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Thirst and vasopressin secretion counteract dehydration in newborn infants
1Department of Women and Child Health, Karolinska Hospital, Stockholm, Sweden.
Insights
Newborns with over 10% body weight loss show increased vasopressin secretion due to hypertonicity, impacting feeding behavior. This hormonal response is likely triggered even with less weight reduction, indicating a physiological adaptation to fluid balance challenges in infants.
Area of Science:
- Neonatal Physiology
- Endocrinology
- Pediatric Hydration
Background:
- Understanding water balance in the first few days of life is crucial for infant health.
- Breast-fed infants undergo physiological changes in body weight and fluid status post-birth.
Purpose of the Study:
- To investigate the water balance in healthy, breast-fed infants during the first five days of life.
- To assess the role of vasopressin in conserving body water in response to dehydration.
Main Methods:
- Cross-sectional measurements of body weight, serum sodium, serum osmolality, and hematocrit in 139 healthy breast-fed infants.
- Measurement of plasma vasopressin levels to evaluate the antidiuretic hormone response.
Main Results:
- Maximal body weight reduction was 5.7%; infants typically began gaining weight by day 3.
- Serum sodium and osmolality increased significantly after day 1, indicating a hyperosmotic state.
- Infants with >10% weight reduction exhibited elevated serum sodium, osmolality, and twofold higher vasopressin levels, alongside reduced feeding intervals.
Conclusions:
- Newborns release vasopressin in response to hypertonicity when body weight reduction exceeds 10%.
- This physiological response, likely including thirst-driven feeding behavior changes, may also occur with lesser weight reduction.
- The findings highlight the infant's adaptive mechanisms for maintaining fluid homeostasis.
Objective And Study Design:
Our goal was to study the water balance in healthy breast-fed infants (n = 139) during their first 5 days, by cross-sectional measurements of body weight, serum sodium, serum osmolality, and hematocrit. We also investigated infants' capacity to conserve body water by increased secretion of vasopressin, the main antidiuretic hormone in human beings.
Results:
The maximal body weight reduction was 5.7% +/- 1.7% (mean +/- SD) of birth weight and most infants started to gain weight when they were 3 days old. The serum sodium level at 16 +/- 4 hours (on day of birth) was 142 mmol/L; the level increased after 1 day (p < 0.01) and remained constantly high for the following 2 days (p < 0.05). The serum osmolality was increased at 1 day (p < 0.01) and 2 days (p < 0.05) compared with the value on the day of birth (296 mOsm/kg). The plasma vasopressin level was constant up to 24 hours (1 day), but decreased during the next 2 days (p < 0.01). Infants with body weight reduction exceeding 10% (n = 15) had a further elevation of the serum sodium level (p < 0.0001) and serum osmolality (p < 0.0001), and the plasma vasopressin level was twofold higher (p < 0.0001) compared with corresponding levels in infants with less weight reduction. These infants also had a reduced interval between two subsequent feedings (p < 0.001). The hematocrit remained unchanged irrespective of the degree of weight reduction.
Conclusions:
When the reduction of body weight exceeds 10%, the newborn infant releases vasopressin in response to fluid hypertonicity. This state also affects feeding behavior, perhaps as an expression of thirst. It is likely that hormone release is also stimulated in parallel with a weight reduction of less than 10%, because it is also accompanied by a hyperosmotic state.