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Pemedolac [cis-1-ethyl-1,3,4,9-tetrahydro-4-(phenylmethyl)-pyrano [3,4-b]indole-1-acetic acid; AY-30,715] exhibited potent analgesic effects against chemically induced pain in rats and mice and against inflammatory pain in rats. In each of the animal models used the analgesic potency of pemedolac was defined by an ED50 of 2.0 mg/kg p.o. or less. Significant analgesic activity was detected in rats at 16 hr after administration of 1 mg/kg p.o. (paw pressure test) and at 10 hr after administration of 10 mg/kg p.o. to mice (p-phenylbenzoquinone writhing). Inasmuch as pemedolac was inactive in the hot plate and tail-flick tests; and its analgesic activity was not antagonized by naloxone (1 mg/kg s.c.), and tolerance did not develop upon multiple administration; this drug does not exert its analgesic effects through an opiate mechanism. Pemedolac differed from standard nonsteroidal anti-inflammatory drugs (NSAIDs) in that the doses which produced analgesia were much lower than those required for either anti-inflammatory or gastric irritant effects. In acute anti-inflammatory tests, pemedolac exhibited only weak activity as evidenced by an ED50 approximately 100 mg/kg p.o. in the carrageenan paw edema procedure. This demonstrates for pemedolac a separation of at least 50-fold between the acute analgesic and anti-inflammatory activities, which was greater than that observed with reference NSAIDs. The compound also had a low ulcerogenic liability with an acute UD50 = 107 mg/kg p.o. and a subacute UD50 estimated to be 140 mg/kg/day p.o. In contrast, the reference NSAIDS (piroxicam, indomethacin, naproxen and ibuprofen) exhibited similar dose-response relationships for the analgesic, anti-inflammatory and gastric irritant effects.(ABSTRACT TRUNCATED AT 250 WORDS)

The optical isomer of mu and kappa opiates, when given i.v., inhibited the cough reflex in the lightly anesthetized cat, the levoisomers being, in general, 2 to 14 times more potent than the dextro-isomers. The optical isomers of the sigma agonist, SKF 10,047, did not show any antitussive activity up to near lethal or lethal doses (5 mg/kg i.v.). Naloxone (1 mg/kg i.v.) did not block or reverse the antitussive effects of (-)- and (+)-codeine but completely antagonized the effects of an ED84 of (-)-, (+)-morphine, (-)-, (+)-methadone, levomethorphan and dextromethorphan. The cough suppressant effects of the kappa opiates were partially blocked by naloxone, (+/-)-ketocyclazocine being more sensitive to the effect of naloxone than (-)-cyclazocine. (-)-SKF 10,047 at 3.0 mg/kg i.v. and the ED16 of (-)-cyclazocine did not inhibit the antitussive effect of codeine but blocked that of morphine, behaving like naloxone. (+)-SKF 10,047 and (+)-cyclazocine did not show in vivo antagonistic effect vs. codeine or morphine. The ED16 of ketocyclazocine partially antagonized codeine but not morphine. The optical isomers of opiates showed good correlation between the in vivo antitussive potencies and their in vitro inhibitory potencies against (-)-codeine binding in homogenates of the guinea-pig medulla. The data confirm the hypothesis that the cough suppressant effects of opiates are mediated by receptors which are less stereoselective and less naloxone-sensitive than the analgesic receptors. The possible involvement of mu and kappa sites as well as their interactions are discussed.

Opiates are known for their stereospecificity. The following studies show that l-codeine was active in the mouse tail-flick test as well as in the hot plate test whether given p.o. or s.c. The ED50 in the first test was 4.09 mg/kg s.c. (2.01-8.34 mg/ kg) and 13.41 mg/kg p.o. (6.91-26.0 mg/kg). In the second antinociceptive test, the ED50 was 20.66 mg/kg s.c. (11.52-37.08 mg/kg) and 20.47 mg/kg p.o. (14.63-28.57 mg/kg). The d-isomer of codeine was inactive ina both tests up to 100 mg/kg but caused hyperexcitability, convulsions and ultimately death. Although l-codeine was more potent than d-codeine inhibiting the cough reflex in the anesthetized cat, the d-compound did have good activity. The ED50 of the l-isomer was 0.27 mg/kgi.v. (0.14-0.47 mg/kg) and that of the d-isomer was 1.61 mg/kg i.v. (0.98-2.65 mg/kg). In these animals, l-codeine did not significantly affect the cardiovascular parameters at the doses tested, whereas d-codeine caused a significant but transient decrease in the blood pressure and heart rate. The specific and nonspecific properties of d- and l-codeine were further delineated in the opiate receptor binding assay. l-Codeine inhibited the stereospecific binding of 2.2 x 10(-9) M [3H]dihydromorphine in mouse brain homogenate with the IC50 being 1.6 x 10(-5) M (1.2 x 10(-5)--2.0 x 10(-5) M). d-Codeine had no effect up to 10(-4) M.

Brains of mice pretreated with saline or 40 micrograms of acetylcholine (ACh) i.c.v. were fractionated according to published procedures. The fractions yielded four peaks of inhibitory activity in the radioreceptor assay. Intraventricular ACh decreased the inhibitory activity of peak I (fractions 10-19), increased that of peak II (fractions 20-24) and peak III (fractions 25-29) and did not change the activity of peak IV in the radiotracer binding assay. Peaks I, III and IV were potent inhibitors of the coaxially stimulated guinea-pig ileum and such inhibitory activity was not destroyed by incubation with trypsin, carboxypeptidase or by naloxone. Intraventricular ACh did not alter the activity of the three peaks on coaxially stimulated ileum bioassay. Peaks II and III both caused a contraction of the nonstimulated guinea-pig ileum and their effect was reduced either by enzymatic treatment (peak II) or by atropine (peak III). No difference was observed between the effects of each peak in saline or ACh-treated mice in this test. All four peaks were active in the writhing test. The results suggest the presence of several opiate-like materials in the brain. The endogenous opioids appear to be a mixture of endorphin-like peptides as well as nonpeptides. The data also indicate the presence of spasmogenic peptides with some opiate properties.