Direct pituitary inhibition of prolactin secretion by dopamine and noradrenaline in sheep

Thomas, Graham H.; Cummins, J. T.; Doughton, B. W.; Griffin, Nicola; Smythe, GA; Gleeson, Robert M.; Clarke, I. J.

doi:10.1677/joe.0.1230393

Cited by 29 publications

(24 citation statements)

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“…For example, active immunization against PRL, which results in an important decrease in plasma PRL concentrations, does not affect plasma LH concentration in the ram (Ohlson et al 1981). Also, increased plasma PRL concentrations as a result of hypothalamo-neurohypophysial tract disruption did not change plasma LH concentrations in the ewe (Thomas et al 1989). Moreover, the inverse relationship between PRL concentrations and reproductive activity normally seen during the year is not critical to the changes in seasonal reproductive activity (Worthy & Haresign 1983, Worthy et al 1985.…”

Section: Discussionmentioning

confidence: 93%

Implication of D2-like dopaminergic receptors in the median eminence during the establishment of long-day inhibition of LH secretion in the ewe

Bertrand

Thiéry²,

Picard³

et al. 1999

Journal of Endocrinology

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In ewes, photoperiod modulates LH release and dopaminergic terminals in the median eminence (ME) have a critical role in the establishment of long-day inhibition of LH secretion. This study was undertaken to determine the type of dopaminergic receptors, D1-like or D2-like, that mediate the action of dopamine on LH secretion at the ME level in this situation. This was assessed, in ovariectomized and estradiol-treated ewes, with the use of reverse microdialysis in the ME in three experiments: first, when LH secretion was stimulated by short days, by determining the response to three doses (0·01, 0·1 or 1 mg/ml) of a D1-like (SKF38393) and a D2-like (quinpirole) agonist; secondly, during early long-day inhibition of LH secretion, by determining the ability of SKF38393 and quinpirole (1 mg/ml) to mimic the inhibitory effects of dopamine, after a blockade of its synthesis with -methyl-paratyrosine ( MPT; 2 mg/ml); and thirdly, during early long-day inhibition of LH secretion, by determining the response to three doses (0·009, 0·09 or 0·9 mg/ml) of a D1-like (SCH23390) and a D2-like (sulpiride) antagonist.In none of the conditions was effect of the D1-like analogs on LH secretion found, compared with the control treatments. In contrast, the D2-like analogs caused changes in LH secretion. First, with short days, quinpirole in the highest dose significantly reduced mean LH concentration (P<0·05) and LH pulse frequency (P<0·01). Secondly, with long days, addition of quinpirole to MPT caused a significant decrease in LH secretion relative to MPT alone (P<0·05). Thirdly, with long days, sulpiride at the highest dose significantly increased mean LH concentration (during the first 3 h of treatment, P<0·05) and LH pulse frequency (P<0·05). Prolactin secretion was also determined in these experiments, and D2-like agonist and antagonist caused an inhibition and a stimulation of prolactin secretion, respectively. These results demonstrate that, in the ME, inhibitory action of dopamine on LH secretion, critical for the initiation of long-dayinduced inhibition, is mediated by D2-like, not D1-like, dopaminergic receptors.

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Section: Discussionmentioning

confidence: 93%

Implication of D2-like dopaminergic receptors in the median eminence during the establishment of long-day inhibition of LH secretion in the ewe

Bertrand

Thiéry²,

Picard³

et al. 1999

Journal of Endocrinology

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“…By comparison, injection of a D2 antagonist is followed by a pro¬ longed increase in prolactin (Thomas et al 1989). The long duration of this effect is probably due to pro¬ longed blockade of the pituitary D2 receptor which would prevent short-loop feedback from returning prolactin levels to normal.…”

Section: Discussionmentioning

confidence: 99%

“…Thus it has been known for some time that treatment with dopamine or a dopamine D2 receptor agonist such as bromocrip¬ tine suppresses plasma prolactin levels (MacLeod et al 1970; Besser et al 1972) and treatment with D2 antagonists has the opposite effect (Dickerman et al 1972). Experiments in vitro and in vivo have con¬ firmed that these effects are mediated at the level of the pituitary (Birge et al 1970;Thomas et al 1989). …”

mentioning

confidence: 99%

Dopamine D1 receptor analogues act centrally to stimulate prolactin secretion in ewes

Curlewis

Clarke

McNeilly

1993

Journal of Endocrinology

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It is well known that prolactin secretion is inhibited by dopamine activity via the pituitary dopamine D2 receptor. Dopamine D1 receptor analogues also affect prolactin levels although the mechanisms and physiological significance are poorly understood. The present study of the ewe was undertaken to characterize the effects of the D1 receptor agonist SKF 38393 and antagonist SCH 23390 on prolactin in this species and to determine whether the prolactin response to both drugs requires an intact hypothalamo-pituitary axis. Ovariectomized ewes were injected intravenously with vehicle, 0.2, 2 or 20 mg SKF 38393 (D1 agonist) or SCH 23390 (D1 antagonist). At the 20 mg dose, plasma prolactin concentrations were significantly (P < 0.01) increased by each drug and returned within an hour to control levels. When injected directly into the lateral ventricles of the brain (intracerebroventricular (i.c.v.) injection), a 100-fold lower dose of SKF 38393 (0.2 mg; P < 0.05) was sufficient to stimulate prolactin secretion. In contrast, i.c.v. injection of SCH 23390 (0.02 and 0.2 mg) had no effect on prolactin levels and at no dose was there evidence for suppression of prolactin levels. These results are in accord with earlier studies in the rat which suggested that the D1 agonist stimulated prolactin secretion via a direct effect on central dopamine D1 receptors whereas the D1 antagonist interacted with the pituitary dopamine D2 receptor to increase prolactin secretion. In a further experiment this hypothesis was tested in hypothalamo-pituitary disconnected ewes which were infused with dopamine (0.5 microgram/kg per min) for 3 h.(ABSTRACT TRUNCATED AT 250 WORDS)

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“…Release of norepinephrine may also contribute to MDMAelicited prolactin release because selective norepinephrine reuptake inhibitors, such as reboxetine, elicit prolactin secretion (Schule et al, 2004). However, the relationship between norepinephrine release and prolactin secretion has not been fully elucidated as, in apparent contrast to the effects of drugs that increase norepinephrine levels, central administration of norepinephrine attenuates prolactin secretion (Thomas et al, 1989). Furthermore, the effects of norepinephrine on prolactin secretion seem to depend on whether it is the ␣ or ␤ receptor subtypes that are stimulated (Dodge and Badura, 2004).…”

Section: Effects Of S(ϩ)-mdma (F) Sr(ϯ)-mdma (‚) and R(ϫ)-mdmamentioning

confidence: 99%

Endocrine and Neurochemical Effects of 3,4-Methylenedioxymethamphetamine and Its Stereoisomers in Rhesus Monkeys

Murnane¹,

Fantegrossi²,

Godfrey³

et al. 2010

J Pharmacol Exp Ther

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3,4-Methylenedioxymethamphetamine (MDMA) is an amphetamine derivative that elicits complex biological effects in humans. One plausible mechanism for this phenomenon is that racemic MDMA is composed of two stereoisomers that exhibit qualitatively different pharmacological effects. In support of this, studies have shown that R(Ϫ)-MDMA tends to have hallucinogen-like effects, whereas S(ϩ)-MDMA tends to have psychomotor stimulant-like effects. However, relatively little is known about whether these stereoisomers engender different endocrine and neurochemical effects. In the present study, the endocrine and neurochemical effects of each stereoisomer and the racemate were assessed in four rhesus monkeys after intravenous delivery at doses (1-3 mg/kg) that approximated voluntary self-administration by rhesus monkeys and human recreational users. Specifically, fluorescence-based enzymelinked immunosorbent assay was used to assess plasma prolactin concentrations, and in vivo microdialysis was used to assess extracellular dopamine and serotonin concentrations in the dorsal striatum. R(Ϫ)-MDMA, but not S(ϩ)-MDMA, significantly increased plasma prolactin levels and the effects of S,R(Ϯ)-MDMA were intermediate to each of its component stereoisomers. Although S(ϩ)-MDMA did not alter prolactin levels, it did significantly increase extracellular serotonin concentrations. In addition, S(ϩ)-MDMA, but not R(Ϫ)-MDMA, significantly increased dopamine concentrations. Furthermore, as in the prolactin experiment, the effects of the racemate were intermediate to each of the stereoisomers. These studies demonstrate the stereoisomers of MDMA engender qualitatively different endocrine and neurochemical effects, strengthening the inference that differences in these stereoisomers might be the mechanism producing the complex biological effects of the racemic mixture of MDMA in humans.Racemic 3,4-methylenedioxymethamphetamine (MDMA; ecstasy) is a substituted phenethylamine with significant abuse liability. Although MDMA was placed into Schedule 1 of the Controlled Substances Act, its behavioral effects do not clearly fit into traditional delineations of drugs of abuse. Specifically, the racemic mixture of MDMA has both stimulant and hallucinogen-like effects (Shulgin, 1986;Harris et al., 2002). Moreover, Nichols (1986) postulated that MDMA represented a new class of compounds categorized as "entactogens." In support for this new categorization, Johanson et al. (2006) reported that in a three-choice discrimination procedure approximately half of the human subjects reported that MDMA was similar to the substrate-based dopamine releaser S(ϩ)-amphetamine, whereas the other half reported that it was similar to the serotonin releaser meta-chlorophenylpiperazine (mCPP).Previous studies have suggested that these complex effects are mediated by qualitative differences (i.e., apparent efficacy differences) between MDMA's stereoisomers. For example, one of the earliest studies contrasted the subjective effects of these stereoisomers in humans (A...

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Direct pituitary inhibition of prolactin secretion by dopamine and noradrenaline in sheep

Cited by 29 publications

References 0 publications

Implication of D2-like dopaminergic receptors in the median eminence during the establishment of long-day inhibition of LH secretion in the ewe

Implication of D2-like dopaminergic receptors in the median eminence during the establishment of long-day inhibition of LH secretion in the ewe

Dopamine D1 receptor analogues act centrally to stimulate prolactin secretion in ewes

Endocrine and Neurochemical Effects of 3,4-Methylenedioxymethamphetamine and Its Stereoisomers in Rhesus Monkeys

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