Hypothyroidism alters hormonal profiles in virgin, pregnant and lactating rats and impairs lactation

HAPON MB,; SIMONCINI M,; VIA G,; JAHN GA.

REPRODUCTION

BioScientifica

Lugar: Bristol UK; Año: 2003 vol. 126 p. 371 - 382

1470-1626

Thyroid dysfunctions produce reproductive problems. Untreated maternal hypothyroidism has serious consequences in offspring development, resulting in stunted growth and mental retardation. We studied the effects of propylthiouracyl (PTU)-induced hypothyroidism (0.1 % in drinking water starting 8 days before mating, or given to virgin rats during 30 or 50 days) on the serum profile of hormones related to reproduction and mammary function (PRL, GH, progesterone, corticosterone, estradiol, IGF-I, TSH, T3 and T4), and mammary function in virgin, pregnant and lactating rats. PTU treatment severely reduced circulating T3 and T4 and elevated serum TSH. Virgin rats showed prolonged periods of vaginal dioestrus, elevated circulating progesterone and afternoon PRL peaks suggestive of a PRL-induced pseudopregnancy. PTU treated virgin rats had mammary development comparable to midpregnancy, and half of them had elevated mammary casein and lactose. Serum PRL levels were diminished on the afternoon of day 5 of pregnancy, increased during late pregnancy (days 15 to 21), and normal during lactation. Circulating GH decreased on days 15 to 21 of pregnancy while progesterone levels increased on late pregnancy and early lactation. Circulating estradiol (measured on late pregnancy and in virgins), IGF-I and corticosterone were decreased. While mammary histology showed no differences in degreee of development, casein content was increased in PTU-treated rats on day 21 of pregnancy. Litter growth was severely reduced and the pups, at 20 days of age, were hypothyroid, with decreased GH serum levels. To determine whether some impairment in mammary function or the suckling reflex may account for this, we performed an acute suckling experiment on days 10-12 of lactation. After 8 hs separation of the mothers from the litters and 30 min of suckling, circulating PRL values were not affected by PTU, but serum oxytocin and milk excretion were diminished. In conclusion, hypothyroidism induces various alterations in the hormonal profile of virgin and pregnant rats, and induces pseudopregnancies and mammary development in virgin rats. These alterations do not seem to have overt impact on the outcome of pregnancy and on mammary function during lactation with the exception of the milk ejection reflex that may account at least partially for the diminished litter growth.