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Biomedical subjects

W Lovenberg

Publications and source records attributed to W Lovenberg.

At least 37 records · Page 2Linked to original sources
PubMed1986

Tetrahydrobiopterin administration to rhesus macaques. Its appearance in CSF and effect on neurotransmitter synthesis.

Tetrahydrobiopterin, the hydroxylase cofactor (BH4) was administered (i.v. 20 mg/kg) to Rhesus monkeys. Within 90 min of its administration CSF cofactor levels increased significantly above baseline levels. Peak CSF levels were attained at 90-180 min time period following cofactor injection and returned to baseline gradually over the next 15 hrs. The increased brain cofactor levels had no apparent effect on synthesis of dopamine, norepinephrine or serotonin as evidenced by a lack of change in the levels of the metabolites homovalillic acid, 3-methoxy-4-hydroxyphenyleneglycol, and 5-hydroxyindoleacetic acid. The present results using primates suggest no apparent effect of increased cofactor levels on monoamine biosynthesis. However, it remains to be explored whether monoamine synthesis could be affected by increased cofactor levels in the pathological situation.

Animals↗
PubMed1986

Tetrahydrobiopterin in dystonia: identification of abnormal metabolism and therapeutic trials.

The pteridine cofactor of tyrosine and tryptophan hydroxylases, tetrahydrobiopterin (BH4), is concentrated in the striatum and other sites of brain monoamine synthesis and is a regulatory factor in the rate-limiting step of catecholamine synthesis. CSF content was decreased in eight patients with dystonic disorders (mean, 13.0 +/- 0.8 pmol/ml CSF compared with 20.6 +/- 1.4 in age-matched normals). We gave several trials of synthetic BH4 intravenously to 10 dystonic patients with benefit for 2 subjects with diurnally fluctuating dystonia, 1 with hemidystonia and parkinsonism, and 1 with generalized torsion dystonia. The findings of biopterin abnormality and the observed clinical improvements may point to a role for the cofactor in the pathogenesis and, possibly, the treatment of some forms of primary dystonia.

Adult↗
PubMed1986

Characterization and autoradiographic localization of multiple tachykinin binding sites in gastrointestinal tract and bladder.

Binding sites for the [125I]Bolton-Hunter-labeled tachykinins substance K (BHSK), eledoisin (BHE) and substance P (BHSP) were investigated using crude membrane suspensions and autoradiography. In smooth muscle membranes from guinea-pig small intestine and rat duodenum, specific binding of BHSK was saturable and reversible, showing a single class of sites with a KD of 1 to 3 nM and maximum number of specific binding sites of 1 to 2 fmol/mg of wet weight tissue. Pharmacological characterization of this binding revealed a novel receptor site (K) with affinity for substance K greater than kassinin greater than or equal to eledoisin greater than neuromedin K greater than substance P greater than physalaemin. Inhibition of the binding of BHSK in membranes from mouse urinary bladder exhibited a similar K-type pattern. In rat duodenum and mouse bladder membranes, the binding of BHE was inhibited by substance K greater than kassinin greater than eledoisin greater than neuromedin K greater than substance P greater than physalaemin indicating the same receptor site as for BHSK. On the other hand, in rat cerebral cortex membranes BHE binding was inhibited by neuromedin K = kassinin = eledoisin greater than physalaemin greater than substance K greater than substance P indicating a definitive tachykinin E receptor site. The same displacement pattern of BHE binding was also detected in longitudinal muscle membranes from the guinea-pig small intestine. In mouse bladder membranes and in rat and guinea-pig intestine, the binding of BHSP was inhibited by substance P greater than physalaemin greater than substance K greater than or equal to eledoisin = kassinin greater than neuromedin K indicating a definitive tachykinin P receptor site. Autoradiographic binding sites for both BHSK and BHSP were seen in circular muscle of the rat stomach, small intestine and colon and in circular and longitudinal muscle of the guinea-pig small intestine and colon. Binding sites for BHSK, but not for BHSP, were seen in the muscularis mucosae of the gastric fundus and colon of the rat. Binding sites for BHSP, but not for BHSK, were seen in mucosa of guinea-pig colon and were densely clustered over ganglia of the myenteric and submucous plexuses in rat and guinea-pig colon. The guinea-pig intestine probably contains all three types of tachykinin binding sites whereas rat duodenum and mouse bladder contain only K and P sites. Some tissues classified previously as SP-P or SP-E may actually contain P and/or K sites.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Increased non-collagen protein synthesis in the posterior cerebral artery in spontaneously hypertensive rats.

When 3H-proline was administered to spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats, its incorporation into non-collagen protein of the posterior cerebral artery or the mesenteric artery was greater in SHR than WKY. Young SHR were treated with either clonidine or 6-hydroxydopamine (6-OHDA). Administration of clonidine decreased the rate of incorporation of 3H-proline into the non-collagen protein of these arteries concomitantly with a reduction of blood pressure in each rat strain. Administration of 6-OHDA slightly decreased the incorporation of the proline into the non-collagen protein of the SHR posterior cerebral artery, but failed to reduce blood pressure in each rat strain. Ultrastructural pictures of the posterior cerebral arteries of the SHR showed numerous adrenergic ganglion cells. Thus, neural factors, especially in the cerebral arteries, may regulate vascular protein synthesis and may be important for the initiation of hypertension in SHR.

Animals↗
PubMed1986

Comparison of various genetic hypertensive rat strains.

Comparative studies on nine genetic hypertensive rat strains [two stroke-prone spontaneously hypertensive rats (SHRSP) and Dahl salt-sensitive (DS) strains, and one strain each of spontaneously hypertensive rats (SHR), Lyon hypertensive rats (LH), Milan hypertensive strain (MHS), genetically hypertensive rats (GH) and Sabra hypertensive rats (SBH)] and their respective controls [two Dahl salt-resistent (DR) strains and one strain each of Wistar-Kyoto rats (WKY), Lyon normotensive rats (LN); Lyon low blood pressure rats (LL), Milan normotensive strain (MNS), genetically normotensive rats (GN) and Sabra normotensive rats (SBN) and their original strain, Sabra rats (SB)], in groups consisting of 6-10 males from each strain, were carried out at 10-12 weeks of age under the same experimental conditions. After checking the developmental course of blood pressure and changes in body weight, they were killed at 12 weeks of age for blood analysis and organ-weight examinations. The SHRSP and SHR showed markedly higher blood pressure levels and earlier blood pressure rises in comparison with other hypertensive strains, although they had higher blood pressure than their respective controls. Among various organ weights examined, all hypertensive strains commonly showed increases in left ventricular weight in proportion to blood pressure rises. Kidney weights were significantly decreased only in MHS compared with MNS, while they were either unchanged or significantly greater in other hypertensive strains. Weights of adrenal glands were greater in the two strains of DS and in LH than in their respective control strains. These comparative data indicate possible differences in the pathogenic mechanism involved in these genetic hypertensive rat strains.

Animals↗
PubMed1986

Genetic rat models for hypertension: guidelines for breeding, care and use.

Hypertension is a complex, multifactorial, polygenic disturbance of blood pressure homeostasis. The development of genetic rat models has contributed significantly to the acquisition of new knowledge on the pathophysiology of hypertension. Since there are multiple genetic rat models currently available and actively in use, and since there is need for guidelines for the breeding, care and use of such animal models, the National Heart, Lung, and Blood Institute (NHLBI) of the National Institutes of Health (NIH) convened an international committee of experts to prepare such guidelines, a synopsis of which is herein presented.

Animal Welfare↗
PubMed1985

Angiotensin II and phorbol ester enhance isoproterenol- and vasoactive intestinal peptide (VIP)-induced cyclic AMP accumulation in vascular smooth muscle cells.

The importance of Ca2+ and cAMP in the regulation of cellular functions has been well demonstrated. We studied the effect of angiotensin II (AII), a potent Ca2+-mobilizing hormone, on cAMP accumulation induced by isoproterenol (ISO) and vasoactive intestinal peptide (VIP) in cultured vascular smooth muscle cells (VSMC). Although the addition of AII alone caused little increase of cAMP, it enhanced ISO- and VIP-induced cAMP accumulations in a dose-dependent manner. This enhancement was mimicked by tumor-promoting phorbol ester but not by Ca2+ ionophore. This observation suggested that AII enhanced agonist-induced cAMP accumulation through the activation of protein kinase C in VSMC.

Angiotensin II↗
PubMed1985

In vitro demonstration of dopamine uptake by neostriatal serotonergic neurons of the rat.

Dopamine (DA) has been suggested as the penultimate agent in the neurotoxic effects of methamphetamine on serotonergic neurons. DA increases the efflux of tritium from rat neostriatal slices preloaded with [3H]serotonin in a concentration-dependent manner. This serotonin (5-HT) release is inhibited by the same selective uptake blockers previously shown to protect serotonergic neurons from the neurotoxic effects of methamphetamine in vivo. The results indicate that the 5-HT uptake carrier transports DA into the serotonergic neuron by a heteroexchange process with 5-HT. This further suggests that the excessive DA release induced by methamphetamine in vivo could lead to the uptake of DA into serotonergic neurons.

Animals↗
PubMed1985

Vasopressin-induced calcium increases in smooth muscle cells from spontaneously hypertensive rats.

Cytosolic free Ca2+ concentrations [( Ca2+]i) were measured in smooth muscle cells (SMC) from spontaneously hypertensive rats (SHR) and age and sex matched Wistar-Kyoto rats (WKY). Resting levels of [Ca2+]i were 114 +/- 6 nM and 116 +/- 5 nM in SMC from WKY and SHR, respectively. Angiotensin II (AII) induced a dose-dependent large increases in [Ca2+]i in SMC. There were no significant differences in resting or AII-stimulated levels of [Ca2+]i when SMC from WKY and SHR were compared. Arg-vasopressin (AVP) caused a similar but smaller [Ca2+]i increase than AII in SMC. AVP caused larger [Ca2+]i increases in SMC from SHR than in SMC from WKY. Although concentrations of AVP higher than those ordinarily detected in plasma were necessary to obtain different responses between SHR and WKY, these differences may be related to the pathogenesis of hypertension.

Aminoquinolines↗
PubMed1985

Increase in cytosolic calcium and phosphoinositide metabolism induced by angiotensin II and [Arg]vasopressin in vascular smooth muscle cells.

Effects of angiotensin II and [Arg]vasopressin on cytosolic free Ca2+ concentration ([Ca2+]i) and phosphoinositide metabolism were studied in cultured aortic smooth muscle cells obtained from Wistar-Kyoto rats and their spontaneously hypertensive substrain. [Ca2+]i was measured using the fluorescent Ca2+ indicator quin2. No clear differences in basal [Ca2+]i were detected between cells derived from the two strains. High concentrations of angiotensin II (greater than or equal to 10 nM) and [Arg]vasopressin (greater than or equal to 100 nM) elicited large and rapid increases in [Ca2+]i, followed by a rapid return to control values. Low concentrations of these peptides (less than or equal to 1.0 nM) elicited small and slow increases in [Ca2+]i that persisted for minutes. These responses were blocked by specific antagonists for each of these peptides. Only high concentrations of angiotensin II caused [Ca2+]i increases in "Ca2+-free" medium, which suggested that high concentrations of angiotensin II could release Ca2+ from intracellular pools. A high concentration of angiotensin II and [Arg]vasopressin elicited progressive accumulations of inositol phosphates. Only high concentrations of angiotensin II caused inositol phosphate accumulation in Ca2+-free medium. Maximal accumulation of inositol phosphate elicited by angiotensin II and [Arg]vasopressin was found to be additive. A desensitization to the effects of both peptides on Ca2+ mobilization occurred despite the continued accumulation of inositol phosphates. These observations indicated that angiotensin II and [Arg]vasopressin interacted with independent receptors, both of which are linked to phosphoinositide breakdown and Ca2+ mobilization.

Adenosine Triphosphate↗
PubMed1985

Thermal denaturation of rat pulmonary and testicular angiotensin-converting enzyme isozymes. Effects of chelators and CoCl2.

In an attempt to assess the biochemical consequences resulting from structural differences between rat pulmonary and testicular angiotensin-converting enzyme, the thermal stability of crude and purified preparations of each enzyme was compared. Structural heterology was verified by molecular weight determinations and by peptide mapping after limited proteolysis with Staphylococcus V8 proteinase. Thermal stability was monitored by changes in catalytic activity following incubations at 55 degrees C in the presence of chelators and CoCl2. Purified pulmonary angiotensin-converting enzyme was more sensitive to inhibition by the chelators EDTA and 1,10-phenanthroline and by the site-directed inhibitor captopril than was the testicular isozyme. Although the pulmonary holoenzyme was unaffected by cobalt, the testicular holoenzyme was inhibited by cobalt in a concentration-dependent manner. Crude pulmonary angiotensin-converting enzyme was significantly more resistant to thermal denaturation than its crude testicular counterpart. The differences in the thermal lability of each isozyme were still present in purified preparations, although the purified enzymes appeared to be more thermally stable than their crude counterparts. Both chelators and cobalt markedly potentiated the thermal denaturation of each isozyme. These data suggest that the structural heterology of the pulmonary and testicular isozymes may affect the interaction of zinc with the respective enzymes and that zinc may contribute to the structural integrity and thermal stability of angiotensin-converting enzyme in each tissue.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1985

Stoichiometric methylation of calcineurin by protein carboxyl O-methyltransferase and its effects on calmodulin-stimulated phosphatase activity.

Calcineurin, a calmodulin-stimulated protein phosphatase, was a substrate for purified bovine brain protein carboxyl O-methyltransferase (protein O-methyltransferase; EC 2.1.1.24) and incorporated up to 2 mol of CH3 per mol of calcineurin. Carboxyl methylation was dependent on the concentrations of S-adenosyl-L-[methyl-3H]methionine and was prevented by addition of the carboxyl methylation inhibitor S-adenosylhomocysteine. The stoichiometry of methyl group incorporation was related to the ratio of methyltransferase/calcineurin. The rate of spontaneous hydrolysis of carboxyl methylester groups on calcineurin increased rapidly above pH 6.5 with those on native carboxyl-methylated calcineurin substantially more labile than for trichloracetic acid-precipitated calcineurin. Polyacrylamide gel electrophoresis in the presence of NaDodSO4 (pH 2.4) confirmed that the A subunit of calcineurin (Mr = 61,000) was the primary site of carboxyl methylation with little, if any, modification of the B subunit (Mr = 18,000). When carboxyl-methylated calcineurin (approximately 1-2 mol of CH3 per mol of protein) was assayed for p-nitrophenyl phosphatase activity at pH 6.5, a marked inhibition of calmodulin-stimulated activity was observed while there was little effect on Mn2+-stimulated phosphatase activity. Thus, calcineurin appears to be an excellent substrate for protein carboxyl O-methylation and this modification, which impairs calmodulin stimulation of phosphatase activity, may be of functional significance.

Animals↗
PubMed1985

Enhanced sympathetic-adrenal medullary response to cold exposure in spontaneously hypertensive rats.

To investigate the regulation of sympathetic-adrenal medullary function in spontaneously hypertensive (SHR) male rats, we measured urinary catecholamine excretion for 4 h at room temperature and also during cold exposure (4 degrees C) in groups of four and 12-week-old stroke-prone SHR (SHRSP), stroke-resistant SHR (SHRSR) and normotensive Wistar-Kyoto (WKY) rats. The effect of cold exposure on 12-week-old adrenal denervated rats was also examined. At room temperature, urinary excretion of epinephrine, but not norepinephrine or dopamine, was increased significantly in four-week-old SHRSP and SHRSR rats compared with age-matched WKY. The enhanced excretion of epinephrine at room temperature was not observed in hypertensive rats at 12 weeks of age. During cold exposure, urinary concentrations of each catecholamine increased markedly in rats of all three strains. In addition, the epinephrine response was significantly enhanced in SHRSP rats and the norepinephrine, epinephrine and dopamine responses were significantly enhanced in SHRSR rats. Following adrenal denervation, the urinary epinephrine response to cold exposure was abolished in all strains. These results reveal an enhancement of sympathetic and neurally-mediated adrenal medullary responses in prehypertensive SHR rats and a greater urinary epinephrine response to cold exposure in four and 12-week-old SHR rats. This alteration in catecholamine secretion may be important in the development and maintenance of this type of experimental hypertension.

Adrenal Medulla↗
PubMed1985

Is Ca2+-calmodulin-dependent protein phosphorylation in rat brain modulated by carboxylmethylation?

Calmodulin stimulation of protein kinase activity in calmodulin-depleted preparations of rat brain cytosol or synaptosomal membranes was attenuated by prior carboxylmethylation of the enzyme source with purified protein-O-carboxylmethyltransferase. Similarly, calmodulin stimulation of highly purified Ca2+-calmodulin-dependent protein kinase was reduced if the kinase was exposed to methylating conditions prior to addition of calmodulin. Biochemical and acidic sodium dodecyl sulfate-gel electrophoretic analyses indicated that all sources of protein kinase activity were substrates for methylation. The specific activity of methyl group incorporation into protein kinase increased with increasing purity of the preparation, reaching values of 1.72 pmol CH3/micrograms protein or 0.15-1.12 mol CH3/mol of holoenzyme. Analysis of ATP binding in cytosol with the use of the photoaffinity probe [32P]8-azido-ATP indicated that carboxylmethylation reduced ATP binding. These results suggest that carboxylmethylation of Ca2+-calmodulin protein kinase may modulate the activity of this enzyme in rat brain.

Animals↗
PubMed1985

Endocrinological control and cellular localization of rat testicular angiotensin-converting enzyme (EC 3.4.15.1).

Hypophysectomy of prepubescent (3-week-old) rats prevented the pubertal development of testicular, but not pulmonary, angiotensin-converting enzyme (EC 3.4.15.1). Additionally, hypophysectomy resulted in a loss of testicular converting enzyme activity in 10-week-old rats that had achieved puberty and had developed enzyme activity. Hormone regimens consisting of FSH/LH (7.5 U/rat X day), hCG (10 U/rat X day), or testosterone (1 mg/rat X day) were employed to ascertain their ability to maintain activity in hypophysectomized rats. All three of the above hormone regimens, if initiated on the first day after hypophysectomy of 10-week-old rats, were capable of maintaining testicular converting enzyme activity. Centrifugal elutriation of dispersed testicular cells indicated that the majority of enzyme activity in mature rats was associated with the germinal cells, a result consistent with the data accumulated from the hormonal studies. Lastly, [3H]captopril bound specifically to cellular fractions enriched in germinal cells. The above studies suggest that the pituitary gland is required for the development and maintenance of testicular angiotensin-converting enzyme in the rat by stimulating steroidogenesis in the testes. Furthermore, the sensitivity of converting enzyme activity to androgen coupled with the centrifugal elutriation and [3H] captopril binding studies strongly support the notion that testicular converting enzyme is associated with germinal cells.

Animals↗