Moxonidine: A Second-generation Central Antihypertensive Agent

1. A simple method of stimulating different segments of the autonomic outflow from the spinal column in the pithed cat and rat is described.2. Using a movable Teflon-shielded electrode inserted into the vertebral canal and an indifferent electrode under the skin, reproducible responses were obtained from the adrenals, the bladder, the blood vessels, the colon, the heart and the vas deferens. The level and number of segments stimulated was altered by varying the depth of insertion of the Teflon tube and the length of central steel electrode protruding from it.3. The degree of localization of the stimulus seemed satisfactory since it was possible by stimulating the sacral parasympathetic outflow to the bladder and colon or the lumbar sympathetic outflow to the vas deferens, to elicit responses from these organs with little effect on the cardiovascular system. Stimulation at higher levels of the thoracic sympathetic outflow permitted discrimination between the pressor and cardio-accelerator responses.4. Hexamethonium (1 mg/kg) inhibited all the responses, but the colonic response, which occurred only after a latent period, was especially sensitive to ganglion blockade. Atropine (1 mg/kg) inhibited the bladder response by 50% but only prolonged the latency of the colonic response without affecting its magnitude. Physostigmine (1 mg/kg) enhanced the bladder and colonic responses and reversed the effects of hexamethonium on these organs. Phentolamine (1 mg/kg) abolished the pressor responses to stimulation of the thoracolumbar sympathetic outflow but did not affect the cardio-accelerator response.