HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 288/4/R1014    most recent 00479.2003v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by El-Haddad, M. A. Articles by Ross, M. G. Search for Related Content PubMed PubMed Citation Articles by El-Haddad, M. A. Articles by Ross, M. G.

DEVELOPMENTAL PHYSIOLOGY AND PREGNANCY

Central angiotensin II AT1 receptors mediate fetal swallowing and pressor responses in the near-term ovine fetus

Perinatal Research Center, David Geffen UCLA Medical School, Research and Educational Institute, Harbor-UCLA Medical Center, Torrance, California

Submitted 22 August 2003 ; accepted in final form 11 November 2004

Swallowed volumes in the fetus are greater than adult values (per body weight) and serve to regulate amniotic fluid volume. Central ANG II stimulates swallowing, and nonspecific ANG II receptor antagonists inhibit both spontaneous and ANG II-stimulated swallowing. In the adult rat, AT1 receptors mediate both stimulated drinking and pressor activities, while the role of AT2 receptors is controversial. As fetal brain contains increased ANG II receptors compared with the adult brain, we sought to investigate the role of both AT1 and AT2 receptors in mediating fetal swallowing and pressor activities. Five pregnant ewes with singleton fetuses (130 ± 1 days) were prepared with fetal vascular and lateral ventricle (LV) catheters and electrocorticogram and esophageal electromyogram electrodes and received three studies over 5 days. On day 1 (ANG II), following a 2-h basal period, 1 ml artificial cerebrospinal fluid (aCSF) was injected in the LV. At time 4 h, ANG II (6.4 µg) was injected in the LV, and the fetus was monitored for a final 2 h. On day 3, AT1 receptor blocker (losartan 0.5 mg) was administered at 2 h, and ANG II plus losartan was administered at 4 h. On day 5, AT2 receptor blocker (PD-123319; 0.8mg) was administered at 2 h and ANG II plus PD-123319 at 4 h. In the ANG II study, LV injection of ANG II significantly increased fetal swallowing (0.9 ± 0.1 to 1.4 ± 0.1 swallows/min; P < 0.05). In the losartan study, basal fetal swallowing significantly decreased in response to blockade of AT1 receptors (0.9 ± 0.1 to 0.4 ± 0.1 swallows/min; P < 0.05), while central injection of ANG II in the presence of AT1 receptor antagonism did not increase fetal swallowing (0.6 ± 0.1 swallows/min). In the PD-123319 study, basal fetal swallowing did not change in response to blockade of AT2 receptor (0.9 ± 0.1 swallows/min), while central injection of ANG II in the presence of AT2 blockade significantly increased fetal swallowing (1.5 ± 0.1 swallows/min; P < 0.05). ANG II caused significant pressor responses in the control and PD-123319 studies but no pressor response in the presence of AT1 blockade. These data demonstrate that in the near-term ovine fetus, AT1 receptor but not AT2 receptors accessible via CSF contribute to dipsogenic and pressor responses.

ovine fetus; angiotensin receptors; swallowing