FS 205-397: a new antipyretic analgesic with a paracetamol-like profile of activity but lack of acute hepatotoxicity in mice.

FS 205-397 has been designed to mimic or improve the antipyretic/analgesic profile of paracetamol but without inducing hepatic failure. FS 205-397 offers advantages over acetylsalicylic acid since it has caused no gastric lesions in rats and unlike paracetamol it produced no hepatotoxicity in animal models. The antinociceptive potency of FS 205-397 was at least that of acetylsalicylic acid and paracetamol and in some models it was somewhat more potent. FS 205-397 was even active in the hot plate test, a model in which most non-narcotics are inactive. FS 205-397 will offer potent analgesic and antipyretic therapy in man based on an innovative biochemical principle which eliminates the undesirable toxic effects associated with most other non-narcotic analgesics.

CY 208-243: a unique combination of atypical opioid antinociception and D1 dopaminomimetic properties.

Here we describe the potent antinociceptive action of the indolophenanthridine, CY 208-243, which has high affinities to the dopamine D1 binding and the opioid sites as well as to the 5-HT1A site. The antinociceptive action was comparable to that of morphine in most, but not all models of nociception, nevertheless, basic differences exist in its overall profile. Antagonism of CY 208-243's antinociceptive action was only possible with either high doses of naloxone or not at all and no cross-tolerance with morphine in CY 208-243 tolerant rats occurred. The biochemical basis for dependence liability may be absent and no opioid activity was observed in cultured hippocampal cells. Physical dependence did not occur after programmed administration in the rhesus monkey, nor did CY 208-243 cause respiratory depression in the rat (rather a stimulation). Lack of generalization in fentanyl-trained rats strongly suggests that CY 208-243 lacks opioid-like subjective cues. The coexistence of D1 dopaminergic and atypical opioid agonist properties represents a unique pharmacodynamic combination which is not shared with any other analgesic, and may provide safe and innovative pain therapy.

Weakening of naloxone antagonism in vitro and in vivo with octreotide (SMS 201-995).

Octreotide, a potent long-acting somatostatin analogue, has been shown to have a wide range of physiological actions. We have demonstrated a somatostatin-like inhibition of the electrically evoked contractions of the mouse vas deferens and an opioid antagonistic property in the same tissue. In addition, pretreatment with octreotide reduced the potency of naloxone antagonism in vitro in the mouse vas deferens and in vivo in the mouse charcoal meal test. The latter effect suggests that the agonist receptor interactions are taking place on sites allosteric to the agonist site and that the conventionally accepted concept of opioid antagonism may have to be modified.

Fiber tracts that contain more opioid binding sites than gray matter does: a quantitative autoradiographic study in the guinea-pig.

Opioid binding sites were localized in cryostat sections of guinea-pig brain by in vitro autoradiography using (-)-[3H]bremazocine. Quantification of binding sites in gray matter was accomplished using standard samples of tritium mixed in brain gray matter. The binding sites in fiber tracts were quantified using standards made from white matter to compensate for the quenching caused by myelin. Binding in gray matter corroborated previous findings that the moderately high densities of opioid sites in the cerebellum are of the kappa type, and that the V and VI laminae of the cerebral cortex, the substantia nigra, and olfactory bulb contain high levels of opioid sites in the guinea-pig. Several fiber tracts such as cerebellar white matter and the corpus callosum contained densities of (-)-[3H]bremazocine binding sites equal to, or higher than, the most densely labeled gray matter areas. The dorsal hippocampal commissure and the splenium of the corpus callosum contained 2200 fmol sites/mg protein, two and one half times more than the most densely labeled gray matter areas, the external plexiform layer of the olfactory bulb. These sites may be receptors in transport, but their density constitutes a massive volume of receptors for which a physiological role still needs to be more clearly defined.

Distribution of opioid binding sites in the guinea pig hippocampus as compared to the rat: a quantitative analysis.

In vitro autoradiography of cryostat sections revealed major differences between the distribution of opioid binding sites in the hippocampus of the guinea pig and the rat. Only very low binding was found in the pyramidal cell layer, the dentate granular cell layer and the commissural-associational zone of the dentate molecular layer of the guinea pig, whereas these areas were moderately to densely labeled in the rat. In the guinea pig an enrichment of sites was observed in the terminal field of the mossy fiber system in the hilus which was absent in the rat. Binding sites in the guinea pig were found to be mainly of the kappa and mu type. The distribution of [Leu]enkephalin immunoreactivity does not correlate well with the distribution of delta opioid binding sites in the hippocampus. Quantification of opioid binding sites in the hippocampus demonstrates that no one type of site can be assigned to a specific hippocampal subregion nor does the intensity or the pattern of distribution of binding types agree well with the distribution of endogenous opioid peptides.

Opioid binding sites in the nigrostriatal system of the guinea pig are not located on nigral dopaminergic neurons.

Unilateral 6-hydroxydopamine injection into the compact zone of the guinea pig substantia nigra was used to destroy nigral dopamine neurons. The glyoxylic acid method for monoamine fluorescence was employed to ascertain the loss of dopaminergic fibers in the striatum and substantia nigra. It could be shown that there was no change in the number of [3H](-)-bremazocine binding sites in the substantia nigra or the striatum on the lesioned side of these guinea pigs.

Opioid binding sites of the kappa-type in guinea-pig cerebellum.

(-)-[3H]Bremazocine interacts almost equally well with the mu-, delta- and kappa-types of opioid binding sites. In homogenates of guinea-pig cerebellum, it was bound with high affinity (KD = 0.046 nM) and the maximum binding capacity was 7.04 pmol/g wet wt of tissue. When the mu- and delta-binding of (-)-[3H]bremazocine was prevented with unlabelled ligands, a KD of 0.034 nM and a capacity of 5.94 pmol/g tissue was found for the kappa-binding site, which therefore comprised 84% of the opioid binding sites in the cerebellum. Autoradiographic analysis showed that the binding of (-)-[3H]bremazocine was relatively low in lobules IX and X and that it was predominantly located in the molecular and to a lesser extent in the granular layers. The addition of unlabelled mu- and delta-ligands did not alter the distribution. Thus, the guinea-pig cerebellum contains opioid binding sites of which almost all are of the kappa-type and is therefore an ideal tissue for the isolation of kappa-receptors and for the investigation of their biochemical and pharmacological properties.

Kappa opiate binding sites in the substantia nigra and bulbus olfactorius of the guinea pig as shown by in vitro autoradiography.

The purpose of the present study was to further map the distribution of the kappa subtype of opiate binding sites in the guinea pig brain. Cryostat sections of brain were incubated in 2 nM [3H] (-)-bremazocine with or without the addition of D-Ala2,MePhe4,Gly-ol5-enkephalin and/or D-Ala2,D-Leu5-enkephalin at 1 - 3000 nM. A sheet of [3H] Ultrofilm R (LKB) was exposed to the dry sections for up to 207 days. A computer coupled to a microdensitometer and a television camera was used to convert grey areas of the film to femtomoles of binding sites per mg protein. The substantia nigra and lamina plexiformis externa of the bulbus olfactorius remained densely labeled even in the presence of 3000 nM of both enkephalins. The guinea pig is the only species studied thus far which exhibits this distribution, but the physiological significance is not yet understood.

Autoradiographic localization of opiate kappa-receptors in the guinea-pig brain.

Opiate binding sites of the kappa-subtype were visualized in guinea-pig brain sections using in vitro autoradiography. kappa-Binding sites, defined as [3H](-)-bremazocine binding in the presence of high concentrations of [D-Ala2,MePhe4,Gly-ol5]enkephalin and [D-Ala2,D-Leu5]enkephalin, were found in the cortical laminae V and VI, hippocampal dentate gyrus, and lateral habenulae. The distribution of kappa-sites in the guinea-pig differs considerably from the distribution of mu- and delta-sites which others have found in the rat.