Aspects of the regulation of liver lipase

It is evident that factors that influence the activity of liver lipase could be important because of the role of liver lipase in HDL-cholesterol metabolism. At the start of this study not much was known about the regulation of liver lipase. The activity had been found to be decreased after fasting (10,34), during hypercortisolism {12), hypothyreoidism {35). insulin deficiency in diabetes {35,12) and by estrogen treatment {36) suggesting a role for respectively insulin~ corticosteroids, thyroxine and estrogens in the regulation of the activity of the enzyme, respectively. This thesis describes the effects of several hormones (corticosteroids, catecholamines, insulin, thyroxin) on the liver lipase activity in vivo and in vitro. In chapter II and appendix paper I the model used to study the regulation of liver lipase in vitro is shown in addition to several factors influencing the liver lipase activity in vitro. Aspects of the regulation of liver lipase in vivo are described in chapter III including the turnover of liver lipase and the influence of essential fatty acid (EFA) deficiency. In chapter IV factors influencing the enzyme activity are discussed by an integration of literature data with our own experiment

Equivalence of renormalized covariant and light-front perturbation theory: I. Longitudinal divergences in the Yukawa model

Light-front perturbation theory has been proposed as an alternative to covariant perturbation theory. Light-front perturbation theory is only acceptable if it produces invariant S-matrix elements. Doubts have been raised concerning the equivalence of light-front and covariant perturbation theory. One of the obstacles to a rigorous proof of equivalence is the occurrence of longitudinal divergences not present in covariant perturbation theory. We show in the case of the Yukawa model of fermions interacting with scalar bosons at the one-loop level how to deal with the longitudinal divergences. Invariant S-matrix elements are obtained using our method.Comment: 11 pages, epsf, revtex, contains more elaborate explanation of Forced Instantaneous Loops (FILs

Cross-ladder effects in Bethe-Salpeter and Light-Front equations

Bethe-Salpeter (BS) equation in Minkowski space for scalar particles is solved for a kernel given by a sum of ladder and cross-ladder exchanges. The solution of corresponding Light-Front (LF) equation, where we add the time-ordered stretched boxes, is also obtained. Cross-ladder contributions are found to be very large and attractive, whereas the influence of stretched boxes is negligible. Both approaches -- BS and LF -- give very close results.Comment: 11 pages, 7 figure