Failure of (+)-naloxone to accelerate feline colonic transit

To determine whether the colonic transit accelerating effect of (-)-naloxone (0.3 mg/kg, i.m.) is due to an action at opioid receptors or a direct pharmacologic effect, its enantiomer, (+)-naloxone (0.3 mg/kg, i.m.), was administered to cats and compared to saline control using colonic transit scintigraphy. Transit was not accelerated by (+)-naloxone. The effects of naloxone on colonic transit are thus stereospecific, and are probably mediated by opioid receptors.

Formalin nociception in the mouse does not lead to increased spinal serotonin turnover

The mouse formalin test is a model of tonic (continuous), chemical/inflammatory nociception. To test the hypothesis that bulbospinal serotonergic pathways modulate such nociception, whole spinal cords from mice pretreated with probenecid and sacrificed at 15, 30, 45 and 60 min after injection of 5% formalin or 0.9% saline in the hindpaw were assayed by high performance liquid chromatography with electrochemical detection for the serotonin metabolite, 5-hydroxyindoleacetic acid, as an index of turnover. No difference in serotonin turnover was found between formalin and saline groups, indicating that increased spinal serotonin release is not a normal response to formalin nociception in the mouse.

[D-Pen2, D-Pen5]enkephalin, the standard delta opioid agonist, induces morphine-like behaviors in mice

[D-Pen2, D-Pen5]enkephalin (DPDPE; 3-30 micrograms) and morphine (10 micrograms) both caused Straub tails, increased locomotion, and circling after ICV administration to ICR mice. DPDPE-induced tail stiffening was reduced when mice were pretreated with naloxone (0.5 mg/kg SC) or beta-funaltrexamine (10 micrograms ICV), but not with ICI 174864 (2 mg/kg SC), the selective antagonist at delta opioid receptors. These results point to (a) mu receptors mediating the tail stiffening and (b) the loss of delta receptor selectivity after 10 and 30 micrograms DPDPE.

Statistical analysis of drug-drug and site-site interactions with isobolograms

The use of more than one drug to achieve a desired effect has been a common practice in pharmacologic testing and in clinical practice. For example, combinations of analgesics are frequently prescribed with a view to enhancing pain relief and reducing adverse effects. It is also well established that administration of more than one drug may give effects that are greater than, or less than, the additive effect of each drug given individually. A non-mechanistic method of characterizing the effect resulting from the administration of two compounds is the isobologram. It is relatively simple to draw and interpret isobolograms. However, this graphical technique, which employs equieffective concentrations of individual drugs and combinations of these, obtains the concentrations as random variables from concentration-effect data, usually transformed to a parallel line assay. Thus, statistical confidence limits from such assays, as well as from non-parallel designs, must be expressed on the isobologram if this diagram is to establish superadditive, subadditive, or merely additive effects. We now present a detailed statistical analysis of the isobolographic method illustrated with examples of the statistical procedures, a rational basis for selecting proportions of each drug in the combination, and a relatively novel application of the isobolographic concept, i.e., interactions involving different anatomical sites.

Fully effective contraception in male and female guinea pigs immunized with the sperm protein PH-20

Immunization of male and female animals with extracts of whole sperm cells is known to cause infertility. Also, men and women who spontaneously produce antisperm antibodies are infertile but otherwise healthy. Although the critical sperm antigens are unknown, these observations have led to the proposal that sperm proteins might be useful in the development of a contraceptive vaccine. The guinea pig sperm surface protein PH-20 is essential in sperm adhesion to the extracellular coat (zona pellucida) of the egg, a necessary initial step in fertilization. Here, we report that 100% effective contraception was obtained in male and female guinea pigs immunized with PH-20. Antisera from immunized females had high titres, specifically recognized PH-20 in sperm extracts, and blocked sperm adhesion to the egg zona pellucida in vitro. The contraceptive effect was long-lasting and reversible: immunized females, mated at intervals of six to fifteen months after immunization, progressively regained fertility.

Direct dependence studies in rats with agents selective for different types of opioid receptor

The objective of this study was to describe, quantitate and compare naloxone-induced abstinence syndromes in rats infused centrally (Sylvian aqueduct) with agonists that are currently the most selective for mu [( D-Ala2, MePhe4, Gly-ol5]enkephalin), delta [( D-Pen2, D-Pen5]enkephalin) and kappa (3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl) cyclohexyl]benzeneacetamide) (U-50,488H) opioid receptors, respectively. Morphine, ethylketazocine and dynorphin A served as reference compounds. After 70 hr of infusion from s.c. implanted osmotic minipumps, three levels of abstinence were associated with the injection of naloxone (3 mg/kg s.c.): 1) negligible syndromes (scores of less than 21) were obtained in rats on water or the kappa-directed ligands, U-50,488H and dynorphin A; 2) a low-to-moderate abstinence score (37-38) was recorded with rats receiving [D-Pen2, D-Pen5]enkephalin and ethylketazocine; and 3) a high abstinence score (64-73) was obtained with rats on morphine and DAGO. These results reinforce the concept of developing selective, nonbenzomorphan kappa agonists as clinically useful analgesics and emphasize that, when evaluating new analgesics, high selectivity for delta receptors does not, in itself, guarantee freedom from physical dependence.

Methodological refinements to the mouse paw formalin test. An animal model of tonic pain

The formalin tonic pain test has recently been adapted for use in mice. We have observed two problems with this procedure. First, compared to a vehicle control group, the majority of mice injected in a hind paw with dilute formalin exhibited a significant nociceptive response (paw licking), including peaks of activity, well beyond the end of the recommended observation period; and, second, an unacceptably wide variation in response occurred. We report two modifications that eliminate these difficulties: a) extending the observation period to 20-45 min postformalin injection, and b) lightly anesthetizing the mice with ether before injection of formalin into the paw. The modified protocol was tested by evaluating morphine, pentazocine and zomepirac (analgesic A50 values were 2.1, 23.8, and greater than 100 mg/kg, s.c., respectively). An intrathecal or intracerebroventricular injection of saline, given to the lightly anesthetized mouse, did not interfere with the nociceptive behavior; this finding widens the applicability and usefulness of the test. Collectively, these refinements significantly improve the mouse formalin model of tonic pain.

Purification of the guinea pig sperm PH-20 antigen and detection of a site-specific endoproteolytic activity in sperm preparations that cleaves PH-20 into two disulfide-linked fragments

Previous work has indicated that the guinea pig sperm membrane protein, PH-20, functions in sperm-egg adhesion and that its surface expression is regulated by the acrosome reaction. The PH-20 protein was purified by monoclonal antibody affinity chromatography. Sixty-seven to one hundred percent of the PH-20 antigenic activity present in an octylglucoside (OG) extract of sperm was recovered in the purified protein. From 10(10) sperm, approximately 0.4 mg of PH-20 protein was obtained, which was about 0.24% of the total protein in the OG extract. The purified protein retained the ability to bind the three anti-PH-20 monoclonal antibodies we have isolated. Silver staining of purified PH-20 on overloaded sodium dodecyl sulfate (SDS) gels allowed the estimate that silver-stainable contaminants were present at a level of one part in 2000. The purified PH-20 protein exists in three forms separable on SDS-polyacrylamide gel electrophoresis: a major form with a molecular mass of 64 kDa, a minor form of 56 kDa, and an endoproteolytically cleaved form composed of two disulfide-linked fragments of 41-48 kDa and 27 kDa. Cleveland digests of the 64 kDa and 56 kDa polypeptides indicated that they were structurally related. A proportion of the 64 kDa polypeptide in each purified preparation had undergone endoproteolysis at a specific site, so that it was cleaved into the two disulfide-linked fragments, 41-48 kDa and 27 kDa. It is speculated that the site-specific endoproteolysis of PH-20 may occur during the acrosome reaction and have biological significance.

Neurokinin-induced salivation in the anesthetized rat: a three receptor hypothesis

Substance P (3 micrograms/kg), neurokinin A (20 micrograms/kg), neurokinin B (6 micrograms/kg) and acetylcholine (875 micrograms/kg) all produced salivation upon i.v. infusion in the anesthetized rat. Against single equivalent agonist doses, atropine (135 micrograms/kg i.v.) blocked both acetylcholine- and neurokinin B-, but not substance P- or neurokinin A-induced salivation. [D-Pro2,D-Trp7,9]-substance P (1 mg/kg i.v.), a putative substance P antagonist, reduced responses to mammalian neurokinins but caused a 2-fold potentiation of acetylcholine-induced salivation. [D-Pro2,D-Trp6,8,Nle10]-Neurokinin B (1 mg/kg i.v.), a novel putative neurokinin B antagonist, significantly reduced substance P- and neurokinin B- but not acetylcholine- or neurokinin A-induced salivation. The three agonists (at doses that produced salivation) and [D-Pro2,D-Trp6,8,Nle10]-neurokinin B (1 mg/kg i.v.) lowered blood pressure in anesthetized rats by 35 to 40%. [D-Pro2,D-Trp7,9]-Substance P (1 mg/kg i.v.) had no significant effect on blood pressure. Hydralazine at 0.60 mg/kg (i.v.), a dose which lowered blood pressure by 47%, did not reduce substance P-induced salivation. Thus, blockade of neurokinin-induced salivation by [D-Pro2,D-Trp6,8,Nle10]-neurokinin B was probably not due to hypotension. Based on the differential effects of the three antagonists on neurokinin- and acetylcholine-induced salivation, we hypothesize the existence of three distinct neurokinin receptors in rat salivary gland, and suggest that neurokinin B receptors reside presynaptically.

Supraspinal and spinal potency of selective opioid agonists in the mouse writhing test

Three agonists with the highest degree of selectivity available for mu ([D-Ala2,NMePhe4,Gly-ol]enkephalin, DAGO), delta ([ D-Pen2,D-Pen5]enkephalin, DPDPE) and kappa (U-50,488H, U50) opioid receptors were compared for their activity in inhibiting acetic acid-induced writhing in mice. Additionally, three reference agonists for mu (morphine), delta ([ D-Ala2,D-Leu5]enkephalin, DADLE) and kappa (ketocyclazocine, KC) receptors were also studied in this test. The agonists were given directly into the lateral cerebral ventricle (i.c.v.) or into the lumbar spinal subarachnoid space (intrathecal), and the potency of each compound was compared across injection sites and with data previously obtained in a thermal analgesic test (mouse hot-plate test). The rank order of potency for inhibition of writhing after i.c.v. administration was DAGO greater than DADLE greater than morphine greater than DPDPE; KC and U50 showed no significant activity by this route. After intrathecal administration, the compounds inhibited writhing with a rank potency order of DAGO greater than KC greater than morphine = DADLE greater than DPDPE greater than U50. All compounds were more potent in inhibiting writhing at spinal sites than at supraspinal sites; DPDPE and DAGO were 15 and 24 times more potent after intrathecal than after i.c.v. administration, respectively. The proposed delta agonists DPDPE and DADLE inhibited writhing at both spinal and supraspinal sites. Further, although the proposed kappa-acting compounds KC and U50 were effective at relatively low doses at spinal levels, these compounds lacked activity at supraspinal sites at doses not causing sedation.(ABSTRACT TRUNCATED AT 250 WORDS)

Intrathecal bombesin-induced inhibition of gastrointestinal transit: requirement for an intact pituitary-adrenal axis

The role of the pituitary-adrenal axis in the inhibition of gastrointestinal transit caused by intrathecal administration of bombesin was examined. Bombesin (0.3-10 micrograms) slowed transit by this route in a dose-related manner. Either hypophysectomy or adrenalectomy prevented the inhibition of gastrointestinal transit associated with bombesin (10 micrograms, i.th.). The inhibitory gut effects of this peptide were not prevented in sham-operated rats. Intrathecal bombesin-induced inhibition of gastrointestinal transit is thus dependent upon an intact pituitary-adrenal axis.

Independent central and peripheral mediation of morphine-induced inhibition of gastrointestinal transit in rats

The individual contributions of central (brain) and peripheral (enteric) sites in the mediation of the systemic actions of opioids are not well established. In this study, we made use of naltrexone methobromide, a quaternary analog of naltrexone, to separate the central and peripheral components of the slowing action of morphine on gastrointestinal transit in rats. It was established that i.c.v., but not s.c., administration of quaternary naltrexone antagonized morphine-induced analgesia in the radiant-heat tail-flick assay in rats. Thus, quaternary naltrexone probably does not enter the central nervous system in significant amounts after systemic administration. Systemic quaternary naltrexone antagonized, in a dose-related manner, the delaying effects of morphine on the movement of a charcoal meal along the gastrointestinal tract. Quaternary naltrexone was 30 or 100 times less potent than naltrexone when administered s.c. or i.c.v., respectively. Unlike naltrexone, quaternary naltrexone antagonized morphine-induced slowing of gastrointestinal transit only when administered by the same route (i.e., both s.c. or both i.c.v.). The apparent pA2 for s.c. quaternary naltrexone against s.c. morphine was not significantly different from the apparent pA2 for i.c.v. quaternary naltrexone against i.c.v. morphine. Distinct and independent central and peripheral systems appear to mediate morphine-induced inhibition of gastrointestinal transit in rats. However, the receptors are probably of the same type. Peripherally selective antagonists such as quaternary naltrexone may be useful in reversing morphine-induced inhibition of gastrointestinal transit without affecting analgesia.

Intrathecal morphine slows gastrointestinal transit in rats

Intrathecal (i.th.) (by direct lumbar puncture) and intraperitoneal (i.p.) administration of morphine (30-100 micrograms/rat) caused a dose-related inhibition of gastrointestinal transit in the rat. Pretreatment with i.th. naloxone (5 micrograms at -5 min) reversed the effects of i.th., but not i.p., morphine. These results suggest that the spinal cord appears to be a target site for the inhibitory effects of morphine on gastrointestinal transit in the rat.

Rat cold water tail-flick: a novel analgesic test that distinguishes opioid agonists from mixed agonist-antagonists

The models currently used to assess antinociceptive efficacy in animals are far from ideal. Those procedures that detect both opioid agonists and mixed agonist-antagonists fail to differentiate between them unless the noxious stimulus is adjusted. Furthermore, changes in the sensitivity of the test often result in positive responses being elicited from agents that are either not analgesics or only weak ones, at best. The technique described in this report uses cold water as the noxious stimulus in rats. It is simple, requires no complicated instrumentation or training, correlates well with clinical efficacy in man, and allows separation of opioid agonists from mixed agonist-antagonists without detecting non-opioid agents.

Cross-tolerance between morphine- and bombesin-induced inhibition of intestinal transit in rats

Intracerebroventricular (i.c.v.) injection of either morphine or bombesin to rats inhibits intestinal transit of an intraduodenally administered radiochromium marker. In this work, we show that tolerance develops to this effect of bombesin after i.c.v. infusion of the peptide (0.5 micrograms/h for 4 days via an s.c. implanted Alzet 2001 osmotic minipump). Tolerance also develops to the inhibition of intestinal transit associated with i.c.v. morphine after s.c. injections of morphine. Bombesin-induced delay of transit is not attenuated by naltrexone (10 mg/kg, s.c.), a standard narcotic antagonist. Nevertheless, two-way cross-tolerance develops between bombesin and morphine in this system. This is a surprising result since both bombesin and morphine are believed to act on different receptors and cause opposite effects on intestinal motility in rats.

Effects of bombesin on behavior

This report describes the influence of bombesin on the gross behavior of goldfish, frogs, mice, rats, guinea pigs, rabbits, chicks, pigeons and monkeys. Goldfish, frogs, chicks and pigeons were overtly unaffected by bombesin given centrally and/or peripherally. Mice, rats, guinea pigs, rabbits and monkeys responded quickly to intracerebroventricular (i.c.v.) and/or intrathecal (i.th.) administration of bombesin by displaying a range of behaviors suggestive of altered skin sensation. In mice, bombesin was essentially equipotent as a scratch inducer by i.c.v. and i.th. routes (A50 = 0.010-0.019 microgram) but 6800 times less potent i.p. In rats, bombesin-induced grooming and scratching behaviors were shown to be qualitatively different from those associated with ACTH-(1-24) and thyrotropin releasing hormone. Spantide and [D-Arg1, D-Pro2, D-Trp7,9, Leu11]substance P (both at 0.20, 0.50 and 0.80 microgram i.c.v.), two proposed bombesin receptor antagonists, did not markedly influence bombesin-induced scratching or hypothermia in rats.

Mu and delta, but not kappa, opioid agonists induce contractions of the canine small intestine in vivo

Extraluminal strain gage transducers were sutured along the transverse axis of the duodenum in order to monitor circular muscle contractile activity in the pentobarbital anesthetized dog. Administration by intravenous bolus of a variety of mu- and delta-directed opioid ligands resulted in a dose-dependent increase in duodenal contractile activity. In contrast, all kappa-directed ligands were devoid of stimulatory activity. Naloxone reversed the effects of normorphine and [Met5]enkephalin but was 20 times more effective against normorphine than [Met5]enkephalin. Based on the inactivity of all kappa ligands examined and the differential potency of naloxone against [Met5]enkephalin and normorphine, we suggest that this model may be useful in the classification of opioid ligands as to their receptor selectivity in vivo. Further, these data indicate that the stimulation of duodenal contractile activity is not mediated by enteric kappa receptors.

Studies in vivo with ICI 174864 and [D-Pen2, D-Pen5]enkephalin

We studied the in vivo pharmacology of a selective agonist (DPDPE) and a selective antagonist (ICI 174864) at delta opioid receptors. ICI 174864 (10 micrograms icv) caused postural abnormalities, barrel rotation and hypothermia in rats. DPDPE induced behavioural arousal (at 75 micrograms icv) and barrel rotation (at 125 micrograms) in rats. ICI 174864 (10 micrograms icv) attenuated acetic acid induced writhing in mice. This action was antagonized by naloxone (10 but not 2 mg/kg s.c.). A lower, non-agonist dose of ICI 174864 (5 micrograms) antagonized DPDPE (3 micrograms icv) in this test without affecting DAGO (0.0006 micrograms icv), a selective agonist at mu receptors. In the mouse tail flick test, ICI 174864 (10-50 micrograms icv) did not significantly antagonize the agonist actions of DPDPE (40 micrograms icv) or DAGO (0.3 micrograms icv). At 10-50 micrograms icv, ICI 174864 had no marked effect on gastrointestinal transit in mice. ICI 174864 (25 micrograms icv or 20 mg/kg s.c.) did not interact with mu opioid receptors in mice rendered physically dependent on morphine.

Xorphanol

Xorphanol is a new mixed agonist-antagonist from the morphinan class of analgesics. On the basis of animal experiments, the physical dependence liability of xorphanol is predicted to be of a low order in man. Conceptually, xorphanol is of interest since in vitro experiments have revealed anti-naloxone properties and resistance to antagonism by opioid antagonists. At the practical level, xorphanol is a well tolerated, orally active analgesic that provides effective pain relief clinically.

Pituitary-adrenal mediation of bombesin-induced inhibition of gastrointestinal transit in rats

Centrally administered bombesin (0.1-3.5 micrograms, i.c.v.) inhibits gastrointestinal transit of a charcoal meal in a dose-related manner in rats. The roles of pituitary and adrenal glands in the mediation of this effect were assessed. The inhibition of gastrointestinal transit associated with bombesin (0.5 microgram, i.c.v.) was prevented by either hypophysectomy or adrenalectomy. Bombesin-induced inhibition of gastrointestinal transit is therefore mediated through the pituitary-adrenal axis. This is in contrast to bombesin-induced scratching and inhibition of gastric acid secretion which are not markedly influenced by either hypophysectomy or adrenalectomy.