Magnetic resonance imaging (MRI) of retracted blood clots embedded in nonretracted clots was used to follow their lysis with urokinase in a plasma milieu in vitro. The two types of clots that were imaged in the same plane differed in signal intensity on T₂-weighted spin echo MR images throughout the 20-hour observation period. It was thus possible to delineate the contours of both clot types and measure their relative sizes by digital image processing. Lysis of retracted clots proceeded significantly slower than lysis of nonretracted clots. Our in vitro results suggest that MRI might prove useful in detecting thrombus retraction in vivo and in predicting the outcome of thrombolytic therapy.

The cholinesterases have been investigated in terms of the effects of methanol and ethanol on substrate and carbamate turnover, and on their phosphorylation. It was found: 1) that at low substrate concentrations the two alcohols inhibit all three tested cholinesterases and that the optimum activities are shifted towards higher substrate concentrations, but with a weak effect on horse butyrylcholinesterase; 2) that methanol slows down carbamoylation by eserine and does not influence decarbamoylation of vertebrate and insect acetylcholinesterase and 3) that ethanol decreases the rate of phosphorylation of vertebrate acetylcholinesterase by DFP. Our results are in line with the so-called 'approach-and-exit' hypothesis. By hindering the approach of substrate and the exit of products, methanol and ethanol decrease cholinesterase activity at low substrate concentrations and allow for the substrate inhibition only at higher substrate concentrations. Both effects appears to be a consequence of the lower ability of substrate to substitute alcohol rather than water. It also seems that during substrate turnover in the presence of alcohol the transacetylation is negligible.