Se. Morrissey et al., EFFECT OF OVARIECTOMY AND STEROID-HORMONE REPLACEMENT ON THE RECOVERYOF ARTERIAL BLOOD-PRESSURE FOLLOWING HEMORRHAGE IN ANESTHETIZED BRATTLEBORO RATS, European journal of endocrinology, 136(3), 1997, pp. 330-337
There is increasing evidence that ovarian steroids inhibit vascular re
sponsiveness to the neurohypophysial hormone vasopressin. The present
study examined the recovery of the arterial blood pressure following a
single (2 ml/100 g body weight) haemorrhage in ovariectomized (OVX) B
rattleboro rats with hereditary hypothalamic diabetes insipidus (BDI)
and rats of the parent Long Evans (LE) strain. Some groups of OVX rats
received subcutaneous implants of either (17)beta-oestradiol (E(2)) o
r progesterone 7 days prior to haemorrhage. The arterial blood pressur
e recovery immediately following haemorrhage was significantly impaire
d in both groups of steroid-treated OVX LE rats compared with the OVX
controls (both comparisons P <0.05). The impairment in blood pressure
recovery seen in the steroid-replaced OVX LE rats was similar to that
seen in pro-oestrous rats (when ovarian steroid levels are raised) com
pared with male rats of this strain (P <0.05). In contrast, ovariectom
y with or without steroid replacement in BDI rats had no further effec
t on the already attenuated recovery of arterial blood pressure after
haemorrhage in this strain. Heart rate responses to haemorrhage also s
howed strain differences, which were dependent on steroid treatment, P
ro-oestrous female Le rats showed a small decrease in heart rate after
haemorrhage, followed by a recovery process, and this initial bradyca
rdia was markedly enhanced in the OVX steroid-treated animals. In cont
rast, untreated OVX LE rats showed an initial and sustained increase i
n heart rate which was significantly higher than in the steroid-treate
d OVX animals (P <0.05). ALL BDI rats, irrespective of treatment, cons
istently showed an increased heart rate after haemorrhage. In conclusi
on, ovarian steroid replacement in OVX LE, but not vasopressin-deficie
nt BDI, rats was associated with an attenuated presser recovery after
haemorrhage. This provides further evidence for the existence of an im
portant inhibitory interaction between ovarian steroids and vasopressi
n. The initial decrease in heart rate observed in pro-oestrous and ste
roid-treated OVX LE rats after haemorrhage also appears to be related
to an ovarian steroid-vasopressin interaction.