Morphine reduces spinal c-fos expression dose-dependently during experimental laparotomy in pigs: A combined pharmacokinetic and surgical study

A systematic review of porcine models in translational pain research

Translating basic pain research from rodents to humans has proven to be a challenging task. Efforts have been made to develop preclinical large animal models of pain, such as the pig. However, no consistent overview and comparison of pig models of pain are currently available. Therefore, in this review, our primary aim was to identify the available pig models in pain research and compare these models in terms of intensity and duration. First, we systematically searched Proquest, Scopus and Web of Science and compared the duration for which the pigs were significantly sensitized as well as the intensity of mechanical sensitization. We searched models within the specific field of pain and adjacent fields in which pain induction or assessment is relevant, such as pig production. Second, we compared assessment methodologies in surrogate pain models in humans and pigs to identify areas of overlap and possible improvement. Based on the literature search, 23 types of porcine pain models were identified; 13 of which could be compared quantitatively. The induced sensitization lasted from hours to months and intensities ranged from insignificant to the maximum attainable. We also found a near to complete overlap of assessment methodologies between human and pig models within the area of peripheral neurophysiology, which allows for direct comparison of results obtained in the two species. In spite of this overlap, further development of pain assessment methodologies is still needed. We suggest that central nervous system electrophysiology, such as electroencephalography, electrocorticography or intracortical recordings, may pave the way for future objective pain assessment.

Urinary Kinetics of Heroin Metabolites in Pigs Shortly After Intake

In previous experimental studies on heroin metabolites excretion in urine, the first sample was often collected a few hours after intake. In forensic cases, it is sometimes questioned if a positive urine result is expected e.g., 30 min after intake. The aim of this study was to investigate urinary excretion of heroin metabolites (morphine, 6-monoacetylmorphine (6-MAM) and morphine-3-glucuronide (M3G)) every 30 min until 330 min after injection of a 20 mg heroin dose in six pigs. Samples were analyzed using a previously published, fully validated liquid chromatography-tandem mass spectrometry method. All metabolites were detected after 30 min in all pigs. The time to maximum concentration (Tmax) median (range) for 6-MAM and morphine was 30 min (first sample) (30-120), and 90 min (30-330) for M3G. In four of the six pigs, the Tmax of 6-MAM and morphine was reached within 30 min. All analytes were still detectable at the end of study. This study showed that positive results in urine are expected to be seen shortly after use of heroin in pigs. Detection times were longer than previously indicated, especially for 6-MAM, but previous studies used lower doses. As the physiology of these animals resembles that of the humans, transferability to man is expected.

Pharmacokinetics of heroin and its metabolites in vitreous humor and blood in a living pig model

Vitreous humor (VH) is an alternative matrix for drug analysis in forensic toxicology. However, little is known about the distribution of xenobiotics, such as opioids, into VH in living organisms. The aim of this study was to simultaneously measure heroin and metabolite concentrations in blood and VH after injection of heroin in a living pig model. Six pigs were under non-opioid anesthesia during the surgical operation and experiment. Ocular microdialysis was used to acquire dialysate from VH, and a venous catheter was used for blood sampling. Twenty milligrams of heroin was injected intravenously with subsequent sampling of blood and dialysate for 6 h. The samples were analyzed by ultra-performance liquid chromatography–tandem mass spectrometry. Heroin was not detected in VH; 6-monoacetylmorphine (6-MAM) and morphine were first detected in VH after 60 min. The morphine concentration in VH thereafter increased throughout the experimental period. For 6-MAM, C_max was reached after 230 min in VH. In blood, 6-MAM reached C_max after 0.5 min, with a subsequent biphasic elimination phase. The blood and VH 6-MAM concentrations reached equilibrium after 2 h. In blood, morphine reached C_max after 4.3 min, with a subsequent slower elimination than 6-MAM. The blood and VH morphine concentrations were in equilibrium about 6 h after injection of heroin. In conclusion, both 6-MAM and morphine showed slow transport into VH; detection of 6-MAM in VH did not necessarily reflect a recent intake of heroin. Because postmortem changes are expected to be small in VH, these experimental results could assist the interpretation of heroin deaths.

Endogenous opiates and behavior: 2008

This paper is the 31st consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2008 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).