Congenital abnormality of pituitary-thyroid axis in spontaneously hypertensive rats (SHR) and stroke-prone rats (SPR)

In an attempt to study whether TSH abnormality was genetically determined in SHR and SPR, plasma T4, T3, TSH and prolactin concentrations were measured in the animals with intervals of 1 to 3 months. Hypertension was found in 6-month-old SHR and SPR, but it was not found in younger animals. In contrast, a decrease of plasma T3 and an increase of plasma TSH were found in 15-day-old SHR. Also, an increase of TSH was found in 1-month-old SPR in spite of normal plasma T3 concentration. These abnormalities in SHR and SPR increased progressively with age. It is suggested that thyroid-pituitary abnormality was genetically determined in SHR and SPR.