Sympathetic and metabolic mechanisms of the cerebrovasomotor function of the caudal ventrolateral medulla in rats.
We attempted to elucidate the cerebrovasomotor function of the caudal ventrolateral medulla. Sixty-one rats were anaesthetized, paralysed and artificially ventilated. The microsphere method was employed for the measurement of blood flow. Microinjection of an antagonist of excitatory amino acids, kynurenate (2 nmol), into functionally identified depressor sites within the caudal ventrolateral medulla produced arterial hypertension of about 140 mmHg. We found that the cerebral blood flow was substantially increased, but was maintained at the same level (17 rats) as that observed under phenylephrine-induced hypertension (26 rats). Bilateral severing of the cervical sympathetic trunks resulted in a further increase in blood flow in all brain regions studied (18 rats). The response was most significant in the cerebral parasagittal cortex (164 +/- 31% of baseline without, and 211 +/- 43% with sympathectomy; mean +/- S.D.; P < 0.001). The contributions of the cerebral metabolic mechanism to this flow increase under denervation was minimal, as evidenced by the observation of disproportionately smaller changes in cerebral metabolic rate for oxygen during any type of hypertension. We conclude that the cerebrovasomotor functions of the caudal ventrolateral medulla may operate to keep an equilibrium between simultaneously working tonic inhibitions against sympathetic vasoconstriction as well as against vasodilatation. This dual effect is mediated by excitatory amino acid receptors located within this particular brain area. The vasodilator mechanism may be of neurogenic origin. When the function of the brain area is suppressed, the subsequently disinhibited vasodilator mechanism dominates the cerebrovascular autoregulatory function.(ABSTRACT TRUNCATED AT 250 WORDS)
Nakai
M
M
National Cardiovascular Center Research Institute, Osaka, Japan.
Tamaki
K
K
Maeda
M
M
D000818:Animals; D001784:Blood Gas Analysis; D001923:Brain Chemistry / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003427:Cross Circulation; D006973:Hypertension / Q000139:chemically induced / Q000503:physiopathology; D007736:Kynurenic Acid; D008297:Male; D008526:Medulla Oblongata / Q000378:metabolism / Q000502:physiology*; D009474:Neurons / Q000502:physiology; D010101:Oxygen Consumption / Q000502:physiology; D010656:Phenylephrine; D051381:Rats; D017208:Rats, Wistar; D013562:Sympathectomy; D013564:Sympathetic Nervous System / Q000502:physiology*
D010656:Phenylephrine; D007736:Kynurenic Acid