The present study investigates the population of β2-receptors
on lymphocytes in pregnant women with premature
labor between the 29th and 34th week of pregnancy.
The population of receptors on lymphocytes correlates
with that on the myometrium, which is not accessible for
study during pregnancy. Fourteen patients received a
pulsatile tocolysis, while ten women received a continuous
tocolysis with Fenoterol. Assuming an equal population
of receptors in both groups before commencement
of therapy, the numbers of receptors in the patients with
continuous tocolysis fell to about 35% of the initial value
after 72 hours. Under pulsatile tocolysis, the numbers of
receptors remained unchanged for a period of three days
and was still only just below 70% of the initial value by
the seventh day.
Our data demonstrate that continuous administration
of the short-acting β2-agonist Fenoterol resulted in a
substantial loss of β2-adrenoceptors on lymphocytes.
In contrast, intermittent administration of the same
β2-adrenergic agonist prevented the onset of receptor
down-regulation in pregnant women with preterm labor.
Further studies are required to investigate the impact of
the decreased loss of β2-adrenoceptor density on the
good clinical experience with intermittent tocolysis.