ENDOGENOUS MARINOBUFAGENIN-LIKE FACTOR IN ACUTE PLASMA-VOLUME EXPANSION

The aim of the study was to further investigate the nature of endogeno us digitalis-like factors stimulated by acute plasma volume expansion (VE). 10 male Fisher 344XNB rats were given intravenous (iv) saline in fusion (4% of the body mass) for 30 min, which caused a fall in % hema tocrit (35.9+/-0.69 vs. 41.8+/-1.05; vs. 10 controls, P<0.01). EDLF wa s measured in C-18 reverse-phase extracted (32%+/-80% acetonitrile) ti ssues. VE was associated with an increase in plasma marinobufagenin-li ke factor (MLF)(0.49+/-0.05 vs. 0.2+/-0.06 nmol/L, P<0.01) and pituita ry ouabain-like compound (OLC) (30.9+/-3.12 vs. 3.2+/-2.3 pmol/g, P<0. 01). Plasma OLC decreased (0.087+/-0.018 vs. 0.21+/-0.04 nmol/L, P<0.0 2), and pituitary MLF did not change (0.05+/-0.01 vs. 0.07+/-0.02 pmol /g) after VE. Chloroform extracted urine from 5 volume-expanded male m ongrel dogs was fractionated on reverse-phase HPLC columns in a linear gradient of 0-80% acetonitrile. The material cross-reacting with mari nobufagenin antibody eluted from HPLC column as a single peak, demonst rated absorbance at 300 nm, and was distinct from ouabain-like materia l. Digoxin antibodies interacted with both marinobufagenin-like and ou abain-like immunoreactive material. These results provide further evid ence for the presence of a bufodienolide EDLF in the mammals, and demo nstrate that EDLF response to VE includes stimulation of brain OLC and plasma bufodienolide.