Maurice W. Meyer

EFFECTS OF ORAL FLORA ON PLATELETS : POSSIBLE CONSEQUENCES IN CARDIOVASCULAR DISEASE

During episodes of dental bacteremia, viridans group streptococci encounter platelets. Among these microorganisms, certain Streptococcus sanguis induce human and rabbit platelets to aggregate in vitro. In experimental rabbits, circulating streptococci induced platelets to aggregate, triggering the accumulation of platelets and fibrin into the heart valve vegetations of endocarditis. At necropsy, affected rabbit hearts showed ischemie areas. We therefore hypothesized that circulating S. sanguis might cause coronary thrombosis and signs of myocardial infarction (MI). Signs of MI were monitored in rabbits after infusion with platelet-aggregating doses of 4 to 40 × 109 cells of S. sanguis 133-79. Infusion resulted in dose-dependent changes in electrocardiograms, blood pressure, heart rate, and cardiac contractility. These changes were consistent with the occurrence of MI. Platelets isolated from hyperlipidemic rabbits showed an accelerated in vitro aggregation response to strain 133-79. Cultured from immunosuppressed children with septic shock and signs of disseminated intravascular coagulation, more than 60% of isolates of viridans streptococci induced platelet aggregation when tested in vitro. The data are consistent with a thrombogenic role for S. sanguis in human disease, contributing to the development of the vegetative lesion in infective endocarditis and a thrombotic mechanism to explain the additional contributed risk of periodontitis to MI. J Periodontol 1996;67:1138-1142.

Vascular Effects of Hypertonic Solutions

During the course of an investigation into the treatment of metabolic acidosis arising from total body perfusion, it was noticed that the intra-arterial administration of concentrated alkalies resulted in a fall in arteriovenous pressure difference at constant flow. A similar decline in peripheral resistance could be produced by hypertonic sugar and salt solutions. This response was found to be independent of the central nervous system. The role of the vasodilatation in the complex vasomotor reaction to the rapid intravenous injection of hyperosmotic agents was then investigated in the intact and vagotomized dog. It was found that when concentrations of up to 1,500 mOsm./L. were used, the predominant response was a delayed hypotension consistent with peripheral vasodilatation. This reaction was complicated by preliminary pulmonary hypertension when solutions containing more than 2,000 mOsm./L. were administered. Twenty per cent NaCl produced such a severe initial phase that the animals frequently died from acute cor pulmonale. The site of obstruction to blood flow through the lungs was variable. Fifty percent glucose could incite pulmonary hypertension, but urea was anomalous in that it was never observed to produce pulmonary vascular effects. Studies in the isolated perfused lung indicated that, again with the exception of urea, all solutions with an osmolarity equal or greater than 5 per cent NaCl evoked pulmonary hypertension. The increase in pulmonary vascular resistance was transitory in spite of recirculation. No response could be elicited when red cells were absent from the perfusate even though, under these conditions, the lung was still sensitive to serotonin. Microscopic examination of the circulation through the brain, lung, mesentery and thigh of both cat and dog demonstrated that intravascular red-cell agglutination occurred after regional arterial injection of highly concentrated salt and sugar solutions. This alteration in the stability of the red-cell stream is considered to be responsible for the obstructive effects of hyperosmotic agents previously attributed to vasospasm.

Distribution of Cardiac Output to Oral Tissues in Dogs

Isotope fractionation and particle distribution methods were used in conjunction to quantitate blood flow in the oral mucosa, alveolar bone, tongue, masseter muscle, and dental pulp. Infiltration of epinephrine in lidocaine (Xylocaine) and lidocaine alone and inhalation of 5% CO2 provided experimental conditions to alter flow in some tissues.

Blood Flow in the Central and Peripheral Nervous System of Dogs Using a Particle Distribution Method

In this study known activities of 85Sr and 169Yb-labeled microspheres were injected sequentially into the left ventricle of anesthetized dogs. Cardiac output was determined before and after each microsphere injection. Blood flow to brain, brain stem, spinal cord, and sciatic nerve was measured from fractional distribution of the microspheres in the tissue samples. Both blood flow and fractional uptake value tended to be higher for brain and brain stem than for spinal cord or sciatic nerve. Increases in arterial PCO2 were positively correlated with increases in blood flow to both central and peripheral nervous tissue. Initial trapping of the labeled microspheres seems to have little effect on subsequent flow to the tissue capillary bed. It appears that the particle distribution technique may provide a reasonable estimate of blood flow in central and peripheral nervous tissue of dogs.

Host-pathogen interactions in bacterial endocarditis : streptococcal virulence in the host

To identify streptococcal genes that are expressed during experimental endocarditis, we developed a promoter-less dual reporter gene-fusion (amy, cat) plasmid, pAK36. Chromosomal DNA from S. gordonii V288 was digested with Sau3Al. The resulting fragments were ligated into pAK36. Following transformation into S. gordonii, the library of random gene fusion clones was inoculated into a rabbit to induce experimental endocarditis. Chloramphenicol treatment effected positive selection. Upon euthanization of the rabbits, the valvular vegetations were excised in a sterile field. Surviving clones were isolated and screened in vitro for chloramphenicol sensitivity and negative amylase activity. From the 48 randomly picked, double-negative clones. DNA was isolated and analyzed by Southern hybridization with labeled pAK36 probe. Different insertion patterns were identified, suggesting that no fewer than 13 S. gordonii genes were induced. Therefore, S. gordonii genes are induced during experimental endocarditis, which may contribute to virulence.

Quantification of Pulpal Blood Flow in Developing Teeth of Dogs

Pulpal blood flow in developing teeth was determined by the isotope fractionation method incorporating diffusible and nondiffusible tracers. While the calculated blood flow to some cephalic tissues did vary according to tracer, blood flow to the total pulp remained essentially the same throughout tooth development.

Clearance of Radioactive Isotopes by Circulation in the Dental Pulp

It has been suggested that clearance of tracer substances injected into muscle tissue may be a measure of local circulation (S. S. KETY, Amer. Heart J. 38:321-27, 1949; P. F. SALISBURY, C. E. CROSS, R. W. OBLATH, and P. A. RIEBEN, J. A pp. Physiol. 17:475-78, 1962). Others have indicated that clearance of Na24 did not measure total blood flow in a muscle (T. C. PRENTICE, R. R. STAHL, N. A. DIAL, and F. V. PONTERIO, J. cdin. Invest. 34:545-58, 1955). However, clearance of Na24 was considered to be a measure of capillary flow in skeletal muscle at very low flow rates (N. S. LASSEN, J. dlin. Invest. 43:1805-12, 1964). This study was intended to assess radioactive clearance as a method for investigating pulpal circulation in dogs. Since injection procedures are not practical, deep cavities (60 to 80jA of dentin remaining) were prepared in canine teeth. Radioactive solutions of Na24 (NaCl), IJll (NaIO3), or K42 (KCl) were adjusted to isotonicity, pH of 7.2 and activity of 300 to 500 jC./ml. and kept at 370 C. The head of the dog was adjusted and rigidly supported so that a small quantity (0.01 ml.) of isotope solution could be placed in the cavity for each experimental condition and covered with mineral oil to minimize evaporation. A 6-mm. scintillation probe* equipped with a collimator was placed above the cavity. Activity was either continuously recorded with a rate meter or counted on a decade counter for 2-

Sympathetic regulation of cephalic blood flow.

Blood flow to bilateral tissues (cranial and extracranial) was studied by means of the particle distribution method in two groups of anesthetized dogs (five using 25-/* radioactive microspheres, six using 15-M microspheres) and five anesthetized stumptail Macaques monkeys (8-/4 spheres) during unilateral sympathetic stimulation. The stimulatory parameters were adjusted to produce maximum pupillary dilatation. In the five dogs hemispheric and regional cerebral blood flow decreased but not significantly. Flow to the extracranial tissues decreased 82%. Hemispheric brain blood flow averaged 0.70 ml/min/gm for Paco, of 40 mm Hg. In the six dogs sympathetic stimulation did not significantly decrease cerebral blood flow but decreased flow to extracranial tissues (72.3%). At an average Paco, of 33.5 mm Hg, hemispheric blood flow to the unstimulated side averaged 0.51 ml/min/gm. In the five monkeys findings were essentially the same as those observed in the dogs. The hemispheric blood flow averaged 0.36 ml/min/gm on the nonstimulated side for an average Paco, of 36.6 mm Hg. Under the conditions studied, electrical stimulation of the cervical sympathetic nerves does not appear to modify regional or total brain blood flow in dogs and Macaques monkeys. The vascular response in oral and other extracranial tissues is very dramatic, however.

RED CELL AGGREGATION FROM CONCENTRATED SALINE AND ANGIOGRAPHIC MEDIA.

Zahn in 1875 (1) observed aggregation of red blood cells in the mesenteric circulation of the frog following the topical application of salt crystals. A similar phenomenon was described by Read et al. (2) in various circulatory beds (mesenteric, subcutaneous, pulmonary, and pial) of dogs and cats after the intravascular administration of concentrated salt solutions including angiographic media. The purpose of the present study was to provide further information regarding this agglutinative and crenation property and, in particular, to document and extend our previous preliminary microscopic observations. Methods Adult mongrel dogs were anesthetized by the intravenous administration of pentobarbital sodium. The mesenteric circulation was microscopically examined and photographed by a technic which has been previously described (3). Observations were made before and after the intraarterial injections of 2 to 3 ml. of a solution of either 15 per cent sodium chloride or 90 per cent Hypaque. (The latter was em...

Tissue pertechnetate and iodinated contrast material in ischemic stroke.

Isotope uptake during static radionuclide scanning and contrast enhancement during CT scanning, which may result from similar pathophyslologlc mechanisms after ischemic infarction, were investigated in an animal model. Infarction was produced by transorbital occlusion of the middle cerebral artery in cats killed one, 2, 4, 8, or 16 days later. Sodium pertechnetate containing technetium-99m and 30% methyl-glucaraine iothalamate labeled with 1-125 were administered intravenously 60 and 15 min respectively prior to sacrifice. A coronal section through the infarct was parceled into 30 portions which were assayed for concentration of each isotope. Adjacent brain was prepared for histopatbologic correlation. Concentrations of the 2 materials were highest in infarcted brain at 4 and 8 days. Strong positive correlation was found between tissue concentrations of the 2 materials in all brain samples. Elevated tissue levels correlated with necrosis, macrophage infiltration, and vascular byperplasia. The results support the probability that radionuclide scan positivity and CT contrast enhancement reflect the same pathophysiologic development, probably extravasation of the respective labels, after ischemic stroke.