Dilation of blood vessels in response to a large number of agents has been shown to be dependent on an intact vascular endothelium. The present studies examine some aspects of endothelium-dependent vasodilation in blood vessels of the rabbit and rat. Using the rabbit ear artery and the subtype-selective muscarinic antagonist pirenzepine, muscarinic receptors of the endothelium and smooth muscle cells were shown to be of the low affinity M₂ subtype. Inhibition of [³H](-)quinuclidinyl benzilate was used to determine affinity for the smooth muscle receptors while antagonism of methacholine induced vasodilation yielded the endothelial cell receptor affinity. The effect of increasing age (1-27 months) on endothelium-dependent relaxation was studied in aortic rings, perfused tail artery and perfused mesenteric bed of the Fisher 344 rat. Both aortic ring segments and perfused caudal arteries showed an age-related increase in sensitivity of endothelium-mediated relaxation to the cholinergic agonist methacholine. This increased sensitivity occurs between the ages of 6 and 12 months, with no further significant increase up to 27 months of age, suggesting this is a consequence of growth and development rather than old age. No difference with age in cholinergic relaxation was observed in the perfused mesenteric bed indicating either no change of sensitivity in smaller resistance vessels or an effect which is hidden in this more complex perfused system. In contrast to findings with cholinergic stimution, responses of the perfused caudal artery to the calcium ionophore A23187 were not altered with age. This suggests that the alteration with age in response to methacholine involves the muscarinic receptor or receptor coupling mechanism rather than the generation of, or response to, endothelium-derived relaxing factor (EDRF). The influence of endothelium on contractile responses was examined using the perfused caudal artery. Endothelium removal significantly increased contraction to the α-adrenergic agonists methoxamine and BH-T 920 as well as to transmural nerve stimulation. Inhibition of contraction to agents which must first cross the smooth muscle layer before reaching the endothelium suggests that a continuous or basal level of EDRF release is responsible for decreased contraction rather than an receptor stimulated release of EDRF.

To study the pulmonary responses to toxic insult, the biochemical and physiological effects of a known pulmonary toxicant (monocrotaline) were investigated. Monocrotaline is a pyrrolizidine alkaloid obtained from the seeds of Crotalaria spectabilis. When this alkaloid is administered to rats in their drinking water (20 mg/1) for 3 weeks, the lung is damaged, resulting in pulmonary hypertension, inhibition of serotonin transport by the pulmonary endothelium, and right heart hypertrophy. Preceeding the hypertrophy is a doubling of the mass of the lung and right ventricle. The change in mass of the lung preceeds that of the right ventricle. The increases in both organs is characterized by elevated RNA but not DNA. The lung mass increase is not accompanied by changes in collagenous proteins but is accompanied by an 86% increase in total lipids. The right ventricle however, responds to monocrotaline with a 400% increase in collagen protein and no change in lipid content, thereby indicating the lung and right ventricle respond differently to monocrotaline. Time course experiments established that the earliest observable event in monocrotaline induced lung damage is pulmonary edema which develops by day 5 and is resolved by day 10. Monocrotaline metabolites generated by an isolated liver and perfused through an isolated lung do not cause pulmonary edema even at concentrations of monocrotaline metabolites near 1 mM. These metabolites do however, alter the pulmonary endothelial transport of serotonin while other endothelial functions such as norepinephrine transport, angiotensin convertining enzyme and 5'-nucleotidase activities are unchanged. The effect of monocrotaline metabolites on pulmonary endothelial cell transport of serotonin is attenuated when the isolated livers are perfused under conditions which inhibit the formation of metabolites. Therefore, one of the pulmonary effects of monocrotaline that takes weeks to develop in vivo, inhibition of pulmonary endothelial transport of serotonin, can be observed under in vitro conditions. These results also directly demonstrate that the pulmonary damage caused by monocrotaline is a result of hepatic metabolism of monocrotaline to a pneumotoxic form.

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A thesis presented for the degree of Doctor of Philosophy in Medicine of the University of the Witwatersrand, Johannesburg 1972 / For centuries iron was regarded as a source of health and vigour, and it has been known for at least 200 years that it is a component of blood and effective in the treatment of chlorosis. However, its metabolism remained largely a mystery until the advent of radioactive iron isotopes in 1938. Since then most of the major pathways of this metal into, through and out of the body have been elucidated. In addition the functions which it subserves have been partially characterized. / IT2018

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Die In-vitro-Kultivierung von cornealem Endothel, einer funktionalen, beim Menschen nicht regenerierbaren Schicht in der Hornhaut des Auges, eröffnet weitreichende Möglichkeiten zum Zell- und Gewebeersatz. Dieser Artikel beschreibt aktuelle und künftige Optionen für zellbasierte Therapieansätze sowie die Bedeutung unbegrenzt proliferationsfähiger (immortalisierter) Zellpopulationen als Modellsystem für die Entwicklung neuartiger Methoden. In diesem Zusammenhang werden schaltbare Zellkulturträger als Möglichkeit zur schonenden Gewinnung transplantierbarer „cell sheets“ vorgestellt. Darüber hinaus wird die serumfreie Kultivierung als wichtige Voraussetzung für eine Anwendung am Menschen diskutiert. / The in vitro cultivation of corneal endothelium – a functional, non-regenerable layer of the human cornea – is a promising approach for cell and tissue replacement. This paper introduces options for cell-based therapies and points out the importance of immortalised cell populations as a model system to develop tissue engineering strategies. In particular, the use of stimuli-responsive cell culture carriers for the gentle harvesting of “cell sheets” is described. Furthermore, serum-free cultivation is discussed as a prerequisite for future applications.

EphB4, a known venous marker, represents a potential therapeutic target in modern vascular medicine. This study looked at the role of EphB4 as it pertains to basic cell functions in a mouse lung endothelium model (MLEC). Basic science techniques of microscopy, blotting and antibody labeling were used to evaluate and measure cellular response to EphB4 stimulation and manipulation. We found significant changes in MLEC cellular functions due to heterozygous knockout of the EphB4 receptor. These changes included decreased cellular migration and proliferation in knockout cells. We also saw increases in other cellular functions, such as tube formation and nitric oxide formation. From these data we were able to conclude that EphB4 is an active kinase in differentiated cells with a significant inhibitory effect. In EphB4 +/- knockout cell lines there was a lack of EphB4 inhibition and AKT and ERK showed increased activity. This work clearly implicates EphB4 as a major regulator of the basic cellular function of endothelia and highlights the need for further investigation into the specific pathways by which it functions.

Thesis (Ph. D.)--School of Biomedical Engineering, Georgia Institute of Technology, 2004. Directed by Hanjoong Jo. / Vita. Includes bibliographical references (leaves 104-124).