Earlier onset of puberty in girls: relation to increased body mass index and race

OBJECTIVE

A recent study conducted by the Pediatric Research in Office Settings network provided evidence that girls in the United States, especially black girls, are starting puberty at a younger age than earlier studies had found, but the reasons for this are not known. Because nutritional status is known to affect timing of puberty and there is a clear trend for increasing obesity in US children during the past 25 years, it was hypothesized that the earlier onset of puberty could be attributable to the increasing prevalence of obesity in young girls. Therefore, the objective of this study was to reexamine the Pediatric Research in Office Settings puberty data by comparing the age-normalized body mass index (BMI-ZS; a crude estimate of fatness) of girls who had breast or pubic hair development versus those who were still prepubertal, looking at the effects of age and race.

RESULTS

For white girls, the BMI-ZS were markedly higher in pubertal versus prepubertal 6- to 9-year-olds; for black girls, a smaller difference was seen, which was significant only for 9-year-olds. Higher BMI-ZS also were found in girls who had pubic hair but no breast development versus girls who had neither pubic hair nor breast development. A multivariate analysis confirms that obesity (as measured by BMI) is significantly associated with early puberty in white girls and is associated with early puberty in black girls as well, but to a lesser extent.

CONCLUSIONS

The results are consistent with obesity's being an important contributing factor to the earlier onset of puberty in girls. Factors other than obesity, however, perhaps genetic and/or environmental ones, are needed to explain the higher prevalence of early puberty in black versus white girls.

Third-year medical student survey of office preceptorships during the pediatric clerkship

OBJECTIVE

To assess medical students' interest in a career in pediatrics following their categorical pediatric clerkship.

DESIGN

Satisfaction questionnaire to 704 third-year clerks in 5 university medical schools following the pediatric clerkship.

METHODS

Analysis of the influence of the community office-based experience compared with the inpatient experience, and examination aspects of the office preceptorship most valued by the medical students.

MAIN OUTCOME MEASURE

Satisfaction questionnaire addressing office-based experiences.

RESULTS

Third-year pediatric clerks report that the private office setting provides a valuable learning experience, particularly when there is exposure to a wide spectrum of disease and when the preceptor had time to teach. Feelings about pediatrics as career choice rose during the clerkship from neutral to positive, and the frequency of strongly positive feelings rose from 9.2% to 28.6%. In deciding about pediatrics as a career, experiences with patients and residents in the inpatient setting still seem to count more than those experiences in the outpatient setting.

CONCLUSION

Categorical pediatric clerkships provide learning environments that influence students positively toward pediatrics as a career choice. This choice is enhanced by encouraging community practitioners with students in their office to expose them to a wide variety of issues and devote time to teaching.

Reexamination of the age limit for defining when puberty is precocious in girls in the United States: implications for evaluation and treatment. Drug and Therapeutics and Executive Committees of the Lawson Wilkins Pediatric Endocrine Society

In 1997 a study from the Pediatric Research in Office Settings network, based on pubertal staging of >17,000 girls between 3 and 12 years of age, indicated that breast and pubic hair development are occurring significantly earlier than suggested by our current guidelines, especially in African-American girls. In response to this article, the Lawson Wilkins Pediatric Endocrine Society undertook a comprehensive review of this topic. The primary conclusions of this review are: 1. The current recommendation that breast development before age 8 is precocious is based on outdated studies. Until 1997, no data were available on pubertal staging in US girls that could have documented a trend to earlier maturation. 2. The 1997 study indicates that stage 2 of breast and pubic hair development is being achieved ~1 year earlier in white girls and 2 years earlier in African-American girls than previous studies have shown. 3. Concerns that girls with moderately precocious puberty will be significantly short adults are overstated; most have adult height within the normal range. 4. Therapy with gonadotropin-releasing hormone agonists has not been proven to have a substantial effect on adult height in most girls whose puberty starts between 6 and 8 years of age. 5. New guidelines propose that girls with either breast development or pubic hair should be evaluated if this occurs before age 7 in white girls and before age 6 in African-American girls. No changes in the current guidelines for evaluating boys (signs of puberty at younger than 9 years) can be made at this time.normal puberty, breast development, pubic hair.

Weight relative to height before and during growth hormone therapy in prepubertal children

We used the Genentech National Cooperative Growth Study database to examine differences in weight relative to height (weight for height standard deviation score or WTHTZ) in 3460 patients at enrollment and after one year of therapy with recombinant human growth hormone (rhGH), and in a subset of 450 patients treated for three years with rhGH. The major diagnostic categories were idiopathic growth hormone deficiency (IGHD), organic GH deficiency (OGHD), and idiopathic short stature (ISS). Children with IGHD and ISS were underweight for height at baseline but had a progressive increase in WTHTZ during three years of rhGH therapy. The same pattern applied to children with IGHD associated with septo-optic dysplasia and CNS trauma or infection. However, children with OGHD associated with craniopharyngiomas, other CNS tumors, leukemia, or CNS irradiation were overweight when starting rhGH and showed a decrease in WTHTZ during the first year of rhGH therapy. The increase in WTHTZ during rhGH treatment in children with ISS and OGHD suggests that the GH-induced increase in muscle mass exceeded loss of fat mass. Because children with neoplasm-related OGHD were overweight at baseline, the decline in WTHTZ during the first year of rhGH therapy suggests that loss of fat mass is the predominant effect in this subgroup.

Homozygous nonsense mutation in the insulin receptor gene of a patient with severe congenital insulin resistance: leprechaunism and the role of the insulin-like growth factor receptor

Severe congenital insulin resistance in the syndrome of leprechaunism is caused by mutations in the insulin receptor gene. We report a patient with leprechaunism who was homozygous for a mutation resulting in the absence of cell surface insulin receptors. To determine whether the receptor for Insulin-like growth factor-I (IGF-I) is involved in the phenotype of leprechaunism, we studied the effect of insulin and of IGF-I on cells from this patient. The patient had a homozygous C-->T substitution at base pair 8212 in exon 12 of the insulin receptor gene, creating a premature stop codon. This nonsense mutation is in the extracellular portion of the receptor and truncates the insulin receptor proximal to its transmembrane anchor, resulting in the absence of cell surface insulin receptors. This finding indicates that complete absence of the insulin receptor is compatible with life. Secondly, DNA synthesis was studied in skin derived fibroblasts in response to increasing concentrations of either insulin or Insulin-like growth factor-I (IGF-I), and was assessed by 3H-thymidine incorporation. In this patient's cells, both of these hormones increased 3H-thymidine incorporation, and the effect was blocked by alpha-IR3, a monoclonal antibody that blocks activation of the IGF-I receptor. These findings confirmed the absence of the insulin receptor and indicated that insulin acts here through activation of the IGF-I receptor. These data support the contention that the phenotypic and metabolic abnormalities of leprechaunism result from the combination of lack of insulin receptor action and over-activation by insulin of the type 1 IGF receptor.

The effect of the pediatric clerkship on medical student attitudes toward pediatrics at 11 medical schools

OBJECTIVES

To investigate how the pediatric clerkship affected student attitudes toward pediatrics, and to determine if correlations existed between changes in attitudes toward pediatrics and in ratings of certain aspects of the clerkship with an increased interest in a pediatric career.

METHODS

A one-page survey measuring interest in a career in pediatrics and agreement or disagreement with seven statements about pediatrics was administered at the beginning and end of the pediatric clerkship at 11 medical schools for the 1992-1993 academic year.

RESULTS

The proportion of students with a strong interest in a pediatric career increased from 6.7% before the clerkship to 15.2% after the clerkship (for women, 11% to 22%; for men, 4% to 11%). Attitudes toward pediatrics were more favorable at the end vs the beginning of the clerkship. The change that correlated best with change in interest in a pediatrics career was agreement that children are enjoyable to work with. Of the eight aspects of the clerkship rated, the patients worked with on the ward received the most positive mean score. The item that correlated best with increased career interest was a positive feeling toward the ward residents.

CONCLUSION

The recent trend for women to have a greater interest in careers in pediatrics than men is continuing. Finding ways to make students more comfortable when they interact with children and improving the teaching skills of residents could improve recruitment of medical students into pediatrics.

Effect of growth hormone therapy on final versus predicted height in short twelve- to sixteen-year-old boys without growth hormone deficiency

The effect of growth hormone therapy on final height in 28 short boys without growth hormone deficiency was evaluated retrospectively. The boys had received growth hormone for at least 2 years and were close to final height when therapy was stopped. The mean estimated final height was very close to that predicted from the pretherapy bone age. The fact that bone age advanced a mean of 4.9 years during a mean of 3.5 years of therapy may account for the lack of effect on final height.

Altered blood pressure reactivity in adolescent diabetics

OBJECTIVE

We examined hemodynamic responses to a variety of physiologic stimuli in 14 normotensive adolescents with type I diabetes and 45 healthy controls to determine whether structural vascular changes contribute to a reduced vasodilator capacity in adolescent diabetics. We asked, in adolescents with type I diabetes: (1) Are structural vascular changes present? (2) Are changes in the systemic vascular bed reflected in abnormal blood pressure regulation? and (3) Is abnormal vascular reactivity associated with either diabetes duration or control?

METHODOLOGY

Diabetic subjects were outpatients treated at the Medical College of Virginia, ages 13 to 18 years. Diabetes duration averaged 7.5 years. Each subject underwent an echocardiogram, dynamic and isometric exercise testing, and forearm plethysmography.

RESULTS

Compared to controls, diabetic subjects had (1) higher systolic and diastolic blood pressure during dynamic and handgrip exercise, (2) decreased forearm vasodilator capacity in response to ischemia, and (3) an increased aortic peak velocity. Group diastolic filling abnormalities were found, but these did not persist after adjustment for heart rate. The following variables were related to both diabetes duration and control (average glycosylated hemoglobin): (1) diastolic blood pressure during dynamic exercise, (2) resting forearm vascular resistance, and (3) forearm vascular reactivity. In addition, diabetes duration correlated with isometric exercise diastolic blood pressure, and diabetes control correlated with resting diastolic blood pressure.

CONCLUSION

In young diabetics we found that (1) abnormalities of the resistance vessels of the forearm may be present, (2) the degree of vascular change is related to diabetes duration and control, and (3) aortic distensibility may be impaired.

Discordant metabolic actions of insulin in extreme lipodystrophy of childhood

Congenital lipodystrophy includes a group of disorders characterized by total or partial absence of adipose tissue and insulin resistance. In this study we investigated the nature of insulin resistance in an 11-yr-old girl with one form of congenital lipodystrophy. We examined in vivo insulin and glycemic responses to feeding and iv glucose and in vitro amino acid and thymidine incorporation responses of skin fibroblasts to insulin exposure. In addition, we used stable isotope infusions of glucose, glycerol, and amino acids to investigate the in vivo metabolic actions of insulin on carbohydrate, fat, and protein. At 5 yr of age, she first demonstrated clinical glucose intolerance. Her basal insulin levels were normal (129 and 114 pmol/L), but increased markedly (peak values, 1304 and 5045 pmol/L) after iv glucose and a mixed meal. Insulin antibodies were undetectable, and specific [125I]insulin binding to her skin fibroblasts was normal. Both [3H]aminoisobutyric acid transport and [3H]thymidine incorporation by her fibroblasts were similar to responses obtained using control cells. At 11 5/12 yr of age, while receiving an infusion of stable isotopes, infusions of insulin at doses of 0.1 and 0.3 U/kg BW.h were ineffective in reducing her blood glucose despite elevating her serum insulin level to approximately 2500 pmol/L. Resting metabolic rate, respiratory quotient, VCO2, carbohydrate and lipid oxidation rates, glucose production rate, glycerol appearance rate, and plasma glycerol concentrations were unperturbed by the insulin infusions. By contrast, the insulin infusions reduced plasma leucine concentrations (124.2 to 86.1 to 66.7 mumol/L) and 13CO2 production rates (0.034 to 0.017 to 0.011 mumol/kg/min; baseline, 0.1, and 0.3 U insulin/kg.h, respectively). The leucine appearance rate declined (1.96 to 1.72 mumol/kg.min) in response to the 0.1 U/kg.h dose, but did not decline further in response to the 0.3 U/kg.h dose. The leucine oxidation rate also declined (0.87 to 0.39 to 0.25 mumol/kg.min), and there was a dose-related reduction in most plasma amino acid concentrations. Finally, nonoxidative leucine disposal increased progressively (1.09, 1.34, and 1.48 mumol/kg.min), suggestive of an insulin-induced increase in protein synthesis. These data indicate profound metabolic resistance to the carbohydrate and lipid actions of insulin, with preservation of protein anabolism. These observations suggest that in this patient, the biological effects of insulin on carbohydrate, lipid, and protein are distinct metabolic actions, regulated independently.

Fingernail angle in girls with Ullrich-Turner syndrome

Increased angle of insertion of the fingernails is known to be a common finding in girls with Ullrich-Turner syndrome (UTS), but there are few data on the frequency of this finding and no quantitative data that define what is a normal fingernail angle. To assess the usefulness of this measurement in evaluating patients with suspected UTS, we obtained tracings of 6 different fingernails to determine the mean fingernail angle (MFA) in 40 patients with UTS and compared the results with control girls and adults. As a group, the 24 girls with 45,X had an average MFA of 8.9 degrees, compared to 6.8 degrees for the 16 mosaics and variants, 3.0 degrees for normal children and 1.3 degrees for normal adults. Although there was overlap between the groups, 79% of 45,X girls and 56% of variants had an MFA of > 6 degrees, whereas only 8% of the combined control individuals had an MFA of > 6 degrees. Reproducibility of MFA determinations based on tracings obtained at consecutive visits was excellent (r = 0.92). There was no clear correlation between the MFA and the severity of the UTS phenotype. Determination of MFA is a simple, objective measurement which, when combined with other clinical findings, may aid the clinician in making a diagnosis of UTS.

Congenital hypopituitarism and microphthalmia. Report of two cases

Two children are described who had microphthalmia (one with unilateral and one with bilateral) noted at birth, and whose early onset of poor linear growth and weight gain led to a diagnosis of hypopituitarism prior to two years of age. Both children had growth hormone and thyroid-stimulating hormone deficiencies, and evidence of partial ACTH deficiency. Administration of growth hormone resulted not only in rapid linear growth but it also reversed the poor weight gain and head growth noted in these children. These cases suggest that hypopituitarism and microphthalmia may be associated with each other more frequently than has been recognized previously.

Monozygotic twins discordant for Ullrich-Turner syndrome

We describe 9-year-old twin girls who were thought to be monozygotic but who differed greatly in physical appearance and growth pattern. One twin had Ullrich-Turner syndrome (UTS), 45,X/46,XX mosaicism in peripheral blood, and only 45,X cells in skin fibroblasts. The phenotypically normal twin also had 45,X/46,XX mosaicism in blood but only 46,XX cells in cultured fibroblasts. Analysis of DNA marker patterns in blood lymphocytes and in skin fibroblasts confirmed monozygosity with a probability of 99.97%. This case is compared with other reported cases of discordance for UTS in twins. It is concluded that essentially all of the differences between the two twins can be explained by loss of an X chromosome early in embryogenesis with complete separation of 45,X and 46,XX cell lineages at the time of the twinning event. The presence of mosaicism in the peripheral blood of both twins is presumably due to anastomoses between the placentae resulting in a mixture of the two cell populations in the hematopoietic tissue.

Steroid cell tumor of the ovary in a child

An 8-year-old girl exhibited severe, progressive virilization of 2 years' duration associated with markedly elevated circulating testosterone concentrations. Based on her initial clinical presentation and results of a chemical evaluation, she was originally thought to have non-classic 21-hydroxylase deficiency, but her condition did not respond to corticosteroid therapy. Further evaluation confirmed the presence of an ovarian neoplasm. The excised ovary contained an attached gray-brown mass. Light microscopic and ultrastructural examination revealed the mass to be a steroid cell tumor. Because Reinke's crystals were not present, it was designated to be a steroid cell tumor not otherwise specified. This case represents one of 22 reported cases of steroid cell tumor occurring in children described in the literature, most of which have been associated with heterosexual precocity. To our knowledge, steroid cell tumors are benign when they occur in prepubertal children. Although they are rare, steroid cell tumors of the ovary should be considered in cases of childhood virilization.

Diagnostic value of testosterone therapy in boys with delayed puberty

A brief course of testosterone injections is known to be an effective treatment for boys with constitutional delayed puberty. In this study, data from seven boys at least 14 years old who received testosterone enanthate (100 mg intramuscularly monthly for four months) were analyzed to see if linear and testicular growth responses could be useful diagnostically in excluding growth hormone deficiency (GHD) and isolated gonadotropin deficiency, two conditions that are often difficult to distinguish from constitutional delayed puberty. During four months of testosterone therapy, growth rate increased from 4.0 +/- 1.0 cm/y to 10.7 +/- 2.3 cm/y, and was greater than 8 cm/y in all patients. Since testosterone-induced stimulation of linear growth is largely GH-mediated, the large increase in growth rate in all boys is considered indicative of GH sufficiency. Testis length, which did not increase during testosterone therapy, increased by 0.6 to 0.8 cm in every patient (from 2.7 +/- 0.3 cm to 3.4 +/- 0.4 cm) over the following four months, indicating normal gonadotropin secretion and normal pubertal progression; in contrast, the increase in serum testosterone concentrations after discontinuation of testosterone treatment was more variable. It is concluded that the growth response to a four-month course of testosterone is helpful in excluding GHD in boys with delayed puberty, and an additional four months of follow-up is sufficient to document the onset of puberty, thereby eliminating the possibility of isolated gonadotropin deficiency.

Antimitogenic actions of lectins in cultured human fibroblasts

It was previously reported that the lectins wheat germ agglutinin (WGA) and concanavalin A (Con A) inhibit the mitogenic actions of multiple peptide growth factors in human fibroblasts without having a significant effect on mitogen binding. The current studies were designed to further examine the mechanisms of this antimitogenic action of lectins. Addition of WGA at progressively later times after stimulation of fibroblasts with peptide mitogens revealed significant inhibition of DNA synthesis even when the lectin was added 16-20 h after growth factors. This suggests an inhibitory effect on a pathway occurring late in G1, or close to the G1/S boundary. WGA also inhibited stimulation of DNA synthesis by non-peptide agents such as colchicine and vanadate ion, indicating that the lectin inhibits a common distal step in the mitogenic response, rather than acting primarily on events occurring at the level of the growth factor-receptor interaction. WGA had a rapid (within 30 min) inhibitory effect on insulin-stimulated amino acid uptake, but Con A, which like WGA blocked mitogen-stimulated 3H-dT incorporation, had little effect on stimulation of amino acid uptake. Thus the inhibition of DNA synthesis and amino acid uptake by lectins appear to be mediated by distinct mechanisms. WGA binding to fibroblasts persisted even when the lectin was removed from the incubation medium, but unlike 125I-EGF, which was rapidly internalized at 24 degrees C, little 125I-WGA was internalized. Incubation of fibroblasts for 20 h with WGA or Con A was not toxic to cells, since reversal of lectin binding by the appropriate saccharide allowed normal subsequent stimulation of DNA synthesis by EGF and insulin. However, the observation that cells exposed to antimitogenic lectins undergo a marked decrease in cell spreading suggests that changes in cell shape may be relevant to the mechanism by which lectin-treated fibroblasts become unresponsive to mitogenic stimulation.

Glucocorticoids enhance somatomedin-C binding and stimulation of amino acid uptake in human fibroblasts

The regulation of growth by the GH-dependent mitogen somatomedin-C (Sm-C) may involve not only changes in circulating levels of Sm-C, but also alterations in cellular sensitivity to Sm-C induced by humoral factors. Glucocorticoids have been reported to enhance the stimulatory effect of Sm-C on DNA synthesis and cell replication in cultured human fibroblasts, but the cellular alteration responsible for this effect was not fully defined. Using an assay for cellular sensitivity to Sm-C based on stimulation of uptake of the amino acid analog aminoisobutyric acid, a 20-h preincubation with 100 nM dexamethasone was found to enhance both the sensitivity and the maximal responsiveness of human fibroblasts to a 3-h incubation with Sm-C. This effect was found using fibroblasts from multiple normal donors of different ages, and dexamethasone was approximately 10-fold more potent than hydrocortisone. The glucocorticoid antagonist RU486 (100 nM) largely reversed the enhancing effect of 100 nM dexamethasone on Sm-C action. Binding of [125I]Sm-C to intact fibroblast monolayers or trypsin-dispersed cells could be increased by 60-80% by glucocorticoid preincubation, and this increase correlated well with enhanced stimulation of [3H]aminoisobutyric acid uptake, suggesting that the enhancement of Sm-C action in glucocorticoid-treated cells may be mediated at the level of the Sm-C receptor.

Enhancement of linear growth and weight gain by cyproheptadine in children with hypopituitarism receiving growth hormone therapy

Cyproheptadine (Cp), an antihistamine serotonin antagonist drug with appetite-stimulating activity, was given to children with growth hormone (GH) deficiency to test the hypothesis that increased weight gain would enhance the effect of GH on linear growth. Six patients with idiopathic GH deficiency received GH 0.08 U/kg three times per week plus Cp 0.25 to 0.4 mg/kg/day for 4-month periods, alternating with 4-month periods of GH plus placebo, on average for 16 months. Overall, height velocity (HV) increased from 9.1 +/- 2.4 with GH alone to 12.1 +/- 2.1 cm/yr with GH-Cp (P = 0.01) and weight velocity (WV) increased substantially from 1.3 +/- 1.3 to 7.8 +/- 3.6 kg/yr (P = 0.01). For 10 of 11 8-month treatment intervals completed, HV was greater during GH-Cp treatment than during GH alone, and there was a good correlation between HV and WV for each 4-month observation period (r = 0.64, P less than 0.002). These findings should be considered preliminary because of the small number of patients, but suggest that weight gain induced by cyproheptadine results in improved linear growth in patients given GH and that this drug may be useful in optimizing the response to GH therapy.

Cushing's syndrome resulting from primary pigmented nodular adrenocortical disease

In a 10-year-old boy with Cushing's syndrome, the dexamethasone suppression test, the metyrapone test, and both basal and corticotropin-releasing factor-stimulated corticotropin levels all indicated a primary adrenal disorder. However, a computed tomographic scan failed to detect an adrenal tumor. At surgery, the adrenal glands were not enlarged but were studded with small pigmented nodules composed of enlarged nonmalignant adrenocortical cells. This unusual abnormality, referred to as primary pigmented nodular adrenocortical disease, is associated with autonomous hypersecretion of cortisol primarily in children and young adults. Our patient was cured by total bilateral adrenalectomy and corticosteroid replacement therapy, the treatment of choice for this condition.

Premature adrenarche. Clinical and diagnostic features

Premature adrenarche (PA) or isolated growth of sexual hair in young children, is a benign condition that may initially be confused with true precocious puberty or pathologic virilizing disorders. The clinical findings, family history, and serum concentrations of dehydroepiandrosterone sulfate (DHEA-S) were compared in 24 children with PA (79% black females) seen in a 2-year period and in an age-matched control group of 17 black females. Twenty three of 24 patients, but none of the controls, had an adult-type axillary odor. There was a positive family history of PA in only three of 24 children with PA, and in one of 17 controls. The mean serum DHEA-S was significantly higher in the PA children than in the controls, but there was a broad range of concentrations (10-143 micrograms/dl), with values in 10 of 24 cases falling within the control range for age. We conclude that: (1) PA is a relatively common finding in black females between ages 3 and 8, (2) an axillary odor is almost always present in children with PA, and (3) determination of serum DHEA-S may be of some help in confirming the clinical impression of a modest increase in adrenal androgen secretion and in ruling out a more serious disorder. In most cases, however, the diagnosis of PA can be made on the basis of the history, physical examination, and lack of rapid progression over time; the use of laboratory tests to rule out a pathologic virilizing process may best be reserved for those children with very early onset, increased linear growth, or other signs of virilization.

Wheat germ agglutinin and concanavalin A inhibit the response of human fibroblasts to peptide growth factors by a post-receptor mechanism

The effect of plant lectins on amino acid uptake and DNA synthesis in cultured human skin fibroblasts stimulated by various peptide mitogens was studied. Wheat germ agglutinin (WGA), at a concentration of 5 micrograms/ml, which by itself had little effect on 3H-aminoisobutyric acid (AIB) uptake, markedly inhibited stimulation of 3H-AIB uptake by somatomedin-C, insulin, epidermal growth factor (EGF) and platelet-derived growth factor. This inhibition could not be overcome by increasing the concentration of peptide added. Neither WGA nor concanavalin A (Con A) significantly affected basal 3H-thymidine incorporation. However both lectins, at concentrations of 5-20 micrograms/ml, decreased EGF- and insulin-stimulated DNA synthesis while succinyl Con A, a divalent lectin derivative, did not. The inhibitory effects of lectins on mitogenic stimulation were reversed by alpha-methyl mannose (Con A) or N-acetylglucosamine (WGA), and were not due to a reduction in the binding of growth factors to their receptors. It is concluded that certain lectins noncompetitively inhibit the response of human fibroblasts to multiple peptide mitogens at the post-receptor level, possibly by interfering with lateral mobility and aggregation of mitogen-receptor complexes.

Stimulation by somatomedin-C of aminoisobutyric acid uptake in human fibroblasts: a possible test for cellular responsiveness to somatomedin

The effect of purified somatomedin-C (Sm-C)/insulin-like growth factor I on the uptake of alpha-aminoisobutyric acid (AIB) by confluent cultures of human fibroblasts was studied. An increase in [3H]AIB uptake was observed within 30 min of Sm-C addition, and a maximal effect was reached at 2.5 h (averaging 200% of control AIB uptake). Under the conditions employed, less Sm-C was required for maximal stimulation of [3H]AIB uptake (10 ng/ml in most cell lines) than for a maximal effect on [3H]thymidine incorporation (greater than 30 ng/ml). In multiple experiments with different lines of foreskin-derived and nongenital fibroblasts, the concentration of Sm-C resulting in half-maximal stimulation of [3H]AIB uptake was reproducible and was between 1.7 and 4.8 ng/ml in all cell lines tested except one. No significant difference was observed in the Sm responsiveness of cells from newborns and that of those from normal older children. Determination of binding of [125I]Sm-C to confluent monolayers of one fibroblast line revealed that the concentration of Sm-C resulting in half-maximal binding was nearly identical to that producing half-maximal [3H]AIB uptake stimulation. Stimulation of AIB uptake by an optimal concentration of epidermal growth factor (5 ng/ml) was also determined in several normal cell lines and was consistently close to 140% of the control value. Since epidermal growth factor and Sm interact with different receptors, this response may be a useful measure of cell integrity which is independent of the Sm receptor. The techniques for measurement of AIB uptake described in this report may prove useful in determining whether some children with growth failure of unknown etiology have target cell resistance to Sms.

Fibroblasts from a patient with leprechaunism are resistant to insulin, epidermal growth factor, and somatomedin C

Leprechaunism is a rare inherited disorder characterized by severe intrauterine growth retardation and insulin resistance. Cultured skin fibroblasts from an infant with Leprechaunism were previously reported to show decreased stimulation of DNA synthesis by insulin despite apparently normal binding of [125I]insulin and [125I]somatomedin C. We have now further investigated the growth of this patient's fibroblasts and compared their metabolic responses to insulin and various peptide growth factors with responses in normal foreskin-derived fibroblasts. The doubling time of Leprechaun fibroblasts was prolonged (90 vs. 29 h), and their morphology was abnormal. Stimulation of [3H]glucose uptake was minimal with low insulin levels (1--10 ng/ml) relative to controls, but was comparable at higher insulin concentrations (1--10 micrograms/ml). Stimulation of [3H] aminoisobutyric acid uptake by insulin, epidermal growth factor (EGF), multiplication-stimulating activity, and somatomedin C (Sm-C) in Leprechaun cells was diminished relative to control cells at all concentrations tested. Furthermore, stimulation of [3H]thymidine incorporation in Leprechaum cells by EGF, Sm-C, and fibroblast growth factor was also subnormal. Binding of [125I]EGF to Leprechaun fibroblasts was not decreased. It is concluded that fibroblasts from this patient are resistant to the metabolic effects of insulin, EGF, Sm-C, and fibroblast growth factor. Since receptors for three of these peptides are apparently normal, it is likely that the defect in these cells is at the postreceptor level, perhaps involving a metabolic pathway common to the action of multiple growth factors.

Stimulation of embryonic mouse limb bud mesenchymal cell growth by peptide growth factors

The possible role of peptide growth factors in mammalian intrauterine cell growth has been investigated using primary cultures of undifferentiated mesenchymal cells from 11-day mouse embryo limb buds. When grown as monolayer cultures, proliferation is greatly favored by high cell densities. In medium containing 0.2% serum, purified epidermal growth factor (EGF), fibroblast growth factor (FGF), multiplication stimulating activity (MSA), insulin, and somatomedin-C (Sm-C) do not increase cell growth, but a 30-40,000 molecular weight component of mouse fetal liver conditioned medium is stimulatory. On the other hand, when limb bud cells are grown as high density or micromass cultures, a method which better approximates in vivo growth conditions, all of the purified growth factors tested stimulate cell growth significantly. These growth factors have additive effects when used in combination, the best stimulation being observed with liver medium (10% v/v), EGF (10 ng/ml), FGF (200 ng/ml), and either insulin (1 microgram/ml) or Sm-C (20 ng/ml). We conclude that the response of limb bud cells to growth stimulation is influenced by the manner in which the cells are cultured and that at least four different growth factors are required for optimal in vitro proliferation. One of these, the active component of liver medium, appears to be a previously uncharacterized growth factor.

Radioimmunoassay of vasopressin in familial cental diabetes insipidus

We examined plasma arginine-vasopressin concentrations by radioimmunoassay in two brothers, aged 6 and 7.5 years, with familial central diabetes insipidus inherited as an autosomal dominant trait. Plasma AVP was measured in relation to increasing plasma osmolality induced by water deprivation and hypertonic saline infusion. The brother with the more severe urinary concentrating defect had no detectable AVP when his plasma osmolality was as high as 306 mOsm/kg; the other brother had detectable but clearly subnormal AVP concentrations. The one brother tested had an apparently normal end-organ response to exogenous vasopressin. Chlorpropamide had a significant antidiuretic effect in the brother with detectable AVP levels, and a lesser effect in the other brother . Our findings suggest that intrafamilial variation in the severity of congenital DI is related to the degree of vasopressin deficiency.

Peripheral resistance to thyroid hormone in an infant

Peripheral resistance to thyroid hormone, a syndrome characterized by elevated serum total and free thyroid hormone levels and abnormal TSH suppression without manifestations of hyperthyroidism, was studied in a clinically euthyroid 6-month-old infant. Initial serum concentrations of T4, T3, and TSH were 22.1 micrograms/dl, 334 ng/dl, and 7.6 microunits/ml, respectively; infusion of synthetic TRH increased the serum TSH to 47.4 microunits/ml, an exaggerated response. Pituitary insensitivity to T3 was investigated by measuring these parameters in response to consecutive 7-day courses of increasing doses of T3. Four times the calculated replacement dose of T3 (40 micrograms/day) was required to normalize the serum T4 and the serum TSH response to TRH. After administration of 80 micrograms/day T3, the serum TSH response to TRH was virtually abolished, but no clinical signs of thyroid hormone excess were observed. High doses of T4 blunted the serum TSH response to TRH in a manner similar to T3. Prednisone also decreased the TSH response to TRH but had no effect on serum thyroid hormone concentrations. In an attempt to determine the mechanism of thyroid hormone resistance, specific nuclear T3 binding was compared in cultured skin fibroblasts from the patient and a normal infant. Normal fibroblast nuclei had a single binding site with a Ka of 3.1 X 10(9) M-1. In contrast, the Scatchard plot of the patient's T3 binding was curvilinear, compatible with a high affinity site that had a Ka (4.2 X 10(9) M-1) similar to that of the normal fibroblasts and a second low affinity site (Ka = 2.7 X 10(8) M-1). Supraphysiological concentrations of T3 elicited a dose-related increase in fibroblast glucose consumption, which was similar in cells from both the patient and from a normal infant. In conclusion, pituitary and peripheral resistance to thyroid hormone has been demonstrated in this infant, but despite the abnormality of nuclear T3 binding, the cellular mechanisms remain unclear.

Stimulation of DNA synthesis by ouabain and concanavalin A in cultures of embryonic neural retina cells

Ouabain and concanavalin A, agents which bind to specific sites in the cell membrane, stimulate DNA synthesis and cell replication in monolayer cultures of neural retina cells from late chick embryos. The results suggest a relationship between control of retina cell replication and properties of the cell membrane. The experiments involved measurements of 3H-thymidine incorporation in primary monolayer cultures (24-48h) of retina cells from embryos of different ages. Stimulation by ouabain was greatest in cells from 14-day embryos, and its magnitude was similar to that elicited in these cell cultures by concanavalin A. Simultaneous treatment of 14-day retina cells with both agents resulted in a greater than additive stimulation of DNA synthesis. Our results demonstrated that, although during normal embryogenesis cell replication in the neural retina has virtually ceased by day 14 of development, some cells retained a capacity for mitogenesis when exposed to conditions such as provided in these experiments. By autoradiography the responding cells were identified as large epithelioid retina cells (LER cells). Under optimal conditions of simultaneous treatment with ouabain and Con A about 20% of the LER cells showed stimulation of DNA synthesis. The nature of LER cells and other aspects of our findings are discussed.