INFLUENCE OF THE POSTERIOR PITUITARY HORMONE ON THE THYROIDAL IODIDE PUMP AND ¹³¹I UPTAKE

Abstract

The effect of Pitressin on the thyroidal function was studied using the T/S ratio, thyroidal ¹³¹I uptake at 3-hour interval and the histological examination.
The T/S of rats intraperitoneally injected with 60mU of Pitressin per 100g body weight was not different from the control value 24 hours after the injection at 20°C. A single dose of Pitressin in the same amount given shortly before the T/S measurement showed no effect either.
The administration of peanut oil once daily for 3 days, which was used for the vehicle for Pitressin tannate, resulted in an enlargement of thyroid and an increase in the T/S ratio, however, Pitressin tannate in oil in a dose of 100mU per 100g body weight did not elevate the T/S ratio further or increase the thyroid weight above those of the rats treated with the vehicle only.
The exposure of rats to cold environment, 10°C, for 1 week, caused a marked increase in the T/S as well as the thyroid weight.Pitressin in a dose of 40mU per 100g body weight twice daily during the period of cold exposure resulted in a suppression on the rise of T/S due to the cold exposure. This result well coincided with the findings in the histological examination.
Pitressin in a dose of 100mU or 25mU per rat failed to modify the 3-hour interval ¹³¹I uptakely by rat's thyroid glands.