Gender difference in cardiopulmonary reflex inhibition of sympathetic nerve activity

We tested the hypothesis that reflex responses to mechanical [increase in left atrial pressure (LAP) 0-25 mmHg] and chemical stimulation [left atrial injection of phenylbiguanide (PBG), 0.5-10 mg/kg] of cardiopulmonary receptors are greater in female (n = 9; 335 +/- 9 g) than in male (n = 10; 558 +/- 23 g) age-matched rats. Anesthetized (500 mg/kg urethan and 80 mg/kg alpha-chloralose), tracheotomized, and artificially ventilated (100% oxygen), sinoaortic-denervated animals were instrumented with left atrial, femoral venous, and arterial catheters and a Tygon occluder around the ascending aorta. Reflex inhibition of lumbar sympathetic nerve activity (LSNA) vs. LAP and dose PBG was higher in female rats. A two-way analysis of variance revealed a significant gender effect, males vs. females (P = 0.023), and a significant gender x dose interaction (P < 0.001) for LSNA vs. LAP. There was also a significant gender x dose interaction (P < 0.001) for LSNA vs. PBG. However, there was no influence of gender on the reflex inhibition of mean arterial pressure (P = 0.751) or heart rate (P = 0.561). These responses were associated with a higher left ventricular weight-to-body weight ratio in females (2.14 +/- 0.06 vs. 1.95 +/- 0.07 g/kg, P = 0.039).