On the Role of Dopamine Receptors in the Naloxone-Induced Hormonal Changes in Man

Delitala, G.; Devilla, L.; Musso, Natale R.

doi:10.1210/jcem-56-1-181

Cited by 19 publications

(9 citation statements)

References 30 publications

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“…High doses of fenfluramine may also block dopaminergic receptors (Jori & Bernardi, 1972;Fuller ef al., 1976); however the dose used in this study, as indicated by previous experiments, probably did not block dopaminergic receptors (Quattrone et a/.. 1978;Ferrari et al, 1980;Foresta et al, 1985b). Moreover, we have recently demonstrated (Foresta et al, 1985a), as first suggested by Delitala et al (1983). that in man drugs with specific antidopaminergic effects, such as sulpiride and metoclopramide, did not influence the naloxone-induced LH increase.…”

Section: Discussionsupporting

confidence: 52%

“…Metergoline pretreatment significantly enhanced the stimulatory effects of naloxone on LH secretion. It has been suggested that metergoline may act also as a dopaminergic agent, however in man it has been demonstrated that dopaminergic drugs block the stimulatory effects of naloxone on LH secretion (Delitala et al, 1983;Foresta el al., 1985b). Therefore the hypothesis that opioid peptides influence LH secretion through the involvement of the serotoninergic system is further supported.…”

Section: Discussionmentioning

confidence: 99%

“…Opioid peptides exert their neuroendocrinological effects at the hypothalamic level probably by modulating noradrenergic, dopaminergic and/or serotoninergic neurotransmitter systems, which may regulate LHRH release 574 C. Foresta et al (Simpkins & Kalra, 1980;Kalra & Simpkins. 1981;Ropert el al., 1981;Van Vugt et al, 1981;Crowley et al, 1982;Bhanot & Wilkinson, 1983;Delitala et al, 1983;Adler & Crowley, 1984;Johnson & Crowley, 1984;Foresta et al. 1985a).…”

Section: S U M M a R Ymentioning

confidence: 99%

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Evidence for Serotoninergic System Involvement in Opioid Control of Luteinizing Hormone Secretion in Man

Mioni

Scandellari

1986

Clinical Endocrinology

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Endogenous opioid peptides tonically inhibit LH by acting on hypothalamic mechanisms which regulate LHRH secretion. Opiates increase hypothalamic serotonin turnover but the involvement of the serotoninergic system in the opioid mechanisms regulating LH secretion in man is not clear at present. This study was designed to evaluate whether the tonic inhibitory effect on LH secretion induced by opiates involves the serotoninergic system. We have studied 10 healthy young men (aged 20-28 years). Five subjects were infused with naloxone (10 mg/h for 3 h) before and 120 min after fenfluramine administration (60 mg orally) on two different occasions. In five other subjects naloxone was infused before and after metergoline pretreatment (8 mg on first and second day and 4 mg on the third day, orally, at 0 time of naloxone infusion). After fenfluramine, naloxone infusion failed to induce any increase in LH plasma levels; metergoline pretreatment significantly enhanced the naloxone-induced LH increase. These data suggest that in man a hypothalamic serotoninergic system may be involved in the opioid mechanisms regulating LH secretion.

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Section: Discussionsupporting

confidence: 52%

Section: Discussionmentioning

confidence: 99%

Section: S U M M a R Ymentioning

confidence: 99%

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Evidence for Serotoninergic System Involvement in Opioid Control of Luteinizing Hormone Secretion in Man

Mioni

Scandellari

1986

Clinical Endocrinology

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“…Secondly and probably more importantly, they contradict the findings in man of Morley et al [5] and Delitala el al. [7] who could not find any effect of naloxone at high doses (10 and 20 mg i.v. respectively) on the release of PRL caused by metoclopramide, another selective dopamine receptor antagonist 181.…”

Section: Discussionmentioning

confidence: 93%

Naloxone inhibits sulpiride‐induced hyperprolactinaemia in man

Bernini

Pedrinelli

Salvetti

et al. 1985

Eur J Clin Investigation

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In order to evaluate the interaction between the opiate-like peptidergic pathways and the dopaminergic system in modulating prolactin (PRL) secretion, ten normal volunteers were studied according to a double-blind, cross-over, randomized experimental design. A group of five subjects was given a fixed dose of sulpiride (a selective antidopaminergic agent, 25 mg i.v.) plus either placebo or three different doses of naloxone (a selective opioid antagonist, 0.2, 0.4, 0.8 mg i.v.) while a second group of five subjects received the same drugs in a 'reverse' protocol, i.e. a fixed dose of naloxone (0.4 mg i.v.) plus either placebo or increasing doses of sulpiride (25, 50, 100 mg i.v.). In both groups, the drugs were injected simultaneously and blood samples for PRL determination were taken at various intervals during the 15 min preceding drug injections and then over the following 4 h. Naloxone (0.4 mg i.v.) per se did not induce any modification of plasma PRL levels, but reduced to a significant extent sulpiride-induced hyperprolactinaemia (P less than 0.02). However, a higher dose of naloxone (0.8 mg i.v.) did not cause significant changes in sulpiride-stimulated PRL levels. Increasing dosages of sulpiride (up to 100 mg i.v.) reversed the blunted response of PRL after sulpiride, 25 mg, in presence of naloxone. Our data show that naloxone, at a dose of 0.4 mg i.v. inactive per se on basal PRL levels, is able to blunt significantly sulpiride-induced hyperprolactinaemia. This suggests that, in man, opioid peptides are able to influence PRL release after antidopaminergic stimuli.

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“…observa tions] further supports this view. Moreover, Delitala et al [7] reported recently that metoclopramide failed to antago nise the naloxone-induced rise in plasma LH in normal hu man male subjects, suggesting a direct rather than dopa mine-mediated suppressive action of opioid peptides on GnRH release.…”

Section: Discussionmentioning

confidence: 99%

Evidence That Opioid Peptides and Dopamine Participate in the Suckling-Induced Release of Prolactin in the Ewe

Knight¹,

Howles²,

Cunningham³

1986

Neuroendocrinology

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A pharmacological approach was used to study the involvement of opioid peptides and dopamine in mediating the suckling-induced release of prolactin in the lactating ewe (10–20 days post partum). To promote reliable and predictable suckling activity lambs were fitted with elasticated masks to prevent sucking for 4.5 h. After a 1-hour control period of frequent blood sampling, ewes were treated (i.v. injections every 5 min) for a further 75 min with either saline vehicle, an opioid antagonist (naloxone; 4.17 mg/5 min), a dopamine antagonist (metoclopramide; 1.25 mg/5 min), a mixture of naloxone + metoclopramide or a dopamine agonist (apomorphine; 6.6 mg/5 min). Blood was withdrawn at 5-min intervals for determination of plasma prolactin and luteinizing hormone (LH) by radioimmunoassay. Plasma LH concentrations (<1 µg/1) were not significantly affected by any of the drug treatments and there was no evidence for an acute fall in LH associated with suckling- or TRH-induced increases in prolactin secretion. Naloxone significantly (p < 0.05) reduced the mean incremental change in prolactin concentration (ΔPRL) in response to suckling (+ 7 ± 18 µg/ml) compared with saline-infused controls (+79 ± 26 µg/ml), an effect which was completely reversed by combined treatment with naloxone and metoclopramide (+146 ± 56 µg/ml). Metoclopramide alone raised basal prolactin levels by 46% (p< 0.01) but did not affect ΔPRL in response to suckling (+115 ± 52 µg/ml). Neither naloxone, metoclopramide nor a combination of the two drugs affected the subsequent prolactin to TRH (10 µg). Apomorphine, however, completely abolished both the suckling- and TRH-induced release of prolactin. These data are consistent with the hypothesis that the suckling-induced release of prolactin in the ewe depends on a reduced activation of dopamine receptors on pituitary lactotrophs which may be the result of a transient inhibition of dopamine release by endogenous opioid peptides.

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On the Role of Dopamine Receptors in the Naloxone-Induced Hormonal Changes in Man

Cited by 19 publications

References 30 publications

Evidence for Serotoninergic System Involvement in Opioid Control of Luteinizing Hormone Secretion in Man

Evidence for Serotoninergic System Involvement in Opioid Control of Luteinizing Hormone Secretion in Man

Naloxone inhibits sulpiride‐induced hyperprolactinaemia in man

Evidence That Opioid Peptides and Dopamine Participate in the Suckling-Induced Release of Prolactin in the Ewe

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