Date of Award


Degree Type


Degree Name



Department of Biology

First Advisor

Dr. Joseph B. Ifyers


The objective of this investigation was to determine converting enzyme activity (CEA) in the lungs and the plasma of conscious rabbits during periods of rapid plasma volume expansion and depletion. Blood pressure changes and plasma renin activity (PRA) were measured also for possible correlations with CEA. Fifteen male New Zealand white rabbits (4-5 kg) wdre divided into 3 groups, controls, plasma volume expansion (PVE) and plasma volume depletion (FVD). Direct blood pressure was monitored via a carotid cannula for a period of 20 min in order to establish normal levels. The plasma volume of 5 conscious rabbits was expanded by infusing a protein-buffered saline solution at a rate of 1.7 ml/min for 15 min. Plasma volume expansion caused a 177. increase in blood pressure with a simultaneous decrease in PRA. When 5 conscious rabbits were hemorrhaged at a rate of 1.7 ml/min for 15 min a 24% decrease in blood pressure was seen while PRA increased significantly. Initial and final PRAs for PVE were 16.0 and 7.0 ng/ml/hr and 14.8 and 20.0 ng/ml/hr for PVD, respectively. Rapid plasma volume expansion and depletion had no significant effect on plasma CEA. Initial values were, controls 5.12 + 2.67, FVD 5.81 + 3.01 and PVE 4.67 + 2.09 ng/ml/hr. Final values were 3.82 + 1.99 for controls, 1.98 + 0.82 and 3.03 + 1.99 ng/ml/hr for PVD and PVE, respectively The final enzyme preparation for the lung converting enzyme resulted in a significant increase in specific activity in all 3 groups of tissue. Partial purification resulted in a 65-fold increase in specific activity in the control group. The PVD group showed the greatest increase in specific activity (72-fold), while the PVE had the lowest increase (37-fold). These findings suggest that the lung converting enzyme is important during periods of rapid plasma volume depletion, and that the lung is the major source of the converting enzyme. No direct correlations between PRA and plasma CEA were seen, but lung CEA increased simultaneously with PRA during plasma volume depletion.