Hormonal changes after supine posture, immersion, and swimming.

Area of Science:

• Physiology
• Endocrinology
• Exercise Science

Background:

• Hydrosaline equilibrium is crucial for maintaining bodily fluid balance.
• Hormonal regulation, including atrial natriuretic peptide (ANP), arginine vasopressin (AVP), plasma renin activity (PRA), and aldosterone (ALDO), plays a key role in this balance.
• The effects of different physical activities and postures on these hormones are not fully understood.

Purpose of the Study:

• To investigate the impact of supine posture, water immersion, and swimming on key hormones regulating hydrosaline equilibrium.
• To compare the hormonal responses to passive immersion versus active swimming.
• To explore correlations between hormonal changes and hematocrit levels.

Main Methods:

• Eight untrained young adults (5 males, 3 females) participated in the study.
• Hormone levels (ANP, AVP, PRA, ALDO) were measured using radioimmunoassay.
• Blood samples were collected under control (standing), after 20 minutes of supine rest, 20 minutes of water immersion (28°C), and 20 minutes of backstroke swimming.

Main Results:

• Arginine vasopressin (AVP) levels did not change significantly with any intervention.
• Aldosterone (ALDO) and plasma renin activity (PRA) significantly increased only after swimming and were positively correlated.
• Atrial natriuretic peptide (ANP) significantly increased after immersion, with no further increase after swimming. Post-swimming hematocrit was inversely correlated with ANP.

Conclusions:

• Moderate-intensity swimming is sufficient to elevate aldosterone and plasma renin activity.
• Atrial natriuretic peptide response is primarily stimulated by water immersion, with higher intensities potentially needed for further increases.
• Different physical activities elicit distinct hormonal responses influencing hydrosaline balance.