Gastroenteropankreatische Peptide, Streß- und flüssigkeitsregulierende Hormone bei LBNP-induziertem Orthostase-Streß

Purpose: Aim of the present study on one hand was to investigate and to evaluate different humeral systems in special consideration of the gastroenteropancreatic (GEP) peptide systems during isolated orthostatic stimulation and controlled hydration conditions. On the other hand, a potential effect of the test subjects hydration state on their orthostatic tolerance and on their incidence of nausea symptoms was investigated. Thereby, the occurrence of Motion Sickness-typical symptoms during high orthostatic stress and possible accompanied changes in the GEP-system were especially considered. The orthostatic stress was applied by using a lower body negative pressure (LBNP)-device. 2 standardized profiles of orthostatic stress were used which differed with respect to the sequences and intensities of negative pressure steps. Material / Methods: 18 healthy (10 males, 8 females) test subjects participated in the first standardized orthostatic stress profile down to the rather mild negative pressure step of -30 mmHg. After a time period of 2 months all of the male subjects (n = 10) additionally underwent a second tolerance orthostatic stress profile down to the negative pressure step of -80 mmHg. This profile, however, was discontinued in case that symptoms of orthostatic collapse occurred. Each of the LBNP experiments was performed twice with the respective male or female test subjects being once adapted to a rather “dehydrated” and once to a “well hydrated” hydration state. In a cross-over design, the sequence of “well hydrated” and “dehydrated” LBNP-experiments was randomly defined. By means of a standardized diet program, strongly controlled food and fluid intake during the experiment days, the test subjects were either adjusted to the “well hydrated” (approx. 200 mosm / kg H2O urine) or to the “dehydrated” (approx. 1000 mosm / kg H2O urine) hydration condition. The various GEP-peptides and other humoral parameters were taken from blood samples before, during and immediately after orthostatic stress and finally analyzed by specific radioimmunoassays. Results: As main physiological changes during LBNP an activation of the sympathico-adrenergic system and a reduction in vagal activity are observed. The latter suppression during orthostatic stress is, in particular, detectable by means of declining serum levels of the vagally influenced peptides PP, CCK and gastrin. Although the sympathetic system is progressively becoming dominant in the course of orthostatic stress – with distinct elevations in the serum levels of all stress homones – some vagally controlled GEP-petides may play an important role in the adaptation of the gastrointestinal system during the (pre)syncopal circulation conditions, too. These conditions are characterized by an inhibition of digestive processes and peristaltic movements, corresponding to a predominate gastrointestinal hypoactivity. Especially during and after the fainting period, as observed in the context of the tolerance LBNP-profile in the male test subjects, the different changes of several GEP-peptides demonstrate a complex system composed of regulatory and release patterns: Whereas the decrease of CCK is continued after fainting, the levels of PP and Gastrin synchronously turn and increase during the post-fainting period. At that time, Motilin and Somatostatin are released, which can be explained as a secondary reaction to the predominate gastrointestinal hypoactivity. In 75 % of all male test subjects symptoms of nausea occur during tolerance LBNP, but these symptoms are not paralleled by any additional significant changes in the serum levels of the GEP-peptides. Moreover, the various GEP-peptides are only negligibly influenced by temporarily restricted fluid supply, which in itself leads to any diminished nausea symptoms or reduced orthostatic tolerance. Discussion: Because of specific regulation of GEP-peptides during LBNP, it is supposed that the GEP-peptides may play an important role in the adaptation of the gastrointestinal system during orthostatic stress. The effect of a single GEP-peptide can be understood both as a mediator for other GEP-parameters and as a secondary indicator of neural activity without any further physiological effects. Moreover, the GEP-peptides directly influence tonus and peristaltic movements of the gastrointestinal system. However, in contrast to recent hypothesis, the usage of a GEP-peptide as a specific marker for discriminating between orthostatic stress and motion sickness has not been confirmed by the present study. Nevertheless, a definitive conclusion concerning the role of a specific GEP-peptide as an indicator of motion sickness can only be judged during environmental conditions which have more direct provocative attributes for motion sickness than orthostatic stress. Based on the LBNP-related data, the prophylactic restriction of fluid intake before launch seems to be rather ineffective as a countermeasure to prevent the astronauts and cosmonauts from the development of space motion sickness symptoms.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2001

Author dc:creator

• Brucker, Peter

Contributors dc:contributor

• Drummer, Christian

• info:eu-repo/classification/ddc/610
• Medizin

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-118952%22

OAI record oai:identifier

https://publications.rwth-aachen.de/oai2d?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai%3Apublications.rwth-aachen.de%3A56875