SummaryIn serum incubated at 36° C for 18-24 hours a factor (DAS) develops which on intravenous injection into cats evokes platelet aggregation followed by an increase in pulmonary vascular resistance (PVR). This change in PVR is mediated via the platelets since it significantly correlates with the preinjection platelet count. There is evidence that phosphatidic acids (PA) and lysophosphatidic acids (LPA) are the active components of DAS. Investigations performed on platelet-rich plasma from man, cat, pig, dog, rabbit, guinea pig, and rat demonstrate that only human and feline platelets exposed to PA or to LPA are aggregated. Feline platelets are more sensitive to either compound than are the platelets from men; however, human platelets exhibit two exceptional properties, a) the sensitivity rapidly declines with time, b) pretreatment with subthreshold concentrations of LPA or PA induces a specific tachyphylaxis.

Dedicated to Professor Max Schmidt on the occasion of his 65th birthdayMagnesium and other alkaline-earth and alkali metals play an important role in the biochemistry of virtually all living organisms. In contrast to "trace elements", these "common metals" are distributed in most cells and tissues, often in considerable concentrations, and a constant supply is indispensable for unrestricted performance of biological functions. In contemporary medicine, various forms of magnesium therapy are recommended in order to compensate for magnesium deficiency due to certain dysfunctions as well as to loss from excessive transpiration. In addition, there are numerous indications for prophylaxis. Magnesium is usually administered orally in the form of "complexes" with "natural" anions derived from L-aspartic, L-glutamic, L-pyroglutamic (pidolic), citric, and orotic acid. Analytical, electrochemical, and spectroscopic investigations of aqueous solutions of these pharmaceuticals, together with X-ray diffraction studies of crystalline samples, have given a detailed knowledge of these coordination compounds. Only certain combinations can be addressed as magnesium complexes, whereas others are only present as aquo complexes both in aqueous solutions and in the solid state. Thus, a delicate balance of metal complexation and hydrogen bonding exists for the components of the drugs, which is relevant for the metal carrier functions of the organic ligands. Compared with the more flexible stereochemistry of Ca, Sr, Ba, Mn", Zn, Li, Na, and K complexes, which have coordination numbers between 4 and 9, octahedral hexacoordination is found exclusively for magnesium, the most stereoselective of these metals.

Copper (Cu) is an essential trace element with many physiological functions. Homeostatic mechanisms exist to allow Cu to act as a cofactor in enzymatic processes and to prevent accumulation of Cu to toxic levels. The aim of this commentary is to better understand the role of dietary Cu supply in deficiency and under physiological and pathological conditions. The essentiality of Cu can be attributed to its role as a cofactor in a number of enzymes that are involved in the defence against oxidative stress. Cu, however, has a second face, that of a toxic compound as it is observed with accumulating evidence in hepatic, neurodegenerative and cardiovascular diseases. The destructive potential of Cu can be attributed to inherent physico-chemical properties.The main property is its ability to take part in Fenton-like reactions in which the highly reactive and extremely deleterious hydroxyl radical is formed. Diseases caused by dietary Cu overload could be based on a genetic predisposition. Thus, an assessment of risk-groups, such as infants with impaired mechanisms of Cu homeostasis regarding detoxification, is of special interest, as their Cu intake with resuspended formula milk may be very high. This implies the need for reliable diagnostic markers to determine the Cu status. These topics were introduced at the workshop by the participants followed by extensive group discussion. The consensus statements were agreed on by all members. One of the conclusions is that a re-assessment of published data is necessary and future research is required.