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Biomedical subjects

M Tennant

Publications and source records attributed to M Tennant.

At least 55 records · Page 3Linked to original sources
PubMed1996

Long-term structural alterations to endothelial cells in vein-to-artery grafts: a quantitative electron microscopic study.

The intracellular structure of endothelium lining vein-to-artery grafts in rats was analysed, using transmission electron microscopy and morphometry, to determine the ultrastructural adaptations of endothelial cells in this altered vascular environment. Autogenous 4-mm sections of iliolumbar veins were inserted microsurgically into the left common iliac arteries of 16 male Wistar rats. At 3, 6, 26 and 52 weeks the cytoplasmic-vesicular, mitochondrial and rough endoplasmic reticular contents of endothelial cells lining the grafts, the opposite iliac arteries and the remaining ilio-lumbar veins were analysed morphometrically. There was a significant increase in the amount of all these cytoplasmic structures in endothelial cells at 3, 6 and 26 weeks, at 52 weeks there was also a significant increase in the volumes of mitochondria and cytoplasmic vesicles, but not in rough endoplasmic reticulum. It was concluded that the ultrastructure of endothelial cells lining these grafts is changed chronically after graft insertion, and we propose that this may be attributable to altered haemodynamic stresses within the graft.

Animals↗
PubMed1996

Children's health camps in New Zealand: the making of a movement, 1919-1940.

The children's health camp movement in New Zealand was the product of early twentieth century concerns about national efficiency and racial strength. Inspired by open-air schools in Europe and the United States, the movement shows how overseas models were translated into a distinctive New Zealand institution, based on a national appeal for funds, and combining voluntary effort with solid government support. Although health camps had a strong socialization function, it was easier for doctors and laypersons to intervene in children's lives in the name of health, than under any other rubric. In the space of 20 years health camps changed from informal summer events held under canvas, into substantial institutions operating on a year-round basis. By 1940 their symbolic status was more important than any demonstrated achievement in improving child health.

Adolescent↗
PubMed1996

The effect on the insulin-like growth factor system in human prostate epithelial cells of immortalization and transformation by simian virus-40 T antigen.

The insulin-like growth factor (IGF) system has been demonstrated to be important for proliferation and differentiation in tissues. This system has also been demonstrated to be an important regulator of the growth of normal prostate epithelium and has been implicated in the process of transformation to human epithelial prostate cancer. This study examined the function of the various components of the IGF system in benign prostate epithelium (BPE), simian virus-40 (SV40)-T antigen-immortalized prostate epithelial cells, P69SV40-T (P69), and two sublines generated from the parental line by serial passage through athymic mice: one tumorigenic (M2182) and one metastatic (M12). IGF-II messenger ribonucleic acid (mRNA) and protein were detected in BPE cells, and each of the three P69 cell lines. IGF-II protein levels were significantly higher in medium collected from the P69, M2182, and M12 cells than in BPE. Proliferation in response to IGF was P69 > BPE > M2182 > M12. The proliferative responses in the four cell types were paralleled by an increase in c-jun. In addition, as the cells became progressively more tumorigenic, the basal level of c-jun mRNA increased. IGF-binding protein-2 (IGFBP-2), -3, -4, -5, and -6 could be detected in the primary epithelial cell medium; however, as the cells became progressively more tumorigenic, there was a decrease in IGFBP-2, -3, -5, and -6 in the medium. The type 1 IGF receptor (IGFr) also decreased as the cells became more tumorigenic. The M12 cells had 80% fewer receptors than the P69 cells and 70% fewer than M2182 cells. There was no change in the Kd for IGF between the cell lines. Based on these data it would appear that the difference in proliferation between the BPE cells and P69s may be due to an increased concentration of inhibitory IGFBPs in the P69 medium. The decrease in proliferation seen in response to IGF in M2182 and M12 cells compared to the P69s would appear at least in part to be due to a decreased IGFr number. IGFr mRNA is represented by 11.0- and 7.0-kilobase bands in the BPE and P69 cells, but only by an 11.0-kilobase band in M2182 and M12 cells. These data indicate that there are significant changes that occur in the IGF system during the process of malignant transformation of the prostate epithelium. The changes described in the P69 cell system are similar to those seen in vivo and suggest that an intact IGF system may be important in maintaining a differentiated epithelial cell.

Animals↗
PubMed1996

A morphometric technique for the histological quantification of skeletal muscle regeneration.

Variation in the regenerative capacity of damaged skeletal muscle between different strains of mice has been well documented but no precise quantitative method has been established to measure directly the phenotypic influences on muscle regeneration. We have developed such a method which allows clear distinction between the regenerative responses in Quackenbush and BALB/c mice. To quantitate regeneration, crushed tibialis anterior muscles taken from Quackenbush, BALB/c and F2 offspring 10 d postinjury were analysed morphometrically by light microscopy. Myotubes in the intermediate crush zone of transverse muscle sections were abundant in Quackenbush but sparse in BALB/c mice. In F2 offspring, regeneration responses reflected those of the parental strains, with no intermediate phenotypes. Statistical analyses indicated a high level of precision and accuracy in the determination of significant differences between regeneration in the different strains and in the F2 offspring. The data presented indicate that this method of quantification of skeletal muscle regeneration may be used for studies on the assessment of the genetic basis for phenotypic variation.

Animals↗
PubMed1993

Transient neovascularisation of the frog retina during optic nerve regeneration.

In conditions such as diabetic retinopathy, degenerative events in the retina are associated with neovascularisation. It is well established that a proportion of retinal ganglion cells die during optic nerve regeneration in the frog. The present study has determined whether neovascularisation takes place during this regenerative process. To do so, the pattern of blood vessels overlying the retinal ganglion cell layer was analysed in the frog Litoria (Hyla) moorei. We examined normal animals and those undergoing optic nerve regeneration following nerve crush. Blood vessels were visualised by perfusion with Indian ink and retinae were prepared as wholeamounts. In normal animals, the vascular tree was found to lie superficial to the nerve fibre layer and was more complex in regions overlying the area centralis and visual streak. After nerve crush, abnormal blood vessels transiently formed between the existing branches of the vascular tree. The new vessels were concentrated as an annulus centred on the optic nerve head and over the area centralis in midtemporal retina. The neovascularisation became most extensive between 6 and 10 weeks postcrush and disappeared by 12 weeks. The spatiotemporal sequence of neovascularisation suggests that it is triggered by accumulations of degenerating material formed as a proportion of the ganglion cells die during optic nerve regeneration.

Animals↗
PubMed1993

Novel microsurgical model of experimental vascular neointimal hyperplasia.

Neointimal hyperplasia is a common finding after trauma to blood vessels and also as a primary change in atherosclerosis. In this study we have developed a simple model, using microsurgical techniques, for the initiation of neointimal hyperplasia in the rat. In 24 Wistar rats, a 2 mm-diameter arteriotomy in the aorta was repaired with a "patch" of iliolumbar vein, using eight evenly spaced 10-0 Ethilon sutures. The patch overlapped the edges of the arteriotomy, and the sutures fastened the patch to the subjacent aorta. At 2, 6 and 12 weeks after surgery, the venous patch grafts and segments of the adjacent aortae of eight rats were removed. One-half of the specimens were analyzed by scanning electron microscopy and the other one-half by light microscopy. All patch grafts were surgically successful. Endothelial cells regenerated to cover the patch within 2 weeks of insertion. By 6 weeks after surgery, neointimal hyperplasia, consisting predominantly of smooth muscle, had developed in all patches to a thickness that was not significantly different from that of the adjacent aorta. These findings are consistent with data from other more complex experimental models of neointimal hyperplasia in the rat. We consider that this venous patch technique is a simple but effective model for the initiation of neointimal hyperplasia in the rat and may easily be used to study the experimental effects of various injurious or therapeutic agents on neointimal hyperplasia.

Animals↗
PubMed1993

Adaptive remodelling of smooth muscle in the neo-intima of vein-to-artery grafts in rats: a detailed morphometric analysis.

End-to-end autogenous vein-to-artery grafts in rats have been used extensively as a model for neointimal thickening (hyperplasia), which develops over the first 6 weeks after grafting. This study employed computerised morphometric techniques to analyse 16 grafts, in order to quantitate precisely how the neointima develops. Two important features were described that have not been identified previously, due to the extensive variation in neo-intimal thickness inherent in vein grafts. Firstly, the proximal region of the graft was significantly thicker than the distal region, up until 6 months after grafting. The smooth muscle cells in the graft may have developed more rapidly in the proximal region, due to the altered haemodynamics within the graft. Secondly, within the central region of the graft the characteristic focal nature of neo-intimal hyperplasia was evident throughout the period of the study, but by 6 months the neo-intima tended to be distributed more evenly. By 6 months remodelling of smooth muscle throughout the graft neo-intima had occurred, and the neo-intima had matured to a thickness equivalent to that of the intima plus media of the adjacent iliac artery.

Adaptation, Physiological↗
PubMed1993

Lipoprotein(a) and its role in occlusive vascular disease.

An increased serum level of lipoprotein(a) (LP(a)) is acknowledged as an independent risk factor for occlusive vascular disease, especially atherosclerosis. Recently, a considerable amount of data has been produced on the structure and functional relationships between Lp(a) and the primary cellular interactions of atherosclerosis. In this review we discuss the structure and function of Lp(a) with specific reference to its role in the proposed mechanisms of atherosclerosis.

Arteriosclerosis↗
PubMed1992

The role of cell proliferation and migration in the development of a neo-intimal layer in veins grafted into arteries, in rats.

The development of a thickened (hyperplastic) fibro-cellular neo-intima is a significant event in the adaptation of a vein grafted into an artery. The histogenesis of tissues in vein grafts was explored in a rat model where the source of endothelial and smooth muscle cells was from the adjacent artery. Cell proliferation was assessed by the incorporation of tritiated thymidine and autoradiography, up to 18 months after grafting. Cell migration was detected by prelabelling in the first 5 days after grafting and sampling at later times. The proliferation of cells in the arterial media adjacent to the graft was elevated above control levels as early as 2 days after grafting; it was maximal at 3 days and returned to low levels by day 21. During the first week, prelabelled smooth muscle cells in the tunica media of the adjacent artery migrated to the subendothelial space, where they continued to proliferate to produce arterial intimal hyperplasia. The migration of endothelial and smooth muscle cells proceeded across the anastomosis to populate the vein graft neo-intima, where smooth muscle cells continued to proliferate until 28 days after grafting. Cell migration and proliferation were significant factors in the histogenesis of vein graft neo-intimal hyperplasia in this model. These processes were controlled, perhaps by local regulatory factors, to form a vein graft, the wall of which was similar in thickness and structure to that of the host artery.

Animals↗
PubMed1992

A breakdown of the blood-brain barrier is associated with optic nerve regeneration in the frog.

We have examined the integrity of the blood-brain barrier during optic nerve regeneration in the frog Litoria (Hyla) moorei using rhodamine B-labeled bovine serum albumin (RBA). A transient localized breakdown of the blood-brain barrier was observed between 1 and 5 weeks after extracranial optic nerve crush. The zone of breakdown progressed along the experimental optic nerve, ascended the opposite optic tract, and swept rostro-caudally across the tectum contralateral to the crushed nerve. By 7 weeks, the blood-brain barrier was once again intact along the length of the optic pathway. In a concurrent series of frogs, regenerating optic axons were visualized by anterograde transport of horseradish peroxidase (HRP). At each stage examined, the region reached by the front of regenerating axons corresponded to that in which the blood-brain barrier had been shown to break down. In contrast to the results after nerve crush, the blood-brain barrier remained intact along the length of the optic pathway following optic nerve ligation to prevent regeneration. We conclude that the breakdown of the blood-brain barrier which occurs during optic nerve regeneration in the frog is triggered by the regenerating axons.

Animals↗
PubMed1992

A biological basis for re-stenosis after percutaneous transluminal angioplasty: possible underlying mechanisms.

Intravascular catheterization is a commonly used diagnostic tool and percutaneous transluminal angioplasty is used to dilate stenosed blood vessels. Although these techniques are very successful diagnostically and therapeutically they may precipitate a number of acute and chronic complications. Chronic intimal changes following balloon angioplasty can result in re-stenosis. Intimal hyperplasia can be a long-term complication of both diagnostic and interventional vascular catheterization. This article details these long-term structural changes, specifically relating experimental in vivo and in vitro changes to those seen clinically.

Angioplasty, Balloon↗
PubMed1992

Vein to artery grafts: a morphological and histochemical study of the histogenesis of intimal hyperplasia.

Failure of vein to artery grafts has been associated with intimal thickening (hyperplasia) and atherosclerosis. Current theories of intimal development, derived from arterial studies, show that smooth muscle cells migrate from the media to the intima after endothelial damage, where they proliferate and produce intimal hyperplasia. However, little is known of the histogenesis of these lesions in vein grafts. Experimental ilio-lumbar vein to iliac artery autografts were placed in 52 rats and analysed by light microscopy and histochemistry from 2 to 140 days after surgery. On day 2 the grafts and adjacent artery were severely damaged. Regeneration of damaged arterial tissue occurred by day 5, and thickening was already evident in the arterial intima. The intimal cells had histochemical characteristics of smooth muscle. By day 15, this hyperplastic intima was continuous across the anastomosis from the artery into the graft. After day 28 a wedge of densely packed cells was present in the vein graft intima for approximately 2 mm into the graft. By day 140, all the grafts were fully re-endothelialized. Intimal hyperplasia was present in all grafts and varied in thickness from 3 to 20 cells. Histochemical staining of these cells showed them to be of smooth muscle origin.

Anastomosis, Surgical↗
PubMed1991

Platelet-derived growth factor and its role in atherogenesis: a brief review.

A number of locally acting growth factors are now widely understood to be important in the regulation of cellular activity. Platelet-derived growth factor (PDGF) is one of the best known and is an important mitogenic stimulant of vascular tissues. PDGF is stored primarily by platelets but other cells, including endothelium and smooth muscle, can act as sources. The mitogenic properties of PDGF may be influential in the pathogenesis of atherosclerosis. PDGF has access to the vascular intima and may act upon smooth muscle cells to produce proliferation, a primary feature of atherosclerosis. In this brief review we examine the structure, function and influences of PDGF with special emphasis on its potential role in the pathogenesis of atherosclerosis.

Animals↗
PubMed1991

A computerised morphometric technique for the analysis of intimal hyperplasia.

The aim of this study was to design, develop and employ a method for the acquisition of a significant data base of thickness measurements. The integration of standard histological techniques (step serial sectioning), modern computer technology and a personally developed software package (specifically designed for thickness measurement) produced a novel technique suitable for the task. The technique allowed the elucidation of a larger data set from tissue samples. Thus a detailed and accurate quantitative assessment of general and focal changes in intimal hyperplasia could be produced. A technique for the 3-dimensional reconstruction of the intimal thickness data was also developed. The new technique was tested on 4 autogenous vein grafts (2 months after insertion) and revealed a significant decrease in intimal thickness from proximal to distal levels.

Animals↗
PubMed1990

Blood vessel structure and function: a brief update on recent advances.

This article briefly reviews recent advances in knowledge of the histology and function of blood vessels. It focuses upon the multifunctional roles of endothelium and smooth muscle cells. Particular reference is made to the synthesis of a number of factors now known to be involved in maintenance of the integrity of the vessel wall and the initiation of arterial disease. The cells of the vascular wall are much more versatile and dynamic than previously thought.

Arteriosclerosis↗
PubMed1990

Persisting hallucinations following childhood sexual abuse.

Hallucinations can persist for many years after childhood sexual abuse. If we recognise this, we will not mis-diagnose psychosis and we may treat with psychotherapy (talk). The hallucinations are distinct from hallucinations in schizophrenia though patients have frequently been given that diagnosis. They would generally be classified as pseudo-hallucinations. They are generally self-referential. They can involve all sensory modalities. Three case reports illustrate this link. Methods for interviewing and providing ongoing help are discussed. Issues in phenomenology and diagnosis are considered. Post-traumatic stress disorder is the best diagnostic fit, though psychotic depression may explain some cases. Freud's case of Frau P (1896) was an early report of this link.

Adolescent↗
PubMed1990

Histogenesis of arterial intimal hyperplasia and atherosclerosis.

This article briefly reviews the histological evidence for the genesis of intimal hyperplasia and atherosclerosis in arteries. It concentrates upon the origin, structure and behaviour of vascular smooth muscle cells in the intimal (subendothelial) layer. The interactions between these intimal muscle cells, the endothelium and the blood are discussed with particular reference to their role in the histogenesis of intimal hyperplasia and atherosclerosis.

Arteries↗