Effect of dipyridamole on prostanoid production in rat isolated atria.

The effect of 0.01 microM dipyridamole on prostanoid production was studied in atria from normal, acute diabetic and insulin-treated diabetic rats. Diabetes was induced by i.v. administration of 65 mg/kg of streptozotocin (STZ) and the rats were killed 5 days later. Atria were incubated during 60 min in Krebs solution. The prostanoids 6-keto-prostaglandin (PG) F1alpha (6-keto-PGF1alpha) and thromboxane (TX) B2, stable metabolites of prostacyclin and TXA2, respectively, as well as PGE2 were measured by reversed phase high-performance liquid chromatography-UV. In diabetic atria, 6-keto-PGF1alpha production was reduced by 50% whereas TXB2 release was increased two-fold compared to the controls, with a significant decrease in the 6-keto-PGF1alpha/TXB2 ratio. The preincubation with 0.01 microM dipyridamole for 30 min increased 6-keto-PGF1alpha production in control, diabetic and insulin-treated diabetic atria whereas TXB2 release was not modified. This effects provoked an significant increase in the 6-keto-PGF1alpha/TXB2 ratio. In conclusion, STZ diabetes reduces the 6-keto-PGF1alpha/TXB2 ratio impairing the functional status of the atria. Dipyridamole increased this ratio in atria from diabetic and insulin-treated diabetic rats, thus opposing the effects of STZ diabetes. This fact suggests the possibility of a participation of the drug in pathologies characterized by an imbalance in the production of vasodilator and vasoconstrictor prostanoids.

Prostanoid production in hypoxic rat isolated atria: influence of acute diabetes.

The effects of hypoxia on prostanoid production were studied in atria from normal, acute diabetic and insulin-treated diabetic rats. Diabetes was induced by intravenous administration of 65 mg/kg of streptozotocin, the rats were killed 5 days later. Hypoxia was performed by incubation of the atria during 60 min in nitrogen-equilibrated glucose free Krebs' solution followed by 15 min of reoxygenation. The prostanoids 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha) and thromboxane B2 (TXB2), stable metabolites of prostacyclin and TXA2, respectively, as well as PGF2, were measured by reversed phase HPLC-UV. In control atria, the production of 6-keto PGF1 alpha was equivalent to that of PGE2, whereas TXB2 was released in a much smaller amount. In diabetic atria, 6-keto PGF1 alpha production was reduced by 65%, whereas TXB2 release was increased by 158% compared to the controls. When the normal atria were exposed to 60 min of hypoxia, the release of 6-keto PGF1 alpha increased by 142% compared to basal values and remained elevated after 15 min of reoxygenation whereas in diabetic and insulin-treated diabetic tissues the 6-keto PGF1 alpha production was not modified by the hypoxia-reoxygenation period. The release of TXB2 was increased after 60 min hypoxia in normal as well as in diabetic and insulin-treated diabetic tissues and remained elevated during the reoxygenation. The PGE2 output increased only after the onset of the reoxygenation in the three groups studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Benzodiazepines decrease the release of [3H]noradrenaline and of [3H]acetylcholine in the cat superior cervical ganglion.

The effects of two benzodiazepines, diazepam and clonazepam, were studied on the release of [3H]noradrenaline and of [3H]acetylcholine elicited by preganglionic stimulation of the cat isolated superior cervical ganglion and on the contractile responses evoked by either nerve stimulation or exogenous noradrenaline in the cat isolated nictitating membrane. Both 10 microM diazepam and 10 microM clonazepam reduced by approximately 50% the release of [3H]noradrenaline and of [3H]acetylcholine in the cat ganglion whereas they did not modify the contractile responses in the nictitating membrane. It is concluded that benzodiazepines are also peripheral neuroactive agents and that they exhibit a tissue-selective action within the same animal species.

Ionic mechanisms involved in the release of 3H-norepinephrine from the cat superior cervical ganglion.

It has previously been reported that in the isolated cat superior cervical ganglion (SCG) labeled with tritiated norepinephrine (3H-NE), the stimulation of the preganglionic trunk at 10 Hz as well as the exposure to 100 microM exogenous acetylcholine (ACh), produced a Ca++-dependent release of 3H-NE. The present results show that a Ca++-dependent release of 3H-NE was produced also by exposure to either 50 microM veratridine or 60 mM KCl. Tetrodotoxin (0.5 microM) abolished the release of 3H-NE induced by preganglionic stimulation, ACh and veratridine but did not modify the release evoked by KCl. The metabolic distribution of the radioactivity released by the different depolarizing stimuli showed that the 3H-NE was collected mainly unmetabolized. In the cat SCG neither the release of 3H-NE evoked by KCl nor the endogenous content of NE was modified by pretreatment with 6-OH-dopamine (6-OH-DA). On the other hand, this chemical sympathectomy depleted the endogenous content of NE in the cat nictitating membrane, whose nerve terminals arise from the SCG. The data presented suggest that the depolarization-coupled release of NE from the cat SCG involves structures that are different to nerve terminals and that contain Na+ channels as well as Ca++ channels.

Possible relationship between pervasive developmental disorders and platelet monoamine oxidase activity.

1. The present study was undertaken to determine if the platelet monoamine oxidase (MAO) activity of children with childhood-onset Pervasive Developmental Disorders (PDD), atypical PDD and autistic children differs from MAO of normal children of the same age. 2. The kinetic parameters of MAO activity (Km and Vmax for kynuramine as substrate in 100 mM sodium phosphate buffer, pH 7.4 at 37 degrees C) were determined for platelets from autistic (N = 6), childhood onset PDD (N = 6) and atypical PDD (N = 6) children and 14 controls aged 6-10 years. 3. PDD children had significantly lower Km (4.41 +/- 0.26 vs 5.30 +/- 0.23 microM) and Vmax (16.77 +/- 1.56 vs 22.15 +/- 2.16 nmol h-1 mg protein-1) than control children. The reduction in Vmax was demonstrable in MAO activity measured with 100 microM substrate (14.93 +/- 1.13 vs 20.96 +/- 2.10 nmol h-1 mg-1). 4. These data show that childhood-onset PDD patients, in which the syndrome was complete, presented the lowest levels of platelet MAO activity.

Enzymatic activities in brains of diabetic rats treated with vanadyl sulphate and sodium tungstate.

The hypothesis of the present study was that diabetes mellitus might affect brain metabolism. Streptozotocin (STZ)-induced diabetic rats, treated with vanadyl sulphate (V) and sodium tungstate (T) were employed to observe the aspartate aminotransferase (AST), alanine aminotransferase (ALT) and creatine kinase (CK) activities in brain homogenates. Significant increases in AST, ALT and CK activities were found in diabetic brain homogenates against controls, suggesting increments of transamination in brain and/or increases in cell membrane permeability to these enzymes. The increase in brain CK possibly expresses alterations in energy production. The decrease in CK activity caused by V and T treatment in diabetic rats suggests that both agents tend to normalize energy consumption. It is also possible that V and T-induced hypoglycemic effects cause metabolic alterations in brain.

Effect of a reserpine-like agent on the release and metabolism of [3H]NA in cell bodies and terminals.

1. The reserpine-like agent, Ro4-1284 (2-hydroxy-2ethyl-3-isobutyl-9,10-dimethoxy-1,2,3,4,6,7-hexahydro- 11b-[H] benzo (a)quinolizine) releases [3H]noradrenaline ([3H]NA) from prelabelled superior cervical ganglion (cell bodies) and nictitating membrane (nerve endings) of the cat. 2. The potency of Ro 4-1284 29.0 microM was higher in the cell bodies than in the nerve endings. 3. In both tissues, exposure to the reserpine-like agent Ro 4-1284 induced a selective increase in the spontaneous outflow of [3H]DOPEG, while the [3H]OMDA metabolites to the release induced by Ro 4-1284 was very small. 4. The desamination is the preferential way of the metabolic inactivation of the [3H]NA released by the reserpine-like agent in both parts of the noradrenergic neuron.

In vitro release of [3H]noradrenaline by tyramine from the superior cervical ganglion and in the nictitating membrane of the cat.

1. The release and the metabolism of [3H]noradrenaline ([3H]NA) induced by tyramine was studied in the superior cervical ganglion (cell bodies) and in the nictitating membrane (nerve endings) of the cat. 2. Exposure of the ganglia to 58.0 and 174.0 microM tyramine resulted in the release of 13.7 and 11.8% respectively of the total tissue radioactivity. In the nictitating membrane, the fractional release of radioactivity was directly proportional to the concentration of tyramine (5.8, 58.0 and 174.0 microM). 3. In ganglia [3H]DOPEG accounted for 55.8% of the radioactivity released by 58.0 microM tyramine and only 10.5% of the radioactivity was unmetabolized NA. In presence of 174.0 microM tyramine, [3H]NA increased to 28.0% of the total radioactivity and [3H]DOPEG and [3H]OMDA decreased to 45.3 and 18.9% respectively. 4. In the nerve endings, the contribution of [3H]NA, [3H]DOMA and [3H]NMN increased with the concentration of tyramine while [3H]DOPEG decreased. 5. The deamination is the first step of the metabolic inactivation of [3H]NA induced by tyramine in the cell body of the postganglionic adrenergic neuron while in the nerve endings [3H]NA is preferentially O-methylated.

In vitro metabolism of [3H]NA induced by pargyline in the superior cervical ganglion.

The deaminated glycol, [3H]DOPEG, is the main metabolite in spontaneous outflow from ganglia labelled with [3H]NA. After exposure to pargyline 0.5 mM, [3H]NMN formation may be the first step of the metabolism of [3H]NA in the cat superior cervical ganglion.

Effect of nomifensine on platelet monoamine oxidase activity in chronic schizophrenic patients.

1. The levels of platelet MAO activity increase and the frequency of affective symptoms diminish in the depressed chronic schizophrenics treated with nomifensine. 2. Nomifensine has no inhibitory effect in vitro on platelet MAO activity in depressed schizophrenic pellets.

Pertussis toxin sensitive effects of dipyridamole on rat atrial rate.

1. In the spontaneously beating rat isolated atria the effects of dipyridamole (0.01, 0.1, 1 and 10 microM) and of adenosine (10 microM) on the chronotropic responses to exogenous noradrenaline (NA) were compared. 2. Dipyridamole (0.01 microM) reduced the chronotropic responses to NA throughout the entire concentration-response curve. A decrease in the maximal response to the agonist was also observed. 3. Neither the spontaneous outflow of [3H]-NA nor its metabolic distribution were altered by dipyridamole (0.01 microM). 4. As observed with dipyridamole, the concentration-response curve to NA was shifted to the right by 10 microM adenosine. 8-Phenyltheophylline (8-PT), 10 microM prevented the decrease in the chronotropic response to NA produced by both 10 microM adenosine and 0.01 microM dipyridamole. 5. The preincubation of rat atria with 1 micrograms ml-1 pertussis toxin prevented the diminution in the chronotropic responses to NA produced by 0.01 microM dipyridamole. 6. The present results suggest that the decrease caused by dipyridamole in rat atrial chronotropic responses involves the participation of adenosine, probably through the interaction with type A1 adenosine receptors.

In vitro release of 3H-noradrenaline by amphetamine from the superior cervical ganglion of the cat.

The release and metabolism of 3H-noradrenaline (3H-NA) produced by d-amphetamine was studied in the superior cervical ganglion of the cat (cell bodies) and in the nictitating membrane (nerve endings). Exposure of the nictitating membrane to 10 microM d-amphetamine, resulted in the release of 5.1% of the total radioactivity. This was mainly collected as 3H-normetanephrine (3H-NMN) and as 3H-NA; 3H-3,4-dihydroxyphenylglycol (3H-DOPEG) did not contribute to the drug-induced outflow of radioactivity. In contrast, exposure of ganglionic cell bodies to 10 microM d-amphetamine for 10 min released only 1.74% of the total tissue radioactivity and 3H-DOPEG represented the most important fraction of the released radioactivity. When ganglia were exposed to 30 microM d-amphetamine, the radioactivity released was 5.2%; the proportion of 3H-NA and 3H-NMN increased and 3H-DOPEG was reduced. These results show that: a) d-amphetamine releases 3H-NA from prelabeled cell bodies and nerve endings; b) the potency of d-amphetamine was higher in nerve terminals than in cell bodies, and c) at low concentrations of d-amphetamine, the metabolism of the released neurotransmitter differed between both parts of the adrenergic neuron.

Potassium-evoked efflux of [3H]purines from the rat submaxillary gland.

1. Normal, atrophied and denervated submaxillary glands were incubated with [3H]adenine for 1 h. The accumulation of [3H]adenine, expressed as microCi/g tissue, did not differ significantly when the sympathetically denervated glands were compared with the control group. The radioactivity retained in both control and denervated tissues was also similar. 2. In atrophied glands 3H-accumulation as well as 3H-retention were 2-fold higher than these obtained in controls per unit weight, but 30% lower when expressed per gland. 3. The spontaneous efflux of radioactivity, expressed as fractional release, from normal, atrophied and denervated glands prelabelled with [3H]adenine was similar. 4. The outflow of radioactivity was enhanced by exposure of the tissues to 60 mM K+ during 2.5 min. 5. In all three groups, the purine release induced by K+ was the same. 6. Phentolamine 3.1 microM enhanced the K+-induced release of [3H]purine compounds in control and atrophied glands but not in denervated glands. 7. Propranolol 0.3 microM produced no changes among the three experimental groups. 8. Atropine 1 microM and phentolamine 3.1 microM plus atropine 1 microM did not modify the release of tritiated purine compounds in control and denervated glands. 9. Our results cannot discriminate between neuronal or non-neuronal elements as the source of purines released by depolarization but suggest that classical pharmacological tools such as phentolamine and atropine may affect purine metabolism in a complex fashion.