Federation proceedings最新文献

The distribution of pressures within the arcading microvessels in numerous tissues is described and evaluated relative to potential sites for the control of blood flow and/or pressure. In various tissues a large fraction of the total systemic pressure is dissipated by small arteries and/or large arterioles and by small arterioles, the classical high-resistance vessels. Thus, these sites must be linked to the regulation and distribution of blood flow and pressure within the network as evidenced by the shifts in the profiles of pressures in these vessels after vasoactive stimuli. In fact, there may be some coupling of vasoactivity between these areas of vascular resistance. The vasodilator activity may predominate in small arterioles whereas the neural control may be directed to the small arteries and large arterioles. Thus, physiological, pharmacological, and pathological influences may affect the control of blood flow and/or pressure at one or both of these sites.

Recent studies of the visceral sensory system, using both electrophysiological and neuroanatomical methods, indicate that there is representation of multiple visceral modalities at all levels of the central nervous system. In the nucleus of the solitary tract gustatory afferents are represented rostrally, and general visceral afferents caudally. At the pontine relay, the parabrachial nucleus, the gustatory afferents are represented medially, and the general visceral afferents laterally. Although the evidence for anatomical separation of visceral projections is incomplete for the hypothalamus and amygdala, the visceral sensory thalamus and cortex are viscerotopically organized. The results indicate that the ascending visceral sensory system is viscerotopically organized at all levels of the brain, and that this information is important for the integration of autonomic responses at all levels of the neuroaxis.

The observation has previously been made that receptor-bearing cells in culture compete with each other for their ligand. As a result, at a fixed concentration of ligand, the fractional occupancy of the receptor will tend to fall as the number of cells is increased. We have demonstrated that T cells in culture also compete for their ligand, the combination of foreign antigen and the Ia molecule (antigen-Ia), and that this manifests itself as shifts in the antigen dose-response curves as the number of responding T cells is increased. Because of the complexity of T cell activation, modifications to the antigen that affected its stimulatory capacity (i.e., its potency) could come about by altering its interaction with either the T cell receptor or the Ia molecule. We could distinguish between these two possibilities by studying the extent to which the antigen dose-response curves shifted as the T cell number was increased. Amino acid substitutions in the antigen that affected the interaction with the T cell receptor caused changes in the dose-response curve shifts, whereas substitutions that decreased potency by other means did not cause such changes. Finally, two allelic forms of the Ia molecule that differed only slightly in their amino-terminal domain were used to present a single antigen to a T cell clone. Despite a difference in antigenic potency in the presence of these two Ia molecules, no difference was demonstrated in the avidity of the T cell receptor for either antigen-Ia combination. These results suggest that the antigen and the Ia molecule make physical contact during the process of antigen recognition, and that the potency of an antigen can vary as a result of its interaction with either the T cell receptor or the Ia molecule.

Thromboxane A2 (TxA2) appears to be an important mediator of ischemia and hypoxia. Despite its short half-life and the fact that it may not circulate in the blood until its values become quite high, TxA2 contributes to the pathogenesis of cardiopulmonary diseases (e.g., sudden death, myocardial ischemia, circulatory shock). It does so because it propagates its own formation by activating platelets and constricting blood vessels, thus activating more TxA2 and trapping it locally within an ischemic or hypoxic region. TxA2 concentrations in the extracellular fluid of lymph of ischemic regions may be much higher than that occurring in nonischemic, normally perfused regions. Specific and potent Tx receptor antagonists (TxRA) have recently become available for study. The TxRA are useful tools in the study of the pathophysiology of Tx-dependent disease processes and have been found to be effective in a variety of ischemic disorders including circulatory shock, myocardial ischemia, and sudden cardiopulmonary death. Moreover, inasmuch as early work indicates that these agents are both safe and effective in humans, Tx receptor antagonists may be employed as therapeutic agents in several cardiovascular disease states. Further investigation is necessary to clarify the role of TxRA as therapeutic agents.

There is accumulating evidence that opioid systems are involved in the regulation of fundamental behavioral and physiological processes in invertebrates. Feeding is a basic physiological function that is essential for maintaining homeostasis. Results of studies examining the feeding responses of molluscs and arthropods treated with various opiate agonists and antagonists indicate that delta, kappa, mu, and possibly sigma opioid systems differentially and selectively mediate the components of their natural feeding behavior. Moreover, it appears that at an early evolutionary stage the mu and kappa systems have developed to selectively affect the components of feeding behavior associated with the acquisition and ingestion of food. In addition, evidence suggests that neuropeptides that have been proposed as possible endogenous antagonists of opioid-mediated feeding in mammals may also be involved in the control of feeding in invertebrates. This indicates that there may be an interplay of opioid agonists and antagonists in the regulation of feeding and satiation in invertebrates analogous to that proposed for vertebrates. Moreover, these findings indicate that opioid influences on feeding have been conserved through evolution.

Prostaglandins (PGs) are potent vasoactive substances that may participate in the control of coronary blood flow, platelet aggregation, and inflammation. An important action of PGs may be the stimulation of c fibers in general and vagal cardiac c fibers in particular. The Bezold-Jarisch reflex after intracoronary injection of Veratrum alkaloids is very similar to the vagal bradycardia elicited by stimulation of cardiac PG synthesis or injection of prostacyclin (PGI2). The characteristic features of this reflex are 1) stimulation of c fibers, 2) inferoposterior wall location of receptors, 3) vagal afferents, 4) vagal efferents to the heart, 5) sympathetic efferents to peripheral blood vessels, and 6) interaction with other reflexes. Vagal cardiac c fibers are activated by intracoronary injections of PGI2 or arachidonic acid, resulting in a vagal reflex bradycardia and hypotension due to withdrawal of peripheral alpha-adrenergic tone to resistance vessels. The cardiac receptors are located predominantly in the inferoposterior wall of the left ventricle. When stimulated by PGs, cardiac receptors may also modify the regulation of arterial pressure by the baroreflexes, altering the inverse relationship between systemic arterial pressure and heart rate. Thus, there is a striking parallelism between the veratridine-induced Bezold-Jarisch reflex and PG-induced cardiac reflexes, although the physiological and clinical significance of these reflexes remains to be determined.

Peptides released from peripheral nerve endings in mammals, including the tachykinin substance P (SP) and vasoactive intestinal polypeptide (VIP), are potent mediators of smooth muscle and vascular functions. Significant neurophysiological activities of SP and VIP include the transmission of nociceptive and interneuron excitatory signals, respectively. SP has been shown to modulate distinct immediate hypersensitivity responses by stimulating the generation of arachidonic acid-derived mediators from mucosal mast cells but not basophils. Functions of mononuclear and polymorphonuclear leukocytes that characterize the inflammatory response and that are altered by SP include chemotaxis, lysosomal enzyme release, and phagocytic activities. The effects of SP on cell-mediated immunity are largely stimulatory, in that synthesis of DNA, protein, and immunoglobulin by mature T and B lymphocytes, respectively, is significantly enhanced at nanomolar concentrations of the neuropeptide. Functionally relevant receptors for SP on T lymphocytes have been demonstrated by cell sorter and radioligand-binding techniques, and the lymphocyte membrane proteins that comprise the SP receptor are currently being isolated and purified to homogeneity. The characterization of the structure of the SP lymphocyte receptor and identification of the receptor gene will permit detailed analyses of the molecular interactions between the immune and nervous systems.