A dynamic and screening-compatible nanoluciferase-based complementation assay enables profiling of individual GPCR-G protein interactions.

G protein-coupled receptors (GPCRs) are currently the target of more than 30% of the marketed medicines. However, there is an important medical need for ligands with improved pharmacological activities on validated drug targets. Moreover, most of these ligands remain poorly characterized, notably because of a lack of pharmacological tools. Thus, there is an important demand for innovative assays that can detect and drive the design of compounds with novel or improved pharmacological properties. In particular, a functional and screening-compatible GPCR-G protein interaction assay is still unavailable. Here, we report on a nanoluciferase-based complementation technique to detect ligands that promote a GPCR-G protein interaction. We demonstrate that our system can be used to profile compounds with regard to the G proteins they activate through a given GPCR. Furthermore, we established a proof of applicability of screening for distinct G proteins on dopamine receptor D2 whose differential coupling to Gαi/o family members has been extensively studied. In a D2-Gαi1versus D2-Gαo screening, we retrieved five agonists that are currently being used in antiparkinsonian medications. We determined that in this assay, piribedil and pergolide are full agonists for the recruitment of Gαi1 but are partial agonists for Gαo, that the agonist activity of ropinirole is biased in favor of Gαi1 recruitment, and that the agonist activity of apomorphine is biased for Gαo We propose that this newly developed assay could be used to develop molecules that selectively modulate a particular G protein pathway.

Parkinsonian apathy responds to dopaminergic stimulation of D2/D3 receptors with piribedil.

Apathy is one of the most common symptoms encountered in Parkinson's disease, and is defined as a lack of motivation accompanied by reduced goal-directed cognition, behaviour and emotional involvement. In a previous study we have described a delayed withdrawal syndrome after successful motor improvement related to subthalamic stimulation allowing for a major decrease in dopaminergic treatment. This withdrawal syndrome correlated with a diffuse mesolimbic dopaminergic denervation. To confirm our hypothesis of parkinsonian apathy being related to mesolimbic dopaminergic denervation, we performed a randomized controlled study using piribedil, a relatively selective D2/D3 dopamine agonist to treat parkinsonian apathy, using the model of postoperative apathy. A 12-week prospective, placebo-controlled, randomized, double-blinded trial was conducted in 37 patients with Parkinson's disease presenting with apathy (Starkstein Apathy Scale score > 14) following subthalamic nucleus stimulation. Patients received either piribedil up to 300 mg per day (n = 19) or placebo (n = 18) for 12 weeks. The primary end point was the improvement of apathy under treatment, as assessed by the reduction of the Starkstein Apathy Scale score in both treatment groups. Secondary end points included alleviation in depression (Beck Depression Inventory), anxiety (Beck Anxiety Inventory), improvement of quality of life (PDQ39) and anhedonia (Snaith-Hamilton Pleasure Scale). Exploratory endpoints consisted in changes of the Robert Inventory score and Hamilton depression scales. An intention to treat analysis of covariance analysis was performed to compare treatment effects (P < 0.05). The number of premature study dropouts was seven in the placebo and five in the piribedil groups, mostly related to intolerance to hypodopaminergic symptoms. At follow-up evaluation, the apathy score was reduced by 34.6% on piribedil versus 3.2% on placebo (P = 0.015). With piribedil, modifications in the Beck depression and anxiety scores were -19.8% and -22.8%, respectively versus +1.4% and -8.3% with placebo, without reaching significance level. Piribedil led to a trend towards improvement in quality of life (-16.2% versus +6.7% on placebo; P = 0.08) and anhedonia (-49% versus -5.6% on the placebo; P = 0.08). Apathy, assessed by the Robert Inventory score, improved by 46.6% on piribedil and worsened by 2.3% on placebo (P = 0.005). Depression, measured by the Hamilton score, improved in the piribedil group (P = 0.05). No significant side effects were observed. The present study provides a class II evidence of the efficacy of the dopamine agonist piribedil in the treatment of apathy in Parkinson's disease.

Piribedil loaded thermo-responsive nasal in situ gelling system for enhanced delivery to the brain: formulation optimization, physical characterization, and in vitro and in vivo evaluation.

Methyl cellulose (MC) based nasal in situ gels were developed to enhance the brain delivery of piribedil (PBD), an anti-Parkinson's drug. Different grades of MC and several solutes (NaCl, KCl, Na.Citrate, STPP, PEG-6000, sucrose, etc.) were screened to formulate thermo-responsive nasal in situ gelling systems. Formulations were evaluated for their sol-gel transition temperature and time, rheological behaviour, in vitro drug release, mucociliary clearance (MCC), ex vivo nasal toxicity, and in vivo brain availability studies in Wistar rats. Intranasal (i.n.) administration was carried out using a cannula-microtip setup to deliver PBD at the olfactory region of the nose. The concentration and viscosity grade of MC and also the concentration and type of solute used were found to affect the rheological behaviour of the formulations. Among the solutes tested, NaCl was found to be effective for formulating MC in situ gels. The developed in situ gels significantly delayed the MCC of PBD from the site of administration when compared with conventional suspension (p < 0.05). Further, formulations with higher gel strength showed lower in vitro drug release rate and longer intranasal residence (delayed MCC) (p < 0.05). The absolute brain availability (brain AUC0-t) of PBD increased to 35.92% with i.n. delivery when compared to 4.71% with oral administration. Overall, it can be concluded that intranasal delivery of PBD is advantageous when compared to the currently practiced oral therapy. Graphical abstract.

Blockage of dopaminergic D(2) receptors produces decrease of REM but not of slow wave sleep in rats after REM sleep deprivation.

Dopamine (DA) has, as of late, become singled out from the profusion of other neurotransmitters as what could be called a key substance, in the regulation of the sleep-wake states. We have hypothesized that dopaminergic D(2) receptor blockage induced by haloperidol could generate a reduction or even an ablation of rapid eye movement (REM) sleep. Otherwise, the use of the selective D(2) agonist, piribedil, could potentiate REM sleep. Electrophysiological findings demonstrate that D(2) blockage produced a dramatic reduction of REM sleep during the rebound (REB) period after 96 h of REM sleep deprivation (RSD). This reduction of REM sleep was accompanied by an increment in SWS, which is possibly accounted for the observed increase in the sleep efficiency. Conversely, our findings also demonstrate that the administration of piribedil did not generate additional increase of REM sleep. Additionally, D(2) receptors were found down-regulated, in the haloperidol group, after RSD, and subsequently up-regulated after REB group, contrasting to the D(1) down-regulation at the same period. In this sense, the current data indicate a participation of the D(2) receptor for REM sleep regulation and consequently in the REM sleep/SWS balance. Herein, we propose that the mechanism underlying the striatal D(2) up-regulation is due to an effect as consequence of RSD which originally produces selective D(2) supersensitivity, and after its period probably generates a surge in D(2) expression. In conclusion we report a particular action of the dopaminergic neurotransmission in REM sleep relying on D(2) activation.

Comparative effects of the dopaminergic agonists piribedil and bromocriptine in three different memory paradigms in rodents.

The potential memory-enhancing properties of two dopamine agonists currently used in patients with Parkinson's disease, piribedil (1, 10 mg/kg/day, subcutaneously) and bromocriptine (5 mg/kg/day, subcutaneously), were evaluated in three experiments. Although piribedil (10 mg/kg) and bromocriptine equally enhanced spontaneous object recognition in young adult rats (experiment A), only piribedil displayed beneficial effects against aging-related memory impairments in two radial-maze experiments in mice. First (experiment B), a two-stage paradigm of spatial discrimination was used to assess relational/declarative memory in aged mice; piribedil (1 and 10 mg/kg) selectively and significantly improved the performances of aged mice in the critical tests for relational/declarative memory, whereas bromocriptine had no effect. Second, in a novel working memory task (experiment C), vehicle- or bromocriptine-treated aged mice displayed, compared with (vehicle) younger controls, a severe and persistent deficit in short-term retention of successive arm-visits, performing close to chance whichever the retention interval. Performances of piribedil (10 mg/kg) group remarkably improved across testing-days and reached young adults' level. The restoration of specific mnemonic impairments, in aged mice, highlights the memory-enhancing properties of piribedil. The efficacy of this drug in treating cognitive impairment of Parkinson's disease should now be assessed in more specific models.This work was published in an abstract form: ECNP Abstracts, 2005 (P8060 & P8065).

Nucleus accumbens mediates the pronociceptive effect of sleep deprivation: the role of adenosine A2A and dopamine D2 receptors.

Sleep disorders increase pain sensitivity and the risk of developing painful conditions; however, the underlying mechanisms are poorly understood. It has been suggested that nucleus accumbens (NAc) influences sleep-wake cycle by means of a balance between adenosine activity at A2A receptors and dopamine activity at D2 receptors. Because the NAc also plays an important role in pain modulation, we hypothesized that the NAc and its A2A and D2 receptors mediate the pronociceptive effect of rapid eye movement (REM) sleep deprivation (SD). We found that 24 hours of REM-SD induced an intense pronociceptive effect in Wistar rats, which decreases progressively over a sleep rebound period. Although the level of fecal glucocorticoid metabolites increased with SD within group, it did not differ between sleep-deprived group and control group, indicating a stress response with similar magnitude between groups. The pronociceptive effect of REM-SD was prevented by excitotoxic lesion (N-Methyl-D-aspartate, 5.5 µg) of NAc and reverted by its acute blockade (Qx-314, 2%). The administration of an A2A receptor antagonist (SCH-58261, 7 ng) or a D2 receptor agonist (piribedil, 6 µg) into the NAc increased home cage activity and blocked the pronociceptive effect of REM-SD. Complementarily, an A2A receptor agonist (CGS-21680, 24 ng) impaired the reversal of the pronociceptive effect and decreased home cage activity, as it did a D2 receptor antagonist (raclopride, 5 µg). Rapid eye movement SD did not affect the expression of c-Fos protein in NAc. These data suggest that SD increases pain by increasing NAc adenosinergic A2A activity and by decreasing NAc dopaminergic D2 activity.

Protective effects of dopamine D2/D3 receptor agonist piribedil on learning and memory of rats exposed to global cerebral ischemia-reperfusion.

Global cerebral ischemia-reperfusion (GCI/R) may occur after any of several clinical conditions such as cardiac arrest and anesthetic accident. Some dopamine receptor agonists possess neuroprotective effects. However, some of them may produce side effects during treatment. Piribedil, which is a dopamine D2/D3 receptor agonist, has fewer side effects and is well tolerated. This study investigated the effects of piribedil on learning and memory of rats with GCI/R according to modified neurological severity score (mNSS) scoring and Morris water maze test (MWM). Rats with GCI/R were treated with piribedil 25 or 50 mg/kg/d, and mNSS was performed at 6 h, 1 day, 3 days, and 1 and 2 weeks after injury. The MWM test was employed to evaluate learning and memory of rats at 1 and 2 weeks after injury. The results showed treatment with piribedil reduced the mNSS score and prolonged the time in the target quadrant compared with untreated rats although no obvious differences of the 25 and 50 mg/kg/d piribedil intervention groups were observed statistically. Piribedil is effective in improving the neurological function and learning and memory of rats after GCI/R.

Piribedil disrupts the MLL1-WDR5 interaction and sensitizes MLL-rearranged acute myeloid leukemia (AML) to doxorubicin-induced apoptosis.

Targeting WT MLL for the treatment of MLL-r leukemia, which is highly aggressive and resistant to chemotherapy, has been shown to be a promising strategy. However, drug treatments targeting WT MLL are lacking. We used an in vitro histone methyltransferase assay to screen a library consists of 592 FDA-approved drugs for MLL1 inhibitors by measuring alterations in HTRF signal and found that Piribedil represented a potent activity. Piribedil specifically inhibited the proliferation of MLL-r cells by inducing cell-cycle arrest, apoptosis and myeloid differentiation with little toxicity to the non-MLL cells. Mechanism study showed Piribedil blocked the MLL1-WDR5 interaction and thus selectively reduced MLL1-dependent H3K4 methylation. Importantly, MLL1 depletion induced gene expression that was similar to that induced by Piribedil and rendered the MLL-r cells resistant to Piribedil-induced toxicity, revealing Piribedil exerted anti-leukemia effects by targeting MLL1. Furthermore, both the Piribedil treatment and MLL1 depletion sensitized the MLL-r cells to doxorubicin-induced apoptosis. Our study support the hypothesis that Piribedil could serve as a new drug for the treatment of MLL-r AML and provide new insight for further optimization of targeting MLL1 HMT activity.

Effects of the dopamine agonist piribedil on prefrontal temporal cortical network function in normal aging as assessed by verbal fluency.

Normal aging has been associated with impaired performance in verbal fluency suggesting a prefrontal temporal cortical network (PFTCN) deficiency. In this study, we investigated the effects of a 2-month treatment period with a dopaminergic agonist (DA) on PFTCN function. Forty healthy, elderly volunteers were assessed on semantic and phonemic verbal fluency after two months of a placebo or a DA treatment (i.e. piribedil 50 mg/day) in a double-blind crossover design. Protocols were scored considering clustering, (i.e. production of words within semantic or phonemic categories, depending on the integrity of temporal lobe), and switching (i.e. the ability to shift between clusters, depending on frontal lobe functioning). Results revealed no significant main effect of the DA treatment on either verbal fluency variables but showed a significant interaction with working memory capacities, with high-capacity span subjects improving phonemic switching on DA whereas low-capacity span subjects performed more poorly on the drug than off. These data are consistent with the literature and confirm the crucial link between working memory capacities and dopamine agonist effects. The present study also provides evidence that pharmacological remediation of age-related cognitive decline has to be taken into consideration.

[The agonist of dopamine receptors piribedil in treatment of Parkinson's disease]. / Agonist dofaminovykh retseptorov piribedil v terapii bolezni Parkinsona.

In this paper, the authors review the current foreign and domestic literature on a role of the agonist of dopamine receptors piribedil in the treatment of Parkinson's disease. The results of the main studies of the efficacy and safety of piribedil, mechanisms of actions and a comparative characteristics with other dopamine receptors agonist are reviewed.

Activation of D2-like receptors induces sympathetic climactic-like responses in male and female anaesthetised rats.

In anaesthetised male rats an intravenous (i.v.) injection of p-chloroamphetamine (PCA) produced a specific patterned bursting response in the sympathetic vas deferens nerve (VDN) that corresponds to ejaculation. In the present, study selective dopamine agonists and antagonists were used to investigate whether dopaminergic mechanisms influence the generation of this ejaculatory-related response. Administration of a mixed D(1/2) receptor agonist (0.1-1.0 mg kg(-1) apomorphine i.v.) also evoked the characteristic bursting pattern responses in the VDN. Similar, but fewer, burst pattern responses could also be evoked by a selective D(2/3) receptor agonist (0.1-2.0 mg kg(-1) piribedil). Responses to 1.0 mg kg(-1) apomorphine were blocked by pretreatments with either 0.5 mg kg(-1) remoxipride (D(2) receptor antagonist) or 0.5 mg kg(-1) nafadotride (D(3) receptor antagonist), suggesting that D(2)-like receptors were involved. Responses could not be evoked by i.v. injections of apomorphine (1.0 mg kg(-1)) in anaesthetised male rats with a midthoracic spinal section, indicating that activation of D(2)-like receptors at supraspinal sites leads to an increase in the excitability of the lumbosacral pattern generator for ejaculation. In anaesthetised female rats a similar patterned bursting response occurred in the uterine nerve (UN) in response to apomorphine (0.5-2.0 mg kg(-1) i.v.). Thus a common neural mechanism may regulate sexual climactic reflexes in both sexes.

Persistence, distribution, and impact of distinctly segmented microparticles on cochlear health following in vivo infusion.

Delivery of pharmaceuticals to the cochleae of patients with auditory dysfunction could potentially have many benefits from enhancing auditory nerve survival to protecting remaining sensory cells and their neuronal connections. Treatment would require platforms to enable drug delivery directly to the cochlea and increase the potential efficacy of intervention. Cochlear implant recipients are a specific patient subset that could benefit from local drug delivery as more candidates have residual hearing; and since residual hearing directly contributes to post-implantation hearing outcomes, it requires protection from implant insertion-induced trauma. This study assessed the feasibility of utilizing microparticles for drug delivery into cochlear fluids, testing persistence, distribution, biocompatibility, and drug release characteristics. To allow for delivery of multiple therapeutics, particles were composed of two distinct compartments; one containing polylactide-co-glycolide (PLGA), and one composed of acetal-modified dextran and PLGA. Following in vivo infusion, image analysis revealed microparticle persistence in the cochlea for at least 7 days post-infusion, primarily in the first and second turns. The majority of subjects maintained or had only slight elevation in auditory brainstem response thresholds at 7 days post-infusion compared to pre-infusion baselines. There was only minor to limited loss of cochlear hair cells and negligible immune response based on CD45+ immunolabling. When Piribedil-loaded microparticles were infused, Piribedil was detectable within the cochlear fluids at 7 days post-infusion. These results indicate that segmented microparticles are relatively inert, can persist, release their contents, and be functionally and biologically compatible with cochlear function and therefore are promising vehicles for cochlear drug delivery. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1510-1522, 2016.

The effects of dopaminergic agonists on genital reflexes in paradoxical sleep-deprived male rats.

Dopamine (DA) agonists provide evidence that different receptor subtypes in the central nervous system (CNS) have influence in sexual behavior. Sleep deprivation induces supersensibility of DA receptors and previous work has shown that the DA agonist apomorphine enhances spontaneous genital reflexes (penile erection-PE and ejaculation-EJ) in rats deprived of paradoxical sleep. The present study sought to extend the latter finding by assessing the effects of other DA agonists in paradoxical sleep-deprived (PSD) male rats. The DA drugs (bromocriptine and piribedil) were acutely administered to rats that had been deprived of sleep for 4 days and to normal controls. Sleep deprivation alone induced PE and this effect was potentiated by piribedil, with maximal effects occurring with the 8 mg/kg dose, whereas only one dose of bromocriptine (8 mg/kg) induced more PE in PSD rats than in non-deprived treated controls. EJs were increased in piribedil PSD groups but this response was absent after bromocriptine treatment in the dose range tested. Our data show the genital reflexes that occurred in PSD rats are potentialized by piribedil and not by bromocriptine. These DA agonists showed distinct effects in sexual response suggesting that these effects are probably due to PSD-induced DA receptor supersensitivity even though different mechanisms are involved.

On the mode of the prolactin release-inhibiting action of the serotonin receptor blockers metergoline, methysergide, and cyproheptadine.

Using animals with large electrolytic lesions of the median eminence-mediobasal hypothalamus, we confirmed earlier findings that metergoline (ME) and methysergide (MS) inhibit PRL secretion through activation of the dopamine receptors of the pituitary lactotrophs and established, in a quantitative manner, that their dopaminergic potencies are comparable to the potency of the dopamine receptor agonist, piribedil, with ED50 in the order of 0.35 to 0.22 mg/kg. Cyproheptadine (CYP), acting by an unknown mechanism, had only a weak inhibiting effect (ED50 greater than 20.0 mg/kg) in these experimental conditions. In the second part of the study, the PRL-inhibiting actions of ME, MS, CYP, and piribedil, respectively, were tested against the PRL release-stimulating effect of activation of the central serotonergic system that was induced by administration of a large dose of L-5-hydroxytryptophan (5HTP; 100 mg/kg), a small dose of 5HTP (15 mg/kg) in rats pretreated with fluoxetine, or by the serotonin receptor agonist quipazine (10.0 mg/kg, ip). The inhibiting potencies of ME (ED50 0.019, 0.014, and 0.048 mg/kg, respectively) against these three stimuli were much larger than in the lesioned animals or than the corresponding potencies of piribedil (ED50 2.2, 0.24, and 0.41 mg/kg, respectively). It is assumed that in these experimental conditions ME inhibited PRL release by blockade of the central serotonin receptors in addition to its dopaminergic effect and that at low doses (0.1 mg/kg or less) the entire inhibiting effect of ME was probably due to its antiserotonergic activity. With MS, which is a weaker serotonin receptor blocker than ME (ED50 0.178, 0.075, and 0.55 mg/kg, respectively, for the three serotonergic stimuli of PRL release), the antiserotonergic component in its PRL-inhibiting effect was evident but less clearly separable from the dopaminergic component in experiments with 5HTP and with fluoxetine plus 5HTP, whereas in experiments with quipazine the entire action could be accounted for by its dopaminergic activity. CYP was the least potent among the three blockers (ED50 0.6, 0.4, and 1.37 mg/kg, respectively, for the three serotonergic stimuli of PRL release), but appropriate tests indicated that it acted only as a serotonin receptor blocker and not by virtue of its antihistaminic, anticholinergic properties or by a direct action on the pituitary lactotrophs. SQ 10,631, another serotonin receptor blocker that was also tested, had no PRL-inhibiting activity. Because of the dual nature of the PRL-inhibiting mechanism of ME and MS and the low effectiveness of CYP, combined possibly with other actions, the serotonin receptor blockers have limited value in studies concerning the role of the central serotonergic system in the regulation of PRL secretion.

Decline of tuberoinfundibular dopaminergic function resulting from chronic hyperprolactinemia in rats.

The effect of hyperprolactinemia on tuberoinfundibular dopaminergic (TIDA) neurons was studied after sc transplantation of a PRL-secreting pituitary tumor (MtT.W15) to young female rats. TIDA activity was determined by measuring the concentration of dopamine (DA) in pituitary stalk portal blood, the uptake and release of [3H]DA by the median eminence in vitro, and the presynaptic DA receptor activity. Eight weeks after transplantation of the tumor, serum PRL increased to approximately 100 times higher values than those in nontumor-bearing animals. Both the DA concentration and the content in pituitary stalk blood collected from rats bearing tumors for 6 weeks were significantly lower than those in nontumor-bearing rats. Injection of a DA uptake blocker, nomifensine, significantly increased stalk blood DA in nontumor-bearing rats, but did not increase DA release in tumor-bearing rats. The uptake of [3H]DA in vitro by the median eminence of rats bearing pituitary tumors for 8 weeks was lower than that in control rats. Basal and electrically induced release of [3H]DA from the median eminence in vitro from rats with tumors for 8 weeks were also significantly lower than in rats without tumors. Piribedil, a DA receptor agonist, reduced stimulated release of [3H]DA in vitro from the median eminence of rats without tumors, presumably by activating presynaptic DA receptors. However, piribedil had no effect on release of [3H]DA from the median eminence of rats with tumors. These results indicate that chronic elevation of PRL can produce a decline in TIDA function.

Further evidence for inhibition of episodic luteinizing hormone release in ovariectomized rats by stimulation of dopamine receptors.

Stimulation of dopamine receptors by apomorphine inhibits episodic LH release in ovariectomized rats. The present study was designed to examine further the role of dopamine in this process. Unrestrained, unanesthetized rats with indwelling right atrial cannulae were bled continuously (30 or 50 microliters of whole blood/5 min for 3-6 h) and whole blood samples analyzed for LH by radioimmunoassay. Animals were treated with various compounds reported to stimulate or block dopamine receptors. ET 495, a long acting dopamine receptor stimulating agent, caused a marked inhibition of episodic LH release (2 1/2-4 h). Control injections of distilled water had no effect. d-Butaclamol, a blocker of dopamine receptors, did not itself alter episodic LH release but prevented the inhibitory effects seen following apomorphine or ET 495. I-butaclamol, a biologically inactive form of butaclamol, had no effect. Measurement of plasma corticosterone levels in these same animals indicated increased values following apomorphine or ET 495 alone (when LH release was inhibited), as well as after apomorphine or ET 495 administration to d-butaclamol-pretreated rats (when LH levels did not change). These data support our previous hypothesis that in ovariectomized adult rats, activation of dopamine receptors is capable of inhibiting episodic LH release, but that dopamine may not play an inhibitory role under normal physiological conditions in the modulation of LH secretion. In addition, the inhibitory action of apomorphine and ET 495 does not appear to be exerted via a stress-induced release of adrenal corticosterone.

Decreased activity of adrenal S-adenosylmethionine decarboxylase in rats subjected to dopamine agonists, metabolic stress, or bodily immobilization.

The activity of S-adenosylmethionine decarboxylase (SAM-DC) has been measured in the adrenal gland of rats given treatments that are known to result in increased activity of ornithine decarboxylase in this organ. In contrast to the effects of the dopamine agonists piribedil and apomorphine on the latter enzyme, the administration of these drugs caused decreases of SAM-DC in both parts of the gland. After piribedil the activity decreased rapidly to a minimum at 2-4 h, with recovery by 6 h. The stress of immobilization or the administration of insulin or 2-deoxyglucose (2-DG) also decreased adrenal SAM-DC activity. The results contrast with those observed in other rat tissues where SAM-DC is generally induced by treatments that induce ornithine decarboxylase. Denervation of the adrenal gland did not clearly affect the reduction in adrenomedullary SAM-DC after 2-DG. Hypophysectomy resulted in reduced SAM-DC activity in both adrenal medulla and cortex; the activity could be restored by giving the animals 2 IU ACTH daily for 4 days. These changes in activity were parallelled by changes in immunoreactive protein. 2-DG did not decrease SAM-DC in hypophysectomized rats receiving maintenance ACTH dosage. This indicates the presence of hormonal control over the activity of SAM-DC in the adrenal medulla and cortex. Acute administration of an additional 10 IU ACTH to hypophysectomized rats on maintenance dosage of ACTH resulted in decreased SAM-DC activity in both adrenal medulla and cortex. These decreases were not abolished by inhibition of corticosteroid synthesis with metopirone. PRL and GH had no significant effect on adrenal SAM-DC activity of hypophysectomized rats. The reduction of SAM-DC activity in both parts of the gland of hypophysectomized rats with administration of (Bu)2cAMP suggests that cAMP may mediate the decreases in SAM-DC caused by the above treatments.

Selective antagonism of the hypotensive effects of dopamine agonists in spontaneously hypertensive rats.

Agonists of dopamine receptors can lower blood pressure by vasodilation through action on dopamine1 receptors, inhibition of sympathetic nerve activity by action on dopamine2 receptors, or actions in the central nervous system. Fenoldopam, a selective dopamine1 agonist, piribedil, a selective dopamine2 agonist, and dipropyl dopamine, a mixed dopamine1 and dopamine2 agonist, were injected intravenously in pentobarbital-anesthetized, spontaneously hypertensive rats (SHR). The mechanism for the antihypertensive effect was evaluated by administration of the selective dopamine1 antagonist SCH 23390 and the selective dopamine2 antagonist domperidone. While SCH 23390 only antagonized the hypotensive effects of fenoldopam, domperidone abolished the fall in blood pressure produced by dipropyl dopamine and piribedil but not by fenoldopam. Increments in heart rate and plasma norepinephrine levels accompanied the hypotensive effects of fenoldopam. The increase in heart rate was abolished by a dose of SCH 23390 sufficient to completely block the hypotensive effects and was significantly attenuated by the ganglionic blocking agent hexamethonium, which suggests that the increase in heart rate was due to a baroreceptor reflex. Fenoldopam does not cross the blood-brain barrier, which suggests that its hypotensive effect was mediated by peripheral dopamine1 receptors. Since domperidone does not cross the blood-brain barrier and significantly antagonized the hypotensive and bradycardic effects of dipropyl dopamine and piribedil, these effects were mediated primarily by peripheral dopamine2 receptors. These results indicate that SCH 23390 and domperidone are useful agents to identify the receptor subtype mediating the action of dopamine agonists in SHR.

Effects of a dopaminergic agonist (piribedil) on cerebral blood flow in man.

In baboons, the intravenous administration of piribedil, a dopaminergic agonist, was associated with marked dose dependent increases in CBF and cerebral oxygen consumption. We have studied the effects of piribedil on CBF in 20 normal, human volunteers of comparable ages. Ten received 0.1 mg/kg piribedil intravenously for 30 min; the other ten received 0.2 mg/kg. In the first group, CBF did not vary significantly, in the second group, there was a mean increase in CBF of 21.8% (p less than or equal to 0.005). In man, as in animals, piribedil provokes an increase of CBF.

Reversibility of hemodynamic hypofrontality in schizophrenia.

Regional cerebral blood flow (CBF) was studied in 51 young schizophrenics. A significant decrease of CBF was seen in frontal and prefrontal regions (hypofrontal pattern) in chronic patients whose disease had evolved for more than 2 years and who were in remission. This hypofrontal pattern was reversible, as it disappeared during exacerbation of the disease. In 10 patients who had not been treated with neuroleptics for several weeks, we found a dopaminergic hypersensitivity in the frontal lobes, as a weak dose of piribedil restored near-normal frontality. This may reflect either the role of neuroleptic washout or a primitive dopaminergic depletion, as proposed by some authors in the chronic form of schizophrenia.