Cardiac sympathetic nerve activity and catecholamine kinetics in cat hearts

To understand the catecholamine kinetics in the heart during hypotension, we simultaneously measured cardiac sympathetic nerve activity (CSNA), concentrations of norepinephrine (NE) and epinephrine (Epi) in arterial and coronary sinus blood, and coronary sinus plasma flow in 11 cats. With hypotension, NE and Epi concentrations in arterial blood increased more than those in coronary sinus blood. The arteriovenous difference between NE and Epi concentrations increased, whereas coronary sinus plasma flow decreased. The net cardiac uptake of NE from coronary arterial blood was not significant (0.826 +/- 0.506 ng/min) under the control condition. With hypotension, it increased significantly to 9.658 +/- 3.182 ng/min (P less than 0.05) in spite of a CSNA increase to 302.0 +/- 30.3% of that during the control condition. The net cardiac uptake of Epi was significant (1.574 +/- 0.542 ng/min) under the control condition, and, with hypotension, it increased significantly to 4.721 +/- 1.049 ng/min (P less than 0.01). We concluded that during hypotension NE was supplied to the heart from sympathetic nerve endings distributing to the heart and also from coronary arterial blood.