Teaching gross anatomy using living tissue.

Embalmed cadaver tissues and organs that are dissected in gross anatomy laboratories lack many characteristics of fresh or living tissues. The purpose of this study was to assess the educational value of allowing first-year medical students to experience first-hand the color, texture, delicacy and other qualities of living porcine tissues and organs that are similar to those of human tissues. Guided by a laboratory protocol, medical students palpated and inspected organs of the opened thorax, abdomen and pelvis of anesthetized pigs on pulmonary ventilators. The learning experience was rated highly by the students as well as by the participating faculty. A further review of the medical students' later experiences at autopsies and in surgical clerkships showed that the living-tissue experience in their gross anatomy course represented a large part of their medical school exposure to unembalmed tissues.

Postnatal development of the human sternum.

Postnatal development and maturation of the human sternum are highly variable. Endochondral ossification centers (sternebrae) form within each cartilaginous segment of the sternum, with each center enveloped by a spherical growth plate. Within a cartilaginous center there may be either one or two ossification centers, those with two centers retaining and reflecting features of their bilateral embryonic origin. Malaligned bifid centers are clearly associated with rib articulation asymmetry as well. Expansion of individual ossification centers progresses within the peripheral cartilaginous domains of the sternum. With respect to the rostrocaudal axis, sternebrae form between the costosternal articulations. Consistent with the biology of endochondral transition, cartilage canals are evident throughout unossified regions of the hyaline matrix. Expanding ossification of adjacent sternebrae results in depletion of the common area of cartilage between the two sternebrae, and eventually in physiologic epiphysiodesis. Fusion of the mesosternebrae reciprocates the initial pattern of sternebral ossification site appearance, proceeding in a caudal-to-cranial direction. Union of adjacent sternebrae, initiated through a central osseous bridge, progresses through anterior, lateral, cephalocaudal, and posterior domains to achieve synostosis. Accessory and bifid centers of ossification within the same intercostal space coalesce prior to adjoining adjacent sternebrae. Manubriosternal fusion is rare due to the presence of a fibrocartilaginous joint restricting ossification. The xiphoid process remains connected to the most caudal mesosternum via a common zone of hyaline cartilage that ossifies by middle to late adulthood. A single pattern of development does not appear fundamental to successful growth of the sternum, as morphological variants were common.

Metallic dissolution of a civil war bullet embedded in a sternum.

The contemporary trend of converting departments of anatomy into departments of cell biology has brought with it the task of examining archive collections and storage facilities to figure out how to best utilize the available space. During one such inspection at the University of Louisville School of Medicine, a human sternum containing a dull metal projectile was uncovered. The projectile was easy to characterize as a bullet that had been deeply embedded in the bone. Less clear, however, were the circumstances detailing how the bullet had become lodged in the sternum, or how long the sternum might have been in storage at the University of Louisville. Radiographs of the sternum revealed a halo of surrounding density that dissipated in intensity from the margins of the bullet. Our initial hypothesis was that lead had been leached from the bullet into the bone matrix. To better assess what in fact contributed to this density, the sternum and the bullet were analyzed by energy-dispersive spectroscopy (EDS) to determine their elemental composition. That the bullet was composed of lead and aluminum was not surprising, but the extent to which the presence and dissolution of the bullet had affected the composition of the bony sternum was not entirely expected. The contribution of metal ions from the bullet to the inorganic matrix of bone was most notable for aluminum but nearly negligible for lead. This finding confirmed that bone affinity for metals is dependent upon the metal and supports previous reports that have suggested that lead is released from bone as soluble blood product during bony remodeling, whereas aluminum results in a significant elevation of bone density.

Lipoxygenase activity in rat embryos and its potential for xenobiotic oxidation.

This paper reports dioxygenase activity in rat embryos and demonstrates for the first time the ability of rat embryo lipoxygenase (LO) to oxidize xenobiotics in vitro. Significant dioxygenase activity towards linoleic acid was found in cytosol isolated from rat embryos in different developmental stages on day 9 and 10 of gestation. All four xenobiotics tested were oxidized at significant rate by the LO in the presence of linoleic acid. Both dioxygenase activity and benzidine oxidation were inhibited by the known inhibitors of LO, i.e. nordihydroguaiaretic acid and eicosatriynoic acid. These findings suggest that LO may be an important pathway for xenobiotic metabolism in the rat embryo.

Rat hepatic glutathione S-transferase-mediated embryotoxic bioactivation of ethylene dibromide.

The embryotoxic effects of ethylene dibromide (EDB) bioactivation, mediated by purified rat liver glutathione S-transferases (GST), were investigated using rat embryos in culture. Significant EDB metabolism was observed with rat liver GST purified by affinity chromatography (specific activity of 188 +/- 11.3 nmol/min/mg protein). The reaction was enzymatic in nature and the conjugation rate was proportional to the concentration of EDB (up to 0.75 mM) and the enzyme present in the reaction medium. EDB activation by 100 units (1 unit = 1 nmol of glutathione consumed per min) of purified rat liver GST caused a significant reduction in general development as measured by crown-rump length, yolk sac diameter, somite number, and the composite score for different morphological parameters (Brown and Fabro methodology). Structures most significantly affected were the central nervous and olfactory systems as well as the yolk sac circulation and allantois. The results of this study clearly indicate that under in vitro conditions, bioactivation of EDB by GST can lead to embryotoxicity.

A novel model to assess developmental toxicity of dihaloalkanes in humans: bioactivation of 1,2-dibromoethane by the isozymes of human fetal liver glutathione S-transferase.

Glutathione S-transferase (GST) isozymes from human fetal liver (16-18 weeks gestation) were purified by affinity chromatography followed by ion-exchange high performance liquid chromatography (HPLC). The purified isozymes were used to investigate toxicity of 1,2-dibromoethane(EDB) in an in vitro model of rat embryos in culture as passive targets. At least five isozymes of GST were found in the human fetal liver. Two anionic forms [pI values 5.5 (P-2) and 4.5 (P-3)] and one basic form [pI value 8.7 (P-6)] were clearly separated. The presence of two near-neutral forms was also identified. All the isozymes of the human fetal liver GSTs tested metabolized EDB (specific activities were 2.1, 7.0, and 2.0 mumol of GSH consumed/min/mg protein for P-2, P-3, and P-6 isozymes, respectively). Covalent binding of EDB to DNA and protein was 144% and 212% higher, respectively, with the P-3 anionic isozyme when compared to the P-6 basic isozyme of GST. No covalent binding to either protein or DNA was observed with the P-2 isozyme. EDB bioactivation by the GST isozyme P-3 (15 units; 1 unit = 1 nmol of GSH consumed/min) resulted in toxicity to cultured rat embryos. Significant reductions of crown rump length, yolk sac diameter, and the composite score of morphological parameters (Brown and Fabro method) were observed. The central nervous system, optic and olfactory systems, and the hind limb were most significantly affected. The results of this investigation suggest that EDB may be classified as a suspected developmental toxicant in humans.