Renin-Angiotensin-aldosterone system and hypothalamic-pituitary-adrenal axis in hospitalized newborn foals.

The research investigates the activities of the renin-angiotensin-aldosterone system (RAAS) and hypothalamic-pituitary-adrenal axis (HPAA), two key physiological systems, in critically ill newborn horses (foals). The researchers hypothesized that the RAAS and HPAA show specific changes in activity in response to illness and high ACTH/cortisol and ACTH/aldosterone ratios in sick foals suggest adrenal insufficiency isn’t only restricted to a part of the adrenal gland (zona fasciculata).

Context and Purpose of the Study

• The connection between the renin-angiotensin-aldosterone system (RAAS) and the hypothalamic-pituitary-adrenal axis (HPAA) is vital to maintaining organ function in states of illness and low blood perfusion.
• Modifications in these systems, including HPAA dysfunction and relative adrenal insufficiency (RAI), have been seen in sick foals, particularly those with sepsis. However, less established data exists regarding the RAAS role and the response of a hormone called aldosterone within the context of RAI in these clients.
• Thus, this study aimed to examine these factors and their possible associations with specific clinical findings in hospitalized foals, with the premise that these foals’ critical illnesses would lead to an overactive RAAS and abnormally low aldosterone levels as part of their RAI.

Research Methods

• The study utilized a prospective, multicenter, cross-sectional design, focusing on 167 foals aged three days or less. The subjects were divided into groups of 133 hospitalized foals, 74 of which had sepsis, and 59 were sick without sepsis, and 34 healthy foals.
• Blood samples were taken from all subjects on admission. Key markers and hormones related to the RAAS and HPAA, including Plasma Renin Activity (PRA), Angiotensin-II (ANG-II), aldosterone, Adrenocorticotropic Hormone (ACTH), and cortisol, were measured in each sample.

Key Findings

• The results showed that markers ANG-II, aldosterone, ACTH, and cortisol, as well as the ACTH/aldosterone and ACTH/cortisol ratios, were generally higher in septic foals than healthy ones.
• No significant difference was found in the PRA between the different groups.
• The data also suggested associations between high serum potassium and low serum chloride levels on one hand and excessive aldosterone levels (hyperaldosteronemia) on the other in septic foals.

Concluding Observations and Implications

• The study concluded that an activated RAAS in critically ill foals is marked by increased ANG-II and aldosterone concentrations.
• High ACTH/cortisol and ACTH/aldosterone ratios suggesting adrenal insufficiency in these foals were not limited to the zona fasciculata (a central region of the adrenal glands), contradicting previous beliefs.
• This finding could be significant in understanding and addressing the impact of critical illnesses on foals, possibly leading to improved treatment strategies.