Predominantly beta-adrenergic control of equine sweating.

Single equine sweat glands were found to secrete for more than 1 h in vitro in response to pharmacologic secretagogues. The adrenergic agonists epinephrine and norepinephrine evoked maximal sweat rates of 2.0 nl X gland-1 X min-1. However, the concentration of norepinephrine (10(-5) M) required to evoke the maximal response was 10 times higher than that for epinephrine. Maximal sweat rates also were stimulated with the beta 2-adrenergic agonist terbutaline. This stimulation was blocked by the beta-adrenergic antagonist propranolol. Moderate sweating responses were also obtained with the alpha-adrenergic agonists phenylephrine and methoxamine, but these responses also were blocked by propranolol. Neither the muscarinic blocker atropine nor the alpha-adrenergic antagonist phentolamine inhibited any of the pharmacologically induced sweat responses. Unlike most other mammalian exocrine glands, cholinergic agonists were ineffective in stimulating sweat secretion. Therefore equine sweat glands apparently are under predominantly beta-adrenergic control.