Drinking in the rhesus monkey: peripheral factors.

Area of Science:

• Physiology
• Neuroscience
• Animal Behavior

Background:

• Understanding the physiological mechanisms that regulate thirst and drinking behavior is essential for comprehending homeostatic processes.
• Previous research suggests that both sensory input from the oropharyngeal region and gastric distension play roles in satiety, but the precise contributions remain debated.

Purpose of the Study:

• To investigate the role of oropharyngeal, gastric, and intestinal factors in the termination of drinking behavior in rhesus monkeys.
• To determine if signals originating beyond the stomach are necessary for inhibiting continued water intake.

Main Methods:

• Rhesus monkeys were surgically prepared with chronic cannulae in the stomach and duodenum.
• Water intake was measured under conditions of free drinking, gastric drainage (sham drinking), and duodenal drainage (sham drinking).
• Duodenal infusions of water and saline were administered to assess their effects on sham drinking.

Main Results:

• Free drinking resulted in a mean intake of 137 ml.
• Gastric and duodenal sham drinking led to significantly increased water intake (878 ml and 634 ml, respectively), indicating insufficient satiety signals from the mouth and stomach alone.
• Duodenal water infusions dose-dependently inhibited sham drinking, while saline had no effect, suggesting a specific role for water absorption or osmolality in the distal intestine.

Conclusions:

• Oropharyngeal stimulation and gastric passage of water are insufficient to terminate drinking in rhesus monkeys.
• Post-absorptive signals originating in the intestine, distal to the duodenum, are critical for inhibiting excessive water intake.
• These findings highlight the complex interplay of sensory and post-absorptive cues in regulating fluid homeostasis.