Impaired angiotensin-induced drinking in spontaneously hypertensive rats

The drinking response during the 30 minutes following intracerebro-ventricular injection of angiotensin II (AII) (1 to 200 ng) was compared in male spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto control rats (WK). SHR drank significantly less than WK at the 10, 50 and 100 ng doses. In contrast, responses to intracerebroventricular carbachol and intraperitoneal hypertonic saline were not different between SHR and WK. These agents are believed to induce drinking by mechanisms independent of angiotensin. Binding of I125-labelled AII to particles prepared from the hypothalamus, thalamus, septum and midbrain (HTSM) region was measured in one month old male and two month old female SHR and their respective age matched WK controls. No differences were found in binding between SHR and WK of either sex. These data demonstrate an impairment of drinking responses in the SHR which seem to be specific for angiotensin. This finding supports the hypothesis that the CNS angiotensin system might be abnormal in these animals.