Predominantly beta-adrenergic control of equine sweating.

This research studied how certain drugs impact sweating in horses and found that horse sweat glands are primarily controlled by beta-adrenergic signals, meaning it is mostly influenced by adrenaline-related processes, which differs from most other mammals.

Research Methodology and Findings

• The team carried out in vitro tests, meaning in a controlled environment outside of a living organism, with individual sweat glands from horses.
• They found that these glands could continue to secrete sweat for over an hour when stimulated with certain drugs, referred to as ‘pharmacologic secretagogues’.
• Two particular adrenergic agonists, epinephrine and norepinephrine, which are hormones that manage the body’s reaction to stress, were able to stimulate the glands to a maximal sweat rate.
• However, they found that the required concentration of norepinephrine to achieve this was 10 times higher than that for epinephrine.
• Another beta 2-adrenergic agonist, terbutaline, was also able to stimulate the maximal sweat rate. However, this could be blocked by the beta-adrenergic antagonist propranolol, a substance which counters the effects of adrenaline-likes substances on beta receptors.
• Moderate responses were also induced by alpha-adrenergic agonists, such as phenylephrine and methoxamine. These triggered responses were also blocked by propranolol.

Comparative Observations

• The muscarinic blocker atropine and the alpha-adrenergic antagonist phentolamine did not inhibit any sweat responses to the drugs. This suggests that these factors do not play a key role in equine sweat regulation.
• The researchers also noted that unlike many mammals, the horse’s sweat glands are not triggered by cholinergic agonists, chemicals which mimic the behaviour of acetylcholine, a neurotransmitter.
• Their findings indicate that equine sweat glands are predominantly under beta-adrenergic control, meaning these glands are influenced primarily by adrenaline-related processes.