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Parotid secretion patterns during meals and their relationships to the tonicity of body fluids and to gastrin and pancreatic polypeptide in sheep

Published online by Cambridge University Press:  09 March 2007

Richard R. Carter ,
W. Larry Grovum  and
Gordon R. Greenberg
Richard R. Carter
Affiliation:
Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, Ontario NIG 2W1, Canada
W. Larry Grovum
Affiliation:
Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, Ontario NIG 2W1, Canada
Gordon R. Greenberg
Affiliation:
Faculty of Medicine, Clinical Sciences Division, University of Toronto, Ontario M5S 1A8, Canada
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Abstract

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The flow pattern of unilateral parotid saliva in sheep was compared when a total of 800 g lucerne (Medicago sativa) hay was offered as one, two, four or eight distinct meals. These patterns were related to changes in the tonicity of rumen fluid and plasma and to plasma concentrations of gastrin and pancreatic polypeptide. Sheep having ad lib access to hay overnight were offered fresh hay from 08.00 to 09.00 hours and were then given one, two, four or eight meals of fresh hay according to a schedule such that the mean deprivation period was 6.5 h for each meal frequency-size. Neither the peak in saliva flow rate nor the time of this peak differed among the different meal sizes. The flow rate decreased rapidly after reaching a maximum at 3.2 min into the meal. After 7 min of eating, the tonicity of plasma and rumen fluid had increased by only 2.2 and 8.2 mosmol/kg respectively. These increases would not cause the rapid decline in parotid flow observed after 3.2 min of eating. There was no postprandial change in the concentration of gastrin in jugular plasma. However, it did increase significantly (P = 0.0043) from 16 to 4 min before eating commenced. There was a postprandial peak in plasma pancreatic polypeptide concentration after 4.5 min of eating. However, the parotid flow rate remained low after the concentration of this peptide returned to prefeeding levels. The rapid decrease in parotid secretion rate observed early in the meal may be due to subsiding central excitation rather than to an inhibitory factor limiting production.

Keywords

GastrinPancreatic polypeptideSalivaSheep
Type
Feeding Behaviour and Metabolism
Information
British Journal of Nutrition , Volume 63 , Issue 2 , March 1990 , pp. 319 - 327
Copyright
Copyright © The Nutrition Society 1990

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