Pressor action

Suekawa M, Aburada M, Hosoya E. (1986). Pharmacological studies on ginger. II. Pressor action of (6)-shogaol in anesthetized rats, or hindquarters, tail and mesenteric vascular beds of rats. J Pharmacobiodyn. 9(10) 842-52. 

If adrenaline is administered to an animal which has been pretreated with propranolol the pressor action is potentiated because the a-adrenergic vasoconstriction is not affected but the P vasodilator action is blocked. 

Figure 4. Prevention of Pressor Action of Renin and Hypertensin (Angiotonin) by Amine...

Amine oxidase also was found to have the ability of diminishing or abolishing the pressor action of renin. When an active preparation of the enzyme was injected intravenously into rats, subsequent injections of renin had little effect (Figures 4 and 5). Hypertensin, however, showed only a modified response in these preparations, probably because of the relative slowness of action of the enzyme. Similar results were found with other pressor agents. 

In some recent comparisons of the pressor responses of adrenaline and noradrenaline, the appreciably longer duration of pressor action of the nor compound was noticed, and this is evidenced in the figures shown by Luduena and co-workers (10) in their recent careful quantitative studies on the relative activities of the two compounds as estimated by various methods on different animals and organs of the body. This longer duration of action of noradrenaline indicates that the over-all inactivation rate in the body is indeed slower. This is in agreement with the indications from the work of West (15) on jugu-lar/portal and splenic artery/vein equipressor ratios that the two compounds are apparently inactivated differently by the liver and spleen. 

A significant loss of insulin activity occurred when solutions of amorphous insulin were exposed to ultraviolet radiation (1). The ultraviolet irradiation of phenylephrine HCl results in the formation of a product with demonstrated bronchodilator potency greater than that of the original solution, when tested on perfused guinea pig lungs (2). A solution of epinephrine exposed to radiation from a quartz mercury burner for 35 minutes was reported to produce practically no pressor, but depressor action, when tested on an anesthetized dog. However, the nonirradiated solution produced a marked pressor action with little depressor effect (3). 

Verda DJ, Kneer L, Burge WE. The effect of ultraviolet radiation on the pressor action of epinephrine. J Pharm Expt Therap 1931 42 383-385. 

It is to this substance that the principal physiological action of extracts of ergot are due in exerting a strong pressor action on the circulation thus raising the blood pressure. Besides being found in ergot this compound is found also in cheese and in putrid meat. 

At a dosage of 5 mg/kg (i.v.), tetrandrine was found to inhibit the pressor action of norepinephrine release induced by electrical stimulation of spinal cord Tn-L2. However, tetrandrine (5 mg/kg, i.a.) did not obviously attenuate the hypertensive responses to norepinephrine (0.51-16.91 pg/kg, i.v.), indicating that the alkaloid did not affect a1-adrenoceptor-mediated vasoconstriction. Tetrandrine (5 mg/kg, i.a.) was found to decrease the pressor responses to norepinephrine (0.05 and 0.17 pg/kg, i.v.) and markedly reduce the dose-dependent hypertensive responses to a selective a2-adrenoceptor agonist (B-HT920, i.v.), suggesting that the alkaloid reduced a2-adrenoceptor-mediated vasoconstriction [321]. 

On the contrary, when blood pressure is low, along with low neurogenic tone, as after destruction of the spinal cord, it has a pure pressor action. The response, then, to a large degree reflects neurogenic tone. 

Alkaloid Contraction of guinea pig ileum Pressor action in pithed rat Release of catecholamines from cat adrenal Contraction of frog rectus Blockade of contraction of diaphragm Inhibition of cat knee jerk Inhibition of cat flexor reflex Inhibition of chick flexor reflex Inhibition of chick crossed extensor reflex... 

Vasopressin levels in patients with vasodilatory shock are inappropriately low, and such patients are extraordinarily sensitive to the pressor actions of vasopressin. The combination of vasopressin and norepinephrine is superior to NE alone in the management of catecholamine-resistant vasodilatory shock. Although the efficacy of vasopressin in the resuscitation of patients with ventricular fibrillation or pulseless electrical activity is similar to that of epinephrine, vasopressin followed by Epi appears to be more effective than Epi alone in the treatment of patients with asystole. 

The pressor action of hydroxytyramine is higher than that of tyramine, showing that an additional OH group at the m-position increases the potency. Its other effects are typically sympathomimetic. 

Tryptamine (XIV) is found in some species of Acacia (7). It may be formed by putrefaction bacteria from tryptophan-containing media (63). N-Methyltryptamine (XV) is said to be idential with dipterin which occurs in Girgensohnia diptera Bge. and Arthrophytum leptocladum Popov (64). Results of pharmacological studies show that tryptamines are musculo-tropic and not sympathomimetic (65). They do not dilate the rabbit s pupil and they contract both the rabbit s isolated intestine and guinea pig s uterus. The pressor action of tryptamine is higher than that of N-methyltryptamine. The former is metaboMzed to indoleacetic acid by deamination in the body (13). 

Of the aliphatic and alicyclic amines, the optimal length of the chain should have seven or eight carbon atoms. Any decrease or increase in the number of carbon atoms results in lowering of the intensity of pressor action. Thus isoamylamine or 4-methyl-2-aminooctane is decidedly less active than forthane or clopane. Prolonged duration of action is acquired by the presence of a methyl group adjacent to the nitrogen atom. Such compounds tend to produce tachyphylaxis and inhibit amine oxidase. 

A -Methylation usually weakens the pressor action. Thus A -methyl-ephedrine is less potent than ephedrine. Tyramine is much more active than hordenine. Tryptamine exceeds the activity of its methylated homologs (65). The generalization is, however, not without exception. Clopane is about one-fourth more active than its primary amine, 2-amino-l-cyclopentylpropane (80). If the A -methyl group is replaced by long alkyl chains, the pressor and the sympathomimetic action may be lost (81). 

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