title: Stimulation of gastric osmoreceptors but not the sodium monitor increases renal angiotensin-converting enzyme activity.
abstract: 1. Stimulation of the gastric sodium monitor has been reported to cause a decrease in renal nerve activity and also a decrease in plasma renin activity in renal venous blood. This suggests that changes in sympathetic nerve activity and in the intrarenal renin-angiotensin system may mediate the natriuresis that occurs following gastric sodium administration. In the present study we sought to determine whether gastric sodium administration also modulates angiotensin-converting enzyme (ACE) activity in the kidney. 2. Male Sprague-Dawley rats were equilibrated on a low-sodium (0.008%) diet for 7 days. On the day of the experiment, rats were anaesthetized and kidneys were harvested and immediately snap frozen at 0 and 60 min after intragastric administration of a saline load (1.5 mmol/kg as 3 mol/L saline) or an equivalent volume of iso-osmotic urea (5.95%). Angiotensin-converting enzyme activity was determined by incubation of kidney homogenates with hippuryl-histidyl-leucine and fluorometric assay of the histidyl-leucine generated. 3. Angiotensin-converting enzyme activity in the kidney increased in response to the intragastric administration of both sodium chloride and urea. Angiotensin-converting enzyme activity increased significantly from control levels (189.9 +/- 24.3 nmol/min per g protein) by 60 min in both NaCl-and urea-treated groups (492.3 +/- 27.3 and 468.6 +/- 28.7 nmol/min per g protein, respectively; P < 0.0005). 4. We conclude that instillation of sodium chloride or isoosmotic urea into the stomach increase ACE activity in the kidney. The results of the present study suggest that this effect is due to changes in osmolality rather than stimulation of the gastric sodium monitor.
authors.affiliation: Hypertension Laboratory, Liverpool Hospital, Sydney, New South Wales, Australia.
authors.forename: V Z
authors.initials: VZ
authors.lastname: Ye
authors.forename: K A
authors.initials: KA
authors.lastname: Duggan
mesh_terms: D000818:Animals; D002628:Chemoreceptor Cells / Q000187:drug effects*; D007441:Intubation, Gastrointestinal; D007668:Kidney / Q000187:drug effects / Q000201:enzymology*; D008168:Lung / Q000201:enzymology; D008297:Male; D009994:Osmolar Concentration; D007703:Peptidyl-Dipeptidase A / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism*; D012965:Sodium Chloride / Q000008:administration & dosage*; D012982:Sodium, Dietary / Q000008:administration & dosage*; D013270:Stomach / Q000187:drug effects* / Q000294:innervation
chemical_list: D012982:Sodium, Dietary; D012965:Sodium Chloride; D012964:Sodium; D007703:Peptidyl-Dipeptidase A