Scavenging effects of dopamine agonists on nitric oxide radicals

It has recently been considered that free radicals are closely involved in the pathogenesis of Parkinson's disease (PD), and the level of nitric oxide radical (.NO), one of the free radicals, is reported to increase in PD brain. In the present study, we established a direct detection system for .NO in an in vitro .NO-generating system using 3-(2-hydroxy-1-methylethyl-2-nitrosohydrazino)-N-methyl-1-propa namine as an .NO donor and 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (carboxy-PTIO) by electron spin resonance (ESR) spectrometry and examined the quenching effects of the dopamine agonists pergolide and bromocriptine on the amount of.NO generated. .NO appeared to be scavenged by pergolide and, to a lesser extent, by bromocriptine. In the competition assay, the 50% inhibitory concentration values for pergolide and bromocriptine were estimated to be approximately 23 and 200 microM, respectively. It was previously reported that in vivo treatment of pergolide and bromocriptine completely protected against the decrease in levels of striatal dopamine and its metabolites in the 6-hydroxydopamine-injected mouse. Considering these findings, pergolide and probably bromocriptine may also protect against dysfunction of dopaminergic neurons because of its multiple effects; not only does it stimulate the presynaptic autoreceptors, but it also directly scavenges .NO radicals and hence protects against .NO-related cytotoxicity. This ESR spectrometry method using carboxy-PTIO may be useful for screening other drugs that can quench .NO.

Double-blind assessment of potential pergolide-induced cardiotoxicity

Possible pergolide-induced cardiotoxicity has been reported in open trials. Over a 6-month period of observation, we prospectively analyzed ECGs and 24-hour ambulatory ECG in 23 patients with Parkinson's disease who were randomized in a double-blind fashion to pergolide or placebo treatments. Pergolide therapy was associated with a mild and transient bradycardiac effect, but no clinically significant cardiotoxicity.

SCH 23390 antagonizes apomorphine- and ergot-induced hypothermia

The reportedly specific D-1 dopamine (DA) receptor antagonist SCH 23390 significantly reduced the hypothermia elicited by various DA receptor agonists like apomorphine, pergolide and lisuride. When tested against equihypothermic doses of each agonist, SCH 23390 significantly reduced the hypothermia elicited by apomorphine (0.2 mg/kg s.c.) and by pergolide (0.1 mg/kg i.p.) at doses of 0.025 mg/kg s.c. Doses of 0.050 mg/kg s.c. of SCH 23390 were necessary to reduce the hypothermia elicited by 0.012 mg/kg s.c. of lisuride. Pretreatment with the specific D-2 antagonist (-)sulpiride (50 mg/kg i.p.) completely prevented the hypothermia elicited by lisuride (0.012 mg/kg i.p.), pergolide (0.1 mg/kg i.p.) and apomorphine (0.2 mg/kg s.c.) and shifted to the right the dose-response curve for agonist-induced hypothermia. A study of the interaction between 0.05 mg/kg s.c. of SCH 23390 with various doses of the agonists showed that the effectiveness of SCH 23390 in antagonizing the hypothermia was maximal towards apomorphine and least towards lisuride for which significant antagonism was observed only against the lowest dose tested (0.012 mg/kg s.c.). The reportedly specific D-1 receptor agonist SKF 38393 given in doses up to 20 mg/kg i.p. or intracerebroventricularly up to 100 micrograms failed to influence body temperature while it evoked intense grooming and stimulated motility.

The effect of apomorphine and pergolide on the potassium-evoked overflow of GABA in rat striatum studied by microdialysis

The extracellular GABA concentration in the rat striatum was measured by the microdialysis technique. Addition of pergolide (10(-4) M) to the perfusion medium decreased the GABA overflow induced by high K+ but apomorphine (10(-4) M) had no effect on the GABA overflow. When sulpiride (10(-4) M) was added to the perfusion medium, the pergolide effect on stimulated GABA overflow was abolished. The results indicate that D2-receptors are able to modulate GABA overflow in the striatum.

Neurophysiological evidence that D-1 dopamine receptor blockade attenuates postsynaptic but not autoreceptor-mediated effects of dopamine agonists

The putatively selective D-1 dopamine receptor antagonist SCH 23390 was used to study the role of the D-1 dopamine receptor in mediating the pre- and postsynaptic effects of dopamine agonists in the basal ganglia. SCH 23390 (1 mg/kg) had no significant effect on the tonic activity of substantia nigra dopamine neurons in 47% of the 19 cells studied, while the firing rates of 53% of the cells were increased. SCH 23390 did not shift the dose response of these cells to apomorphine, whereas the selective D-2 antagonist, YM-09151-2 completely blocked apomorphine's inhibitory effects on nigral dopamine cell activity. These results suggest that SCH 23390 does not interact with the D-2 dopamine autoreceptors, but does excite a subpopulation of dopamine neurons presumably through postsynaptic actions. In contrast to its inability to modify the effects of apomorphine on dopamine autoreceptors, SCH 23390 partially to fully reversed the effects of apomorphine on globus pallidus and substantia nigra pars reticulata cell activity and significantly attenuated the effects of apomorphine, pergolide, quinpirole (LY 171555) and d-amphetamine on firing rates of globus pallidus neurons. The D-1 antagonist alone had no significant effect on tonic globus pallidus neuronal activity. SCH 23390 was more potent than haloperidol in its ability to attenuate the effects of apomorphine on pallidal activity, but unlike haloperidol, was unable to totally inhibit these effects, suggesting that the two antagonists block the excitatory effects of apomorphine on pallidal cell firing rates by different mechanisms. The serotonin2 receptor antagonist, ketanserin, had no effect on pallidal or dopamine cell activity, indicating that the effects of SCH 23390 were not mediated through interactions with serotonin2 receptors. These results suggest that D-1 receptor blockade attenuates the postsynaptic, but not autoreceptor-mediated effects of dopamine agonists.

Release of endogenous dopamine and cholecystokinin from rat striatal slices: effects of amphetamine and dopamine antagonists

The release of immunoreactive cholecystokinin (CCK) and dopamine was monitored simultaneously from superfused rat striatal slices. Exposure of the tissue to medium containing elevated K+ or veratrine, induced a marked release of both substances. The addition of dopamine (10(-7) and 10(-6) M), the dopamine agonist pergolide (10(-7) M), the D2-antagonist sulpiride (1 microM) or the D1-antagonist (SCH 23390) had no significant effect on basal overflow or on evoked release of CCK. On the other hand, preincubation of striatal slices with D-amphetamine (10(-5) M) enhanced basal and veratrine-stimulated dopamine release but markedly suppressed evoked CCK release. Sulpiride blocked this action of amphetamine whereas SCH 23390 was ineffective. The data suggests that whereas it is difficult to observe any effects of exogenous dopamine agonists or antagonists on evoked CCK release, endogenously released dopamine appears to interact with D2-receptors to suppress evoked CCK release from rat striatal slices.

Long-term efficacy of pergolide in patients with Parkinson's disease

We report the clinical course of 35 patients with Parkinson's disease who experienced an initially favorable response to pergolide and who were taking the drug for at least 6 months. The duration of pergolide treatment was 6-50 (25 +/- 16 SD) months. Of the 14 patients who remained on pergolide for over 2 years, 12 remained less disabled for 26 +/- 17 SD months, seven enjoyed increased "on" time for 39 +/- 8 SD months, and nine had a lower Hoehn-Yahr stage for 25 +/- 17 SD months. Pergolide was discontinued after 5-39 months in eight patients; six patients then deteriorated. Pergolide can remain efficacious in the treatment of Parkinson's disease for up to 50 months.

Discordant responses of prolactinoma to two different dopamine agonists

A 19-year-old woman presented with headaches, temporal lobe epilepsy and primary amenorrhoea. There was a family history of multiple endocrine adenomatosis. Investigation revealed normal visual fields and acuity, hyperprolactinaemia (48 000 mU/l) and a very large pituitary tumour with extrasellar spread. Treatment with bromocriptine reduced the tumour size and the prolactin level to 2440 mU/l. Six months after the start of therapy, resistance to bromocriptine developed and the prolactin concentration progressively rose to pretreatment levels, despite increasing the dose of bromocriptine to 40 mg/d. At this stage treatment with a second dopamine agonist, pergolide, was effective in reducing the prolactin concentration to normal within four months. Serial CT scans at 1, 6 and 12 months on dopamine agonist therapy showed a progressive decrease in tumour size, which seemed to be maintained even during the period of rising prolactin concentrations due to bromocriptine resistance. This case illustrates that during dopamine agonist therapy a discrepancy may exist in the clinical response as judged by reduction in tumour size and decrease in the circulating prolactin level. Furthermore, in patients with prolactinomas, pergolide may induce a response when resistance to bromocriptine develops.

Variability and selectivity of anterior pituitary response to dopamine agonists throughout the normal menstrual cycle

To clarify whether there is a variation of dopamine effect throughout the normal menstrual cycle, 24 studies were performed during the follicular, periovulatory, and luteal phase in seven ovulatory women. The subjects were studied for 24 hours after receiving two different dopamine agonists, 2.5 mg of bromocriptine in one cycle and 50 micrograms of pergolide in a subsequent cycle. Baseline plasma luteinizing hormone, follicle-stimulating hormone, prolactin, and thyrotropin were followed through time, and the dynamic responses to gonadotropin-releasing hormone and thyrotropin-releasing hormone before and at 6 and 22 hours after medication were studied. Since the results obtained with both agonists were similar, the data have been combined in a single group. Baseline luteinizing hormone levels (but not follicle-stimulating hormone) were significantly suppressed (p less than 0.01) during the follicular phase only, and the plasma luteinizing hormone and follicle-stimulating hormone response to gonadotropin-releasing hormone was not affected by the agonists in any of the three cycle phases. Baseline plasma prolactin was suppressed equally (p less than 0.005) in all phases of the cycle, and the response to thyrotropin-releasing hormone was similarly suppressed in all phases only at 6 hours (p less than 0.002). Baseline thyrotropin also was suppressed (p less than 0.01) in all phases but the degree of inhibition was greater in the luteal than in the follicular phase (p less than 0.05). The response to thyrotropin-releasing hormone was inhibited, with the smallest response seen at 22 hours (p less than 0.01). In conclusion, these results suggest that the modulatory effect of dopamine on pituitary hormone secretion is variable and selective throughout the normal menstrual cycle. The greatest inhibition is on prolactin release, which is similar in all phases, followed by thyrotropin, which is greater in the luteal phase, and then by luteinizing hormone in the follicular phase only; it has no effect on follicle-stimulating hormone release.

Pergolide and bromocriptine for the treatment of patients with hyperprolactinemia

A prospective study of 22 women with hyperprolactinemia from various causes was performed with use of bromocriptine in nine patients and pergolide in 13 patients. The administration of 50 micrograms of pergolide followed by 100 micrograms on the second day showed significant decrements (p less than 0.01) in systolic and diastolic blood pressure in either standing or lying position. However, 25 micrograms of pergolide followed by 50 micrograms did not lower blood pressure. Both 25 and 50 micrograms of pergolide induced a maximal and significant (p less than 0.005) inhibition of prolactin at 8 hours and remained suppressed for at least 24 hours. Long-term treatment with either bromocriptine or pergolide was continued for 48 weeks. Both dopamine agonists demonstrated a similar degree of prolactin inhibition throughout time. However, only patients treated with pergolide had higher levels (p less than 0.05) of luteinizing hormone and follicle-stimulating hormone. Resumption of spontaneous menses and cessation of galactorrhea occurred at similar times in both groups. It can be concluded that either dopamine agonist can be safely given to patients with hyperprolactinemia.

Elevation of acetylcholine levels in striatum of rat brain by LY163502, trans-(-)-5,5a,6,7,8,9a,10-octahydro-6-propylpyrimido less than 4,5-g greater than quinolin-2-amine dihydrochloride, a potent and stereospecific dopamine (D2) agonist

LY163502, a partial ergoline and a trans-levorotatory enantiomer, does not stimulate adenylate cyclase in striatal membranes but inhibits 50% binding of 3H-apomorphine, 3H-pergolide and 3H-spiperone at 10, 13 and 151 nM (IC50), respectively. The racemic mixture (LY137157) is less effective, with 3, 2.7 and 1.4 times higher IC50 values, respectively, whereas the dextrorotatory isomer (LY175877) is inactive. LY163502 inhibits binding of 3H-clonidine with an IC50 value of 2600 nM, but not the binding of 3H-WB4101, 3H-dihydroalprenolol, 3H-serotonin, 3H-quinuclidinyl benzilate and 3H-pyramilamine or the uptake of serotonin, norepinephrine or dopamine, suggesting selective affinity toward dopamine receptors in vitro. Both LY163502 and LY137157 elevate striatal acetylcholine (Ach) levels. The elevation of Ach levels by LY163502 is reversed by dopamine antagonists haloperidol, cis-flupenthixol and metoclopramide. Therefore, the levorotatory enantiomer exhibits pharmacology of a D2 type of dopamine agonist.

Effects of dopaminomimetics on the secretion of VIP-like immunoreactivity in conscious dogs

The effects of some dopaminomimetics on VIP levels in peripheral venous blood of conscious dogs were analysed with a radioimmunoassay. The dopamine D2 agonist pergolide, like apomorphine and bromocriptine, increased VIP levels. The putative DA autoreceptor agonist 3PPP, as well as the D1 agonist SK&F 38393 were devoid of action. The D1 antagonist SCH 23390 did not abolish the effect of apomorphine. It is suggested that monitoring of VIP levels could be an interesting screening test for activity at D2 receptors. Amphetamine did not modify VIP levels suggesting that DA neurons are not involved in the mechanism leading to a release of VIP. The VIP response to apomorphine was not suppressed by an infusion of somatostatin. Decreasing blood pressure with nitroglycerin or with the adrenergic antagonist prazosin did not release VIP. The mechanism by which administration of dopaminomimetics lead to a release of VIP is further discussed.

Efficacy of pergolide and mesulergine

The activity of pergolide, a clavine ergolene, and mesulergine, an 8-alpha amino ergoline, were compared in 18 patients with advanced Parkinson's disease. All of the patients were no longer satisfactorily responding to levodopa, and 16 patients had diurnal oscillations in performance. Pergolide, mean dose 2.7 mg, when added to levodopa resulted in a significant (27%) decrease in Parkinson disability and a significant improvement in diurnal oscillations in performance (136% increase in hours 'on'). Twelve of the 18 patients (67%) improved. However, after 2 years pergolide was discontinued in all of the patients because of decreased efficacy, adverse effects, or both. At this time, mesulergine, mean dose 9.3 mg., when added to levodopa resulted in a significant (37%) decrease in Parkinson disability and a significant improvement in diurnal oscillations (61% increase in hours 'on'). Twelve of the 18 patients (67%) improved. Adverse effects (dyskinesias) were less with mesulergine than with pergolide. A declining response to one agonist does not preclude a successful response to another agonist of a different class.

Effects of pergolide on diethylstilbestrol-induced rat pituitary hyperplasia

Hyperplastic anterior pituitary glands were produced in female rats by treatment with 10 mg of diethylstilbestrol in Silastic tubing. This led to increased numbers of immunoreactive prolactin cells and increased serum prolactin levels. After 6 weeks of diethylstilbestrol treatment, one group of rats was treated with daily injections of pergolide for 3 weeks. Pergolide produced a significant decrease in pituitary gland weight and in serum prolactin levels but did not change the percentage of prolactin cells significantly, compared with that of control rats. Ultrastructural studies showed a significant increase in the numbers of prolactin secretory granules and numerous large intracellular bodies with associated secretory granules in pituitaries from rats treated with pergolide. In one group of rats in which the diethylstilbestrol was discontinued for 3 weeks after 6 weeks of treatment there was a significant decrease in pituitary gland weight and serum prolactin and a significant decrease in the percentage of prolactin cells, compared with values in the rats treated with diethylstilbestrol for 9 weeks. These results indicate that pergolide causes decreased release of prolactin from secretory granules in anterior pituitary prolactin cells and an increase in the numbers of PRL secretory granules per cell but does not change the percentage of prolactin-producing pituitary cells after 3 weeks of treatment.

Pharmacological, hemodynamic and biochemical mechanisms involved in the blood pressure lowering effects of pergolide, in normotensive and hypertensive dogs

In pentobarbital-anesthetized normotensive dogs, clonidine (20.0 micrograms/kg i.v.), in contrast to pergolide (30.0 micrograms/kg i.v.), reduced significantly both aortic blood pressure and plasma concentration of norepinephrine. However, in dogs that had been made hypertensive by sectioning the vagi and carotid sinus nerves, pergolide, like clonidine, lowered the blood pressure and plasma concentrations of epinephrine and norepinephrine that were enhanced markedly by deafferentation. Furthermore, in this preparation pergolide decreased the calculated resistance in vascular regions supplied by the upper abdominal aorta and the innervated femoral and renal arteries, but it increased vascular resistance in the denervated hind leg. Pergolide (1.0 microgram/kg) injected intracisternally (i.c.m.) induced a fall in blood pressure of comparable magnitude to that produced by a 30 times higher i.v. dose. Intravenously and i.c.m. administered pergolide lowered blood pressure by acting at distinct anatomical sites inasmuch as i.v. sulpiride blocked the effects of i.v. but not i.c.m. pergolide. The combination of sulpiride plus yohimbine injected i.c.m. was necessary to abolish the decrease in blood pressure evoked by i.c.m. pergolide. In atropinized spinal dogs, i.v. pergolide inhibited the vasoconstriction elicited by electrical stimulation of the lumbar sympathetic chain, an effect which was antagonized by sulpiride. Similarly, pergolide (30.0 micrograms/kg i.v.) like clonidine, reduced the heart rate and coronary venous plasma norepinephrine concentration raised by sustained electrical stimulation of the cardioaccelerator nerve. Sulpiride, but not phentolamine, antagonized this pergolide-induced inhibition of sympathetic nerve function. In chlorisondamine-pretreated dogs, pergolide produced a transient pressor response due to stimulation of postsynaptic vascular alpha-2 adrenoceptors. In conclusion, the failure of i.v. pergolide to decrease aortic blood pressure in pentobarbital-anesthetized normotensive dogs is presumably due to the inability of pergolide to produce a significant inhibition of the vascular sympathetic tone in this preparation. However, in neurogenic hypertensive dogs which are characterized by an elevated level of sympathetic drive, i.v. pergolide reduced blood pressure and aortic plasma norepinephrine concentration. These effects of pergolide are compatible with a DA-2 dopamine receptor stimulation on peripheral sympathetic nerve fibers. In contrast, the antihypertensive effects of i.c.m. pergolide would appear to be mediated by both alpha-2 adrenoceptors and DA-2 dopamine receptors located within the central nervous system.

Rotational behaviour elicited by intracerebral injections of apomorphine and pergolide in 6-hydroxy-dopamine-lesioned rats. II: The striatum of the rat is heterogeneously organized for rotational behaviour

The present study compares the role of the nucleus accumbens and the striatum, as well as various regions of the striatum, in the ability of intracerebral injections of the dopamine agonists apomorphine and pergolide to elicit rotational behaviour in 6-hydroxy-dopamine-lesioned rats. We found that apomorphine and pergolide elicit rotational behaviour when injected into the denervated striatum, but not when injected into the ipsilateral nucleus accumbens. The striatum seems heterogeneously organized as regards rotational behaviour since maximal-apomorphine rotation was elicited from the corpus of the striatum as compared to the effects produced by injections into the head and the tail of the striatum. This topographical distribution is similar to the distribution of dopamine-stimulated cyclic AMP. The pergolide response is more evenly distributed in the striatum. It is suggested that the difference in the topographical distribution of the ability of apomorphine and pergolide to elicit rotational behaviour reflects a regional distribution of dopamine receptors in the striatum of the rat.

Rotational behaviour elicited by intracerebral injections of apomorphine and pergolide in 6-hydroxy-dopamine-lesioned rats. I: Comparison between systemic and intrastriatal injections

Rotational behaviour in unilaterally 6-hydroxy-dopamine-denervated rats has been attributed to stimulation of dopamine receptors on striatal as well as limbic areas. In the present study the rotational behaviour elicited by local intrastriatal injections of apomorphine or pergolide was compared to the rotation elicited by systemic injections of the drugs. We found that intrastriatal injections induced rotational behaviour almost identical to the behaviour occurring after systemic treatment. Furthermore, studies of the spread of [3H]apomorphine in brain tissue showed that at the peak of rotation the radioactivity was confined within the limits of the striatum. Non-significant amounts of radioactivity was found in the nucleus accumbens. On the basis of these data we conclude that rotational behaviour elicited by systemic injections of apomorphine or pergolide originates from stimulation of striatal sites. The difference in rotational patterns elicited by these drugs is more likely to relate to differences in receptor stimulation within the striatum than differences in, for example, relative distribution between limbic and striatal areas.

Is inhibition of striatal synaptosomal tyrosine hydroxylation by dopamine agonists a measure of dopamine autoreceptor function?

Rat striatal synaptosomal tyrosine hydroxylation was inhibited dose- and pH dependently by a number of dopamine agonists. The catecholic agonists apomorphine and (-)N-n-propylnorapomorphine inhibited synaptosomal tyrosine hydroxylase completely, with IC50 values of around 0.3 mumol/l at pH 6.6. The noncatechol agonists pergolide and bromocriptine and the putative dopamine autoreceptor agonists 3-PPP(-), 3-PPP(+), HW-165 and B-HT 920 produced only partial inhibition of synaptosomal tyrosine hydroxylation at high concentrations. Comparison of the inhibition of synaptosomal and soluble tyrosine hydroxylase indicated that the inhibition produced by apomorphine could be ascribed to a direct effect on the enzyme, whereas this was not the case for the noncatechol agonists. The inhibition produced by pergolide and 3-PPP(-) was not antagonised by either dopamine receptor or alpha-adrenoceptor antagonists. The present results have been compared with results reported in the literature for inhibition of synaptosomal tyrosine hydroxylation and for two other tests of dopamine autoreceptor agonist activity (inhibition of dopamine release from striatal slices in vitro, and inhibition of the gamma-butyrolactone induced increase in dopamine synthesis in vivo). It is concluded that inhibition of striatal synaptosomal tyrosine hydroxylation by dopamine agonists does not fulfil the criteria required for it to be considered as a useful measure of dopamine autoreceptor function.

Pergolide therapy in Parkinson's disease: a double-blind, placebo-controlled study

A double-blind, placebo-controlled study was conducted of pergolide as an adjunctive treatment to levodopa in 17 patients with advanced Parkinson's disease. There was a significant improvement (p less than 0.05) in total disability score, in gait, and in "wearing off" and "on-off" phenomena. Pergolide is a useful drug in patients with advanced Parkinson's disease.

Differential effects of selected dopaminergic agents on locomotor activity in normotensive and spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) exhibit a significantly higher level of spontaneous locomotor activity than age-matched normotensive controls (WKY). The direct-acting dopamine agonists, apomorphine and pergolide, produced a biphasic effect on locomotor activity levels in normotensive controls. Low doses of these agonists decreased activity levels, while higher doses of these agonists dramatically stimulated activity. In marked contrast to these results was the effect observed in the SHR, in which these agonists at all doses tested decreased activity. Amphetamine, a dopamine releaser, stimulated activity levels in both the WKY and SHR; however, the magnitude of the increase was somewhat attenuated in the SHR.

The use of pergolide and lisuride, two experimental dopamine agonists, in patients with advanced Parkinson disease

Pergolide, an experimental dopamine agonist, was administered to 56 patients with advanced Parkinson disease who were no longer satisfactorily responding to levodopa, including 45 patients with diurnal oscillations in performance: "on-off" phenomena. Lisuride, an experimental dopamine agonist was administered to 63 patients with advanced Parkinson disease. Pergolide or lisuride, when added to levodopa, resulted in a significant decrease in disability in both the "on" and the "off" period, and an increase in the number of hours in which patients were "on". Forty-one of 56 patients (73%) improved on Pergolide. Thirty-seven of 63 patients (59%) improved on lisuride. Mean dose of pergolide was 2.5 mg. (range 0.2 to 10.0 mg.). Mean dose of lisuride was 2.6 mg. (range 0.2 to 5.0 mg.). Pergolide was discontinued in 18 patients because of adverse effects, including an organic confusional syndrome (six patients), dyskinesias (four patients) and cardiovascular abnormalities (three patients). Lisuride was discontinued in 26 patients because of adverse effects, including an organic confusional syndrome (15 patients), dyskinesias (five patients) and vasospasm (two patients). Pergolide was discontinued in nine patients and lisuride in 12 because of a lack of effect or a declining effect. Both drugs are equally useful in patients with advanced Parkinson disease.

Hyperactivity induced by stimulation of separate dopamine D-1 and D-2 receptors in rats with bilateral 6-OHDA lesions

The effects of DA agonists and antagonists with different dopamine (DA) D-1 and D-2 receptor selectivity have been studied in rats with bilateral 6-OHDA lesions. The D-1 agonist SK & F 38393, the D-2 agonist pergolide and the mixed agonist apomorphine all induced marked hyperactivity in lesioned rats in doses which were without stimulant effect in sham-operated animals. The hyperactivity induced by SK & F 38393 was blocked by the DA D-1 antagonist SCH 23390, but unaffected by the D-2 antagonists spiroperidol or clebopride. Pergolide-induced hyperactivity showed the reverse selectivity. The mixed D-1/D-2 antagonists, cis(Z)-flupentixol and cis(Z)-clopenthixol, however blocked the effect of both agonists. Apomorphine-induced hyperactivity was neither blocked by selective D-1 nor D-2 antagonists, but was dose-dependently inhibited by cis(Z)-flupentixol and cis(Z)-clopenthixol. Potent blockade was also obtained by combined treatment with SCH 23390 and spiroperidol, indicating the need of blocking both D-1 and D-2 receptors simultaneously. The results indicate that D-1 and D-2 receptor function can be independently manipulated in denervated rats and they confirm similar results obtained in rats with unilateral 6-OHDA lesions using circling behaviour.

The medical treatment of the hypersecreting pituitary gland

Pituitary adenomas may produce local endocrine and neurological effects, as well as systemic metabolic complications due to hormonal hypersecretion. Medical therapy with pharmacological agents has been developed and is based on the neurotransmitter regulation of normal pituitary hormonal secretion. 189 patients with secretory pituitary adenomas underwent medical therapy for the hypersecretory state. 156 of these were prolactin-secreting adenomas, 16 of which were in males. The response of bromocriptine was almost universal with lowering of serum prolactin and reversal of the clinical symptoms, as well as tumor shrinkage of most large adenomas with suprasellar extension. 23 patients with acromegaly were treated with bromocriptine, with 11 noting clinical improvement, and decreased tumor size in two. Five patients with Cushing's disease were treated with cyproheptadine, with only one showing a biochemical and clinical improvement. Two patients with Nelson's syndrome each had progressive tumor growth stabilized with cyproheptadine and bromocriptine in one, and sodium valproate in the other. There appears to be a role for medical therapy in the majority of prolactin-secreting pituitary tumors, some growth hormone secreting pituitary tumors, and selected adrenocorticotropin secreting-pituitary tumors.

Behavioral effects of pergolide mesylate on food intake and body weight

In a crossover design experiment, pergolide mesylate significantly suppressed food intake and body weight in spayed female rats. Inhibition of food intake by a constant dose of pergolide progressively diminished with repeated administrations. Pergolide continued to suppress body weight with no indications of tolerance. When pergolide was discontinued, body weight increased sufficiently to compensate for the loss and failure to gain during drug treatment. A second experiment investigated the observation that animals injected first with vehicle showed greater anorexia when subsequently injected with pergolide than did animals injected first with pergolide. In addition, tolerance was further assessed by administering on two occasions a higher dose of pergolide. Following chronic pergolide treatment, this dose was insufficient to reinstate anorexia; however, after a period of abstinence, this dose produced anorexia comparable to that observed at the beginning of pergolide treatment. Due to pergolide mesylate's action as a postsynaptic dopamine agonist, a dopaminergic neural system is implicated in pergolide induced anorexia.

Behavioural stimulation is induced by separate dopamine D-1 and D-2 receptor sites in reserpine-pretreated but not in normal rats

The dopamine (DA) D-1 agonist SK&F 38393 as well as the D-2 agonist pergolide and the mixed D-1/D-2 agonist apomorphine induced strong hypermotility and oral stereotypy in rats pretreated with a daily dose of reserpine for 2 and in particular for 4 days (3 and 5 injections, respectively). SK&F 38393 had no behavioural stimulant effect in saline-pretreated rats, whereas pergolide and apomorphine produced stimulation, although only after higher doses. Agonists at 5-HT and muscarinic receptors and at alpha 1-adrenoceptors were ineffective in reserpine-pretreated rats whereas the alpha 2-adrenoceptor agonist, clonidine, and the muscarinic antagonist, scopolamine, produced weak locomotor stimulation. The hypermotility induced by SK&F 38393 in reserpinized rats was blocked by pretreatment with the DA D-1 antagonists, SCH 23390 and SK&F 83566c, whereas the DA D-2 antagonists, YM 09151-2, clebopride and spiroperidol were weak or ineffective. In contrast pergolide-induced hypermotility was blocked by low doses of the D-2 antagonists but was weakly or not influenced by the D-1 antagonists. Selectivity ratios between drug potencies in the two models ranged from 65 to more than 600. The mixed D-1/D-2 antagonists, cis(Z)-flupentixol and cis(Z)-clopenthixol, blocked the effect of both SK&F 38393 and pergolide. The alpha 1-adrenoceptor antagonist, prazosin, and the 5-HT2 receptor antagonist, ketanserin, did not modify the effect of SK&F 38393 or pergolide. Stereotyped behaviour induced by a high pergolide dose in normal rats was, in contrast to the effect in reserpinized rats, blocked by low doses of either SCH 23390 or spiroperidol. Finally, the hypermotility induced by apomorphine in reserpinized rats was markedly antagonized by both SCH 23390 and spiroperidol. The results suggest a close relation between D-1 and D-2 receptor sites in normal rats. After prolonged reserpine treatment, the D-1 agonist acquires full DA agonist efficacy. Furthermore, behavioural stimulation under these conditions is mediated by two separate D-1 and D-2 receptor sites which can be manipulated independently by antagonists. The mechanism by which this phenomenon occurs is unknown but the adaptational changes show close similarities to those observed after 6-hydroxyDA-induced denervation.

Interactions between estrogens, prolactin, and growth hormone on the growth of N-nitrosomethylurea-induced rat mammary tumors

Rats bearing N-nitrosomethylurea-induced mammary tumors regressing after ovariectomy were assigned to control or treatment groups. All control tumors continued to regress, while the serum prolactin levels were subnormal. Estrogen replacement stimulated tumor regrowth, and increased the serum prolactin. Pergolide further suppressed the postovariectomy serum prolactin, and all tumors continued to regress. When estrogen and pergolide were given together, 32% of tumors progressed despite low serum prolactins. Ovine prolactin, delivered to ovariectomized rats at a rate of 40 micrograms/hr, caused 3 of 10 tumors to progress, 3 to become static, and 4 to continue regression. Prolactin also maintained the growth of 4 of 8 tumors after hypophysectomy, and arrested regression of 3 others. Posthypophysectomy regression was also prevented and growth maintained by the simultaneous administration of estrogen and growth hormone.

[Clinical study of pergolide in Parkinson's disease]

Pergolide is thought to stimulate both D1 and D2 dopaminergic receptors. Its effects on Parkinson's disease were evaluated in an open trial, using clinical assessment scales and objective tests. Nine patients had previously been treated with L-dopa, but the drug had either gradually lost its effectiveness or produced invalidating side-effects. Pergolide in doses of 2 mg per day considerably and durably improved the parkinsonian symptoms and enabled the patients to reduce L-dopa dosage by about 50%. Dyskinesia and "on-off" phenomena partially regressed. Significant improvement was also observed in 3 of 4 patients with Parkinson's disease who had not previously received L-dopa. The side-effects of pergolide were fairly frequent in both groups, but they were relatively mild and reversible.

Pergolide mesylate: lack of cardiac toxicity in patients with cardiac disease

In a 12-month open-label trial, pergolide mesylate was administered in doses with antiparkinsonian efficacy to six patients with stable heart disease. Cardiac status did not worsen in any patient. Parkinson's disease improved in all patients. Pergolide is a safe and effective therapy for Parkinson's disease, even in patients with heart disease.

Bromocriptine in Parkinson disease

Bromocriptine is an ergopeptine derivative and dopamine agonist that predominantly stimulates the striatal D2 non-adenyl cyclase-linked dopamine receptors. Bromocriptine, unlike other dopamine agonists, has mixed "agonist-antagonist" properties at these receptors. The striatal dopamine receptors exist in two different affinity states: a low and a high affinity state. Bromocriptine, unlike other dopamine agonists, does not differentiate between the low and the high affinity state of the D2 receptors, and bromocriptine does not induce a conformational change in these receptors. Bromocriptine, in low doses, is effective in patients with mild to moderate Parkinson's disease, while bromocriptine in higher doses is needed in patients with advanced disease. Both in low doses and in high doses, bromocriptine combined with levodopa is usually more effective than bromocriptine alone. The efficacy of low dose (5-30 mg/day) and high dose (31-100 mg/day) bromocriptine alone and with levodopa was examined in 27 studies encompassing 790 patients. Forty-six % of the studies were done in a double blind manner. In four studies of 79 patients, low dose bromocriptine (16 mg/day) without levodopa resulted in improvement in 58% of the patients. Only 9% of the patients experienced adverse effects. Most of the patients (63%) and mild or moderate Parkinson disease. In seven studies of 143 patients, high dose bromocriptine (56 mg/day) without levodopa resulted in improvement in 62% of patients, but with 27% having adverse effects. Most of these patients (77%) had mild or moderate disease. Diurnal oscillations in performance, the "wearing off" or "on-off" effect, were not seen during treatment with bromocriptine alone. In nine studies of 201 patients, low dose bromocriptine (23 mg/day) and levodopa resulted in improvement in 71% of patients with 26% having adverse effects. Most of these patients (66%) had advanced disease, and many had diurnal oscillations in performance. In seven studies of 367 patients, high dose bromocriptine (48 mg/day) and levodopa resulted in improvement in 58% with 37% having adverse effects. Most of these patients (85%) had advanced disease. The increased effectiveness of bromocriptine in combination with levodopa may be explained as follows. Bromocriptine by itself does not discriminate between the low and the high affinity states of the dopamine receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

Primate mammary development. Effects of hypophysectomy, prolactin inhibition, and growth hormone administration

The pituitary gland has been found to be an important factor in mammary development in primates. Hypophysectomy in 12 sexually immature monkeys caused significant inhibition of estradiol (E2)-induced mammary growth and development. A histological index of mammary development in sexually immature hypophysectomized animals was lower (0.82) than in intact E2-treated controls (3.4; P less than 0.008). Hypophysectomy also inhibited growth of the mammary gland as judged by a size index. Despite the hypophysectomy, E2 stimulated some, albeit blunted, mammary growth and development, which may have been due to incomplete hypophysectomy. Selective inhibition of prolactin by ergot drugs in intact animals did not prevent full mammary development, suggesting that there may be pituitary mammogens other than prolactin, or that very low or unmeasurable concentrations of prolactin were sufficient to synergize with E2 to cause full acinar development. The mean histological index was 3.08 in E2-treated animals and 3.16 in animals treated with E2 plus pergolide. There was also no difference in the size of the glands. We evaluated the effect of growth hormone on mammary development by treating three hypophysectomized animals with pure 22,000 mol wt human growth hormone (hGH) (Genentech, Inc., South San Francisco, CA). We found that physiological or slightly supraphysiological concentrations of hGH in animals with unmeasurable prolactin were incapable of restoring the capacity of E2 to induce full mammary growth. These findings suggest that, if growth hormone is a mammary mitogen, that physiological concentrations are insufficient to synergize with E2 to induce full mammary growth or that other forms of hGH are mammogenic. Our studies suggest that the role of the pituitary gland in mammary mitogenesis in primates is more complicated than previously thought. They also raise the possibility that heretofore unidentified pituitary substances may be mammogenic.

Selective D2 dopamine receptor agonists prevent catalepsy induced by SCH 23390, a selective D1 antagonist

SCH 23390, an apparently selective antagonist of central D1 dopamine receptors, produced profound catalepsy at low doses (0.1 mg/kg, s.c.). Pretreatment with the selective D2 receptor agonists LY 141865, RU 24213 or LY 171555, the active (-) enantiomer of LY 141865, elicited a dose-dependent inhibition of the cataleptic response. Pergolide and apomorphine were also effective. This effect was not due to altered disposition or penetration of SCH 23390 into the brain since pretreatment with a dose of LY 171555 which completely blocked catalepsy had no effect on the ID50 of SCH 23390 to inhibit 3H-cis-piflutixol binding to D1 receptors measured ex vivo. Alternative mechanisms are considered to explain the results, which offer new insights into striatal dopaminergic regulation of motor activity.

Long-term experience with pergolide therapy of advanced parkinsonism

Nine patients with idiopathic Parkinson's disease were treated with pergolide to a daily maintenance dose of 2.2 +/- 0.9 mg (mean +/- SD) for 17.3 +/- 8.3 months. After 1 month, there was an average 68% increase in mobile on-time, but the improvement declined to 30% by 6 months, 23% by 1 year, and virtually disappeared by 18 months of therapy. Pergolide was discontinued in seven patients because of loss of efficacy (4 patients), confusion (1 patient), or myocardial infarction or ventricular ectopy (2 patients). Partial but temporary restoration of mobility was observed in seven patients who were switched to an alternate-day dosing schedule after 9.2 +/- 2.4 months. Two patients with advanced Shy-Drager syndrome were treated with pergolide without benefit.

Comparison of the clinical activity of mesulergine and pergolide in the treatment of hyperprolactinaemia

The clinical activity of the new ergoline, mesulergine, was compared to pergolide in the treatment of hyperprolactinaemia. Mesulergine was given to 22 women and five men with hyperprolactinaemia. Serum prolactin was substantially lowered in 10 women; two subsequently conceived and completed normal pregnancies. Twelve women stopped treatment due to side-effects, usually nausea and vomiting, or inadequate responses. The side-effects were generally similar to those on bromocriptine; in one patient they were better and in four worse than on bromocriptine. The male patients were more tolerant of mesulergine, and substantial falls in serum prolactin were seen with evidence of tumour shrinkage. Twenty-seven women with hyperprolactinaemia received pergolide; serum prolactin was lowered or normalized in 16. Side-effects necessitating cessation of treatment were similar to those seen with bromocriptine. Nevertheless, four women tolerated pergolide better than bromocriptine and two women adequately treated with mesulergine had previously been intolerant of pergolide. We conclude that both pergolide and mesulergine may be useful and effective drugs in the treatment of hyperprolactinaemia as alternatives to bromocriptine.

Chronic agonist therapy for Parkinson's disease: a 5-year study of bromocriptine and pergolide

We used pergolide to treat 10 patients with idiopathic Parkinson's disease who had first responded to, and then failed, bromocriptine therapy. At the end of 5 years, patients had improved when compared with study entry. Peak efficacy, equal with both drugs, was seen at 12 months. After a mean treatment of 29 months, bromocriptine was no longer effective, but pergolide was still beneficial.

The effect of dopamine agonist therapy on large functionless pituitary tumours

Fifteen patients (12 male) with large pituitary tumours and serum prolactin levels below 1000 mU/l were given dopamine agonist therapy (bromocriptine, mesulergine or pergolide) for a mean of 9 months (range 3-36 months). Serum prolactin became undetectable in all. Despite this, significant suprasellar extensions and any associated neurological defect remained in 14 patients, who therefore were referred for surgery. In one patient there was evidence of spontaneous pituitary infarction unrelated to dopamine agonist therapy. At operation 12 patients had apparently functionless pituitary adenomas which failed to immunostain for prolactin, one had an epidermoid cyst and one a Rathke's pouch cyst. We conclude that patients with large pituitary tumours and only a mildly elevated serum prolactin are unlikely to have prolactinomas, and that such tumours are not likely to show significant tumour shrinkage with medical treatment with dopamine agonists.

Neuroleptic drugs and their action on different neuronal pathways

The occurrence of tardive dyskinesia has been related to treatment with most typical neuroleptic drugs. It has been hypothesized that risk of the disorder may be less with some atypical antipsychotic agents. Other contributing risk factors may include an underlying vulnerability of the nervous system. Understanding of these features of tardive dyskinesia should be enhanced through more information on functional differences between dopamine receptors and on how different types of antipsychotic drugs affect such receptors. In our animal studies, we have found evidence that dopamine D-1 and D-2 receptors are functionally linked to different behavioral phenomena in the rat, that they are differently affected by dopamine agonist and antagonist drugs, and that they may be selectively localized to different postsynaptic neuronal systems. We suggest that the development of antipsychotic drugs with a low risk of inducing tardive dyskinesia or of novel treatments for this condition may arise from improved understanding of the functions of various dopamine receptors in the brain.

Pergolide mesylate inhibits exercise-induced prolactin release in man

The effects of Pergolide, a potent dopamine agonist, on exercise-induced plasma prolactin (PRL) changes were studied in normal men. Exercises consisted of a graded bicycle ergometer test and of a 20-km endurance run. In both circumstances, treatment with Pergolide, when compared with placebo or control values, resulted in a significant suppression of basal PRL (P less than 0.001) as well as of exercise-induced PRL increase (P less than 0.01). From these experiments it was concluded that augmented levels of PRL in plasma, as seen during or after muscular exercise, are caused by increased pituitary secretion, rather than decreased elimination.

Inhibitory effects of apomorphine and pergolide on neurogenic vasoconstriction in the hindquarters of the rat

The effects of locally administered apomorphine and pergolide were studied in the isolated autoperfused hindquarters of the rat, in an attempt to assess the possible role of presynaptic dopamine receptors at that level in the hypotensive effect of these dopamine agonists. Local infusion of apomorphine (1 micrograms . kg-1 . min-1 for 5 min) or pergolide (1 micrograms . kg-1 . min-1 for 5 min) [into the hindquarters] did not alter perfusion pressure per se, but reduced the pressor response to electrical stimulation of the lumbar sympathetic chains for the whole frequency range used during a cumulative frequency-response curve (0.25-16 Hz, 1 ms, supramaximal voltage). Apomorphine and pergolide reduced the pressor response elicited by 4 Hz electrical stimulation (applied until maximum response was reached) to 54.8 +/- 7.1% and 53.9 +/- 1.7% respectively, but they did not modify similar increases of perfusion pressure produced by locally administered noradrenaline. The inhibition by apomorphine and pergolide of the 4 Hz stimulation-evoked pressor response was completely antagonized by local administration of the dopamine antagonist haloperidol (1 microgram . kg-1), but was not influenced by the alpha 2-antagonist rauwolscine (100 micrograms . kg-1). This dose of rauwolscine antagonized the inhibitory effect of the alpha 2-agonist UK-14,304, which was not influenced by haloperidol. Local administration of rauwolscine increased the pressor response to stimulation at 4 Hz by 37.4-46.2%. In contrast, local administration of haloperidol did not influence the 4 Hz stimulation-evoked pressor response.(ABSTRACT TRUNCATED AT 250 WORDS)

Pergolide elevation of MHPG sulphate concentration in rat hypothalamus blocked by spiperone and mimicked by other dopamine agonists

Pergolide increased the concentration of MHPG sulphate (3-methoxy-4-hydroxy-phenylethylene glycol sulphate) in rat hypothalamus, and the increase was prevented by pretreatment with spiperone, a dopamine antagonist. An increase in hypothalamic MHPG sulphate concentration similar to that caused by pergolide was found after injection of quinpirole, a 'partial ergoline' that is a selective D2 agonist not affecting alpha-adrenoceptors, and by (-)-N-propylnorapomorphine, a dopamine agonist not related to the ergolines. Although the increase in MHPG sulphate concentration produced by pergolide had earlier been assumed to result from blockage of alpha-adrenoceptors, the present data indicate that it is an effect produced by dopamine D2 receptor stimulation.

Reversal of sleep disturbance in Parkinson's disease by antiparkinsonian therapy: a preliminary study

In a previous study, the sleep pattern in Parkinson's disease patients was found to be altered. The disturbance consisted of a "light fragmented sleep pattern" with increased muscle activity. Using a combined polysomnographic and electromyographic recording technique, we found that a reversal of the light fragmented sleep pattern and normalization of muscle activity during sleep occurred after clinical improvement with dopaminergic treatment. The effect of dopaminergic treatment on sleep disturbance was analyzed. There is an intimate relationship between sleep pattern and the normalization of sleep muscle activity produced by dopaminergic agents.