Bradycardia induced by mivazerol, a selective alpha 2-adrenoceptor agonist, is amplified during mild hypothermia in the pentobarbital-anesthetized rat.

Mivazerol, 3-[1(H-imidazol-4-yl)methyl]-2-hydroxybenzamide hydrochloride, is a selective alpha 2-adrenoceptor agonist designed for the prevention of myocardial infarction in perioperative patients. Because unintended hypothermia occurs frequently during surgery, we were interested, in this study, to examine the relationship between body temperature and the bradycardic response induced by mivazerol. Experiments were carried out in pentobarbital-anesthetized and artificially ventilated rats. The femoral artery and vein were cannulated for the measurement of blood pressure and heart rate, and for intravenous infusion. Rectal temperature was maintained at 37.5 +/- 0.3 degrees C for normothermic groups or at 35.5 +/- 0.3 degrees C for hypothermic groups. Intravenous infusion of vehicle had no significant effect on mean arterial pressure and heart rate between the normothermic and hypothermic rats. Mivazerol dose-dependently produced a decrease in heart rate in normothermic rats, which became more pronounced in mildly hypothermic rats, but did not induce any significant change in mean arterial pressure in either thermic condition. These results show that the bradycardic effect of mivazerol, an alpha 2-adrenoceptor agonist, is amplified during mild hypothermia, a condition that occurs frequently in perioperative patients.

Mivazerol, a selective alpha 2-adrenoceptor agonist, attenuates tachycardia by intrathecal injection of N-methyl-D-aspartate in the rat.

The intravenous (i.v.) infusion of mivazerol, a new selective alpha 2-adrenoceptor agonist, produced a significant decrease in heart rate but not in blood pressure in pentobarbital-anesthetized Sprague-Dawley rats. The tachycardic response to intrathecal (i.t.) injection of N-methyl-D-aspartic acid (NMDA) was significantly attenuated by the i.v. infusion of mivazerol. The i.t. pretreatment with yohimbine significantly attenuated the bradycardic response to i.v. mivazerol and blocked the effect of mivazerol on the tachycardic response to i.t. NMDA. These results suggest that (1) the bradycardic effect of mivazerol is mediated, at least partly, by spinal alpha 2-adrenoceptors; and (2) there is a possibility of functional antagonism between spinal alpha 2-adrenoceptors and NMDA receptors in the regulation of heart rate.

Methyl-beta-carbolinium analogs of MPP+ cause nigrostriatal toxicity after substantia nigra injections in rats.

Eleven beta-carbolinium compounds (beta C+s) and MPP+ were stereotaxically injected (40-200 nmol in 5 microliter of vehicle) unilaterally into the substantia nigra of anesthetized adult male Sprague-Dawley rats. The rats were sacrificed after three weeks. The ipsilateral striatum was analyzed for dopamine and DOPAC levels with HPLC. The brainstem injection site was fixed and cut coronally. The largest lesion area in each animal was measured using NIH IMAGE. Three beta C+s produced lesions whose mean areas were nearly as large as that produced by MPP+ (defined as 100%): 2,9-Me2-harman (94%), 2-Me-harmol (74%), and 2,9-Me2-norharman (57%). Three other compounds produced somewhat smaller lesions: 2-Me-harmaline (34%), 6-MeO-2-Me-harman (29%), and 2-Me-harmine (25%). The remaining compounds were ineffective (< or = 12%): norharman, 2-Me-norharman, 2-Me-harman, harmine, and 2-Me-6-MeO-harmalan. A 40 nmol dose of MPP+ reduced ipsilateral striatal dopamine to 0.6% of control. None of the beta C+s approached this, although several did significantly reduce striatal dopamine at doses of either 40 nmol (2,9-Me2-harman (37%), 2,9-Me2-norharman (42%), and 2-Me-harman (63%)) or 200 nmol (2-Me-harmaline (23%), norharman (63%), and 2-Me-norharman (64%)). There was a moderate negative correlation between lesion size and dopamine level (r = -0.65). There were also moderately strong correlation between lesion size and dopamine level (r = -0.65). There were also moderately strong correlations (r = 0.39-0.78) between the beta C+ nigral lesion area or striatal dopamine level potencies and their previously described IC50 values for inhibiting mitochondrial respiration or their toxicity to PC12 cells in culture. Interestingly, our correlation analysis revealed a remarkably strong correlation between beta C+ Ki MAO-A values and their toxicity to PC12 LDH release (r = -0.84) or PC12 protein loss (r = 0.79). Although beta C+s appear to be less specific toxins than MPP+, their levels in human substantia nigra are 8-20-fold higher than in cortex, making their role as relatively selective nigral toxins in Parkinson's disease plausible.

ucb 11056, a new potential nootropic drug, amplifies induced cyclic AMP formation in rat brain tissue.

ucb 11056 [2-(4-morpholino-6-propyl-1,3,5-triazin-2-yl)aminoethanol] induced a significant (approximately 25%) increase in cyclic AMP levels in different brain areas following its intraperitoneal injection. This effect started as early as 2 min postinjection and lasted for 30 min, after which cyclic AMP levels returned to normal. In hippocampal slice preparations in vitro, ucb 11056 exerted a strong potentiation of cyclic AMP levels when it was combined with agents such as norepinephrine, forskolin, and isoproterenol. Only a slight effect on cyclic AMP levels was measured when ucb 11056 was incubated alone with hippocampal slices. The potentiating effect of ucb 11056 on norepinephrine-stimulated cyclic AMP formation was partially reduced when slices were pretreated with yohimbine and totally abolished when slices were treated with propranolol. These combined data indicate that (a) ucb 11056 rapidly increases cyclic AMP levels in the rat brain in vivo and (b) ucb 11056 potentiates stimulated cyclic AMP formation in vitro. The data also suggest that the central effect of ucb 11056 might be via the modulation of cyclic AMP generation, most probably mediated through adenylate cyclase activation mechanisms combined with a weak inhibitory activity on the cyclic nucleotide phosphodiesterase activity.

UCB 29120, a novel, potential psychotropic agent, alters norepinephrine and dopamine content of rat brain.

UCB 29120 belongs to a novel family of compounds possessing interesting behavioral and physiological properties. Behavioral studies in the rat have revealed the ability of the compound to inhibit scopolamine-induced amnesia while physiological studies demonstrated a significant drug-induced hypothermic response and increase corticosterone plasma levels following acute administration of the compound. In the present study we examined the time-course effects of acute administration of UCB 29120 on levels of catecholamines (norepinephrine, NE; dopamine, DA), indoleamines (serotonin, 5-HT) and metabolites (3,4-dihydroxyphenylacetic acid, DOPAC; 5-hydroxyindoleacetic acid, 5-HIAA) in the rat hypothalamus. Hippocampal, septal and striatal tissue content of the same were also examined at the longest time point employed. In the hypothalamus, UCB 29120 induced significant decreases in NE content 30 min following administration which persisted for at least an additional 30 min, while significant increases in DA and/or DOPAC (and the DOPAC/DA ratio) were measured as early as 5 min following administration and persisted through at least a total of 120 min. Similar, significant changes in dopaminergic parameters were also evident in the other three brain regions at 120 min post-administration. No significant alterations in hypothalamic 5-HT or 5-HIAA were measured at any time point. Acute administration of UCB 29120 may selectively influence catecholaminergic neurotransmitter systems in rat brain.

Dopamine uptake inhibitory capacities of beta-carboline and 3,4-dihydro-beta-carboline analogs of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) oxidation products.

Potentially endogenous beta-carboline and 3,4-dihydro-beta-carboline alkaloidal compounds were compared, generally as 2-methylated (quaternary) and normethylated pairs, to the neurotoxin, 1-methyl-4-phenyl-dihydropyridinium ion (MPP+), with respect to inhibition of [3H]dopamine uptake into rat striatal synaptosomal preparations. Although less potent than MPP+, several compounds displayed IC50 values for inhibition in the moderate range (12-24 microM). Notably, quaternization generally did not improve inhibitory potency, and the 3,4-dihydro-compounds often were more effective inhibitors than their heteroaromatic analogs. The partially competitive nature of inhibition by one of the more effective pairs, 2-methyl-harmine and harmine, was consistent with uptake of the beta-carbolines by the synaptosomal dopamine uptake system, as was the fact that the accumulation of 2-[14C]methyl-harmine was significantly reduced by low Na+ media and by nomifensine, a potent inhibitor of the dopamine transporter. When viewed with reports that certain 2-methyl-beta-carbolines show MPP+-like toxicity in vitro and in vivo, these studies support the proposal that a mammalian beta-carbolinium compound may be taken up by nigrostriatal neurons and provoke the neuronal degeneration underlying Parkinson's disease.

Elevated cytosolic calcium in cerebrocortical nerve terminals of rats during prolonged ethanol ingestion.

Increases in cytosolic free calcium concentrations ([Ca++]i) may underlie acute neuronal degeneration during ischemic or anoxic episodes, seizures and excitotoxin treatment. With quin-2 and fura-2 fluorescent probes, we have obtained evidence for elevated [Ca++]i in cerebrocortical terminals of adult rats following chronic consumption of ethanol-containing liquid diets for "neurotoxic" durations. Compared to isocaloric carbohydrate-fed controls, ethanol-fed rats had significantly higher [Ca++]i in P2 synaptosomal fractions after 4 months of diet intake, and in purified cerebrocortical synaptosomes after diet ingestion for 10 months. In addition, [Ca++]i in the synaptosomal fractions of ethanol-fed rats from either exposure time were markedly resistant to K(+)-dependent potentiation. Persistently increased synaptic [Ca++]i and a blunted response to K+ depolarization following chronic ethanol ingestion lead us to associate impaired Ca++ homeostasis in the neurodegenerative processes of alcoholism.

Striatal dopaminergic toxicity following intranigral injection in rats of 2-methyl-norharman, a beta-carbolinium analog of N-methyl-4-phenylpyridinium ion (MPP+).

Methylated beta-carboline compounds are mammalian indole metabolites that we have proposed to be endogenous neurotoxins due to their structural similarity to MPP+, the active oxidized product of the dopaminergic toxin, N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Several laboratories have demonstrated that MPP+ administration into the substantia nigra or median forebrain bundle of rats results in extensive depletion of striatal dopamine and its metabolites. We now report that three weeks after intranigral injection of the beta-carboline, 2-methyl-norharman, striatal dopamine, DOPAC, and homovanillic acid (HVA) concentrations ipsilateral to the injection are reduced 41-64% compared to vehicle-injected controls; in individual animals dopamine depletions of 96% were achieved. In addition, at the 2-methyl-norharman injection site in the substantia nigra, large lesions and gliosis were apparent under light microscopic examination. This is the first direct demonstration that a 2-methyl-beta-carbolinium ion is neurotoxic. It lends further validity to the hypothesis that MPP+-like beta-carbolines may be endogenous causative agents in Parkinson's disease.

Uterine total lactic dehydrogenase and isozymes of rats administered steroids.

Endometrial scrapings from intact immature and adult rats as well as from ovariectomized series injected subcutaneously daily for 4 days with estradiol benzoate (0.053 mumol/rat/day) displayed marked increases in total LDH and LDH5 over the controls. The uterine luminal fluids from the estrogen-treated animals were lower in total enzyme and, of the isozymes, LHD5 occurred at levels higher than in the scrapings, and LHD1--LDH3, inclusive, were very low to absent. A few of the fluids which were purulent contained greater total LDH contents. Progesterone (19.1 mumol/rat/day) depressed the control LDH in intact adults but had very little influence on an ovariectomized series, and the distribution of isozymes followed the control patterns. However, estradiol benzoate + progesterone elicited overall LDH levels exceeding the respective controls, being more in the range of the estrogen-treated groups and with a trend toward decreases in LDH5 relative to the estrogen-injected rats.

Total lactate dehydrogenase and its isoenzymes in serum in the presence of penicillamine and other sulfhydryl compounds.

Toward delineation of changes in total lactate dehydrogenase (LDH) and in the distribution of LDH isoenzymes as assessed by polyacrylamide disc electrophoresis, we inbucated human and rat sera with various agents, notably sulfhydryl compounds. Although artefacts were apparent when these agents were used without preliminary adjustment of pH, we saw little alteration in total unitage when one or two volumes of serum was mixed with one volume of any of several thiols, especially penicillamine, at an initial concentration of 0.4 mol/liter and pH 7.0-7.5. Under these conditions, penicillamine caused a loss in LDH-5 after incubation for 1 h at 25 degrees C together with small decreases in mobility of the other four isoenzymes toward the anode. A zymosan region appeared below the albumin and tracking dye area. With longer periods of incubation of rat serum with penicillamine or alpha-mercaptosuccinate, a novel band in the zymogram was noted just above the LDH-4 peak. The observations are discussed in terms of allosteric effectors.