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The placental transfer of thallium cations in pregnant mice was investigated by determining the thallium concentrations in fetal and maternal tissue 0.5 to 24 h after application of thallium. The maternal dose of thallium was 8 mg/kg body weight throughout. Uterus and fetus were found not to differ from other organs like heart and liver in time course and magnitude of thallium uptake with an initial surge during the first few hours of exposure to thallium and a rapid decrease to steady 12 and 24 h values somewhat lower than those found in the kidney. Diaplacental transfer is therefore assumed comparatively rapid and a specific placental barrier for thallium does not seem to exist. For the determination of thallium concentrations Field Desorption Mass Spectrometry was utilized as a reliable, fast, and sensitive method for the analysis of metal cations in biological material. This method does not require extensive pretreatment of the tissue and total sample amounts in the range of milligrams and less are sufficient for quantitative analysis.

To conclude our investigation of thallium effects on cardiac tissues, we studied the slow inward current of sheep cardiac Purkinje fibres exposed to 10-7to 10-5 ᴍ Tl+for extended periods of up to 80 min. Our previous results had suggested a possible involvement of the slow inward current during thallium intoxication: a) the modification of contractility staircases observed during thallium exposure, b) action potential recordings of ventricular muscle, c) changes in spontaneous beating in sino-atrial preparations. The thallium levels chosen were between those yielding strong positive inotropic transients and those producing a marked long­term decay of contraction force.

Attention has recently focussed on the heavy metal thallium as an environmental contaminant of increasing importance. From accidental or suicidal ingestions of thallium it has been known for many years that cardiovascular disorders regularly emerge, and for this reason, a variety of investigations of cardiological interest have been conducted. Amongst these, the effects of thallium on the contractile force o f isolated myocardial tissues have been studied. Previous experiments were all carried out at concentrations far beyond those encountered during intoxication and yielded controversal data. We therefore reinvestigated the effects of thallium on myocardial tissue at levels between 10-8and 10-3 ᴍ, thus covering the range o f thallium concentrations encountered after uptake from a polluted environm ent through those seen after unintentional or intentional ingestion to levels at which previous studies were performed.