Pathophysiological states modify levels in rat plasma of factors which inhibit synthesis and enhance breakdown of PG

We have shown recently that adaptive changes in the apparent amount of enzymes which synthesize and inactivate prostaglandins (PGs) occur in a reciprocal manner (see accompanying paper and refs 2-4). For example, PG synthetase activity in several rat organs is reduced but that of PG-metabolizing enzymes ('prostaglandinases') is increased after treatment with anti-inflammatory steroids. In view of recent reports that the synthesis of PG-like substances may be influenced by plasma factors, we wondered whether our findings may be explained in whole or in part by the presence in varying amounts of substances which affect PG synthesis and inactivation in opposite directions. We show here that rat plasma contains a protein factor(s) which inhibits the synthesis of PGs and enhances their enzymatic breakdown in vitro and which we provisionally call prostaglandin 'reciprocal coupling factor' (RCF). Furthermore, RCF is rapidly released in response to anti-inflammatory steroids and its levels are altered in the two model pathophysiological states so far investigated.     

Selective population inversion in NMR

Population inversion of a selected region of a spectrum is a concept which has wide application in both NMR spectroscopy and imaging. While inversion of population at any one frequency is a trivial matter, ensuring an accurate inversion over a specified bandwidth, with negligible perturbation of the magnetization outside that bandwidth, is a major problem. However, by using as a driving function a complex radiofrequency (r.f.) pulse with an envelope of the form (sech beta t)1+5i where 1/beta is the temporal width and t is time, we have found that above a critical r.f. power threshold, magnetization is accurately inverted over a very sharply defined bandwidth, while outside that region, magnetization is returned to its initial position, and population is unaffected. Within the broad limits imposed by our equipment, we have also discovered that the phenomenon is independent of the incident r.f. power.