Genetic polymorphism at the glutathione S-transferase (GST) P1 locus is a breast cancer risk modifier

The isolation of full-length cDNAs of naturally occurring GSTP1 gene variants, and the demonstration that these alleles are distributed in the normal population, have provided conclusive evidence that the human GSTP1 gene locus is polymorphic and that specific GSTP1 alleles may be associated with different risk for cancers or other diseases. Recent data have indicated that the different GSTP1 alleles encode proteins with different enzymatic activities against carcinogens. In this case-control study, we examined the effect of the GSTP1 genetic polymorphism and its interaction with other factors to determine breast cancer risk. GSTP1 and GSTM1 genotypes of 220 breast cancer patients and 196 controls, all residents of western France, were examined. Data on menopausal status and family cancer history were obtained from 195 patients and 147 controls. Exons 5 and 6 of the GSTP1 gene, which contain the polymorphic nucleotide transitions, were analyzed by DNA polymerase chain reaction-restriction fragment length polymorphism to distinguish between the GSTP1 alleles. In the control population, GSTP1 allelic frequencies were 64.3%, 26.0% and 9.7%, respectively, for GSTP1*A, GSTP1*B and GSTP1*C. In the breast cancer patients, the frequencies were 67.9% for GSTP1*A, 26.8% for GSTP1*B and 5.3% for GSTP1*C. In multivariate analysis, breast cancer risk increased by 7.7-fold (p < 0.001) in women with a family history of cancers and 2.18-fold (p = 0.026) in non-GSTP1*C individuals. GSTM1 genotypes did not emerge as risk factor. Our results show that in addition to well-known risk factors, in particular, a family history of cancer, GSTP1 allelopolymorphism is a significant modifier of breast cancer risk. The results also suggest a protective role against breast cancer for the GSTP1*C allele.

Allelotype influence at glutathione S-transferase M1 locus on breast cancer susceptibility

The influence of polymorphisms of the glutathione S-transferase gene GSTM1 in breast cancer susceptibility has been assessed in this study. Previous studies correlated the absence of the GSTM1 protein with an increased risk of developing some cancers, especially lung or bladder cancers, in heavy smokers. In this study, we determined GSTM1 polymorphisms in a population of 437 female controls from the west of France and 361 community breast cancer patients. Three distinct alleles of this gene exist: GSTM1*A, GSTM1*B and GSTM1*0 (deleted allele). Null subjects (GSTM1 null) are homozygous for this deletion. The comparative analysis of GSTM1 allelotypes in our two populations did not demonstrate a statistically significant difference in distribution (P = 0.22), although the null genotype was more frequent in cancer patients. However, breast cancer risk was increased in null subjects > or = 50 years of age compared with non-null subjects [odds ratio = 1.99 (1.19-3.32), P = 0.009], but not in null subjects < 50 years of age compared with non-null subjects (P = 0.86). Our results suggest that the GSTM1 null genotype may play a role in post-menopausal breast cancer development. They also point to a putative protective role of the A allele in the older female control group, especially in hemizygous subjects [odds ratio = 0.42 (0.23-0.77), P = 0.03].

In vivo effects of the GH-releasing heptapeptide GHRP-1 in lambs

The novel synthetic growth hormone-releasing heptapeptide GHRP-1 is reported to be more potent than growth hormone-releasing hormone (GHRH) in eliciting GH release in vivo in rats and man. However, in ovine pituitary cells in primary culture in a perifusion system, GHRP-1 was 10-fold less active than GHRH. The purpose of this work was to study the effect of GHRP-1 in sheep in vivo. Ovine GH release stimulated by either GHRP-1 or GHRH(1-29)NH2, in eight pre-ruminant lambs, was determined. GHRP-1 was administered at doses of 1.2, 2.4 and 6 nmole/kg by i.v. bolus, and GHRH(1-29)NH2 at 0.3 nmole/kg. Mean+/-s.e.m. peak GH levels in the plasma after injection of saline, 1.2, 2.4, 6 nmole/kg GHRP-1 and 0.3 nmole/kg GHRH were 2.2+/-0.9, 9.3+/-2.5, 8.8+/-2.4, 35.1+/-5.8 and 51.6+/-10.5 ng/mL, respectively. As spontaneous 20 ng/mL peaks were observed, only peaks above this level can be considered as significant. The highest dose of GHRP-1 (6 nmole/kg) elicited oGH release, but its action was surpassed by GHRH 0.3 nmole/kg. Furthermore GHRP-1 and GHRH appear to behave inversely when response amplitudes are considered. Animals exhibiting a strong reaction to GHRH-1, show a correspondingly weak reaction to GHRH and vice-versa. This may reflect differences in intracellular mechanisms at the pituitary level. Our data support the results in vitro that in sheep GHRP-1 is a weaker stimulant of GH secretion than GHRH.

Allelic deletion at glutathione S-transferase M1 locus and its association with breast cancer susceptibility

Glutathione S-transferases (GSTs) are a family of isoenzymes involved in cellular detoxification. Previous studies have correlated the absence of the GSTM1 protein with an increased risk of developing some cancers, especially lung or bladder cancer, in heavy smokers. In this study, we determined GSTM1 gene polymorphisms in a French western population of 437 female controls and 361 community breast cancer patients. Three distinct alleles of this gene may be identified: GST M1* A allele, GST M1* B allele, and GST M1* 0 allele (which is deleted). Null patients (GSTM1 0) are homozygous for the deletion. We determined in our two populations, patients with no, one or two GSTM1 alleles. The comparative analysis of our two populations did not demonstrate any statistically significant difference in GSTM1 allelotype distribution between the two groups (P = 0.43), although the null genotype was the more frequent in patients. The predominance of the null genotype was significant in the oldest group of patients (> or = 55) (P = 0.006), suggesting that GSTM1 null genotype may play an important role in breast cancer susceptibility in the elderly. This was not observed in the youngest age group, i.e. < 40 year old patients (P = 0.25), or in the patients aged from 40 to 55 years old (P = 0.37). Our results also point out a putative protective role of the A allele in the older female control group (P = 0.02), especially in subjects hemizygous for these alleles (P = 0.03). A prospective study will be of interest to investigate the effect of dosage of the gene.

French multicentric evaluation of mdr1 gene expression by RT-PCR in leukemia and solid tumours. Standardization of RT-PCR and preliminary comparisons between RT-PCR and immunohistochemistry in solid tumours. French Network of the Drug Resistance Intergroup, and Drug Resistance Network of Assistance Publique-Hôpitaux de Paris

Since there is no consensus on the techniques for multidrug resistance (MDR) phenotype evaluation, many discrepancies concerning the importance and frequency of mdr1 gene expression in leukemias and solid tumors are observed in the literature. In order to establish an inter-laboratory consensus in France, a multicenter study was carried out to propose further guidelines for MDR phenotype evaluation. The techniques used by the 38 laboratories participating in the trial were: immunodetection (immunohisto and/or cytochemistry, flow cytometry), functional tests, reverse transcription-polymerase chain reaction (RT-PCR) or Northern blot. We present the results obtained by 19 laboratories concerning the measurement of mdr1 gene expression assessed by RT-PCR or Northern blot in: (1)19 samples of tumor cells obtained from leukemic patients; (2) six solid tumor samples obtained at surgery; (3) eight cell lines exhibiting variable levels of resistance, and; (4)10 preparations of RNA and of cDNA obtained from solid tumors. Standardization of the RT-PCR technique and preliminary results comparing RT-PCR with immunohistochemistry in solid tumors are also reported.

Chemotherapeutic inhibition of erb-B2 oncogene expression on a non-small-cell cancer line (NSCLC-N6) by marine substances

The inhibitory effect of natural substances of marine origin on the erb-B2 oncogene of a human NSCLC-N6 line was demonstrated in vitro by simultaneous study of the expression of the gene and its product, using respectively an erb-B2 specific probe and an anti-c-erb-B2 polyclonal antibody. Preliminary results indicate inhibition ranging from 17-77% of oncogene expression and from 77-90% of product expression. The fact that substances of this type, with different chemical structures, have the common ability to induce terminal differentiation in an experimental model after irreversible blockade in G1 phase suggests a relationship between the inhibition of certain oncogenes and terminal differentiation.

Effects of insulin-like growth factor-I (IGF-I) infusion and dietary tri-iodothyronine (T3) supplementation on growth, body composition and plasma hormone levels in sex-linked dwarf mutant and normal chickens

This study used a sex-linked dwarf mutant (SLD) chicken to evaluate growth-promoting and metabolic effects of recombinant human insulin-like growth factor-I (rhIGF-I) treatment. The SLD chicken is characterized by a 30% reduction in body weight and by high plasma GH levels, low plasma IGF-I and triodothyronine (T3) levels and very low GH binding on liver membranes, suggesting reduced functional GH receptors compared with normal chickens. The effects of a continuous s.c. infusion by osmotic mini-pump of 0.1 mg rhIGF-I/kg per day from 4 to 8 weeks of age on body weight, bone growth and body composition were investigated in female SLD and normal chicks. In addition, half of the birds received a dietary supplement of T3 (0.1 parts per million). Plasma levels of IGF-I, GH, T3, thyroxine and insulin were followed during the treatment. In normal chicks, rhIGF-I infusion had no effect on growth and little effect on plasma hormone levels except for a decrease in plasma insulin. In dwarf chicks, rhIGF-I infusion slightly increased body weight but had no effect on longitudinal bone growth. In addition, plasma GH levels were decreased and T3 levels remained lower than in normal chicks. Normal and dwarf chicks showed a decrease in abdominal fat after both IGF-I administration and T3 supplementation, the treatments having additive effects in dwarf chicks only. The combined rhIGF-I and T3 treatment restored a quasi-normal hormonal pattern in dwarf chicks, except for insulin which remained lower than in normal chicks. These results suggest that IGF-I in the chicken has no direct endocrine effect on statural growth.

GRF treatment of late pregnant ewes alters maternal and fetal somatotropic axis activity

To examine the effects of anabolic agents given during late gestation on the maternal and fetal somatotropic axes, we injected pregnant ewes twice daily with 0.15 mg somatocrinin (GRF)-(1-29) for 10 days beginning on day 130 of gestation. Maternal and fetal endocrine changes were compared with control animals using both in vivo and in vitro approaches. Treatment with GRF increased maternal plasma levels of growth hormone (GH) and insulin-like growth factor I (IGF-I;P less than 0.05) but not IGF-II. Under in vitro test conditions, maternal pituitary cells showed a greater maximal response (P less than 0.001) to GRF. In the fetuses of treated ewes, cord plasma GH levels were not significantly increased compared with controls. These animals had similar IGF-I but higher IGF-II (P less than 0.05) plasma levels. The maximal response of fetal pituitary cells to GRF was increased (P less than 0.001). GRF treatment had no influence on maternal and fetal pituitary cell responses to somatostatin under either basal or GRF-stimulated conditions. In addition, these treatments did not affect plasma levels of placental lactogen, glucose, or free fatty acids in the maternal and fetal sheep. These data are compatible with the hypothesis that treatment of pregnant ewes in the last days of gestation with GRF could support accelerated fetal growth.

Application of preparative high-performance liquid chromatography to the purification of a fetal ovine insulin-like growth factor II: N-terminal sequence determinations using two different carriers

A highly efficient procedure for the purification to homogeneity of an ovine fetal insulin-like growth factor II (IGF II) is described. Fetal sheep serum was used as the source material, and the bioactivity was followed throughout purification by an IGF II radioreceptor assay. Ovine IGF II was isolated by a combination of gel permeation, ion-exchange chromatography and reversed-phase high-performance liquid chromatography. The amino-terminal sequence of the first 36 amino acid residues was compared using two supports (polyethylenimine and polybrene) as carrier for protein sequencing. Ovine fetal IGF II was found to differ from human IGF II in three residues of the C-domain, with serine, isoleucine and asparagine substituted for alanine, valine and serine, respectively, at positions 32, 35 and 36. The final yield of highly purified ovine fetal IGF II was 134 micrograms, starting from 450 ml of serum.

Effects of a chronic GRF treatment on lambs having low or normal birth weight

The effects of a long term treatment with human GRF(1-29)NH2 on plasma growth hormone (GH), somatomedin C (Sm-C), histomorphometric parameters of bone growth and body composition were investigated in normal and low birthweight male lambs. The animals were divided into two groups according to their birthweight: 24 normal birthweight (NBW) lambs weighing more than 4 kg and 22 low birthweight (LBW) lambs weighing less than 2.5 kg at birth. Half of the animals in each group received two daily subcutaneous injections (8 micrograms/kg body weight) of hGRF(1-29) NH2 (GRF) from birth to slaughter at 45 or 90 days of age. The other animals received the solvent only. At the beginning and at the end of the treatment, plasma GH and serum Sm-C concentrations were measured in all groups. After slaughter, a histomorphometric study was performed on undecalcified sections of metacarpal growth plates, and the remaining of the carcass was pulverized to study the chemical body composition. GRF induced GH release in both GRF-treated groups. However, plasma GH reached higher (P less than .001) concentrations and the GRF-induced GH peak lasted longer in LBW than in NBW lambs. At day 45, the GRF treatment increased (P less than .05) serum Sm-C concentrations in LBW. Most of histomorphometric parameters reflecting the metacarpal growth in length, were not statistically modified under GRF treatment. However, the size of degenerative cells was smaller (P less than .05) in LBW treated lambs as compared to controls. Consequently, the cell production in the growth plate was increased (P less than .05) under GRF treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Instantaneous secretion rate of growth hormone in lambs: relationships with sleep, food intake, and posture

Relationships among sleep, feeding behavior, posture, and GH secretion were investigated in two groups of ruminant lambs in January (n = 6) and May (n = 3). Lambs were placed in individual cages and fed ad libitum. Behavioral features were obtained from continuous polygraphic recording. Blood was collected from undisturbed sheep every 3 min for 24 h via an indwelling catheter connected to a peristaltic pump. One month after the sampling session, ovine GH (oGH) was iv administered to evaluate oGH kinetic parameters. From GH plasma concentrations and oGH kinetic parameters, the instantaneous secretion rate of GH was reconstituted using a numerical deconvolution method. All lambs exhibited normal behavioral patterns. The clearance of oGH was similar for the two groups, and the daily production rates of GH were estimated at 14.60 +/- 7.99 micrograms/kg.24 h in January and 10.57 +/- 5.21 micrograms/kg.24 h in May. Analysis of concentration profiles indicate an episodic pattern of GH secretion into plasma. The mean number of peaks was 16.22 +/- 4.47/24 h, and the mean duration was 47.2 +/- 12.8 min for the nine sheep. When instantaneous secretion rates were taken into account, the number of identified peaks was similar, but the mean duration was reduced (32.9 +/- 9.8 min for the nine sheep). Significant relationships were not found between GH plasma concentration profiles and the state of vigilance, food behavior, or posture. Conversely, when the instantaneous secretion rates were taken into account, the highest GH production rate was detected during rest, i.e. slow wave sleep and rapid eye movement sleep, absence of food intake or rumination, and lying down. It is emphasized that the use of GH instantaneous secretion rate instead of GH concentration is of importance when evaluating the relationships between GH dynamics and short duration events. It is concluded that the influence of vigilance on GH secretion, which has already been demonstrated in humans, is likely to exist in other species.

Growth hormones. II. Structure-function relationships

Localization of the somatotropic activity of growth hormones from several species and from different organs was attempted using different approaches. Sequences were compared in order to detect one or several regions with a common homology. The technique of peptide recombinants as well as chemical changes affecting some amino acids was applied to these hormones; the biological function in vivo of growth or binding to somatotropic receptors was then estimated. The few data available on biosynthetic molecules and secondary structures of natural growth hormones are reported. This study indicates the somatotropic function of particular sites.

In vitro regulation of growth hormone (GH) release from ovine pituitary cells during fetal and neonatal development: effects of GH-releasing factor, somatostatin, and insulin-like growth factor I

Using a monolayer approach, we have examined the acute (3 h) effects of GRF, somatostatin (SRIF), and insulin-like growth factor I (IGF-I) on GH release from pituitary cells of male and female 70-, 100-, and 130-day-old fetuses and newborn lambs and of prepubertal male lambs. GRF stimulated basal GH release in a dose-dependent (10(-12)-10(-8) M) manner at each stage in development. There was no linear relationship between maximal response and increasing age of the donor animals. The ED50 values for GRF were similar in all groups, except in the pituitaries from male and female 130-day-old fetuses, where the ED50 values were significantly higher. SRIF elicited a dose-related (10(-10)-10(-6) M) inhibition of basal GH secretion at each stage of fetal life and in the prepubertal period; although the response was lower in the youngest fetal pituitaries, there was no significant change in maximal response during the fetal or prepubertal period. No effect of SRIF on basal GH secretion was observed in newborn lambs. However, SRIF (10(-7) M) was able to block GRF (10(-8) M)-stimulated GH release in 100- and 130-day-old fetal and prepubertal as well as newborn lamb pituitary cells. Plasma IGF-I concentrations increased from 15.0 +/- 0.7 (mean +/- SE) and 13.8 +/- 0.9 ng/ml for male and female animals, respectively, at 70 days gestation to 55.8 +/- 3.2 and 51.8 +/- 11.1 ng/ml at the time of birth. The increase was much more pronounced in prepubertal lambs, especially in male animals, where IGF-I levels reached 300.8 +/- 37.7 ng/ml. IGF-I (100 ng/ml) had no effect on basal GH release in 70- and 100-day-old fetal, newborn, and prepubertal lamb pituitary cultures, but significantly inhibited basal GH secretion from 130-day-old fetal cells. This dose of IGF-I had no effect on GRF (10(-9) M)-stimulated GH release at 70 days gestation. It significantly inhibited this effect at 100 days and in prepubertal lamb cells. In 130-day-old fetal and newborn lamb pituitary cultures, IGF-I completely blocked the GH response to GRF.(ABSTRACT TRUNCATED AT 400 WORDS)

Growth hormones. 1. Polymorphism (minireview)

Pituitary growth hormone (GH) is not a single molecular species, but a whole set of similar molecules, the individual specific characteristics of which constitute the polymorphism of this hormone. The present paper deals mainly with various forms of human GH, called "variants", and touches on this polymorphism in other species as well. The 22 K variant (MW = 22,000 daltons) is the predominant form of GH to which all other variants are compared as to chemical structure and biological effect. These variants are classified into two large groups: 1) mass variants, the molecular weight of which is modified in comparison with that of 22 K; these can be subdivided into aggregated and non-aggregated forms, and 2) charge variants with modified electrophoretic mobility. Outside this classification are entities which are not yet well known; these include bioinactive GH, correctly detected by RIA but deprived of biological activity or, on the contrary, strongly bioactive GH lacking immunoreactivity and consequently difficult to study. Another outsider is the SV-hGH-2 variant encoded from a gene different from the hGH-N gene normally coding for the other variants. In this case, the product could be considered a true isohormone of 22 K and no longer a variant. The pituitary expression of this gene has never been evidenced to date, but according to recent data, it could be expressed at the placental level and be implicated in human placental growth hormone (hPGH) synthesis. hPGH is a newly-found GH in pregnant women which takes over pituitary GH from the 25th week onwards. After the GH molecules are released by the pituitary in the blood stream, they are partially taken up and carried by binding proteins. The physiological role of this phenomenon could be the setting up of a GH reservoir and a GH sparing process since the metabolic clearance rate of the complex GH-binding protein is slower than that of free GH, thus increasing the biological half-life of the hormone.

Ovine chorionic somatomammotropin and foetal growth

Ovine chorionic somatomammotropin (oCS) enhances the weight and bone growth of hypophysectomized rats. It acts as a bifunctional hormone, since it binds both to lactogenic and somatotropic receptors. Ovine foetus weight gain is closely related to oCS and oGH serum levels. oCS is able to stimulate somatomedins by foetal liver. Moreover, oCS specific receptors are present in some foetal tissues. So, all these facts involve oCS in foetal growth, whereas pituitary growth hormone intervenes in postnatal growth. A study of structure function relationships between growth hormones and placental hormones is exposed in order to localize somatotropic sites.

[Oligo-arthritis associated with type IV hyperlipoproteinemia]

A case of chronic, corticosteroid-responsive arthritis affecting particularly one ankle in a patient with type IV hyperlipoproteinaemia is reported. After gout or inflammatory rheumatism of another nature had been excluded, and following synovial fluid examination and synovial membrane biopsy, a diagnosis of type IV hyperlipoproteinaemia rheumatism was made. At electron microscopy, the synovial membrane showed numerous large spumous cells and a peculiar appearance of the capillary vessels.

Characteristics of growth hormone response to the administration of growth hormone-releasing hormone (GRF) in the lamb

Human growth hormone releasing hormone (GRF 1-44 or GRF 1-29) was administered to lambs at two different physiological stages (suckling: 5-6 week-old and weaned: 14-15 week-old) when growth hormone (GH) secretory patterns were different: suckling lambs exhibited flat basal GH profiles (5-10 ng/ml) while the weaned lambs had frequent spontaneous episodes of GH release (15-65 ng/ml). The iv injection of GRF evoked an immediate release of GH. In each case, plasma GH levels reached a maximum 1-4 min after the injection. The secretory spike was multiphasic and lasted 30-60 min. Administration of GRF (0.1 microgram/kg) in weaned lambs induced GH pulses with an amplitude comparable to that of endogenous peaks. The induction of a GH peak occurred even when a spontaneous peak immediately preceded the GRF injection. Also, spontaneous peaks were observed during the hour following a GRF-induced GH peak. In suckling lambs, GRF injected intravenously as a single bolus in a range of 0.01 to 0.5 microgram/kg (2 to 100 pmoles/kg) stimulated GH release in a dose-dependent manner. Chronic administration of GRF (0.75 nmole GRF 1-44 or GRF 1-29 per kg twice daily for 21 days) in newborn lambs increased significantly (p less than 0.001) the acute response to GRF during the course of the treatment. GH response to GRF 1-44 and GRF 1-29 was the same. These data show that lambs are highly responsive to GRF action during both suckling and weaning and suggest that there is no in vivo desensitization of the pituitary gland after acute or chronic GRF administration.

Secretory profiles and production rate of growth hormone in ruminant lambs

Secretory profiles and production rates of growth hormone (GH) were determined in 6 ruminant lambs during winter. The mean GH concentrations (3.78 +/- 2.17 ng/ml) calculated were based upon blood sampling obtained every 3 min using a withdrawal pump. Body clearance (0.162 +/- 0.031 1/h/kg) was calculated from bolus intravenous oGH administration. The data were analysed by non-linear regression analysis; a bicompartmental model was selected to describe the data. production rate was 14.6 +/- 7.98 micrograms/kg/24 h. It has been emphasized that the experimental design used gave an accurate estimate of GH production rate.

Effects of TRH and GRF administration on GH, TSH, T4 and T3 secretion in the lamb

The effects of various amounts of thyrotropin-releasing hormone (TRH) injected subcutaneously or intravenously (alone or in combination with growth hormone-releasing factor: GRF 1-44) on growth hormone (GH), thyroid-stimulating hormone (TSH), thyroxine (T4) and triiodothyronine (T3) were studied in the plasma of 2-week, 2-month and 3-month old lambs. After subcutaneous TRH administration, increases in plasma TSH, T4 and T3 levels were equivalent, whatever the amount of TRH used (1,2,5 or 10 micrograms/kg). These responses lasted longer after 5 and 10 micrograms/kg. After intravenous TRH administration in 2-week old lambs, the maximal increase in plasma TSH levels occurred after the injection of 0.25 microgram/kg. However, plasma T4 and T3 responses were not different, whatever the amount used. As previously, the amount of TRH affected the duration of these responses more than the magnitude of the pituitary-thyroid axis response. Whatever the injection route, amount used or animal age, TRH alone did not increase GH secretion in lambs. However, it slightly delayed the GH response to GRF. GRF did not affect the response of TSH and T4 to TRH; however it could inhibit T3 increase. In conclusion, in contrast to results obtained in calves by Hodate et al. (1985), TRH did not enhance GH secretion in lambs but, as expected, induced sharp increases in plasma thyroid hormone levels. Its classification as a "growth factor" is therefore questionable, at least in lambs.

Effects of hypothalamic hormones (GRF, TRH, somatostatin) and insulin-like growth factor I on growth hormone secretion from prepubertal male lamb pituitary cultures

We have examined the regulation of GH secretion from monolayer cultures of prepubertal male lamb anterior pituitary cells. Growth hormone-releasing factor (GRF 1-44) stimulated GH release in a dose-related manner: the maximal effective dose was 10(-10) M, which caused a 500% increase in basal GH secretion, while the half-maximal effect was reached with a dose of 2.5 x 10(-11) M (ED50). Thyrotropin-releasing hormone (TRH) also elicited a dose-dependent stimulation of GH secretion, although it was approximately 1000 times less potent than GRF. GRF and TRH did not have additive or synergistic effects on GH secretion. Somatostatin (SRIF) at a concentration of 10(-7) M maximally inhibited basal GH release to 40% of that of the control; the ED50 was 2.0 x 10(-9) M. Moreover, 10(-7) M SRIF blocked the stimulation of GH secretion induced by 10(-8) M GRF. However, when the cells were incubated with these two peptides at an identical concentration (10(-8) M), GH secretion was stimulated significantly above control values. When added at the same concentration (10(-7) M, TRH ans SRIF nullified their respective effects. A dose of 100 ng/ml of synthetic IGF-I was without effect on basal GH release, but significantly decreased 10(-9) M GRF-induced stimulation of GH secretion. these data indicate that in prepubertal male lambs: the stimulatory effect of GRF is predominant over the inhibitory effect of SRIF, somatostatin inhibits TRH stimulation of GH secretion in vitro, and IGF-I may control GH secretion by modulating GRF effects at the pituitary level.

The Brattleboro rat: normal growth hormone secretion, decreased hepatic growth hormone receptors and low plasma somatomedin activity

Three-month-old male Brattleboro rats with hereditary diabetes insipidus (DI) present a growth defect; Brattleboro rats were studied together with age-matched Long-Evans (LE) rats. Pituitary growth hormone (GH) content was comparable in both groups of rats. Pulsatile GH release and mean 6 h GH plasma levels did not appear significantly different in chronically catheterized DI and control animals. In parallel with the growth defect, the plasma somatomedin bioactivity was significantly lower in DI than in LE rats. The specific binding of [125I]iodo-hGH to liver microsomal membranes of DI rats was 59.7% that of controls. The number of the GH binding sites rather than the affinity of the binding was decreased. The specific binding of [125I]iodo-insulin was oppositely affected by the DI state: it was 1.5 times higher in liver membranes of DI rats than in membranes of LE rats. These findings make a non-specific effect of the DI state on liver membrane proteins unlikely. The Brattleboro rats present a growth failure without reduction of their GH secretion. The decreased number of the hepatic GH receptors and the subsequent low plasma somatomedin activity could explain the growth retardation of the DI rats.

Bioassay of growth-stimulating activity of serum: comparison of lymphocyte and cartilage assays in normal and growth hormone-deficient children

The somatomedin and/or growth-stimulating activity of serum from hypopituitary children and short children with normal growth hormone (GH) response to stimulation tests were studied using different bioassays: thymidine incorporation into human activated lymphocytes; sulfate incorporation into chick embryo cartilage; and simultaneous thymidine uptake into the same cartilages. The results showed that lymphocyte assay is highly sensitive to small amounts of serum and is GH-dependent in children with low GH secretion. On the contrary, the cartilage assays need higher serum concentration and their GH-dependence appears only in subjects with normal or low-normal GH secretion. The lack of correlation between the results of the three bioassays suggests that they measure both somatomedins and different serum factors involved in the regulation of growth.

Growth hormone receptors in rat liver membranes: effects of fasting and refeeding, and correlation with plasma somatomedin activity

The effects of fasting and refeeding on hepatic growth hormone receptors, on insulin receptors and on plasma somatomedin activity were studied. Female rats were either subjected to fasting for 4 days, refed for 3 days after a 4-day fasting, or allowed free access to food (controls). The specific binding of 125I-labelled bovine growth hormone was low in liver microsomal membranes (45% that of controls) and in plasma membranes (52% that of controls) of fasted rats. The number of somatotropic sites rather than the affinity of the binding was decreased. Lactogenic sites as judged by the binding of 125I-labelled human growth hormone were not significantly reduced in liver membranes of fasted rats. 125I-labelled insulin specific binding was enhanced in microsomal (184% that of controls) and plasma membranes (136% that of controls) of fasted rats; these modifications were associated with a decreased insulinemia. But immunoreactive rat growth hormone levels were not different in plasma of fasted, refed and control animals. Decreased plasma bioassayable somatomedin was associated with the low number of somatotropic binding sites in liver membranes of fasted rats. Somatomedin activity of refed animals was comparable to controls. A significant correlation between the plasma bioassayable somatomedin and the hepatic level of somatotropic binding sites was found. It is proposed that, in fasting, the loss of somatotropic binding sites in the liver is one of the possible causes of the decreased plasma somatomedin bioactivity.

Somatomedin-A bioactivity in rabbit serum after hypophysectomy

Hall's bioassay was used to determine the somatomedin (Sm) activity pattern after hypophysectomy in young (40 days) and adult (180 days) rabbits. In the young animals, Sm activity decreased a little, but the serum remained slightly active. The serum of the older rabbits progressively lost its sulphation activity and inhibited SO4 uptake after 2 weeks following hypophysectomy. The inhibitory activity could not be destroyed by heating. Concomitantly, the same serum continued to stimulate thymidine uptake. From the present results on bioactivity, it appeared that Sm generation was only partially pituitary-dependent, that the pituitary might control inhibitor synthesis, and that the SO4 and thymidine factors were separate entities, each having its own inhibitor(s).

Development of growth hormone receptors in rabbit and lamb liver after hypophysectomy

The prolactin receptors of rat liver are pituitary-dependent, and previous studies have shown that prolactin itself plays a role in inducing and maintaining their presence. This study tried to determine if hepatic growth hormone (GH) receptors are comparably dependent on the pituitary. Young 47-day and older 116-day old rabbits were either hypophysectomized (H) or sham-operated (S). Hypophysectomy completely arrested the growth of the older rabbits but only reduced it by 50 p. 100 in the young ones. After 21 days, the specific binding (sb) of 125I-labelled human GH (hGH) to liver membranes was measured in H and S animals. The sb of hGH in H rabbits compared to S animals (older, young) was 14.9 p. 100 in older H rabbits and 45.5 p. 100 in young H animals. Similar studies in lambs showed that the sb of hGH in H lambs (compared to S animals) was 23.9 p. 100. When some H lambs were treated with 1 mg/kg of oGH or bGH 3 times per week, the sb of hGH was significantly increased to 56.1 p. 100 of the S levels. All changes in sb reflected changes in receptor number, as shown by the dose response binding curves. This study demonstrates that hepatic GH receptors in both the rabbit and the lamb are pituitary-dependent. The level in rabbits is correlated with the growth rate. Since GH receptor levels were partially restored in GH-treated lambs, it is possible that GH plays a role in inducing its own receptors.

Somatomedin-A (Sm-A) bioactivity in serum and amniotic fluid as related to weight in the fetal pig

Serum and amniotic fluid Sm-A bioactivity has been assayed in the fetal pig using a double labelling technique. 3H-thymidine activity was always higher in fetuses and lower in sows than 35S activity. 35SO4 uptake was not stimulated or was inhibited in about 30 p. 100 of the fetal sera. 3H-thymidine uptake was stimulated in all of them. There was a significant correlation (P less than 0.001) between fetal weight and serum Sm, as judged with both 35SO4 and 3H-thymidine. No correlation was found between fetal weight and amniotic fluid Sm, between amniotic fluid and serum Sm or between 35SO4 and 3H activities. It is concluded that the latter activities were due to two or more factors instead of only one.