Novel 8 alpha-ergolines with inhibitory and stimulatory effects on prolactin secretion in rats

The effects of additional treatment with terguride, a partial dopamine agonist, on hyperprolactinemia induced by antipsychotics in schizophrenia patients: a preliminary study

Hyperprolactinemia is a frequent consequence of treatment with antipsychotics. Earlier studies have indicated that terguride, which is a partial dopamine agonist, reduces the prolactin levels that are induced by prolactinemia. Thus, we examined the dose effects of adjunctive treatment with terguride on the plasma concentrations of prolactin in patients with elevated prolactin levels resulting from antipsychotic treatment. Terguride was concomitantly administered to 20 schizophrenic patients (10 males and 10 females) receiving paliperidone and risperidone. The dose of terguride was 1.0 mg/day. Sample collections for prolactin were conducted before terguride (baseline) and 2-4 weeks after administration. The samples were obtained after the morning dose of terguride. The average (± standard deviation) plasma prolactin concentration during terguride coadministration was significantly lower than the baseline concentration in females (82.3±37.1 ng/mL versus 56.5±28.5 ng/mL, P<0.01) but not in males (28.8±18.0 ng/mL versus 26.2±13.1 ng/mL, not significant). Additionally, a significant correlation between the ratio of prolactin reduction and the baseline prolactin concentration was identified in males (r s=-0.638, P<0.05) but not in females (r s=-0.152, not significant). Many patients complained of various adverse events following terguride administration, such as insomnia, agitation, and/or the aggravation of hallucinations. This study suggests that additional treatment with terguride decreases the prolactin concentrations in females experiencing high prolactin levels as a result of antipsychotic treatment. However, its utility for schizophrenia may be diminished because of its low tolerability.

Proterguride, a highly potent dopamine receptor agonist promising for transdermal administration in Parkinson's disease: Interactions with α1-, 5-HT2- and H1-receptors

Dopamine receptor agonists play an important role in the treatment of Parkinson's disease and hyperprolactinemic conditions. Proterguride (n-propyldihydrolisuride) was already reported to be a highly potent dopamine receptor agonist, thus its action at different non-dopaminergic monoamine receptors, alpha(1A/1B/1D), 5-HT(2A/2B)- and histamine H(1), was investigated using different functional in vitro assays. The drug behaved as an antagonist at alpha(1)-adrenoceptors without the ability to discriminate between the subtypes (pA(2) values: alpha(1A) 7.31; alpha(1B) 7.37; alpha(1D) 7.35) and showed antagonistic properties at the histamine H(1) receptor. In contrast, at serotonergic receptors (5-HT(2A), 5-HT(2B)) proterguride acted as a partial agonist. The drug stimulated 5-HT(2A) receptors of rat tail artery in lower concentrations than 5-HT itself but failed to evoke comparable efficacy (proterguride: pEC(50) 8.34, E(max) 53% related to the maximum response to 5-HT; 5-HT: pEC(50) 7.03). Agonism at 5-HT(2B) receptors is presently considered to be involved in drug-induced valvular heart disease. Activation of 5-HT(2B) receptors in porcine pulmonary arteries by proterguride (pEC(50) 7.13, E(max) 49%; E(max) (5-HT) 69%), however, occurred at concentrations much higher than plasma concentrations achieving dopaminergic efficacy in humans. The results are discussed focussing on the relevance of action at 5-HT(2B) receptors as well as their significance for a transdermal administration of proterguride. Since it is well accepted that pulsatile dopaminergic stimulation is associated with treatment-related motor complications in the dopaminergic therapy of Parkinson's disease, the transdermal route of administration is of great clinical interest due to the possibility to achieve constant plasma concentrations.

Terguride as a new anti-hyperprolactinemic agent: characterization in rats and dogs in comparison with bromocriptine

Terguride, a derivative of the ergot alkaloid, was characterized as a new anti-hyperprolactinemic agent in rats and dogs in comparison with bromocriptine. Terguride was found to bind selectively to the pituitary dopamine D2-receptors with a high affinity (Kd = 0.39 nM). In reserpinized rats, terguride at 0.03 mg/kg, p.o. significantly reduced the serum prolactin (PRL) level. The PRL lowering effect and the effective dose were longer lasting and about 30 times lower than those of bromocriptine, respectively. In rats bearing estrogen-induced pituitary prolactinoma, chronic terguride induced shrinkage of the prolactinoma as well as reduction of the high serum PRL level. In lactating rats, terguride (1.0 mg/kg, s.c.) reduced milk production in the mammary gland, whereas bromocriptine showed no significant effect up to 10 mg/kg, s.c. Terguride (10 mg/kg, p.o.) did not induce any stereotypy and hypermotility in reserpinized rats, while bromocriptine induced both stereotypy and hypermotility significantly at 10 mg/kg, p.o. In dogs, terguride, like bromocriptine, reduced the serum PRL level, but did not affect the serum levels of growth hormone and luteinizing hormone. In dogs, bromocriptine induced both emesis and PRL-lowering at almost the same dose, whereas emesis-inducing doses of terguride were about 100 times higher than the PRL-lowering dose. These results suggest that terguride as a dopamine D2-agonist is a potent inhibitor of PRL secretion with less neurotropic side effects compared to bromocriptine, and thus a useful drug for the treatment of galactorrhea and hyperprolactinemia including prolactinoma.

Terguride in fluctuating parkinsonian patients: a double-blind study versus placebo

Terguride (TER), a semisynthetic derivative of lisuride, has been found to display dopamine (DA) agonist and DA antagonist effects in animals, depending on the experimental model used. TER (2 mg/day) was compared to placebo in 41 fluctuating Parkinson's disease patients to test its effect on akinesia and dyskinesia. Mean hours "off" decreased at weeks 6 and 12 (p < 0.05) in the TER group but the overall difference from the placebo group was not significant. Only the TER group displayed a decrease over time in mean Columbia University Rating Scale total score "on" and "off" (p = 0.001 and p = 0.03, respectively). Duration of involuntary movements and resulting disability were not significantly different between patients on TER and those on placebo administration. In the overall evaluation, patients preferred TER (p = 0.01). Tolerance of TER was very good in all but one patient whose wearing-off increased; no one dropped out because of side effects. This 3-month double-blind study showed that TER, added to stable doses of L-dopa, may have slight antiparkinsonian efficacy.

2-Bromolisuride, an ergot derivative, with dopamine antagonistic and serotonin agonistic properties

The open-field test was used to study the involvement of dopaminergic and serotonergic mechanisms in the effects of 2-bromolisuride on locomotor activity in the rat. 2-Bromolisuride produced a dose-dependent inhibition of spontaneous locomotor activity. This is most likely due to an antagonistic action at postsynaptic dopamine receptors. Low doses of 2-bromolisuride potentiated apomorphine-induced hypermotility. This potentiating effect was not mediated by a blockade of presynaptic dopamine receptors, because it was not prevented by 6-OHDA lesion of the nucleus accumbens. The potentiating effect of 2-bromolisuride was completely blocked by the serotonin antagonists cyproheptadine and ritanserin. It is suggested that 2-bromolisuride possesses dopamine antagonistic and serotonin agonistic properties.

Relative dopamine D1 and D2 receptor affinity and efficacy determine whether dopamine agonists induce hyperactivity or oral stereotypy in rats

The effects of a range of dopamine (DA) agonists on stereotyped behaviour in rats were analysed and compared both with the affinity of the compounds for D1 and D2 receptor binding sites in vitro and their ability to stimulate the adenylate cyclase activity in rat striatal homogenates. Full and partial agonists at the D1 receptor coupled to adenylate cyclase do not induce sterotypies when given alone, whereas full D2 agonists (e.g. quinpirole) induce hyperactivity but not oral sterotypies. Partial D2 agonists (e.g. (-)-3-PPP) only induce sedation. Mixed D1/D2 agonists (e.g. apomorphine) induce both hyperactivity and oral stereotypies. Maximum stereotypies were induced by combination of SK & F 38393 and a series of D2 agonists, including full agonists and the partial D2 agonist B-HT 920, whereas partial agonists with low intrinsic activity (e.g. (-)-3-PPP, EMD 23448) did not induce stereotypies when given together with SK & F 38393. However, these partial agonists reduced the maximum effect of apomorphine, whereas the full agonists (e.g. quinpirole, (-)-NPA) and B-HT 920 had no apomorphine antagonistic activity. The mixed D1/D2 agonists apomorphine and N,N-dipropyl-5,6-ADTN were only weakly influenced by SK & F 38393, or not at all. D1 agonists with central effects, including SK & F 38393, SK & F 81297 (with relatively high efficacies), and the partial agonist SK & F 75670 with low efficacy, changed the hyperactivity induced by quinpirole into maximum oral stereotypy, whereas the peripheral D1 agonist fenoldopam had no such effect. Inhibition of DA and NA synthesis with alpha-methyl-p-tyrosine depleted striatal DA levels by 72 per cent and antagonized the hyperactivity induced by the D2 agonists quinpirole and (-)-NPA, but not that of apomorphine. Combination of SK & F 38393 and quinpirole induced maximum stereotypy in DA-depleted animals. These results suggest that D1 receptor tonus is a necessary prerequisite for the expression of a DA agonist's effect. The hyperactivity induced by full D2 agonists appears to be mediated by D1 tonus provided by endogenous DA activity, but stronger D1 stimulation is necessary to induce oral stereotypy. A high degree of D1 receptor activation increases the ability of partial D2 agonists to induce hyperactivity or oral stereotypies since treatment with both SK & F 38393 and B-HT 920 had marked effects while B-HT 920 was ineffective.(ABSTRACT TRUNCATED AT 400 WORDS)

Pharmacokinetics of proterguride in rat and cynomolgus monkey

1. The pharmacokinetics of proterguride were studied in rat and cynomolgus monkey using 3H- and 14C-labelled drug and a radioimmunoassay for concentration measurements of unchanged drug. 2. Proterguride was rapidly and completely absorbed at low doses but not completely at higher dose levels, especially in rat. 3. Bioavailability was 18% in the monkey (low and high doses) and 79% (low doses) and 38% (high dose), respectively, in the rat. 4. Proterguride was able to pass the blood-brain barrier achieving concentrations in brain similar to those in plasma. 5. Excretion of labelled compounds was mainly in the faeces in rat, but in monkey elimination was equal in faeces and urine.

Pharmacokinetics of bromerguride, a new dopamine-antagonistic ergot derivative in rat and dog

Bromerguride is a novel dopamine antagonistic ergot derivative in which a complete reversed pharmacodynamic profile has been obtained by bromine substitution at position 2 as compared to dopamine agonistic lisuride. The pharmacokinetics of the new drug has been investigated following i.v. and i.g. administration of the 14C-labelled compound to rat (R) and beagle dog (D) with regard to drug registration requirements and to serve other preclinical disciplines (toxicology, pharmacology). Because of incomplete absorption the oral bioavailability was approx. 40% at dose levels of 0.25 mg/kg (R, D) and 4 mg/kg (D) and 20% after i.g. dosing of 5 mg/kg (R). Most of the 14C-label in plasma consisted of unchanged bromerguride apart from small amounts of the N-monodesethyl metabolite, which was also obtained as a biodegradation product in a rat liver perfusion experiment. Bromerguride plasma levels declined with half-lives of 0.7 h and 9 h (R) and 0.2 h and 2.7 h (D) after i.v. treatment. Peak levels in rat brain and plasma were observed within 1-2 h after oral dosing; brain levels accounting for 1/10 of bromerguride plasma levels. Whole body autoradiographs in rat demonstrated that the 14C-label was rapidly distributed into tissues and organs, readily passed the blood-brain and the placental barrier. Bromerguride was excreted to less than 10% unchanged with urine. Excretion was mainly biliary. Most of the 14C-label was recovered in the excreta within 24 h postdose.

Pharmacokinetics and pharmacodynamics in man of the dopamine antagonist ergot derivative, bromerguride

The plasma levels and urinary excretion of the dopamine antagonist, bromerguride, were measured by radioimmunoassay in healthy male volunteers given 50 micrograms i.v. and oral doses of 1 and 2 mg. Plasma prolactin was also measured by radioimmunoassay. Following i.v. injection, the concentration of bromerguride declined biphasically, with half-lives of 7 min and 1.2 h. The total clearance was 32 ml X min-1 X kg-1 and the apparent volume of distribution was 3.61/kg. The bioavailability of oral bromerguride was 29% after 1 mg and 25% after 2 mg. The drug was almost totally metabolized and less than 0.05% of the dose was excreted in urine in 24 h after oral administration. Plasma prolactin levels were increased in a dose-dependent manner for about 8 h. Side-effects were minimal, mainly being tiredness and headache in some of the volunteers.

Therapeutic efficacy of a partial dopamine agonist in drug-free parkinsonian patients

Terguride, a mixed agonist-antagonist of central dopamine receptors, was administered to eight patients with Parkinson's Disease. The clinical symptomatology of all patients improved significantly. The maximum neurological effect of terguride was noted at the highest daily dose (1.2 mg) after 21 days of treatment in all subjects, with a statistically significant average of 50.6% neurological improvement on the Webster scale in respect to admission. All single scores of the Webster scale decreased significantly: swing of the arms, facial expression, bradikinesia, rigidity and gait, particularly. No significant adverse reactions were observed during treatment. Our study in drug-free parkinsonian patients demonstrated that terguride is able to improve the neurological symptoms similar to DA agonists, but without their typical side effects.