Correlation between osmolality and baroreceptor discharge in the pregnant rat

1. Tina Hines, Dawn Grimes, Jessica Veeh, Katherine Martinez and Sarang Abhyankar UMKC School of Nursing Correlation between osmolality and baroreceptor discharge in the pregnant rat Summary and conclusions:Baseline pOsm was significantly lower in pregnant compared with virgin animals (Fig 1). In pregnant rats, a higher osmotic load was required to increase pOsm (Fig 2), and a 200mOsm load did not decrease pOsm in either group. Our data indicate that osmolality has minimal effect on ADNA, in spite of pOsm increases of 15-20 mOsm/L. (Fig 3). Introduction:Baroreceptor firing decreases in response to hyponatremia in vitro in male rats. Pregnancy is associated with a reduction in plasma sodium, osmolality (pOsm) and baroreceptor activity. Hypothesis: Osmolality may contribute to alterations in baroreceptor discharge during pregnancy. Methods:20-day pregnant and control virgin rats were anesthetized (inactin 110mg/kg ip.) and femoral vessels cannulated for measurement of arterial pressure, blood withdrawal, and drug infusion. A tracheotomy was performed, and the aortic depressor nerve (ADN) was isolated to record changes in baroreceptor afferent discharge. pOsm was measured before and 30 min after graded IP injections (1.8mL/100g body wt. in pregnant; 2mL/100g body wt. in virgin) of NaCl (200, 300, 700, 1200, 1500mOsm/L). Arterial pressure, heart rate, and ADN activity (ADNA) were measured continuously. Fig 1: Baseline osmolality was significantly lower in pregnant compared to virgin rats. Fig 2: Osmolality increased in a concentration-dependent manner after IP injections in virgin rats, and showed a similar trend in the pregnant animals. Fig 3: Mean arterial pressure (top) and baroreceptor discharge (bottom) following IP injections of 1200 mOsm/L NaCl. The salt load did not significantly alter ADNA in either group.