No abstract

It has recently been demonstrated that both Tl+ and Li+ produce concentration- and time-dependent positive inotropic effects in guinea-pig atrial preparations although Tl+ inhibits and Li+ stimulates isolated Na+,K+-ATPase in vitro. In order to elucidate the mechanism of the positive inotropic actions of these cations, the effects of Tl+ and Li+ on sodium pump activity were studied. Active 86Rb uptake in guinea-pig ventricular slices, an estimate of sodium pump activity, was highly sensitive to the inhibitory effect of the cardiac glycosides. Preincubation of slices with Tl+ caused a dose- and time-dependent inhibition of active 86Rb uptake. Similar concentration- and time-dependent inhibition of active 86Rb uptake was observed when Na+ in a Krebs-Henseleit solution was partially replaced with Li+. Lithium, however, stimulated a partially purified Na+,K+-ATPase in vitro. During heart slice incubation, Tl+ and Li+ accumulated in a time-dependent manner. This accumulation was not readily reversible when slices were transferred into Tl+- or Li+-free solutions. It appears that the inhibition of sodium pump activity is related to the positive inotropic action of these cations.

No abstract

Fetal 'leaching' of maternal Cr has been suggested by scattered observations of elevated Cr levels in the term and unusually low Cr levels in the pre-term infant as well as by diminishing maternal Cr levels with increasing gestation and parity Available data suggest an inverse relation between Cr levels and glucose tolerance. This study represents an ongoing attempt to develop normative data on Cr in the perinatal period. AF Cr was measured in a graphite furnace (coeff. of var. 11%; recovery rate 95-105%) in 31 from 24 patients.