TEMPERATURE CHANGES INDUCED BY IMIDAZOLINE SYMPATHOMIMETICS IN THE RAT

¹ Department of Pharmacology, School of Medicine and the Brain Research Institute, University of California, Los Angeles, California

The imidazoline derivatoves naphazoline and tetrahydrozoline produce a fall in body temperature when injected systemically into the rat. Direct injection of the drugs into the hypothalamic thermoregulatory centers causes hyperthermia. The hyperthermic response is blocked by prior intracerebral injection of the alpha blocking drug tolazoline. Both naphazoline and tetrahydrozoline block the response of the cat's superior cervical ganglion to i.a. injection of McN A-343, as judged by contraction of the nictitating membrane, whereas the response to 1,1-dirnethyl-4-phenylpiperazinium iodide is unaffected. The blocking action on the ganglion is also prevented by previous administration of tolazoline. The hypothermia after systemic injection of the drugs appears to be the result of an overriding effect at peripheral thermoregulatory sites. The rise in temperature, when the drugs act directly on the rostral hypothalamus by analogy to the action of sympathomimetics on the superior cervical ganglion, may be due to hyperpolarization of neurons in the thermoregulatory centers.