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Biomedical subjects

D A Cameron

Publications and source records attributed to D A Cameron.

At least 91 records · Page 5Linked to original sources
PubMed1982

Reflex mechanisms responsible for early spontaneous termination of paroxysmal supraventricular tachycardia.

The incidence and possible mechanism of early spontaneous termination of paroxysmal supraventricular tachycardia was studied in 20 consecutive patients. Episodes of induced tachycardia that terminated spontaneously within the 1st minute after initiation were included. Tachycardias ending spontaneously were associated with a reproducible course of hypotension at the onset followed by blood pressure recovery above control levels and termination. Spontaneous termination of tachycardias occurred within the A-V node 18 to 45 seconds (mean +/- standard error of the mean 27.9 +/- 5.3) after their onset. In the supine position (0 degrees) 9 (45 percent) of 20 patients showed spontaneous termination in 36 (16 percent) of 219 episodes of tachycardia. In the head-dependent position (-20 degrees) only 1 (8 percent) of 13 patients manifested spontaneous termination in 2 (4 percent) of 54 episodes. In the head up position (+60 degrees) only 1 (6 percent) of 18 patients exhibited termination in 2 (2 percent) of 102 episodes. After partial cholinergic blockade with intravenous hyoscine butylbromide, 20 mg, or atropine, 0.6 mg, none of five patients showed spontaneous termination in 25 episodes. After beta adrenergic blockade with 10 mg of propranolol intravenously, none of 16 patients showed spontaneous termination in 87 episodes of tachycardia. We conclude that the initial hypotension during tachycardia evokes a sympathetic response that increases blood pressure and this increase in turn causes a rise in vagal tone that breaks the tachycardia.

Adrenergic beta-Antagonists↗
PubMed1982

Collagenolytic activity by malignant tumours.

Five carcinomas and 5 sarcomas were investigated in relation to their production of neutral proteases capable of digesting polymeric collagen. The carcinomas were far more active than the sarcomas but all the malignant tumours produced enzymes which were capable of causing collagenolysis in vitro. collagenolytic enzymes were recovered from extracts of neoplastic cells from long-term culture, from the media in which these cells were cultured, from the media of mixed cell cultures (neoplastic, stromal and inflammatory cells from minced tumours), and from normal fibroblasts cultures. In contrast to the cultures of non-neoplastic fibroblasts, the tumour cells produced active enzymes, since limited proteolysis with trypsin or treatment with p-aminophenyl-mercuric acetate (APMA) caused no increase in enzyme activity. These tumours possess collagenolytic ability in vitro which may be partly responsible for their invasive nature in vivo.

Animals↗
PubMed1981

Peripheral nerve contains heterogeneous growth factors that support sensory neurons in vitro.

The availability of dissociated cultures of embryonic neurons has given impetus to a number of studies which have detected trophic factors in many mammalian and avian tissues maintained in vivo and in vitro [1, 2, 4-8, 10, 11, 13, 16, 18-21]. Using a single sensory neuron biological assay for mouse nerve growth factor (NGF) [17] as a reference standard, we report here that neurite promoting activity is highly enriched in segments of adult mouse peripheral nerve. Neurite outgrowth at 30 h, kinetics of neurite appearance and inhibition with rabbit antiserum to mouse NGF indicate that the trophic activities are heterogeneous and support both NGF-dependent and NGF-independent neuron populations of chick embryo sensory ganglia.

Animals↗
PubMed1981

Neurite growth promoting factors of embryonic chick--ontogeny, regional distribution, and characteristics.

A single neuronal cell biological assay for NGF has been used to quantitate factors in soluble extract of chick embryo that promote neurite outgrowth. The neurite growth promoting activity is detected as early as day 1.5 of embryonic life. Specific activity increases to maximum over the first four days and then decreases from day 5 to 6 during a growth spurt of the embryo. The tissue distribution of neurite growth promoting activity at eight embryonic days shows higher specific activity in peripheral structures that are richly innervated. Extract from all embryonic stages and from all tissues studied induces neurite outgrowth that is inhibited only partially by antibody to mouse NGF. Furthermore, the kinetics of neurite outgrowth and the neuronal populations responsive to extract differ from that of NGF. These observations indicate heterogeneity of the neurite growth promoting factors in soluble extracts of embryonic chick and demonstrate the presence of these factors before the responsive neurons leave the cell cycle and begin their differentiation processes.

Aging↗
PubMed1981

Continuous on-line beat-to-beat analysis of AV conduction time.

A simple analog circuit is described which is capable of measuring on a beat-to-beat basis P-R, R-P, P-P, and R-R intervals during sinus rhythm and paroxysmal supraventricular tachycardia. In addition the circuit will emit a pulse when the consecutively alternating P and R wave sequence is interrupted thereby signalling a trigger problem or a change in rhythm. The operation of the device requires proper P and R wave sensing and provides outputs which are linear over a range of rates which are applicable to the human heart.

Atrioventricular Node↗
PubMed1980

Vagal techniques for termination of paroxysmal supraventricular tachycardia.

Maneuvers that reflexly increase vagal tone were deployed to terminate the tachycardia in 68 consecutive patients with paroxysmal supraventricular tachycardia. The order and success rate of the protocol was as follows: 57 episodes were terminated with carotid sinus pressure alone or after pretreatment with edrophonium, 5 were terminated with the Valsalva maneuvers and 6 were terminated with phenylephrine. Potency testing showed that phenylephrine evoked the greatest increase in vagal tone. All cases demonstrated slowing of tachycardia ranging from 40 to 220 ms +/- standard error of the mean (mean 79.0 +/- 3.8 ms) followed by abrupt termination. Pauses after termination ranged from 900 to 3,300 ms (mean 1,683.8 +/- 66.6) with 54 patients showing pauses of 2,000 ms or less. Termination was highly reproducible showing an overall success of 148 (92 percent) of 160 trials among 22 selected cases. The extent of increased vagal tone needed to terminate paroxysmal supraventricular tachycardia was raised by augmented sympathetic tone (infusion of isoproterenol) and decreased by reduced sympathetic tone (pretreatment with propranolol). Thus, paroxysmal supraventricular tachycardia can be rapidly, safety and consistently terminated by maneuvers that reflexly increase vagal tone.

Adolescent↗
PubMed1979

Uptake of liposome-entrapped mannitol by diaphragm.

Tissue uptake of liposome-entrapped radioactive mannitol was examined in rats and mice after both intravenous and intraperitoneal injection. In accord with results from other laboratories, liver and spleen effectively accumulated liposomes. Diaphragm also took up significant amounts of label. In nearly all cases the radioactive content of perfused tissues was less than tissues which were not perfused but this was statistically significant in only a few comparisons.

Animals↗
PubMed1977

Enhanced osteosarcoma growth produced in rats by osteosarcoma allografts.

Transplanted syngeneic osteosarcomas (induced by 32P in DA rats) grew significantly larger in DA rats receiving a simultaneous transplant of allogeneic osteosarcoma than in rats receiving syngeneic tumour only (P less than 0-01). Two other malignant allogeneic tumours, and allogeneic spleen cells, did not alter the growth of the transplanted syngeneic osteosarcomas. When the allogeneic osteosarcoma was given 7 days before the syngeneic tumour, the reverse effect (retardation) occurred. When given 7 days after the syngeneic tumour cells, the effect on both syngeneic and allogeneic tumour growth was variable. Some possible reasons for these findings are discussed, and the argument is presented that immunological phenonema are involved in the reaction.

Animals↗
PubMed1976

Influence of exogenous tRNA on growth of transplantable 32P-induced osteosarcomata.

The weights of osteosarcomata that arose 22 days after the s.c. injection of cell suspensions (of whold tumours) that had been exposed in vitro to tRNA were significantly different from the weights of those arising from untreated cells. The tRNA was isolated by phenol extraction and DEAE-cellulose chromatography from eviscerated full-term rat embryos, from rat mesenchymal (granulation) tissue and from rat anaplastic osteosarcomata. Tumours developing from osteosarcoma cells treated with either embryonic or normal mesenchymal tRNA were reduced in weight by 76% and 60% respectively. These effects could not be explained as a toxic consequence, because tumour weight was increased by 128% after exposure of cells to osteosarcoma tRNA. In this osteosarcoma model it appears that tumour weights can be influenced in different ways by tRNA from different sources.

Animals↗
PubMed1967

Changes in the fine structure of bone cells after the administration of parathyroid extract.

This paper describes the effect of parathyroid extract on the fine structure of bone cells in the proximal metaphysis of the tibia. The extract was given to rats intraperitoneally, in single or repeated doses of 1-14 units (USP) per gram body weight, over short or extended periods, and the tissue was examined between 6 and 26 hr after the commencement of injection. During this period, osteoblasts showed the greatest changes. Their mitochondria became swollen and contained dense granules; both rough- and smooth-surfaced vesicles were distended; ribosomes were separated from the membranes; and various dense bodies appeared in the cytoplasm. Osteocytes were similarly but less affected, and osteoclasts differed little from those in normal animals. Eventually after repeated injections, the fine structure of many of the cells was disrupted. These changes were accompanied by erosion of the bony trabeculae without any great increase in numbers of osteoclasts. It is possible that the alterations in fine structure were the result of damage to the cells by the parathyroid extract. However, since the extract did not seem to stimulate classical osteoclastic activity, the mitochondrial swelling and dense bodies could have been related to the removal of mineral and matrix, respectively.

Animals↗
PubMedDate not supplied

The cone photoreceptor mosaic of the green sunfish, Lepomis cyanellus.

Recent empirical and theoretical evidence has implicated the geometrical birefringence of the double cones of the green sunfish (Lepomis cyanellus) as the biophysical basis of this vertebrate's sensitivity to polarized light. Because of the intimate link between the organization of the cone-photoreceptor mosaic and the psychophysical details of polarization sensitivity, we have examined the structural features of the green sunfish cone-photoreceptor mosaic, in particular the orientation of the elliptical cross sections of the double cones. Our primary observations are that (1) the arrangement of the cone-photoreceptor mosaic is constant across the retina (with two regional exceptions), with double cones arranged in a rhombic mosaic and aligned roughly +/- 45 deg to the nearest retinal margin; (2) the double-cone/single-cone ratio is everywhere the same; (3) cone density is inhomogeneous across the retina, with the highest densities in the temporal hemiretina. These results are discussed as they relate to the animal's retinal growth and visual mechanisms, particularly the sensitivity to polarized light.

Animals↗
PubMedDate not supplied

Asymmetric retinal growth in the adult teleost green sunfish (Lepomis cyanellus).

Previous studies on fish retina have suggested that a curved, non-fused embryonic fissure is associated with, and perhaps caused by, asymmetric growth along the retina's marginal germinal zone (where neurons and Müller glia are added appositionally throughout life). In this report retinal growth was measured directly in adult green sunfish (Lepomis cyanellus), which has a curved, non-fused embryonic fissure. Growth was asymmetric in both small and large fish: ventral and nasal retina grew more than temporal and dorsal retina. This asymmetry was due to different net rates of cellular addition, rather than differential passive expansion. The absolute rates of retinal growth in the centroperipheral direction were roughly exponential functions of fish size--smaller fish grow faster than large fish--but the area of new retina added per unit time did not vary with fish size. Visual implications of asymmetric retinal growth are evaluated.

Animals↗