Influence of x-rays on diurnal viration in 131I uptake by guinea pig thyroid.

The 131I uptake by guinea pig thyroid is subject to distinct diurnal variation. In control males, peak values occurred at 12 h, and minima at 24 h. In control females, peak values were also at 12 h, but minima at 6 h. In guinea pigs irradiated with 500 R of X-rays, a rise in 131I uptake began 1 h after termination of irradiation in both sexes and at all intervals, but maximum and minimum values were at the same time as in controls.