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This study reports on the in vivo effects of four endomorphin-2 (EM-2) derivatives (EMD1-4) containing unnatural amino acids, i.e. 2-aminocyclohexanecarboxylic acid (Achc2), para-fluorophenylalanine (pFPhe4), β-methylphenylalanine (βMePhe4) and/or 2',6'-dimethyltyrosine (Dmt1). After induction of osteoarthritis by monosodium iodoacetate into the ankle joint of male Wistar rats, a chronic intrathecal catheter was inserted for spinal drug delivery. The mechanical threshold was assessed by a dynamic aesthesiometer. Intrathecal injection of the original EM-2 and the ligands (0.3-10 μg) caused dose-dependent antiallodynic effects. The comparison of the different substances revealed that EMD3 and EMD4 showed more prolonged antinociception than EM-2, and the effects of the highest dose of EMD4 were comparable to morphine, while EMD3 caused paralysis at this dose. The potency of the different ligands did not differ from EM-2. The results show that the derivatives of EM-2 have similar in vivo potency to the original ligand, but their effects were more prolonged suggesting that these structural modifications may play a role in the development of novel endomorphin analogues with increased therapeutic potential.

Changes in peripheral clinico-chemical parameters packed cell volume (PCV), hemoglobin (HGB), serum glucose, carbamide-nitrogen (CN), and creatinine were investigated in mice during the development of acute morphine tolerance. Acute morphine treatment (in drug-naive organism) altered the PCV, HGB, serum glucose and CN levels in a naloxone-reversible manner. Acute tolerance developed in PCV, HGB and CN values. The data raise the possibility of a relationship between clinico-chemical and pharmacological tolerance.

The effect of dipeptides was studied on naloxone-precipitated morphine withdrawal in the mouse. In accordance with previous data, s.c. treatment with Z-prolyl-D-leucine delayed the onset of withdrawal jumpings . Replacement of L-proline by L-glutamate or L-pyroglutamate resulted in dipeptides which were more potent in morphine withdrawal than was Z-prolyl-D-leucine.

Two doses (0.3 and 3 ng peptide/animal) of oxytocin (OXT) and lysine-8-vasopressin (LVP) were earlier found to inhibit the development of tolerance to the hypothermic effect of ethanol in mice upon icv. administration. In the present paper the possible central monoaminergic correlates of the behavioral data were investigated. In tolerant animals the steady-state level of noradrenaline (NA) was increased in the hypothalamus, as was that of dopamine (DA) in the medulla oblongata; the serotonin (5-HT) and DA levels were decreased in the striatum as compared to those in the non-tolerant control. In the peptide-pretreated animals the NA level was increased in the hypothalamus, the DA level in the striatum, and the 5-HT level in the hippocampus and striatum. Opposite changes were observed in the steady-state levels of the monoamines in the hippocampus and striatum as compared to those in the tolerant controls. The data suggest that the central monoamines may be involved in mediating the actions of neurohypophyseal peptides on ethanol tolerance.

The effect of a transitory increase in plasma FSH and LH levels on puberty has been investigated. Hormonal changes were induced by bilateral ovariectomy (OVX) at 20 days of age followed by implantation of two ovaries (donor animals 20-day-old) beneath the kidney capsule 1, 2 or 3 days later. In an other group of animals the two interventions were made in reversed order. Rats in which OVX was made first showed early vaginal opening. If ovarian implantation preceded OVX, these two interventions did not affect the time of vaginal opening. More than 1/3 of the ovarian implanted animals exhibiting early opening of the vagina contained corpora lutea three days after vaginal opening. FSH and LH levels of OVX + ovary implanted rats were from the third day on following implantations markedly different from the OVX controls and were in the range of intact or sham-operated rats. The present findings indicate that a transitory increase in plasma gonadotropin levels around twenty days of age may lead to precocious puberty.

Structurally modified prostaglandins have been synthesized, PGF2 alpha skeleton being substituted at the 13 and 17 position. The prostacyclin analogues were modified at the 3,13 or 17 positions of the prostacyclin skeleton. The effect of these compounds was studied on the development of gastric mucosal damage produced by the intragastric administration of 96% ethanol. The different compounds were given intraperitoneally 30 min before the administration of ethanol. The number and severity of gastric mucosal lesions (ulcers) were recorded without and with the use of different compounds. The prostanoids and prostacyclin analogues were given in doses of 1, 5, 25 or 126 micrograms/kg. Among the tested compounds several fairly active molecules could be found. The significance and practical usefulness of these modifications of prostaglandins and prostacyclins are discussed with special respect to the stereochemistry of molecules.

The effects of lysine8-vasopressin (LVP) on the open-field activity and passive avoidance behaviour in rats were studied following intracerebroventricular (i.c.v.) and intracisternal (c.m.) administration. Following i.c.v. administration, LVP caused a long-lasting facilitation of the passive avoidance behaviour and did not influence open-field activity. When injected into the cisterna magna, on the other hand, the same amount of LVP was without effect on the passive avoidance behaviour, while decreasing open-field activity. It is concluded that the site of injection in the cerebrospinal space might be of importance in determining the behavioural effects of neuropeptides.

The main aims of the research for new PGI2 analogues are to increase (1) the duration of action and/or (2) biological selectivity. To meet requirement (1), the structure of PGI2 had to be stabilized chemically and biologically. To achieve chemical stabilization an electron-withdrawing group (e.g. oxo-, phenyl) was inserted adjacent to the enol-ether unit into the PGI2 molecule. Such compounds as 7-oxo-PGI2, 4-oxo-PGI2, m-interphenylene-2,3,4-trinor-PGI2 are stable to hydrolysis although they possess a somewhat diminished biological activity as measured by the antiaggregatory activity and in vivo hypotensive action. There was no significant change in the selectivity between the two kinds of activities. "Biological stabilization" was attempted by elaborating the series of m-interphenylene-PGI2-s with modification of the PG-skeleton. Compounds such as m-interphenylene-2,3,4-trinor-13,14-didehidro-20-methy l-PGI2 is considered to be "fully stabilized". There was a gain in selectivity, however the increase in the duration of action was not significant. However, even PGI2 has certain activities of the "hit and run" type revealed mainly in the cytoprotective effect at different organs. Such an example, the delayed antiischaemic effects of PGI2 and 7-oxo-PGI2 in dogs are discussed.

Earlier it was found that oxytocin (OXT) treatment inhibited the development of tolerance to ethanol. In the present study the possibility was investigated whether the effect of OXT on ethanol tolerance was related to peptide fragments derived from the C-terminal part of the molecule. The actions of different doses of the C-terminal tripeptide (prolyl-leucyl-glycinamide, PLG) and of a synthetic dipeptide derivative (Z-prolyl-D-leucine, Z-Pro-D-Leu) on the development of tolerance to the hypothermic effect of ethanol in CFLP mice were therefore investigated. Peptide treatment did not affect body temperature in ethanol-naive animals. The acute effects (hypothermia, sleeping time) of a single ethanol injection were also unaffected by these peptides. In contrast, both PLG and Z-Pro-D-Leu inhibited the development of tolerance to the hypothermic effect of ethanol. Accordingly, it might be speculated that a sequence active in affecting ethanol tolerance is located in the C-terminal part of the OXT molecule.

Prolyl-leucyl-glycinamide (PLG) and its substituted and protected analogues were tested on the steady-state level of noradrenaline (NA), dopamine (DA) and serotonin (5-HT) in various brain areas. The tripeptides were structurally modified at the N-terminal proline residue either by protection with benzoxycarbonyl (Z group) or by tertiary butyroxycarbonyl (BOC), or by substitution with homoproline (HPRO). C-terminal modification was performed by substitution of the amino group of glycine (GLY-NH2) by methylester (GLY-OMe). The parent molecule (PLG) increased the 5-HT content in the striatum and the NA and DA levels in the dorsal hippocampus. N-terminal protection by Z-group resulted in a loss of these effects. Striatal effects re-appeared if a methylester group was introduced in the C-terminal glycine. Substitution of the N-terminal with HPRO or that of the C-terminal amine group by OMe resulted in a tendency to increase the 5-HT level in the hypothalamus.

The effect of modified and substituted analogues of prolyl-leucyl-glycinamide (PLG, MIF-I) was investigated on the steady-state level of noradrenaline (NA), dopamine (DA) and serotonin (5-HT) in various brain regions. Proline was replaced by D- or L-pipecolic acid (D- or L-Pip), which analogues in turn were protected by benzoxy-carbonyl (Z) group. Substitution by D- or L-pipecolic acid caused opposite changes in the DA level of the dorsal hippocampus. These effects were absent it the N-terminal of either analogues was protected by Z-group. Following the above mentioned N-terminal modification, the amino group of the C-terminal glycine was also substituted by methyl-esther (Gly-OMe), Z-D-Pip-Leu-Gly-OMe decreased the mesencephalic DA level, while Z-L-Pip-Leu-Gly-OMe increased the 5-HT content of the mesencephalon and striatum. In general, N-terminal substitution by D-pipecolic acid decreased, whereas that by L-pipecolic acid increased the monoamine level in the brain.

The dose-related effects of cysteamine treatment on hypothalamic and striatal neurotransmission were investigated. Cysteamine pretreatment with a dose of 150 mg/kg slightly increased the dopamine, and markedly decreased the noradrenaline, content of the hypothalamus in a dose-related manner. The serotonin levels of the hypothalamus and striatum were not affected. Cysteamine pretreatment with a higher dose (300 mg/kg sc) slightly increased the uptake of noradrenaline into hypothalamic slices. The drug did not influence dopamine and serotonin uptake into hypothalamus and striatal slices. These results suggest that cysteamine decreases rather selectively the noradrenaline content of the hypothalamus.

A modification of previously published fluorimetric methods for brain noradrenaline (NA), dopamine (DA), and serotonin (5-HT) assay is presented in this paper. The modification improved the sensitivity to 5-HT and resulted in a less time-consuming and less expensive method for noradrenaline and dopamine determination. The assay can be used for simultaneous estimation of NA, DA and 5-HT as well as for turnover studies, utilizing catecholamine synthesis inhibition or monoaminoxidase inhibition.

The effects of intracerebroventricularly (icv.) administered oxytocin (OXT) and lysine-8-vasopressin (LVP) on the development of hypothermic tolerance to ethanol were investigated. Mice equipped with an icv cannula were pretreated with graded doses of OXT or LVP (3 ng, 300 pg, 30 pg or 3 pg/animal) before the daily intraperitoneal ethanol (4 g/kg) injection. Two doses of OXT or LVP (3 ng or 300 pg/animal) blocked the development of hypothermic tolerance to ethanol. Smaller doses of the peptides were ineffective in inhibiting the gradual decrease in hypothermia upon repeated ethanol administration, which effect was observed in the control group. The data presented show that the central administration of these neurohypophyseal peptides blocks the development of tolerance to ethanol.