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M C Rubio

Publications and source records attributed to M C Rubio.

9 recordsLinked to original sources
PubMed1992

Effects of i.c.v. lithium chloride administration on monoamine concentration in rat mediobasal hypothalamus.

We investigated the acute effects of a single i.c.v. injection of lithium chloride (LiCl) the neuroamine content of the rat mediobasal hypothalamus (MBH). The effects of lithium on amine synthesis and degradation enzymes were also studied in vitro. Noradrenaline (NA), dopamine (DA), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) concentrations were reduced 10 min after i.c.v. injection of 24 nmol of LiCl and returned to control values 30 min after the injection. Two nmol of LiCl reduced the concentration of DA (10 and 30 min after injection) and 5-HIAA (30 min after injection). LiCl (0.5-10 mM) inhibited tyrosine hydroxylase activity (catecholamine synthesis) in vitro in a concentration dependent manner. The i.c.v. administration of a high dose of LiCl reduced the content of neuroamines in the MBH. This might result from and inhibition of synthesis. A possible link between the observed changes and some reported side effects of lithium therapy is discussed.

Animals↗
PubMed1979

Modulatory role of catecholamines on tyrosine hydroxylase induction.

The possible modulatory role of cytoplasmic catecholamines on tyrosine hydroxylase induction was studied. Rat superior cervical ganglia were kept in organ culture and after 48 h tyrosine hydroxylase activity was determined. Exposure to 10(-4) M carbachol during 4 h almost doubled the control activity. Incubation with 10(-5) M noradrenaline or 10(-5) M dopamine impaired the carbachol-mediated induction of the enzyme. This effect was not blocked by 10(-7) M propranolol, 2.4 X 10(-6) M haloperidol or 3.1 X 10(-6) M phentolamine. Inhibition of monoamine oxidase activity by 5.1 X 10(-4) M pargyline inhibited the effect of carbachol. When the pool of endogenous catecholamines was decreased by alpha-methyl-p-tyrosine, carbachol induced tyrosine hydroxylase to the same extent as in non-depleted ganglia. It is suggested that the long-term regulation of tyrosine hydroxylase is modulated by a strategic cytoplasmic pool of catecholamines.

Animals↗
PubMed1978

Acetylcholine-like activity in the fruit of the black nightshade (Solanaceae).

The presence of acetylcholine in aqueous extracts of the fruit of Solanum nigrum Linn. (black nightshade) has been established based upon the following pharmacological tests: a) isotonic contraction of the isolated toad rectus abdominis; b) negative chronotropic and inotropic action on the isolated toad heart; c) isotonic contraction of the isolated guinea pig's ileum; d) isotonic contraction of the rat's isolated jejunum; 3) decrease on the cat's arterial blood pressure; f) secretory effects on the rat's submaxillary gland. These actions were selectively blocked by curate or atropine and disappeared after incubation of the extract at 37 C with plasma. Further evidence showing that the fruit of the black nightshade contains acetylcholine was obtained by chromatographic separation of the aqueous extract. The average content of acetylcholine was found to be 250 micrograms/g of fruit.

Acetylcholine↗
PubMed1978

Biosynthesis and subcellular localization of histamine in H-110 lymphoma.

The histidine decarboxylase activity has been studied in the H-110 Lymphoma implanted in Balb-c mice. The enzymatic activity has been determined using DL-Histidine 1-14C by measuring the I--14CO2 liberated during the incubation. It has been found that the histidine decarboxylase activity in the tumor is the highest of the studied tissues. The pretreatment for 5 days with two cytostatic drugs, cyclophosphamide and 5-fluoruracile, determined a decrease of the enzymatic activity in the tumor of 33 and 54 per cent, respectively. This effect has not been observed in the lung. The pretreatment of the animals during 10 days with 0.1 mg per kg body of histamine, which in other experimental tumors induces an increase of the endogenous content of histamine, produces a decrease of the tumoral histidine decarboxylase activity. The histamine-14C uptake was not modified by this pretreatment. The subcellular localization of the radioactivity after pretreatment with histamine-14C evidenced that the nuclear fraction of the tumor contained between 2 and 10 times the radioactivity of other tissues of the same animal.

Animals↗
PubMed1977

Effects of db cAMP on tyrosine hydroxylase activity of ganglia and nerve endings.

Preincubation of intact superior cervical ganglia or nictitating membrane for 2 h with dibutyryl cyclic AMP (db cAMP) increased the hydroxylation of tyrosine. This effect was not blocked by the protein synthesis inhibitor, cycloheximide. The Km of tyrosine hydroxylase for the substrate, tyrosine, and for the cofactor, reduced pteridine, were decreased by db cAMP. There were no changes in the Vmax of the enzyme. The inhibitory potency of noradrenaline on the hydroxylation of tyrosine was also decreased. Thus an inductive effect may be ruled out. The activation of the enzyme was only observed when the tissues were preincubated with the db cAMP and not when the cyclic nucleotide was added to the isolated enzyme. Preincubation of cervical ganglia for 4 h with db cAMP increased activity of decarboxylase and monoamine oxidase in tissue homogenates without changing the tyrosine hydroxylase activity.

Animals↗
PubMedDate not supplied

Hemodynamic effects on hepatic blood flow of a selective beta 2-adrenoceptor agonist, clenbuterol, in rat.

Acute clenbuterol administration (50 micrograms/kg, i.v.) to anesthetized normotensive rats, produce a marked reduction in the mean blood pressure, (MBP), about 58 mm Hg. Indocyanine Green clearance analysis (control, 1.83 +/- 0.15: clenbuterol, 1.10 +/- 0.20 ml/min/100 g, P < 0.05) showed that the action in the hepatic vascular bed is opposite to its systemic vasodilator effects. The hepatic blood flow (HBF) appears significantly reduced (control, 8.24 +/- 0.35: clenbuterol, 3.83 +/- 0.71 ml/min/100 g, P < 0.05) whereas the hepatic uptake and excretion proceedings were apparently not affected (control hepatic extraction coefficient, 0.225 +/- 0.024: clenbuterol, 0.300 +/- 0.04, NS). These findings show that a marked reduction in HBF follows systemic vasodilator effects produced by clenbuterol.

Animals↗