Effect of irradiation on mouse salivary glands during the prereplicative phase of isoproterenol-stimulated DNA synthesis.

When mice were given a single injection of isoproterenol (IPR), the salivary gland cells were stimulated to enter DNA synthesis in a fairly synchronous manner after a lag period of about 18 hr. γ-ray irradiation of these cells in the early prereplicative phase effectively inhibited the stimulation of DNA synthesis caused by IPR. However, irradiation in the late prereplicative phase or in mid-DNA synthesis phase was less effective in inhibiting IPR-stimulated DNA synthesis. The administration of a sialogog, pilocarpine, prior to irradiation did not affect the inhibitory effect of irradiation on the response of salivary gland cells to IPR. These results indicate that the highly radiosensitive phase, 1 hr after the second injection of IPR, was not related only to the ability of IPR to produce secretion in the salivary glands but was related rather to the early biochemical events leading to DNA synthesis in salivary gland cells.