Anticonvulsant effects of mu (DAGO) and delta (DPDPE) enkephalins in rats

The effects of highly selective mu and delta opioid peptide agonists were determined in two rat models of experimentally-induced convulsions, the flurothyl threshold test and the maximal electroshock test. Intracerebroventricular injections of the mu selective enkephalin DAGO (0.3-2.2 nmol) resulted in a dose-related protection in both seizure models. Pretreatment with a low dose of naloxone (29 nmol) or the irreversible mu antagonist beta-FNA (21 nmol), but not the delta opioid antagonist ICI 154,129 (50 nmol), antagonized the anticonvulsant actions of DAGO. Intracerebroventricular injections of the delta selective enkephalin DPDPE (70-140 nmol) also resulted in seizure protection. These effects were selectively antagonized by the delta antagonist ICI 174,864 (2.8 nmol), but not by pretreatment with beta-FNA. Thus, using agonists and antagonists highly selective for mu and delta opioid receptors, anticonvulsant actions of enkephalin have been described against chemically- and electrically-induced convulsions in rats.     

Anabolic effects of recombinant human parathyroid hormone (1 - 84) and synthetic human parathyroid hormone (1 - 34) on the mandibles of osteopenic ovariectomized rats with maxillary molar extraction.

In rodent osteoporosis models such as ovariectomized (OVX) rats, intermittently administered human parathyroid hormone (hPTH) has an anabolic effect in vertebrae and long bones. In the present experiments, subcutaneously injected hPTH(1 - 34) or hPTH(1 - 84) dose- and time-dependently increased bone mineral density (BMD) as measured by dual energy X-ray absorptiometry in mandibles, L2 to L4 vertebrae and femurs of such rats. The highest dose (15.9 nmol/kg, s. c.) of either peptide given four times weekly for 10 weeks completely reversed the effects of overiectomy on BMD. Significant elevation in lumbar BMD after 10 weeks was observed with hPTH(1 - 34) or hPTH(1 - 84) at 1.1 nmol/kg, whereas hPTH(1 - 34) at 1.1 and 4.2 nmol/kg significantly increased BMD of the whole bone and the metaphysis of the femur and the diaphysis of the bone, respectively. In contrast, significant effects of hPTH(1 - 84) administration on BMD increase in the femur were observed at 4.2 and 15.9 nmol/kg in the whole bone and the metaphysis, and in the diaphysis, respectively. Maxillary molar extraction left mandibular BMD in rats with intact ovaries unchanged, but significantly decreased mandibular BMD in OVX rats. Administration of hPTH(1 - 84) for 10 weeks in OVX rats without or with extraction significantly increased BMD in the mandibular molar region at doses of 15.9 and 4.2 nmol/kg, respectively, indicating that efficacy was increased by extraction. A significant BMD increase in the molar region in OVX rats with extraction occurred at only 1.1 nmol/kg of hPTH(1 - 34) and 4.2 nmol/kg of hPTH(1 - 84). Also, BMD of the ramus region was increased by administration of both peptides to a lesser extent than that of the molar region in these rats. Thus, intermittent administration of hPTH, especially hPTH(1 - 34), has an anabolic effect on bone, particularly alveolar bone. Such treatment may increase alveolar bone mass in postmenopausal women with osteoporosis.     

Angiotensin-(1-7) stimulates oxidative stress in rat kidney

The effect of two different doses of angiotensin-(1-7) and angiotensin II on the oxidative stress generation was analyzed in rat kidney. Animals were injected intraperitoneally with a single dose of angiotensin-(1-7) or angiotensin II (20 or 50 nmol/kg body weight) and killed 3 h after injection. Production of thiobarbituric acid reactive substances (TBARS), measured as indicator of oxidative stress induction, was significantly increased in rat kidney after Ang-(1-7) administration up to 30% and 50% over controls, at 20 and 50 nmol/kg, respectively. Reduced glutathione (GSH), the most important soluble antioxidant defense in mammalian cells, showed a significant decrease of 13% and 20% at 20 and 50 nmol/kg of angiotensin-(1-7), respectively. When the antioxidant enzyme activities were determined, it was found that catalase activity was not altered by the assayed angiotensin-(1-7) doses while superoxide dismutase and glutathione peroxidase activities were significantly reduced by injection of 20 nmol/kg (34% and 13%, with respect to controls) and 50 nmol/kg of angiotensin-(1-7) (54% and 22%, respectively). In contrast, angiotensin II injections did not produce significant changes neither in TBARS levels nor in soluble and enzymatic defense parameters at the two doses used in this work. These results suggest that angiotensin-(1-7) is undoubtedly related to oxidative stress induction.     

Enterostatin (VPDPR) has anti-analgesic and anti-amnesic activities

Enterostatin (VPDPR), an anorexigenic peptide derived from the amino terminus of procolipase, significantly inhibited analgesia induced by the mu-opioid agonist morphine (5 mg/kg, s.c.) after i.c.v. administration to mice at a dose of 100 nmol. On the other hand, VPDPR (approximately 200 nmol, i.c.v.) did not attenuate analgesia induced by the kappa-opioid agonist D-Phe-D-Phe-D-Nle-D-Arg-NH2 (100 microg/mouse, i.c.v.) or delta-opioid agonist DTLET (4 nmol/mouse, i.c.v.). VPDPR (100 nmol, i.c.v.) significantly improved amnesia induced by scopolamine (0.2 mg/kg, i.p.) in mice. However, VPDPR did not enhance memory in normal mice at the same dose.     

Enterostatin (VPDPR) Has Anti-analgesic and Anti-amnesic Activites

Enterostatin (VPDPR), an anorexigenic peptide derived from the amino terminus of procolipase, significantly inhibited analgesia induced by the μ-opioidagonist morphine (5 mg/kg, s.c.) after i.c.v. administration to mice at a dose of 100 nmol. On the other hand, VPDPR (～200 nmol, i.c.v.) did not attenuate analgesia induced by the κ-opioid agonist D-Phe-D-Phe-D-Nle-D-Arg-NH₂ (100 μg/mouse, i.c.v.) or δ-opioid agonist DTLET (4 nmol/mouse, i.c.v.). VPDPR (100 nmol, i.c.v.) significantly improved amnesia induced by scopolamine (0.2 mg/kg, i.p.) in mice. However, VPDPR did not enhance memory in normal mice at the same dose.     

The Neurosteroid Pregnenolone Sulfate Increases Cortical Acetylcholine Release: A Microdialysis Study in Freely Moving Rats

Abstract: The effects of pregnenolone sulfate (Preg-S) administrations (0, 12, 48, 96, and 192 nmol intracerebroventricularly) on acetylcholine (ACh) release in the frontal cortex and dorsal striatum were investigated by on-line microdialysis in freely moving rats. Following Preg-S administration, extracellular ACh levels in the frontal cortex increased in a dose-dependent manner, whereas no change was observed in the striatum. The highest doses (96 and 192 nmol) induced a threefold increase above control values of ACh release, the intermediate dose of 48 nmol led to a twofold increase, whereas after the dose of 12 nmol, the levels of ACh were not different from those observed after vehicle injection. The increase in cortical ACh reached a maximum 30 min after administration for all the active doses. Taken together, these results suggest that Preg-S interacts with the cortical cholinergic system, which may account, at least in part, for the promnesic and/or antiamnesic properties of this neurosteroid.     

Colocalization of Glucagon-Like Peptide-1 (GLP-1) Receptors, Glucose Transporter GLUT-2, and Glucokinase mRNAs in Rat Hypothalamic Cells: Evidence for a Role of GLP-1 Receptor Agonists as an Inhibitory Signal for Food and Water Intake

Abstract: This study was designed to determine the possible role of brain glucagon-like peptide-1 (GLP-1) receptors in feeding behavior. In situ hybridization showed colocalization of the mRNAs for GLP-1 receptors, glucokinase, and GLUT-2 in the third ventricle wall and adjacent arcuate nucleus, median eminence, and supraoptic nucleus. These brain areas are considered to contain glucose-sensitive neurons mediating feeding behavior. Because GLP-1 receptors, GLUT-2, and glucokinase are proteins involved in the multistep process of glucose sensing in pancreatic β cells, the colocalization of specific GLP-1 receptors and glucose sensing-related proteins in hypothalamic neurons supports a role of this peptide in the hypothalamic regulation of macronutrient and water intake. This hypothesis was confirmed by analyzing the effects of both systemic and central administration of GLP-1 receptor ligands. Acute or subchronic intraperitoneal administration of GLP-1 (7–36) amide did not modify food and water intake, although a dose-dependent loss of body weight gain was observed 24 h after acute administration of the higher dose of the peptide. By contrast, the intracerebroventricular (i.c.v.) administration of GLP-1 (7–36) amide produced a biphasic effect on food intake characterized by an increase in the amount of food intake after acute i.c.v. delivery of 100 ng of the peptide. There was a marked reduction of food ingestion with the 1,000 and 2,000 ng doses of the peptide, which also produced a significant decrease of water intake. These effects seemed to be specific because i.c.v. administration of GLP-1 (1–37), a peptide with lower biological activity than GLP-1 (7–36) amide, did not change feeding behavior in food-deprived animals. Exendin-4, when given by i.c.v. administration in a broad range of doses (0.2, 1, 5, 25, 100, and 500 ng), proved to be a potent agonist of GLP-1 (7–36) amide. It decreased, in a dose-dependent manner, both food and water intake, starting at the dose of 25 ng per injection. Pretreatment with an i.c.v. dose of a GLP-1 receptor antagonist [exendin (9–39); 2,500 ng] reversed the inhibitory effects of GLP-1 (7–36) amide (1,000 ng dose) and exendin-4 (25 ng dose) on food and water ingestion. These findings suggest that GLP-1 (7–36) amide may modulate both food and drink intake in the rat through a central mechanism.     

Effects of rat and chicken calcitonin gene-related peptides (CGRP) upon calcium metabolism in chicks

In vivo effects of intravenously injected chicken(c-) and rat(r-) calcitonin gene related peptide (CGRP) upon plasma total (Ca_t), ionized (Ca_i) calcium, inorganic phosphate (P_i) and clearance of an acutely administered ⁴⁵Ca label have been examined in chicks.

Both peptides were hypercalcaemic in fasted chicks, unlike previously reported hypocalcaemic response in mammals. r-CGRP was hypercalcaemic at doses of both 0.26 and 1.31 nmol/100 g body wt, the lower dose produced a significant elevation of Ca_t one hour after injection into 12-h-fasted chicks, the upper dose had a similar effect at 20 min. Ca_i was also non-significantly elevated by r-CGRP. P_i was slightly increased by r-CGRP at both doses, 20 and 60 min after injection.

c-CGRP produced a dose (0.26–4.17 nmol/100 g body wt) dependent elevation of Ca_t and Ca_i in 22-h-fasted chicks. A greater response was however seen in fed animals. Peak responses were observed 45 min after injection. c-CGRP (1.04 nmol/100 g body wt) caused a significant decline in plasma P_i (P < 0.05) in fasted chicks. P_i was elevated in control fed animals compared with fasted controls. c-CGRP (1.04 nmol/100 g) did not effect plasma P_i in fed chicks.

Whilst both peptides elevated plasma Ca, clearance of an acutely administered ⁴⁵Ca label from plasma was greater in both r-CGRP treated 12-h-fasted chicks and c-CGRP treated 22-h-fasted chicks. In contrast, the rate of ⁴⁵Ca clearance in fed chicks was not affected by c-CGRP treatment.

The differential effects of these peptides upon plasma ⁴⁵Ca clearance and other plasma parameters of Ca metabolism, suggest a complex mode of action of the peptide upon avian Ca homeostasis, possibly involving direct actions upon kidney and bone.     

Effects of dose and time after administration of 4-isopropyl-2,6,7-trioxa-1-phosphabicyclo (2,2,2)octane-1-oxide (IPTBO) on cyclic nucleotide concentrations in mouse cerebellum

The concentrations of cyclic AMP and cyclic GMP in the mouse cerebellum after intracerebroventricular administration of a range of doses of IPTBO have been studied with particular interest in the temporal changes after injection. A non typical dose relationship was observed. After the lowest and non-convulsive dose used (0.06 μg/animal) cyclic AMP levels decreased and cyclic GMP levels increased within 1 min, but after higher doses cyclic AMP and cyclic GMP levels were both raised. At three different convulsive doses of IPTBO there were increased levels of cyclic AMP with time which were more apparent in convulsing animals. Raised levels of cyclic GMP however, were not so influenced by convulsions. The results suggest that (1) the immediate decrease in cyclic AMP and the immediate increase in cyclic GMP may play a part in the mechanism of action of IPTBO—possibly by triggering convulsions and (2) there is an increase in cyclic AMP in response to, or because of, the convulsions. It is concluded that time after treatment and time into convulsions are critical when studying cyclic nucleotide changes, particularly for cyclic AMP and that such factors may explain conflicting observations with respect to this nucleotide.     

Differential inhibition of galanin- and ghrelin-induced food intake by i.c.v. GLP-1(7-36)-amide

Feeding regulation involves both anorectic and orexigenic neuropepetides mainly located in the hypothalamus. To gain further insight into the interaction between these two groups of regulators inhibition of feeding induced by glucagon-like peptide-1 (GLP-1) was examined during stimulation of food intake by equimolar doses of ghrelin and galanin. The experiments were carried out in freely feeding rats. Intracerebroventricular (i.c.v.) injections were accomplished through stereotaxically implanted cannulae aimed at the lateral cerebral ventricle. Food intake of standard rat chow pellets was subsequently recorded for 2 h. Ghrelin and galanin stimulated food intake significantly with no difference between these two peptides. During ghrelin stimulation GLP-1 inhibited feeding in doses between 0.015 and 1.5 nmol. During galanin stimulation of food intake a ten fold higher dose (0.15 nmol) was required to inhibit food intake. In conclusion equimolar doses of i.c.v. ghrelin and galanin are similarly effective stimuli of food intake when given alone. However in combination with an anorectic neuropeptide such as GLP-1 they have substantially different potencies of feeding stimulation. Such interaction could also be of interest for therapeutic strategies involving both regulating groups of neuropeptides.     

Reversal of the effects of centrally-administered morphine on colonic motility in dogs by the benzodiazepine receptor antagonist RO 15-1788

The effects of intravenous (i.v.) and intracerebroventricular (i.c.v.) administration of morphine on jejunal and colonic motility were investigated in conscious dogs chronically prepared with strain gage transducers and compared to those of i.c.v. DAGO, a highly selective opiate mu agonist. Morphine i.v. (100 micrograms/kg) and i.c.v. (10 micrograms/kg) administered 3 hrs after a meal stimulated colonic motility for 3-5 hrs and induced a phase 3 on the jejunum, which appeared after a 15-60 min delay following i.c.v. administration. These effects were reproduced by DAGO administration at doses of 2 micrograms/kg i.v. and 0.2 micrograms/kg i.c.v. The effects of i.v., but not those of i.c.v., morphine and DAGO on jejunal and colonic motility were blocked by a previous administration of naloxone (100 micrograms/kg i.v.). The colonic stimulation but not the jejunal phase 3 induced by i.c.v. morphine and DAGO were blocked by RO 15-1788 (1 mg/kg i.v.), a selective benzodiazepine antagonist. The colonic stimulation induced by i.v. morphine or DAGO was not modify by i.v. RO 15-1788. It is concluded that i.c.v. administration of mu agonist involved benzodiazepine but not opiate receptors to stimulate colonic motility in dogs.     

The distribution of (5E)-(10S)-10,19-dihydroercalciol and its metabolites in serum of rats

The distribution of radioactivity in serum of male rats (275 g) after oral administration of tritium labelled (5E)-(10S)-10,19-dihydroercalciol (dihydrotachysterol2) has been studied as a function of time and dose level. Nine distinct radioactive substances, chromatographing in the range between calciol and calcitriol, could be demonstrated. No attempt was made to establish chemical structures. After a single dose of 1.84 nmol, (5E)-(10S)-10,19-dihydroercalciol is very rapidly metabolized to more polar forms. The time course of appearance, ranging between 30 min and 1 day after administration, and the polarity of these substances indicated that they might be formed in sequence. The highest serum concentrations of the major substances occurred between 2 h and 10 h after administration, but compared with the dosage they were very low. In response to daily administration the concentrations of the major substances achieved steady-state levels within 1-4 days. The metabolism of (5E)-(10S)-10,19-dihydroercalciol was apparently not affected by its nutritional status at the dose level studied. After single administration of progressively increasing doses, ranging from 1.84 nmol to 1.84 mumol, the relative increments of the concentrations of the major substances rose in proportion to the relative increases of the dosage. The mechanisms responsible for the appearance of these substances in serum were found to be closely related. At dose levels up to 18.4 nmol feedback control was apparently absent.     

Supraspinal and spinal effects of [Phe1psi(CH2-NH)Gly2]-nociceptin(1-13)-NH2 on nociception in the rat

A new derivative of the neuropeptide nociceptin (NC) has recently been developed. This molecule, the pseudopeptide [Phe1psi(CH2-NH)Gly2]-nociceptin(1-13)-NH2 was found to antagonize NC inhibitory effects in peripheral smooth muscle preparations in vitro. However, contrasting results have appeared as regards its pharmacodynamic profile in the CNS. Here, we investigated the pseudopeptide effects, in vivo, on nociceptive responses in the rat. [Phe1psi(CH2-NH)Gly2]-nociceptin(1-13)-NH2 was administered intracerebroventricularly (i.c.v.) or intrathecally (i.t.) (alone or in combination with NC), and tail-flick latencies (TFL) to radiant heat were assessed. I.c.v. [Phe1psi(CH2-NH)Gly2]-nociceptin(1-13)-NH2 (1-10 nmol/rat) caused a short-lasting decrease (5 min) of TFL and did not antagonize the threshold lowering effect of i.c.v. NC (1 nmol/rat). At the spinal level, the i.t. administration (0.2-10 nmol/rat) of [Phe1psi(CH2-NH)Gly2]-nociceptin(1-13)-NH2 produced a dose-dependent and long-lasting antinociceptive effect that was not modified by the administration of a high dose (30 nmol/rat i.t.) of the opioid antagonist naloxone. The i.t. co-administration of the pseudopeptide (10 nmol/rat) did not block the antinociceptive effect of i.t. NC (10 nmol/rat). These data indicate that the pseudopeptide behaves as an NC agonist at supraspinal and spinal levels in the rat tail-flick test of nociception. These different profiles in the periphery and the CNS could suggest differences between central and peripheral NC receptor/s and provide a basis for further development of antagonist molecules suitable for their characterization.     

Effects of dynorphin A(1-13) and of fragments of beta-endorphin on blood pressure and heart rate of anesthetized rats.

The effect on blood pressure and heart rate of central administration of dynorphin A(1-13) and of beta-, gamma-, and alpha-endorphin related peptides was studied in urethane-anesthetized rats. Intracerebroventricular (i.c.v., 0.1-10 micrograms) administration of beta-endorphin resulted in a dose-dependent, naltrexone-reversible hypotension and bradycardia. N-terminally modified fragments of beta-endorphin did not reduce blood pressure and heart rate. On the other hand, a dose of 10 micrograms of beta-endorphin(1-27), which lacks the four C-terminal amino acid residues of beta-endorphin, induced a fall in blood pressure and had a biphasic effect on heart rate. These responses, however, were resistant to pretreatment with naltrexone. None of the fragments of beta-endorphin smaller than beta-endorphin(1-27) affected blood pressure when administered i.c.v. in a dose of 10 micrograms. A small transient bradycardia was observed after i.c.v. administration of 10 micrograms of beta-endorphin(1-26), alpha, and gamma-endorphin. The naltrexone-reversible bradycardic response of alpha- and gamma-endorphin was not present in des-tyrosine- and des-enkephalin-alpha- and gamma-endorphin and also not in alpha-endorphin(10-16) and gamma-endorphin(10-17). Upon i.c.v. administration (0.1-50 micrograms) a dose-dependent, naltrexone-reversible decrease in blood pressure and heart rate was induced by dynorphin A(1-13). The present data indicate a hypotensive influence of beta-endorphin, beta-endorphin(1-27), and dynorphin A(1-13), whereas other fragments of beta-endorphin had little or no effect on the cardiovascular parameters investigated.     

Hyposensitivity to the amnesic effects of scopolamine or amyloid beta(25-35) peptide in heterozygous acetylcholinesterase knockout (AChE(+/-)) mice

We examined the sensitivity of AChE(+/-) mice to the amnesic effects of scopolamine and amyloid beta peptide. AChE(+/-) and AChE(+/+) littermates, tested at 5-9 weeks of age, failed to show any difference in locomotion, exploration and anxiety in the open-field test, or in-place learning in the water-maze. However, when treated with the muscarinic receptor antagonist scopolamine (0.5, 5mg/kg s.c.) 20min before each water-maze training session, learning impairments were observed at both doses in AChE(+/+) mice, but only at the highest dose in AChE(+/-) mice. The central injection of Abeta(25-35) peptide (9nmol) induced learning deficits only in AChE(+/+) but not in AChE(+/-) mice. Therefore, the hyper-activity of cholinergic systems in AChE(+/-) mice did not result in increased memory abilities, but prevented the deleterious effects of muscarinic blockade or amyloid toxicity.     

Intracerebroventricular injections of cholecystokinin octapeptide suppress feeding in rats--pharmacological characterization of this action

Cholecystokinin octapeptide (CCK-8), administered intracerebroventricularly (i.c.v.), will suppress feeding. The aim of the present study was to determine the pharmacological characteristics of this satiety inducing effect in rats. For this purpose, we employed a feeding bioassay model in 24 h fasted rats and examined the effects of CCK-8 and a variety of structurally related analogs on latency to feed after i.c.v. injection and on the amount of food and water consumed as measured after the initiation of feeding in sequential 20-min epochs for 1 h. CCK-8, given in doses of 0.1, 1 and 10 nmol, produced a dose-dependent increase in feeding latency and a reduction of food intake during the first 20 min after initiation of feeding. Food intake during the next 40 min and water consumption were not altered. Plasma levels of CCK-like immunoreactivity after an i.c.v. injection of a dose of CCK-8 which blocked feeding (10 nmol) rose insignificantly from 117 to 125 pg/ml. In contrast, at the minimally effective dose of CCK-8 after i.v. administration (10 nmol), which also produced an inhibition of feeding, the plasma level was 1430 pg/ml. This difference indicates that plasma levels of CCK after i.c.v. CCK-8 are not adequate to produce the observed feeding suppression and suggests that the effects of i.c.v. CCK-8 are not mediated by a peripheral redistribution. Systematic dose response studies revealed the following rank order of potencies: CCK-8 greater than or equal to G-17 II much greater than CCK-8 NS = G-17 I greater than or equal to CCK-4 = CCK 26-29 = 0. Only gastrin-17 II (sulfated) produced an effect comparably significant to CCK-8. I.c.v. proglumide at 2500 nmol failed to modify the effects of CCK-8 at 10 nmol after i.c.v. injection. These data demonstrate that the structural requirements for feeding suppressive activity in rat brain are the carboxyterminus with a sulfated tyrosine residue, located 6 to 7 residues from the carboxyterminus, as present in CCK-8 and gastrin-17 II.     

Enhancement of colonic motor response to feeding by central endogenous opiates in the dog

The role of endogenous opiates in the colonic motor response to feeding has been investigated in four dogs chronically fitted with two strain gages on the proximal and distal colon and a cannula in cerebral lateral ventricle. A daily meal stimulated the colonic motility during 8-10 hrs. The colonic motility index was significantly higher during this period when an enkephalinase inhibitor, tiorphan, was intracerebroventricularly (i.c.v.) administered at a dose of 0.1 mg/kg before the meal. This effect was blocked by a previous i.c.v. administration of naltrexone (0.1 mg/kg) and reproduced by (D-Ala2, Met5) enkephalinamide (DALAMIDE) at a dose of 50 mg/kg. I.c.v. administration of tiorphan or DALAMIDE did not modify the colonic motility in dogs fasted for 48 hrs. The postprandial motility index remained unchanged after intravenous administration of tiorphan or DALAMIDE at the same dosages. These results provide evidence for a central control of the colonic motor response to feeding by endogenous enkephalins in dogs.     

Suppression of generalized seizures activity by intrathalamic 2-chloroadenosine application

In the present study, we investigated the effects of micro-injecting 2-chloroadenosine (2-CADO; an adenosine receptor agonist) into the thalamus alone and with theophylline (a nonspecific adenosine receptor antagonist) pretreatment on pentylenetetrazol (PTZ)-induced tonic-clonic seizures in male Wistar albino rats. Following intrathalamic 2-CADO injection alone or theophylline pretreatment, 50 mg kg(-1) PTZ was given ip after 1 and 24 hrs. The duration of epileptic seizure activity was recorded by cortical electroencephalogram (EEG), and seizure severity was behaviorally scored. Intrathalamic 2-CADO administration induced significant decreases in both seizure duration and seizure severity scores at 1 and 24 hrs, but the effects were more abundant on the seizures induced after 24 hrs. On the other hand, pretreatment with theophylline prevented the inhibitor effect of 2-CADO on seizure activity and increased both seizure duration and seizure scores. Present results suggest that the activation of adenosine receptors in the thalamus may represent another anticonvulsant/modulatory site of adenosine action during the course of the PTZ-induced generalized tonic-clonic seizures and provide additional data for the involvement of the adenosinergic system in the generalized seizures model.     

Degradation and glycemic effects of His(7)-glucitol glucagon-like peptide-1(7-36)amide in obese diabetic ob/ob mice

Glucagon-like peptide-1(7-36)amide (tGLP-1) has attracted considerable potential as a possible therapeutic agent for type 2 diabetes. However, tGLP-1 is rapidly inactivated in vivo by the exopeptidase dipeptidyl peptidase IV (DPP IV), thereby terminating its insulin releasing activity. The present study has examined the ability of a novel analogue, His(7)-glucitol tGLP-1 to resist plasma degradation and enhance the insulin-releasing and antihyperglycemic activity of the peptide in 20-25-week-old obese diabetic ob/ob mice. Degradation of native tGLP-1 by incubation at 37 degrees C with obese mouse plasma was clearly evident after 3 h (35% intact). After 6 h, more than 87% of tGLP-1 was converted to GLP-1(9-36)amide and two further N-terminal fragments, GLP-1(7-28) and GLP-1(9-28). In contrast, His(7)-glucitol tGLP-1 was completely resistant to N-terminal degradation. The formation of GLP-1(9-36)amide from native tGLP-1 was almost totally abolished by addition of diprotin A, a specific inhibitor of DPP IV. Effects of tGLP-1 and His(7)-glucitol tGLP-1 were examined in overnight fasted obese mice following i.p. injection of either peptide (30 nmol/kg) together with glucose (18 mmol/kg) or in association with feeding. Plasma glucose was significantly lower and insulin response greater following administration of His(7)-glucitol tGLP-1 as compared to glucose alone. Native tGLP-1 lacked antidiabetic effects under the conditions employed, and neither peptide influenced the glucose-lowering action of exogenous insulin (50 units/kg). Twice daily s.c. injection of ob/ob mice with His(7)-glucitol tGLP-1 (10 nmol/kg) for 7 days reduced fasting hyperglycemia and greatly augmented the plasma insulin response to the peptides given in association with feeding. These data demonstrate that His(7)-glucitol tGLP-1 displays resistance to plasma DPP IV degradation and exhibits antihyperglycemic activity and substantially enhanced insulin-releasing action in a commonly used animal model of type 2 diabetes.     

Inhibition of metaphit-induced audiogenic seizures by APV in rats.

The influence of APV ((+/-)-2-amino-5-phosphonovaleric acid) on EEG activity and behavior was studied on a model of epilepsy induced by intraperitoneal administration of metaphit (1-(1-(3-isothiocyanatophenyl)-cyclohexyl)-piperidine). Male Wistar rats received an injection of metaphit (10 mg/kg) and were subjected to intense audio stimulation (100+/-3 dB, 60 s) at hourly intervals during the experiment. The seizures were classified according to a four point scale ranging from 0 (no seizure) to 3 (tonic convulsions). In our report we studied the time course which revealed the maximum incidence and severity of seizures 7-12 h after the injection (10 out of 12 rats, with severity of 2.25+/-0.32). APV (0.05, 0.1, 0.2 and 0.3 micromol) was injected intracerebroventricularly at the time of fully developed convulsions. APV inhibited seizures in a dose-dependent manner. The minimum dose, which completely blocked seizures in all animals, was 0.3 micromol, while ED50 were 0.11, 0.10 and 0.07 micromol against running, clonus and tonus, respectively. In contrast to behavioral inhibition of convulsions, metaphit-provoked epileptiform activity was not abolished by APV, and represented a prerequisite for the reappearance of behavioral seizures. It is suggested that APV is rather an anticonvulsant than an antiepileptic agent in this model of epilepsy.