Trypsin Activation, Partial Characterization, and Distribution of Kallikrein-Like and Thrombin-Like Proteases in the Neurointermediate Lobe of the Rat Pituitary

This study examined whether the neurointermediate lobe (NIL) of the rat pituitary contains latent kallikrein- and thrombin-like proteases activated by trypsin. Partial characterization of such proteases was attempted. Also examined were the distribution of proteolytic activity within the NIL and levels in both male and female lobes. NIL homogenates were assayed for proteolytic activity at pH 8.0 before and after incubation with trypsin (10 micrograms/ml). Trypsin caused a 10-fold activation of kallikrein-like activity and a 40-fold activation of thrombin-like activity in NIL homogenates. The kallikrein-like activity was separated into two components using diethylaminoethyl-Sephadex. The predominant kallikrein-like protease was a potent kininogenase closely related or identical to glandular kallikrein and was almost exclusively localized to the intermediate lobe. The second kallikrein-like protease (kallikrein A) was a weak kininogenase sensitive to inhibition by both soybean trypsin inhibitor and aprotinin and was similarly concentrated in both the neural lobe and the intermediate lobe. The thrombin-like protease was sensitive to inhibition by hirudin (a specific thrombin inhibitor), clotted fibrinogen, and was slightly more concentrated in the neural lobe than in the intermediate lobe. NILs from female rats contained approximately 40% less kallikrein activity than NILs from male rats but did not differ in their content of thrombin-like activity.     

Influence of serotonergic and adrenergic antagonists on TRH-induced prolactin release in the monkey.

The influence of methysergide, cyproheptadine and SQ 10,631 (serotonergic receptor blockers) at the dose of 35 μg/kg, 50 μg/kg and 5 mg/kg, respectively, and propranolol, phentolamine and phenoxybenzamine (adrenergic receptor blockers) at the dose of 1 mg/kg on TRH-induced prolactin release was studied in sexually mature female monkeys. The serotonergic antagonists had no effect on TRH-induced prolactin release. Both β and α adrenergic antagonist gave a similar potentiation of the TRH-induced prolactin response but only phenoxybenzamine plus TRH was statistically different (P < 0.05) from TRH alone. The effect of the adrenergic receptor blockers is believed to be due to actions on dopamine receptors.     

Molecular and Pharmacological Characterization of GABAA Receptors in the Rat Pituitary

Abstract: Levels of mRNA for the major subunits of the GABA_A receptor were assayed in the rat pituitary anterior and neurointermediate lobes by ribonuclease protection assay. α1, β1, β2, β3, and γ2s were found to be the predominant subunits in the anterior lobe, whereas α2, α3, β1, β3, γ2s, and γ1 were the predominant subunits expressed in the neurointermediate lobe. α5, α6, and δ subunits were not detectable. Hill and Scatchard analysis of [³H]muscimol binding to anterior and neurointermediate lobe membranes showed high-affinity binding sites with dissociation constants of 5.6 and 4.5 n M , respectively, and Hill coefficients near 1. Muscimol sites were present at a maximum of 126 fmol/mg in the anterior lobe and 138 fmol/mg in the neurointermediate lobe. The central-type benzodiazepine antagonist [³H]Ro 15-1788 bound to a high-affinity site with a dissociation constant of 1.5 n M in both tissues, at a maximum of 60 fmol/mg in anterior pituitary and 72 fmol/mg in neurointermediate lobe. A Hill coefficient of 1 was measured for this site in both tissues. Assays of CL 218 872 displacement of Ro 15-1788 were consistent with a pure type I benzodiazepine site in the anterior lobe and a pure type II site in the intermediate lobe. These results are consistent with both tissue-specific expression of particular GABA_A receptor subunits and receptor heterogeneity within individual cells in the pituitary.     

Met-enkephalin-like immunoreactivity in neurointermediate pituitary is decreased by DA receptor stimulation

The effect of dopamine receptor stimulation by administration of the dopamine analogue bromocriptine on Met-enkephalin-LI was examined in rat hypothalamus, and neurointermediate and anterior lobes of pituitary. Bromocriptine treatment resulted in a dramatic decline of Met-enkephalin-LI in neurointermediate pituitary which was significant by 3 days of treatment. Maximal reduction of Met-enkephalin-LI ranged between 60-70% of pretreatment values and was maintained as long as bromocriptine was administered (4 weeks), with no evidence of desensitization or "escape." The effects of bromocriptine on neurointermediate lobe were of long duration and persisted for at least 4 days after discontinuation of treatment. No significant effects of bromocriptine were detected on Met-enkephalin-LI in hypothalamus or anterior pituitary. Whether these differences represent truly different regional regulation of Met-enkephalin-LI or whether the changes are more sensitively reflected in an area such as neurointermediate lobe that largely consists of nerve terminals, remains to be shown.     

Development of the sex difference in glandular kallikrein and prolactin levels in the anterior pituitary of the rat

Glandular kallikrein is a major estrogen-induced and dopamine-repressed protein of the rat anterior pituitary that appears to originate from lactotrophs. This study examined the development of glandular kallikrein levels in the anterior pituitary in both female and male rats and compared it to anterior pituitary prolactin. In addition, the development of glandular kallikrein levels in the neurointermediate lobe of the pituitary and the kidney were also examined. During puberty, a dramatic surge in glandular kallikrein occurred in female anterior pituitaries (16- to 20-fold increase) and levels remained elevated thereafter. The dynamics of the increase were biphasic--glandular kallikrein increased between Day 30 and 45, plateaued between Days 45 and 55, and then increased again between Days 55 and 65. Female anterior pituitary prolactin increased 7- to 8-fold during puberty. The rise during puberty was biphasic and was generally synchronized with increases in glandular kallikrein. However, the initial rise was proportionately less than that of glandular kallikrein, and the secondary surge was more dramatic. In contrast to females, anterior pituitary glandular kallikrein remained at low levels in male rats; prolactin levels also remained unchanged through puberty and increased moderately thereafter. Glandular kallikrein in the female neurointermediate lobe remained unchanged through Day 55, almost doubled on Day 60, and returned to prepubertal levels by Day 65; males did not exhibit the transient surge in neurointermediate lobe levels. Starting at age 60 days, renal glandular kallikrein was found to be slightly higher (15-20%) in females than in males.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of adrenergic antagonists and apomorphine on prolactin release induced by serotonergic antagonists in the monkey.

The influence of adrenergic receptor blockers on the prolactin releasing effect of methysergide and cyproheptadine was examined in sexually mature female monkeys under ketamine anesthesia. Propranolol, a β-adrenergic blocker, at a dose of 1 mg/kg did not alter the prolactin releasing action of 0.1 mg/kg of methysergide but significantly potentiated (P < 0.025) the prolactin releasing action of 0.5 mg/kg of cyproheptadine. Phentolamine and phenoxybenzamine, both α-adrenergic blockers, at 1 mg/kg blunted the prolactin releasing effect of methysergide and cyproheptadine, but the pattern of prolactin blockade was different between the two putative antiserotonergic drugs. The prior administration of apomorphine, 4 mg/kg, a dopamine receptor stimulator, blocked the prolactin releasing effect of methysergide and cyproheptadine. Evidence presented here and from the literature indicate that the prolactin releasing action of methysergide and cyproheptadine is mediated by an antidopaminergic action directly on the pituitary.     

Corticotropin-releasing factor (CRF) receptors in intermediate lobe of the pituitary: biochemical characterization and autoradiographic localization

CRF receptors were characterized using radioligand binding and chemical affinity cross-linking techniques and localized using autoradiographic techniques in porcine, bovine and rat pituitaries. The binding of 125I-[Tyr0]-ovine CRF (125I-oCRF) to porcine anterior and neurointermediate lobe membranes was saturable and of high affinity with comparable KD values (200-600 pM) and receptor densities (100-200 fmoles/mg protein). The pharmacological rank order of potencies for various analogs and fragments of CRF in inhibiting 125I-oCRF binding in neurointermediate lobe was characteristic of the well-established CRF receptor in anterior pituitary. Furthermore, the binding of 125I-oCRF to both anterior and neurointermediate lobes of the pituitary was guanine nucleotide-sensitive. Affinity cross-linking studies revealed that the molecular weight of the CRF binding protein in rat intermediate lobe was identical to that in rat anterior lobe (Mr = 75,000). While the CRF binding protein in the anterior lobes of porcine and bovine pituitaries had identical molecular weights to CRF receptors in rat pituitary (Mr = 75,000), the molecular weight of the CRF binding protein in porcine and bovine intermediate lobe was slightly higher (Mr = 78,000). Pituitary autoradiograms from the three species showed specific binding sites for 125I-oCRF in anterior and intermediate lobes, with none being apparent in the posterior pituitary. The identification of CRF receptors in the intermediate lobe with comparable characteristics to those previously identified in the anterior pituitary substantiate further the physiological role of CRF in regulating intermediate lobe hormone secretion.     

Enzyme- and immuno-histochemical localization of kallikrein. II. The human kidney

Localization of kallikrein in the human kidney was investigated by two markers: kallikrein-like activity and kallikrein antigenicity. Kallikrein-like activity was demonstrated enzyme-histochemically by using a synthetic substrate for kallikrein, pro-phe-arg-naphthyl-ester. Kallikrein antigenicity was demonstrated by the unlabelled antibody peroxidase-antiperoxidase method using an antiserum against human urinary kallikrein. The kallikrein-like activity was localized in the proximal tubular cells without any corresponding kallikrein antigenicity. Neither kallikrein-like activity nor kallikrein antigenicity was noticed in any other tubular cell. These results are contrary to those in the ductal cells of the human parotid gland where the kallikrein-like activity and the kallikrein antigenicity were identical in their locations. The peroxidase-antiperoxidase method revealed, for the first time, kallikrein antigenicity both in the interstitium and in the basement membrane region of Bowman's capsule and of all the tubules, possibly representing circulating glandular kallikreins deposited in the renal tissue. Thus, the present findings are consistent with the hypothesis that the urinary (renal) kallikreins are derived from circulating glandular kallikreins.     

Enzyme- and immuno-histochemical localization of kallikrein

Summary Localization of kallikrein in the human kidney was investigated by two markers: kallikrein-like activity and kallikrein antigenicity. Kallikrein-like activity was demonstrated enzyme-histochemically by using a synthetic substrate for kallikrein, pro-phe-arg-naphthyl-ester. Kallikrein antigenicity was demonstrated by the unlabelled antibody peroxidase-antiperoxidase method using an antiserum against human urinary kallikrein. The kallikrein-like activity was localized in the proximal tubular cells without any corresponding kallikrein antigenicity. Neither kallikrein-like activity nor kallikrein antigenicity was noticed in any other tubular cell. These results are contrary to those in the ductal cells of the human parotid gland where the kallikrein-like activity and the kallikrein antigenicity were identical in their locations. The peroxidase-antiperoxidase method revealed, for the first time, kallikrein antigenicity both in the interstitium and in the basement membrane region of Bowman's capsule and of all the tubules, possibly representing circulating glandular kallikreins deposited in the renal tissue. Thus, the present findings are consistent with the hypothesis that the urinary (renal) kallikreins are derived from circulating glandular kallikreins.     

Possible involvement of dopamine and dopamine2 receptors in the inhibitions of gastric emptying by escin Ib in mice

It was previously reported that escin Ib isolated from horse chestnut inhibited gastric emptying (GE) in mice, in which the capsaicin-sensitive sensory nerves (CPSN), the central nervous system and endogenous prostaglandins (PGs) were involved. In the present study, the possible involvement of dopamine and dopamine receptors in the inhibition of GE by escin Ib were investigated in mice. GE inhibition by escin Ib (25 mg/kg, p.o.) was attenuated after pretreatment with a single bolus of DL-alpha-methyl-p-tyrosine methyl ester (400 mg/kg, s.c., an inhibitor of tyrosine hydroxylase), reserpine (5 mg/kg, p.o., a catecholamine depletor), 6-hydroxydopamine (80 mg/kg, i.p., a dopamine depletor). Furthermore, pretreatment with spiperone (0.5-5 mg/kg, s.c., a dopamine2 receptor antagonist), haloperidol (0.5-10 mg/kg, s.c.) and metoclopramide (1-10 mg/kg, s.c.) (centrally acting dopamine2 receptor antagonists) attenuated the effect of escin Ib. Domperidone (0.1-5 mg/kg, s.c., a peripheral-acting dopamine2 antagonist) showed a weak attenuation, but SCH 23390 (1-5 mg/kg, s.c., a dopamine, receptor antagonist) did not. It is postulated that escin Ib inhibits GE, at least in part, mediated by CPSN, to stimulate the synthesis and/or release of dopamine, to act through central dopamine2 receptor, which in turn causes the release of PGs.     

Effect of acute ethanol in vivo and in vitro on the beta-endorphin system in the rat

Acute ethanol treatment in vivo (i.p. injection of 3.5 g ethanol/Kg B. wt.) stimulated the release of beta-endorphin like peptides by the pituitary gland as was indicated by the increased content of beta-endorphin like immunoreactivity (beta-EPLIR) in the plasma. Furthermore, a significant decrease in the anterior lobe content of beta-EPLIR was observed, while the decrease in the neurointermediate lobe beta-EPLIR content at 45 min after the i.p. ethanol injection was not statistically significant. In vitro incubation of neurointermediate lobes, from animals injected with either ethanol or saline, in the presence of 3H phenylalanine indicated that the content of beta-EPLIR in the incubation medium was increased, the content of the newly biosynthesized 3H-phenylalanine labelled proteins in the neurointermediate lobe extract was decreased, while the content of 3H-phenylalanine labelled pro-opiomelanocortin, beta-lipotropin and beta-endorphin in the neurointermediate lobes extract were not significantly changed by the ethanol treatment, though a small increase was observed. When neurointermediate lobes from untreated control animals were incubated for 3 hrs with 3H-phenylalanine in the presence or absence of 300 mg ethanol per 100 ml incubation medium, there was no significant difference in the beta-EPLIR content in the incubation medium, or in the content of 3H-phenylalanine labelled proteins, pro-opiomelanocortin, beta-lipotropin and beta-endorphin in the neurointermediate lobe extract. These results suggest that ethanol has little or no direct effect on the beta-endorphin peptides in the pars intermedia cells.     

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.     

Effects of selective dopamine D4 receptor blockers, NRA0160 and L-745,870, on A9 and A10 dopamine neurons in rats

Extracellular single-unit activities of dopamine neurons were recorded using chloral hydrate anaesthetized rats. We examined the reversal effects of the selective dopamine D4 receptor blockers, NRA0160 (2-Carbamoyl-4-(4-fluorophenyl)-5-[2-[4-(3-fluorobenzylidene) piperidin-1-yl] ethyl] thiazole) and L-745,870 (3-[[4-(4-chlorophenyl) piperazin-1-yl] methyl]-1H-pyrrolo [2,3-b] pyridine), on dopamine agonists induced inhibition of dopamine neural activity. The firing rates of the substantia nigra pars compacta (A9) and the ventral tegmental area (A10) dopamine neurons were inhibited by methamphetamine (MAP: 1 mg/kg, i.v.) and apomorphine (APO: 40 microg/kg, i.v). NRA0160 dose-dependently reversed the inhibitory effects of MAP and APO on both A9 and A10 dopamine neurons. NRA0160 was more potent in reversing the inhibitory effects of both MAP and APO on A10 than A9 dopamine neurons. L-745,870 failed to reverse the inhibition produced by MAP on A9 and A10 dopamine neurons, whereas L-745,870, at the highest dose used, significantly reversed APO-induced inhibition of A10 but not A9 dopamine neurons. These results suggest that NRA0160 has different electrophysiological profiles on dopaminergic neural activity compared to L-745,870 and may have atypical antipsychotic effects.     

Pro-opiomelanocortin-derived peptides in the pig pituitary: alpha- and gamma 1-melanocyte-stimulating hormones and their glycine-extended forms

Pro-opiomelanocortin (POMC)-related peptides in extracts of anterior and neurointermediate pituitary lobes from pigs were characterized by gel chromatography, reversed-phase chromatography and radioimmunoassays. The peptide content was ca. 3-fold greater in the anterior lobe compared to the neurointermediate lobe (19.8 nmol POMC/anterior lobe vs 7.0 nmol/neurointermediate lobe). In the neurointermediate lobe 93% of POMC was processed to alpha-melanocyte-stimulating hormone (alpha-MSH) and analogs exclusively of low molecular weight. Most of the remaining adrenocorticotropic hormone (ACTH)-related material consisted of the glycine-extended intermediate ACTH-(1-14) and analogs. In contrast only one fourth to one third of the N-terminal part of POMC (N-POMC) was processed to amidated gamma-MSH and its C-terminal glycine-extended precursor. The relative amount of amidated gamma-MSH was the same as alpha-MSH and analogs (94%). However, more than 95% of these peptides were of high molecular weight. In the anterior lobe 2.3% of N-POMC was processed and 94% was amidated gamma-MSH of only high molecular weight. These results show that gamma-MSH and alpha-MSH are amidated to the same extent and that gamma 1-MSH and gamma 2-MSH immunoreactivity are present in both the anterior lobe and the neurointermediate lobe. The results suggest that the production of amidated peptides is not regulated by the amidation process itself but at an earlier step (e.g. at the proteolytic cleavage).     

Corticotrophin-related peptides in the intermediate lobe of the rodent pituitary gland: characterization by high performance liquid chromatography and radioimmunoassay

High performance liquid chromatography (HPLC) and radioimmunoassay have been used to characterize corticotrophin-related peptides in extracts of the intermediate lobe of the rat and mouse pituitary gland. Multiple peaks have been observed, which resemble corticotrophin-like intermediate lobe peptide (CLIP) in that they cross-react with antisera raised against the COOH-terminal region of corticotrophin (ACTH) but not against NH2-terminal directed antisera. These CLIP-like peptides were released from the incubated neurointermediate lobe and their secretion was inhibited in the presence of dopamine. Heterogeneity of peptide species was also observed with antisera raised against alpha-MSH. Multiple peaks of CLIP and alpha-MSH-like material were identified in pituitary extracts from the mouse and levels were elevated in the genetically obese (ob/ob) animal. The nature and possible functions of multiple forms of intermediate lobe peptides are discussed.     

Rubiscolin-6, a delta opioid peptide derived from spinach Rubisco, has anxiolytic effect via activating sigma1 and dopamine D1 receptors

Rubiscolin-6 (Tyr-Pro-Leu-Asp-Leu-Phe) is a delta opioid peptide derived from the large subunit of spinach d-ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). We previously reported that rubiscolin-6 had an analgesic effect and stimulated memory consolidation. Here we show that intraperitoneally (i.p.) or orally administered rubiscolin-6 has an anxiolytic effect at a dose of 10 mg/kg or 100 mg/kg, respectively, in the elevated plus-maze test in mice. The anxiolytic effects of rubscolin-6 after i.p. (10 mg/kg) and oral (100 mg/kg) administration were blocked by a delta opioid receptor antagonist, naltrindole (1 mg/kg, s.c.), suggesting that the anxiolytic activity of rubiscolin-6 is mediated by delta opioid receptor. The anxiolytic effect of rubiscolin-6 (10 mg/kg, i.p.) was also blocked by a dopamine D(1) antagonist, SCH23390 (30 microg/kg, i.p.), but not by a dopamine D(2) antagonist, raclopride (15 microg/kg, i.p.). The anxiolytic effect of rubiscolin-6 (10 mg/kg, i.p.) was blocked by sigma(1) receptor antagonist, BMY14802 (0.5 mg/kg, i.p.) or BD1047 (10 mg/kg, i.p.). Taken together, the anxiolytic effect of rubiscolin-6 is mediated by sigma(1) and dopamine D(1) receptors downstream of delta opioid receptor.     

GABA differentially regulates the gene expression of proopiomelanocortin in rat intermediate and anterior pituitary

The GABAergic regulation of proopiomelanocortin messenger RNA (POMC mRNA) levels in rat pituitary was investigated using molecular hybridization of DNA complementary to POMC mRNA. Endogenous GABA levels increased, in vivo, by inhibiting the GABA catabolic enzyme GABA-transaminase (GAT) with ethalonamine-O-sulfate (EOS) or with vinyl-GABA (VG). Rats were treated with VG (100 mg/kg or 800 mg/kg) or EOS (100 mg/kg), administered each second day. GABA levels in the neurointermediate lobe (NIL) and anterior lobe (AL) of the hypophysis and in the hypothalamus were significantly increased following 4 days of VG treatment (800 mg/kg). All treatments resulted in a 40-60% decrease in POMC mRNA levels after 4 days in the NIL but not in the AL. A similar decrease of about 60% in POMC mRNA levels in the NIL was seen when EOS was given in the drinking water (5 mg/ml). In this set of experiments the time course of alteration of POMC mRNA in the NIL and the concentration of alpha-MSH, a POMC-derived peptide, were analysed. After one day of EOS treatment, when POMC levels had already decreased by 40%, alpha-MSH levels were significantly elevated (34% above controls), possibly reflecting an inhibition of alpha-MSH secretion. However, after 4 and 8 days, POMC mRNA levels and tissue alpha-MSH levels had significantly decreased. When tested in vitro, on primary cultures of IL cells, GABA (10 microM) reduced POMC mRNA levels by 40% after 3 days of treatment. These results show that GABA exerts a direct inhibitory effect on POMC gene expression in the intermediate lobe.     

Membrane-associated forms of peptidylglycine alpha-amidating monooxygenase activity in rat pituitary. Tissue specificity

Membrane-associated peptidylglycine alpha-amidating monooxygenase (PAM) activity was investigated in rat anterior and neurointermediate pituitary tissues and in pituitary AtT-20/D-16v and GH3 cell lines. A substantial fraction of total pituitary PAM activity was found to be membrane-associated. Triton X-100, N-octyl-beta-D-glucopyranoside, and Zwittergent were effective in solubilizing PAM activity from crude pituitary membranes. The distribution of enzyme activity between soluble and membrane-associated forms was tissue-specific. In the anterior pituitary lobe and pituitary cell lines, 40-60% of total PAM activity was membrane-associated while only 10% of the alpha-amidating activity in the neurointermediate lobe was membrane-associated. Soluble and membrane-associated forms of PAM shared nearly identical characteristics with respect to copper and ascorbate requirements, pH optima, and Km values. Upon subcellular fractionation of anterior and neurointermediate pituitary lobe homogenates on Percoll gradients, 12-18% of total PAM activity was found in the rough endoplasmic reticulum/Golgi fractions and 42-60% was localized to secretory granule fractions. For both tissues, membrane-associated PAM activity was enriched in the rough endoplasmic reticulum/Golgi pool, whereas most of the secretory granule-associated enzyme activity was soluble.     

Protective Effect of L-type Calcium Channel Blockers Against Haloperidol-induced Orofacial Dyskinesia: A Behavioural, Biochemical and Neurochemical Study

Haloperidol is a classical neuroleptic drug that is still in use and can lead to abnormal motor activity such as tardive dyskinesia (TD) following repeated administration. TD has no effective therapy yet. There is involvement of calcium in triggering the oxidative damage and excitotoxicity, both of which play central role in haloperidol-induced orofacial dyskinesia and associated alterations. The present study was carried out to investigate the protective effect of calcium channel blockers [verapamil (10 and 20 mg/kg), diltiazem (10 and 20 mg/kg), nifedipine (10 and 20 mg/kg) and nimodipine (10 and 20 mg/kg)] against haloperidol induced orofacial dyskinesia and associated behavioural, biochemical and neurochemical alterations in rats. Chronic administration of haloperidol (1 mg/kg i.p., 21 days) resulted in a significant increase in orofacial dyskinetic movements and significant decrease in % retention, coupled with the marked increase in lipid peroxidation and superoxide anion generation where as significant decrease in non protein thiols and endogenous antioxidant enzyme (SOD and catalase) levels in rat brain striatum homogenates. All these deleterious effects of haloperidol were significantly attenuated by co-administration of different calcium channel blockers. Neurochemically, chronic administration of haloperidol resulted in significant decrease in levels of catecholamines (dopamine, serotonin) and their metabolites (HVA and HIAA) but increased turnover of dopamine and serotonin. Co-administration of most effective doses of verapamil, diltiazem, nifedipine and nimodipine significantly attenuated these neurochemical changes. Results of the present study indicate that haloperidol-induced calcium ion influx is involved in the pathogenesis of tardive dyskinesia and calcium channel blockers should be tested in clinical trials with nifedipine as the most promising one.     

Effects of dopaminergic drugs on plasma levels of steroid hormones in conscious dogs

Progesterone, cortisol and testosterone levels were measured by radioimmunoassay in peripheral venous blood of conscious dogs. I.v. injections of the dopamine receptor agonists apomorphine (0.05 mg/kg) and bromocriptine (0.1 mg/kg) increased progesterone levels (and cortisol levels, as previously shown) in dogs of both sexes. The response to apomorphine was abolished by pretreatments with peripheral dopamine receptor antagonists (domperidone and halopemide). Progesterone and cortisol responses to the dopamine receptor agonists were parallel, but the ratio of concentration was 1/100. Testosterone levels were not modified. These results suggest that the dopamine receptor agonists stimulate progesterone release from the adrenal glands at a site functionally accessible to the peripheral dopamine receptor antagonists. In addition, the neuroleptic haloperidol (0.1 mg/kg) was shown to cause long lasting increases of progesterone levels.