ACE inhibition prevents Na and water retention and MABP increase during reduction of renal perfusion pressure

Abstract

Two groups of six dogs were studied during 4 control days and 4 days of reduced renal perfusion pressure (rRPP) servo controlled at 20% below the individual dog's 24-h mean arterial blood pressure (MABP) during control days, i.e., below the threshold for renin release. On rRPP days, endogenous activation of plasma aldosterone and angiotensin II was inhibited by the angiotensin-converting enzyme inhibitor captopril. The dogs were kept on a high-Na and high-water intake. Unlike studies during rRPP alone, there was no Na and water retention during rRPP+captopril. Glomerular filtration rate dropped by approximately 9%, and MABP remained in the range of control days. Plasma renin activity rose to values 14 times greater than control, whereas plasma aldosterone decreased by approximately 60%. Atrial natriuretic peptide remained in the range of controls. In conclusion, angiotensin-converting enzyme inhibition can prevent the otherwise obligatory Na and water retention and systemic MABP increase during a 20% reduction in renal perfusion pressure. This is achieved most likely via the captopril-induced fall in angiotensin II and plasma aldosterone levels.

The ‘Body Fluid Pressure Control System’ Relies on the Renin–angiotensin–aldosterone System: Balance Studies in Freely Moving Dogs

“…For reasons of social well‐being, dogs in adjacent kennels accompany the dog under investigation. The chronic lines of the accustomed dog are connected to a swivel system, which allows free movement within the kennel 14,17 . From the swivel, the lines are led to the adjoining laboratory.…”

Are large amounts of sodium stored in an osmotically inactive form during sodium retention? Balance studies in freely moving dogs

“…A total of 81 chronically instrumented female Beagles, about 2 years of age, and weighing 12-16 kg, were studied by standardized methods described in detail in previous papers (10,24,29,30,34,36,37). On completion of the experiments, implants were removed and the dogs were given to suitable private individuals.…”

“…For reasons of social well-being, dogs in adjacent kennels accompanied the dog under investigation. During the 4-day balance study, the chronic lines of the accustomed dog were connected to a swivel system that allows free movement within the kennel (10,30). From the swivel, the lines were led to the adjoining laboratory.…”

“…For protocol Ϫ0.9TBS, continuous ACE-inhibition (ACE-I: Captopril, Bristol-Myers Squibb, New York, NY; 3.5 g ⅐ min Ϫ1 ⅐ kg Ϫ1 ) was used to block endogenous renin-angiotensinaldosterone system stimulation by rRPP in dogs on HSI (n ϭ 5), as described by (10). For protocol Ϫ3.4TBS, TBSodium was reduced by peritoneal dialysis in the morning of the first study day in dogs on LSI (n ϭ 6), according to a previously described method (36).…”

“…We wanted to study alterations in TBSodium that cover the whole range from moderate deficit (about Ϫ10%) to large surplus [about ϩ50%; TBSodium without bone Na ϩ is about 34 mmol/kg body mass (26)]. To this end, we performed another set of experimental protocols, and, in addition, we reanalyzed and included results of specific protocols from previously published studies (10,35,37,38). As we had observed in previous studies (28,35) that TBSodium changes are often accompanied by changes in TBPotassium, we routinely determined K ϩ balances.…”