Exposure to Phthalates in European Children, Adolescents and Adults since 2005: A Harmonized Approach Based on Existing HBM Data in the HBM4EU Initiative.

Phthalates are mainly used as plasticizers and are associated inter alia with adverse effects on reproductive functions. While more and more national programs in Europe have started monitoring internal exposure to phthalates and its substitute 1,2-Cyclohexanedicarboxylic acid (DINCH), the comparability of results from such existing human biomonitoring (HBM) studies across Europe is challenging. They differ widely in time periods, study samples, degree of geographical coverage, design, analytical methodology, biomarker selection, and analytical quality assurance level. The HBM4EU initiative has gathered existing HBM data of 29 studies from participating countries, covering all European regions and Israel. The data were prepared and aggregated by a harmonized procedure with the aim to describe-as comparably as possible-the EU-wide general population's internal exposure to phthalates from the years 2005 to 2019. Most data were available from Northern (up to 6 studies and up to 13 time points), Western (11; 19), and Eastern Europe (9; 12), e.g., allowing for the investigation of time patterns. While the bandwidth of exposure was generally similar, we still observed regional differences for Butyl benzyl phthalate (BBzP), Di(2-ethylhexyl) phthalate (DEHP), Di-isononyl phthalate (DiNP), and Di-isobutyl phthalate (DiBP) with pronounced decreases over time in Northern and Western Europe, and to a lesser degree in Eastern Europe. Differences between age groups were visible for Di-n-butyl phthalate (DnBP), where children (3 to 5-year olds and 6 to 11-year olds) had lower urinary concentrations than adolescents (12 to 19-year-olds), who in turn had lower urinary concentrations than adults (20 to 39-year-olds). This study is a step towards making internal exposures to phthalates comparable across countries, although standardized data were not available, targeting European data sets harmonized with respect to data formatting and calculation of aggregated data (such as developed within HBM4EU), and highlights further suggestions for improved harmonization in future studies.

From science to policy: How European HBM indicators help to answer policy questions related to phthalates and DINCH exposure.

Within the European Human Biomonitoring (HBM) Initiative HBM4EU we derived HBM indicators that were designed to help answering key policy questions and support chemical policies. The result indicators convey information on chemicals exposure of different age groups, sexes, geographical regions and time points by comparing median exposure values. If differences are observed for one group or the other, policy measures or risk management options can be implemented. Impact indicators support health risk assessment by comparing exposure values with health-based guidance values, such as human biomonitoring guidance values (HBM-GVs). In general, the indicators should be designed to translate complex scientific information into short and clear messages and make it accessible to policy makers but also to a broader audience such as stakeholders (e.g. NGO's), other scientists and the general public. Based on harmonized data from the HBM4EU Aligned Studies (2014-2021), the usefulness of our indicators was demonstrated for the age group children (6-11 years), using two case examples: one phthalate (Diisobutyl phthalate: DiBP) and one non-phthalate substitute (Di-isononyl cyclohexane-1,2- dicarboxylate: DINCH). For the comparison of age groups, these were compared to data for teenagers (12-18 years), and time periods were compared using data from the DEMOCOPHES project (2011-2012). Our result indicators proved to be suitable for demonstrating the effectiveness of policy measures for DiBP and the need of continuous monitoring for DINCH. They showed similar exposure for boys and girls, indicating that there is no need for gender focused interventions and/or no indication of sex-specific exposure patterns. They created a basis for a targeted approach by highlighting relevant geographical differences in internal exposure. An adequate data basis is essential for revealing differences for all indicators. This was particularly evident in our studies on the indicators on age differences. The impact indicator revealed that health risks based on exposure to DiBP cannot be excluded. This is an indication or flag for risk managers and policy makers that exposure to DiBP still is a relevant health issue. HBM indicators derived within HBM4EU are a valuable and important complement to existing indicator lists in the context of environment and health. Their applicability, current shortcomings and solution strategies are outlined.

The Joint Effect of Perceived Psychosocial Stress and Phthalate Exposure on Hormonal Concentrations during the Early Stage of Pregnancy: A Cross-Sectional Study.

Phthalates alter the hormonal balance in humans during pregnancy, potentially affecting embryonic and fetal development. We studied the joint effect of exposure to phthalates, quantified by urinary phthalate metabolite concentration, and perceived psychological stress on the concentration of hormones in pregnant women (n = 90) from the Nitra region, Slovakia, up to the 15th week of pregnancy. We used high-performance liquid chromatography, tandem mass spectrometry (HPLC-MS/MS), and electro-chemiluminescence immunoassay to determine urinary concentrations of phthalates and serum concentrations of hormones, respectively. We used Cohen perceived stress scale (PSS) to evaluate the human perception of stressful situations. Our results showed that mono(carboxy-methyl-heptyl) phthalate (cx-MiNP) and a molar sum of di-iso-nonyl phthalate metabolites (ΣDiNP) were negatively associated with luteinizing hormone (LH) (p ≤ 0.05). Mono(hydroxy-methyl-octyl) phthalate (OH-MiNP) and the molar sum of high-molecular-weight phthalate metabolites (ΣHMWP) were positively associated with estradiol (p ≤ 0.05). PSS score was not significantly associated with hormonal concentrations. When the interaction effects of PSS score and monoethyl phthalate (MEP), cx-MiNP, ΣDiNP, and ΣHMWP on LH were analyzed, the associations were positive (p ≤ 0.05). Our cross-sectional study highlights that joint psychosocial stress and xenobiotic-induced stress caused by phthalates are associated with modulated concentrations of reproductive hormones in pregnant women.

Risk of Abdominal Obesity Associated with Phthalate Exposure of Nurses.

Background: Occupational health hazards associated with phthalate exposure among nurses are still not well understood. Methods: We used high-performance liquid chromatography and tandem mass spectrometry to analyze phthalates. Anthropometric measurements and questionnaires were conducted. Results: We observed associations between mono-benzyl phthalate (MBzP) and body mass index (BMI), hip circumference (HC), waist circumference (WC), waist to height ratio (WHtR), and fat mass index (FMI), visceral fat content, BMI risk and hip index risk (HIrisk), adjusted to consumer behavior and consumer practices (r = 0.36−0.61; p ≤ 0.046). In the same model, we detected an association between mono-n-butyl phthalate (MnBP) and waist to hip ratio (WHR; r = 0.36; p = 0.046), mono-carboxy-isononyl phthalate (cx-MiNP) and BMI (r = 0.37; p = 0.043), HC (r = 0.4; p = 0.026) and WHtR (r = 0.38; p = 0.037), between mono-oxo-isononyl phthalate oxo (MiNP) and HC (r = 0.36; p = 0.045), mono-2-ethylhexyl phthalate (MEHP), mono(2-ethyl-5-oxohexyl) phthalate (oxo-MEHP) and HIrisk (r = 0.38−0.41; p ≤ 0.036), between oxo-MEHP and Anthropometric Risk Index (ARI risk; r = 0.4; p = 0.028). We detected a relationship between BMI and MBzP (ß = 0.655; p < 0.001) and mono-2-ethylhexyl phthalate (MEHP; ß = −0.365; p = 0.003), between hip circumference and MBzP (ß = 0.486; p < 0.001), MEHP (ß = −0.402; p = 0.001), and sum of secondary metabolites of diisononyl phthalate (∑DiNP; ß = 0.307; p = 0.016). We observed a relationship between fat content and MBzP (ß = 0.302; p = 0.033), OH-MnBP (ß = −0.736; p = 0.006) and MiBP (ß = 0.547; p = 0.046), visceral fat content and MBzP (ß = 0.307; p = 0.030), HI-risk and MBzP (ß = 0.444; p = 0.001), ARI-risk and sum of di-n-butyl phthalate metabolites (∑DnBP; ß = 0.337; p = 0.018). We observed an association between the use of protective equipment with cx-MiNP. Conclusions: Occupational exposure to phthalates may induce abdominal obesity and result in obesity-related metabolic disorders.

Urinary Phthalate Biomarkers during Pregnancy, and Maternal Endocrine Parameters in Association with Anthropometric Parameters of Newborns.

Adverse birth outcomes present risk factors resulting in neonatal morbidity and mortality. Sufficient maternal hormonal concentrations are crucial for normal foetal development. Previous studies have shown a relationship between phthalate exposure and maternal hormonal levels during pregnancy. This study aims to investigate if neonatal anthropometric parameters are associated with maternal endocrine parameters during the ≤15th week of gestation and the third trimester of pregnancy concerning phthalate exposure in pregnant women from Nitra, Slovakia. We used high-performance liquid chromatography, tandem mass spectrometry (HPLC-MS/MS), and electro-chemiluminescence immunoassay to quantify urinary concentrations of phthalates and serum concentrations of hormones and sex hormone-binding globulin (SHBG), respectively. We observed a mostly positive correlation between neonatal anthropometric parameters (gestational age, birth length, birth weight, head circumference) and maternal concentration of phthalate metabolites (p ≤ 0.05). The hierarchical multivariate regression results showed a statistically significant association between Apgar score at 5 min after delivery, gestational age, birth weight, head circumference, and maternal endocrine parameters during pregnancy (p ≤ 0.05), adjusted to phthalate metabolites. To the best of our knowledge, our study is the first to indicate that prenatal exposure to phthalates may also affect birth outcomes through interaction with the maternal endocrine system.

Effect of prenatal phthalate exposure on the association of maternal hormone levels during early pregnancy and reproductive markers in infants at the age of 3 months.

Phthalates belong to the endocrine-disrupting chemicals, altering the hormonal balance in humans during pregnancy with further effects on the reproductive system. This study aimed to investigate the associations between maternal hormone levels during early pregnancy (≤15th week of pregnancy) and reproductive markers in infant boys (n = 37; 61.67 %; average age 3.51 ±â€¯0.73 months) and girls (n = 23; 38.33 %; average age 3.30 ±â€¯0.33 months) concerning prenatal exposure to phthalates. We used high-performance liquid chromatography, tandem mass spectrometry (HPLC-MS/MS), and electro-chemiluminescence immunoassay to quantify urinary concentrations of phthalates and serum concentrations of hormones, respectively. In Mother-Infant Study Cohort (PRENATAL), we observed positive and negative correlations between infants' reproductive markers and phthalate metabolites (p ≤ 0.05). Next, we noticed associations between the penile length and maternal testosterone (ß = 0.464) and estradiol levels (ß = -0.365) with increasing significance after adjustment to maternal mono-n-butyl phthalate (MnBP) and monobenzyl phthalate (MBzP) (p ≤ 0.05). We observed a positive association (ß = 0.337) between penile width and maternal testosterone with increasing significance after adjustment to maternal mono-iso-butyl phthalate (MiBP) (p ≤ 0.05). In a group of girls, we reported a negative association between ACD/AFD ratio and maternal follicle-stimulating hormone (FSH) and estradiol levels with increasing significance after adjustment to maternal monoethyl phthalate (MEP), MnBP, and mono(hydroxy-iso-butyl) phthalate (OH-MiBP). Our results highlight that prenatal phthalate exposure may modulate the effects of maternal hormone levels during early pregnancy on infants' reproductive markers.

Challenges to Evidence Synthesis and Identification of Data Gaps in Human Biomonitoring.

The increasing number of human biomonitoring (HBM) studies undertaken in recent decades has brought to light the need to harmonise procedures along all phases of the study, including sampling, data collection and analytical methods to allow data comparability. The first steps towards harmonisation are the identification and collation of HBM methodological information of existing studies and data gaps. Systematic literature reviews and meta-analyses have been traditionally put at the top of the hierarchy of evidence, being increasingly applied to map available evidence on health risks linked to exposure to chemicals. However, these methods mainly capture peer-reviewed articles, failing to comprehensively identify other important, unpublished sources of information that are pivotal to gather a complete map of the produced evidence in the area of HBM. Within the framework of the European Human Biomonitoring Initiative (HBM4EU) initiative-a project that joins 30 countries, 29 from Europe plus Israel, the European Environment Agency and the European Commission-a comprehensive work of data triangulation has been made to identify existing HBM studies and data gaps across countries within the consortium. The use of documentary analysis together with an up-to-date platform to fulfil this need and its implications for research and practice are discussed.

Effects and mechanisms of phthalates' action on neurological processes and neural health: a literature review.

During the period of mass industrial production of plastic products, the quality of human health has decreased significantly, especially in children's neurodevelopmental disorders. Phthalates are endocrine-disrupting chemicals that can induce neurological disorders. This review aims to compile evidence concerning the associations between neurological disorders, such as attention-deficit/hyperactivity disorder, autism spectrum disorder, decreased masculine behavior, and phthalate exposure. Phthalates dysregulate the hypothalamic-pituitary-gonadal, adrenal, and thyroid axis, which is crucial for the neurodevelopmental process. Phthalates interfere with nuclear receptors in various neural structures involved in controlling brain functions and the onset of neurological disorders at the intracellular level. It is critical to increase the current knowledge concerning phthalates' toxicity mechanism to comprehend their harmful effect on human health.

Effects and Mechanisms of Phthalates' Action on Reproductive Processes and Reproductive Health: A Literature Review.

The production of plastic products, which requires phthalate plasticizers, has resulted in the problems for human health, especially that of reproductive health. Phthalate exposure can induce reproductive disorders at various regulatory levels. The aim of this review was to compile the evidence concerning the association between phthalates and reproductive diseases, phthalates-induced reproductive disorders, and their possible endocrine and intracellular mechanisms. Phthalates may induce alterations in puberty, the development of testicular dysgenesis syndrome, cancer, and fertility disorders in both males and females. At the hormonal level, phthalates can modify the release of hypothalamic, pituitary, and peripheral hormones. At the intracellular level, phthalates can interfere with nuclear receptors, membrane receptors, intracellular signaling pathways, and modulate gene expression associated with reproduction. To understand and to treat the adverse effects of phthalates on human health, it is essential to expand the current knowledge concerning their mechanism of action in the organism.

Occupational Hazards and Risks Associated with Phthalates among Slovakian Firefighters.

Despite increasing attention to the occupational risk of firefighters, little is known about phthalate exposure. In our study, we detected mono-isobutyl phthalate (MiBP), mono-n-buthyl phthalate (MnBP), mono(2-ethyl-5-hydroxyhexyl) phthalate (5OH-MEHP), mono(2-ethyl-5-carboxypentyl) phthalate (5cx-MECPP), and mono(2-ethyl-5-oxohexyl) phthalate (5oxo-MEHP) in each urine sample. We detected positive association between MnBP, MiBP, mono-2-ethylhexyl phthalate (MEHP), 5OH-MEHP, 5oxo-MEHP, 5cx-MECPP, mono-isononyl phthalate (MiNP), the sum of low (∑LMWP) and high molecular-weight phthalates (∑HMWP). and Tiffeneau-Pinelli index (the ratio of forced expiratory volume in 1/ forced vital capacity; FEV1/FVC; p = 0.001-0.04) and the percent predicted value (%PV) of FEV1/FVC (p = 0.005-0.05) and negative association between MiNP and peak expiratory flow (PEF; r = -0.31; p = 0.084). We observed a positive association between phthalate metabolites (MnBP, 5OH-MEHP, 5oxo-MEHP, 5cx-MECPP, 2cx-MMHP, ∑LMWP, and ∑HMWP) and waist-to-hip ratio (WHR; p = 0.003-0.09) and body shape index (ABSI; p = 0.039-0.09) and a negative association between MnBP, ∑LMWP, and hip circumference (p = 0.005-0.02). We detected association between concentrations of 5OH-MEHP, 5cx-MECPP, 5oxo-MEHP, and MnBP and consumption of food heating in plastic material in microwave (p = 0.02-0.04) and between probands who ate margarines and vegetable fat packed in plastic containers and concentration of MMP (p = 0.03). Results of multivariate regression indicated that exposure to phthalates could be linked with changing body structure, which subsequently affects values of pulmonary functions in firefighters.

Exposure of children to phthalates and the impact of consumer practices in Slovakia.

Phthalates are environmental pollutants that can enter the human body by ingestion, inhalation and dermal absorption. Food constitutes the most important source of human exposure to these chemicals. The aim of our study was the biological monitoring of exposure to eight phthalate metabolites in children (n=107), 10-12 years of age, living in eastern Slovakia. Additionally, we analysed some associations between anthropometric measures, questionnaire data (i.e. eating and drinking habits, practice of personal care products) and concentrations of phthalate metabolites. Because of the short half-life of phthalates, within 24-48 h, we used 24-h recalls to assess dietary intakes. We used high-performance liquid chromatography and tandem mass spectrometry for the analysis of spot urine samples to determine concentrations of phthalate metabolites mono-ethyl phthalate (MEP), mono-n-butyl phthalate, mono-iso-butyl phthalate, mono-benzyl phthalate (MBzP), mono (2-ethyl-5-hydroxyhexyl) phthalate (5OH-MEHP), mono(2-ethyl-5-oxohexyl) phthalate (5oxo-MEHP), mono-carboxy pentyl and mono (2-ethylhexyl) phthalate (MEHP). We found statistically significant association between consumer practices and concentration of some phthalate metabolites, concretely consumption of milk and dairy products with MBzP and margarine with MEP (p<0.01 in both cases) and margarine with 5oxo-MEHP, hot beverages with 5OH-MEHP, baguettes and semifinished products with MEP (p<0.05 in all cases). Further, we found relationship between use of cosmetic products and phthalate concentrations, nail polish application and MEP and use of body lotion and MEHP (p<0.05 in both cases). We concluded that consumer practices (including eating and drinking habits and personal care) represent the substantial source of phthalate exposure in Slovak children.

Occupational exposure to phthalates in relation to gender, consumer practices and body composition.

The aim of our work was to find associations between urinary phthalate metabolite concentrations and occupation, consumer practices and body composition. We divided our cohort (n = 129) into occupationally exposed subjects, community service workers (group A; n = 45) and workers from plastic industry (group B; n = 35) and group of general population (control group C, n = 49). To estimate levels of five phthalate metabolites, we used high-performance liquid chromatography and tandem mass spectrometry analysis. We found in plastic industry workers compared to community service workers and subjects of the control group significantly higher urinary concentration mono (2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), mono (2-ethyl-5-oxohexyl) phthalate (MEOHP), mono (2-etylhexyl) phthalate (MEHP), sum di-(2-ethyl-5-oxohexyl) phthalate (DEHP), mono-iso-butyl phthalate (MiBP) and mono-n-butyl phthalate (MnBP). We identified by multivariate analysis of covariance inverse relationship between MEHP and body parameters as waist-to-height ratio, body mass index, waist-to-hip ratio, hip circumference and waist circumference among females, whereas in males, no significant association was found. Results of our study show, despite of variability in terms of occupational exposure to phthalates, that plastic manufactory represents a higher occupational risk in comparison with waste management. The differences in anthropometric parameters between the two occupationally exposed groups and the general population are suggesting a detrimental effect of occupational exposure on body weight homeostasis.

Marijuana: Views on Its Medical Use Recorded at the Slovak Social Network.

We describe opinions on medical use of Cannabis sativa L under conditions of Slovakia (n = 717). Personal experience with marijuana was detected in 77.42% (n = 553) in age categories younger than 20 years (n = 96) and in 77.06% (n = 457) of adults. Almost 86% of respondents (n = 618) agreed with legal use of marijuana for medical purposes. Furthermore, respondents' views on legal usage of marijuana for medical purposes could be affected by availability of information (r = .12) and personal experience (r = .23). Negative impact of substance abuse in younger age-groups was recognized as threat (r = .47), but knowledge about harmful effect of marijuana use did not affect personal opinion for decriminalization (r = .38).

Relationship between variation of seasonal temperature and extent of occupational exposure to phthalates.

Spot urine samples were collected in summer and winter season to examine the association between temperature variation and phthalate concentration in an occupationally exposed group. We analysed samples by high-performance liquid chromatography with mass spectrometry (HPLC-MS/MS) to determine the concentrations of four phthalate metabolites: mono (2-ethylhexyl) phthalate (MEHP), monobutyl phthalate (MnBP), monoethyl phthalate (MEP), and monoisononyl phthalate (MiNP). We observed significantly higher urinary concentrations of all monitored phthalate metabolites collected during the summer in occupationally exposed group (MEP p < 0.0015, MiNP p < 0.0001, MnBP p < 0.00019, and MEHP p < 0.05); however, in general, population was noticed this difference only for MEHP (p < 0.05) in winter season. We conclude that increasing indoor and outdoor temperature is related to phthalate exposure in specific types of work environment.

Use of selected prediction equations (CG, MDRD4, CKD-EPI) in improving glomerular filtration rate assessment in clinical practice in Slovakia.

Our study aimed to establish the best prediction equation for different age ranges in estimating Glomerular Filtration Rate (GFR) in clinical practice in Slovakia. The GFR by 24-hour creatinine clearance (Ccr) and the estimated GFR (eGFR) using the Cockcroft-Gault (CG), the four-variable Modification of Diet in Renal Disease (MDRD4) and the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations were obtained in adults aged 30-80 (n = 433, 10-years intervals). The correlation between these prediction equations and Ccr was evaluated. Errors in prediction equations were detected by moving average and by comparisons of the formulas for GFR < 1.5 ml/s and > 1.5 ml/s. The best correlations were established between Ccr and MDRD4 for women (r = 0.7790) and men (r = 0.8009), and between Ccr and CKD-EPI for women (r = 0.7780) and men (r = 0.8002) in the 60-69 age range. High correlation was also established between Ccr and CG (r = 0.8655) and MDRD4 (r = 0.8713) for men in the 40-49 age range. With the exception of the 30-40 age range, a low prediction error was observed for each age range in both genders when GFR was < 1.5 ml/s. We recommend utilization of the MDRD4 and CG equations for men (40-49 years) and MDRD4 and CKD-EPI for women and men (60-69 years), as preferred substitutes for Ccr.

Phthalate exposure and health-related outcomes in specific types of work environment.

Many toxic substances in the workplace can modify human health and quality of life and there is still insufficient data on respiratory outcomes in adults exposed to phthalates. The aim of this work was to assess in waste management workers from the Nitra region of Slovakia (n = 30) the extent of exposure to phthalates and health-related outcomes. Four urinary phthalate metabolites mono(2-ethylhexyl) phthalate (MEHP), monobutyl phthalate (MnBP), monoethyl phthalate (MEP) and monoisononyl phthalate (MiNP) were determined by high-performance liquid chromatography with mass spectrometry (HPLC-MS/MS). Urinary concentration of MEHP was positively associated with ratio of forced expiratory volume in 1 s to forced vital capacity % (FEV1/FVC) (r = 0.431; p = 0.018) and MiNP with fat free mass index (FFMI) (r = 0.439; p = 0.015). The strongest predictor of pulmonary function was the pack/year index as smoking history that predicted a decrease of pulmonary parameters, the FEV1/FVC, % of predicted values of peak expiratory flow (PEF % of PV) and FEV1 % of PV. Unexpectedly, urinary MEHP and MINP were positively associated with pulmonary function expressed as PEF % of PV and FEV1/FVC. We hypothesize that occupational exposure to phthalates estimated from urinary metabolites (MEHP, MiNP) can modify pulmonary function on top of lifestyle factors.

Role of ooplasm in nuclear and nucleolar remodeling of intergeneric somatic cell nuclear transfer embryos during the first cell cycle.

Initially, development of the zygote is under control of the oocyte ooplasm. However, it is presently unknown if and to what extent is the ooplasm able to interact with a transferred somatic cell from another species in the context of interspecies somatic cell nuclear transfer (SCNT). Here, one-cell stage embryos were processed at different points in time post activation (2 hpa, 4 hpa, 8 hpa, and 12 hpa) for detailed nuclear and nucleolar analysis by TEM, and immunofluorescence for visualization of nucleolar proteins related to transcription (UBF) and processing (fibrillarin). Bovine and porcine intergeneric SCNT embryos were compared to their parthenogenetic counterparts to assess the effects of the introduced somatic cell. Despite the absence of morphological remodeling (premature chromatin condensation, nuclear envelope breakdown), reconstructed embryos showed nuclear and nucleolar precursor body (NPB) morphology similar to the host ooplasm, which, together with detected posttranslational activity of somatic cell introduced into the bovine ooplasm, suggests a universal function of ooplasmic factors. However, the lack of distinct UBF localization in intergeneric embryos indicates failures in sequence-specific interactions between the ooplasm and chromatin of another genus. In conclusion, the results demonstrate a possible reason why the intergeneric SCNT embryos never reached the full term.

Nuclear and nucleolar reprogramming during the first cell cycle in bovine nuclear transfer embryos.

The immediate events of genomic reprogramming at somatic cell nuclear transfer (SCNT) are to high degree unknown. This study was designed to evaluate the nuclear and nucleolar changes during the first cell cycle. Bovine SCNT embryos were produced from starved bovine fibroblasts and fixed at 0.5, 1, 2, 3, 4, 8, 12, and 16 h postactivation (hpa). Parthenogenetic (PA) embryos were used as control. The SCNT and PA embryos were processed for lacmoid staining, autoradiography, transmission electron microscopy (TEM), and immunofluorescence localization of: upstream binding factor (UBF) and fibrillarin at 4 and 12 hpa. Likewise, starved and nonstarved fibroblasts were processed for autoradiography and TEM. The fibroblasts displayed strong transcriptional activity and active fibrillogranular nucleoli. None of the reconstructed embryos, however, displayed transcriptional activity. In conclusion, somatic cell nuclei introduced into enucleated oocytes displayed chromatin condensation, partial nuclear envelope breakdown, nucleolar desegregation and transcriptional quiescence already at 0.5 hpa. Somatic cell cytoplasm remained temporally attached to introduced nucleus and nucleolus was partially restored indicating somatic influence in the early SCNT phases. At 1-3 hpa, chromatin gradually decondensed toward the nucleus periphery and nuclear envelope reformed. From 4 hpa, the somatic cell nucleus gained a PN-like appearance and displayed NPBs suggesting ooplasmic control of development.