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PubMed1996

Mortyn Jones Memorial Lecture--1995. Calcium checks cyclic AMP--corticosteroid feedback in adenohypophysial corticotrophs.

This paper summarizes a particular aspect of the stress response-the negative feedback control of anterior pituitary adrenocorticotrophin secretion with special focus on the mechanism of action of protein(s) rapidly induced by glucocorticoids. The main thesis is that the principal intracellular mechanism underlying corticosteroid inhibition of corticotroph secretory function is the opposition of cAMP-mediated activation by calcium ions. An increase of intracellular cAMP levels in corticotrophs produces a rise in intracellular free Ca2+ known to be essential for triggering hormone secretion. In parallel, calcium regulates agonist-induced cAMP accumulation through inhibition of adenylyl cyclase and the stimulation of cAMP-degrading phosphodiesterase. Furthermore, a key action of cAMP is the inhibition of a slow, sustained potassium current which is activated by calcium ions. Collectively, the actions of calcium constitute a powerful intracellular feedback inhibition of cAMP-induced cellular activation. Analysis of corticosteroid action in mouse corticotroph tumour (AtT20) cells indicates that the essence of corticosteroid feedback inhibition is the amplification of intracellular calcium feedback. A common mediator of the inhibitory actions of calcium may be the calcium receptor protein calmodulin the de novo synthesis of which is rapidly stimulated by glucocorticoid hormones. Targets of glucocorticoid-induced calmodulin may include the protein phosphatase calcineurin, calmodulin-activated phosphodiesterase(s), and BK-type potassium channels. The net result of calcium feedback inhibition is a reduction of Ca2+ available for the facilitation of secretory activity i.e. calcium-induced desensitization. It is proposed that the intracellular calcium feedback loop outlined above also operates in the CNS components of negative corticosteroid feedback. A personal note: Professor Mortyn Jones introduced me to this field of research. His open-minded and critical approach to experimental work has always remained a guiding principle for my own efforts, and I hope that this paper which is dedicated to his memory will be found worthy of its purpose.

Adrenocorticotropic Hormone↗
PubMedDate not supplied

The Seventh Heymans Memorial Lecture Ghent, February 18, 1995. Physiological aspects of small arteries.

This review provides a brief overview of some of the structural and functional properties of small arteries, and of the factors which determine these. First, the evidence is reviewed concerning the importance of small arteries in the control of peripheral resistance. Then, receptor-mediated and myogenic excitation-contraction coupling mechanisms are discussed, in particular as regards the crucial role of membrane potential in these vessels. Finally, the characteristics of small arteries in hypertension are reviewed, with special attention to the structural abnormalities and their possible participation in the pathogenesis of the disease. The structural abnormalities of small arteries in hypertension are likely responsible for the reduced vascular reserve in this disease and consequent morbidity. It is suggested, however, that the small arteries are not in themselves determinants of blood pressure, rather they act as effector organs of the cardiovascular system. The further understanding of the physiology and pathophysiology of small arteries thus remains an important goal as regards the elucidation of the function of the cardiovascular system in health and disease.

Animals↗
PubMed1996

[Commemorative lecture of receiving Imamura Memorial Prize. Analysis of cellular immunity against tuberculosis in man with special reference to tuberculous pleurisy and cytokines].

Because of containing of numerous immunocompetent cells, tuberculous pleurisy is a good model for analysis of local cellular immunity. When lymphocytes in pleural effusion were cocultured with purified protein derivative (PPD), they reacted to PPD and produced far more interleukin 2 (IL-2) and interferon-gamma (IFN-gamma) than did peripheral blood lymphocytes. Analysis using monoclonal antibody and complement revealed that at least the OKT4+/OKT8- T-cell subset is responsible for the antigen-specific IFN-gamma production in pleural fluid T lymphocytes. Tuberculous pleural fluid itself had far higher levels of IL-2 and IFN-gamma than malignant pleural fluid. Therefore, it is indicated that activated T lymphocytes in tuberculous pleural fluid concern the production of lymphokines at the morbid site. Treatment with IFN-gamma resulted in an increased percentage of human alveolar macrophages ingesting BCG and an increased number of ingested BCG in individual alveolar macrophage in patient with pulmonary tuberculosis. The IFN-gamma treatment also showed increased killing activity of alveolar macrophages. Through these studies, IFN-gamma is an essential cytokine which activates human alveolar macrophages and induces antimycobacterial activity. In conclusion, we could elucidate from the study of tuberculous pleurisy that exudative sensitized pleural fluid T-lymphocytes play a major role in the defence of tuberculosis at the morbid site.

Humans↗
PubMed1996

Beyond DNA cross-linking: history and prospects of DNA-targeted cancer treatment--fifteenth Bruce F. Cain Memorial Award Lecture.

The origin of cancer chemotherapy can be traced to the wartime discovery of the lymphotoxic action of nitrogen mustards. These and other bifunctional agents were later found to produce various types of DNA cross-links, and some of these agents continue to be mainstays of current therapy. The cellular pharmacology of these drugs was studied extensively during the 1970s and 1980s by means of DNA filter elution methodology. In the course of these investigations, DNA topoisomerases were discovered to be targets of anthracyclines and several other classes of anticancer drugs. DNA cross-linkers and topoisomerase blockers have generally similar cytotoxic mechanisms, which depend on DNA damage detection, DNA repair, cell cycle arrest, and cell death by apoptosis. The molecular control of these processes, involving oncogenes and tumor suppressor genes, is being revealed by current research. Cancer cells often have defects within these control systems, and these defects may confer selective sensitivity to appropriately designed drug therapy. Panels of human tumor cell lines may serve to link the molecular defects with specific drug sensitivities. Such correlations could guide the selection of drugs for therapy based on molecular diagnosis of individual tumors.

Antineoplastic Agents↗

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