MONOCLONAL-ANTIBODIES SPECIFIC FOR RAT RELAXIN .8. PASSIVE-IMMUNIZATION WITH MONOCLONAL-ANTIBODIES THROUGHOUT THE 2ND HALF OF PREGNANCY REDUCES WATER-CONSUMPTION IN RATS

Recent studies demonstrated that exogenous relaxin promoted drinking i n nonpregnant rats. The purpose of this investigation was to determine the influence of endogenous relaxin on water consumption in pregnant rats. To that end, a monoclonal antibody specific for rat relaxin, des ignated MCA1, was used to passively neutralize endogenous relaxin thro ughout the second half of pregnancy in intact rats. Five milligrams of highly purified MCA1 were administrated iv to rats daily from days 12 -22 of pregnancy. Controls received either a monoclonal antibody for f luorescein (monoclonal antibody control) or PBS (vehicle control). The amount of water consumed and both the total duration of water consump tion and the total number of episodes when water was consumed were det ermined daily during both dark and light periods for all treatment gro ups. From days 13-22 of pregnancy, all three of these parameters of wa ter consumption increased during the 10-h dark period (P < 0.01), but not during the 14-h light period. The mean daily water consumption in MCA1-treated rats was significantly less than that in controls (P < 0. 05). Relaxin's effects on water consumption were limited to the 14-h l ight period (P < 0.01). No difference was found in daily water consump tion between the MCA1-treated and control groups during the 10-h dark period. There was a tendency during the light period for both the tota l duration of water consumption (P = 0.06) and the total number of epi sodes when water was consumed (P = 0.13) to be less in MCA1-treated ra ts than in controls. Food consumption and body weight increased as pre gnancy progressed, but no differences were found among the three treat ment groups. We conclude that endogenous relaxin has effects on water consumption. It promotes water consumption during the daily Light peri od in the second half of pregnancy in rats. Thus, relaxin may be a dip sogenic agent.