THE EFFECTS OF INTRAVENTRICULAR 6‐HYDROXYDOPAMINE ON BODY TEMPERATURE AND ARTERIAL BLOOD PRESSURE IN CATS AND RABBITS

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Abstract
In unanaesthetized cats, the administration of 6‐hydroxydopamine (6‐OHDA), 750 μg, via the lateral cerebral ventricle produced a pronounced fall in rectal temperature but only a slight fall when repeated 7 days later. At this time hypothalamic noradrenaline concentration had diminished to 4% of control. In these animals, the hypothermic response to exogenous noradrenaline, 100 μg, given via the same route was uninfluenced by pretreatment with 6‐OHDA. In unanaesthetized rabbits, intraventricular noradrenaline, 100 μg, produced a rise in rectal temperature and a biphasic effect on arterial pressure, a rise lasting 30 min followed by a fall. Intraventricular 6‐OHDA, 750 μg, in unanaesthetized rabbits produced a rise in body temperature and a rise in arterial pressure. The same dose given to rabbits depleted of central noradrenaline with central 6‐OHDA produced rises in body temperature and arterial pressure of similar magnitude, but of slower onset. These results suggest that intraventricular 6‐OHDA releases noradrenaline from central neurones and that these neurones subserve thermoregulatory functions in both species. In the rabbit, central noradrenergic neurones can raise arterial pressure.