In pregnancy, blood volume and baseline sympathetic nerve activity are increased,
while baseline arterial blood pressure is slightly decreased. Relaxin, an ovarian
hormone which is secreted in pregnancy, activates the subfornical organ, a circumventricular
organ, and regions within the brain parenchyma which are associated with control of
blood volume and sympathetic nerve activity. The current experiments phenotyped cells
in the paraventricular nucleus of the hypothalamus which are activated by relaxin.
Carotid and femoral artery and femoral vein catheters were implanted in female virgin
rats. Spinally projecting cells were retrogradely labeled by microinjection of fluorogold
or cholera toxin-b (CTb) (90 nl) into the intermediolateral cell column. After 5 days human relaxin-2 (1 μg/h) or saline (1 ml/h) was infused (1.5 h) into the forebrain circulation (intra-carotid artery, ica) of conscious rats. Relaxin
(n=5) resulted in a modest increase in mean arterial pressure (+7±1 mm Hg) while saline (n=5) had no effect (+1±1 mm Hg). Rats were deeply anesthetized, transcardially perfused with 4% paraformaldehyde,
brains sectioned (35 μm), and Fos-, CTb-, and vasopressin (VP-) immunoreactivity (IR) were evaluated. Following
relaxin, cells in the lateral margins of the subfornical organ expressed Fos-IR, consistent
with activation of neurons which project to the paraventricular nucleus. Overall 23%
of VP-IR cells and 20% of spinally projecting cells were activated (Fos-IR) by ica
relaxin. In contrast, co-labeling with Fos was minimal in saline treated rats. These
data provide an anatomical substrate for a role of relaxin in the adaptations in regulation
of vasopressin and sympathetic nerve activity in pregnancy. HL091164(CMH).
To read this article in full you will need to make a payment
© 2010 Published by Elsevier Inc.