Changes In Relative Organ Weights Research Articles

Hydroalcoholic Extract of Rabbiteye Blueberry (Vaccinium ashei) Leaves Mitigates Unpredictable Chronic Mild Stress Model Inducing Depressive-Like Behavior in Rats.

Several studies reported that rabbiteye blueberry (Vaccinium ashei Reade) leaves present promising biological properties. To the best of our knowledge, no study investigated the possible application of their hydroalcoholic extract for treating mood disorders. Herein, we evaluated if the hydroalcoholic extract of rabbiteye blueberry (Vaccinium ashei Reade) leaves (HEV) promotes an antidepressant-like effect in rodents using chronic experimental approaches. The effect of repeated administration of HEV (50 mg/kg, p.o.) on the immobility time was assessed in the forced swimming test (FST) in an unpredictable chronic mild stress (UCMS) model. Repeated treatment with HEV reversed the depressive-like behavior induced by UCMS by reducing the immobility time. Besides, the exposure to HEV caused no changes in relative organ weights in rats submitted to UCMS. The results indicated that HEV administration presented antidepressant-like action devoid of toxic effects. Thus, it is possible to suggest its potential as a safe and accessible therapeutic tool in the management of depression and other related mood disorders.

Safety and toxicologic evaluation of Edible Pongamia Oil: A novel food ingredient

Edible Pongamia Oil (EPO) was evaluated in an acute oral toxicity study, GLP 14-Day and 90-Day repeated dose isocaloric dietary toxicity studies in rats, and in vitro Bacterial Reverse Mutation, and in vivo Mammalian Bone Marrow Chromosome Aberration genotoxicity studies for potential use as a food ingredient. In a non-GLP acute study, an LD50 > 5000 mg/kg was determined. Subacute 14-day repeated dose dietary administration of 0, 5, 10 and 15% oil revealed no adverse changes in clinical pathology, liver histology, body weight or weight gain, food consumption or food efficiency. In a 90-day dietary study fed 0, 2.5, 5.0, 7.5 and 10.0%, no mortalities, clinical or ophthalmologic signs, body weight, body weight gain, food consumption, food efficiency or Functional Observational Battery/Motor Activity changes occurred with EPO consumption, nor were there any adverse changes in hematology, clinical chemistry, coagulation, urinalysis, or thyroid hormone values. There were no adverse macroscopic, estrus cycle, histopathologic or spermatogenesis findings, or absolute or relative organ weight changes related to administration of EPO. The No-Adverse-Effect-Level (NOAEL) was 10% in the diet, the highest dose tested, equivalent to 5163 (male) and 6469 (female) mg/kg/day in rats. No mutagenic or clastogenic genotoxic potential was reported.

Studying the Toxicity of Hydroalcoholic Caraway Seeds Extract in Female Rats

Caraway seeds are widely used as spice for flavoring and seasoning foods, like bread and salads, because of their pungent and anise like flavor and aroma. Carum carvi was utilized in folk medicine for the management of many diseases. It is useful in hypothyroidism,
 
 liver and gall bladder problems, common cold, fever, bronchitis, diarrhea, and eczema. It also relives GIT spasms, fullness feelings and relieves baby's flatulent colic. The extracts of caraway have diverse compounds, including carvone and limonene, linalool, γ-terpinene and α-pinene. One or combination of these compounds may participate in the pharmacologic effects of caraway. Aim of this study was to assess toxicity of caraway extract on female rats. Carium carvi extract submitted to chemical analysis (Phytochemical screening and Gas chromatography-mass spectrometry (GC-MS) analysis). Acute toxicity study has been performed using 24 female rats divided randomly in 4 groups (n=6 for each group) that received different doses of hydroalcoholic seed extract of caraway 1000, 3000 and ,5000 mg/kg for 14 days. On day 15, the rats were euthanized and whole blood collected to examine complete blood picture. The liver, kidney and the heart have been harvested for histopathologic study and relative organ weight changes. Caraway extract considered relatively safe on blood profile and immune system within the studied doses, as it shown a non-significant change on complete blood counts (CBCs) in a dose-dependent manner (Hb and RBCs increased slightly, while WBCs and PLTs decreased slightly) and without any change in body weight and relative weight percentage of different organs. As conclusion, hydroalcoholic extract of caraway seeds was relatively safe in rats at a dose up to 5000 mg/kg

Studying the Toxicity of Hydroalcoholic Caraway Seeds Extract in Female Rats

Caraway seeds are widely used as spice for flavoring and seasoning foods, like bread and salads, because of their pungent and anise like flavor and aroma. Carum carvi was utilized in folk medicine for the management of many diseases. It is useful in hypothyroidism, liver and gall bladder problems, common cold, fever, bronchitis, diarrhea, and eczema. It also relives GIT spasms, fullness feelings and relieves baby's flatulent colic. The extracts of caraway have diverse compounds, including carvone and limonene, linalool, γ-terpinene and α-pinene. One or combination of these compounds may participate in the pharmacologic effects of caraway. Aim of this study was to assess toxicity of caraway extract on female rats. Carium carvi extract submitted to chemical analysis (Phytochemical screening and Gas chromatography-mass spectrometry (GC-MS) analysis). Acute toxicity study has been performed using 24 female rats divided randomly in 4 groups (n=6 for each group) that received different doses of hydroalcoholic seed extract of caraway 1000, 3000 and ,5000 mg/kg for 14 days. On day 15, the rats were euthanized and whole blood collected to examine complete blood picture. The liver, kidney and the heart have been harvested for histopathologic study and relative organ weight changes. Caraway extract considered relatively safe on blood profile and immune system within the studied doses, as it shown a non-significant change on complete blood counts (CBCs) in a dose-dependent manner (Hb and RBCs increased slightly, while WBCs and PLTs decreased slightly) and without any change in body weight and relative weight percentage of different organs. As conclusion, hydroalcoholic extract of caraway seeds was relatively safe in rats at a dose up to 5000 mg/kg

In vivo safety assessment of Lactobacillus fermentum strains, evaluation of their cholesterol-lowering ability and intestinal microbial modulation.

Despite the growing importance of probiotics apparent health benefits, an impediment to the use of new probiotic cultures is their safety. Hence there is a need to strictly examine the biosafety as well as health benefits of probiotics in in vivo model systems. In this study, two lactic acid bacterial (LAB) cultures Lactobacillus fermentum NCMR 2826 and FIX proven for their in vitro probiotic properties were investigated for their in vivo safety in Wistar rats. An acute toxicity study (14 days) with a high dose of biomass (1016 colony-forming units (CFU) mL-1 ) followed by a subchronic test for 13 weeks with oral feeding of the probiotic cultures in three different doses (107 , 108 and 1010 CFU mL-1 ) on a daily basis revealed the safety of the L. fermentum cultures. The probiotic feeding had no toxic effects on survival, body weight and food consumption with any of the dosages used throughout the treatment period. No statistically significant changes in relative organ weights and serum biochemical and hematological indices were found between the control and the probiotic fed animals. In addition to the safety attributes, the L. fermentum culture fed rats showed reduced serum cholesterol levels, macrovesicular steatosis and hepatocyte ballooning compared with control animals. Further, quantification of intestinal microbiota using real-time polymerase chain reaction (PCR) analysis from animal feces indicated a significant increase and stability of Lactobacillus and Bifidobacterium counts but a decrease of Escherichia coli numbers. This study of safety and beneficial features highlights the use of the two native L. fermentum isolates as potential probiotic food supplements. © 2019 Society of Chemical Industry.

Effects on the reproductive system of young male rats of subcutaneous exposure to n-butylparaben

This study was aimed at determining whether an in vivo subcutaneous exposure to n-butylparaben (n-ButP) during one complete spermatogenic cycle could be harmful to the reproductive system of young male rats. Animals were subcutaneously given 0, 150, 300 and 600 mg/kg/day of n-ButP with vehicle (peanut oil). Body and organ weights, n-ButP excretion, biochemical parameters, sperm and spermatid count, sperm motility, viability, maturity and morphology were examined. Results showed that after a completed spermatogenic cycle, although n-ButP did not induce dose-related changes in the different biochemical parameters, a significant decrease of triacylglicerides (TAG) –due to the vehicle-was found. Furthermore, no effects of n-ButP on body weight gain and relative organ weight changes were noted. Regarding sexual organs, prostate relative weight was significantly increased at the high dose of n-ButP. On the other hand, a significant increase of abnormal sperm morphology due to n-ButP exposure, accompanied by different alterations in sexual organs histopathology, was found. The current results indicate that subcutaneous exposure of n-ButP in young male rats induced toxic effects on the reproductive system, which could affect the capacity of fertilization of animals.

Sub-acute toxicity study on the aqueous extract of <i>Albizia zygia</i> stem bark

Albizia zygia DC (Fabaceae) is widely used in herbal medicine for the treatment of bronchial diseases, fever (including malaria), diarrhea, sores, wounds and toothache. This study was aimed at determining the sub-acute toxicity of the aqueous extract of Albizia zygia stem bark. The sub-acute toxicity was evaluated after administering daily oral doses of 100, 200 and 500 mg/kg of extract for 42 days to rats. Morphological (body weight and organ weight indices), haematological {white blood cell (WBC), red blood cell (RBC), haemoglobin, haematocrit, and platelet counts}, biochemical {alanine aminotransferase (ALT), aspartate amino transferase (AST), alkaline phosphatase (ALP), total protein, total bilirubin (TB), creatinine, urea} and histopathological parameters were assessed using standard procedures. There was no mortality up to the highest dose of 5000 mg/kg in both mice and rats on oral acute administration of A. zygia . Administration of A. zygia (500 mg/kg/day) for 42 days caused a significant (p<0.05) increase in WBC count, decrease in creatinine and no significant changes in relative organ weights or serum concentrations of ALT, ALP, TB, albumin and urea in the treated rats compared to the control. Histologic analysis of the various organs showed mild activation of the lymphocytes of the lungs and the liver, sinus histiocytes of the spleen and mild interstitial congestion in the kidneys, indicating activation of the local immune system of the lungs, liver, kidney and spleen. The results of the study suggest that the aqueous extract of Albizia zygia stem bark can be considered relatively safe on sub-acute exposure. Keywords: Albizia zygia ; Acute toxicity; Histopathology; Spleen

Essential oil of Syzygium aromaticum reverses the deficits of stress-induced behaviors and hippocampal p-ERK/p-CREB/brain-derived neurotrophic factor expression.

Syzygium aromaticum has been widely used in traditional medicine. Our study investigated the safety and antidepressant-like effects of the essential oil of S. aromaticum after acute or long-term treatment. Using GC-MS, a total of eight volatile constituents were identified in the essential oil of S. aromaticum. The single LD50 was approximately 4500 mg/kg based on a 24-h acute oral toxicity study. In a long-term repeated toxicity study of this essential oil (100, 200, and 400 mg/kg, p. o.), only 400 mg/kg induced a significant decrease in body weight. In addition, no significant changes in relative organ weights and histopathological analysis were observed in all doses of essential oil-treated mice compared with the control group. Furthermore, acute S. aromaticum essential oil administration by gavage exerted antidepressant-like effects in the forced swimming test (200 mg/kg, p < 0.05) and tail suspension test (100 and 200 mg/kg, p < 0.05). Long-term S. aromaticum essential oil treatment via gavage significantly increased sucrose preference (50 mg/kg, p < 0.05; 100 and 200 mg/kg, p < 0.01) as well as elevated the protein levels of hippocampal p-ERK, p-CREB, and brain-derived neurotrophic factor in mice exposed to chronic unpredictable mild stress. These results confirmed the safety of the essential oil of S. aromaticum and suggested that its potent antidepressant-like property might be attributed to the improvement in the hippocampal pERK1/2-pCREB-BDNF pathway in rats exposed to chronic unpredictable mild stress.

Changes in relative organ weights and intestinal transporter gene expression in embryos from white Plymouth Rock and WENS Yellow Feather Chickens

This study was conducted to evaluate the embryonic development of broilers with different growth rates and correlate the differences between the amino acid transporter and peptide transporter gene expression patterns to the growth of the small intestine. The results showed that the body and yolk weights of the White Plymouth Rock (WPR) embryos were higher than those of the WENS Yellow Feather Chicken (WYFC) embryos although the relative embryonic body weights were inversely correlated. We studied nine organs and classified them into four clusters according to their changes in relative weight during the hatching process. The levels of gene expression of SLC7A9, SLC1A1 and SLC15A1 in the small intestine increased during embryo development and were affected by breed. Breed-specific differences in embryonic development were observed for SLC7A9, SLC1A1 and SLC15A1 gene expression. When represented as a function of SLC7A9, SLC1A1 or SLC15A1 gene expression, strong correlations were observed for the weight of small intestine. We conclude that WPR embryos have a higher absolute growth rate but a lower relative growth rate in comparison with WYFC embryos. Moreover, the expression levels of the SLC7A9, SLC1A1 or SLC15A1 genes can be used as indicators for the growth of the small intestine.

Effects of combined administration of vitamins C and E on some Plasmodium berghei-induced pathological changes and oxidative stress in mice

This study examined the effects of combined administration of vitamins C and E to Plasmodium berghei-induced anaemia and organ weight alterations as well as changes in endogenous antioxidant status in mice. Three groups of mice were intraperitoneally infected with chloroquine-sensitive P. berghei (NK 65) among which a group was intraperitoneally treated with a combination of vitamins C (100 mg/kg body weight, bw) and E (1,000 i.u./kg bw) whereas another group was treated with chloroquine (25 mg/kg bw). The remaining infected group was left untreated. Data from these groups were compared with those from the uninfected group that was treated with vitamins C and E and the uninfected untreated group. Treatment with vitamins C and E did not significantly (P > 0.05) affect the levels of parasitized red cells for the entire 15-day experimental period except at days 8 and 9 post-infection. At the termination of the experiment, the P. berghei infection was found to induce anaemia, significantly (P < 0.05) increased the relative weight of the liver, spleen and kidney but significantly decreased (P < 0.05) the relative brain weight. However, the parasite-induced anaemia and relative organ weight changes were ameliorated by the vitamin administration to varying degree. Furthermore, malonyldialdehyde concentration in the serum, liver and brain of infected animals was significantly (P < 0.05) elevated whereas superoxide dismutase and catalase activities were significantly (P < 0.05) decreased by the infection, but the vitamin treatment tended to restore the disease-induced alterations in these oxidative stress markers. Data from this study suggest that combined vitamins C and E could be beneficial in alleviating P. berghei-induced anaemia and other pathological effects in mice.

Safety evaluation of arachidonic acid rich Mortierella alpina biomass in albino rats—A subchronic study

Safety evaluation of arachidonic acid rich Mortierella alpina biomass was carried out in Wistar rats by acute and subchronic oral toxicity studies. A preliminary acute toxicity study revealed that the biomass was safe at acute doses and that the LD50 exceeded 5000 mg/kg BW, the highest dose used in the study. In subchronic study, rats were fed diet containing 0, 2500, 5000, 10,000, 20,000 and 30,000 mg/kg, M. alpina biomass for a period of 13 weeks. Results indicated that biomass fortification had a positive influence on growth with no overt toxic effects on the survival, food consumption and body weight gain throughout the treatment interlude. The statistically significant changes in relative organ weights, serum biochemical and hematological indices in M. alpina fed groups’ viz., higher relative weights of spleen, liver, brain and ovary in females, reduced hemoglobin concentration in males, elevated WBC counts at highest dose, reduction in serum triglycerides and increased alkaline phosphatase activity were not concomitant with pertinent histopathological changes and hence toxicologically inconsequential. No microscopic or macroscopic lesions attributable to the treatment were manifested in the experimental groups. The results of the present study strongly advocate the safety of M. alpina biomass in rats at levels used in the study.

Efficacy of modified montmorillonite nanocomposite to reduce the toxicity of aflatoxin in broiler chicks

Effects of adding 3 g modified montmorillonite nanocomposite (MMN)/kg diets containing 0.1 mg aflatoxin (AF)/kg were determined in broiler chicks from 0 to 42 days of age. Compared to the control, AF alone significantly decreased BW gain and feed efficiency. However, no differences in BW gain and feed/gain ratio were found between the chicks fed 3 g MMN or 3 g MMN plus AF/kg treatment groups and the control group, indicating apparent protection against the deleterious effects caused by AF. Treatment-related changes in relative organ weights, hematological values, serum and liver biochemical values and enzymatic activities were also observed. Most of the parameters measured for the birds fed 3 g MMN/kg diet did not alter. The addition of 3 g MMN/kg AF-contaminated diet diminished the adverse effects of AF on most relative organ weights, hematological values, serum and liver biochemical values and enzymatic activities associated with aflatoxicosis. These findings suggested that MMN can effectively reduce the toxicity of AF in broiler chicks and MMN can be a potential ameliorator of aflatoxicosis in broiler chicks.

Physiological responses of a natural antioxidant flavonoid mixture, silymarin, in BALB/c mice: III. Silymarin inhibits T-lymphocyte function at low doses but stimulates inflammatory processes at high doses.

Silymarin is a mixture of bioactive flavonoids isolated from Milk Thistle (Silybum marianum). Crude extracts from this plant have been used for centuries as a natural remedy and silymarin is now effectively used in the treatment of inflammatory liver toxicity and disease in humans. In vitro studies show that silymarin can inhibit the production and damage caused by tumor necrosis factor alpha (TNFalpha) and is a potent antioxidant both in vitro and in vivo. Such findings suggest silymarin may impact the immune system but little information exists following in vivo exposure. Therefore, we tested the hypothesis that exposure to silymarin will modulate the inflammatory immune response. Male BABL/c mice (6/group) were treated intraperitoneally once daily for five days with 0, 10, 50 or 250 mg/kg of silymarin. Silymarin exposure did not produce any signs of overt toxicity or any changes in relative organ weights. Flow cytometric examination of splenic lymphocyte populations showed that the absolute number of CD3+ T-lymphocytes was reduced in the 10 and 50 mg/kg groups although significance was evident only in the 10 mg/kg group. Concomitant decreases in CD4+ and CD8+ T-cell populations were observed but only the CD4+ population in mice treated with 10 mg/kg of silymarin was significantly different from control. Functional examination of secondary lymphoid cells revealed that phytohemagglutinin-induced T-lymphocyte proliferation was increased in the lowest dose group only. B-lymphocyte blastogenesis induced by lipopolysaccharide was increased following exposure to 10 and 50 mg/kg of silymarin. Similarly, expression of TNFalpha, inducible nitric oxide synthase, IL-1beta and IL-6 mRNA were increased dose-dependently. The expression of IL-2 and IL-4 were reduced in mice treated with 10 and 50 mg/kg of silymarin although only the 10 mg/kg group was significantly different from control. The results indicate that in vivo parenteral exposure to silymarin results in suppression of T-lymphocyte function at low doses and stimulation of inflammatory processes at higher doses. Further studies investigating the effects of silymarin on the immune system are warranted.

Reproductive traits in common toad Bufo bufo from the vicinity of Belgrade

Common toad Bujo bufo is a species with wide geografical and altitudinal distribution in Europe (A I' n old 2002). Although it prefers forests, mainly deciduous, it also occurs in fields, meadows, gardens and human settlements (R ado van 0 vic 1951). The aims of this study were to analyse the annual reproductive cycle of Bufo bufo, as a part of the study on reproductive traits in amphibian populations from human-altered habitats, with special emphasis on sites in the vicinity of Belgrade; to compare seasonal changes in relative organ weights in both sexes; to examine variation in fecundity and relationship between fecundity and body size.

Toxicological investigations in the semiconductor industry: I. Studies on the acute oral toxicity of a complex mixture of waste products from the aluminium plasma etching process.

In dry etching processes--one of the sources of potential exposure to toxic wastes in the semiconductor industry--complex mixtures of inorganic and organic compounds arise from reactions between feed stock gases (BCl3/Cl2), top layers (aluminium photoresist), and the carrier gas (N2). Two different fractions of the complex mixture--one an ethanolic solution (ES) and the other an insoluble liquid residue (LR)--were examined for acute oral toxicity in rats. Analytical data showed that the ethanol soluble fraction contained mainly inorganic compounds, whereas the residue contained various halogenated hydrocarbons. Neither death nor behavioral changes occurred after oral administration and observation up to 23 days. ES caused a lower mean arterial blood pressure in both sexes, increased P-R-intervals in male rats, and caused some mild biochemical and hematological alterations and changes in relative organ weights compared to the control groups. Exposure to LR influenced food and water intake, and caused a significant decrease in body weights, signs of polyurie, as well as changes in various relative organ weights and biochemical and hematological parameters. The blood pressure of the male animals fell and the heart rates of both sexes decreased.

Effects of a Hydrated Sodium Calcium Aluminosilicate on Growing Turkey Poults During Aflatoxicosis

Effects of adding .5% of a hydrated sodium calcium aluminosilicate (HSCAS) to diets containing 1 or .5 mg aflatoxin (AF)/kg were determined in male turkey poults from 1 day to 3 wk of age. Body weight gains were significantly reduced by 51 and 19% in turkey poults fed 1 and .5 mg AF/kg, respectively; efficiency of feed utilization was not affected. There were no deaths in poults fed .5 mg AF/kg; however, the mortality rate was 88% in poults fed 1 mg AF/kg. The addition of .5% dietary HSCAS resulted in a 68% decrease in mortality to 28% for the 3-wk experimental period. Treatment-related changes in relative organ weights, hematological values, serum biochemical values, and enzyme activities were observed. The HSCAS in the absence of AF did not alter any of the parameters measured. The HSCAS diminished the adverse effects of AF on body weight gains, most relative organ weights, hematological values, serum biochemical values, and enzyme activities associated with .5 mg AF/kg, but not 1 mg AF/kg. These findings indicate that HSCAS may diminish many of the adverse effects of AF in an AF-sensitive species, the turkey.

Oncogenicity study of trifluralin in B6C3F 1 mice

B6C3F 1 mice were maintained for 24 months on diets containing 0, 563, 2250 or 4500 ppm trifluralin. These dietary concentrations corresponded to daily doses of approximately 70, 285 or 570 mg/kg body weight, respectively. The control group contained 120 mice/sex and treated groups consisted of 80 mice/sex. There were no treatment-related effects on the survival, appearance or behaviour of the mice. Survival at test termination was at least 67% in each group. Compared with controls, mean body weight was significantly reduced in a dose-related manner in mice of both sexes given the 2250 and 4500 ppm diets. At 21 months, the reduction in body weight was ⩾ 15 and ⩾ 30%, respectively. At study termination, dose-related decreases in erythrocytic and leucocytic values were also observed at dietary levels of 2250 and 4500 ppm. In clinical chemistry evaluations, blood urea nitrogen levels and alkaline phosphatase activity in mice of both sexes were significantly increased at trifluralin levels of 2250 and 4500 ppm. Blood urea nitrogen also showed a marginal increase in females given the low dose of trifluralin. Alanine aminotransferase activity was significantly increased in males at all treatment levels. Although there were a number of absolute and relative organ weight changes in all three treatment groups that were significantly different from the control values, the reduced relative kidney weights in males and the increased relative liver weights in both sexes at dietary levels of 2250 and 4500 ppm were the only changes that could be correlated with altered clinical chemistry values. Apart from an increase in the incidence and severity of progressive glomerulonephritis in females of the high-dose group, there was no evidence of a treatment-related effect on any pathological condition. Chronic dietary administration of high doses of trifluralin did not cause an increase in the incidence of benign or malignant neoplasms in B6C3F 1 mice.

Effect of dietary sub-lethal doses of lima bean lectin on relative organ weights, pancreatic and intestinal trypsin (EC 3.4.21.4) and chymotrypsin (EC 3.4.21.1) in the rat.

The dietary implications of feeding sub-lethal doses of extracted and purified lectin from lima bean were assessed in weanling rats using changes in relative organ weights, pancreatic and intestinal trypsin and chymotrypsin activities as the response indices. Liver weights decreased significantly (p less than 0.05) while the heart showed a slight but non-significant increase in response to dietary lectin levels. The kidneys, pancreas and spleen were not significantly affected by dietary lectin. Although the activities of the pancreatic enzymes tended, for the most part, to decrease with increasing dietary lectin, such decreases were not significant when compared with the control. Intestinal trypsin and chymotrypsin activities were significantly (p less than 0.05) decreased in the small intestine while the activity values in both the large intestine and caecum were relatively unaffected. Activities of both enzymes showed significant (p less than 0.05) negative quadratic relationship with dietary lectin levels in the small intestine as judged by the magnitude of the R2, coefficients of multiple determination, of 0.77 and 0.76 for trypsin and chymotrypsin respectively.

A quantitative histologic analysis of selected tissues in growing mice

Summary Quantitative histologic methods were utilized to determine some of the changes that take place in selected tissues of normal growing mice from birth to 30 days of age. Four groups of mice were sacrificed at the ages of 0, 10, 20, and 30 days, respectively. Body and selected organ weights were obtained, and the organs were processed histologically. Cellular or structural measurements were made, using the stereologic methods of planimetry and line analysis. Changes in relative organ weights, component volumes, and relative component dimensions were analyzed. Because of the loss of extramedullary hematopoietic cells, relative liver weight was reduced in 10-day-old animals. Relative heart weight decreased throughout the period studied. Relative kidney weight increased from birth to 10 days, but returned to the original level from 20 to 30 days. Liver cell numbers increased at a decreasing rate throughout the investigation. Changes in hepatic cell size were erratic. The number of fibers in the left ventricle of the heart increased from birth to 10 days, after which further growth was by fiber enlargement. Kidney growth was the result of tubular expansion, occurring first in both the medulla and cortex, and later involving primarily the cortex. Little postnatal increase in size or number of glomeruli was observed.