Quantification of the response of equine apocrine sweat glands to beta2-adrenergic stimulation.

This research focused on understanding how horses react to a chemical that stimulates sweating. The scientists found that certain concentrations of this stimulant resulted in a peak sweat rate, but higher concentrations led to decreasing amounts of sweat production. This implies that horse sweat glands may operate under a combination of hormonal and neural controls.

Experiment and Methodology

• The study involved the observation of the sweating responses in 6 horses. The horses were subjected to randomly infused concentrations of adrenaline.
• Eight different levels of adrenaline concentrations were used. The focus was on the response of equine apocrine sweat glands, a particular type of sweat gland found in horses, to these adrenaline doses.
• Parameters such as the sweating rate, skin temperature on the neck and gluteal region, and plasma concentrations of adrenaline and noradrenaline (another stimulant) were measured.

Findings and Interpretation

• It was found that the peak sweating rate was approximately 15 g/m2/min on the neck and roughly 9 g/m2/min in the gluteal region during the infusion of 1.0 and 2.0 microg/kg bwt/min adrenaline.
• Sweat production per nmol/l plasma adrenaline peaked when 0.075 microg/kg bwt/min adrenaline was administered. However, higher concentrations of adrenaline infusion led to a decrease in the amount of sweat produced.
• For infusions between 1.0 and 2.0 microg/kg bwt/min, a plateau of about 6 g/m2/(nmol/l) plasma adrenaline was noted.
• The peak sweat rates observed during this experiment were significantly lower than those reported in previous studies on horse sweat rates during exercise.

Conclusions

• In conclusion, the study found no evidence of sweat gland fatigue or vasoconstriction during the adrenaline infusion, implying that the sweat glands might have reached their maximum capacity—indicating possible saturation of sweat gland beta2 receptors.
• These findings suggest that the sweating mechanism in horses involves a combination of hormonal and neural controls, which provide dual controls over the process.