The vascular relaxing effect of a factor released by rat atria distension

1. In order to develop a technique to obtain and preserve the atrial natriuretic factors (ANFs) which may be useful for eventual studies on the properties of these factors, we performed experiments on rat isolated atrium. 2. The two atria of adult Wistar rats (200-300 g body wt) deprived of food and water for 48 hr, were set up in an organ bath with modified Krebs-Henseleit solution and submitted progressively to increasing tensions of 0.5, 1.5 and 3.0 g. A sample of 2 ml obtained from the bath was treated with acetic acid 1 M and kept at -12 degrees C. Within 2 days the samples were evaluated for the activity of ANFs on isolated rat aortic rings. Aortic rings previously contracted with a submaximal concentration of phenylephrine were slowly relaxed by the samples. 3. Samples from atria submitted to the highest tension shifted the dose-response curve of contraction induced by increasing cumulative doses of phenylephrine to the right. This activity was absent from samples obtained from the solution in which the atria were dissected. This experimental model allows one to obtain and preserve a vascular relaxing factor from atrial myocardium.