Renogastric Reflex Pathway in Renal or Ureteric Colic
The renogastric reflex is a neurally-mediated pathway where rapid distension of the renal pelvis or ureter triggers increased pyloric sphincter pressure, resulting in the characteristic nausea, vomiting, and epigastric pain that accompany renal colic. 1
Mechanism of the Reflex
The pathway operates through the following sequence:
- Trigger: Rapid distension of the renal pelvis (≥10 mL) or ureter (≥1 mL) activates mechanoreceptors in the collecting system
- Afferent pathway: Sensory signals travel via renal and ureteral nerve fibers
- Central processing: Neural integration occurs at the spinal cord/brainstem level
- Efferent pathway: Motor signals return to the gastrointestinal tract
- End effect: Increased pyloric sphincter pressure, gastric stasis, and associated symptoms
Key Clinical Features
The reflex demonstrates several important characteristics that distinguish it from other causes of gastrointestinal symptoms 1:
Speed-dependent activation: The reflex only occurs with rapid distension. Slow distension of the renal pelvis or ureter causes loin pain but does not trigger nausea, vomiting, or pyloric sphincter pressure changes. This explains why acute obstruction from stones causes more severe gastrointestinal symptoms than chronic hydronephrosis.
Reproducible response: At 10-12 mL rapid renal pelvic distension, all subjects experience loin pain, epigastric pain, and nausea, with vomiting occurring in approximately 36% of cases.
Anesthetic blockade: When the renal pelvis or ureter is anesthetized, distension produces no gastric pressure changes and no nausea or vomiting, confirming the neural (rather than humoral or mechanical) nature of the reflex.
Anatomic specificity: The reflex affects only the pyloric sphincter and gastric corpus. No pressure changes occur in the lower esophageal sphincter or esophagus, which explains why patients with renal colic typically do not experience reflux symptoms.
Clinical Implications
This reflex pathway explains why NSAIDs are first-line treatment for renal colic 2. NSAIDs work by:
- Reducing inflammation and prostaglandin-mediated ureteral smooth muscle contraction
- Decreasing intrarenal pelvic pressure
- Breaking the cycle of distension that triggers the renogastric reflex
The reflex also explains why opioids, particularly pethidine, are associated with higher rates of vomiting compared to NSAIDs 2 - they provide analgesia but do not address the underlying distension and reflex activation.
Common Pitfall
Do not assume gastrointestinal symptoms in renal colic patients indicate a primary gastrointestinal pathology. The renogastric reflex is a direct consequence of urinary tract obstruction and will resolve with appropriate management of the stone and relief of obstruction.