Naloxone effects on blood pressure, analgesia and diuresis in spontaneous hypertensive and normotensive rats.

Studies were performed in unanesthetized normotensive and spontaneously hypertensive rats (SHR) to compare the effects of naloxone. In normotensive Wistar rats, naloxone did not change blood pressure (BP) and nociceptive threshold, but it induced a dose-related diuretic response. Whereas in SHR naloxone decreased nociceptive threshold and lowered BP when given intracerebroventricularly, it failed to significantly modify diuresis. These differences between hypertensive and normotensive rats in their responses to naloxone may be explained by the fact that vasopressin (VP) levels and opioid activity are different in SHR.