脳循環における自己調節作用と神経性因子に関する実験的研究

EXPERIMENTAL STUDIES ON THE NEUROGENIC FACTORS IN AUTOREGULATION OF REGIONAL CIRCULATION IN DOGS' BRAINS

I．はじめに

　Kety　＆　Schmidt^17）のN₂O法による脳循環の定量的測定がなされるようになつてから，脳循環の研究は急速な発展を遂げてきた。近年では脳循環に自己調節作用が存在することは定説となり^{5,6,9,20,26）}，その機序に関しては，組織圧説^16），代謝産物説^2,30），血管平滑筋説^1,7,8）たどが提唱され，さらに自己調節作用とは別に，化学調節機構の存在が確認されつつある^11）。

　脳循環に対する神経性因子の関与は当初否定されていたが^31,34），近年脳循環の自己調節作用と神経性因子の関係が多く報告されてきた^{12,15,22,23）}。教室の大内^28）は皮質部と視床部の循環を比較検討して，視床部循環の特異性を報告し，同じく木元^18）もその視床部循環の特異性について化学調節機構の面から研究を進め，視床部循環に神経性因子が関与していることを示唆した。

Regional cerebral blood flow was measured in the cerebral cortex, thalamus, and cerebellar cortexof dogs' brains, using oxygen electrodes made of enamelled copper wire. Neurogenic factors in auto-regulation of the regional circulation were studied with autonomic blocking agents such as phenoxy-benzamine, propranolol and atropine. The findings were as follows:

1) Autoregulation was found in both cortical and thalamic circulation when the systemic blood pressure was experimentally increased or decreased.

2) Dysautoregulation of the thalamic circulation was induced by intravenous injection of the alpha adrenergic blockade, phenoxybenzamine, while auto-regulation of the cortical circulation was not effected.

3) No effect from the beta adrenergic blockade, propranolol, was observed on the autoregulation of the cortical and thalamic circulation.

4) Intravenous injection of the cholinergic blockade, atropine, did not change the autoregu-lation of cortical circulation, but that of thalamic circulation disappeared.

It was thought from these findings that auto-regulation of the thalamic circulation might be effected by alpha adrenergic receptors and also cholinergic fibers. However, because of the doubt that the neurogenic system, as the author under-stood it affected only autoregulation, CO₂ inhalation was used to find whether the neurogenic factors had any effect on the chemical control of regional cerebral blood flow or not. The effect of CO₂ in-halation on the cerebral blood flow in the thalamus was increased by the alpha adrenergic blockade, but nullified by the beta adrenergic blockade. Blocking of the cholinergic fibers did not alter the effect of CO₂ inhalation on the cortical and thalamic circulation. Therefore, the neurogenic system affects not only the autoregulation, but also the chemical control of thalamic circulation. The neurogenic factors of chemical control, however, were different from those of autoregulation. Be-cause of these studies, it is thought that the thalamic circulation is controled by the neurogenic system, which is independent from both autoregu-lation and chemical control systems in the thalamus.