Matti K. Paasonen

Taurine in the osmoregulation of the Brattleboro rat

The function of taurine in mammalian osmoregulation was studied in the Brattleboro rat with hereditary hypothalamic diabetes insipidus (DI). DI rats are chronically dehydrated because of their inability to synthesize vasopressin. One day of water deprivation did not affect the water balance in rats with normal vasopressin synthesis, whereas DI rats were markedly dehydrated and lost considerably body weight. Taurine content and 3H-taurine accumulation by platelets were significantly higher in DI rats, with a further increase after one day of water deprivation. In DI rats, water deprivation also evoked a clear taurine increase in skeletal muscle and in the brain. These findings indicate that taurine has an osmoregulatory function in mammals.

5-Hydroxytryptamine in the blood platelets of cirrhotic and hypertensive patients.

Die Konzentration und Aufnahme von 5HT in die Thrombozyten bei Patienten mit Leberzirrhose waren signifikant niedriger als bei Kontrollen. Die Aufnahme von 5HT in die Thrombozyten bei hypertensiven Patienten war eine Tendenz kleiner als bei Normotensiven, obgleich die endogenen Konzentrationen von 5HT bei beiden Gruppen ähnlich waren.

Blood Platelet as a Model for Monoaminergic Neurons

Publisher Summary Platelets contain usually a number of vacuoles of various shapes and dimensions. These organelles can be involved in the phago- and exocytotic activities of platelets. Vacuoles, small vesicles and fine channels seen in platelets, have been theorized as forming a canalicular system with connections to the cell surface. The platelets of man, rabbit, cattle, and dog also exhibit considerable monoamine oxidase (MAO) activity, while this is missing in cat, horse, and rat platelets. Typical of blood platelets is a marginal bundle of microtubules lying along the cell membrane in the equatorial plane of the cell. The diameter of the platelet microtubules is about 20 to 30 nm, and they are composed of about 12 filamentous subunits. These subunits resemble the filaments or microfibrils that are seen in platelets crossing in the cytoplasm. The microfibrils have been suggested to be thrombosthenin—the contractile protein of platelets. Platelet microtubules are labile structures and disappear when platelets become spherical in cold or incubated with rather high concentrations of various agents such as colchicine, vinca alkaloids, and chlorpromazine.

Inactivation of 5-hydroxytryptamine by mammalian blood platelets

Abstract When the platelet-rich plasma of rabbit is incubated in vitro with 20 μg/ml of tetrabenazine most of the 5-hydroxytryptamine released from the platelets is inactivated. This inactivation is done by the platelets themselves and not by the plasma outside. It is prevented by monoamine oxidase inhibitors and by incubation in nitrogen atmosphere instead of air. Under similar conditions, the human platelets inactivate about 30 per cent of their 5-hydroxytryptamine released and those of rat less than 10 per cent. It is possible that also when released by other mechanisms, 5-hydroxytryptamine is inactivated in blood platelets and that this inactivation has an important role in the metabolism of the amine.

Taurine diet decreases spontaneous and increases exploratory activity of spontaneously hypertensive rats.

Summary Male spontaneously hypertensive Wistar rats (SHR) and normotensive Wistar-Kyoto rats (WKR) were maintained on low taurine (T-) diet and high T (T+) diet (T 3 % in the drinking fluid) and their spontaneous motility and open field exploratory activity were measured at the age of three months. T+ diet decreased the spontaneous motility of the SHR when compared to controls. SHR showed significantly greater open field activity than WKR. This exploratory activity was further enhanced by both T+ and T- diets in the SHR but not in the WKR strain. There were no significant differences between total brain T and 5-HT contents due to the strain or the diet. Taurine rich diet seems to inhibit the spontaneously very intensive activity of the SHR but at the same time to decrease their reactivity to stressful stimuli.

The role of noradrenaline and 5-hydroxytryptamine in the central action of Rauwolfia alkaloids and benzoquinolizine derivatives

Abstract Sedative-like Rauwolfia alkaloids lower the content of 5-hydroxytryptamine and noradrenaline in brain and other tissues. Benzoquinolizine derivatives lacking an indole group have a similar effect upon these amines. A difference in these two classes of compounds was found when the latter substances produced a short sedative effect and brief depression of the amines. In general the results suggest a causal relation between the pharmacological action of the two types of drugs upon the central nervous system and monoamine metabolism. Studies with other benzoquinolizine compounds show a differential effect upon the two amines so that noradrenaline depletion may cause sedation. Reserpine-like drugs do not have identical effects upon brain and peripheral amines. It is possible that tranquilizing effects are exerted through depletion of noradrenaline or its precursors or of other substances yet unknown.

Influence of β-phenylisopropylhydrazine on the ability of blood platelets to retain 5-hydroxytryptamine

Abstract Platelet-rich plasma of rabbits, rats and humans was incubated under various treatments and the 5-hydroxytryptamine (5HT) content of separated platelets was analysed per ml of original plasma volume. More 5HT was found after the incubation when monoamine oxidase (MAO) inhibitor, β-phenyl iso propylhydrazine (PIH) was present in concentrations of 10 −4 or 10 −3 M. Incubation in nitrogen instead of air had similar effect. At higher concentrations (10 −3 or 10 −2 M, according to the species) PIH produced a marked 5HT depletion. Iproniazid, as well as isoniazid, which is not a MAO inhibitor, decreased the platelet 5HT when tested on rat platelet-rich plasma at 10 −2 M. In rabbits platelets PIH (from 10 −5 to 10 −3 M) partly inhibited the release of 5HT produced by tetrabenazine. A nitrogen atmosphere had the same effect and PIH in addition to nitrogen offered no further inhibition. Isoniazid 10 −3 M was ineffective. In suitable concentrations PIH also had an inhibitory action on the 5HT release from platelets of rats and humans. The inhibition of 5HT depletion is assumed to be connected with the inhibition of the platelets ability to inactivate their 5HT.

The Uptake and Metabolism of Noradrenaline in the Isolated Heart of Spontaneously Hypertensive Rat

Isolated hearts of spontaneously hypertensive rats (SHR) were perfused with 3 × 10–7 M 3 H- d , l -noradrenaline. After 5–40-mi

β-alanine and α-L-alanine inhibit the exploratory activity of spontaneously hypertensive rats

1% β-alanine and α-L-alanine, when given for 7 days as the only drinking fluid, inhibited the exploratory activity of adult male spontaneously-hypertensive rats (SHR)_but not that of the normotensive Wistar-Kyoto rats (WKR). β-Alanine decreased the taurine level in the liver of both strains and in the platelets of SHR. α-Alanine decreased the taurine level in the liver of WKR and in the platelets of SHR.