|dc.contributor.author||O' Brien, John Anthony||en
|dc.description.abstract||The kinetics of the permeation of cardiac muscle cells by
glucose and the effect of insulin on this process were examined
in the isolated perfused rat heart. Previous attempts to
determine the parameters of permeation by glucose are considered
to be imprecise because endogenous insulin influenced experi¬
mental results, intracellular glucose was inaccurately measured
and estimates of glucose utilisation were not associated with
defined concentrations of extracellular or intracellular
In principle the parameters of permeation can be deter¬
mined from a steady state relationship between glucose uptake
and the intracellular and extracellular concentration of glucose.
Alternatively they can be determined from the relationship
between the uptake and the extracellular concentration of glucose.
if the kinetics of glucose metabolism are taken into account.
A novel apparatus for cardiac perfusion was therefore
developed in which hearts were brought to a steady state of
glucose permeation and utilisation. In the apparatus hearts
were perfused with a small volume of perfusate under well
controlled conditions. Glucose concentration in perfusates was
estimated by rapid and accurate automated methods which met the
requirements of the procedure. The utilisation of glucose was
determined not only in the steady state but also throughout the
approach to that state.
The first method for the determination of the parameters
of permeation was impracticable because accurate estimates of
intracellular glucose could not be made with methods currentlyavailable.
Consequently the kinetics of glucose utilisation
were compared with the predictions of a mathematical model in
which permeation was assumed to be a simple carrier mechanism
and the phosphorylation of glucose to be an irreversible enzymecatalysed
reaction. Agreement was found. Estimates made of
the parameters of permeation in the presence and absence of insulin
were in qualitative accord with previous work. The hormone
increased the half saturation constant at least 3-fold and the
maximum rate of permeation 5-fold.
The estimates of the parameters of permeation in the presence
of insulin may be inaccurate because in their determination the
possibility of a concentration gradient in the extracellular
glucose was ignored. However, the estimates provide a reason¬
able explanation of a phenomenon which was observed when the
time-course of glucose utilisation was studied in the absence
of exogenous insulin. A stimulation of utilisation, presumably
by endogenous insulin, occurred consistently only at concentra¬
tions of glucose greater than ImM.
It was concluded that the estimates are an improvement on
previous values and that the apparatus is a useful addition to
the methods available for the study of the metabolism of isolated
|dc.publisher||The University of Edinburgh||en
|dc.relation.ispartof||Annexe Thesis Digitisation Project 2016 Block 4||en
|dc.title||Kinetics of metabolism in the perfused heart||en
|dc.type||Thesis or Dissertation||en
|dc.type.qualificationname||PhD Doctor of Philosophy||en