Predominantly beta-adrenergic control of equine sweating

Area of Science:

• Physiology
• Pharmacology
• Equine Science

Background:

• Sweat secretion is vital for thermoregulation in horses.
• The precise physiological control mechanisms of equine sweat glands are not fully understood.
• Most mammalian exocrine glands are regulated by cholinergic pathways.

Purpose of the Study:

• To investigate the pharmacological control of equine sweat gland secretion.
• To determine the role of adrenergic and cholinergic pathways in stimulating sweat production in horses.
• To elucidate the predominant signaling pathway regulating equine sweat secretion.

Main Methods:

• In vitro studies using single equine sweat glands.
• Application of various adrenergic agonists (epinephrine, norepinephrine, terbutaline, phenylephrine, methoxamine) and antagonists (propranolol, phentolamine).
• Assessment of sweat rates in response to different pharmacologic agents, including cholinergic agonists and antagonists (atropine).

Main Results:

• Equine sweat glands secreted continuously for over an hour in response to secretagogues.
• Epinephrine and norepinephrine evoked maximal sweat rates (2.0 nl x gland-1 x min-1), with norepinephrine requiring a 10-fold higher concentration.
• Beta-adrenergic stimulation (terbutaline) induced maximal sweating, blocked by propranolol, while alpha-adrenergic agonists showed moderate responses also blocked by propranolol. Cholinergic agonists were ineffective.

Conclusions:

• Equine sweat glands are predominantly under beta-adrenergic control.
• Unlike most mammals, equine sweat secretion is not significantly stimulated by cholinergic agonists.
• This study identifies beta-adrenergic pathways as the primary regulators of sweat production in horses, crucial for understanding equine thermoregulation.