Neonatal glucocorticoid overexposure alters cardiovascular function in young adult horses in a sex-linked manner.

This research examines the impact of excessive cortisol exposure in the neonatal period on the cardiovascular function of young adult horses, highlighting significant differences in the effects experienced by males and females.

Background to the Study

• The analysis originates from previous studies proving that overexposure of an unborn organism to glucocorticoids can program the cardiovascular function once the organism reaches adulthood.
• In horses, hormonal changes that happen late into pregnancy play a vital role in the development of the foetus. This includes an increase in cortisol production post-birth, particularly in premature and underdeveloped foals.

Research Method

• The researchers exposed full-term male and female ponies during the neonatal period to high levels of cortisol through the administration of the hormone adrenocorticotropic (ACTH).
• When the ponies reached 2-3 years of age, their cardiovascular performance was tested through a series of procedures, including measurements of basal arterial blood pressure and heart rate, and responses to the drugs phenylephrine (PE) and sodium nitroprusside (SNP). This testing allowed assessment of cardiac baroreflex sensitivity – an important measure of cardiovascular function.

Findings and Implications

• Researchers discovered that males who had been exposed to high levels of cortisol in the neonatal period displayed a reduced reaction to PE, evidenced through both decreased blood pressure response and reduced slowing of the heart rate. This reaction was not observed in the female horses.
• In females, however, increased cortisol exposure was associated with an increased initial blood pressure drop response to SNP, a slower recovery of blood pressure after infusion, and a decrease in baroreflex sensitivity. These responses were not observed in the corresponding male group.
• The study confirmed that exposure to elevated levels of cortisol during the neonatal period has long-term effects on the cardiovascular health of young adult horses and that these effects are sex-specific.
• This research therefore highlights the impact of neonatal stress events on long-term health and emphasizes the importance of early life developmental conditions and their potential long-term biological implications.