Endogenous opioids and electrolyte excretion after contralateral renal exclusion

Area of Science:

• Nephrology
• Renal Physiology
• Neuroendocrinology

Background:

• Acute reductions in functioning renal mass trigger compensatory increases in ion excretion by the remaining kidney.
• The precise mechanisms, particularly the role of endogenous opioid systems, remain incompletely understood.

Purpose of the Study:

• To investigate the involvement of endogenous opioids in the renal response to acute reductions in functioning renal mass.
• To elucidate the role of opiate receptors in mediating changes in sodium and potassium excretion by the contralateral kidney.

Main Methods:

• Acute unilateral nephrectomy (AUN) and acute unilateral ureteral occlusion (UUO) were performed in rats to simulate reduced renal mass.
• Opiate receptor blockade was achieved using continuous naloxone infusion.
• Morphine tolerance was induced to assess the involvement of opioid pathways.

Main Results:

• AUN and UUO significantly increased contralateral kidney sodium (U Na V) and potassium (U K V) excretion without altering GFR or mean arterial pressure.
• Naloxone administration completely blocked the increase in U Na V and U K V following AUN or UUO.
• Rats tolerant to morphine also failed to exhibit increased cation excretion after AUN.

Conclusions:

• Acute reductions in functioning renal mass stimulate cation excretion by the contralateral kidney via reflex pathways.
• These reflex pathways critically involve endogenous opioid systems and opiate receptors.