Dual effect of dihydroergotamine and dihydroergotoxin in isolated human femoral veins and arteries

Pharmacology of Oedema Protective Drugs

Objective:

To review the drugs used in the treatment of chronic venous diseases of the lower limb.

Data sources:

Published papers referring to the pharmacology of drugs used in the management of chronic venous insufficiency and varicose veins of the lower limb.

Study selection:

Sixty-four papers referring to the use of horse chestnut extract (aescin), flavonoids, tribnoside and calcium dobesilate have been included.

Data extraction:

Papers were examined to establish the mechanism of action of ‘oedema protective’ drugs.

Data synthesis:

Oedema protective drugs modify the permeability of the microcirculatory endothelium in animal models of oedema and probably in patients with venous disease to reduce transcapillary loss of fluid into the tissues. The exact mechanisms of action remain unclear.

Conclusion:

Animal and clinical studies demonstrate that drugs of the four types included in this review moderate the development of tissue oedema.

Pharmacological opportunities and pitfalls in the therapy of migraine

The mild vasoconstrictor effects of modern antimigraine drugs, such as serotonin (5-HT; 5-hydroxytryptamine)1B/D agonists, have led to a search for nonvasoconstrictor approaches to therapy. Such approaches have included substance P (neurokinin I) antagonists, endothelin antagonists and highly specific 5HT1D agonists. All of these substances are effective in animal models and have no significant vasoconstrictive effects. However, all of them failed to demonstrate any antimigraine effects. Current clinical and experimental evidence therefore supports the view that isolated peripheral trigeminal nerve inhibition is insufficient to relieve acute migraine.

Alpha-adrenoceptors, 5-hydroxytryptamine receptors and the action of dihydroergotamine in human venous preparations obtained during saphenectomy procedures for varicose veins

Changes in tension were monitored isometrically on spiral strips from human saphenous veins obtained during surgical removal of varicose veins. Concentration-response curves for noradrenaline and 5-hydroxytryptamine (5-HT) were established by cumulative administrations, curves for dihydroergotamine were constructed from the mean responses to single concentrations. The use of the antagonists prazosin, yohimbine and pizotifen provided evidence for the existence of both postjunctional alpha 1- and alpha 2-adrenoceptors and for the existence of 5-HT receptors. The venoconstrictor effects of dihydroergotamine were unchanged by prazosin. Yohimbine antagonized both dihydroergotamine and 5-HT at about 60 times higher concentrations than required against noradrenaline whereas pizotifen inhibited responses to both dihydroergotamine and 5-HT at about 100 times lower concentrations than those to noradrenaline. These new results are in contrast to conclusions drawn from animal studies and do not support the suggestion that in man the venoconstrictor activity of dihydroergotamine is mediated through stimulation of alpha-adrenoceptors. The present results strongly suggest that in human saphenous veins the constrictor activity of dihydroergotamine is mediated at least in part through stimulation of 5-HT receptors.

The recording of venous compliance in the conscious dog: a method for the assessment of venoconstrictor agents

Determinations of drug-induced changes in venous compliance were performed in conscious dogs using a linear variable differential transformer. Changes in the diameter of the canine saphenous vein, produced by inflation to 45 mmHg of a sphygmomanometer cuff placed on the upper hind leg, were recorded. The cuff was inflated at 5-min intervals for 2 min before and after drug administration. Validation studies of this new method were performed by investigating the venoconstrictor activity of dihydroergotamine (Dihydergot). The intravenous administration of DHE, either locally or systemically, elicited dose-dependent and longlasting venoconstrictor responses with extremely small interindividual variations. Comparison of the present results to those reported for man suggests that recording of venous compliance in the conscious dog provides data with good predictability.

Pharmacological actions of the main metabolites of dihydroergotamine

Dihydroergotamine (DHE) and 5 of its main metabolites, namely 8'-hydroxy-dihydroergotamine (8'-OH-DHE), 8',10'-dihydroxy-dihydroergotamine (8',10'-OH-DHE), 2,3seco,N(1)formyl,3-keto,8'-hydroxy-dihydroergotamine (8'-OH,N(1)formyl-DHE), dihydrolysergic acid amide (DH-LSA) and dihydrolysergic acid (DH-LS) were investigated on human and canine veins in vitro, on canine veins in situ, and in the ganglion-blocked rat in vivo. Like DHE, the metabolites 8'-OH-DHE, 8', 10'-OH-DHE and DH-LSA caused constriction of human varicose veins and only weak alpha-adrenoceptor blockade. On canine femoral vein strips the same compounds produced predominantly alpha-adrenoceptor blockade and only negligible stimulation. 8'-OH,N(1)formyl-DHE and DH-LS were largely inactive. The same compounds, which were agonists on human vein strips in vitro, induced dose-dependent reduction of venous compliance when infused locally into the dog saphenous vein in situ. In the ganglion-blocked rat, only 8'-OH-DHE and 8',10'-OH-DHE besides the parent drug produced an increase in diastolic blood pressure when injected intravenously. It is concluded that DHE metabolites with considerable venoconstrictor activity may contribute to the selective therapeutic action of DHE.

Characterisation of postjunctional alpha-adrenoceptors in isolated human femoral veins and arteries

In order to characterise the pharmacological properties of postjunctional alpha-adrenoceptors, both the contractile effects of alpha-adrenoceptor agonists and the blocking potencies of selective alpha-adrenoceptor antagonists were studied in isolated human femoral veins and arteries. The veins were more sensitive to noradrenaline than the arteries. Guanfacine had a higher intrinsic activity in veins than in arteries, whereas the reverse was true for phenylephrine. The antagonists rauwolscine and yohimbine were more potent against noradrenaline in the veins than in arteries, while corynanthine was equally potent in either tissue. They antagonised the noradrenaline response in a competitive manner. Prazosin proved to be the most potent competitive antagonist in arteries, while in veins it exerted weak and non-competitive antagonism. The results suggest that the alpha-adrenoceptor population at the postjunctional site differs between human femoral veins and arteries. The veins seem to contain more alpha 2- than alpha 1-adrenoceptors postjunctionally, whereas in the arteries the alpha 1-subtype prevails. The results indicate the possibility of influencing selectively adrenergic reactions in the capacitance and resistance vessels.