Effect of desipramine on directly or indirectly elicited catecholamine pressor responses in rats

Effect of desipramine on spontaneous arterial pressure oscillations in the rat

There has been no previous report on the effect of the noradrenaline uptake inhibitor desipramine on short-term variability of arterial pressure. Mean arterial pressure was recorded in 9 conscious resting rats during 4 consecutive 30-min periods: (1) under baseline conditions, (2) after desipramine administration (2 mg/kg i.v., followed by 1 mg/kg every hour), then after (3) cardiac autonomic blockade with methylatropine and atenolol, and (4) alpha-adrenoceptor blockade with phentolamine. Fast Fourier transform analysis was applied to beat-to-beat data after resampling at 10 Hz of consecutive 205-s time series. Desipramine did not change the mean level and overall variability of mean arterial pressure. However, spectral power in the mid-frequency (0.3-0.5 Hz) band containing the Mayer waves was reduced by more than 80%, and power in the low-frequency (0.05-0.2 Hz) band was enhanced by approximately 50%, especially due to the appearance of a major oscillation centred at 0.095 +/- 0.005 Hz. This slow oscillation was further enhanced after cardiac autonomic blockade and was abolished after alpha-adrenoceptor blockade. In conclusion, desipramine profoundly alters short-term arterial pressure variability in resting rats, mainly by shifting vasomotor waves from 0.4 to 0.1 Hz. Desipramine may prove a valuable pharmacological tool to study the dynamic aspects of arterial pressure control.

Effects of progesterone on cardiovascular responses to amines and to sympathetic stimulation in the pithed rat

1. Blood pressure and heart rate responses to adrenaline, noradrenaline, tyramine, 5-hydroxytryptamine and stimulation of the spinal sympathetic outflow were measured in pithed rats pretreated either with progesterone (20 mg/kg daily for 14 days) or the vehicle solution of ethyl oleate.2. Pretreatment with progesterone increased the durations but not the magnitudes of the blood pressure and heart rate responses to adrenaline and that phase of the response to sympathetic stimulation attributable to amine release from the adrenal medulla.3. Responses to noradrenaline, tyramine, 5-hydroxytryptamine and that phase of the response to sympathetic stimulation associated with amine release from the sympathetic nerves were not significantly different in the two groups.4. Pyrogallol (5 mg/kg) increased the duration but not the magnitude of responses to adrenaline, noradrenaline and sympathetic stimulation in both experimental groups. The increases in duration were consistently less in animals pretreated with progesterone than in controls.5. Pretreatment with progesterone did not affect the total amount of radioactivity nor the proportion of catechol to non-catechol metabolites excreted in the urine during a period of 7.25 h following an intraperitoneal injection of (+/-) isoprenaline-7-(3)H.6. It is concluded that the effects of progesterone may result from a localized decrease in catechol O-methyl transferase activity within the cardiovascular system.

The effect of cocaine and imipramine on tyramine-induced release of noradrenaline-3H from the rat vas deferens in vitro

1. Tyramine 10(-4)M significantly increased release of noradrenaline-7-(3)H (NA-7-(3)H) from rat vas deferens in vitro.2. Neither cocaine 10(-5)M nor imipramine 10(-7)M-10(-6)M significantly reduced tyramine-induced release of NA-7-(3)H.3. Increasing the exposure time to cocaine and imipramine from 10 to 20 min or pre-incubating the tissue with a wide range of NA-7-(3)H concentrations (3.3-333.3 ng/ml.) did not affect the lack of inhibition by cocaine and imipramine.4. It is suggested that the tyramine receptor in rat vas deferens differs from that in other systems and that blockade of tyramine-released noradrenaline at alpha-adrenergic receptors may be the most important mechanism for tyramine antagonism by imipramine-like drugs in this tissue.

The effects of drugs inhibiting catecholamine uptake on tyramine and noradrenaline-induced contractions of the isolated rat vas deferens

1. Cocaine did not antagonize the tyramine-induced contractile response of the isolated rat vas deferens at the same concentrations which markedly potentiated the contractile response to noradrenaline.2. Imipramine and amitriptyline non-competitively antagonized the contractile response to tyramine but did not potentiate noradrenaline. Desmethylimipramine produced both potentiation of noradrenaline and antagonism of tyramine.3. Dexchlorpheniramine non-competitively antagonized the contractile response to tyramine. It also produced an atypical potentiation of noradrenaline in which lower concentrations of noradrenaline were potentiated to a greater extent than higher ones.4. Imipramine inhibited the in vitro uptake of noradrenaline-(3)H in rat vas deferens as did cocaine, desmethylimipramine and dexchlorpheniramine. These results suggest that the alpha-adrenergic blocking property of imipramine masks the potentiation of noradrenaline by uptake inhibition.5. Evidence is also presented which suggests that alpha-adrenergic blockade of released noradrenaline may be the major mechanism for tyramine inhibition by imipramine-like drugs. This may explain why cocaine, which has no real alpha blocking action, is ineffective against tyramine.

Effect of desipramine on the depolarized isolated renal artery

Depolarization of the isolated renal artery of the rat by a potassium-rich solution caused a triphasic response. The artery contracted submaximally then relaxed partially, this relaxation being followed by a slowly developing contracture. Desipramine reduced the height of the initial contraction, increased the relaxation and reduced the contracture. The latter action was antagonized by increasing the calcium ion concentration of the depolarizing solution. Calcium caused a contraction of the depolarized artery and the contraction was reduced by the drug. The results suggest that the relaxation of the depolarized artery produced by desipramine may be due to interference with the action of calcium in initiating and maintaining a contraction of the arterial smooth muscle.