Histamine- and acetylcholine-induced changes in the permeability of the blood-brain barrier of normotensive and spontaneously hypertensive rats.

Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats were given saline, histamine (1.25, 2.5 or 5.0 micrograms/kg) or acetylcholine (1.0 or 2.0 micrograms/kg). Both agents caused a dose-dependent decrease in blood pressure which was greater in the spontaneously hypertensive animals. The permeability of the blood brain-barrier was measured with 131I-labelled serum albumin (RISA) or with 99mTc-sodium pertechnetate (TcO4-). The lowest dose of histamine caused a decrease in permeability of the blood-brain barrier to serum albumin in normotensive rats and acetylcholine caused an increase. Only the largest dose of histamine increased the permeability of the blood-brain barrier to serum albumin in spontaneously hypertensive rats. All doses of histamine and acetylcholine increased the permeability of the blood-brain barrier to sodium per technetate in nomotensive rats and the two lower doses of histamine increased the permeability in spontaneously hypertensive animals. This provides another example of the dissociation of change in the systemic blood pressure and change in the permeability of the blood-brain barrier.