Localization and secretion of epidermal growth factor in the parotid gland and its intragastric kinetics in sheep.
Ruminants secrete a large quantity of saliva that is rich in electrolytes; however, it remains unclear whether their parotid saliva contains epidermal growth factor (EGF). The present study was set up to examine the distribution of EGF and transforming growth factor-alpha (TGF-alpha) in the ovine parotid and submandibular glands and the salivary secretion of EGF-like binding activity (EGF-LBA) as the sum of EGF and TGF-alpha in conscious sheep. We also measured changes in the intragastric concentration of EGF-LBA in the ovine rumen and abomasum, and examined the effect of bilateral diversion of parotid saliva on intragastric EGF-LBA concentration in sheep. Both the ovine parotid and, to a lesser extent, the submandibular glands contained EGF-LBA. Immunohistochemical study showed that EGF and TGF-alpha-immunoreactivities were localized in the ductal epithelium in both glands. Transcriptional expression of EGF and TGF-alpha mRNA was demonstrated in both glands by reverse transcription-polymerase chain reaction (RT-PCR). In conscious sheep, the parotid gland continuously secreted EGF-LBA in the saliva before feeding, and the secretion of parotid EGF-LBA was markedly increased during feeding. After diversion of the parotid saliva for 1 week, EGF-LBA concentration in the ruminal fluid, but not in the abomasal fluid, decreased in the postprandial period, indicating that parotid EGF-LBA is a primary source of EGF-LBA for the rumen fluid during the postprandial period in sheep. Moreover, RT-PCR detected the expression of TGF-alpha mRNA in the rumen and abomasum and that of EGF in the abomasum, implying that these stomachs possibly supply, in part, EGF-LBA to the luminal fluid.
Onaga
Takenori
T
Veterinary Physiology, Department of Biosciences, School of Veterinary Medicine, Rakuno Gakuen University, Japan. onaga@rakuno.ac.jp
Shimizu
Yasuhito
Y
Hayashi
Hideaki
H
Tsuji
Masayoshi
M
Endoh
Daiji
D
Okada
Hiroyuki
H
D000018:Abomasum / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002851:Chromatography, High Pressure Liquid; D004815:Epidermal Growth Factor / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D019084:Fluorescent Antibody Technique, Indirect; D015870:Gene Expression; D007124:Immunoenzyme Techniques; D008297:Male; D010306:Parotid Gland / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012417:Rumen / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D012463:Saliva / Q000737:chemistry / Q000378:metabolism; D012756:Sheep; D013363:Submandibular Gland / Q000378:metabolism; D016211:Transforming Growth Factor alpha / Q000032:analysis / Q000235:genetics / Q000378:metabolism
D012333:RNA, Messenger; D016211:Transforming Growth Factor alpha; D004815:Epidermal Growth Factor