The hypotensive response to compound 48/80 in normotensive and hypertensive rats

1. The administration of an initial dose of 50 micrograms/kg of 48/80 produced a sharp fall in the blood pressure of normotensive rats but produced little change in blood pressure in spontaneously hypertensive rats. 2. The administration of an additional 50 micrograms/kg and 100 micrograms/kh of 48/80 in normotensive and spontaneously hypertensive rats resulted in equivalent decreases in pressure in both groups. 3. Both groups had equivalent decreases in blood pressure in response to methylhistamine. 4. Spontaneously hypertensive rats appear to have a reduced ability to release histamine in response to 48/80 due to either an increased threshold for 48/80 or a diminished histamine storage pool.