Requirement for solutions with oncotic pressure to release ANF during blood volume expansion in conscious and anesthetized rats.

We examined the effect of a 30% blood volume expansion with either blood, isotonic saline, or isotonic saline plus albumin on the release of immunoreactive-atrial natriuretic factor (IR-ANF) in conscious and barbiturate-anesthetized rats. Immediately prior to volume expansion, resting plasma IR-ANF levels were significantly (p less than 0.05) higher in the conscious animals (61 +/- 5 pg/mL, n = 19) compared to the anesthetized animals (41 +/- 3 pg/mL, n = 19). Volume expansion with blood from donor rats significantly (p less than 0.05) elevated IR-ANF in both groups, but the increase in the conscious rats (+492 +/- 32 pg/mL, n = 6) was significantly (p less than 0.05) greater than that of the anesthetized rats (74 +/- 25 pg/mL, n = 6). Similarly, volume expansion with isotonic saline containing 38 mg/mL albumin significantly (p less than 0.05) elevated IR-ANF levels in both groups, but the increase in the conscious group (379 +/- 102 pg/mL, n = 7) was significantly (p less than 0.05) greater than that of the anesthetized group (94 +/- 32 pg/mL, n = 7). These elevations in IR-ANF levels were not significantly different between either of the conscious groups or either of the anesthetized groups. Volume expansion with isotonic saline alone did not have any significant effect upon resting IR-ANF levels in either conscious (+8 +/- 14 pg/mL, n = 6) or anesthetized (-7 +/- 6 pg/mL, n = 6) animals. From these results, it would appear that a) isotonic saline alone does not stimulate IR-ANF release when used to expand blood volume, and b) barbiturate anesthesia significantly lowers resting plasma IR-ANF levels and attenuates the release of IR-ANF in response to volume expansion.