The Central Nervous System as Target forAntihypertensive Actions of a Proline-Rich Peptide from Bothrops jararaca Venom

ABSTRACT

Pyroglutamyl proline-rich oligopeptides, present in the venom of the pit viper Bothrops jararaca (Bj-PROs), are the first described naturally occurring inhibitors of the angiotensin I-converting enzyme (ACE). The inhibition of ACE by the decapeptide Bj-PRO- 10c (venom peptides in mammals resulting in a decrease of bloodpressure. Recent studies, however, suggest that ACE inhibition alone is not sufficient for explaining the antihypertensive actions exerted by these peptides. In this study, weshow that intracerebroventricular injection of Bj-PRO-10c induced a significant reduction of mean arterial pressure (MAP) together with a decrease of heart rate (HR) in spontaneously hypertensive rats, indicating that Bj-PRO-10c may act on the centralnervous system. In agreement with its supposed neuronal action, this peptide dosedependently evoked elevations of intracellular calcium concentration ([Ca21]i) in primary culture from postnatal rat brain. The N-terminal sequence of the peptide was not essential for induction of calcium fluxes, while any changes of C-terminal Pro or Ile residues affected Bj-PRO-10c’s activity. Using calcium imaging by confocal microscopy and fluorescence imaging plate reader analysis, we have characterized Bj-PRO-10cinduced[Ca21]i transients in rat brain cells as being independent from bradykininmediated effects and ACE inhibition. Bj-PRO-10c induced pertussis toxin-sensitive Gi/ o-protein activity mediated through a yet unknown receptor, influx and liberationof calcium from intracellular stores, as well as reduction of intracellular cAMP levels. Bj-PRO-10c promoted glutamate and GABA release that may be responsible for its antihypertensive activity and its effect on HR.