Reflex modulation of catecholamine secretion and adrenal sympathetic nerve activity by acupuncture-like stimulation in anesthetized rat

The effects of acupuncture-like stimulation of the abdomen and a hindlimb on the secretion rates of adrenal medullary catecholamine hormones (adrenaline and noradrenaline) and adrenal sympathetic efferent nerve activity were studied using urethane-anesthetized rats. Acupuncture needles (diameter of 340 mu m) were inserted into the skin and underlying muscles of either the abdomen or a hindlimb to a depth of 10 mm and then twisted at a frequency of about 1 Hz for 90 s. The stimuli induced three types of response in both catecholamine secretion and adrenal sympathetic nerve activity (i.e., decrease, increase, and no change). These different responses corresponded with three similar types of response in mean arterial pressure. In spinalized animals, the stimuli produced only increases in both catecholamine secretion and nerve activity, and abdominal stimulation elicited a larger response than hindlimb stimulation. The responses of adrenal nerve activity were eliminated after surgically severing the afferent nerves innervating the abdomen and hindlimb. These findings indicate that the secretion of adrenal medullary hormones is controlled reflexively by acupuncture-like stimulation via excitation of somatic afferent nerves and also via the reflex responses of adrenal sympathetic efferent nerves. Both the spinal cord and supraspinal structures act as reflex centers. The excitatory reflex properties at the propriospinal and segmental levels are modified into a generalized, either excitatory or inhibitory, response by supraspinal structures.