Cardiorespiratory effects of prolonged angiotensin II block in resting conscious dogs

Intravenous (iv) infusion of the angiotensin II (ANG II) receptor blocker s aralasin in resting conscious dogs during physiological pertubations, such as hypotension and prolonged hypoxia, indicates the presence of an ANG II d rive to increase respiration and decrease the arterial partial pressure of CO2 (Pa-CO2). In contrast, in eupneic resting dogs on a regular chow diet, iv infusion of saralasin for short periods (up to 30 min) provides no evide nce of a tonic effect of circulating levels of ANG II on acid-base balance, respiration, metabolism, or circulation. However, ANG II influences physio logical processes involving salt, water, and acid-base balances, which are potentially expressed beyond a 30 min time period, and could secondarily af fect respiration. Therefore, we tested the hypothesis that blocking ANG II with iv saralasin would affect respiration and circulation over a 4-h perio d. Contrary to the hypothesis, iv infusion of saralasin in resting consciou s eupneic dogs on a regular chow diet over a 4-h period had no effects on p lasma strong ions, osmolality, acid-base balance, respiration, metabolism, or circulation when compared with similar control studies in the same anima ls. Thus, ANG II does not play a tonic modulatory role in respiratory contr ol under "normal" physiological conditions.