Pilot Trial of Intravenous Lipid Emulsion Treatment for Severe Nifedipine-Induced Shock.

Animal studies and human case reports show promise in using lipid rescue to treat refractory calcium channel antagonist toxicity. However, the majority of research and clinical experience has focused on non-dihydropyridine agents. Thus, we sought to investigate the value of lipid emulsion (ILE) therapy for dihydropyridine-induced shock. This IACUC-approved study utilized seven swine that were sedated with alpha-chloralose, mechanically ventilated, and instrumented for drug delivery and hemodynamic measures. After stabilization and basal measures, nifedipine (0.01875 mg/kg/min) was infused until imminent cardiac arrest (seizure, end tidal CO2 < 10 mmHg, bradydysrhythmia, or pulseless electrical activity). Animals then received a 7 mL/kg bolus of 20% lipid emulsion via central catheter. Lipid circulation was visually confirmed by the presence of fat in peripheral arterial blood. Hemodynamics were continuously monitored until 10 min after lipid bolus. Surviving animals were euthanized. Pre- and post-lipid treatment parameters were analyzed using the Wilxocon signed rank test (p <0.05 significant). Nifedipine toxicity was characterized by vasodilatory hypotension, impaired vascular contractility, and tachycardia with terminal bradycardia. The median time to imminent cardiac arrest from start of nifedipine infusion was 218 min. Lipid treatment did not improve hemodynamics or restore circulation in any animal. There was no benefit from lipid rescue in this model of nifedipine toxicity. Further study of ILE for dihydropyridine toxicity is warranted but initial animal model results are not promising.

A new small animal model for the study of spine fusion in the sand rat: pilot studies.

Spine fusion is used to treat traumatic or degenerative lumbar instability in the cervical or lumbar spine. Although degenerative radiological changes in discs adjacent to a fusion have been well-recognized, histopathological changes in adjacent discs have not been studied and are poorly understood. An economical small animal model for lumbar fusion would be a useful research tool. Study objectives were to: (1) develop a model of non-instrumented spine fusion in the sand rat, a rodent with spontaneous, age-related disc degeneration; (2) use radiological-histological analyses to study fusion and disc degeneration in cranial and caudal discs adjacent to the fusion. Studies were approved by our Institutional Animal Care and Use Committee. A small segment of outer annulus tissue was surgically removed from lumbar discs, radiographs obtained and the animal allowed to recover and age. At surgical harvest, radiographs of 28 spine fusion specimens were scored and statistically analysed for adjacent disc space narrowing, wedging, endplate sclerosis and irregular disc margins. At harvest, the incidence of these radiological indices of disc degeneration were significantly greater than at time of surgery. Pilot studies presented here indicate that this model provides a novel addition to basic science approaches studying the clinically important topic of spinal fusion and adjacent segment changes. The resulting fusion site can be assessed statistically with radiological scoring to determine development/progression of disc degeneration in adjacent segments, and correlative histological features can be examined. The sand rat is well-suited for use in spine fusion studies because of reliable/reproducible progression of disc degeneration and the favourable economics of small rodent studies.

Analysis of cell death and vertebral end plate bone mineral density in the annulus of the aging sand rat.

BACKGROUND CONTEXT: The relationship between disc degeneration and end plate sclerosis is poorly understood. The sand rat is an excellent, economical small-animal model in which disc degeneration is age related, spontaneous, reliable, and well characterized. This model is used here to evaluate disc degeneration, disc cell viability, and vertebral end plate bone mineral density (BMD) in lumbar sites. PURPOSE: To determine the proportion of live and dead cells and end plate bone mineral density in the aging sand rat annulus. STUDY DESIGN: Young and old sand rats were used in work approved by the Institutional Animal Care and Use Committee. Outcome measures were the percentage of live/dead annulus cells in the disc and the BMD of cranial and caudal end plates of lumbar vertebrae. METHODS: Bone densitometry was used to obtain endplate BMD on lumbar spines of 16 young sand rats aged 2 to 6 months and 26 older animals aged 22 to 46 months. X-ray films were analyzed for wedging, end plate calcification, and disc-space narrowing. Additional discs were also harvested and incubated with fluorochromes, and the percentage of live or dead cells were determined for the outer, inner annulus, and entire annulus. RESULTS: Radiographically old animals had significantly greater incidence of lumbar wedging (p<0.004) and a significantly greater incidence of end plate calcification and disc-space narrowing (p<0.01). In the live-dead study, the mean percentage of dead annulus cells for the three age groups were significantly different for the outer annulus (p<0.001), inner annulus (p=0.005), and total annulus (p<0.0001). The percentages of dead cells for the entire annulus were 46.14%+/-7.99% (age 2-6 months), 48.13%+/-17.32% (age, 13-19 months), and 76.80%+/-7.27% (age 26-38 months). The percentage of dead disc cells correlated significantly with age for outer annulus, inner annulus, and total annulus (p<0.006). The percentage of dead cells in the entire annulus and the inner annulus correlated significantly with end plate BMD (p<0.02). CONCLUSIONS: Data are novel and show that in very aged sand rats, end plate BMD is significantly greater than that of young animals. Live/dead cell analyses showed increasing cell death in both outer and inner annulus, which correlated significantly with age and with end plate BMD.

Vertebral endplate and disc changes in the aging sand rat lumbar spine: cross-sectional analyses of a large male and female population.

STUDY DESIGN: Lumbar vertebral segments from a large cross-sectional population of male and female sand rats were assessed for quantitative determination of lumbar endplate bone mineral density (BMD) and radiologic features. OBJECTIVE: To determine radiologic and BMD characteristics in the lumbar spines of males and females ranging in age from 1.5 to 46.0 months. SUMMARY OF BACKGROUND DATA: The sand rat provides an excellent economical model in which disc degeneration is reliable and well characterized. A major advantage of this model is that disc degeneration is spontaneous and does not need to be induced by stab surgical procedures. Previous work has only examined a small group of male sand rats for radiologic and BMD features of the lumbar spine; more complete data on both genders and a wider age range are lacking. METHODS: BMD data were obtained for 99 male or female sand rats aged 1.5 to 46.0 months using the GE Lunar PIXImus bone densitometer; results were assessed for changes related to age, weight, gender, lumbar vertebral site, and radiologic characteristics of disc degeneration (disc space narrowing, wedging, and endplate calcification). Four age groups were studied: Group 1, 1 to 3.9 months of age; Group 2, 4 to 11.9 months of age; Group 3, 12 to 23.9 months of age, and Group 4, 24 to 46 months of age. RESULTS: Group 1 females showed a greater incidence of radiologic disc space narrowing and wedging at L1-L2, L2-L3, L3-L4, L4-L5, and of wedging at sites L5-L6, L6-L7, and L7-S. Group 2 females had significantly greater disc space narrowing at L3-L4 and L4-L5. By the time animals reached the age of Groups 3 and 4, males showed more wedging at L1-L2 and L3-L4. BMD data showed that Group 1 females had significantly lower BMD than Groups 2, 3 and 4 at all lumbar levels, and Group 4 had significantly higher BMD than Group 3. For males, there were no differences in younger animals, but older Group 3 and 4 animals had significantly greater BMD than Groups 1 and 2. Caudal BMD values were generally significantly higher than cranial values. Averaged BMD levels correlated significantly with both age and body weight, but the correlation with age at each lumbar level accounted for much more of the variation than did weight. Averaged BMD was significantly greater in disc sites showing disc space narrowing than in sites without narrowing for L1-L2 and L3-L4 through L7-S (P < or = 0.002 for each spinal level). CONCLUSION: Results expand our understanding of the association of age and gender to endplate sclerosis patterns in the lumbar spine, and support the hypothesis that endplate sclerosis may play a role in disc degeneration.

Vertebral endplate architecture and vascularization: application of micro-computerized tomography, a vascular tracer, and immunocytochemistry in analyses of disc degeneration in the aging sand rat.

STUDY DESIGN: Lower lumbar vertebral endplates from young and old sand rats were assessed in an Institutional Animal Care and Use Committee approved study for architectural endplate features using micro-computerized tomography (CT) 3-dimensional (3D) models and vascularization studies by an in vivo vascular tracer or immunocytochemical identification of blood vessels. OBJECTIVE: To assess endplate porosity and vascularization using microCT architectural analysis, an in vivo vascular tracer, and immunocytochemical identification of blood vessels in the endplate. SUMMARY OF THE BACKGROUND DATA: The vertebral endplates, also called cartilage endplates, form the superior and inferior, or cranial and caudal, boundaries of the disc. In the human being and sand rat, the cartilaginous endplate undergoes calcification with aging and is replaced by bone. Endplate sclerosis has long been thought to play a role in disc degeneration by decreasing nutrient availability to the disc, but this is still poorly understood. Previous work has identified increasing bone mineral density with aging and disc degeneration in the sand rat model. METHODS: microCT models of the lower lumbar endplates of vertebrae at L5-6 and L6-7 were constructed from 6 younger (mean age 11 months) and 21 older (mean age 25.6 months) sand rats. Architectural features were scored on a semiquantitative scale for smoothness of the endplate face, irregularities on the endplate margin, and endplate thickness. There were 2 smaller sets of animals (n = 18) evaluated for endplate vascularity following in vivo injection of a fluorescent vascular tracer or by the use of immunocytochemistry to identify blood vessels. RESULTS: microCT revealed a solid bony surface to the endplate, which was not penetrated by vasculature; with aging/disc degeneration, there was roughening and pitting of the plate surface, and the development of irregular margins. In L5-6 and L6-7, sites of prominent disc degeneration evident on radiographs, the proportion of abnormalities in surface smoothness, margin irregularity, and endplate thickening were all statistically significant in both younger and older animals (P < or = 0.0027). More severe changes were evident in the caudal versus cranial endplate surfaces. Histologic study of vascular tracer showed that there was no penetration of the disc by vascular supply from the endplate; this was verified by immunocytochemical identification of blood vessels. The canal system within the endplate was a complex 3D interconnected network. CONCLUSIONS: Findings show that disc degeneration in the sand rat occurs concomitantly with marked architectural bony changes on the endplate face, including loss of smoothness and development of irregular bony margins. Vascular connections were not present between the endplate and disc; this was verified with microCT studies, in vivo vascular tracers, and traditional immunocytochemistry. The canal system within the imaged endplate was revealed to consist of a complex 3D interconnected network.

Bone mineral density of lumbar vertebral end plates in the aging male sand rat spine.

STUDY DESIGN: Lumbar vertebral segments from young and old male sand rats were assessed for quantitative determination of lumbar end plate bone mineral density. OBJECTIVES: To determine whether bone mineral density increases in the lumbar end plate with age in the male sand rat and to investigate its relationship to disc degeneration. SUMMARY OF THE BACKGROUND DATA: Few basic science studies evaluated the end plate and disc degeneration. The sand rat provides an excellent economical model in which disc degeneration is reliable and well characterized. METHODS: Bone mineral density data on cranial and caudal lumbar end plates of young (mean age 6.8 months) and old (mean age 23.3 months) male sand rats were assessed for changes related to age, lumbar position, and radiologic features. RESULTS: Mean bone mineral density was significantly greater in end plates in older compared to younger males (P