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J F Cara

Publications and source records attributed to J F Cara.

29 records · Page 2Linked to original sources
PubMed1989

Growth hormone deficiency impedes the rise in plasma insulin-like growth factor I levels associated with precocious puberty.

We tested the hypothesis that growth hormone (GH) mediates the rise in insulin-like growth factor I (IGF-I) concentrations in children with precocious puberty. We studied three groups of patients. Group 1 included six children with GH deficiency and precocious puberty (precocious GH-deficient); group 2 included 10 GH-sufficient patients with idiopathic true precocious puberty (precocious GH-sufficient); and group 3 included 9 prepubertal children with GH deficiency (prepubertal GH-deficient). Growth rates, pubertal status, and plasma IGF-I concentrations were determined at regular intervals. The precocious children with GH deficiency had a mean (+/- SD) growth rate of 7.2 +/- 2.1 significantly below that of the precocious GH-sufficient patients (10.5 +/- 2.5 cm/yr, p less than 0.05) but above that of the prepubertal GH-deficient children (3.9 +/- 1.4 cm/yr, p less than 0.05). The mean IGF-I concentration in the precocious GH-deficient children was 0.77 +/- 0.39 U/ml, significantly lower than the mean level of 2.2 +/- 0.67 U/ml in the precocious GH-sufficient patients (p less than 0.01). However, precocious GH-deficient patients had significantly higher IGF-I values than the prepubertal GH-deficient children (0.24 +/- 0.10 U/ml, p less than 0.05). IGF-I values did not rise with the onset of precocious puberty in four of the precocious GH-deficient children evaluated before and after the development of precocious puberty. However, three patients who began GH treatment did have a rise in plasma IGF-I concentrations to levels of 1.2, 3.4, and 3.7 U/ml, respectively. These findings are compatible with the concept that sex steroids increase IGF-I levels in precocious puberty primarily by increasing GH production. A small but direct effect of sex steroids on IGF-I production may also exist. The onset of precocious puberty in children with organic GH deficiency may mask the abnormal growth pattern of these children and delay diagnosis; determinations of plasma IGF-I concentrations may be helpful in assessing the GH status of these patients.

Adolescent↗
PubMed1989

A new test of combined pituitary-testicular function using the gonadotropin-releasing hormone agonist nafarelin in the differentiation of gonadotropin deficiency from delayed puberty: pilot studies.

There is evidence that the capacity to synthesize gonadotropins is less in teenage boys with gonadotropin deficiency (GD) than in those with constitutional delay of puberty (DP). We hypothesized that this might predispose the latter group to have a greater pituitary-testicular response to the potent long-acting GnRH agonist nafarelin. We evaluated GD patients 14.3-24.0 yr of age (n = 8) and prepubertal DP boys 14.8-17.6 yr of age (n = 3). In most subjects the response to nafarelin was compared to that of frequent nocturnal blood sampling for LH and testosterone levels. All subjects received a single dose of nafarelin (1.0 micrograms/kg, sc), and blood was then sampled at 0.5- to 4.0-h intervals for 24 h. Patients with GD could not be distinguished from those with DP by pubertal staging criteria or by baseline values of LH, FSH, or testosterone. Patients with GD exhibited no rise in plasma LH levels during sleep, in contrast to those with DP. All GD patients had LH and FSH responses distinctly less than those of the DP group between 3-24 h postnafarelin. The peak incremental responses of GD and DP to nafarelin were, respectively: LH, 5.5 +/- 2 3 (+/- SEM and 77.2 +/- 8.6 IU/L (P less than 0.02); FSH, 2.7 +/- 1.2 and 9.4 +/- 0.8 IU/L (P less than 0.005). Testosterone peak responses were lower as well (0.26 +/- 0.2 vs 1.6 +/- 0.5 nmol/L, P = 0.05). This pilot study suggests that the response to a single test dose of nafarelin distinguishes GD from DP in the teenage years as well as does measurement of nocturnal LH levels. The testosterone response to the GnRH agonist adds a new dimension to GnRH testing. Nafarelin also allows assessment of the bioactivity of endogenous gonadotropin, is a more potent stimulus of pituitary-testicular function than endogenous GnRH secretion, and is more cost-effective than nocturnal sampling.

Adolescent↗
PubMed1988

Structural determinants of ligand recognition by type I insulin-like growth factor receptors: use of semisynthetic insulin analog probes.

We undertook a systematic analysis of the structural determinants necessary for ligand recognition by the type I insulin-like growth factor (IGF) receptor by investigating the binding of semisynthetic insulin analogs to IGF receptors from human placental cell membrane fragments. Analogs were prepared by synthetic and semisynthetic methods. Three groups of insulin analogs were synthesized: the first group contained insulin analogs modified at the amino-terminal position of the insulin A chain and included acetyl-insulin and human proinsulin; the second group included analogs in which B chain residues B26-B30 [despentapeptide insulin (DPI)], B25-B30 (deshexapeptide insulin), and B24-B30 (desheptapeptide insulin) were removed; the third group contained insulin analogs in which B chain residues B26-B30 were removed (DPI) and phenylalanine(B25) substituted with other amino acids, including alanine, serine, leucine, and tyrosine. Half-maximal inhibition of binding of radiolabeled IGF-I to placental cell membrane fragments was used as an index of relative binding affinity (K1/2). To determine further if semisynthetic insulin analogs bound to the type I IGF receptor, placental membrane fragments were affinity labeled with radiolabeled IGF-I in the presence and absence of submaximal concentrations of unlabeled hormone, insulin, or semisynthetic analogs, and the labeled proteins were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Insulin had a 500 times lower affinity for the type I IGF receptor than IGF-I [K1/2 = 140 +/- 69 nM (mean +/- SD)] whereas proinsulin and acetyl insulin had a more than 100 times lower affinity than insulin for this receptor type. Removal of insulin B chain amino acid residues 26-30 (DPI) did not negatively affect the binding of the insulin-derived peptide and actually increased the apparent affinity of ligand-receptor association approximately 2-fold. However, further removal of phenylalanine(B25) (deshexapeptide insulin) and phenylalanine(B24) (desheptapeptide insulin) decreased the binding of ligand to the type I IGF receptor progressively by several orders of magnitude. Substitution of phenylalanine(B25) of DPI with tyrosine, a substitution that actually increased the homology of this analog to IGF-I, resulted in a 4- to 5-fold increase in the relative apparent affinity of the analog for the type I IGF receptor (K1/2 = 31 +/- 4 nM). On the other hand, substitution of phenylalanine(B25) with alanine, serine, and leucine decreased the relative apparent binding affinity approximately 2- to 8-fold.(ABSTRACT TRUNCATED AT 400 WORDS)

Affinity Labels↗
PubMed1988

Insulin-like growth factor I and insulin potentiate luteinizing hormone-induced androgen synthesis by rat ovarian thecal-interstitial cells.

We tested the hypothesis that insulin-like growth factor I (IGF-I) and insulin play a role in androgen production by rat ovarian thecal-interstitial cells. Collagenase/DNase-dispersed rat ovarian thecal-interstitial cells obtained from immature hypophysectomized Sprague-Dawley rats were cultured at a concentration of 10(6) cells/ml in serum-free medium in the presence of increasing concentrations of LH, IGF-I, or insulin. The medium was replaced every 48 h, and the androsterone concentration in the culture supernatants was used as an index of androgen production. In the absence of added hormones (control) androsterone levels were consistently less than 0.1 ng/ml. Increasing concentrations of LH stimulated androsterone synthesis in a dose-dependent manner. IGF-I, in the absence of LH, did not significantly increase androsterone levels above control values. However, when combined with 10 ng/ml LH, IGF-I increased androsterone synthesis above levels seen with LH alone in a dose-related fashion: for example, the peak androsterone levels seen with LH and 100 ng/ml (13 nM) IGF-I at 96 h of culture were significantly greater than the peak level seen with 10 ng/ml LH alone (302 +/- 71 vs. 17 +/- 7 ng/ml; P less than 0.0125). Similarly, while insulin alone did not increase androsterone synthesis above control values, androsterone concentrations were increased by insulin in combination with 10 ng/ml LH; a peak value of 240 +/- 67.7 ng/ml was observed at 96 h of culture with 100 ng/ml (18 mM) insulin (P less than 0.025 vs. LH alone) Androsterone levels were slightly less with insulin than with IGF-I, but this difference was not significant. The combination of IGF-I and insulin did not increase levels of androsterone synthesis above those observed with each hormone alone. IGF-I bound to a high affinity binding site on ovarian cell monolayer cultures with an apparent binding affinity of 1.3 x 10(-9) M. Insulin also competed for binding with radiolabeled IGF-I in a dose-dependent manner, but the affinity of insulin was approximately 500-fold less; half-maximal inhibition of [125I] IGF-I binding occurred with an insulin concentration of approximately 300 nM (or approximately 1700 ng/ml). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of thecal-interstitial cell monolayers affinity labeled with radiolabeled IGF-I in the absence and presence of unlabeled hormone revealed proteins with characteristics of type I IGF receptors. Affinity labeling to a protein of a relative molecular mass of approximately 45,000 was also noted, probably representing IGF carrier proteins synthesized by thecal-interstitial cell monolayers.(ABSTRACT TRUNCATED AT 400 WORDS)

Androgens↗
PubMed1988

A monoclonal antibody to the type 1 insulin-like growth factor and insulin receptors stimulates deoxyribonucleic acid synthesis in human and murine fibroblasts.

Insulin-like growth factor I (IGF-I) and insulin are polypeptide hormones that stimulate their cellular responses by binding to specific cell membrane receptors. These receptors, while chemically distinct, have similar structural and functional characteristics. This manuscript describes the production and characterization of a monoclonal antibody that binds to both type I IGF and insulin receptors. This antibody did not inhibit hormone binding to either receptor type, but stimulated DNA synthesis in both human and murine fibroblasts. Ten BALB/c-BYJ mice were immunized with human placental membrane fragments, and their splenic lymphocytes were fused with SP2 AG0 mouse myeloma cells. Of approximately 3000 hybridoma clones thus obtained, 1 viable clone, designated V3,8 D7, was found to produce an antibody directed against the type I IGF receptor. Solubilized radiolabeled placental membranes immunoprecipitated with affinity-purified antibody and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions revealed bands with relative molecular masses corresponding to the nonreduced intact receptor (approximately 350 x 10(3], the alpha-subunit (130-140 x 10(3], and the beta-subunit (90 x 10(3] of the type I IGF receptor. Clonal supernatant and affinity-purified antibody precipitated solubilized receptors affinity labeled with [125I]IGF-I. Antibody V3,8 D7 also precipitated solubilized placental membranes affinity labeled with [125I]insulin. However, solubilized receptors affinity purified by the monoclonal antibody bound IGF-I much better than insulin, suggesting that this antibody has a higher affinity for the type I IGF receptor than for the insulin receptor. Affinity-purified antibody did not inhibit the binding of IGF-I or insulin to receptors on human placental membranes, suggesting that it is directed against a site on the type I IGF and insulin receptor not involved in hormone binding. However, affinity-purified monoclonal antibody stimulated DNA synthesis in human GM 498 and murine BALB/c-3T3 clone A 31 fibroblasts, as determined by [3H]thymidine incorporation. The combination of IGF-I and affinity-purified antibody did not increase thymidine incorporation above levels observed with either substrate alone, suggesting that these factors may be operating through a common mechanism. These results suggest that antibody V3,8 D7 can stimulate receptor responses by binding to a site on the type I IGF and/or insulin receptors that is not involved in hormone binding. These data support the concept that hormone receptors themselves possess the biological information required for stimulating specific cellular responses.

Animals↗
PubMed1988

Quantitation of urinary somatomedin-C and growth hormone in preterm and fullterm infants and normal children.

Urinary GH and somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I) excretion were measured in 12-h urine collections obtained from 43 infants (27 stable preterm infants and 16 healthy fullterm infants) and 31 normal children, aged 3-17 yr. Urinary Sm-C/IGF-I was excreted as the free hormone, since no binding of radiolabeled Sm-C/IGF-I to any urine protein with a mol wt similar to those described for plasma Sm-C/IGF-I-binding proteins was found. The preterm infants excreted significantly more urinary GH [13.5 +/- 2.1 (+/- SE) ng/kg.12 h] than either the fullterm infants (5.3 +/- 1.6 ng/kg.12h) or the children (0.27 +/- 0.02 ng/kg.12 h; P less than 0.01). The mean urinary Sm-C/IGF-I excretion in the preterm infants (98.9 +/- 7.5 mU/kg.12 h) was comparable to that in fullterm infants (87.6 +/- 9.7 mU/kg.12 h); both groups excreted significantly more urinary Sm-C/IGF-I than children (28.4 +/- 2.1 mU/kg.12 h; P less than 0.01). The group differences were similar when the results were expressed in terms of creatinine excretion. Urinary GH excretion correlated positively with urinary Sm-C/IGF-I excretion (r = 0.68). The higher output of these peptides in rapidly growing infants and their positive correlation in urine provide additional support for the Sm hypothesis.

Adolescent↗
PubMed1987

A longitudinal study of the relationship of plasma somatomedin-C concentration to the pubertal growth spurt.

Cross-sectional studies from our institutions (Wyler Children's Hospital, Chicago, and Children's Hospital of Philadelphia) and others have shown that plasma somatomedin-C (Sm-C) concentrations rise during puberty. To determine the relationship between rising plasma Sm-C levels and the growth spurt at puberty, we undertook a longitudinal study of 11- to 18-year-old children. Twelve male and eight female subjects were followed up on a yearly basis for two to seven years (mean, 4.4 years). Height velocity, plasma Sm-C concentrations, and stage of sexual development were determined during each visit. All patients progressed normally in puberty during the study. The plasma Sm-C level rose during early puberty in each child and reached a maximal level of at least 2 U/mL In midpuberty, approximately one year after the attainment of peak height velocity. Maximal plasma concentrations of Sm-C were similar in male (3.5 +/- 0.71, mean +/- SEM) and female (3.5 +/- 1.46) subjects. Plasma Sm-C levels subsequently decreased slowly but remained above normal adult values for as long as four years after peak height velocity was reached. Plasma Sm-C concentrations increased steadily with increasing height velocity until peak height velocity was attained with a mean rise of approximately 0.5 U for each centimeter per year increase in height velocity. Since Sm-C levels remained elevated while height velocity decreased, there was no significant correlation between Sm-C levels and height velocity throughout puberty. These results suggest that caution is required in interpreting Sm-C concentrations during puberty; while normal pubertal levels may be in the acromegalic range for adults, a plasma Sm-C level of less than 1 U/mL in early puberty or less than 1.5 U/mL during middle to late puberty must be considered subnormal.

Adolescent↗
PubMed1985

The prolactin response to thyrotropin-releasing hormone does not distinguish teenaged males with hypogonadotropic hypogonadism from those with constitutional delay of growth and development.

We attempted to confirm the results of a previous study in which patients with hypogonadotropic hypogonadism (HH) could be readily distinguished from normal adolescents with constitutional delay of growth and development (CDGD) by their lower serum PRL responses to TRH. We compared the PRL responses to TRH of 13 teenaged males with HH to those of 14 teenaged males with CDGD. Although the mean maximum serum PRL concentration after TRH in HH patients (29.5 ng/ml) was significantly less (P less than 0.05) than that in the CDGD subjects (41.1 ng/ml), there was considerable overlap between the 2 groups. Seven of the 13 HH patients had peak serum PRL concentrations in response to TRH that were greater than 25 ng/ml, the lowest value in the CDGD subjects. These results suggest that a normal PRL response to TRH in a male who has delayed puberty does not exclude the diagnosis of HH, but that a subnormal response probably does support that diagnosis.

Adolescent↗