Search Results
You are looking at 1 - 10 of 36 items for
- Author: D Hill x
- Refine by access: All content x
Search for other papers by D. J. HILL in
Google Scholar
PubMed
The actions of cortisol were investigated in vitro on separated zones of cartilage from the calf costochondral junction, and from the structural costal cartilage. Cortisol had no direct effect in plasma-free medium on the uptake of [3H]thymidine, [3H]leucine or [35S]sulphate in any zone of growth plate or structural cartilage until pharmacological concentrations (10−4–10−3 mol/l) were present, when the incorporation of all three isotopes was significantly reduced. In the presence of a somatomedin stimulus of normal rat plasma the addition of cortisol at supraphysiological concentrations (10−8–10−6 mol/l) had no effect on the incorporation of any isotope in structural cartilage, but significantly reduced the uptake of [3H]thymidine in the growth plate region of proliferating chondrocytes, and at a concentration of 10−6 mol/l appeared to increase the uptake of [35S]sulphate in the region of maturing chondrocytes. This was not accompanied by a general increase in protein synthesis as assessed by [3H]leucine incorporation, and could reflect the decreased rate of proteoglycan degradation in the presence of cortisol. It could not be proven in the present experiments that the actions of cortisol at supraphysiological levels were dependent on the presence of growth hormone dependent somatomedin.
Search for other papers by D. J. HILL in
Google Scholar
PubMed
The actions of rat plasma somatomedin activity dependent on growth hormone were investigated in vitro on separated zones of cartilage from the calf costochondral junction. Plasma somatomedin maximally stimulated the uptake of [3H]thymidine into cartilage cells of the proliferating region. Cartilage deeper in the growth plate possessed the highest uptake of [35S]sulphate which was also stimulated by somatomedin. Somatomedin, therefore, appears to promote both cell replication and matrix synthesis throughout the growth plate cartilage although the two processes were greatest in different cartilage regions. Growth hormone or tri-iodothyronine did not directly alter the uptake of either isotope into the growth plate cartilage.
Search for other papers by M. J. Parkes in
Google Scholar
PubMed
Search for other papers by D. J. Hill in
Google Scholar
PubMed
ABSTRACT
Fetal lambs were hypophysectomized and, after 8 days of recovery, given infusions of GH, prolactin, thyroxine and insulin with glucose. Hypophysectomy caused no consistent reduction in fetal plasma somatomedin-like activity. Fetal infusions of GH or prolactin caused no consistent change in plasma somatomedin-like activity. It was concluded that fetal somatomedin-like activity is not GH dependent. After hypophysectomy fetal lambs showed no reduction in body weight or length at term.
J. Endocr. (1985) 104, 193–199
Search for other papers by C. D. HILL in
Google Scholar
PubMed
Search for other papers by BERTHA SINGER in
Google Scholar
PubMed
SUMMARY
The adrenal response to adrenocorticotrophin (ACTH), as determined by the secretion of corticosterone into adrenal vein blood,was measured in hypophysectomized rats in the presence of low and high levels of corticosterone in the peripheral circulation. To ensure that the level of corticosterone was low in the peripheral blood, the animals were hypophysectomized 24 hr. before the experiment, and one adrenal was removed before the start of infusion of ACTH. After the onset of the infusion the effluent from the remaining gland was collected in a receptacle, thus preventing any corticosterone produced under the influence of ACTH from reaching the general circulation. To study the effect of a high level of circulating corticosterone on the adrenal response to ACTH, corticosterone was injected subcutaneously, in beeswax and arachis oil, before the start of infusion of ACTH. In these experiments, too, the steroid secreted under the influence of ACTH was prevented from entering the general circulation. The peripheral levels attained by the injection of corticosterone were within the range observed during surgical stress, i.e. about 40 μg./100 ml. blood. When the corticosterone levels were within this range the response to a continuous infusion of ACTH was reduced by approximately 22% when compared with animals which had received no corticosterone and whose peripheral corticosterone levels were hardly measurable. These results suggest that corticosterone is probably involved in a direct feedback mechanism of adrenocortical secretion in the rat as its inhibitory effect on the response to ACTH can be demonstrated at peripheral levels of corticosterone which are within the range found during surgical stress.
Search for other papers by A. Logan in
Google Scholar
PubMed
Search for other papers by D. J. Hill in
Google Scholar
PubMed
The regulation of cell growth and function that occurs during development, in differentiated cell homeostasis and in wound healing, is determined by two distinct classes of trophic factors: classical endocrine hormones and paracrine or autocrine growth factors. Regulation of hormone activity is achieved by tight control of their synthesis, and especially release, by cells in discrete glands, linked to the limited expression of high-affinity receptors by defined, distant target cells. In contrast, growth factors and their receptors are often constitutively expressed and the former are exported to the extracellular milieu by most normal tissues. How then are target cells protected from constitutive activation by locally produced growth factors? This may be achieved by another tier of target cell-specific regulatory signals.
Once exteriorized, many growth factors are stored in significant quantities in pericellular depots adjacent to their target cells, often complexed with other binding molecules either in the tissue fluid or
Search for other papers by D. J. Hill in
Google Scholar
PubMed
Search for other papers by R. D. G. Milner in
Google Scholar
PubMed
ABSTRACT
The actions of partially purified porcine platelet-derived growth factor (PDGF) and highly purified multiplication-stimulating activity (MSA) II and MSA III-2, which are somatomedins, were investigated on the incorporation of [3H]thymidine and [35S]sulphate by fetal rat costal cartilage in vitro. This was compared with their effects in the presence of 1% fetal calf serum (FCS) on the uptake of thymidine by growth-arrested fetal rat fibroblasts. Platelet-derived growth factor at concentrations of 0·21–21 μg/l enhanced the incorporation of both isotopes by fetal cartilage in the presence of 1% FCS, but had an inconsistent action on thymidine uptake and no significant action on sulphate uptake in serum-free medium. Platelet-derived growth factor promoted thymidine uptake by growth-arrested, isolated fetal rat fibroblasts. Multiplication-stimulating activity II (10–100 μg/l) stimulated the uptake of thymidine and sulphate by fetal cartilage in medium containing 1% FCS but had no consistent action in serum-free medium, although MSA II and PDGF had a synergistic effect on thymidine uptake in the absence of serum. Multiplication-stimulating activity III-2 had no consistent action on thymidine or sulphate incorporation by fetal cartilage in either serum-free or serum-supplemented medium. However, the same preparation of MSA III-2 stimulated the uptake of [3H]thymidine into fetal rat fibroblasts with a half-maximal response at a concentration of 5–10 μg/l. The results identify PDGF as a possible mitogenic agent for fetal rat connective tissues in vitro and show a differential sensitivity of fetal cartilage to MSA peptides.
J. Endocr. (1984) 103, 195–203
Search for other papers by D. J. Hill in
Google Scholar
PubMed
Search for other papers by A. Logan in
Google Scholar
PubMed
Search for other papers by M. McGarry in
Google Scholar
PubMed
Search for other papers by D. De Sousa in
Google Scholar
PubMed
ABSTRACT
Chondrogenesis is thought to be controlled by interactions between circulating anabolic hormones and locally produced peptide growth factors, and involves ordered changes in matrix composition which ultimately allow endochondral calcification. We have used a model of isolated ovine fetal growth-plate chondrocytes to examine the actions and interactions of basic fibroblast growth factor (basic FGF), insulin-like growth factors-I and -II (IGF-I and -II), insulin and transforming growth factor-β1 (TGF-β1) on total protein, collagen or non-collagenous protein and sulphated glycosaminoglycan synthesis. These parameters were determined by assessment of the incorporation by monolayer cultures of early passage chondrocytes of [3H]leucine, [14C]proline and [35S]sulphate respectively, followed by partial molecular characterization. Basic FGF enhanced total protein synthesis with a half-maximal effective concentration of 270 ± 60 pmol/l (mean ± s.e.m., four animals) and was sixfold more active on a molar basis than IGF-I or insulin, and 28-fold more active that IGF-II which is the endogenously synthesized IGF. The actions of basic FGF were additive to those of IGF-I or insulin. More detailed analysis of extracellular-matrix component synthesis showed that basic FGF, IGF-I and insulin each caused significant increases in the synthesis of collagen and sulphated glycosaminoglycans. TGF-β1 had no effect on total protein synthesis by chondrocytes when present alone at concentrations of 200 pmol/l or less, but was inhibitory at 400 pmol/l. However, the use of this parameter masked a stimulatory action of 50 or 100 pmol TGF-β1 on sulphated glycosaminoglycan synthesis and a relative shift in the ratio of collagen: non-collagenous protein synthesis in favour of the former. A synergistic interaction existed between TGF-β1 (20–100 pmol/l) and basic FGF which potentiated total protein and collagen synthesis, and their actions on sulphated glycosaminoglycan production were additive. The same concentrations of TGF-β1 inhibited the ability of IGF-I or insulin to stimulate total protein or collagen synthesis, but were additive to their stimulatory effects on sulphated glycosaminoglycan synthesis. The results suggest that matrix-molecule composition and the anabolic status of the epiphyseal growth-plate may be modulated in utero by multiple interactions between peptide growth factors produced locally, such as basic FGF, IGF-II and TGF-β1, and circulating hormones such as insulin and IGF-I.
Journal of Endocrinology (1992) 133, 363–373
Search for other papers by C. A. Ollis in
Google Scholar
PubMed
Search for other papers by D. J. Hill in
Google Scholar
PubMed
Search for other papers by D. S. Munro in
Google Scholar
PubMed
ABSTRACT
Human thyroid epithelial cells in monolayer culture were found to release radioimmunoassayable insulinlike growth factor-I (IGF-I) over a 48-h culture period in serum-free medium. In the presence of supraphysiological concentrations of TSH (1–100 mU/ml) known to be inhibitory to DNA synthesis by human thyroid cells, the release of IGF-I was found to be inhibited in six thyroid cultures studied. In only one out of the six was IGF-I release increased in the presence of physiological mitogenic concentrations of TSH (0·1–100 μU/ml). Human thyroid fibroblasts, established by long-term culture of thyroid epithelial cells under fibroblast-selective conditions, also secreted IGF-I which was unaffected by the presence of TSH at both low and high concentrations.
Using a monoclonal antibody against human IGF-I, monolayer cultures of both human thyroid epithelial cells and human thyroid fibroblasts showed positive immunocytochemical staining for IGF peptide. However, fixed sections of intact thyroid tissue only showed positive staining for IGF peptide associated with the fibrous layers surrounding the thyroid follicle, with no staining of the follicular epithelial cells.
The growth of human thyroid epithelial cells was also found to be increased by IGF-I (25–100 ng/ml) added in medium plus 1 % fetal calf serum as assessed by the incorporation of [3H]thymidine into DNA. In the presence of a monoclonal antibody to IGF-I the increase in [3H]thymidine uptake in response to IGF-I was abolished as was that seen in response to TSH.
This study indicates a possible paracrine/autocrine role of IGF-I in the regulation of human thyroid epithelial cell proliferation by interaction with TSH.
Journal of Endocrinology (1989) 123, 495–500
Search for other papers by C. J. Crace in
Google Scholar
PubMed
Search for other papers by D. J. Hill in
Google Scholar
PubMed
Search for other papers by R. D. G. Milner in
Google Scholar
PubMed
ABSTRACT
Insulin has been implicated in the regulation of fetal growth. The aim of these studies was to determine if insulin has a direct mitogenic effect on fetal and neonatal rat cells in vitro. Myoblasts and fibroblasts were isolated from skeletal muscle and grown until myotube formation began or until fibroblasts were confluent. The cultures were then incubated in the presence of insulin (10−5–10−1 units/ml) and its effects were measured by the cellular incorporation of [3H]-thymidine. Myoblasts from fetuses of 21 days of gestation showed a marked, linear dose–response to insulin, significant increases over control values being observed at 2 × 10−5 units/ml or 2 × 10−4 units/ml in five out of seven experiments. Neither myoblasts from 19-day fetuses or neonates nor fibroblasts from animals of any of the three ages showed a significant thymidine uptake response to insulin. Myoblasts released immunoreactive somatomedin-C-like activity into the culture medium, but this was not related to fetal age nor to the presence of insulin in the culture medium. The results suggest that insulin may have a direct role in fetal muscle growth.
J. Endocr. (1985) 104, 63–68
Search for other papers by D. J. HILL in
Google Scholar
PubMed
Search for other papers by P. DAVIDSON in
Google Scholar
PubMed
Search for other papers by R. D. G. MILNER in
Google Scholar
PubMed
One rabbit foetus within each litter was decapitated in utero on day 24 of gestation. Plasma somatomedin activity and costal cartilage metabolism were studied 5 days later in the experimental foetuses and control litter-mates. Somatomedin was assayed by the uptake of [35S]sulphate in vitro into costal cartilage from intact foetuses. Uptake was proportional to logarithmic increases in the concentration of both foetal and maternal rabbit plasma. The mean (± 1 s.d.) somatomedin activity of four plasma pools, each pool being derived from the intact foetuses within each of four litters, was 1·3 ± 0·3 compared with a potency of unity for the reference pool of maternal plasma. The plasma somatomedin activity of decapitated foetuses did not differ significantly from that of control litter-mates when analysed by rank test, but the costal cartilage of decapitated foetuses took up less [35S]-sulphate in basal medium when compared with that of intact litter-mates. The headless body weight of the decapitated foetuses did not rank in a position significantly different from the one expected. The concentration of plasma growth hormone in the decapitated foetuses was less than 5 ng/ml and that of the intact foetuses was more than 157 ng/ml. It is concluded that plasma somatomedin activity in the rabbit foetus is not dependent on foetal growth hormone.
