AJP - Regulatory, Integrative and Comparative Physiology, Vol 256, Issue 4 816-R821, Copyright © 1989 by American Physiological Society
Role of rumen and saliva in the homeostatic response to rehydration in cattle
N. Silanikove
Migal-Galilee Technological Centre, Kiryat Shmona, Israel.
It has been shown recently that the circulation created by the continuous
secretion of voluminous amounts of saliva rich in Na+ to the large store of
fluid sequestered in the rumen and its reabsorption from the gut is an
integral part of water and Na+ homeostasis in cattle. The role of this
system in water and Na+ restitution following acute dehydration and rapid
rehydration was studied. Cattle were able to withstand dehydration of 18%
of their initial mass and to replenish their water losses in one drinking.
The water imbibed was first retained in the rumen and slowly released.
Rapid expansion (or dilution) of their blood as a result of large influxes
of hypotonic water from the rumen was prevented by a parallel increase in
the secretion of hypotonic saliva. The accelerated saliva secretion
refluxed back to the rumen almost half of the water absorbed. Saliva
electrolyte concentration varied simultaneously with an increase or
decrease in saliva flow. Na+, HCO3-, HPO3-, and pH were inversely related
to saliva flow rate while Cl and K+ were positively related. It seems that
visceral afferent response was involved in activation of salivary flow
rate.
