Sympatho-adrenal activity and the clinical sedative effect of detomidine in horses.

This study investigated how the sedative drug detomidine affects the behavior and certain hormone levels in horses. Results showed that detomidine significantly reduced stress hormones and their metabolites, with higher initial stress levels corresponding to reduced sedative effects.

Study Context and Design

• The study involved forty-five horses, with thirty-nine of them receiving an intravenous injection of detomidine, a sedative drug, while the other six received saline as a control group.
• This was done prior to minor procedures, and then blood samples were collected immediately before and 20 minutes after the treatment to measure hormone levels.
• The behavior of each horse and the degree of sedation were observed and recorded at the time of detomidine injection.

Impact of Detomidine on Hormone Levels

• The researchers found that administration of detomidine led to a significant decrease in the following substances in the horses’ blood: adrenaline, noradrenaline (both stress hormones), two derivatives of these hormones (DHPG and DOPAC), and cortisol (another stress hormone).
• In contrast, these measures remained constant in the control group that received the saline injection instead of detomidine.

Initial Stress Levels and Sedative Effectiveness

• The researchers also noted that horses with higher adrenaline levels before receiving the detomidine injection, exhibited a diminished sedative effect. This indicates a correlation between an animal’s initial stress level and the effectiveness of a sedative drug.

The Role of Catecholamines in Sedation

• The study also found a relationship between the degree of sedation and the concentrations of adrenaline, noradrenaline and DHPG in plasma after detomidine injection.
• The reduction in levels of these hormones might have been partially caused by decreased secretion due to the calming effects of detomidine. However, the researchers suggest that detomidine might also act directly on sympatho-adrenal activity, leading to a decrease in catecholamine levels.

In conclusion, detomidine affects both hormone levels and sedative effectiveness in horses, with intial stress levels also playing a significant role in the sedative’s effectiveness.