Vasopressor responses and hyperthermia by intracerebroventricular injections of penicillin, a pyrogen, in rats: involvement of brain angiotensin II.

Because hypothalamus is a center for both the blood pressure and thermoregulation, we assumed that there is a close interrelationship between them. To prove this hypothesis, effects of intracerebroventricular (ICV) injections of a pyrogen, penicillin-G (Pc), on the blood pressure and rectal temperature (RT) were investigated. The ICV injections increased the mean arterial pressure (MAP), heart rate (HR) and the abdominal sympathetic activity (SNA) dose-dependently in urethane-anesthetized rats. In conscious rats, Pc (100 U) elicited the two components of rises in MAP (+19 +/- 1 and +20 +/- 1 mm Hg), and both the RT and HR increased corresponding to the second phase of MAP responses (+1.0 +/- 0.1 degree C and +60 +/- 7 beats/min). ICV injections of an angiotensin II (ang II) antagonist significantly decreased the MAP (-30 +/- 4 mm Hg), HR (-106 +/- 13 beats/min), and the RT (-0.9 +/- 0.1 degree C). ICV injections of Pc elicited drinking behavior (the vehicle group; 1.1 ml/90 min vs Pc group; 8.6 ml) in rats water-deprivated for 24 hours. In spontaneously hypertensive rats (SHRs), ICV injections of Pc elicited augmented responses in the first phase but diminished in the second pressor phase. ICV injections of an ang II antagonist elicited augmented effects in both the MAP (-39 +/- 1 mm Hg) and RT (-0.8 +/- 0.1 degree C) in SHRs. Thus, RT fluctuated corresponding to the blood pressure level in the latter phase, where a brain ang II mechanism may be involved.(ABSTRACT TRUNCATED AT 250 WORDS)