The expression of two forms of PRL receptor messenger RNA was measured at different stages of pregnancy and lactation in mammary gland and liver from Sprague-Dawley rats, using 32P-labeled complementary DNA probes encoding the extracellular part of the receptor (E probe), common to the two forms and a probe encoding the intracellular part of the long form of the receptor (I probe), that only recognizes sequences specific to the long form of the receptor. Hybridizations were performed in Northern blots obtained from electrophoreses of poly (A+) enriched RNA preparations from mammary glands and livers of rats on days 0, 6, 12, 19, and 21 of pregnancy and 5, 10, 15, and 20 of lactation. The Northern blots were also hybridized with a chicken beta-actin probe, to correct for the amount of mRNA added and the different metabolic states of the tissues. Both tissues expressed the same forms of PRL receptor mRNAs, namely bands at 2.5, 3, and 5.5 kilobases encoding the long form of the receptor and a major band at 1.8 kilobases encoding the short form. The liver expressed all the receptor mRNA forms in much higher quantity than the mammary gland, independent of the reproductive state. In liver there was an increase of all the transcripts on day 19 of pregnancy, followed by an abrupt decline at the onset of lactation, to levels lower than those of virgin rats. In contrast, mammary gland PRL receptor mRNAs were low in virgin and pregnant animals, increased significantly at day 21 of pregnancy, and continued to increase throughout lactation. Treatment of day 19 pregnant rats with the antiprogesterone RU 486 induced, 24 h later, PRL receptor mRNAs in mammary gland but not in liver. There were no significant differences in the relative proportions of long to short forms of PRL receptor mRNAs at the different reproductive states, but the proportion of the long form was slightly greater in mammary gland than in liver. Membrane PRL receptor concentrations were also measured in the same tissues used for the mRNA study by binding to a 125I-labeled monoclonal antibody (U5), which specifically recognizes the PRL receptor at a site different from the hormone binding site. The quantity of receptor measured by U5 binding was approximately 3 times higher than that measured with 125I-labeled ovine PRL.(ABSTRACT TRUNCATED AT 400 WORDS)

Untreated maternal hypothyroidism (hypoT) has serious consequences in offspring development that may result from the effect on lactation of maternal metabolism dysfunction. We studied the effects of prolonged propylthiouracyl (PTU)-induced hypoT (0.1% PTU in drinking water starting 8 days before mating until day 21 of pregnancy or for 30 days in virgin rats) on liver and mammary lipid metabolism and serum lipid concentrations. In virgins, hypoT reduced hepatic mRNAs associated with triglyceride (TG) and cholesterol synthesis (including fatty acid synthase and 3-hydroxy-3-methylglutaryl coenzyme A reductase), and induced lobuloalveolar mammary development. Thyroid hormones influence all major metabolic pathways. Their most obvious and well-known action is an increase in basal energy expenditure through actions on protein, carbohydrate, and lipid metabolism. With specific regard to liver lipid metabolism, thyroid hormones stimulate fatty acid and cholesterol synthesis (1, 2), increase mobilization of plasma cholesterol and triglycerides (TGs) (3, 4), and stimulate fatty acid and cholesterol degradation (5, 6). Disturbances in thyroid function are commonly associated with alterations in plasma lipid levels. Experimental hypothyroidism (hypoT) induced by propylthiouracyl (PTU) treatment is characterized by the accumulation of plasma LDL cholesterol, and decreased VLDL and plasma TGs (7), generally reflecting reduced binding activity of the hepatic LDL receptor (LDLR), which can be normalized after substitution therapy with thyroid hormone (3,8).Pregnancy is a state of dynamic changes in metabolism and nutrient utilization. The insulin-resistant condition and the increase in plasma estrogen levels occurring during late pregnancy are the main factors responsible for the development of a state of maternal hypertriglyceridemia that has been extensively studied in humans and rats (9)(10)(11). This condition benefits the progeny in two ways. First, it supplies essential fatty acids that are critical to normal fetal development and that circulate primarily esterified and associated with lipoproteins. A linear correlation between maternal and fetal plasma TGs has been described that has an important implication in newborn weight (12, 13). Second, it contributes to milk synthesis in preparation for lactation, providing circulating TG in the form of lipoprotein to the mammary gland (MG) for milk lipid synthesis (9).It has been demonstrated that the induction of hypothyroidism in dairy cows suppresses milk production during the treatment period (14). On the other hand, ad-

We studied the effects of daily administration of 1 mg/kg thyroxine (T4) starting 10\p=n-\15 days before mating, on parturition, maternal behavior and lactation in rats. Treated rats had elevated serum titers of T3 and T4, a greater number of fetuses and parturition was advanced approximately 12 h and lasted longer than in controls. None of the treated rats were able to lactate because of defects in maternal behavior and milk ejection; the litters died usually within 48 h postpartum. In rats sacrificed at 10.00 on day 21 of pregnancy, mammary gland content of total protein, phospholipids, casein and lactose were significantly increased, but total lipid was markedly reduced. Lipogenesis was also significantly increased, as well as the activity of the lipogenic enzymes glucose-6-phosphate dehydrogenase, fatty acid synthetase and isocytrate dehydrogenase. These results are indicative of normal albeit premature

BackgroundRats made hypothyroid with propilthyouracil start showing abnormal cycling on the second cycle after the start of the treatment, with a high proportion of spontaneous pseudopregnancies and reduced fertility.MethodsTo investigate some of the mechanisms involved in these reproductive abnormalities, hypothyroidism was induced in virgin rats by propilthyouracil (0.1 g/L in the drinking water) and we determined circulating hormones by radioimmunoassay and whole ovary expression of ovarian hormone receptors, growth factors and steroidogenic enzymes using semi-quantitative RT-PCR.The study was performed on days 6 to 9 of treatment, corresponding to diestrus I (at 20.00-22.00 h), diestrus II (at 20.00-22.00 h), proestrus and estrus (both at 8.00-10.00 h and 20.00-22.00 h) of the second estrous cycle after beginning propilthyouracil treatment. Another group of rats was mated on day 8 and the treatment continued through the entire pregnancy to evaluate reproductive performance.ResultsHypothyroidism increased circulating prolactin and estradiol on estrus 5 to 7-fold and 1.2 to 1.4-fold respectively. Growth hormone and insulin-like growth factor 1 diminished 60 and 20% respectively on proestrus morning. Hypothyroidism doubled the ovarian mRNA contents of estrogen receptor-beta on proestrus and estrus evenings, cyp19A1 aromatase mRNA on estrus evening and of growth hormone receptor on proestrus evening. Hypothyroidism did not influence ovulation rate or the number of corpora lutea at term, but a diminished number of implantation sites and pups per litter were observed (Hypothyroid: 11.7 +/- 0.8 vs. Control: 13.9 +/- 0.7).ConclusionsShort term hypothyroidism alters normal hormone profile in the cycling rat increasing the expression of estrogen receptor-beta and cyp19A1 aromatase on estrus, which in turn may stimulate estradiol and prolactin secretion, favouring corpus luteum survival and the subsequent instauration of pseudopregnancy.