Relationship between the resting blood pressure and depressor responses evoked by stimulation of the aortic nerve

Correlations between the resting blood pressure and magnitude of depressor responses evoked by graded stimulation of the aortic nerve, were studied in rabbits anaesthetized with urethane. The strength of stimulation ranged from 1 to 10 times the threshold, and activated the myelinated afferents. The frequency of stimulation was 5 and 50 cycles/sec. At lower frequency of stimulation the correlations become significant when the intensity of stimulation is 3 times the threshold and they increase at the highest strengths of stimulation. Correlation coefficients calculated for responses obtained at the frequency of 50 cycles/sec are significant in 8 out of 9 intensities of stimulation. With increase in the strength of stimulation they increase, attain their maximum at twice the threshold and decrease at the largest used stimulus strengths. The changes in the values of the correlation coefficients are not paralleled by alterations in the mean size of depressor responses. Since all correlation coefficients are positive, it is inferred that the depressor responses produced by stimulation of the aortic nerve follow WILDER's "law of initial value". The conformity with this rule is the better the higher the values of the correlation coefficients. The strength of relationship between the resting blood pressure and the size of depressor responses is considered to reflect the efficiency of the homeostatic circulatory mechanism.