Puberty alters renal water handling

Area of Science:

• Pediatric Endocrinology
• Circadian Biology
• Renal Physiology

Background:

• Circadian rhythms regulate numerous physiological processes, including fluid balance.
• Antidiuretic hormone (arginine vasopressin, AVP) plays a crucial role in water homeostasis.
• The influence of sex and puberty on circadian AVP regulation and urine production in children is not fully understood.

Purpose of the Study:

• To investigate the impact of sex and puberty stage on circadian urine production.
• To examine the relationship between circadian AVP levels and urine production in healthy children.
• To explore potential differences in renal water handling and AVP sensitivity between prepubertal and pubertal children.

Main Methods:

• A 24-hour inpatient study was conducted on 39 healthy children (prepuberty and midpuberty boys and girls).
• Standardized fluid and sodium intake was maintained throughout the study.
• Blood samples were collected every 4 hours for plasma AVP, estradiol, and testosterone measurements.
• Urine was fractionally collected for analysis of electrolytes, aquaporin-2 (AQP2), and PGE2.

Main Results:

• A significant nighttime decrease in diuresis was observed, driven by increased solute-free water reabsorption (TcH2O).
• Plasma AVP exhibited a circadian rhythm with a nighttime increase, independent of sex or puberty stage.
• Prepubertal children demonstrated significantly higher nighttime TcH2O and increased urinary AQP2 excretion, suggesting greater renal AVP sensitivity.

Conclusions:

• A circadian rhythm of plasma AVP exists in children, unaffected by sex or puberty stage.
• Prepubertal children exhibit enhanced nighttime renal water reabsorption and AVP-mediated water conservation.
• These findings suggest a higher renal sensitivity to AVP in prepubertal children compared to pubertal children.