Initial transient phase of salivary secretion by the submandibular glands of rats under anoxic conditions.

Salivary secretion of the rat submandibular gland exhibits two phases upon administration of acetylcholine (ACh, 10(-6) M): an immediate initial transient phase of rapid secretion lasting 5 min followed by a longer steady phase of slower secretion. Application of an anoxic perfusate bubbled with 100% N2 for 10-20 min had no effect on the initial phase of secretion, but caused a marked decrease in secretion in the steady phase following stimulation with 10(-6) M ACh. After secretion under the anoxic condition, a recovery period without stimulation was performed for 30 min by perfusion with HEPES Ringer's solution bubbled with 100% O2 and containing various potassium concentrations. The initial secretion rate measured with application of an anoxic perfusate was markedly increased by the high-K+ recovery perfusate (25 mM) and decreased by the K(+)-free recovery perfusate. Administration of 10(-3) M ouabain in the normal perfusate resulted in inhibition of secretion during the steady phase similar to that seen under the anoxic condition, while the secretory rate during the initial phase remained unchanged. We concluded that the initial phase of secretion is relatively resistant to anoxia, and that oxygen supply and Na(+)-K+ pump activity were essential for maintaining the steady phase of secretion.