Effects of testosterone and estradiol on serum somatomedin A and growth rate of rats

The mode of involvement of sex steroids in the growth spurt during adolescence was studied in Wistar rats with a special reference to the level of serum somatomedin A (SMA) determined by radioreceptor assay. Intramuscular administration of testosterone propionate (T; 1 mg/day, alternately for 10 days) to female or gonadectomized male rats provoked a small but significant increase in their body weight or body length without affecting the serum SMA level. In contrast, in hypophysectomized (hypox) male rats T caused a considerable increase in body weight and the serum SMA level only when administered concurrently with bovine growth hormone (bGH; 0.2 U/day, ip). T did not affect the sulfation activity in vitro. These results suggest that androgen participates in the growth spurt during adolescence by enhancing the SMA effect and/or potentiating the SMA production by GH. Estradiol benzoate (E2; 100 micrograms/day, alternately for 10 days) caused a decrease in the serum SMA level and the growth rate in normal male rats. However, E2 produced an increase in the SMA level when administered to hypox male rats, although the growth was retarded and sulfation potency of the serum was sharply reduced. These results indicate that E2 may suppress the growth by lowering SMA generation in normal rats and cause a production of biologically inactive SMA in hypox male rats.     

Influence of early nutrition on growth and adipose tissue characteristics in male and female rats

The purpose of this investigation was to assess the effects of early nutrition on adipose tissue characteristics and growth by altering litter size. After birth, rats were redistributed into large (15-18 pups), control (10 pups), or small (4 pups) litters. During the postweaning phase of growth half of the small-litter animals were pair-fed to animals raised in large litters for 5 wk and then allowed to feed ad libitum until they were 80 days of age. The small-litter males gained weight at a more rapid rate than the other litter types, both before and after weaning, and attained a final body weight twofold greater than the other groups. The small-litter males had significantly higher (P less than 0.05) numbers of adipocytes per epididymal fat pad than the other litter groups with 60.4, 51.4, and 79.0% greater cell number per pad than control, large, and pair-fed animals, respectively. Limiting food intake to small-litter animals after weaning (pair-fed) inhibited this growth and prevented fat cell proliferation. Litter manipulation had significant effects on male rats, but the same treatment did not influence female rats. Litter size influenced fat cell characteristics but had little effect on the adipocytes' ability to take up or metabolize glucose. The major finding, in terms of insulin responsiveness, was the difference between the sexes. The uptake of tritiated 2-deoxyglucose by the fat cells of female litter groups was significantly higher than that of the males whether insulin was present or not, whereas the conversion of [1-14C]glucose to CO2 by the adipocytes of females was lower than that of the males.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ontogeny of somatomedin during development in the mouse. Serum concentrations, molecular forms, binding proteins, and tissue receptors

The purpose of this study was to assess the ontogeny of serum concentrations and molecular forms of somatomedin during fetal and postnatal development and to define the changes in serum binding proteins for somatomedin-C during various stages of development. The finding that fetal, placental, and decidual mouse tissues possess receptors for somatomedin suggests a role for somatomedin in fetal growth and possibly in the maintenance of pregnancy. Serum somatomedin-C was measured using a highly specific, heterologous radioimmunoassay (RIA) and a less specific membrane binding assay (MBA) which is more sensitive to the influence of somatomedins other than somatomedin-C. The assays were validated for mouse serum by showing that serum concentrations were reduced in genetically growth hormone-deficient mice and in hypophysectomized mice and were increased by growth hormone therapy. As in the human, the RIA measures only a portion of the somatomedin-C present in mouse serum. This “covering up” of somatomedin is attributed to the presence of serum binding proteins and is corrected by treatment of serum samples with acid. By both RIA and MBA, serum somatomedin concentrations are low in fetal and newborn mice, begin to rise in the fourth postnatal week, and reach adult values by 7 weeks of age. The chromatographic pattern of adult mouse serum on Sephacryl 200 is similar to that observed with human sera: The immunoreactive material elutes at apparent molecular weights of 140,000 and 30,000–40,000. The elution profile of ¹²⁵I-labeled somatomedin-C bound to components of serum is nearly identical to the pattern of endogenous activity. As with human serum, somatomedin-C in acidified mouse serum elutes at a lower molecular weight, coincident with insulin and purified somatomedin-C. Maternal serum somatomedin declines in the last half of gestation at the time when placental lactogen levels rise. Along with the absolute decline in somatomedin content is the appearance of unsaturated sites on somatomedin binding proteins. These findings are unexpected and unexplained since somatomedin rises late in pregnancy in humans and several lines of evidence suggest that placental lactogen has the capacity to stimulate somatomedin production. We previously have presented evidence that explants of multiple fetal mouse tissues synthesize somatomedin-C. The present study shows that the immunoreactive somatomedin-C in fetal mouse serum shares identical characteristics with those reported previously for media obtained from mouse liver explants. It seems possible that somatomedin's actions are exerted primarily at or near its site of production and that circulatory levels do not reflect the importance of somatomedin-C on fetal growth. While elucidation of the dramatic developmental changes in serum content and molecular forms of somatomedin-C and in somatomedin binding proteins may be essential to clarifying the role of somatomedin on fetal growth, proof that somatomedin stimulates fetal growth will depend in large part on studies of its biological actions on fetal tissues.     

The consequences of differences in litter size for the nursing cat and her kittens

Seventy-one litters of kittens (mean litter size 4.4) were studied from birth to eight weeks of age in order to measure kitten growth and maternal body condition. Few sex differences in growth occur; male and female kittens place a similar burden on their lactating mother. A mother's weight (non-pregnant, non-lactating) interacts with litter size to determine the fate of her growing kittens. A large litter places a burden on both the mother and on the kittens, whose growth is affected; small mothers with large litters are particularly at risk. An acceleration in kitten growth occurs at about 32 days as the kittens take more solid food. This change in growth rate is more marked in large litters. Kittens of light mothers and kittens in large litters are weaned at a lower weight, and kittens of light mothers are weaned earlier. Our results indicate that, under poor environmental conditions, large litters would be less successful than small litters; kitten growth and survival would be affected and providing milk for a large litter would have a detrimental effect on the mother's health. The cost of lactation appears to have been a major evolutionary factor in determining mean litter size.     

Trade-offs in Energy Allocation During Lactation

SYNOPSIS. During lactation, mothers require energy to meet bothmaternal and offspring requirements. If a mother exports toomuch energy to dependent offspring (in milk), her weight lossmay be excessive and maternal risk may increase. Conversely,too little energy allocation to offspring may reduce the growthrate or induce mortality of dependent offspring. This paradigmwas evaluated in cotton rats (Sigmodon hispidus) supportingsmall (3 pup) and large (6 pup) litters from early to late lactation.Several types of evidence indicate that physiological constraintslimit the ability of mothers with large litters to provide resourcesto offspring. Mothers with large litters produced a dilute,energy-poor milk and their rates of food intake, weight lossand energy export per litter appeared to approach physiologicalmaxima. Whereas the energy exported to pups in small littersincreased from early to late lactation, the energy flow perpup in large litters was consistently low; consequently, offspringin large litters had low growth rates. An increase in eithermaternal food intake or weight loss (catabolism of maternaltissue) could have provided additional energy to offset thelow growth rate of pups in large litters. However, mothers withlarge litters did not substantially increase their food intakeor weight loss compared with mothers supporting small litters.These results indicate that the maternal support of offspringin large litters is limited. The pattern of energy allocationshown by cotton rats with large litters likely reflects a compromisebetween meeting maternal and offspring energy requirements (cf.,Parker and Macnair, 1979). The energy flow is greater than optimalfor the parent but less than optimal for the offspring. Lessmaternal-offspring conflict occurs in small than large littersbecause offspring in small litters maintain a high growth rateat a relatively low maternal cost. Yet, under favorable environmentalconditions, the reduction in maternal-offspring conflict hasno apparent fitness benefit.     

The effect of overfeeding the young in early postnatal ontogeny on brown fatty tissue

We studied the effects of overfeeding of neonatal Wistar rats on O2 consumption by the interscapular brown adipose tissue and DNA content in the tissue. The overfeeding was induced by reducing the litter size to two to three pups per dam compared with standard litters of five to ten pups. All animals were allowed free access to water and forage and were kept at 24 +/- 1 degrees C. Newborn and 16-day-old rat pups were used in the experiments. The body weight of overfed pups was significantly higher than that of standard fed pups (p < 0.001). There were no differences between groups of 16-day-old rats in the resting metabolic rate. The mass of dried brown adipose tissue relative to the body mass in overfed pups was lower than in the control pups (p < 0.01). O2 consumption in the rats from small litters was 35% higher (p < 0.001). DNA content (mg/g brown adipose tissue) in overfed rats was 35% lower as compared to the control pups (p < 0.001). These results indicate that overfeeding at the preweaning stage of life affects growth, cellularity, and thermogenic function of brown adipose tissue.     

Decrease in serum receptor-reactive somatomedin in diabetes.

Somatomedin in rat serum has been measured by a sensitive radioreceptor assay using 125I-labelled human somatomedin and human placental membrane. In rats made diabetic with strepotzotocin, receptor-reactive somatomedin levels were decrease by up to 75%. The decrease followed the time course of increasing serum glucose and occurred to the same extent in rats aged between 4 and 40 weeks. Endogenous serum receptor-reactive somatomedin appeared exclusively in high molecular weight fractions on gel chromatography. In diabetes the decreased somatomedin was due to a fall in this high molecular weight activity, but was not accompanied by a fall in somatomedin binding protein. These results suggest a role for insulin in maintaining serum somatomedin levels.     

Comparison of crowding and food restriction effects on growth, body weight gain and endocrine status in the rat

The present work compares the effects of post-weaning crowding and those of food restriction on growth, body weight gain and the levels of several hormones, in male Sprague-Dawley rats. Crowding resulted in reduced food intake and diminished body weight gain. Rats daily receiving the same amount of food as that eaten by crowded rats (food-restricted group) showed similar body weight gain as crowded rats, but higher growth rate. Neither crowding nor food restriction altered the pituitary-adrenal axis. In contrast, both treatments decreased serum insulin, growth hormone (GH), somatomedin C (Sm-C) and thyroid-stimulating hormone (TSH) as compared to control rats. The reduction of GH and Sm-C levels was similar in crowded and food-restricted rats but that of TSH was higher in food-restricted, rather than in crowded rats. The present data indicate that the effects of crowding could only be partially explained by the concomittant reduction of food intake and that the serum levels of the hormones studied could not explain the differences between the crowded and food-restricted rats with regard to growth.     

Binding protein of somatomedin A in serum from men and rats

After gel chromatography of human and rat serum at pH 7.4, all endogenous somatomedin A was recovered in the high molecular weight range. The largest peak was found in the gamma-globulin (II) region and the next largest peak found in the albumin region (III). The amounts of somatomedin A in the peak II region increased in serum from acromegalies and decreased in serum from growth hormone deficient patients. Four radioactive peaks were observed after gel chromatography of serum incubated with 125I-somatomedin A. Only the two peaks corresponding to peaks II and III out of the four peaks were displaced by adding 50 microgram of partially purified cold somatomedin A. The radioactivity of peak II decreased in sera from growth hormone deficient patients and increased after growth hormone administration. These observations support the hypothesis that the growth hormone regulates not only somatomedin A but also its carrier protein.     

Delayed appearance of liver growth hormone binding sites and of growth hormone-induced somatomedin production during rat development

The present study was designed to determine whether the apparent paradox of high circulating growth hormone levels in the fetus and the minimal effect of this hormone on growth might reflect a diminished responsiveness of fetal target organs to GH. Specific uptake by rat liver of [125I] bGH was very low in fetuses as compared to suckling and adult rats. Also, liver uptake of the iodinated hormone decreased proportionally with the simultaneous injection of increasing amounts of growth hormone, but was not modified by the simultaneous injection of unlabelled chemically-related hormones. Since the water content is significantly greater in fetal than adult tissues, results were expressed by liver dry weight and again, [125I] bGH liver uptake continued to increase with age. After bovine growth hormone administration to adult rats, plasma somatomedin C concentrations increased significantly, while they had no effect in fetuses. These results suggest that reduced liver somatogenic binding sites in the fetus prevents growth hormone from inducing growth-promoting effects during intrauterine life.     

Adaptation of siblings of female rats given ethanol effect of N-acetyl-L-cysteine

Summary Ethanol administration to female rats before and during pregnancy resulted in decreased number of litters and increased activities of serum GOT, GPT and ALP. The hepatotoxicity of ethanol was indicated by the histological alterations both in the mother and siblings. There was increased levels of tissue lipids in mother and litters born to alcoholic rats. The concentration of TBARS in the liver and kidney were significantly increased in alcohol treated rats and their litters. The activities of the anti-peroxidative enzymes SOD and CAT were decreased on alcohol treatment in female rats. The glutathione content in liver and kidney decreased significantly in litters born to alcoholic rats.We have observed that the treatment with N-acetylcysteine offers protection against the toxic effect of alcohol in female rats during pregnancy and litters born to them. In N-acetylcysteine treated rats the number of litters as well as the average birth weight were close to that of control animals. Nacetylcysteine decreases the activities of serum GOT, GPT and ALP in female rats. We have also observed decreased levels of tissue lipids in mother and litters born to alcoholic rats given N-acetylcysteine when compared to alcoholic rats. The levels of TBARS in liver, kidney were also decreased both in mother and litter born to alcohol + N-acetylcysteine, while the activities of SOD and CAT were increased in liver of alcoholic rats given N-acetylcysteine when compared to alcoholic rats. Histopathological studies also showed the protective effect of N-acetylcysteine in both mother and litter in liver and kidney against alcoholic induced toxicity.     

Role of the mouse visceral yolk sac in nutrition: inhibition by a somatomedin inhibitor

A low molecular weight somatomedin inhibitory serum fraction (SI), obtained from streptozotocin-induced diabetic rats, causes morphological abnormalities and growth reduction in mouse embryos grown in whole embryo culture (WEC). These abnormalities are thought to be caused, at least in part, by a failure of the visceral yolk sac (VYS) to properly degrade proteins, a process that normally provides the conceptus with amino acids and peptides for de novo protein synthesis (histiotrophic nutrition). To test this hypothesis, embryos exposed to the SI were provided with a mixture of ten essential amino acids (supplemented group) in an attempt to circumvent SI-induced VYS dysfunction. Results showed that 82.4% (14/17) of embryos in the amino acid-supplemented group exhibited improved growth and development compared to those embryos exposed to medium containing the SI alone (unsupplemented group). Supplemented embryos showed greater expansion of the brain regions, improved visceral arch development, and increased protein content compared to nonsupplemented SI-treated embryos. However, these parameters were still reduced compared to controls. VYSs from both the unsupplemented and amino acid-supplemented groups were identical with respect to alterations in morphology and increased protein content compared to VYSs from conceptuses cultured in control medium (with or without amino acid supplementation). The improvement in embryonic growth and development due to amino acid supplementation in spite of VYS abnormalities supports the hypothesis that nutritional deprivation is one aspect of SI-induced teratogenesis.     

Preweaning over- and underfeeding alters onset of puberty in the rat without affecting kisspeptin

The perinatal nutritional environment can permanently influence body weight, potentially leading to changes in puberty onset and reproductive function. We hypothesized that perinatal under- or overfeeding would alter puberty onset and influence concentrations of a neuropeptide crucial for successful puberty, kisspeptin. We manipulated Wistar rat litter sizes to derive small (SL), control (CL), and large (LL) litters containing 4, 12, and 20 rat pups respectively. This manipulation results in an overweight phenotype in SL rats and a lean phenotype in LL that persists throughout life. To investigate whether successful puberty onset is affected by neonatal under- or overfeeding, we examined indices of growth and development, including the onset of puberty, as well as the central expression of Kiss1 mRNA in these pups. Male LL rats reached puberty later than those from CL. These males also had reduced plasma testosterone and elevated 17beta-estradiol concentrations at puberty. The age at puberty onset was not affected in SL males despite accelerated growth. In females, puberty onset was not significantly delayed by having a lean phenotype, and steroid hormones were not affected. The age at onset was, however, younger in the SL females. Kiss1 mRNA in the hypothalamus was not affected by neonatal nutrition either at puberty or 7 days later. Our findings show early life underfeeding in males and overfeeding in females significantly affects puberty onset, altering steroid hormone concentrations in males, but this is not related to changes in hypothalamic kisspeptin.     

The influence of the sex of litter-mates on subsequent maternal behaviour in Rattus norvegicus.

Female rats reared in unisexual (U) or bisexual (B) cross-fostered litters were mated at 75 days of age and their maternal behaviour compared by periodic observation over 20 days following birth of their litters. In two separate experiments, U-females showed a lower incidence of pregnancy and, at birth, of litters with ten or more pups than B-females (P less than 0-05). Litters culled to ten animals on the day after birth were significantly heavier in B- than in U-females, although this difference was not evident at weaning as litters reared by U-females showed a relatively greater (P less than 0-01) increase in weight during the investigation than the corresponding litters reared by B-females. Using a scoring method, no difference was evident in the opportunities that U- and B-females offered for their pups to suck, and, when not nursing pups in the nest, both groups of females engaged equally in activities such as grooming, sleeping, eating, and rearing on their hind legs. Throughout the 20-day observation period, B-females maintained significantly more elaborate nests (as scored on an arbitrary scale) than U-females. This difference was evident in females rearing litters of both five and ten animals, and was observed in two separate experiments. In addition, whereas only 15 per cent of U-females were observed nest-building, over 60 per cent of B-females were noted to be engaged in this activity on one or more occasions (P less than 0-001). It is suggested that, in the light of previous findings, these results may reflect differences in oestrogen and/or progesterone metabolism in unisexually-reared and bisexually-reared female rats.     

Passive immunization of lactating mice with stanniocalcin-1 antiserum reduces mammary gland development, milk fat content, and postnatal pup growth

During pregnancy and lactation in rodents, stanniocalcin-1 (STC-1) production by the ovaries is upregulated markedly and released into the circulation. The mammary glands are one target of this systemically delivered hormone. The purpose of this study was to lower serum levels of STC-1 in lactating mice through passive immunization so as to monitor the effects on mammary gland function and postnatal pup growth. Passive immunization significantly reduced circulating hormone levels, and pup growth was significantly compromised (30%), even though control and experimental litters had ingested equal amounts of milk. When mammary glands were analyzed, the alveolar area was significantly reduced in antibody-treated mothers. An analysis of milk composition revealed no changes in lactose, protein, or electrolyte levels but an approximately 40% reduction in triglyceride levels. The latter was due to a significant reduction in mammary gland lipoprotein lipase activity and led to a significant buildup of triglycerides in the serum. Body fat content was also significantly reduced in pups from antibody-treated mothers, whereas pup fecal fat content was increased. In mothers, passive immunization also caused significant behavioral effects, in particular, increased locomotor and hindleg rearing activities. Collectively, the results suggest that systemically derived STC-1 has important effects on mammary gland development and the transfer of serum-based triglycerides into milk. Locomotor effects suggest that STC-1 also has a role in maternal behavior.     

Neonatal overfeeding induced by small litter rearing causes altered glucocorticoid metabolism in rats

Elevated glucocorticoid (GC) activity may be involved in the development of the metabolic syndrome. Tissue GC exposure is determined by the tissue-specific GC-activating enzyme 11β-hydroxysteriod dehydrogenase type 1 (11β-HSD1) and the GC-inactivating enzyme 5α-reductase type 1 (5αR1), as well as 5β-reductase (5βR). Our aim was to study the effects of neonatal overfeeding induced by small litter rearing on the expression of GC-regulating enzymes in adipose tissue and/or liver and on obesity-related metabolic disturbances during development. Male Sprague-Dawley rat pup litters were adjusted to litter sizes of three (small litters, SL) or ten (normal litters, NL) on postnatal day 3 and then given standard chow from postnatal week 3 onward (W3). Small litter rearing induced obesity, hyperinsulinemia, and higher circulating corticosterone in adults. 11β-HSD1 expression and enzyme activity in retroperitoneal, but not in epididymal, adipose tissue increased with postnatal time and peaked at W5/W6 in both groups before declining. From W8, 11β-HSD1 expression and enzyme activity levels in retroperitoneal fat persisted at significantly higher levels in SL compared to NL rats. Hepatic 11β-HSD1 enzyme activity in SL rats was elevated from W3 to W16 compared to NL rats. Hepatic 5αR1 and 5βR expression was higher in SL compared to NL rats after weaning until W6, whereupon expression decreased in the SL rats and remained similar to that in NL rats. In conclusion, small litter rearing in rats induced peripheral tissue-specific alterations in 11β-HSD1 expression and activity and 5αR1 and 5βR expression during puberty, which could contribute to elevated tissue-specific GC exposure and aggravate the development of metabolic dysregulation in adults.     

Cell proliferation in organs of rats bearing hepatoma 3924A: effects of X-rays of surgery

For inbred rats with Morris hepatoma 3924A, increases in tumor size were accompanied by increases in weight and DNA content of spleen, DNA content of tibial marrow, and peripheral white cell concentrations of blood. White blood cell concentrations of rats with tumors weighing more than 5 g were approximately two-fold greater than for rats without tumors. Neutrophils were primarily responsible for the increase in white cells. Local x-radiation of 3750R to the tumor when the tumor was small prevented tumor growth and the increases in spleen weight, incorporation of 3H-thymidine into spleen DNA, white blood cell count, and tibial marrow DNA content related to tumor growth. Surgical removal of large tumors resulted in a return of spleen weight and DNA content to near normal values within 1 week. Despite the evidence for increased cell proliferation in hematopoietic tissues of rats with hepatoma 3924A, no systematic relationship has been observed between tumor size and animal survival following treatment with the cell cycle specific agent 5-fluorouracil when tumors have varied in size from 0.5 g to 5 g at the time of drug treatment.     

Pygmy mouse fibroblasts in tissue culture: evaluation of multiplication stimulating activity (MSA) receptors and growth responses to MSA

The pygmy mouse has been proposed as a model for growth hormone resistance; it has normal serum somatomedin levels and does not respond to growth hormone treatment. In order to determine if the growth impairment is caused by a defect in somatomedin binding or in postreceptor action of somatomedin we compared fibroblasts derived from pygmy mice with those from normal appearing littermates. Using multiplication-stimulating activity (MSA) as a model somatomedin we found a normal Ka of binding to the cell surface MSA receptor but a significantly increased number of MSA receptors on the fibroblasts derived from pygmy mice. Studies of thymidine incorporation into DNA failed to demonstrate a difference between pygmy and normal fibroblasts in their responses to MSA alone, but there was a significantly greater thymidine incorporation into the DNA of normal fibroblasts when both competence factor (platelet-derived growth factor) and progression factors (somatomedins and growth hormone deficient platelet-poor plasma) were present in the test medium. On the other hand, cell proliferation studies did not demonstrate a consistent difference in the growth rate of normal versus pygmy fibroblasts. The data support the conclusion that the imparied growth of the pygmy mouse in vivo may be caused by factors which lie outside of the growth hormone-somatomedin pathway.     

Cold-rearing normalizes capacity for norepinephrine-stimulated thermogenesis but not body temperature in 16-day-old fatty Zucker rats

The effects of a lowered rearing temperature on body weight, core temperature (Tc) and norepinephrine(NE)-stimulated thermogenesis were investigated in 16- to 17-day-old Zucker rat pups. 16-day-old fatty pups were significantly heavier (9%) than lean littermates in litters reared at 18 degrees C ("cold-reared") but not in litters reared at 25 degrees C ("normally-reared"). After 2 h isolation at 25 degrees C, Tc of lean pups was slightly higher (37.1 degrees C) in cold-reared litters than in normally-reared litters (36.4 degrees C), while fatty pups reared at either temperature were severely hypothermic (Tc = 33 - 34 degrees C). At an ambient temperature of 25 degrees C Tc in fatty and lean cold-reared pups increased to 39.5 degrees C after subcutaneous injection of 800 micrograms/kg NE. Normally-reared lean pups reached the same peak Tc after NE injection, while their fatty littermates reached a significantly lower peak Tc of 38.4 degrees C. The hypothermia associated with the onset of excess fat deposition in suckling fatty Zucker rats is not caused by a reduced capacity for NE-stimulated thermogenesis.     

Effect of ovine prolactin on serum somatomedin bioactivity in hypophysectomized female rats.

Ovine prolactin (oPRL) increased serum somatomedin (SM) bioactivity in hypophysectomized female rats. ACTH, in small but not large doses, augmented this oPRL effect. These results suggest that in the female rat PRL may regulate SM production. Adrenal factors may variably modulate SM production or serum SM bioactivity.