Peripheral venous catecholamines versus adrenal secretory rates after brain stem stimulation in cats

The relationship between adrenal catecholamine secretion and peripheral venous catecholamine concentration was assessed in samples collected before and after brief (15-s) periods of brain stem electrical stimulation in cats anesthetized with α-chloralose-urethan. Adrenal blood flow from the left lumboadrenal vein averaged 0.75 ± 0.05 ml/min (means ± SE, n = 56). Peripheral norepinephrine (NE) concentration (1.19 ± 0.07 ng/ml) was not well correlated with adrenal NE secretion (38.18 ± 3.99 ng/min) before stimulation (r = 0.334. P < 0.025). Although brain stem sites that evoked large increases in adrenal NE secretion often caused an increase in peripheral NE, sites that evoked significant decreases in adrenal NE secretion were not accompanied by decreases in peripheral NE. Peripheral epinephrine (E) concentration (0.11 ± 0.01 ng/ml) was well correlated with adrenal E secretion (23.72 ± 2.33 ng/min) before stimulation (r = 0.468, P < 0.001). Brain stem stimulation-evoked changes in adrenal E secretion were generally reflected in changes of peripheral E concentration, although many exceptions were seen. Peripheral dopamine (DA) concentration (0.23 ± 0.02 ng/ml) was well correlated with adrenal DA secretion (0.94 ± 0.11 ng/min) before stimulation (r = 0.505, P < 0.001). However, stimulus-evoked changes in adrenal DA secretion were not reflected in changes of peripheral DA concentration. The data indicate that, whereas brief periods of brain stem stimulation evoke a wide range of adrenal secretory responses, peripheral catecholamine responses best reflected adrenal secretion only when large increases in adrenal secretion were evoked and were poor indicators of decreased adrenal catecholamine secretion. Further, the timing of simultaneously drawn blood samples relative to the stimulus period was a critical determinant of the correlation between evoked adrenal catecholamine secretion and peripheral concentration of catecholamines.