The role of angiotensin II in the central regulation of feed intake in sheep

Abstract

The objective was to determine the role of Angiotensin II (ANG) in the central regulation of feed intake by ruminants. As a control treatment, artificial cerebrospinal fluid (CSF) was given (over a period of 98.5 h) as a continuous intracerebroventricular (ICV) infusion (0.2 mL h–1) into the lateral ventricle of ewes (n = 5). Approximately 9 d later, the infusion was repeated with the same ewes, but the CSF contained ANG (25 g μL–1). The ewes were fed dried alfalfa chaff for 2 h once daily and both water and a 0.5 M NaCl solution were available ad libitum (except that water intake was restricted on the first day of ANG infusion). Infusion of ANG resulted in severe thirst that persisted when water intake was restricted to an amount equal to voluntary intake during the control infusion. Furthermore, when ewes had ad libitum access to water, consumption during ANG infusion was 1.4 to 2.8-fold greater than that during CSF infusion (P < 0.01). Compared with CSF infusion, ANG infusion decreased eating rates by an average of 46.5% (range, 31.8–62.6%; P < 0.01) and feed intake by 25.0% (5.4–48.1%; P < 0.01), and increased salt intake by 273.8% (124.0–417.6%; P < 0.01). We concluded that ANG produced thirst sensations in the brain, resulting in excessive water intake that caused ruminal distension and significantly reduced feed intake. Key words: Angiotensin, brain, thirst, feed intake, sheep