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Biomedical subjects

F Baumann

Publications and source records attributed to F Baumann.

At least 73 records · Page 4Linked to original sources
PubMed1968

Slow and spike potentials recorded from retinula cells of the honeybee drone in response to light.

Responses to light recorded by means of intracellular microelectrodes in isolated heads kept in oxygenated Ringer solution consist of a slow depolarization. Light adaptation increases the rates of depolarization and repolarization and decreases the amplitude of the response. Qualitatively these changes are similar to those observed in Limulus by Fuortes and Hodgkin. They are rapidly reversible during dark adaptation. In retinula cells of the drone eye a large single spike is recorded superimposed on the rising phase of the slow potential. The spike is a regenerative phenomenon; it can be triggered with electric current and is markedly reduced, sometimes abolished by tetrodotoxin. In rare cases cells were found which responded to light with a train of spikes. This behavior was only found under "unusual" experimental conditions; i.e., towards the end of a long experiment, during impalement, or at the beginning of responses to steps of strongly light-adapted preparations.

Adaptation, Physiological↗
PubMedDate not supplied

Gender difference in ifosfamide metabolism by human liver microsomes.

Pharmacokinetic gender-dependent differences in cytochrome P450-mediated drug metabolism, especially CYP3A4, and their clinical implications are increasingly apparent. CYP3A4 seems to be the most important CYP isoform in both bioactivation and N-dechloroethylation of the alkylating prodrug ifosfamide, but informations about possible gender-related differences are lacking. Therefore we compared in 10 male and 10 female liver microsomal preparations the contents and activities of specific isoenzymes, involved in both metabolic pathways, especially CYP3A4, further CYP2A6, CYP2C9 and CYP2B6 and measured the in vitro activities of these microsomes in the ifosfamide 4-hydroxylation and N-dechloroethylation using high-sensitive HPLC/MS and -UV detection methods. Statistically significant differences between male and female livers were found in the mean CYP3A4 contents and activities. These differences had no consequences on the ifosfamide 4-hydroxylation activities of liver microsomes in vitro. In contrast, in the ifosfamide N-dechloroethylation reaction we found a statistically significant difference between the liver microsomes of male and female patients (0.13 +/- 0.05 nmol/min nmol P450 vs. 0.28 +/- 0.13 nmol/min x nmolP450, respectively). In conclusion, we firstly demonstrated such gender-related difference in the ifosfamide N-dechloroethylation, which could result in a higher risk of partly severe neurotoxic side effects in female patients.

Adult↗
PubMedDate not supplied

Hypothalamic-pituitary-adrenal system function in patients with Alzheimer's disease.

The neuropathologic hallmarks of Alzheimer's disease (AD) are very prominent in the hippocampus, a brain site which is pivotal for the regulation of the hypothalamic-pituitary-adrenal (HPA) system. Thus, the combined dexamethasone-suppression/CRH-stimulation-test outcome in patients with AD was compared to that of healthy elderly controls to assess--with a more refined neuroendocrine challenge procedure--HPA function in AD. Cortisol secretion after dexamethasone (DEX) pretreatment and before CRH was increased in Alzheimer's patients and 21% of this group were DST-nonsuppressors. None of the healthy control subjects escaped DEX-induced suppression of cortisol. However, after additional CRH administration, AD patients released significantly less cortisol and ACTH than the control subjects. No correlations were found between any of the endocrine parameters and degree of severity of dementia. It is concluded that the DST part of the DEX/CRH test better reflects glucocorticoid feedback disturbances, probably at a suprapituitary level. The CRH part of the DEX/CRH-test outcome might indicate the loss of endogenous CRH-Arginine-Vasopressin (AVP) synergism of the HPA system of these patients.

Adrenocorticotropic Hormone↗