Manipulating renal responses to noxious stimuli in the cynomolgus monkey : a renal/behavioral model of essential hypertension

Behavioral influences on excretion of Na⁺ and H₂O and on mean arterial blood pressure (MBP) were studied during saline diuresis in three unanesthetized adult female monkeys. Infusions of isotonic saline (70 ml/kg and 0.5 ml/min, iv) caused excretion of 195 ± 3 µl H₂O/kg/min and 31.8 ± 3.0 µeg Na⁺ /kg/min. Inulin clearance (C_In) was 4.3 ± 0.1 ml/kg/min. Naloxone hydrochloride, an opiate receptor antagonist, had no effect on Na⁺ and H₂O excretion or MBP. Electric shock (5 ma, 200 msec, 12/min for 30 min) delivered to the tail reduced excretion of Na⁺ and H₂O to 84 ± 6% and 78 ± 6% of baseline values, but values returned to baseline before the end of the 30 min shock exposure. C_In decreased initially, then rose above baseline values. MBP increased 3.4% ± 2.5% during shock exposure. The role of opiate receptors in adaptation to electric shock was studied by administering naloxone (10 mg/kg, iv) immediately before electric shock was delivered. After naloxone, electric shock reduced Na⁺ and H₂O excretion to 42 ± 10% and 44 ± 10% of baseline values, and delayed return to baseline values. C_In was decreased throughout the 30 minutes. MBP increases were slightly greater than increases in response to shock alone. Continuous broadband noise at 96 dB decreased Na⁺ and H₂O excretion by 20%, but 108 dB noise had inconsistent effects. After naloxone, however, 108 dB noise decreased excretion of Na⁺ and H₂O to 70 ± 17% and 62 ± 15% of baseline values. MBP decreased slightly in response to both levels of noise, but increased by 4% in response to noise after naloxone. Results of these experiments suggest that unconditional renal and blood pressure responses to noxious sensory stimuli are moderated by endogenous opiates.