The lack of change in arterial PO2and PCO2also excludes the possibility of hypoxia that might stimulate fetal swallowing as previously reported [26]. and high-voltage (HV) ECoG Mouse monoclonal to BID temporal distributions, but increased fetal swallowing activity during LV ECoG (1.0 0.1 to 3.5 0.4 swallows/min). Additionally, Ang I evoked an increase in c-fos-immunoreactivity in putative dipsogenic centers, including the supraoptic and paraventricular nuclei of the hypothalamus, accompanied by an increase in fetal plasma OT levels. The expression of c-fos was exhibited in OT neurons in the hypothalamus. The Ang I-mediated increase in fetal swallowing and plasma OT was inhibited by captopril. These results demonstrate the functional development of the fetal brain ACE system in the last trimester of gestation, which plays an important role in the RAS-mediated dipsogenic response and OT release in the regulation of body fluid homeostasis. Key Words:Angiotensin I, Swallowing, Oxytocin, Fetus == Introduction == The brain renin-angiotensin system (RAS) plays an important role in the regulation of hydromineral balance [1]. In adult animals, a central administration of angiotensin (Ang) II has been shown to produce thirst, a reduction in the salt appetite, and the release CASIN of the neurohypophysial hormones vasopressin (VP) and oxytocin (OT) [2,3,4]. However, the development of a functional RAS system in the fetal brain, especially the brain endogenous RAS in utero remains unclear. For example, the physiological function of the angiotensin-converting enzyme (ACE) in the fetal brain is usually unknown, but it is known to exist in the fetal brain [5,6,7]. In the ovine fetus, stimulated swallowing has been exhibited in response to dipsogenic challenges [8]. However, fetuses swallow the amniotic fluids in utero that contain water, electrolytes, and other materials. It is technically difficult to distinguish salt intake from water intake CASIN in the fetus. OT is an important hormone in the regulation of salt appetite [9,10], and previous studies demonstrated that this central Ang II treatment not only stimulated OT release but also activated central OT pathways that were inhibitory to salt appetite, thus limiting the consumption of saline [11]. Our recent work has exhibited that central Ang II increases VP release and the neural activity in the VP neurons in the fetal hypothalamus [12,13], indicating that the central RAS-mediated fetal neuropeptide network is usually functional. Unlike VP, CASIN which acts to regulate vascular and renal function, OT has unique central functions to regulate salt intake beside its peripheral functions. Because it is usually difficult to study fetal salt appetite by measuring swallowing behavior alone, we have altered the experimental strategy and focused on the control center in the brain and measurement of OT release, and the function of OT cells in addition to detecting fetal behavioral responses. Accordingly, the present study was designed to determine the functional responses of fetal brain ACE in relation to swallowing and OT release in utero. We hypothesized that this endogenous ACE in the fetal brain is usually functionally developed by the third trimester of gestation, and it is able to convert exogenous Ang I into Ang CASIN II and to induce Ang-II-like dipsogenic responses and Ang-II-stimulated OT release in the near-term fetal lamb. == Animals and Methods == Animals and Surgical Preparation Fifteen time-dated pregnant ewes (gestational age 125 5 days, term 145 days, singleton) were used. Animals were housed indoors in individual cages and acclimated to a 12:12-hour light-dark cycle. Both food and water were provided ad libitum. All protocols in this study were approved by the institutional animal care committee. Anesthesia was induced by an intramuscular injection of ketamine hydrochloride (20 mg/kg) and atropine sulfate (50 g/kg) and was maintained by maternal endotracheal ventilation with 1 l/min oxygen and 3% isoflurane. Polyethylene catheters (ID = 1.8 mm, OD = 2.3 mm) were inserted into the maternal femoral vein and artery and advanced into the inferior vena cava and abdominal aorta, respectively. The uterus was uncovered by a midline abdominal incision, and a small hysterotomy was performed to provide access to fetal hind limbs. Polyethylene catheters (ID = 1.0 mm, OD = 1.8 mm) were inserted into the fetal femoral vein and artery. Bipolar electromyography (EMG) electrodes were placed on the fetal CASIN thyrohyoid muscle and upper and lower esophagus to determine the swallowing activity, as previously reported.