Daily patterns of vasopressin levels in the brain’s internal clock area of rats

Arginine-vasopressin (AVP) levels in the suprachiasmatic nucleus showed a circadian rhythm peaking during the early light phase.

• AVP exhibited a broad trough in levels during the dark phase under light-dark conditions.
• Circadian rhythmicity of AVP was maintained after 14 days in constant dark and 3 days in constant light.
• The patterns of AVP levels were similar to those of somatostatin, suggesting a shared regulatory mechanism for these peptides in the SCN.

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