CONTEXT The exact mechanism involved in changes in
blood pressure and peripheral
vascular resistance during
pregnancy is unknown.
OBJECTIVE: To evaluate the importance of
endothelium -derivated relaxing factor (EDRF) and its main component,
nitric oxide , in
blood pressure and vascular reactivity in pregnant
rats .
DESIGN: Clinical trial in experimentation
animals .
SETTING: University laboratory of
Pharmacology . SAMPLE
Female Wistar rats with normal
blood pressure , weight (152 to 227 grams) and age (90 to 116 days). INTERVENTION The
rats were divided in to four groups pregnant
rats treated with
L-NAME (13
rats ); pregnant control
rats (8
rats ); virgin
rats treated with
L-NAME (10
rats ); virgin control
rats (12
rats ). The vascular preparations and caudal
blood pressure were obtained at the end of
pregnancy , or after the
administration of
L-NAME in virgin
rats . MAIN MEASUREMENTS The caudal
blood pressure and the vascular response to
acetylcholine in pre-contracted aortic rings, both with and without
endothelium , and the effect of
nitric oxide inhibition, Nw-L-nitro-
arginine methyl-
ester (
L-NAME ), in pregnant and virgin
rats . The
L-NAME was administered in the
drinking water over a 10-day period.
RESULTS: The
blood pressure decreased in
pregnancy . Aortic rings of pregnant
rats were more sensitive to
acetylcholine than those of virgin
rats . After
L-NAME treatment , the
blood pressure increased and
relaxation was blocked in both groups. The fetal-placental unit weight of the
L-NAME group was lower than that of the
control group .
CONCLUSION: Acetylcholine -induced
vasorelaxation sensitivity was greater in pregnant
rats and that
blood pressure increased after
L-NAME administration while the
acetylcholine -induced
vasorelaxation response was blocked.