In response to systemic ABT 200 (30 mg/kg i.p.) or nomifensine (30 mg/kg i.p.), the signals increased in both amplitude and time course, indicating significant inhibition of the norepinephrine transporter. A lower dose (15 mg/kg i.p.) of either ABT 200 or nomifensine had no effect in this paradigm. Local application of ABT 200 (400 microM) or nomifensine (400 microM) prior to pressure-ejection of norepinephrine also significantly increased the amplitude and time course of the norepinephrine signals. In contrast, systemic administration of rauwolscine (30 mg/kg i.p.) or vehicle solution, and local application of vehicle solution, had no effect on the norepinephrine signals. These data indicate that at the higher dose evaluated, both ABT 200 and nomifensine inhibit cerebellar norepinephrine uptake in vivo.

A-61603, a potent alpha 1-adrenergic receptor agonist, selective for the alpha 1A receptor subtype.

N-[5-(4,5-dihydro-1H-imidazol-2yl)-2-hydroxy-5,6,7,8-tetrahydro naphthalen-1-yl] methanesulfonamide hydrobromide (A-61603) is a novel and potent alpha-adrenoceptor agonist. In radioligand binding assays, the compound is at least 35-fold more potent at alpha 1A/a receptors than at alpha 1b or alpha 1d sites. In fibroblast cells transfected with alpha 1a receptors, A-61603 more potently stimulates phosphoinositide hydrolysis than norepinephrine, and is antagonized by prazosin. A-61603 is less potent in cells transfected with alpha 1b or alpha 1d receptors. A-61603 is a potent agonist at alpha 1A receptors in rat vas deferens (200- to 300-fold more potent than norepinephrine or phenylephrine, respectively) and in isolated canine prostate strips (130- to 165-fold more potent than norepinephrine or phenylephrine, respectively). In contrast, A-61603 is only 40-fold more potent than phenylephrine at alpha 1B sites in rat spleen and 35-fold less potent at rat aortic, alpha 1D sites. In an in vivo dog model, A-61603 raises intraurethral prostatic tone to a greater extent than mean arterial blood pressure. A-61603 induces a pressor response in conscious rats at doses 50- to 100-fold lower than phenylephrine, and the response is not attenuated by pretreatment with CEC, whereas YM-617 causes a 100-fold shift in the response. These results indicate that A-61603 is a potent adrenergic agonist, selective for alpha 1A/a receptors, and may prove a useful probe for studies of adrenergic function and alpha 1 adrenoceptor regulation of physiological functions.

Cardiovascular effects of orally administered ABBOTT-81988, an angiotensin II antagonist, in conscious spontaneously hypertensive rats.

ABBOTT-81988 (A-81988), 2-(N-propyl-N[(2'-[1H-tetrazol-5-yl]biphenyl- 4yl)methyl] amino) pyridine-3-carboxylic acid, a nonpeptide angiotensin II (AII) antagonist was studied in the conscious spontaneously hypertensive rate (SHR) (male, 18 to 21 weeks) for cardiovascular effects of oral administration. Oral A-81988 at 0.3 to 3 mg/kg produced a dose-related 10 to 29% decrease in mean arterial pressure (MAP) in SHR (control, 161 to 177 mm Hg; n = 19) for 12 to 24 h without changing heart rate. Oral A-81988 at 3 mg/kg daily maintained MAP in SHR at normotensive levels (97 to 120 mm Hg) during a 5-day protocol with no rebound hypertension at termination of treatment. There was an increase in plasma renin activity in nanograms AI/milliliter/hour in SHR treated with A-81988 (32 +/- 3, n = 6 v 5 +/- 2, n = 6 for vehicle) during its antihypertensive action. The oral potency of A-81988 was enhanced about 10-fold in furosemide-treated SHR. The pressor response to AII was inhibited selectively in SHR even after an 8-day treatment with A-81988 (approximately 3 mg/kg/day orally). Total peripheral resistance was lowered and cardiac output unchanged in SHR administered A-81988 (3 mg/kg/day orally for 2 days). A-81988 (3 mg/kg orally) did not cause orthostatic hypotension in SHR.(ABSTRACT TRUNCATED AT 250 WORDS)

[3H]A-81988, a potent, selective, competitive antagonist radioligand for angiotensin AT1 receptors.

Abbott-81988 (A-81988), 2-(N-n-Propyl-N-[(2'-[1H-tetrazol-5-yl]biphenyl-4- yl)methyl]amino)pyridine-3-carboxylic acid is a potent, competitive, non-peptidic antagonist of angiotensin AT1 receptors. A-81988 was labeled with tritium to high specific activity (16 Ci/mmol) and radioligand binding assays performed in rat liver membranes. [3H]A-81988 bound with high affinity (KD = 0.57 nM) and the KD determined from kinetics assays was similar. Non-specific binding (defined with 10(-6) M angiotensin-II) was very low (< 6% at the KD). The binding of [3H]A-81988 was competitive and exhibited appropriate pharmacological specificity for compounds acting at angiotensin AT1 receptors. These properties demonstrate that [3H]A-81988 will be a useful radioligand for studies of angiotensin AT1 receptors in various tissues.

Characterization of antihypertensive activity of ABBOTT-81988, a nonpeptide angiotensin II antagonist in the renal hypertensive rat.

2-(N-Propyl-N[(2'-[1H-tetrazol-5-yl]biphenyl-4yl)methyl]amin o) pyridine-3-carboxylic acid (ABBOTT-81988), a novel nonpeptide angiotensin II (AII) antagonist, was evaluated to characterize its antihypertensive activity in the conscious renal hypertensive rat. Oral or i.v. administration of ABBOTT-81988 at 0.03 to 0.3 mg/kg produced a dose-dependent, sustained decrease in mean arterial pressure (MAP; control 162-173 mm Hg, n = 27) of approximately 20 to 70 mm Hg. At a dose of 0.3 mg/kg p.o., ABBOTT-81988 lowered MAP to a normotensive level for more than 24 hr and did not change heart rate. During its antihypertensive effect (delta MAP, -28% approximately -35%), ABBOTT-81988 (0.1-03 mg/kg i.v.) decreased total peripheral resistance (delta resistance, -31% approximately -43%), and cardiac output remained either unchanged or slightly elevated. ABBOTT-81988 (0.3 mg/kg i.v.) produced an additional antihypertensive effect (delta MAP, -12 +/- 2%, n = 5) in captopril-pretreated (10 mg/kg i.v.) hypertensive rats, but captopril (10 mg/kg i.v.) had no effect in ABBOTT-81988-pretreated (0.3 mg/kg i.v.) rats. In the normotensive rat, ABBOTT-81988 (0.3 mg/kg p.o.) had no effect on basal MAP, but it inhibited the AII-induced (0.1 microgram/kg i.v.) pressor response by 51% to 91% for 24 hr, whereas the responses to norepinephrine (0.3 microgram/kg i.v.), vasopressin (0.03 IU/kg i.v.) and bradykinin (3 micrograms/kg i.v.) were not affected. It is concluded that ABBOTT-81988 is a safe and efficacious AII antagonist that may have use in the treatment of human hypertension.

Synthesis and structure activity relationships of cis- and trans-2,3,4,4a,9,9a-hexahydro-1H-indeno[2,1-c]pyridines for 5-HT receptor subtypes.

A series of cis- and trans-fused hexahydroindeno[2,1-c]pyridines have been prepared and evaluated for affinity and selectivity at the 5-HT1A subtype of the serotonin receptor. Using molecular modeling studies we predicted that the 5-methoxy-trans-fused members of this class would exhibit affinity for this site. In agreement with these predictions, trans-5-methoxy-N-propyl-2,3,4,4a,9,-9a-hexahydro-1H-indeno[2,1-c]pyridi ne (6a) demonstrated moderate affinity and high selectivity for the 5-HT1A binding site, whereas the cis-fused isomer 5a demonstrated virtually no affinity at this site. Additional trans-fused analogs from this series, where the nitrogen was substituted with a variety of alkylene imide containing appendages, demonstrated high (0.60-51 nM) affinity and excellent selectivity for the 5-HT1A site. Certain of these analogs, independent of ring-fusion stereochemistry, also demonstrated high affinity for the 5-HT2 binding site.

Antihypertensive activity of ABBOTT-81282, a nonpeptide angiotensin II antagonist, in the renal hypertensive rat.

ABBOTT-81282, 4-(N-butyl-N-[(2-'-[1H-tetrazol-5yl]biphenyl-4-yl)methyl]ami no) pyrimidine-5-carboxylic acid is a novel nonpeptide angiotensin II (AII) antagonist. In vivo studies were performed to evaluate ABBOTT-81282 for its antihypertensive effect, pharmacological mechanism(s) of action, and cardiovascular safety. In the conscious renal artery-ligated (RAL) hypertensive rat, a model of high renin hypertension, ABBOTT-81282 (1-10 mg/kg p.o. and 0.1-1.0 mg/kg i.v.) lowered mean arterial pressure (MAP) in a dose-dependent manner with the ED30 values of 2.2 mg/kg for p.o. administration and 0.08 mg/kg for i.v. administration. At 10 mg/kg p.o., ABBOTT-81282 lowered blood pressure in the RAL rat (delta MAP 66 +/- 9 mm Hg from control MAP 167 +/- 7 mm Hg, n = 6) to a normotensive level (MAP, 115 +/- 5 mm Hg) for greater than 24 h and did not change heart rate. The i.v. administration of 1 mg/kg of ABBOTT-81282 also produced a sustained, long-lasting decrease (delta MAP 27-52 mm Hg) in blood pressure that was significantly different from the vehicle group at 8 h postdosing (143 +/- 3 mm Hg, n = 4 for ABBOTT-81282 vs. 181 +/- 3 mm Hg, n = 6 for vehicle group, p < 0.01). When blood pressure in the renal hypertensive rat was maximally lowered (delta MAP 72 +/- 9 mm Hg, n = 4) following the 1 mg/kg i.v. dose (cumulative) of ABBOTT-81282, additional administration of captopril (3 mg/kg i.v.) produced no further decline in blood pressure. In the conscious normotensive rat, 10 mg/kg p.o. of ABBOTT-81282 had no effect on basal MAP (119 +/- 3 vs. 115 +/- 4 mm Hg, pre- vs. 3.5 h postdosing, n = 4) and heart rate (364 +/- 18 vs. 363 +/- 14 beats/min, pre- vs. 3.5 h postdosing, n = 4) but inhibited the AII (0.1 micrograms/kg i.v.)-induced increase in MAP by 64-70%, while the MAP responses to norepinephrine (0.3 micrograms/kg i.v.), vasopressin (0.03 IU/kg i.v.) and bradykinin (3 micrograms/kg i.v.) remained intact. ABBOTT-81282 was also administered to conscious normotensive rats (n = 4) instrumented with ECG telemetry transmitters. At an i.v. dose of 10 mg/kg, which is 125 times greater than the i.v. ED30, ABBOTT-81282 caused a minimal decrease (< 14%) in MAP and had no effect on ECG waveforms. These data demonstrate that ABBOTT-81282 is a safe and efficacious antihypertensive agent with selective AII antagonism.(ABSTRACT TRUNCATED AT 400 WORDS)

Quantitative structure-activity relationships for substituted aminotetralin analogues. II: Inhibition of dopamine uptake.

Quantitative structure-activity relationships of 44 substituted aminotetralin analogues with regard to dopamine (DA) uptake inhibitory potency are examined in this study. Lipophilic substituents at R3 and hydrophilic substituents at R6 and/or R9 positions, as well as the overall lipophilicity of the molecule contribute toward increasing the inhibitory potency. Unlike with norepinephrine uptake inhibition, little effects are seen from the nitrogen substituent. Among the ring substituents examined, an hydroxy group at the R6 position increases the DA uptake inhibitory potency, whereas a methoxy group at the R7 position decreases it. A comparative quantitative structure-activity relationship study shows that a bromine at the R6 position and/or hydrogen at the R9 position make the compound a better norepinephrine uptake inhibitor than a DA uptake inhibitor, whereas hydrogen at the R6 and/or a substituent larger than a propyl group at the R2 position make the compound a more potent DA uptake inhibitor.

Quantitative structure-activity relationships for substituted aminotetralin analogues. I: Inhibition of norepinephrine uptake.

Quantitative structure-activity relationships of 57 substituted aminotetralin analogues, an overview of their syntheses, and their pharmacological activity are described in this study. Lipophilic substituents at R3 as well as the overall lipophilicity of the molecule contribute toward increasing the inhibitory potency. An ethyl group is preferred, and a group larger than a propyl is not desirable as a nitrogen substituent. Among the ring substituents examined, an hydroxy group at the R6 position and either an unsubstituted R9 position or a methoxy substituent at the R9 position increase the inhibitory potency, whereas a methoxy group at the R7 position decreases inhibitory potency.

Actions of A-75200, a novel catecholamine uptake inhibitor, on norepinephrine uptake and release from bovine adrenal chromaffin cells.

The balance between catecholamine (CA) release and reuptake is closely regulated and determines the effective level of transmitter at the synaptic cleft. Drugs that block CA uptake have potential utility as antidepressant medications. One such drug is racemic (+/-)-(1' R*,3R*)-3-phenyl-1-[1',2',3',4'-tetrahydro-5',6'- methylenedioxy-1'-naphthalenyl-methyl]-pyrrolidine methanesulfonate (A-7500), a novel polycyclic compound developed at Abbott Laboratories. This compound is known to bind to CA transporters in the central nervous system, however, its effects on an intact neurosecretory system have not been studied. In this regard, norepinephrine (NE) release from bovine adrenal chromaffin cells (BACC) is a classic model system for CA release and is an excellent system in which to examine the effects of drugs which modulate neurotransmitter release. We compared the effects of A-75200 and its two constituent enantiomers, A-74111 and A-74112, to the effects of three well-characterized uptake inhibitors, desipramine (DMI), nomifensine and cocaine. We found that the Abbott compounds inhibit [3H]norepinephrine ([3H]NE) uptake with an EC50 comparable to cocaine. In addition, unlike nomifensine and cocaine, these compounds inhibited nicotine- and K(+)-stimulated NE release, whereas histamine-stimulated release was preserved. Thus, the Abbott compounds block the effects on secretion of two agonists (nicotine and K+) which depend on a depolarization-dependent influx of extracellular calcium. We conclude that in addition to blocking NE uptake by inhibiting the NE transporter, the Abbott compounds may modulate peripheral NE release by inhibiting calcium flux through voltage-gated channels. This study demonstrates the utility of bovine adrenal chromaffin cells for preclinical trials of drugs that affect catecholaminergic neurotransmission.

Orthostatic hypotension occurs following alpha 2-adrenoceptor blockade in chronic prazosin-pretreated conscious spontaneously hypertensive rats.

1. Studies were performed to evaluate whether chronic prazosin treatment alters the alpha 2-adrenoceptor function for orthostatic control of arterial blood pressure in conscious spontaneously hypertensive rats (SHR). 2. Conscious SHR (male 300-350 g) were subjected to 90 degrees head-up tilts for 60 s following acute administration of prazosin (0.1 mg kg-1 i.p.) or rauwolscine (3 mg kg-1 i.v.). Orthostatic hypotension was determined by the average decrease (%) in mean arterial pressure (MAP femoral) over the 60-s tilt period. The basal MAP of conscious SHR was reduced to a similar extent by prazosin (-23%(-)-26% MAP) and rauwolscine (-16%(-)-33% MAP). However, the head-up tilt induced orthostatic hypotension in the SHR treated with prazosin (-16% MAP, n = 6), but not in the SHR treated with rauwolscine (less than +2% MAP, n = 6). 3. Conscious SHR were treated for 4 days with prazosin at 2 mg kg-1 day-1 i.p. for chronic alpha 1-adrenoceptor blockade. MAP in conscious SHR after chronic prazosin treatment was 14% lower than in the untreated SHR (n = 8). Head-up tilts in these rats did not produce orthostatic hypotension when performed either prior to or after acute dosing of prazosin (0.1 mg kg-1 i.p.). Conversely, administration of rauwolscine (3 mg kg-1 i.v.) in chronic prazosin treated SHR decreased the basal MAP by 12-31% (n = 4), and subsequent tilts induced further drops of MAP by 19-23% in these rats. 4. The pressor responses and bradycardia to the alpha 1-agonist cirazoline (0.6 and 2 micrograms kg-1 i.v.), the alpha 2-agonist Abbott-53693 (1 and 3 micrograms kg-1 i.v.), and noradrenaline (0.1 and 1.0 micrograms kg-1 i.v.) were determined in conscious SHR with and without chronic prazosin pretreatment. Both the pressor and bradycardia effects of cirazoline were abolished in chronic prazosin treated SHR (n = 4) as compared to the untreated SHR (n = 4). On the other hand, the pressor effects of Abbott-53693 were similar in both groups of SHR, but the accompanying bradycardia was greater in SHR with chronic prazosin treatment than without such treatment. Furthermore, the bradycardia that accompanied the noradrenaline-induced pressor effect in SHR was similar with and without chronic prazosin treatment despite a 47-71% reduction of the pressor effect in chronic alpha 1-receptor blocked SHR.(ABSTRACT TRUNCATED AT 400 WORDS)

Molecular design of novel ligands for 5-HT1A receptors.

Serotonin (5-HT) is a potent bioactive substance known to function through a number of different receptor types and subtypes. In our attempt to develop new agents that would interact selectively at certain 5-HT receptors, especially the 5-HT1A subtype, 8-hydroxy-2-di-n-propylamino tetralin (8-OH-DPAT) served as a template for the design of novel agents sharing aspects of the pharmacophore of 8-OH-DPAT and 5-HT. 5-HT contains no center of asymmetry, and 8-OH-DPAT shows only very modest stereospecificity for 5-HT1A receptors. To develop agents having enhanced potency and selectivity for the 5-HT1A site, several ring systems offering enhanced conformational rigidity which approximate the oxygen to nitrogen interatomic distances of 8-OH-DPAT and (to a lesser extent) 5-HT were synthesized. Exemplary ring systems include the 8-alkoxy-hexahydroindeno[1,2-c]pyrrole, 5-alkoxy-hexahydro-1H-indeno-[2,1-c]pyridine, and 9-alkoxy-hexahydro-1H-benz[e]isoindole systems. These conformationally restricted molecules demonstrated moderate stereospecificity in their interaction with the 5-HT1A binding site, which was enhanced in compounds with larger nitrogen substituents. Appropriate choice of such derivatives led to highly potent compounds selective for 5-HT1A sites compared with their activity at other 5-HT and/or adrenergic receptors. The pharmacological profile of compounds which appear to act as agonists at 5-HT1A receptors in the central nervous system to lower blood pressure in animal models of hypertension is presented.

Alpha 2-adrenergic receptors and calcium: alpha 2-receptor blockade in vascular smooth muscle as an approach to the treatment of hypertension.

Vascular contractile effects of postsynaptic alpha 2-adrenergic receptor stimulation are believed to involve transmembrane calcium influx. Although the current knowledge of the alpha 2-receptor response coupling of vascular smooth muscle contractions is still limited, the fundamental mechanism(s) may involve the extracellular calcium utilization process. This is mediated via the alpha 2-receptor operated calcium channel, which can be pharmacologically distinguished from that mediated via the potential-dependent calcium channel. Therefore, vascular selective alpha 2-antagonists may produce vasorelaxation via a calcium inhibitory action that is different from that of the typical calcium channel blockers. The literature on the in vitro isolated vascular tissue models has been reviewed with emphasis on the methodology for study of alpha 2-antagonist-induced vascular relaxation via selective blockade of the alpha 2-receptor-operated calcium channel. The alpha 2-adrenergic receptors, like alpha 1-receptors on vascular smooth muscle, serve an important role in the control of the arterial, as well as the venous tone in experimental animals and humans in relationship to sympathetic and humoral adrenergic activation of the cardiovascular system. Of particular importance is the possibility that alterations in vascular control of alpha 2-adrenergic mechanisms may lead to increased intracellular free calcium concentrations, thereby causing elevated vascular resistance and high blood pressure. This view is consistent with the long held concept that disturbances of cellular calcium metabolism play a primary role in the pathogenesis of various forms of hypertension. Consequently, selective blockade of vascular alpha 2-adrenergic receptors would be a feasible approach for antihypertensive therapy. This type of antihypertensive agent would be expected to exhibit fewer side effects with efficacy, directed towards the etiology of hypertension.