Cardiac contractility and the spinal sympathetic neuron

Changes in cardiac contractility in cats were measured following electrical stimulation of the thoracolumbar spinal cord. Inotropic response sites were highly localized, and inotropic changes were greatest in the region of the intermediolateral nucleus. Cardioaugmentation was elicited from all spinal segments between T1 and L4. Inotropic responses were maximal at a frequency of 25 Hz and, at this frequency, showed strong right-sided preponderance. Similar lateralization was noted for heart rate and blood pressure. The right-sided spinal lateralization of the contractility response appeared to be frequency dependent, with reversal at 10 Hz, a relationship previously demonstrated for zona intermedia pressor responses. Neither adrenalectomy nor change of anesthetic agent affected the magnitude or lateralization of the inotropic response.