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Biomedical subjects

W Lovenberg

Publications and source records attributed to W Lovenberg.

At least 19 recordsLinked to original sources
PubMed1993

Comparative study of various genetic hypertensive rat strains: blood pressure, body weight, growth and organ weights.

In an attempt to compare various genetic strains of hypertensive rats, representative hypertensive strains and associated controls (male, 1-month-old, 6-10 of each strain and 18 strains in total) were collected at a single center (National Institutes of Health; NIH, United States), maintained under the same experimental conditions with normal sodium NIH open formula diet and studied by a single investigator using standard techniques. Animals were measured for blood pressure (BP) by a tail-cuff method without anesthesia and body weight (BW) at 10 and 12 weeks of age and killed to measure organ weights. Hypertension was severe (> 190 mmHg) in spontaneously hypertensive rats (SHR) and their stroke-prone substrains at 12 weeks of age but mild to moderate (145-160 mmHg) in the rest of the hypertensive strains (Dahl's, Milan, Lyon, Sabra, and New Zealand Strains). Regarding organ size, partial correlation analysis showed that organ weights, except for brain and adrenal glands, are good functions of BW and that weight of the left ventricle (LV) was the only one significantly linked to BP levels. A bivariate regression model for LV weight was obtained as follows: LV(mg) = 1.478 BW(g) + 2.13BP(mmHg) - 51(R = 0.878, P < 0.001). The presence of some genetic factor regulating relative organ size independently of BW and BP was suggested in LV weight as well as in the weight of the other organs. Among the strains, MHS was found to be unique for the smallest kidney size and New Zealand strains for the greatest relative LV size when adjusted to allow for the influence of BP.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Endothelin: a review of its effects and possible mechanisms of action.

The recently identified endothelium-derived peptide, endothelin, is a potent vasoconstrictor, but also binds specifically to many types of smooth muscle and to nerve tissue. Endothelin has been detected in plasma and may have physiological or pathological functions. Like other agonists, endothelin increases the turnover of phosphatidyl inositol and liberates intracellular stocks of Ca2+. It also increases plasmalemmal Ca2+ permeability, an effect that is antagonized by calcium entry blockers in some tissues. However, the characteristics of this antagonism are not always typical of that seen when other types of agonists are employed. It seems that in at least some cell types endothelin might activate specific L-type Ca2+ channels indirectly, perhaps secondarily to the activation of another type of cation channel. The endothelin originally described is one of a family of peptides that are closely related to the sarafotoxins. The comparative pharmacology of these peptides and of some analogues of the originally described endothelin have revealed some surprising differences and may indicate the existence of different endothelin receptors.

Amino Acid Sequence↗
PubMed1989

HIV-1 protease: mutagenesis of asparagine 88 indicates a domain required for dimer formation.

Considerable interest exists in the HIV-1 protease for biochemical studies as a potential therapeutic target of acquired immunodeficiency syndrome. We have produced the retroviral enzyme in E. coli from a synthetic gene encoding the protease that was constructed by assembling six overlapping and complementary oligonucleotides into the vector pKK223-3. When expressed in E. coli, the recombinant protease was able to correctly process the HIV-1 core protein p24 from a beta-galactosidase-gag fusion protein and to use a heptapeptide as a substrate for proteolytic cleavage. A single base pair mutation was identified in a recombinant that resulted in the substitution of lysine for asparagine at position 88 and a significant loss of enzyme activity. Through site-directed mutagenesis, the Asn88 was changed to five other residues representative of all classes of amino acids. The correlation between enzyme activity and amino acid substitution suggests that the protease domain surrounding position 88 affects the protein's potential for forming an active homodimeric protein and hence, indicates a biochemical interaction that could be inhibited by novel antiviral compounds.

Amino Acid Sequence↗
PubMed1988

Characterization of inositol 1,4,5-trisphosphate-stimulated calcium release from rat cerebellar microsomal fractions. Comparison with [3H]inositol 1,4,5-trisphosphate binding.

The abilities of D-myo-inositol phosphates (InsPs) to promote Ca2+ release and to compete for D-myo-[3H]-inositol 1,4,5-trisphosphate [( 3H]Ins(1,4,5)P3) binding were examined with microsomal preparations from rat cerebellum. Of the seven InsPs examined, only Ins(1,4,5)P3, Ins(2,4,5)P3 and Ins(4,5)P2 stimulated the release of Ca2+. Ca2+ release was maximal in 4-6 s and was followed by a rapid re-accumulation of Ca2+ into the Ins(1,4,5)P3-sensitive compartment after Ins(1,4,5)P3, but not after Ins(2,4,5)P3 or Ins(4,5)P2. Ca2+ re-accumulation after Ins(1,4,5)P3 was also faster than after pulse additions of Ca2+, and coincided with the metabolism of [3H]Ins(1,4,5)P3. These data suggest that Ins(1,4,5)P3-induced Ca2+ release and the accompanying decrease in intraluminal Ca2+ stimulate the Ca2+ pump associated with the Ins(1,4,5)P3-sensitive compartment. That this effect was observed only after Ins(1,4,5)P3 may reflect differences in either the metabolic rates of the various InsPs or an effect of the Ins(1,4,5)P3 metabolite Ins(1,3,4,5)P4 to stimulate refilling of the Ins(1,4,5)P3-sensitive store. InsP-induced Ca2+ release was concentration-dependent, with EC50 values (concn. giving half-maximal release) of 60, 800 and 6500 nM for Ins(1,4,5)P3, Ins(2,4,5)P3 and Ins(4,5)P2 respectively. Ins(1,4,5)P3, Ins(2,4,5)P3 and Ins(4,5)P2 also competed for [3H]Ins(1,4,5)P3 binding, with respective IC50 values (concn. giving 50% inhibition) of 100, 850 and 13,000 nM. Comparison of the EC50 and IC50 values yielded a significant correlation (r = 0.991). These data provide evidence of an association between the [3H]Ins(1,4,5)P3-binding site and the receptor mediating Ins(1,4,5)P3-induced Ca2+ release.

Animals↗
PubMed1988

Chronic MAO A and MAO B inhibition decreases the 5-HT1A receptor-mediated inhibition of forskolin-stimulated adenylate cyclase.

The effect of chronic administration of various monoamine oxidase (MAO) inhibitors on the ability of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) to inhibit forskolin-stimulated adenylate cyclase activity was studied. Groups of 12 rats were given either saline, (E)-beta-fluoromethylene-m-tyrosine (MDL 72394 0.25 mg/kg p.o.), clorgyline (1 mg/kg p.o.), selegiline (1 mg/kg p.o.) or tranylcypromine (5 mg/kg p.o.) once a day for 21 days. Biochemical determinations were made 72 h after the final dose. MDL 72394 and tranylcypromine produced a nonselective inhibition of MAO but clorgyline and selegiline selectively inhibited MAO A and MAO B respectively. All treatments that inhibited MAO A also increased tissue levels of 5-HT. Chronic treatment with MDL 72394, clorgyline or tranylcypromine reduced the ability of 8-OH-DPAT to inhibit forskolin-stimulated adenylate cyclase activity. These data suggest that chronic nonselective and chronic MAO A inhibition causes a down-regulation of the 5-HT1A-mediated inhibition of forskolin-stimulated adenylate cyclase activity.

Adenylyl Cyclase Inhibitors↗
PubMed1988

Dystonia with marked diurnal variation associated with biopterin deficiency.

Two pairs of siblings with severe dystonia with marked diurnal fluctuation had both reduced CSF concentration of biopterin and marked symptomatic improvement of the dystonia in response to levodopa. Whether the reduced concentration of biopterin reflects focal abiotrophy of biopterin-containing neurons or deficiency of biopterin synthesis is uncertain. A fifth individual, who had a systemic deficiency of biopterin synthesis, shared the features of reduced biopterin in CSF, marked diurnal variation in the degree of dystonia, and clinical improvement in response to levodopa. Generalized dystonia with marked diurnal fluctuation was therefore shared by the four patients in whom biopterin deficiency was limited to the CNS and the patient with systemic deficiency of biopterin.

Adolescent↗
PubMed1987

Development of an anti-idiotypic antibody that blocks substance P primary antibodies and substance P membrane binding.

Polyclonal antibodies against substance P were raised in rabbits and partially purified. This apparently homogeneous immunoglobulin fraction was used to immunize other rabbits. The anti-idiotypic antibodies derived from these rabbits were substantially more effective in competing with substance P than in competing with beta-endorphin for binding to their respective primary antibodies. The anti-idiotypic antibody was also 50 times more potent in competing with substance P binding than in competing with substance K binding to rat duodenal membranes, a tissue containing receptors for substance P and substance K. The anti-idiotypic antibodies exhibited significant enhancement of substance P induced spasmogenic response on the rat uterus and guinea pig ileum (GPI). The results indicate that it is possible to develop anti-idiotypic antibodies that recognize substance P receptors. These antibodies will be of value in studies of the physiological roles of the neuropeptide, substance P.

Animals↗
PubMed1987

In vitro and in vivo neurochemical effects of methylenedioxymethamphetamine on striatal monoaminergic systems in the rat brain.

A single high dose of methylenedioxymethamphetamine, a psychedelic agent, produced a rapid and persistent depletion of striatal indoles similar to that observed following administration of the serotonergic neurotoxin p-chloroamphetamine. The drug had little effect on dopaminergic variables. Like p-chloroamphetamine, methylenedioxymethamphetamine was found to be a relatively selective agent for inducing [3H]serotonin release in vitro. The serotonin uptake inhibitor, citalopram, blocked both [3H]serotonin release in vitro and striatal serotonin depletion in vivo, indicating that both processes were carrier dependent. In vivo comparisons of the stereoisomers of methylenedioxymethamphetamine indicated two phases of serotonin depletion similar to those reported for p-chloroamphetamine. Although both the (+)- and (-)-stereoisomers produced an acute (3 hr) decrease in striatal indoles, the long-term effects of the drug showed stereoselectivity in that the (+)-enantiomer produced the most dramatic serotonin depletion. Comparison of the effects of the stereoisomers of methylenedioxymethamphetamine and its n-desmethyl analog, methylenedioxyamphetamine, on [3H]serotonin and [3H]dopamine release in vitro showed the (+)-enantiomer of both drugs to be the more potent releasing agent. In spite of its reported lack of hallucinogenic activity, (+)methylenedioxyamphetamine was found to be of a potency similar to that of (+)methylenedioxymethamphetamine in inducing [3H]serotonin release in vitro. The results are discussed in terms of the neurochemical similarities between methylenedioxymethamphetamine and p-chloroamphetamine as well as the proposed role of serotonin release in the behavioral effects of methylenedioxymethamphetamine.

3,4-Methylenedioxyamphetamine↗
PubMed1987

Rapid purification and revised amino-terminal sequence of hirudin: a specific thrombin inhibitor of the bloodsucking leech.

Hirudin is a specific polypeptide thrombin inhibitor consisting of 65 amino acids that is produced by the leech, Hirudo medicinalis. We describe a rapid method for the purification of hirudin from a leech extract. Crude hirudin, purchased from a commercial source, was first fractionated on a DEAE-HPLC column using a salt gradient. Hirudin activity was monitored by inhibition of the thrombin-mediated hydrolysis of a synthetic substrate H-D-Phenylalanyl-Pipecolyl-Arginine-p-Nitroanilide. The fractions containing antithrombin activity were pooled and further purified by reverse-phase HPLC. The homogeneity of purified hirudin was confirmed by a single amino-terminal sequence for 43 residues with Val-Val as the first two amino acids. Residue 33 was Asn rather than Asp as reported previously.

Amino Acid Sequence↗
PubMed1987

Dephosphorylation of synaptosomal proteins P96 and P139 is regulated by both depolarization and calcium, but not by a rise in cytosolic calcium alone.

Depolarization of intact synaptosomes activates calcium channels, leads to an influx of calcium, and increases the phosphorylation of several neuronal proteins. In contrast, there are two synaptosomal phosphoproteins labeled in intact synaptosomes with 32Pi, termed P96 and P139, which appear to be dephosphorylated following depolarization. Within intact synaptosomes P96 was found in the cytosol whereas P139 was present largely in membrane fractions. Depolarization-stimulated dephosphorylation was fully reversible and continued for up to five cycles of depolarization/repolarization, suggesting a physiological role for the phenomenon. The basal phosphorylation of these proteins was at least partly regulated by cyclic AMP, since dibutyryl cyclic AMP produced small but significant increases in P96 and P139 labeling, even in the presence of fluphenazine at concentrations that inhibited calcium-stimulated protein kinases. Depolarization-dependent dephosphorylation was independent of a rise in intracellular calcium, since agents such as guanidine and low concentrations of A23187, which increase intracellular calcium without activating the calcium channel, did not initiate P96 or P139 dephosphorylation. These agents did sustain increases in the phosphorylation of a number of other proteins including synapsin I and protein III. The results suggest that the phosphorylation of these two synaptosomal proteins is intimately linked to the membrane potential and that their dephosphorylation is dependent on both the mechanism of calcium entry and calcium itself, rather than simply on a rise in intracellular free calcium.

Animals↗
PubMed1986

Calcium channel agonists and antagonists regulate protein phosphorylation in intact synaptosomes.

Protein phosphorylation in intact synaptosomes is highly sensitive to alterations in calcium fluxes and was used to probe the possible mechanism of action of the calcium channel agonist BAY K 8644 and antagonists verapamil and nifedipine. These agents (at 1 microM) all increased the basal phosphorylation of a specific set of 4 synaptosomal phosphoproteins termed P139, P124, P96 and P60, but did not alter depolarization-dependent protein phosphorylation. The increases could not be explained by a direct stimulation of protein kinases and appears unrelated to the known effects of these drugs on K+-stimulated neurotransmitter release. This finding may reveal a possible new mechanism of action for drugs which interact with calcium channels.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1986

Methylenedioxymethamphetamine: a potentially neurotoxic amphetamine analogue.

The amphetamine analogue, methylenedioxymethamphetamine (MDMA) has received considerable attention recently as a novel and increasingly popular psychoactive agent. When administered acutely to rats in high doses, MDMA caused a selective and dramatic decrease in brain concentrations of serotonin and its metabolite, 5-hydroxyindoleacetic acid. The depletion of serotonin and its metabolite persisted for up to at least one week after a single injection of MDMA at approximately four to five times the acute dose reported for humans. These results are discussed in terms of the possible neurotoxic effects of MDMA.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1986

Evidence for a specific effect of BHT 920, an azepine derivative, on tyrosine hydroxylase in the dopaminergic system of the rat.

The effect of BHT 920, a putative presynaptic dopamine receptor agonist, on tyrosine hydroxylase was investigated in rats. The activity of the high affinity (BH4) form of striatal tyrosine hydroxylase was investigated dose-dependent manner in rats treated with BHT 920. This effect was pronounced in the dopaminergic system and was not observed to the same extent in the adrenal medulla. In vitro, BHT 920 had no effect upon striatal tyrosine hydroxylase activity. BHT 920 also did not affect either striatal adenylate cyclase activity or the extent of its stimulation by dopamine. The results concerning tyrosine hydroxylase were complemented by measurements of dopamine and DOPA in the striatal and the limbic system. The reduction in DOPA accumulation and in the high affinity form of tyrosine hydroxylase activity elicited by BHT 920 could be blocked by haloperidol, suggesting that BHT 920 may interact with the D2 dopamine receptor although a functional antagonism could not be ruled out. The present results suggest that BHT 920 may exert a specific effect upon tyrosine hydroxylase in dopaminergic nervous tissue which is not mediated by alpha 2-adrenoceptors.

Adenylyl Cyclases↗
PubMed1986

Biological regulation of testicular angiotensin I-converting enzyme.

Angiotensin I-converting enzyme (ACE) from rat testes and lung was purified to homogeneity and partially characterized with respect to physicochemical parameters. Additionally, the biological regulation of testicular ACE by gonadotropins and androgens was investigated was investigated and the cell type with which ACE is associated in testes was identified. Rat testicular ACE is a lower molecular weight, isozymic version of the lung enzyme. Partial proteolysis of each isozyme produces different peptide maps, suggesting unique primary structures for each protein. The sensitivity of each isozyme to Co2+, chelators and thermal denaturation is different, a finding that further supports the hypothesis that structural differences exist between the two isozymes. The pituitary gland is essential for the development during puberty and maintenance during adulthood of testicular ACE. In hypophysectomized mature rats, gonadotropins or androgen can maintain ACE activity to near sham-operated levels. ACE activity in testes appears to be associated almost entirely with various stages of germinal cell development. The function(s) of testicular ACE awaits definition. The mechanism of androgen-maintenance of testicular ACE is unclear. Whether androgen specifically induces gene expression of testicular ACE or simply allows for ACE activity to develop in parallel with spermatogenesis is an unresolved question.

Animals↗
PubMed1986

Inhibition of K+-stimulated [3H]dopamine and [14C]acetylcholine release by the putative dopamine autoreceptor agonist, B-HT 920.

The inhibition of K+-stimulated [3H]dopamine and [14C]acetylcholine release from preloaded rat striatal slices was used to examine the presynaptic selectivity of the putative dopamine autoreceptor agonist, B-HT 920. In the micromolar range, B-HT 920 caused a concentration-dependent inhibition of the release of both labeled neurotransmitters as evoked by 20 mM K+. The effect of B-HT 920 on both [3H]dopamine and [14C]acetylcholine release was completely blocked by (+) butaclamol but not by (-) butaclamol. Sulpiride, a selective D2 antagonist, similarly blocked the inhibitory effect of B-HT 920 on the release of both labeled neurotransmitters indicating both responses were mediated by D2 receptors. (+) Butaclamol alone elevated stimulated [3H]dopamine release suggesting a significant amount of autoreceptor occupancy by endogenously released dopamine. Experiments with tolazoline and the alpha 2 agonist, B-HT 933, did not suggest any involvement of alpha-adrenoceptor activity in the inhibitory effects of B-HT 920 on the release of either transmitter. Inhibition of release was a selective effect of B-HT 920 as the drug was without effect on the K+-stimulated release of [3H]serotonin. The results indicate that in vitro B-HT 920 is active of both pre- and postsynaptic dopamine receptors in contrast to the pattern of effects observed after its in vivo administration.

Acetylcholine↗