Central angiotensin II stimulation of ovine fetal swallowing.

Abstract

In the late-gestation ovine fetus, spontaneous swallowing occurs primarily during fetal low-voltage electrocortical (ECoG) activity in association with fetal breathing movements. Fetal swallowing activity may be stimulated in response to systemic or carotid plasma hyperosmolality, although not to increased plasma angiotensin II (ANG II) levels. In view of the potent dipsogenic effects of central, but not peripheral, ANG II in adult sheep, the present study investigated the effect of intracerebroventricular (ICV) ANG II on fetal swallowing activity. Six ovine fetuses (127 +/- 1 days) were chronically prepared with electromyogram and cortical electrodes and with vascular and lateral ventricle catheters. After a 2-h control period, fetuses received ICV injections of artificial cerebrospinal fluid and increasing concentrations of ANG II (0.1, 1.0, 10, 100, and 500 ng/kg). Fetal ECoG activity did not change, although fetal swallowing activity significantly increased in response to the 100- and 500- ng/kg ANG II doses (1.20 +/- 0.14 to 3.34 +/- 0.59 and 3.46 +/- 0.81 swallows/min of low-voltage ECoG, respectively). In response to the highest ANG II dose, fetal plasma arginine vasopressin levels significantly increased (5.7 +/- 1.2 to 17.2 +/- 4.6 pg/ml). ICV ANG II stimulation of fetal swallowing and arginine vasopressin secretion demonstrates that central ANG II dipsogenic mechanisms are intact by 0.9 of ovine gestation.