Sodium and guanine nucleotide regulation of dopamine receptor agonist and antagonist binding sites in MtTW15 pituitary tumors

The modulation of the dopamine receptor in MtTW15 tumors was investigated. The antagonist dopaminergic binding site in MtTW15 tumors labelled with [3H]spiperone remains unchanged at 25 degrees C in the presence or absence of sodium or guanine nucleotides (Gpp(NH)p); by contrast at 37 degrees C sodium increases the affinity while Gpp(NH)p decreases it slightly. The dopamine receptor in this tumor, such as the intact adenohypophysis, exists in a high and low affinity state for dopamine agonists. These agonist affinity states evaluated with apomorphine competition for [3H]spiperone binding show similar affinities as those of intact tissue but have a lower proportion of the high affinity state. At 25 degrees C, a partial conversion of the high into the low affinity state is obtained in the presence of both sodium and Gpp(NH)p, while at 37 degrees C a complete conversion is observed. These data show differences in the modulation of antagonist and agonist dopaminergic binding sites in MtTW15 pituitary tumors compared with the intact pituitary.     

Dopamine receptors in rat pituitary and estradiol-induced pituitary tumor: effect of chronic treatment with bromocriptine

We have investigated dopamine (DA) receptors in estradiol-induced PRL-secreting pituitary tumors and intact pituitary tissue. Female rats were injected at 3-week intervals with 2 mg estradiol valerate (EV) or with diluent. After 21 weeks, adenomatous changes in the pituitary gland of EV-treated rats were seen and plasma PRL concentrations reached 2 micrograms/ml. Bromocriptine (2.5 mg/kg) was then administered for 1 month to half of the control rats and half of the rats bearing tumors. Anterior pituitary weight was increased in EV-treated rats compared to controls while the affinity and the density of DA receptors as assessed by [3H]spiperone binding remained unchanged. Bromocriptine (CB-154) induced a 70% decrease in the density of DA receptors without any change in affinity both in normal pituitaries and in tumors. Concurrently, the elevated plasma concentrations of PRL in the tumor bearing rats were decreased to control values following the CB-154 treatment. Our data suggest that rats with primary estrogen-induced PRL secreting tumors have normal pituitary DA receptors.     

Antisense Strategy Unravels a Dopamine Receptor Distinct from the D2 Subtype, Uncoupled with Adenylyl Cyclase, Inhibiting Prolactin Release from Rat Pituitary Cells

The antisense strategy was used to unravel the functional contribution of the mRNAs encoding dopamine (DA) receptors to the multiple transduction mechanisms operated by DA in rat pituitary cells. An antisense oligonucleotide was designed to recognize seven nucleotides upstream and 11 nucleotides downstream from the initiation translation codon of the mRNA that encodes the DA D2 receptor. Addition of the antisense oligonucleotide for 7 days to primary culture of rat pituitary cells resulted in a decreased expression of DA D2 receptor as shown by (a) the virtual disappearance of [³H]spiroperidol binding sites and (b) the marked reduction in the levels of both the long and the short splice variant of the D2 receptor mRNAs. After this treatment, the DA D2 receptor agonist bromocriptine lost its capability both to inhibit adenylyl cyclase activity and to reduce prolactin mRNA levels. On the contrary, the inhibition of prolactin release induced by bromocriptine was affected minimally by the antisense oligonucleotide treatment. These data indicate that (a) translation of the mRNA encoding DA D2 receptors results in receptors that are negatively coupled with adenylyl cyclase and functionally linked to inhibition of prolactin synthesis; and (b) the release of prolactin might be regulated, at least in part, by a DA receptor that is encoded by mRNA species distinct from those encoding the D2 receptor.     

CCK-8 antagonizes apomorphine-induced growth hormone secretion in normal subjects

Cholecystokinin octapeptide (CCK-8) (5 ug iv over 10 minutes) administered to normal men had no effect on basal growth hormone (GH) or prolactin secretion but significantly antagonized the GH response to the dopamine (DA) receptor agonist, apomorphine HCI (Apo) (0.5 mg sc), 30 (P less than 0.05) and 45 minutes (P less than 0.01) after Apo injection (n = 8). These results are compatible with an inhibitory effect of CCK-8 on certain DA mechanisms in the hypothalamic-pituitary axis. Whether CCK-8 affects DA function in other brain regions in man is unknown.     

Persistence of low hypothalamic dopaminergic activity after removal of chronic estrogen treatment

The purpose of this study was to determine whether inhibition of tuberoinfundibular dopaminergic (TIDA) neuron function which occurs during chronic estrogen administration persists after removal of the estrogen. Ovariectomized (OVX) Fischer 344 (F344) rats were implanted for 4 weeks with a Silastic capsule containing estradiol-17 beta (E2) and controls with an empty capsule for 4 weeks. Other rats which received E2 for 4 weeks had the capsule removed and experiments performed 4 weeks later. At the end of 4 weeks of E2 treatment, anterior pituitary (AP) weight was increased sixfold, serum prolactin (PRL) 65-fold, and AP DNA content fivefold over OVX control rats. Four weeks after removal of E2, AP weight, serum PRL, and AP DNA content declined, but remained significantly above OVX control values. At the end of 4 weeks of E2 treatment and after E2 withdrawal, release of [3H]dopamine (DA) from median eminence (ME) tissue superfused in vitro was lower than from ME of OVX control rats although [3H]DA accumulation was not significantly different among the treatment groups. Administration of apomorphine (APO), a dopamine agonist, significantly reduced plasma prolactin levels in OVX control rats, in rats at the end of 4 weeks E2 treatment, and in rats after 4 weeks of E2 withdrawal. Injection of haloperidol (HALO) produced similar increases in plasma PRL/estimated PRL-cell DNA in OVX controls, at the end of E2 treatment or after E2 withdrawal. However, injection of morphine (MOR), a drug which increases the release of PRL by inhibiting hypothalamic dopaminergic activity, resulted in a rise in plasma PRL/estimated PRL-cell DNA in OVX control rats that was significantly greater compared to rats at the end of E2 treatment or after E2 withdrawal. Since rats treated with E2 released less [3H]DA from ME tissue in vitro, and were less responsive to MOR, it can be that animals treated for 4 weeks with E2 show a decreased ability to release DA from TIDA neurons which persists even after termination of E2 treatment. These results suggest that chronic high circulating E2 levels result in a depression of TIDA neuronal activity which is sustained after E2 is removed.     

Effect of 3-PPP,a putative dopamine autoreceptor agonist,on rat serum prolactin levels

3-(3-hydroxyphenyl)-N-n-propylpiperidine (3-PPP) has been reported to be a relatively selective agonist for dopamine (DA) auto-receptors in the striatal and limbic region. We have examined the effect of 3-PPP on rat plasma or serum prolactin levels. 3-PPP produced a non-significant decrease in baseline plasma prolactin levels. It produced a dose-dependent inhibition of the increase in serum prolactin levels produced by gamma-butyrolactone. Both doses of 3-PPP tested completely reversed the increase in serum prolactin levels.produced by reserpine and alpha-methylparatyrosine. These results strongly indicate that 3-PPP directly stimulated DA receptors on pituitary lactotrophes. 3-PPP only weakly inhibited the ability of ³H-spiroperidol to bind to pituitary or striatal membranes, suggesting that it may act at a different DA receptor than classical DA receptor blocking drugs. This DA receptor could have properties in common with the autoreceptors of the mesolimbic and nigrostriatal DA neurons.     

Effects of chronic bromocriptine treatment of an estrone-induced, prolactin-secreting rat pituitary adenoma

Bromocriptine (BROM), a dopamine (DA) agonist, is commonly and successfully used for long-term treatment of human prolactinomas. We have studied the effects of chronic BROM administration to female 344 Fisher/Lis rats bearing an estrone-induced, prolactin (PRL)-secreting pituitary tumor recently characterized as a model for human prolactinoma. The animals were injected twice daily with BROM (2.5 mg/kg) or with diluent. After 1 month of treatment, the animals were sacrificed, and plasma collected and stored at -20 degrees C for PRL radioimmunoassay. The pituitary tumors were removed and tumoral mammotrophs dispersed enzymatically for studies of DA receptor binding and PRL release in vitro. BROM treatment significantly reduced tumor weight, cell size, rough endoplasmic reticulum, Golgi complexes and plasma PRL levels. [3H]-spiroperidol binding to tumoral mammotrophs was also evaluated. BROM induced a significant decrease in the number of DA binding sites without any changes in affinity. These results indicate that chronic BROM treatment of an animal model of prolactinoma induces tumor involution, reduction of PRL release and probably synthesis, and down regulation of dopaminergic binding sites.     

Dopamine Efflux from Striatum After Chronic Nicotine: Evidence for Autoreceptor Desensitization

We examined the effect of chronic nicotine treatment on dopaminergic activity by measuring the effects of D1 and D2 dopamine (DA) receptor agonists and antagonists on tritium release from mouse striatum preloaded with [3H]DA. The radioactivity released during superfusion was separated on alumina columns and the distribution and efflux of [3H]DA and its main 3H-labeled metabolites were quantified. After preloading by incubation with [3H]DA, the electrical stimulation-evoked tritium overflow was higher in striatum prepared from nicotine-treated mice, whereas in vitro addition of nicotine caused a similar increase in tritium release from striatum of untreated and chronic nicotine-treated mice. The overflow of [3H]DA and its 3H-metabolites exhibited similar distribution patterns in [3H]DA-preloaded striatum dissected from untreated and chronic nicotine-pretreated mice, indicating that repeated injections with nicotine did not alter the metabolism of [3H]DA taken up by the tissue. (-)-Quinpirole, a selective agonist for D2 DA receptors, and apomorphine, a nonselective D1/D2 agonist, inhibited the electrical stimulation-induced tritium efflux from striatum of untreated mice, whereas (+/-)-sulpiride, a D2 DA receptor antagonist, enhanced the evoked release of tritium. These changes in tritium efflux effected by (-)-quinpirole and (+/-)-sulpiride reflected changes in [3H]DA release and not in DA metabolism, as shown by separation of the released radioactivity on alumina columns. The D1 receptor agonist (+/-)-SKF-38393 did not affect the tritium overflow, whereas the D1 receptor antagonist (+)-SCH-23390 exerted a stimulatory action but only at a high concentration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Long-Term Survival of Intrastriatal Dopaminergic Grafts: Modulation of Acetylcholine Release by Graft-Derived Dopamine

The nigrostriatal dopaminergic system of rats was unilaterally lesioned with 6-hydroxydopamine. Part of the animals was grafted 2 weeks later with fetal dopaminergic cells on the lesioned side; untreated rats of the same strain served as controls. Both 3 and 12-14 months after surgery the striatal dopamine (DA) content and the in vivo rotational response following injection of D-amphetamine showed significant changes in grafted as compared to lesioned animals. At 12-14 months after transplantation, the electrically evoked release of tritiated DA and acetylcholine (ACh) in slices (preincubated with [3H]DA or [3H]choline, respectively) of striata of intact, lesioned, or grafted animals was also investigated. Electrical field stimulation of striatal slices of the lesioned side did not evoke any significant [3H]DA overflow, whereas a marked [3H]DA release was observed in slices of grafted and control striata. Moreover, both DL-amphetamine (3 microM) and nomifensine (10 microM) strongly enhanced basal 3H outflow in these slices. Electrically evoked [3H]ACh release was significantly reduced in slices from all striatal tissues by 0.01 microM apomorphine. In slices from denervated striata a clearcut hypersensitivity for this action of apomorphine was present, indicating supersensitivity of DA receptors on cholinergic terminals; this hypersensitivity was significantly reduced in graft-bearing striata. Furthermore, because this hypersensitivity was unchanged in slices of lesioned striata under stimulation conditions (four pulses/100 Hz) avoiding inhibition by endogenously released DA, it is concluded that lesion-induced DA receptor supersensitivity is caused by an increase in receptor density or efficacy rather than by a decreased competition between endogenous and exogenous agonists. Both reuptake blockade of DA with nomifensine (10 microM) and release of endogenous DA by DL-amphetamine (3 microM) potently reduced [3H]ACh release only in control and grafted but not in lesioned tissue. In experiments using potassium-evoked [3H]ACh release, tetrodotoxin had no effect on the inhibitory activity of amphetamine and nomifensine, indicating that the DA receptors involved in their indirect inhibitory action are located directly on the cholinergic terminals.     

Regional Decreases in α-[3H]Amino-3-Hydroxy-5-Methylisoxazole-4-Propionic Acid ([3H]AMPA) and 6-[3H]Cyano-7-Nitroquinoxaline-2,3-dione ([3H]CNQX) Binding in Response to Chronic Low-Level Lead Exposure: Reversal Versus Potentiation by Chronic Dopamine Agonist Treatment

Abstract: This study evaluated the hypotheses that in vivo lead (Pb) exposure would alter α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor binding and, based on known glutamate-dopamine interactions and Pb-induced changes in dopamine (DA) systems, that AMPA binding might be differentially influenced by DA agonist treatment under conditions of Pb exposure. Alterations in high-affinity ([³H]AMPA) versus total AMPA [6-[³H]cyano-7-nitroquinoxaline-2,3-dione ([³H]CNQX)] receptor binding were determined in medial frontal cortex, dorsal striatum, and nucleus accumbens of rats exposed to 0, 50, or 150 ppm of Pb acetate for 2 weeks or 8 months. Additional 8-month groups received chronic intermittent treatment with saline, the D₁ agonist SKF82958, or the general DA agonist apomorphine. Two-week exposures increased AMPA receptor densities, whereas robust decreases occurred after 8 months of Pb; at the latter time point changes were more pronounced for high-affinity than total AMPA receptor binding, with high-affinity effects expressed preferentially in dorsal striatum and nucleus accumbens. DA agonist treatments almost fully reversed Pb-related declines in [³H]AMPA binding but either had no effect (apomorphine) or even further potentiated (SKF82958) the decreases in [³H]CNQX binding. One possible basis for the long-term (8-month) decrease in AMPA binding is a postsynaptic glutamatergic stimulation of non-NMDA receptors.     

Agonist-induced desensitization of the D-2 dopamine receptor in the intermediate lobe of the rat pituitary gland

The mechanism of agonist-induced desensitization of the D-2 dopamine receptor in the intermediate lobe (IL) of the rat pituitary gland was investigated. Exposure of neurointermediate lobe to 60 microM (-)apomorphine (APO) for 60 min altered the binding of [125I]-N-(p-aminophenethyl)spiperone (NAPS), a D-2 receptor-specific ligand. The capacity of the tissue to bind the ligand (Bmax) was not significantly altered by the exposure to (-)APO but the affinity for [125I]NAPS was decreased 3.6-fold in (-)APO-exposed tissue. The molar potency of YM-09151-2, a D-2 receptor-specific antagonist, showed a minimal difference between in control and (-)-APO-exposed tissue. However, the molar potency of (-)APO towards the D-2 receptor was diminished. The loss of [125I]NAPS binding in (-)APO-exposed tissue was reversed by the addition of guanyl nucleotide. These data suggest that exposure to agonist causes a persistent occupancy of the high affinity state of the receptor. Exposure to (-)APO had no effect on either basal or forskolin-activated adenylate cyclase activity of the intermediate lobe. However, the inhibitory effect of (-)APO upon adenylate cyclase activity of IL homogenates was diminished when the tissue was exposed to (-)APO before homogenization. Furthermore, the ability of GTP but not 5'-guanylyl imidodiphosphate [Gpp(NH)p] to inhibit enzyme activity diminished in the (-)APO-exposed tissue. These data suggest that an agonist-induced desensitization of D-2 receptor in rat IL is thought to occur by uncoupling the receptor from the inhibitory guanyl nucleotide binding protein (Gi) or potentiating the hydrolysis of GTP by Gi.     

Dopamine Stimulates [3H]Phorbol 12,13-Dibutyrate Binding in Cultured Striatal Cells

The effect of dopamine (DA) on the binding of [3H]phorbol 12,13-dibutyrate ([3H]PdBu) in cultured rat striatal cells was examined. DA maximally increased specific [3H]PdBu binding by 70 +/- 10%, an increase comparable to that observed with norepinephrine (NE). This finding suggests that DA activates protein kinase C in cultured striatal cells, because increases in [3H]PdBu binding reflect translocation of protein kinase C. Half-maximal stimulation was observed with 10(-6) M DA. The peak response was observed at 2-3 min after addition of 10(-4) M DA, but [3H]PdBu binding was still increased above basal at 30 min. DA was not acting via an adrenergic receptor. Prazosin (10(-6) M) blocked the response to NE, suggesting mediation by an alpha 1-adrenergic receptor, but had little effect on the response to DA. Conversely, the D1 receptor antagonist SCH-23390 (10(-6) M) blocked the response to DA, but only partially inhibited the response to NE. Morphine (10(-6) M) inhibited the response to DA by 46 +/- 14%, but did not affect significantly the response to NE. The DA effect on [3H]PdBu binding is apparently independent of the increase in cyclic AMP seen on D1 receptor activation. Forskolin, apomorphine, and the D1 agonist SKF-38393 all increased cyclic AMP in striatal cells, but were less effective than DA in stimulating [3H]PdBu binding. The D2 agonist quinpirole was ineffective in stimulating either cyclic AMP or [3H]PdBu binding.     

Prolactin increases the density of striatal dopamine receptors in normal and hypophysectomized male rats

Administration of prolactin to adult male rats, by s.c. injection, significantly increases the density of the striatal dopamine (DA) receptors, without altering the apparent affinity of the receptors for [³H]spiroperidol. Larger doses of prolactin are required to increase the density of the striatal DA receptors in hypophysectomized rates compared to normal rats. These results suggest that prolactin might be the common mediator of the increase in striatal DA receptor density produced by either estrogen or haloperidol administration. Monitoring and/or altering prolactin levels might be informative in neurologic or psychiatric disorders involving striatal DA neurotransmission.     

Dopamine Autoreceptor Stimulation Increases Protein Carboxyl Methylation in Striatal Slices

We have investigated the possibility that protein carboxyl methylation is involved in coupling dopamine autoreceptor stimulation to intracellular events such as inhibition of dopamine synthesis or release. The dopamine agonists apomorphine and TL-99 were found to stimulate methyl ester formation in striatal slices preloaded with [3H]methionine. The stimulatory effects of apomorphine were dose-dependent, were not due to changes in [3H]methionine uptake or S-[3H]-adenosylmethionine formation, and were blocked by the stereospecific dopamine antagonist (+)-butaclamol. Stimulation of methyl ester formation by dopamine agonists is readily observed only when slices are prepared from rats pretreated with reserpine to deplete endogenous brain catecholamines. This suggests that in slices prepared from normal rats endogenous dopamine (DA) released during slice preparation and incubation masks the effects produced by exogenously administered dopamine agonists on protein carboxyl methylase (PCM) activity. Additional experiments suggested that the effects of apomorphine were mediated via an interaction with DA autoreceptors rather than with postsynaptic DA receptors. Destruction of monoamine neurons and their associated autoreceptors by injecting 6-hydroxydopamine into the area of the medial forebrain bundle abolished the stimulatory effects of apomorphine on methyl ester formation in striatal slices. Furthermore the putative selective DA autoreceptor agonist EMD 23 448 was also found to stimulate methyl ester formation in striatal slices. These findings, discussed in terms of calcium-dependent functions, support the hypothesis that PCM may be a key component in the biochemical transduction of DA autoreceptor stimulation.     

Structural Differences Between Dopamine D2 Receptors Present in a Rat Pituitary Adenoma and in Transplantable Rat Pituitary Tumors 7315a and MtTW15

We have investigated the structure of dopamine (DA) D2 receptors present in an estrone-induced, prolactin (PRL)-secreting, DA-sensitive adenoma and in two PRL-secreting and DA-insensitive transplantable tumors 7315a and MtTW15, in order to identify better the anomalies present in DA-resistant lactotrophs. D2 receptors were found in both a high- and a low-affinity state in adenomatous lactotrophs as shown by displacement studies with the agonist N-propylnorapomorphine (NPA), but only in the low-affinity state in the two DA-resistant tumors. Treatment with the alkylating agent N-ethylmaleimide induced a disappearance of the high-affinity state of the D2 receptor in the adenoma and a reduction in receptor concentration, but did not have any effect on the affinity of receptors present in DA-resistant tumors. Moreover, target size analysis and radiation inactivation studies of D2 receptors, using membranes preincubated with NPA and [3H]spiperone as ligand or using [3H]NPA as ligand on membranes preparations, have shown the presence of distinct structural differences between adenomatous and tumoral D2 receptors and between the two tumoral receptors themselves; these results suggest that the normal functional unit of the D2 receptor is a dimer associated with a guanine nucleotide-binding protein (G protein) subunit and that tumoral D2 receptors may exist in various polymeric forms unassociated with G proteins. The anomalies found to be present in tumoral D2 receptor complexes may be responsible for the insensitivity of these tumors to dopaminergic agonists' inhibitory activity on PRL release and tumor growth.     

Expression of prolactin receptors in normal canine mammary tissue, canine mammary adenomas and mammary adenocarcinomas

ABSTRACT: BACKGROUND: Mammary tumors represent the most common neoplastic disease in female dogs. Recently, the promoting role of prolactin (PRL) in the development of human breast carcinoma has been shown. Possible proliferative, anti-apoptotic, migratory and angiogenic effects of PRL on human mammary cancer cells in vitro and in vivo were suggested. The effects of PRL are mediated by its receptor, and alterations in receptor expression are likely to play a role in tumor development. Currently, not much data is available about prolactin receptor (PRLR) expression in canine mammary tumors. To set the basis for investigations on the role of PRL in mammary tumorigenesis in this species, prolactin receptor expression was evaluated by semi-quantitative real time PCR and immunohistochemistry on 10 formalin-fixed, paraffinembedded samples each of canine non-neoplastic mammary tissue, mammary adenomas and adenocarcinomas. RESULTS: The highest PRLR expression levels were found in normal mammary tissue, while adenomas, and to an even higher degree adenocarcinomas, showed a significant decrease in prolactin receptor expression. Compared to normal tissue, PRLR mRNA was reduced 2.4 fold (p =0.0261) in adenomas and 4.8 fold (p = 0.008) in adenocarcinomas. PRLR mRNA expression was significantly lower in malignant than in benign lesions (p = 0.0165). Immunohistochemistry demonstrated PRLR expression in all three tissue types with signals mostly limited to epithelial cells. CONCLUSIONS: Malignant transformation of mammary tissue was associated with a decline in prolactin receptor expression. Further studies are warranted to address the functional significance of this finding.     

The effects of opiate agonists on growth hormone and prolactin release in rats

Various opioid receptor agonists, including Met5-enkephalin amide, Leu5-enkephalin amide, [D-Ala]2-Met5-enkephalin amide, [D-Ala]2-Leu5-enkephalin amide, morphine sulfate, d-methadone hydrochloride, and l-methadone hydrochloride were administered to adult male rats by subcutaneous injection. All opioid receptor agonists except Leu5-enkephalin amide significantly stimulated growth hormone and prolactin release. Naloxone and naltrexone blocked the hormone stimulatory effects of the opioids and both naloxone and naltrexone, when administered alone, significantly reduced serum growth hormone and prolactin concentrations. The dopaminergic agonist apomorphine, but not the alpha-adrenergic agonist clonidine, blocked opiate stimulation of prolactin. Morphine sulfate caused growth hormone release in rats pretreated with alpha-methyl-p-tryosine, a catecholamine synthesis inhibitor. Cholinergic agonists, physostigmine and pilocarpine, antagonized the growth hormone and prolactin release induced by morphine sulfate. The data suggest that the opiates stimulate prolactin via an interaction with catecholaminergic neurons controlling prolactin release and stimulate growth hormone via a mechanism independent of alpha-adrenergic or general catecholaminergic influence. The mechanism through which cholinergic agonists act to inhibit opiate agonist stimulation of growth hormone is presently unknown.     

Induction of turning by direct intrastriatal injection of dopaminomimetic drugs in mice: pharmacological analysis of a simple screening model

A new simple model designed for the screening of dopaminomimetic drugs in mice is presented. When injected directly into the right striatum of conscious mice, the dopamine (DA) receptor agonists apomorphine, SKF 38393 and bromocryptine, the indirect DAmimetic drugs (+)-amphetamine and nomifensine, the atypical DAergic antidepressant drug minaprine, induced contralateral rotations. Rotations induced by DA mimetics were antagonized by i.p. injected haloperidol. A pretreatment with the D1 antagonist SCH 23390 (s.c.) antagonized the turning induced by apomorphine or by the D1 agonist SKF 38393, and, to a lesser extent, that induced by the D2 agonist bromocryptine. In contrast, the D2 antagonist (-)-sulpiride (i.p.) blocked the effects of the 3 agonists to the same extent. A pretreatment with alpha-methylparatyrosine (i.p.) antagonized rotations induced by bromocryptine, (+)-amphetamine and minaprine, but not those induced by nomifensine or apomorphine. The results suggest that this model could represent a useful screening tool for the search of new DAmimetic drugs, and for the assessment of DA receptor blockade.     

Amplified expression of p21 ras protein in hormone-dependent mammary carcinomas of humans and rodents

Western blotting analysis was utilized to determine the amount of a ras oncogene product, p21 present in mammary carcinomas of humans and rats. The levels of p21 in hormone-dependent rat tumors was about 7-fold that of hormone-independent tumors. The majority of human breast carcinomas examined had high p21 levels, about 10-fold that of the normal breast tissue; 70% of these tumors were estrogen and progesterone receptor positive. p21 levels in the remaining tumors were 3-fold that of the normal breast tissue, regardless of the receptor status. Fibroadenomas and fibrocystic disease showed p21 levels similar to that of the normal mammary glands. Moreover, the high p21 levels in the mammary carcinomas correlated directly with high GTPase activity, as revealed by the photo-incorporation of 8-N3-[gamma-32P]GTP into the tumor lysates. The results suggest that hormone-dependency of mammary carcinomas may correlate with quantitative change in 'normal' p21 protein.     

Pituitary and brain D2 receptor density measured in vitro and in vivo in EEDQ treated male rats.

The effect of the alkylating compound N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) (20 mg/kg, 24 h) on dopamine D2 receptor density in rat pituitary and brain was measured using in vitro and in vivo radioligand binding techniques. In the in vitro radioligand binding experiments EEDQ was found to reduce the density (Bmax) of [3H]-spiperone binding sites in the striatum by 86% while in the pituitary the corresponding decrease was only 37%. The affinity (KD) of the remaining striatal and pituitary D2 receptors was not different in EEDQ treated animals as compared to controls. When D2 receptor density was measured in vivo the effect of EEDQ was less pronounced. Thus, in rats given EEDQ the specific binding of either of the two D2 ligands [3H]-raclopride or [3H]-spiperone (administered in a single dose) in striatum and in the limbic forebrain was reduced by 45-62%; moreover, no significant decrease in pituitary D2 receptor density was observed. The data are discussed in relation to the finding (presented in a separate paper) that the same dose of EEDQ that failed to influence pituitary D2 receptor density as measured in vivo effectively antagonizes the prolactin decreasing effect of the partial D2 agonist (-)-3-(3-hydroxyphenyl)-N-n-propyl-piperidine [(-)-3-PPP].