Agonist actions of dihydroergotamine at 5-HT2B and 5-HT2C receptors and their possible relevance to antimigraine efficacy.

1. The pharmaceutical compound, dihydroergotamine (DHE) is dispensed to prevent and reduce the occurrence of migraine attacks. Although still controversial, the prophylactic effect of this drug is believed to be caused through blockade and/or activation of numerous receptors including serotonin (5-HT) receptors of the 5-HT2 subtype. 2. To elucidate if 5-HT2 receptors (5-HT2Rs) may be involved in DHE prophylactic effect, we performed investigations aimed to determine the respective pharmacological profile of DHE and of its major metabolite 8'-hydroxy-DHE (8'-OH-DHE) at the 5-HT2B and 5-HT2CRs by binding, inositol triphosphate (IP3) or cyclic GMP (cGMP) coupling studies in transfected fibroblasts. 3. DHE and 8'-OH-DHE are competitive compounds at 5-HT2B and 5-HT2CRs. 8'-OH-DHE interaction at (5-HT2BRs) was best fitted by a biphasic competition curve and displayed the highest affinity with a Ki of 5 nm. These two compounds acted as agonists for both receptors in respect to cGMP production with pEC50 of 8.32+/-0.09 for 8'-OH-DHE at 5-HT2B and 7.83+/-0.06 at 5-HT2CRs. 4. Knowing that the antimigraine prophylactic effect of DHE is only observed after long-term treatment, we chronically exposed the recombinant cells to DHE and 8'-OH-DHE. The number of 5-HT2BR-binding sites was always more affected than 5-HT2CRs. At 5-HT2BRs, 8'-OH-DHE was more effective than DHE, with an uncoupling that persisted for more than 40 h for IP3 or cGMP. By contrast, the 5-HT2CR coupling was reversible after either treatment. 5. Chronic exposure to 8'-OH-DHE caused a persistent agonist-mediated desensitisation of 5-HT2B, but not 5-HT2CRs. This may be of relevance to therapeutic actions of the compound.

Dihydroergotamine and its metabolite, 8'-hydroxy-dihydroergotamine, as 5-HT1A receptor agonists in the rat brain.

1 In addition to stopping migraine attacks, dihydroergotamine (DHE) is an efficient drug for migraine prophylaxis. Whether 5-HT(1A) receptors could contribute to the latter action was assessed by investigating the effects of DHE and its metabolite, 8'-OH-DHE, on these receptors in the rat brain. 2 Membrane binding assays with [(3)H]8-OH-DPAT and [(3)H]WAY 100635 as radioligands showed that both DHE (IC(50)=28-30 nM) and 8'-OH-DHE (IC(50)=8-11 nM) are high-affinity 5-HT(1A) receptor ligands. 3 Both DHE and 8'-OH-DHE enhanced the specific binding of [(35)S]GTP-gamma-S to the dorsal raphe nucleus and the hippocampus in brain sections, but to a lower extent than 5-carboxamido-tryptamine (5-CT) in the latter area. 4 Both DHE (EC(50)=10.9+/-0.3 nM) and 8'-OH-DHE (EC(50)=30.4+/-0.8 nM) inhibited the firing of serotoninergic neurons in the dorsal raphe nucleus within brain stem slices. 5 Intracellular recording showed that 8'-OH-DHE was more potent than DHE to hyperpolarize CA1 pyramidal cells in rat hippocampal slices. 6 Both the stimulatory effects of DHE and 8'-OH-DHE on [(35)S]GTP-gamma-S binding and their electrophysiological effects were completely prevented by the selective 5-HT(1A) receptor antagonist WAY 100635. 7 As expected of 5-HT(1A) receptor partial agonists, DHE and 8'-OH-DHE prevented any subsequent hyperpolarization of CA1 pyramidal cells by 5-HT or 5-CT. 8 Through their actions at 5-HT(1A) auto- (in the dorsal raphe nucleus) and hetero-(notably in the hippocampus) receptors, DHE, and even more its metabolite 8'-OH-DHE, can exert both an inhibitory influence on neuronal excitability and anxiolytic effects which might contribute to their antimigraine prophylactic efficiency.

Methods for studying drug effects on superficial human veins.

Direct effects of vasoactive substances on superficial human veins in vivo can be investigated by measuring changes in the diameter of a superficial vein at a standardized congestion pressure which reflect changes in venous tone before and after local infusion of the drugs. The diameter of a superficial hand vein is measured with the aid of a linear variable differential transformer mounted directly on the back of the hand. The central core of the transformer positioned over the summit of the vein moves simultaneously with changes in venous diameter and allows continuous recording of these alterations. A series of ergot alkaloids were investigated with this technique and found to elicit a direct constrictor action when infused locally. Studies on the mode of action of the venoconstrictor effects of ergot alkaloids suggest that they are mediated by stimulation of alpha- and 5-HT-receptors. Similarly, guanfacine, a centrally-acting antihypertensive drug, reduces venous compliance after direct local administration as a result of alpha-adrenoceptor stimulation. The venodilator effect of isoprenaline can be shown in veins preconstricted with noradrenaline, whereas with nitroglycerine, venodilatation is observed by local infusions in veins not preconstricted. This method is therefore useful for studying the direct effects of venoconstrictor and venodilator drugs in man. The technique can also be used to study interactions between different agents and thus to investigate the mode of action of drugs. Drugs can be infused locally at doses which do not elicit systemic effects.

Dihydroergotamine-heparin prophylaxis of postoperative deep vein thrombosis. A multicenter trial. The Multicenter Trial Committee.

In a large, prospective, multicenter investigation of the prophylaxis of deep vein thrombosis (DVT) in patients undergoing elective abdominal, pelvic, and thoracic surgery, 880 patients were randomized into five treatment groups: those receiving (1) dihydroergotamine mesylate, 0.5 mg, plus heparin sodium, 5,000 IU; (2) dihydroergotamine mesylate, 0.5 mg, plus heparin sodium, 2,500 IU; (3) heparin sodium, 5,000 IU alone; (4) dihydroergotamine mesylate, 0.5 mg alone; or (5) placebo. Treatment was initiated preoperatively and continued twice daily for five to seven days. Daily radiofibrinogen uptake tests revealed the following DVT rates: Dihydroergotamine mesylate, 0.5 mg, plus heparin sodium, 5,000 IU, 9.4%; dihydroergotamine mesylate, 0.5 mg, plus heparin sodium, 2,500 IU, 16.8%; heparin sodium, 5,000 IU alone, 16.8%; dihydroergotamine mesylate, 0.5 mg alone, 19.4%; and placebo, 24.4%. Dihydroergotamine mesylate, 0.5 mg, plus heparin sodium, 5,000 IU, was significantly superior to all other treatments. Adverse drug experiences did not differ significantly between groups and consisted primarily of postoperative bleeding (2% to 3%), injection site hematoma (6% to 12%), and wound hematoma (1% to 3%).

Investigation of the venoconstrictor effect of 8' hydroxydihydroergotamine, the main metabolite of dihydroergotamine, in man.

The time course of the venoconstrictor effect of dihydroergotamine and its main metabolite 8' hydroxy-dihydroergotamine was investigated in a placebo-controlled study in seven healthy male volunteers, after direct local infusion of 0.08 and 0.4 micrograms into superficial hand veins. Both dihydroergotamine and 8' hydroxy-dihydroergotamine elicited a similar, marked venoconstrictor effect. The time course of the venoconstrictor action was similar for both compounds; about one third of the effect was present at the end of the infusion, which lasted for 10 min, and it took about a further 20 min for the effect to reach its maximum. The effect then remained fairly constant for the rest of the period of observation of 180 min from the start of the infusion. The data indicate that the pharmacological activity of oral dihydroergotamine is due not only to the unchanged drug but also to its main metabolite, 8' hydroxy-dihydroergotamine, which occurs in plasma in concentrations about 5-7 times higher than those of dihydroergotamine itself. The absolute bioavailability of unchanged dihydroergotamine, therefore, does not reflect the markedly higher bioavailability of pharmacologically active drug.

Atropine-resistant secretion of parotid saliva on stimulation of the auriculo-temporal nerve.

Non-adrenergic non-cholinergic parasympathetic secretory responses in parotid glands of rats have been demonstrated by electrical stimulation of the auriculo-temporal nerve after appropriate blocking drugs and compared with secretion in the absence of these drugs. After atropine +/- adrenergic blocking drugs secretion was greatly reduced but some secretion was always evident at frequencies of 5 Hz and higher. The time taken for secretion to appear was greatly increased and this may relate to an absence of accompanying myoepithelial contraction. Continuous stimulation always produced greater flows of saliva than intermittent bursts of stimulation at higher frequencies both in the absence and in the presence of blocking drugs. Thus it is likely in vivo that secretion is induced by relatively steady nerve-impulse traffic at moderate frequencies rather than by bursts of high frequency stimulation. Possible transmitters contributing to the atropine-resistant secretion are considered.

Histamine skin test in cluster headache: effects of dihydroergotamine with timed release.

The histamine skin test, as modified by Giacovazzo, was carried out on 20 patients with cluster headache and on 20 control subjects, 10 of whom suffered from migraine and 10 who were healthy volunteers not presenting any form of headache. The test was carried out before and after 30 days treatment with timed-release dihydroergotamine methanesulphonate in a dose of 10 mg/day. Data recorded on a "headache time chart" before and after treatment were evaluated by statistical analysis. Block variance analysis was used to evaluate results of three parameters (latency time, hyperemia diameter, extinction time) emerging from the histamine skin test before and after treatment. A statistical comparison was also made of data obtained in basal conditions in the three groups of subjects, in order to confirm the usefulness of this simple test in the diagnosis of cluster headache.

DHE retard for prophylactic therapy of migraine: efficacy and tolerability.

The authors evaluated the efficacy of a DHE methanesulphonate for migraine attacks and its tolerability on liver, gallbladder and cardiovascular system functions. Twenty-eight patients affected by migraine were studied. They were withdrawn from preventive therapy for at least one month and treated for three months. The drug showed a good efficacy with a statistical significant reduction of severity and duration of attacks. No variation of the biochemical and morphological parameters of liver, gallbladder and cardiovascular function were found throughout the treatment.

Planned release dihydroergotamine in common migraine and "tension-vascular headache": multicentre clinical trial.

The antimigraine efficacy of dihydroergotamine methanesulphonate in the pharmaceutical form of planned release capsules has been evaluated. Forty-nine subjects were treated, 39 suffering from common migraine 10 from tension vascular headache, for a period of 90 days, with an oral dose of 15 mg twice daily. The product was found to be efficacious in 71% of the common migraine cases, while unsatisfactory or nil results were obtained in the remaining 29%. In the tension-vascular headache cases, efficacy was 40% compared to 60% unsatisfactory or nil results. Tolerance was good in 43 cases, while transient digestive disorders (nausea and vomiting) occurred in 6; in 2 cases the treatment had to be withdrawn for allergic erythema. The results demonstrate that the drug is indicated in cases of common migraine, while it does not appear to significantly influence the course of attacks of tension-vascular headache.

Heparin with and without dihydroergotamine in prevention of thromboembolic complications of major abdominal surgery. A randomized trial.

We compared the results of dihydroergotamine mesylate administered with low-dose heparin sodium with those of low-dose heparin given alone in a randomized trial based on 181 patients who underwent major abdominal surgery. We found no significant difference in the incidence of thromboembolism between the two groups but a higher incidence of abnormal fibrinogen uptake test results in patients given heparin alone. There was no difference in hemoglobin levels and the number of blood transfusions. We concluded that there is little, if any, clinical advantage in adding dihydroergotamine to low-dose heparin to prevent thromboembolic complications in patients who have undergone major abdominal surgery.

[Effects of dihydroergotamine mesylate (DEM) on the cardiovascular and nervous systems (author's transl)].

Effects of DEM on the cardiovascular, autonomic, and central nervous systems were studied using dogs, rats and rabbits. DEM showed relatively weak effects on the EEG in curarized rabbits and on ambulatory and drinking activities in rats. DEM suppressed dose-dependently the pressor responses induced by norepinephrine, serotonin and bilateral carotid occlusion, but had no effect on the depressor responses induced by acetylcholine and electrical stimulation to the postganglionic vagus nerve in anesthetized dogs. DEM produced a dose-dependent increase in blood pressure, a dose-dependent decrease in heart rate, a transient decrease in respiration rate, and little change in the ECG of anesthetized dogs. The pressor responses induced by DEM were inhibited by phentolamine, methysergide, and indomethacin in anesthetized dogs. With canine femoral arteries, DEM-induced contractions were blocked 10% by phentolamine, 60% by methysergide, and enhanced 10% by indomethacin. On the other hand, DEM-induced contractions of the femoral veins were blocked 30% by phentolamine, 60% by indomethacin, and 10% by methysergide. DEM provoked a significant increase in the level of prostaglandin E in the bathing fluid of the veins but not in that of the arteries. The results suggest that the arterioconstrictor responses induced by DEM are mediated mainly through the serotonin receptors, and the venoconstrictor responses induced by DEM mainly through the enhanced synthesis of prostaglandin E.

[Comparative responsiveness of isolated saphenous, femoral and external carotid arteries and veins of dogs to dihydroergotamine mesylate (DEM) (author's transl)].

Changes in tension of spiral strips of saphenous, femoral and external carotid arteries and veins were measured isometrically. DEM stimulated 6 preparations in almost the same concentration ranges (pD2 values were 8.64 to 8.40). However, the dose-response curves for DEM indicted variations in responsiveness among the different arteries and veins. Compared with norepinephrine (NE) (1)( the intrinsic activity of DEM was 0.002 on saphenous arteries, 0.05 on saphenous veins, 0.03 on femoral arteries, 0.18 on femoral veins, 0.13 on external carotid arteries and 0.13 on external carotid jugular veins. Thus DEM contracted more potently the venous strips from the hind limbs. IN femoral and external carotid arteries, antagonism of serotonin by DEM or methysergide was investigated. DEM displaced the dose-contractile response curves for serotonin in a noncompetitive manner, and the antagonistic response of DEM to serotonin was about 8 times more effective in external carotid arteries (pD'2 value=6.96) than in femoral arteries (pD'2 value=6.05). Methysergide, unlike DEM, antagonized the response to serotonin in a competitive manner at low doses but in a noncompetitive manner in high doses, and was fairly equal in antagonizing response to serotonin in external carotid arteries (pA2 value=that the therapeutic value of DEM in the treatment of orthostatic hypotension is due to its selective anti-serotonin activity on the external carotid arteries.