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Biomedical subjects

M Richardson

Publications and source records attributed to M Richardson.

At least 361 records · Page 20Linked to original sources
PubMed1984

Ultrastructural changes in re-endothelialized and non-endothelialized rabbit aortic neo-intima following re-injury with a balloon catheter.

The response by normal rabbit aortas to the removal of the endothelium with a balloon catheter, was compared to the response to the removal of regenerated endothelium from rabbit aortas that had been previously de-endothelialized. De-endothelialization results in the formation of a neo-intima. Thrombus formation following a second balloon catheter injury was compared among injured neo-intima that had been re-endothelialized, non-re-endothelialized neo-intima, and the subendothelium of normal vessels following a single injury. Rabbit aortas were examined by scanning electron microscopy of full circumference segments of the aorta and by transmission electron microscopy. Thirty minutes after a single de-endothelialization injury with a balloon catheter the luminal surface is covered by a monolayer of platelets adhering to the subendothelial connective tissues. Two weeks later there is neo-intimal formation and endothelial regeneration around branch vessel orifices. The remainder of the luminal surface is composed of smooth muscle cells (SMC). A balloon catheter injury to a vessel injured 2 weeks previously results in fibrin formation and platelet-fibrin microthrombi on the aortic intimal surface. The response of the aortic wall to re-injury does not seem to be related to the prior existence of endothelium. Both single and repeated injuries result in a distribution of formed elements which may depend, in part, on haemodynamic factors.

Animals↗
PubMed1984

Spread of carcinoma of the base of the tongue as detected by computer tomography.

21 patients with histologically proven carcinoma involving the base of the tongue were studied with computer tomography utilizing a high dose of intravenous infusion of contrast material. Computer tomography demonstrated not only excellent visualization of the primary carcinoma at the base of the tongue, but also its traditional means of spread to contiguous soft tissues of the pharyngeal walls and lymph node metastasis. Computer tomography also demonstrated the unusual spread to the retropharyngeal lymph nodes and nasopharynx. Computer tomography with high-dose intravenous contrast is the best radiographic modality for the evaluation of carcinoma of the base of the tongue.

Adult↗
PubMed1983

The effect of thrombin on platelet accumulation on the vessel wall - influence of heparin and aspirin.

Rabbit aortae were removed from exsanguinated rabbits, washed, everted on probes, treated with thrombin, washed to remove unbound thrombin and used to measure the accumulation of 51Cr-labeled platelets in vitro. Thrombin pretreatment of normal rabbit aortae did not cause platelet accumulation on the endothelium; platelets appeared to accumulate only at sites where the subendothelium had been exposed. The quantitative data obtained with 51Cr-labelled platelets was reinforced by observations by scanning electron microscopy. 125I-labelled thrombin became associated with the endothelium and also with de-endothelialized vessels, and some of it could be displaced by high concentrations of heparin. Exposure of vessels to heparin after thrombin treatment eliminated the enhanced platelet accumulation caused by the thrombin treatment, probably because heparin displaced thrombin from the aortae, as demonstrated in experiments with 125I-thrombin. Inhibition of PGI2 production by aspirin treatment of the vessels did not enhance platelet accumulation on normal or thrombin-treated aortae. Thus, although thrombin treatment of the endothelium does not cause platelets to adhere to it, thrombin does cause increased platelet accumulation on the areas where the subendothelium is exposed or where endothelial cells are damaged.

Animals↗
PubMed1983

Computed tomography of palatine tonsillar carcinoma.

Twenty-five patients with surgically and histologically proven squamous cell carcinoma of the palatine tonsil were studied with computed tomography (CT) using a high dose intravenous contrast enhancement technique. With this technique, CT demonstrated the primary carcinoma within the palatine fossa as well as its contiguous spread to the base of the tongue, mobile tongue, lateral pharyngeal wall, supraglottic larynx, and nasopharynx and metastasis to local deep cervical lymph nodes.

Adult↗
PubMed1983

Sequence of the amino-terminal part of enterotoxin from Clostridium perfringens type A: identification of points of trypsin activation.

The sequence of the first 66 amino acids of the amino-terminal part of the enterotoxin from Clostridium perfringens type A is presented. The trypsin activation of the enterotoxin involves hydrolysis of Lys15-Glu16 and Lys25-Thr26 bonds. The N-terminal sequence of the trypsin-activated enterotoxin has limited homology with the sequence of the N-terminal region of the cholera toxin B subunit.

Amino Acid Sequence↗
PubMed1983

Reversal of shortened platelet survival in rats by the antifibrinolytic agent, epsilon aminocaproic acid.

Platelet survival in rabbits and rats is shortened by placing indwelling catheters in the aorta; this shortening appears to be at least partly related to the extent of vessel wall injury and platelet interaction with the repeatedly damaged wall. Treatment of rabbit platelets with plasmin and other proteolytic enzymes in vitro shortens their survival when they are returned to the circulation. Because platelets may be exposed to plasmin and other proteolytic enzymes in rabbits and rats with indwelling aortic catheters, we examined the effect of epsilon-aminocaproic acid (EACA) on platelet survival in rats. At a dose of 1 g/kg every 4 h, EACA significantly reduced whole blood fibrinolytic activity and prolonged the shortened platelet survival in rats with indwelling aortic catheters. Mean platelet survival for untreated rats with indwelling aortic catheters was 38.6 +/- 1.9 h, and for rats treated with EACA, 53.8 +/- 3.8 h. Scanning electron microscopy showed that the injured vessel wall of these animals was mainly covered with platelets and fibrin, whereas in control animals that did not receive EACA, the injured surface was mainly covered with platelets and little fibrin was observed. Thus shortened platelet survival during continuous vessel wall injury may result from the local generation of plasmin or the release of proteolytic enzymes at sites where platelets (and possibly leukocytes) interact with the vessel wall.

Aminocaproates↗
PubMed1983

Basophil/mast cell precursors in human peripheral blood.

Semisolid (methylcellulose) hemopoietic cultures revealed the presence of histamine-containing granulocyte colonies derived from precursors (CFU-C) present in human peripheral blood. Light microscopy and histochemical studies of cells in individual histamine-containing colonies demonstrated homogeneous populations of metachromatic basophil/mast cells (BMC) at various stages of maturation. By inverted microscopy, pure BMC colonies were more often found to have the overall appearance of the previously described "eosinophil" (type II), rather than "neutrophil-macrophage" (type I), colony type. Histamine-positive colonies constituted 58% (50/86) of all (type I and type II) granulocyte colonies in repeated cultures from a patient with systemic mastocytosis (SM), and 19% (13/67) of colonies in cultures from 8 patients with chronic myeloid leukemia (CML); this was in contrast to 8% (12/153) of colonies in cultures from 4 patients with urticaria pigmentosa (UP) and 6 normal controls (p less than 0.0001). Calculated frequency of BMC CFU-C was approximately 1 per 2 X 10(6) in normal and 1 per 2 X 10(5) nucleated cells in SM peripheral blood. Taking colony size into account, histamine content per cell in histamine-positive type II colonies in SM cultures was 1.1 +/- 0.19 pg, compared to 0.29 +/- 0.08 pg in CML and less than or equal to 0.10 in normals and UP. Electron microscopy (EM) of individual colonies revealed electron-dense granules with ultrastructural features of BMC in histamine-positive, but not histamine-negative, colonies. Use of these methods may help to further clarify the nature of BMC precursors and the regulation of their proliferation in bone marrow disorders and allergic states.

Basophils↗
PubMed1983

Computer-tomographic appearance of branchial cleft and thyroglossal duct cysts of the neck.

The usefulness of computer tomography (CT) in the evaluation of a congenital neck mass has received little attention in the literature. We present the CT findings in two relatively common congenital neck masses - the thyroglossal duct cyst and the branchial cleft cyst. These cysts present a relatively common CT appearance of a mass with an enhancing capsule and a lucent center measuring between 20 and 35 Houndsfield Units. The branchial cleft cyst commonly occurs along the lateral border of the neck, anterior to the sternocleidomastoid muscle, while the thyroglossal duct cyst occurs along the midline of the neck. CT is excellent for determining the location, size, extent and character of these two common congenital neck masses.

Adolescent↗
PubMed1983

Early changes in venous arterial autografts: a scanning electron microscope study.

The use of autogenous vein as an arterial substitute has been advocated for many years. Methods of harvesting generally cause spasm of the vein and it has been shown that preventing the spasm by applying papaverine improves long-term patency. The present study was undertaken to see if the reported long-term patency of such grafts was associated with improved short-term appearance of the venous endothelium as viewed with the scanning electron microscope. Two groups of dogs were studied; those sacrificed at 3 hours and those at 24 hours after replacing excised segments of the carotid and femoral arteries with cephalic veins. One of the veins was removed in the standard manner allowing spasm followed by distension back to its pre-spasm state; in the other, spasm was prevented by the topical application of papaverine before removal. The study shows that venous endothelial integrity is preserved by the use of papaverine and this improved appearance of the endothelium persists for the first 24 hours after insertion into an arterial milieu. But the study also demonstrated that there was extensive activity of polymorphonuclear leukocytes associated with the endothelium in the early hours after arterialization and that they appeared to have a deleterious effect on the endothelium.

Animals↗
PubMed1982

Motivational management: coping with burnout.

Burnout, the emotional state that accompanies an overload of stress, generally has been ascribed to organizational or personal causes. Motivational management is an approach to identifying the causes of burnout among workers and determining ways to effectively intercede. The authors conducted workshops to help staff combat burnout at a public health agency, a small community hospital, and a preschool for handicapped children. During the first phase of the workshop participants generated a list of problems that contributed to their sense of burnout. They then assigned each problem a personal, organizational, or environmental cause. During the second phase participants decided who should accept responsibility for developing and executing strategies for change. The authors believe motivational management techniques can also be used to explore burnout in other roles such as those of parent, child, friend, or community member.

Adult↗
PubMed1982

Release of lymphotoxin by control and chemical carcinogen-treated lymphocyte cultures derived from black healthy subjects and cancer patients.

In an age-adjusted comparison with white men, black men have a significantly higher increase in esophageal and other types of cancer associated with environmental causes. The basis of this increase in cancer rates in blacks over the last two decades is unknown. Since cancer patients generally show an impairment in cell-mediated immune (CMI) functions, we measured certain CMI reactions in cultured lymphocytes derived from black healthy subjects and cancer patients. We also determined the levels of aryl hydrocarbon hydroxylase (AHH) induced in these lymphocytes. AHH catalyzes the activation of polycyclic aromatic hydrocarbons (PAH) to intermediates which might alter CMI functions.Lymphocytes from 33 black patients with squamous cell carcinoma and 22 healthy volunteers were mitogen-activated with phytohemagglutinin and concurrently treated with the environmental carcinogen, 3-methylcholanthrene (MCA). Measurements were made of the effects of MCA (0.5 to 3.0 μM on blastogenesis, T-cell growth, lymphotoxin (LT) release, and AHH induction in these lymphocyte cultures. MCA treatment depressed blastogenesis but had no depressive effect on T-cell growth in cultures. Blastogenesis and T-cell growth were mitogen dose-dependent, while LT release was independent of mitogen concentration. There was a significantly lower LT release by lymphocytes from lung cancer patients, compared to those from healthy and head/neck cancer subjects. The reduced levels of LT release in lung cancer patients might reflect an impairment in this CMI function. Studies on the role of lymphocyte subpopulations in CMI functions are in progress.

Adult↗
PubMed1982

Effect of dipyridamole and prostacyclin on rabbit platelet adherence in vitro and in vivo.

The adherence of 51Cr-labeled platelets to the subendothelium of rabbit aortas was inhibited in vitro and in vivo by high concentrations of dipyridamole (100 microM in vitro, 2.5 or 12.5 mg/kg in vivo). Dipyridamole (100 microM) inhibited release of 14C-serotonin from platelets that adhered to the subendothelium or to a collagen-coated glass surface; lower concentrations of dipyridamole had only a slight inhibitory effect. Scanning electron microscopy showed that many of the platelets that adhered to the subendothelium were rounded, with few pseudopodia. The combination of dipyridamole with PGI2 was no more inhibitory of platelet adherence than either agent alone; however, this combination of inhibitors exerted synergistic inhibitory effects on aggregation and release of 14C-serotonin from platelets aggregated by collagen. The effects of dipyridamole on platelet adherence are a consequence of the action of dipyridamole alone and do not appear to result from its interaction with PGI2 formed by injured vessels in vivo, since the inhibitory effect is not influenced by aspirin inhibition of PGI2 formation, either at the shear rates in the in vitro studies or under the shear conditions found in rabbit aortas in vivo.

Animals↗
PubMed1982

Thrombin generation and fibrin formation following injury to rabbit neointima. Studies of vessel wall reactivity and platelet survival.

Using platelets prelabeled with 51Cr, we have quantified the effect of injury to the neointima on platelet accumulation, thrombus formation at different times following injury, and the effect of injury to the neointima on platelet survival. Platelet accumulation on the neointima is largely determined by activation of coagulation and thrombus formation; this contrasts with platelet accumulation on the subendothelium where coagulation does not play a major role and where few thrombi form. Heparin treatment significantly inhibits platelet accumulation on the injured neointima but is without effect on platelet accumulation on the subendothelium. Like the subendothelium, the neointima rapidly becomes nonreactive to further platelet accumulation, and the platelets and platelet-fibrin thrombi are lost from the surface in the first few days after injury. Despite the formation of extensive platelet thrombi on the injured neointima, platelet survival is unaffected.

Animals↗
PubMed1982

Lipid accumulation in the neointima formed in normally fed rabbits in response to one or six removals of the aortic endothelium.

In previous experiments it was shown that repeated mechanical or immunologic injury to the arterial intima of normally fed rabbits induced lesions morphologically identical with human atherosclerosis. These regressed in size and lipid content when the injury stimulus was removed. By contrast, repeated injury directed to removal of only the endothelial layer induced lesions in which lipid accumulated in areas of endothelial regeneration and increased with time. In the present report the lesions associated with multiple and with a single episode of endothelial removal, using a Fogarty balloon catheter, are compared. Lipid accumulates in areas of endothelial regrowth following one endothelial injury and is similar in amount to that at comparable time intervals following the first of multiple balloon removals of the endothelium. There is much more lipid in areas of endothelial regrowth than in areas that remain uncovered by endothelium, the lipid tends to increase with time, and there is more lipid in the abdominal aortic than in the thoracic aortic lesions. A correlation was found between lipid content and thickness of lesions, especially in response to multiple removals of the endothelium. Multiple removals resulted in thicker lesions than a single injury. There appeared to be a positive relationship between the level of blood cholesterol and the amount of lipid deposited in areas of endothelial regrowth. This is consistent with trapping of low density lipoprotein by glycosaminoglycans in the neointima covered by regenerated endothelium.

Animals↗