Abstract
The effect of hypophysectomy on hypothalamic blood flow autoregulation was studied in anesthetized, artificially ventilated rats. Local hypothalamic blood flow (HBF, H 2-gas clearance method) was measured. Efficiency of autoregulation was tested by determining HBF during standardized hemorrhagic hypotension when systemic arterial pressure was lowered to 80, 60 and 40 mm Hg by consecutive, step-wise bleeding. HBF autoregulation was well maintained until 80 mmHg, but not completely at 60 and 40 mmHg arterial pressure in the sham-operated control group. In contrast, autoregulation was abolished at all levels in the hypophysectomized rats: HBF followed the changes in arterial pressure in these animals. Following hypophysectomy, the concentration of immunoreactive β-endorphin (β-EP) decreased drastically in plasma but remained unchanged in cerebrospinal fluid. Administration of β-EP (200 pg/100 g b. wt.) to hypophysectomized rats by the intravenous route had no effect on autoregulation, while intracerebroventricular administration of the same dose restored autoregulation. The present findings suggest that the pituitary plays a role in hypothalamic blood flow autoregulation.
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