STIMULATORY ACTION OF ANGIOTENSIN II ON WATER AND ELECTROLYTE TRANSPORT BY THE PROXIMAL COLON OF THE RAT

In segments of isolated proximal colon from bilaterally adrenalectomized and nephrectomized rats 10(-12) g angiotensin/ml added to the serosal medium stimulated fluid transfer and sodium transport whose increase was accompanied by a decrease in transepithelial potential difference and short circuit current. Transepithelial electrical resistance remained unchanged. Replacement of chloride by sulphate in the bathing medium blocked the response to angiotensin. This suggested that angiotensin stimulated a coupled NaCl transport. Administration of aldosterone also blocked the response to angiotensin, suggesting that a low concentration of endogenous aldosterone is partly responsible for the action of angiotensin. This would explain the necessity for some form of pretreatment such as bilateral adrenalectomy and nephrectomy. Hydraulic conductivity of proximal colon sacs was computed from the variation in the water flow from serosa to mucosa in response to an osmotic shock. A significant (P < 0.01) increase in the hydraulic conductivity of the proximal colon of bilaterally adrenalectomized and nephrectomized rats was found when 10(-12) g angiotensin/ml was present in the serosal bathing medium. The observed decrease in the transepithelial potential difference has been related to an action of angiotensin on the paracellular shunt pathway.