Effect of alpha- and beta-adrenergic agonists on fluid and calcium secretion by rat salivary glands

The separate roles of alpha- and beta-adrenergic receptors in regulating fluid and calcium (Ca) secretion by rat salivary glands were examined using phenylephrine (PE), an adrenergic agonist that acts predominantly on alpha-receptors, isoproterenol (ISO), an adrenergic agonist that acts predominantly on beta-receptors, and PE and ISO in combination with beta-adrenergic antagonist propranolol (PROP) and alpha-adrenergic antagonist phentolamine (PHENTO), respectively. PE evoked a greater volume of saliva from submandibular (SM) gland than from parotid (PA) gland, whereas ISO evoked a similar volume of saliva from both glands during 60-min of drug stimulation. PE even at a low dose had beta-adrenergic effects on flow rate of salivary glands because pretreatment of rats with PROP (1 mg/kg) 20 min before PE (5 mg/kg, i.p.) stimulation resulted in a 4-fold reduction in total volume of PE-evoked PA saliva. Thus alpha-adrenergic receptors play a major role in fluid secretion by SM glands but play only a minor role in PA glands. ISO evoked SM and PA saliva with Ca concentration higher than that evoked by PE. ISO (25 mg/kg, i.p.) also had an effect on alpha-adrenergic receptors as well as beta-adrenergic receptors. Although PHENTO did not significantly alter flow rate and volume of ISO-evoked PA or SM saliva, Ca concentration of ISO-evoked saliva was greatly potentiated by PHENTO. Total Ca output of ISO-evoked saliva from either gland was not significantly altered by PHENTO. Thus, in both salivary glands, activation of beta-adrenergic receptors evoked saliva with a high concentration of Ca.(ABSTRACT TRUNCATED AT 250 WORDS)