Effects of induced hypothyroidism on weight gains, lactation, and reproductive performance of primiparous Brahman cows

Management of overt hypothyroidism during pregnancy

Overt hypothyroidism is a common endocrine disorder affecting 1-2% of women of reproductive age. Optimizing treatment in pregnant women with overt hypothyroidism can reduce adverse fetal and maternal outcomes. Ideally, women who are known to have a history of hypothyroidism or those with risk factors for becoming hypothyroid, should have adequate preconception care to ensure euthyroidism from the onset of pregnancy, with a TSH target of below 2.5mIU/L. On women who are already on levothyroxine, an empirical dose increase of 30-50% as soon as pregnancy is confirmed may be considered. During pregnancy, levothyroxine doses should be titrated against TSH, which have trimester-specific ranges. In women who are known to be hypothyroid but are inadequately treated, we recommend a doubling of levothyroxine dose on at least three days a week to rapidly achieve euthyroidism. In newly diagnosed overt hypothyroidism in pregnancy, starting doses of either 100 or 150 mg daily may be considered safe.

2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum

BACKGROUND

Thyroid disease in pregnancy is a common clinical problem. Since the guidelines for the management of these disorders by the American Thyroid Association (ATA) were first published in 2011, significant clinical and scientific advances have occurred in the field. The aim of these guidelines is to inform clinicians, patients, researchers, and health policy makers on published evidence relating to the diagnosis and management of thyroid disease in women during pregnancy, preconception, and the postpartum period.

METHODS

The specific clinical questions addressed in these guidelines were based on prior versions of the guidelines, stakeholder input, and input of task force members. Task force panel members were educated on knowledge synthesis methods, including electronic database searching, review and selection of relevant citations, and critical appraisal of selected studies. Published English language articles were eligible for inclusion. The American College of Physicians Guideline Grading System was used for critical appraisal of evidence and grading strength of recommendations. The guideline task force had complete editorial independence from the ATA. Competing interests of guideline task force members were regularly updated, managed, and communicated to the ATA and task force members.

RESULTS

The revised guidelines for the management of thyroid disease in pregnancy include recommendations regarding the interpretation of thyroid function tests in pregnancy, iodine nutrition, thyroid autoantibodies and pregnancy complications, thyroid considerations in infertile women, hypothyroidism in pregnancy, thyrotoxicosis in pregnancy, thyroid nodules and cancer in pregnant women, fetal and neonatal considerations, thyroid disease and lactation, screening for thyroid dysfunction in pregnancy, and directions for future research.

CONCLUSIONS

We have developed evidence-based recommendations to inform clinical decision-making in the management of thyroid disease in pregnant and postpartum women. While all care must be individualized, such recommendations provide, in our opinion, optimal care paradigms for patients with these disorders.

Effect of hypothyroidism on growth performance, carcass composition and meat quality of fat-tailed Lori-Bakhtiari lambs

The aim of the present study was to investigate the effects of induction hypothyroidism by propylthiouracil (PTU) on the growth performance and meat quality of fat-tailed Lori-Bakhtiari lambs. Eighteen Lori-Bakhtiari male lambs were randomly assigned to one of three groups (n = 6) and received daily treatments (gavage) consisting of 0 (Control: C), 10 (Low: L) or 20 (High: H) mg PTU/kg bodyweight/day for 60 days. PTU decreased plasma triiodothyronine and thyroxine concentration in both L and H (P < 0.0001). Lambs treated with PTU (L and H) had lower feed intake (P < 0.004), feed conversion efficiency (P < 0.003), and greater intramuscular fat than C lambs (P < 0.035). Meat from the L and H lambs had lower cooking loss and shear force, and also higher L* (lightness) than C lambs (P < 0.004, P < 0.015 and P < 0.025, respectively). The meat of H and L lambs was more tender than C lambs (P < 0.032). However, the meat of H lambs required fewer chews before swallowing than C lambs (P < 0.041). Generally, induction of mild hypothyroidism appeared to improve feed conversion efficiency and meat quality of lambs.

Impact of experimental hypothyroidism on monoamines level in discrete brain regions and other peripheral tissues of young and adult male rats

The levels of dopamine (DA), norepinephrine (NE) and serotonin (5-HT) in different brain regions as well as in blood plasma, cardiac muscle and adrenal gland of young and adult male albino rats were measured following experimentally induced hypothyroidism. Hypothyroidism induced by daily oral administration of propylthiouracil (PTU, 5mg/kg body wt) caused a significant reduction in DA levels in most of the tissues examined of both young and adult rats after 21 and 28 days, in NE levels after all the time intervals studied in young rats, and after 21 and 28 days in adult rats. 5-HT exhibited a significant reduction in the selected brain regions and blood plasma after 21 and 28 days and in cardiac muscle after all the time intervals in the two age groups of animals. It may be suggested that the changes in monoamine levels induced by hypothyroidism may be due to disturbance in the synthesis and release of these amines through the neurons impairment or may be due to an alteration pattern of their synthesizing and/or degradative enzymes.

Plasma progesterone, metabolic hormones and beta-hydroxybutyrate in Holstein-Friesian cows after superovulation

Metabolic hormones [insulin, leptin, insulin-like growth factor-I (IGF-I), thyroxine (T4) and triiodothyronine (T3)], progesterone (P4) and beta-hydroxybutyrate (BHB) serum concentrations were evaluated and their effect on the superovulation results of donor cows was investigated in a semi-arid environment. Body weight, body condition score (BCS) and lactation stage were also included in the analysis. Twenty-three Holstein-Friesian cows were superovulated with 600 IU FSHp following the routine procedure and flushed on day 7 in a Multiple Ovulation and Embryo Transfer Centre in the semi-arid area of Brazil. The corpora lutea (CL) were counted and blood samples were collected for assays. All of the hormones investigated and BHB serum concentrations were within the physiological ranges. There was a positive correlation between hormones, except between BHB and all the others. The leptin level was influenced by feeding status, as indicated by the BCS. Insulin, T4, T3 and BHB levels were affected by milking status. Dry cows had higher levels of all hormones except BHB. An optimum level of leptin resulted in the highest number of CL, while the linear increase of P4, T4 and IGF significantly increased the number of CL.

Stimulatory effects of propylthiouracil on pregnenolone production through upregulation of steroidogenic acute regulatory protein expression in rat granulosa cells

Propylthiouracil (PTU) is a common and effective clinical medicine for the treatment of hyperthyroidism. Our previous study demonstrated that short-term treatment with PTU inhibits progesterone production in rat granulosa cells. However, our present results indicate that a 16-h treatment with PTU was able to stimulate pregnenolone production in rat granulosa cells, although progesterone production was diminished by PTU through inhibition of 3β-hydroxysteroid dehydrogenase. Notably, we found that PTU treatment enhanced the conversion of cholesterol into pregnenolone, whereas the protein level of the cytochrome P450 side-chain cleavage enzyme (P450scc, which is the enzyme responding to this conversion) was not affected. Interestingly, the levels of steroidogenic acute regulatory protein (StAR) in both total cell lysate and the mitochondrial fraction were significantly increased by PTU treatment. Furthermore, the binding of steroidogenic factor-1 (SF-1) to the StAR promoter region was also enhanced by PTU treatment, which suggests that PTU could upregulate StAR gene expression. In addition to SF-1 regulation, we found that mitogen-activated protein (MAP) kinase kinase activation is an important regulator of PTU-stimulated StAR protein expression, based on the effects of the MEK inhibitor PD98059. In conclusion, these results indicate that PTU plays opposite roles in the production of progesterone and its precursor, pregnenolone. The regulation of negative feedback on speeding the cholesterol transportation and pregnenolone conversion after a 16-h PTU treatment may be the mechanism explaining PTU's inhibition of progesterone production in rat granulosa cells.

How breastfeeding works

Human milk is a complex secretion that is the sole ideal food for babies for at least the first 6 months of life. The amount and composition of the milk is largely independent of the mother's diet. The composition of the milk changes during lactogenesis II, and these changes can be used as biochemical markers of the onset of copious milk secretion. After 1 month of lactation, there are few further changes in the composition of milk until the volume of milk decreases substantially as the baby weans completely. The amount of milk produced depends on the amount of milk removed from the breast. Successful, exclusively breastfeeding babies show a three-fold variation in the amount of milk they take per day, and in the frequency of breastfeeds and amount of milk consumed during each breastfeed. The fat intake of the baby is independent of the feeding frequency. If a baby is growing normally, the mother can be confident that her baby does not need to follow prescribed breastfeeding regimes. She should respond to her baby's cues for the frequency of breastfeeds, and whether the baby requires one or both breasts for a meal. Continuing research into the physiology of breastfeeding provides a foundation for evidence-based treatment of breastfeeding difficulties.

Influence of exogenous triiodothyronine (T3) on fecal shedding of Escherichia coli O157 in cattle

Fecal prevalence of Escherichia coli O157 in ruminants is highest in the summer months and decreases to low or undetectable levels in the winter. We hypothesize that the seasonal variation of this pathogen is a result of physiological responses within the host animal to changing day length. The thyroid is an endocrine gland known to respond to changing day length. Two experiments were conducted to determine if a hyperthyroid status would initiate fecal shedding of E. coli O157 in cattle during the winter when shedding is virtually nonexistent (winter experiment) or influence cattle actively shedding E. coli O157 (summer experiment). Yearling cattle were group-penned under dry-lot conditions, adjusted to a high concentrate ration, and randomly assigned to treatment: control (1 mL corn oil injected s.c. daily) or triiodothyronine (T(3); 1.5 mg suspended in corn oil injected s.c daily). Cattle were individually processed daily for collection of fecal and blood samples. Treatment with exogenous T(3) produced a significant change in serum thyroid hormone concentrations indicative of a hyperthyroid status in both experiments. No differences (P>0.10) were observed in fecal shedding of E. coli O157 in the winter experiment. In the summer experiment, fecal shedding of E. coli O157 was decreased (P=0.05) by administration of T(3) during the treatment period (days 1-10), tended to be lower (P=0.08) during the following 7-day period of no treatment, and was lower (P=0.01) when examined across the entire experimental period. Results of this research indicate that the thyroid or its hormones may be involved in the seasonal shedding patterns of E. coli O157 in cattle.

Effect of the thyroid on faecal shedding of E. coli O157:H7 and Escherichia coli in naturally infected yearling beef cattle

AIMS

To determine if thyroid function affects faecal shedding of Escherichia coli O157:H7.

METHODS AND RESULTS

Eight yearling cattle (n = 4 per treatment group), previously identified as shedding E. coli O157:H7, received either 0 or 10 mg 6-N-propyl-2-thiouracil (PTU) kg(-1) BW day(-1) for 14 days to reduce serum concentrations of the thyroid hormones, T(3) and T(4). Animals were monitored daily for changes in faecal shedding of E. coli O157:H7 and E. coli (EC) for the 14-day treatment period and an additional 7 days post-treatment. Body weight was measured weekly and serum concentrations of T(3) and T(4) were determined every 3 days. No differences in faecal shedding of E. coli O157:H7 were observed during the 14-day treatment period. However, compared with control animals, a greater percentage of PTU-treated cattle ejected E. coli O157:H7 on day 16 (100 vs 25%) and 18 (75 vs 0%) of the post-treatment period. Serum T(3) was lower in PTU-treated cattle during the 14-day treatment period and greater on day 18 of the post-treatment period.

CONCLUSION

Cattle with chemically altered thyroid hormones had similar shedding patterns of faecal E. coli O157:H7 and EC during the 14-day treatment period. However, faecal shedding of E. coli O157:H7 tended to be greater, and serum concentrations of T(3), were greater for PTU-treated cattle immediately following the termination of PTU treatment.

SIGNIFICANCE AND IMPACT OF THE STUDY

Short-term chemical inhibition of thyroid hormones had minimal effects on faecal shedding of E. coli O157:H7 in naturally infected cattle. However, a hyperthyroid state as observed postdosing might play a role in the seasonal shedding of E. coli O157:H7 in cattle.

Plasma concentrations of thyroxine in dairy cows exposed to 60 Hz electric and magnetic fields

Two experiments were carried out to assess the effects of electric and magnetic fields (EMF) on blood thyroxine (T4) in dairy cattle. In experiment 1, 16 lactating pregnant Holstein cows were exposed to 10 kV/m, 30 microTesla (microT) EMF. The animals were divided into two groups of eight animals each. Each group was exposed to EMF according to one of two treatment sequences of three periods of 28 days each. Sequence 1 was EMF OFF-ON-OFF and sequence 2 was EMF ON-OFF-ON. During the last day of each treatment period, blood samples were collected every 4 h for 24 h to estimate T4 plasma concentrations. In experiment 2, 16 nonlactating, nonpregnant, multiparous Holsteins were exposed to 10 kV/m, 30 microT EMF. The animals were divided into two groups of eight animals each. Each group was exposed to EMF according to one of the two treatment sequences described above, except that each period amounted to the number of days corresponding to one estrous cycle. During treatment, blood samples were collected every other day for T4 analysis. In both experiments, the light cycle emulated a short photoperiod (8 h light/16 h dark). During the ON periods, the animals were exposed to EMF for 16 h, 8 h of the light period plus the first 8 h of during the dark period. In experiment 1, exposed animals did not have any change in T4 plasma concentrations due to treatment (P = .0968), but, the time of sample collection revealed a significant difference (P = .0012). In experiment 2, the effect of period (P = .0009) and the treatment by days interaction (P = .0003) were statistically significant. We conclude that a worst case scenario exposure of dairy cattle to 10 kV/m, 30 microT EMF influences, in a moderate fashion, the blood levels of thyroxine.

Effects of hypothyroidism on mammary and liver lipid metabolism in virgin and late-pregnant rats

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 propylthiouracil (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. Pregnancy increased hepatic mRNAs associated with TG and cholesterol synthesis and uptake (including LDL receptor) and with lipid oxidation, such as acyl CoA oxidase. HypoT decreased mRNAs and the activity of proteins associated with TG synthesis, and mRNAs associated with cholesterol uptake and lipid oxidation. Pregnancy increased mammary mRNAs related to lipid oxidation and decreased cholesterol synthesis, whereas hypoT decreased mRNAs and activities of proteins associated with TG synthesis and decreased epithelial mammary tissue. Virgin and pregnant hypoT rats had increased circulating VLDL + LDL cholesterol. HypoT decreased circulating TGs in pregnant rats. The observed effects of hypoT may result in decreased mammary lipid availability. This, along with the decreased epithelial mammary tissue during lactogenesis, may contribute to the future lactational deficit of hypoT mothers.