Relationship between epidermal growth factor in mouse submandibular glands, plasma, and bile: effects of...

The epidermal growth factor (EGF) concentration in bile is high (approximately 150 fold higher than that in plasma), but little is known about its physiological control. Acute administration of the alpha 1-adrenergic agonist phenylephrine (1.7 mg/kg, iv) to male mice produced a rapid increase in the EGF concentration in bile. We suggest that this EGF originates in submandibular glands and not in the liver. The bases for this are: 1) this increase was parallel to the increase in plasma, and the EGF content of the submandibular glands decreased after phenylephrine injection; and 2) the EGF concentrations in plasma and bile did not increase after phenylephrine administration to sialoadenalectomized mice. The concentration of EGF in bile is not only under pharmacological control, but is also regulated physiologically. Thus, the EGF concentrations in plasma, bile, and submandibular glands increased in fasted mice. All of these changes were reversed by refeeding. As 1) [125I]EGF binding to liver membranes decreased only after 2 days of fasting, but the level of circulating EGF was already increased in 1-day fasted mice, and 2) EGF secretion by submandibular glands from 1-day fasted mice incubated in vitro increased, we suggest that the increase in EGF concentrations in plasma and bile is the consequence of increased endocrine secretion by submandibular glands. Taken together, our results suggest that there is a flux of EGF from submandibular glands to bile in mice, which is under physiological control.