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Biomedical subjects

A Bonaccorsi

Publications and source records attributed to A Bonaccorsi.

At least 37 records · Page 2Linked to original sources
PubMed1977

Plasma nortriptyline and cardiac responses in young and old rats.

1. The relationship between plasma concentrations and cardiac effects of nortriptyline was studied in anaesthetized young and old rats. 2. Nortriptyline was administered by two consecutive intravenous infusions which resulted in a peak plasma concentration followed by steady state values. Increasing infusion rates were followed by proportional increases in the drug plasma concentrations ranging from 0.15 to 6.0 microgram/ml. 3. In young rats, nortriptyline induced an increase in the heart rate, a right rotation of the electrical axis and a prolongation of the PQ interval. Heart rate changes were not correlated with nortriptyline plasma concentrations, while significant correlations were found for the other two parameters. Plasma concentrations inducing 20% increase of the PQ interval and 40 degrees rotation of the electrical axis were 1.65 microgram/ml respectively. Arrhythmias occurred at concentrations higher than 5.2 microgram/ml. 4. Nortriptyline caused more severe cardiac effects in old than in young animals. However, plasma concentrations of nortriptyline in old rats were two to five times higher than those found in young rats at similar infusion rates. A higher concentration of the drug at its sites of action seems to be responsible for the more severe cardiac toxicity of nortriptyline observed in old rats.

Aging↗
PubMed1977

Norepinephrine release in isolated arteries induced by K-free solution.

Helical strips from arteries with a rich sympathetic innervation (rat tail and femoral, and dog mesenteric arteries) develop a sustained contracture when exposed to a K-free physiological salt solution (PSS). The contracture can be blocked by phentolamine and does not occur in arteries whose nerve terminals have been destroyed with 6-hydroxydopamine. The temporal relationship between force development and efflux of NE was determined. Helical strips of rat tail arteries or dog mesenteric arteries were incubated in PSS containing 1-norepinephrine-7-3H([3H]NE). They were then transferred to a superfusion system which allowed isometric recordings and collection of the superfusate for the estimation of [3H]NE content. Following exposure to a K-free PSS force development paralleled NE release and both parameters were potentiated by ouabain. These data demonstrate that this neurogenic mechanism plays a most important role in the K-free contracture of the vascular smooth muscle studied. It is in accord with the observation that NE is released by adrenergic nerves following inhibition of Na+-K+-ATPase.

Animals↗
PubMed1977

Mechanism of potassium relaxation of arterial muscle.

Strips of arterial muscle were prepared from rat tail and femoral arteries and dog mesenteric arteries. All muscles developed a contracture slowly when exposed to a potassium-free solution, but relaxed rapidly when potassium was added to the bath to give a concentration as low as 0.1 mM. The slow contracture is caused by norepinephrine release from intrinsic nerve endings, but the rapid relaxation occurs while the norepinephrine concentration is still high. Contractions produced by exogenous norepinephrine or serotonin in a potassium-free bath were also made to relax by the addition of potassium. After several minutes these relaxations reversed abruptly and spontaneously to return to their original level of contraction. The rapid relaxation was found to be due to an electrogenic transport mechanism which caused hyperpolarization within several seconds after the addition of potassium. This hyperpolarization is believed to be caused by electrogenic ion transport since it exceeded the expected membrane potential based on the potential calculated from potassium concentrations, EK. Hyperpolarization declined within 5-15 min, allowing contraction to redevelop. Ouabain was found to prevent both the potassium-induced relaxation and the cessation of norepinephrine release. However, ouabain prevented relaxation as effectively in denervated as in innervated smooth muscle. We conclude that the initial relaxation of arterial smooth muscle that occurs when potassium is reintroduced into a potassium-free solution is caused by membrane hyperpolarization resulting from the enhanced activity of an electrogenic pump; it is not caused by cessation of norepinephrine release.

Animals↗
PubMed1976

Relationships between chronotropic effect, 1-3H-noradrenaline uptake and tissue concentrations of desipramine, protripyline and doxepin in rat isolated atria.

The pharmacological effects of three tricyclic antidepressant agents (desipramine, protriptyline and doxepin) are evaluated in rat isolated atria in relation to their accumulation and efflux kinetics. The pharmacological effects studed are: inhibition of 1-3H-noradrenaline uptake, potentiation of 1-noradrenaline chronotropic response, and changes in spontaneous atrial rate. All drugs inhibit noradrenaline uptake and potentiate noradrenaline chronotropic response (desipramine congruent to protriptyline greater than doxepin). Desipramine and protriptyline, at concentrations of 10(-7) -- 10(-6)M stimulate the spontaneous rate; higher concentrations (greater than 10(-6)M) depress it. Doxepin has only a negative chronotropic effect. When the drugs are removed from the incubation medium, the depressing effect starts to disappear immediately for doxepin and desipramine and after 20 min for protriptyline. On the contrary the stimulating effect persists after repeatedly washing the preparations. Desipramine, protriptyline and doxepin extensively accumulate in the myocardial tissue (desipramine larger than or equal to protriptyline greater than doxepin). In the efflux studies doxepin is washed out more rapidly than desipramine and protriptyline. Although the kinetics of uptake and efflux of the three compounds are not sufficient to interpret their different pharmacological activities in isolated atria, they give useful information on the persistance of the sympathomimetic effect and the rapid disappearing of the negative chronotropic effect after washing.

Animals↗
PubMed1973

Correlation between desipramine levels and (-)-noradrenaline uptake and chronotropic effect in isolated atria of rats.

1. The uptake of unlabelled and [(14)C]-desipramine was studied in rat isolated atria incubated in a medium containing concentrations of desipramine ranging from 200 pg/ml to 2 mug/ml. The uptake was found to be dose- and time-dependent. Equilibrium was not reached after 2-3 h of incubation unless concentrations of desipramine higher than 1 mug/ml were used.2. The washout curves of atria previously loaded with desipramine showed that the drug is slowly released and that this release is not influenced by its initial tissue concentration.3. The binding appeared to be at non-specific sites and not at sites where noradrenaline is stored since atria taken from rats treated with 6-hydroxydopamine accumulated the drug at the same rate as control atria.4. The inhibition of (-)-noradrenaline uptake and the potentiation of the chronotropic response to (-)-noradrenaline is correlated with the concentration of desipramine in atria for tissue levels of the drug ranging from 0.01 to 1 mug/g. Higher tissue levels show less potentiation of the effect of (-)-noradrenaline or even inhibition of the maximal response to (-)-noradrenaline. These concentrations of desipramine (> 7 mug/g) markedly depressed the atrial rate.5. The results show that despite the accumulation of desipramine by unspecific sites, concentrations of desipramine in the tissue are correlated with the pharmacological response. Furthermore a gradual shift from potentiation to inhibition of noradrenaline response can be obtained with the same bath concentrations of desipramine by increasing the time of incubation.

Animals↗
PubMed1972

Uptake of desipramine by the rat vas deferens.

1. Determinations of desipramine in the isolated rat vas deferens were carried out in order to study the uptake of the drug and to evaluate how this may correlate with the effect on noradrenaline (NA)-induced contraction.2. Vasa deferentia, in contact with concentrations of desipramine of 1 ng-25 mug/ml for 10 min accumulated the drug about 6-fold in respect to the medium. When the time of contact was prolonged to 4 h, desipramine (200 ng/ml) was concentrated about 100-fold. The uptake was not saturable and it was not affected by the presence of imipramine, cocaine, ouabain, dinitrophenol and iodoacetate.3. No metabolic process is involved although the accumulation of desipramine is temperature dependent. The release of desipramine from the vas deferens is exponential and it is not affected by the presence of plasma in the medium.4. No clear correlation was found between tissue concentration of the drug and the potentiation of noradrenaline responses, probably because of the high non-specific binding of the drug to tissue components which may mask specific binding sites for NA resulting in potentiation. However, the concentration of desipramine seems to correlate with the inhibition of NA effect which occurs at high doses of desipramine.

Animals↗