Classification model that predicts medical students' choices of primary care or non-primary care specialties.

To identify factors that influence students to choose primary care or non-primary care specialties, the authors surveyed the 509 graduating students at the Medical College of Georgia School of Medicine in 1988, 1989, and 1990. Using a Likert-type scale, the 404 responding students rated potential influences on their specialty choices from 1, very negative, to 7, very positive. The students choosing primary care specialties were positively influenced significantly more often by their desire to keep options open (85% versus 58%, p less than .001) and their desire for longitudinal patient care opportunities (95% versus 54%, p less than .001). Those choosing non-primary care specialties were more often influenced by their desire for monetary rewards (69% versus 35%, p less than .001) and by their perceptions of lifestyle following residency (74% versus 60%, p less than .01) and prestige of the specialty (57% versus 36%, p less than .001). The authors used multiple discriminant analysis to derive a discriminant function that would permit classification of students into primary care and non-primary care groups. The potential influences of desire for longitudinal care opportunities and desire for monetary rewards were statistically and clinically significant for all three years. Using the discriminant function, the authors correctly classified 81%, 79%, and 78% of the students' specialty choices for 1988, 1989, and 1990, respectively. The authors suggest that addressing the issue of monetary rewards will be necessary before the primary care fields again become attractive to students.     

Acute exertional rhabdomyolysis and its relationship to sickle cell trait

Exertional rhabdomyolysis, a syndrome characterized by skeletal muscle degeneration and muscle enzyme leakage, has been shown to occur in normal, healthy individuals following strenuous exercise. In severe cases, this syndrome can result in renal failure and sudden death. Although anyone who performs strenuous exercise may be at risk for developing exertional rhabdomyolysis, some individuals may be more susceptible than others. A number of case reports of exertional rhabdomyolysis involve persons with sickle-cell trait, leading to the theory that these individuals might be at greater risk for developing the syndrome than those without this trait. This article discusses the etiology of exertional rhabdomyolysis, the associated risk factors for persons with sickle-cell trait, and the recommended preventive measures. Additionally, several case studies of exertional rhabdomyolysis are reviewed.     

Mechanical properties of a light-polymerizing provisional restorative material with and without reinforcement fibers

Interim restorations are vulnerable to inadvertent fracture during mastication. Autopolymerizing acrylic resins have traditionally been selected for fabrication of provisional restorations. Triad light-polymerizing tooth-colored acrylic resin was recently introduced as an alternative material for this procedure. This material does not contain methyl methacrylate monomer and permits an increased working time. Heavy occlusal forces may initiate cracks within these restorations, and propagation of these cracks may ultimately lead to failure. Various forms of reinforcement fibers are available and are marketed for strengthening dental resins used for provisional restorations. Investigators have demonstrated that the mechanical properties of acrylic resins may be improved with the incorporation of reinforcing fibers, but a published evaluation of fiber-reinforced light-polymerizing provisional restorative materials is lacking. This investigation recorded and compared two mechanical properties of one light-polymerizing provisional restorative material with and without incorporation of vertically and horizontally oriented woven, matted, polyethylene fibers. No significant difference in modulus of rupture was recorded between groups with and without fibers. The mean flexural elastic modulus of the group with the horizontally oriented fibers was significantly greater than the mean flexural elastic modulus of the specimens without incorporated fibers.     

Dibenzo[a,l]pyrene-induced DNA adduction, tumorigenicity, and Ki-ras oncogene mutations in strain A/J mouse lung

Dibenzo[a,l]pyrene (DB[a,l]P), an environmental polycyclic aromatic hydrocarbon, is the most potent carcinogen ever tested in mouse skin and rat mammary gland. In this study, DB[a,l]P was examined for DNA adduction, tumorigenicity, and induction of Ki-ras oncogene mutations in tumor DNA in strain A/J mouse lung. Groups of mice received a single i.p. injection of 0.3, 1.5, 3.0, or 6.0 mg/kg DB[a,l]P in tricaprylin. Following treatment, DNA adducts were measured at times between 1 and 28 days, while tumors were counted at 250 days and analyzed for the occurrence of point mutations in codons 12 and 61 of the Ki-ras oncogene. DB[a,l]P in strain A/J mouse lung induced six major and four minor DNA adducts. Maximal levels of adduction occurred between 5 and 10 days after injection followed by a gradual decrease. DB[a,l]P-DNA adducts in lung tissue were derived from both anti- and syn-11,12- dihydroxy-13,14-epoxy- 11,12,13,14-tetrahydrodibenzo[a,l]pyrene (DB[a,l]PDE) and both deoxyadenosine (dAdo) and deoxyguanosine (dGuo) residues in DNA as revealed by cochromatography. The major adduct was identified as a product of the reaction of an anti-DB[a,l]PDE with dAdo in DNA. DB[a,l]P induced significant numbers of lung adenomas in a dose- dependent manner, with the highest dose (6.0 mg/kg) yielding 16.1 adenomas/mouse. In tricaprylin-treated control animals, there were 0.67 adenomas/mouse. Based on the administered dose, DB[a,l]P was more active than other environmental carcinogens including benzo[a]pyrene. As a function of time-integrated DNA adduct levels, DB[a,l]P induced lung adenomas with about the same potency as other PAHs, suggesting that the adducts formed by DB[a,l]P are similar in carcinogenic potency to other PAHs in the strain A/J mouse lung model. Analysis of the Ki- ras mutation spectrum in DB[a,l]P-induced lung tumors revealed the predominant mutations to be G-->T transversions in the first base of codon 12, A-->G transitions in the second base of codon 12, and A-->T transversions in the second or third base of codon 61, concordant with the DNA adduct profile.      

Somatostatin receptor scintigraphy: the definitive technique for characterizing vasoactive intestinal peptide-secreting tumors

Vasoactive intestinal peptide-secreting tumors (VIPomas) are extremely rare and difficult to diagnose. The authors describe a patient who was found to have a VIPoma after 3 years of symptoms. Somatostatin receptor scintigraphy using indium-labeled octreotide localized her tumor and prompted a surgical resection. This is the preferred imaging study for the earliest, most accurate, and cost-effective identification of VIPomas and their metastases.     

Case report: cavernous hemangioma of the liver.

Although cavernous hemangioma is the most common benign tumor of the liver, controversy persists regarding diagnosis and management of these lesions. With the development of multiple noninvasive modalities to visualize the liver, hepatic cavernous hemangiomas are recognized with increased frequency. The authors report the unusual case of a post-menopausal woman on no exogenous estrogen therapy who had a cavernous hemangioma that remained stable for approximately 10 years before dramatically increasing in size. This patient illustrates the vague symptoms associated with cavernous hemangiomas and the unpredictability of growth. Although estrogens have been reported trophic, this patient had no exogenous or endogenous estrogen supply, yet her lesion reached massive proportions. Modalities necessary to assure accurate diagnosis and factors influential in management are discussed.     

Influence of oxygen tension on the viscoelastic behavior of red blood cells in sickle cell disease

Although the rheological behavior of sickle cell suspensions and of hemoglobin S solutions is known to be strongly dependent on oxygen tension (PO2), little data exist concerning the influence of PO2 on the viscoelasticity of individual HbSS RBC. We have used micropipette aspiration techniques to test the deformation response of both HbSS and control HbAA RBC over a wide range of PO2 at 23 degrees C. Sickled, spiculed HbSS cells were present for PO2 approximately less than 35 mm Hg; for a number of these cells, the deformation response was essentially elastic and an effective membrane rigidity (EMR) was calculated. EMR increased with decreasing PO2 and was approximately 5 to 50 times higher than the equivalent rigidity of oxygenated HbSS RBC. In addition, the rate of membrane deformation was very slow for sickled cells; the half-time for the deformation process increased as PO2 was lowered and was about two orders of magnitude longer than the equivalent time for normal RBC. Other sickled cells exhibited plastic deformation when subjected to comparable deforming forces and experienced irreversible membrane deformation and budding. At all PO2 levels tested, some HbSS RBC remained as discocytes; these cells had normal membrane elasticity and membrane viscosity. Furthermore, changes in PO2 did not affect the membrane properties of HbAA RBC. Thus, gross abnormalities in the deformation response of HbSS RBC were only detected after morphological sickling had occurred. These abnormalities most likely arose from changes in the cytoplasmic HbS viscoelasticity and, if present in vivo, would be expected to impair the flow of HbSS cells in the microcirculation.     

Primary structure of the (1-->3,1-->4)-beta-D-glucan 4-glucohydrolase from barley aleurone

During germination of barley grains, the cell walls of the starchy endosperm are degraded by (1→3,1→4)-β-glucanases (EC 3.2.1.73) secreted from the aleurone and scutellar tissues. The complete sequence of the aleurone (1→3,1→4)-β-glucanase isoenzyme II comprises 306 amino acids and was determined by sequencing nine tryptic peptides (110 residues) and aligning them with the amino acid sequence deduced from a cDNA clone encoding the 291 NH₂-terminal residues. Although no amino acid sequence homology with a bacterial (1→3)(1→4)-β-glucanase is apparent, close to 50% homology is found with two large regions of a (1→3)-β-glucanase from tobacco pith tissue. The gene for barley (1→3,1→4)-β-glucanase isoenzyme II shares with that for the α-amylase isoenzyme 1 a strongly preferred use of codons with G and C in the wobble position (94% and 90%, respectively). Both enzymes are secreted from the aleurone cells during germination. Such one-sided codon usage is not characteristic for the gene encoding the (1→3)-β-glucanase of tobacco pith tissue or the hor2-4 gene encoding the B₁ hordein storage protein in the endosperm.