Triiodothyronine-induced hyperthyroidism and reproduction in female rats.
The effect of L-triiodothyronine (L-T3)-induced hyperthyroidism on reproduction in female rats was studied. Treatment groups used were normal control, 1, 2, 4, 8, and 16 micrograms L-T3/100 g body weight (b.w.)/day. Subcutaneous injections of L-T3 began the first day of estrus until day 1 or day 19 of lactation. All rats given 1, 2, or 4 micrograms L-T3 had regular estrous cycles and normal number of pregnancies. Levels of L-T3 at 8 or 16 micrograms results in abnormal estrous cycles. Only one pregnancy occurred in the 8 micrograms group and no rats became pregnant in the 16 micrograms group. While groups on 1 or 2 micrograms L-T3 had normal parturition, groups on 4 micrograms or more showed signs of dystocia. Only the 1 microgram L-T3 group lactated to day 20, but at 67% of normal control. All levels above 1 micrograms showed loss of pups by day 2 of lactation due to lack of milk production, loss of maternal behavior, and cannibalism. Mammary gland wet and dried fat-free tissue (DFFT) weights were decreased in all treated groups except 1 microgram L-T3. The wet and DFFT weights of thyroids and uteri on days 2 or 20 of lactation were not altered by L-T3 treatment, but levels above 1 microgram increased both wet and DFFT weights of adrenal glands and ovaries. The data indicate that the no observed adverse effect level (NOAEL) of L-T3 for female rat reproduction would be below 1 microgram/100 g b.w./day. L-T3 treatment at 1 microgram/100 b.w./day or above is detrimental. These effects may be mediated through a hormonal imbalance due to the accelerated metabolic rate in reproductive tissues associated with hyperthyroidism.
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Department of Dairy Husbandry, University of Missouri-Columbia 65211, USA.
Anderson
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D000311:Adrenal Glands / Q000033:anatomy & histology / Q000737:chemistry / Q000187:drug effects; D000818:Animals; D001835:Body Weight / Q000187:drug effects; D004247:DNA / Q000032:analysis; D004305:Dose-Response Relationship, Drug; D004971:Estrus / Q000187:drug effects; D005260:Female; D006980:Hyperthyroidism / Q000139:chemically induced*; D007743:Labor, Obstetric / Q000187:drug effects; D007774:Lactation / Q000187:drug effects; D008321:Mammary Glands, Animal / Q000033:anatomy & histology / Q000737:chemistry / Q000187:drug effects; D008425:Maternal Behavior / Q000187:drug effects; D009929:Organ Size / Q000187:drug effects; D010053:Ovary / Q000033:anatomy & histology / Q000737:chemistry / Q000187:drug effects; D011247:Pregnancy; D011248:Pregnancy Complications / Q000139:chemically induced; D011270:Pregnancy, Animal / Q000187:drug effects*; D012313:RNA / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D012098:Reproduction / Q000187:drug effects*; D014284:Triiodothyronine / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*; D014599:Uterus / Q000033:anatomy & histology / Q000737:chemistry / Q000187:drug effects
D014284:Triiodothyronine; D012313:RNA; D004247:DNA