Effect of uranyl nitrate-induced renal failure on morphine disposition and antinociceptive response in rats

Pharmacokinetic-pharmacodynamic models that incorporate drug-target binding kinetics

Pharmacokinetic/pharmacodynamic (PK/PD) models predict the effect time course resulting from a drug dose. In this review, we summarize the development of mechanistic PK/PD models that explicitly integrate the kinetics of drug-target interactions into predictions of drug activity. Such mechanistic models are expected to have several advantages over approaches in which concentration and effect are linked using variations of the Hill equation, and where preclinical data are often used as a starting point for modeling drug activity. Instead, explicit use of the full kinetic scheme for drug binding enables time-dependent changes in target occupancy to be calculated using the kinetics of drug-target interactions and drug PK, providing a more precise picture of target engagement and drug action in the non-equilibrium environment of the human body. The mechanistic PK/PD models also generate target vulnerability functions that link target occupancy and effect, and inform on the sensitivity of a target to engagement by a drug. Key factors such as the rate of target turnover can also be integrated into the modeling which, together with target vulnerability, provide additional information on the PK profile required to achieve the desired pharmacological effect and on the utility of kinetic selectivity in developing drugs for specific targets.

The analgesic efficacy of morphine varies with rat strain and experimental pain model: implications for target validation efforts in pain drug discovery

Background

Translating efficacy of analgesic drugs from animal models to humans remains challenging. Reasons are multifaceted, but lack of sufficiently rigorous preclinical study design criteria and phenotypically relevant models may be partly responsible. To begin to address this fundamental issue, we assessed the analgesic efficacy of morphine in three inbred rat strains (selected based on stress reactivity and affective/pain phenotypes), and outbred Sprague Dawley (SD) rats supplied from two vendors.

Methods

Sensitivity to morphine (0.3–6.0 mg/kg, s.c.) was evaluated in the hot plate test of acute thermal nociception, the Complete Freund's Adjuvant (CFA) model of inflammatory‐induced mechanical hyperalgesia, and in a locomotor motility assay in male rats from the following strains; Lewis (LEW), Fischer (F344), Wistar Kyoto (WKY), and SD's from Envigo and Charles River.

Results

F344 and SD rats were similarly sensitive to morphine in hot plate and CFA‐induced inflammatory hyperalgesia (Minimum Effective Dose (MED) = 3.0 mg/kg). WKY rats developed a less robust mechanical hypersensitivity after CFA injection, and were less sensitive to morphine in both pain tests (MED = 6.0 mg/kg). LEW rats were completely insensitive to morphine in the hot plate test, in contrast to the reversal of CFA‐induced hyperalgesia (MED = 3.0 mg/kg). All strains exhibited a dose‐dependent reduction in locomotor activity at 3.0–6.0 mg/kg.

Conclusion

Sensory phenotyping in response to acute thermal and inflammatory‐induced pain, and sensitivity to morphine in various inbred and outbred rat strains indicates that different pathophysiological mechanisms are engaged after injury. This could have profound implications for translating preclinical drug discovery efforts into pain patients.

Significance

The choice of rat strain used in preclinical pain research can profoundly affect the outcome of experiments in relation to (a) nociceptive threshold responses, and (b) efficacy to analgesic treatment, in assays of acute and tonic inflammatory nociceptive pain.

Opioids and renal function

Opioids, both endogenous and exogenous, have a strong influence on the renal function through different mechanisms, producing changes in the renal excretion of water and sodium. Several studies have demonstrated that opioids influence renal function, according to the agonist profile used. Mu, kappa, and delta agonists produce different renal effects, although the mechanisms remain unclear. Experimental data have given the input for a possible therapeutic role of kappa agonists for some specific conditions, for example, in treating water retention or hyponatremia occurring in patients who have hepatic cirrhosis with ascites. On the other hand, changes in renal function might strongly condition the use of opioids in the clinical setting, and the knowledge of the relationship between opioids and renal function is mandatory for a tailored approach to accommodate the individual responses in terms of pain intensity, tolerance, and adverse effects experienced by these groups of patients. The influence of renal function when using different opioids in the clinical setting is reviewed, as well as problems related to transplantation, renal damage induced by opioid addiction, and problems related to the use of opioid antagonists in such conditions.

PERSPECTIVE

Endogenous opioids exert physiologic effects on renal function, and the use of opioids may have an influence on renal activity. Renal impairment has a serious impact on the clearance of most opioids used in the clinical setting. Biochemical and clinical monitoring is mandatory to prevent serious complications.

Deficient prepulse inhibition of acoustic startle in Hooded-Wistar rats compared with Sprague-Dawley rats

1. Prepulse inhibition of acoustic startle has been suggested as a model of sensorimotor gating and central sensory information processing. Prepulse inhibition is impaired in patients with schizophrenia and responses can be restored by antipsychotic drug treatment. In the present study, startle and prepulse inhibition of startle were compared in different rat strains. 2. Sprague-Dawley rats showed robust inhibition of startle responses by increasing intensities of prepulse delivered just before the startle stimulus. In contrast, at both 4 and 10 weeks of age, rats of the Hooded-Wistar line had markedly reduced prepulse inhibition, although startle responses were not different. 3. Treatment with the dopamine receptor agonist apomorphine (0.1 mg/kg) or the N-methyl-d-aspartate (NMDA) receptor antagonist MK-801 (0.1 mg/kg) caused disruption of prepulse inhibition in Sprague-Dawley rats. In Hooded-Wistar rats, apomorphine further reduced the already low level of prepulse inhibition, but MK-801 treatment had no significant effect. This suggests that the impaired prepulse inhibition in Hooded-Wistar rats could be caused by changes in glutamatergic activity and/or NMDA receptors in these rats. 4. In photocell cages, spontaneous exploratory activity and inner zone activity were significantly lower in Hooded-Wistar rats than in Sprague-Dawley rats. Similarly, on the elevated plus-maze, Hooded-Wistar rats showed a lower propensity to visit the open arms. In contrast, amphetamine (0.5 mg/kg)-induced locomotor hyperactivity, an animal model of psychosis, was enhanced in Hooded-Wistar rats. 5. These data suggest that the Hooded-Wistar line could be a useful genetic animal model to study the interaction of glutamatergic and dopaminergic mechanisms in anxiety and schizophrenia.