Early onset of reduced morphine analgesia by ingestion of sweet solutions

The analgesic properties of intraoral sucrose: an integrative review

The treatment of pain is an essential component of the clinical and ethical care of infants. Despite evidence-based practice consensus statements recommending that infants receive analgesia during minor painful procedures, numerous studies have shown that procedural pain remains poorly managed in this population. Oral sucrose administration has been associated with calming effects and reductions in observed pain behaviors with preterm and term infants aged up to 1 year. The objective of this integrative review is to synthesize findings from published randomized controlled trials evaluating the efficacy and safety of oral sucrose as a preprocedural intervention for mild to moderate procedural pain in infants. Overall, studies indicate that oral sucrose is an effective, safe, convenient, and immediate-acting analgesic for reducing crying time and significantly decreases biobehavioral pain response following painful procedures with infants.

Reduced infant response to a routine care procedure after sucrose analgesia

OBJECTIVES

Sucrose has analgesic and calming effects in newborns. To date, it is not known whether the beneficial effects extend to caregiving procedures that are performed after painful procedures. Our objective was to determine the effect of sucrose analgesia for procedural pain on infant pain responses during a subsequent caregiving procedure.

PATIENTS AND METHODS

We conducted a double-blind, randomized, controlled trial. Healthy neonates within 2 strata (normal infants and infants of diabetic mothers) were randomly assigned to a sucrose or placebo water group before all needle procedures after birth. Pain response during a diaper change performed after venipuncture for the newborn screening test was determined by using a validated multidimensional measure, the Premature Infant Pain Profile.

RESULTS

The study was conducted between September 15, 2003, and July 27, 2004. Altogether, 412 parents were approached; 263 consented. Twenty-three infants were not assigned, leaving 240 for participation (n = 120 per group), with an equal number in each infant strata. Of those, 186 (78%) completed the study. There were no significant differences in birth characteristics between groups. During diaper change, sucrose-treated infants had lower pain scores than placebo-treated infants. The relative risk of having pain, defined as a Premature Infant Pain Profile score of >/=6, was 0.64 with sucrose compared with placebo.

CONCLUSIONS

This study demonstrates that when used to manage pain, sucrose reduces the pain response to a subsequent routine caregiving procedure. Therefore, the benefits of sucrose analgesia extend beyond the painful event to other aversive and potentially painful procedures.

Saccharin effects on morphine-induced antinociception in the mouse formalin test

This study was performed to investigate the role of sweetness and taste sensations of the non-caloric sweetener saccharin on pain and morphine antinociception by the formalin test in mice. The formalin test was chosen because it measures the response to a long-lasting nociceptive stimulus and thus may closely resemble clinical pain. The total time (seconds) spent licking and biting the injected paw (indices of nociception) during periods of 0-5 min (early phase) and 10-30 min (late phase) were measured as an indicator of pain and inflammatory responses. A 12 days pretreatment of animals with saccharin (0.04%, 0.08%, 0.16%) produced complex effects on the action of morphine. All doses significantly potentiated the low dose (1.5 mgkg(-1)) of morphine-induced analgesia in the early phase significantly but antagonized the effect of morphine (3 mgkg(-1)). The effect of high doses of morphine (6-9 mgkg(-1)) was antagonized by the low dose of saccharin (0.04%), but the effect of morphine (6 mgkg(-1)) was potentiated with high concentrations of saccharin (0.08% and 0.16%). All doses of saccharin decreased the analgesic effect of morphine at a dose of 9 mgkg(-1). Analgesic effects of low doses of morphine (1.5-3 mgkg(-1)) were decreased by all doses of saccharin in the late phase. Different concentrations of saccharin also affected the antagonistic effect of naloxone (0.4 mgkg(-1)) on morphine-induced analgesia in both phases of the formalin test. The high dose of saccharin (0.16%) potentiated the effect of naloxone in the late phase. The results obtained suggest that sweet sensation is an important factor in mediating morphine analgesic properties. It is therefore inappropriate to use different concentrations of sweet saccharin solutions interchangeably.

Tolerance to morphine-induced antinociception is decreased by chronic sucrose or polycose intake

Chronic intake of palatable fluids alters morphine-induced antinociception. Two experiments were conducted to evaluate how long-term access to palatable fluids alters the development of tolerance to morphine-induced antinociception. In Experiment 1, 40 adult male Long-Evans rats were used. In addition to ad lib chow and water, 10 rats were given a 0.15% saccharin solution, 10 were given a 32% sucrose solution, and 10 were given a 32% Polycose solution to drink for 3 weeks. Ten rats were given chow and water alone, and served as dietary controls. Morphine-induced antinociception was assessed using the radiant-heat tail-flick method (TF). Half of the animals in each dietary condition were given preexposure to 7.5 mg/kg morphine; the other half received saline. All rats were given a TF 30-min postinjection. To determine whether tolerance developed, a cumulative dose paradigm (0.625, 1.25, 2.5, 5.0, 10.0 mg/kg) was employed 1 week after initial morphine injections, and was repeated at weekly intervals for 3 weeks. Antinociception was significantly lower in rats preexposed to morphine relative to rats preexposed to saline. Although all rats displayed decreased antinociception relative to the first morphine injection, rats that drank saccharin showed greater reductions in morphine-induced antinociception relative to rats that drank sucrose or Polycose. Experiment 2 was conducted to determine whether initial pairing of the TF with morphine preexposure produced differences in the development of opioid tolerance. All conditions and procedures were identical to Experiment 1, except that the initial morphine and saline injections were not followed by TF. As in Experiment 1, rats that drank saccharin showed less antinociception than rats that drank sucrose or Polycose. The present results suggest that long-term intake of palatable nutritive solutions curbs tolerance to morphine-induced antinociception, whereas long-term intake of a nonnutritive, sweet saccharin solution does not.

Altering dietary levels of protein or vitamins and minerals does not modify morphine-induced analgesia in male rats

Previous research has demonstrated that chronic intake of nutritive sweet solutions, but not nonnutritive sweet solutions, enhances morphine's analgesic potency. To separate out the effects of sweet taste from other changes in dietary intake, which result when rats consume a sucrose solution, the effects of altering dietary levels of protein, or vitamins and minerals on morphine-induced analgesia were examined. In Experiment 1, 40 male Long-Evans rats were fed standard chow or a semipurified diet containing either 10, 20, or 40% protein. Three weeks later, antinociceptive responses to morphine were examined using the tail flick procedure. Tail flick latencies were measured immediately prior to and 30, 60, and 90 min after the administration of morphine sulfate (0.0, 1.25, 2.5, and 5.0 mg/kg, SC). At all three measurement times, antinociceptive responses increased directly as a function of the dose of morphine, but did not differ as a function of diet. In Experiment 2, 24 rats were maintained on either standard laboratory chow or semipurified diets containing 20% protein and either 100% or 25% of the recommended levels of vitamins and minerals for 3 weeks. Tail flick latencies were measured immediately prior to and 30 min after injections (SC) of 2.5 mg/kg morphine sulfate. This procedure was repeated until a cumulative dose of 10.0 mg/kg was obtained. Tail flick latencies increased significantly as a function of drug dose, but did not differ across dietary conditions. These results demonstrate that the increase in morphine-induced analgesia seen in rats consuming a sucrose solution is not due to alterations in either protein or micronutrient intake.

Dietary Sucrose Lowers Nociceptive Latencies Independently of Thermogenic Effects

Previous reports indicate that chronic sucrose feeding produces a significant reduction in the latency of response in the radiant heat tail-flick test. Other earlier studies have shown a relationship between tail-skin temperature and tail-flick latency, while others yet have shown an increase in tail-skin temperature following sucrose feeding. Together these previous findings suggest the possibility that dietary-induced alterations in nociceptive latencies occur as an artifact secondary to diet-related changes in tail-skin temperature. The data presented in this study show that chronic sucrose feeding significantly increased tail-skin temperature (p < 0.0001) and decreased tail-flick latency (p < 0.0001) with significant correlations between tail-skin temperatures and tail-flick latencies in both the control and sucrose fed groups. However, while the slopes of the regression lines were similar for both groups, the elevations of the lines were significantly different (p = 0.0068) suggesting a dietary impact on nociceptive thresholds independent of the temperature effect. The data were also subjected to a previously reported temperature-correction procedure and comparisons in the methods of data analysis are discussed.

Beyond sweet taste: saccharin, sucrose, and polycose differ in their effects upon morphine-induced analgesia

The effects of saccharin, sucrose, or Polycose intake on morphine-induced analgesia (MIA) were examined in 40 adult male Long-Evans rats. Rats were tested for MIA on a tail-flick apparatus following acute (5-h) and chronic (3-wk) intake of a 0.15% saccharin solution, a 32% sucrose solution, a 33.68% Polycose solution, or water. During the chronic phase, all rats were given a choice between the test solution and water. Morphine sulfate was administered according to a cumulative dosing procedure beginning with 2.5 mg/kg morphine. The same dose was administered every 30 min. Tail-flick latencies were measured immediately prior to injections and 30 min following each injection. After acute intake of flavored solutions or water, there were no differences in MIA as a function of diet. However, after drinking the flavored solutions or water for three weeks rats drinking Polycose or sucrose showed significantly enhanced MIA relative to rats drinking saccharin. Rats drinking Polycose also showed enhanced MIA relative to rats drinking water. Comparison between the acute and chronic phases of the study demonstrated that tolerance to morphine's analgesic effects did not develop in rats drinking Polycose or sucrose, but did develop in rats drinking saccharin or water. The results support the hypothesis that, in addition to palatability, the nutritive value of flavored solutions influences MIA.

Duration of sucrose availability differentially alters morphine-induced analgesia in rats

The effects of duration of sucrose consumption on morphine-induced analgesia (MIA) were examined in 20 adult male Long-Evans rats. Ten rats were tested for MIA on a tail-flick apparatus following acute (5 h), chronic (3 weeks) intake, and subsequent removal of a 32% sucrose solution. Ten rats that never received the sucrose solution served as controls. Morphine sulfate was administered according to a cumulative dosing procedure beginning with 2.5 mg/kg morphine. The same dose was administered every 30 min until a total dose of 15 mg/kg was achieved. Tail-flick latencies were measured immediately prior to injections, and 30 min following each injection. After acute intake of sucrose, there was a trend for animals drinking the sugar solution to show suppressed MIA relative to animals drinking water. In contrast, after drinking the sucrose for 3 weeks, rats showed an enhanced MIA relative to rats drinking water. Three weeks after sucrose removal, there were no differences in MIA as a function of prior dietary conditions. The results support the hypothesis that length of exposure to sucrose influences morphine-induced analgesia and suggest that any change in physiology resulting from sucrose exposure may be reversible.

Endogenous opiates: 1993

This paper is the sixteenth installment of our annual review of research concerning the opiate system. It is restricted to papers published during 1993 that concern the behavioral effects of the endogenous opiate peptides, and does not include papers dealing only with their analgesic properties. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; development; immunological responses; and other behaviors.