Stimulatory Effect Of GH Research Articles

GH prevents adipogenic differentiation of mesenchymal stromal stem cells derived from human trabecular bone via canonical Wnt signaling.

The imbalance between osteogenesis and adipogenesis, which naturally accompanies bone marrow senescence, may contribute to the development of bone-associated diseases, like osteoporosis. In the present study, using primary human mesenchymal stromal cells (hMSCs) isolated from trabecular bone, we assessed the possible effect of GH on hMSC differentiation potential into adipocytes. GH (5 ng/ml) significantly inhibited the lipid accumulation in hMSCs cultured for 14 days in lipogenic medium. GH decreased the expression of the adipogenic genes, CCAAT/enhancer-binding protein alpha (C/EBPα) and adiponectin (ADN) as well as the expression of two lipogenesis-related enzymes, lipoprotein lipase (LPL) and acethylCoA carboxylase (ACACA). In parallel, GH induced an increase in the gene expression and protein levels of osterix (OSX) and osteoprotegerin (OPG). These effects were ascribed to enhanced Wnt signaling as GH significantly reduced Wnt inhibitors, Dickkopf 1 (DKK1) and the secreted frizzled protein 2 (SFRP2), and increased the expression of an activator of Wnt, Wnt3. Accordingly, the expression of β-catenin and its nuclear levels were raised. Wnt involvement in GH anti-adipogenic effect was further confirmed by the silencing of β-catenin. In silenced hMSC, both the inhibitory effect of GH on the expression of the adipogenic genes, ADN and C/EBPα and the lipogenesis enzymes LPL and ACACA, were prevented together with the stimulatory effect of GH on the osteogenic genes OSX and OPG. The present study supports the hypothesis that when GH secretion declines as in aging, the fat in the bone-marrow cavities increases and the osteogenic capacity of the MSC pool is reduced due to a decrease in Wnt signaling.

Expression and functional characterization of intrafollicular GH–IGF system in the zebrafish ovary

The somatotrophic axis plays important roles in influencing reproduction. All key members of this axis including growth hormone (GH, gh), GH receptors (ghra and ghrb), insulin-like growth factors (IGFs, igf1, igf2 and igf3) and IGF receptors (igf1ra and igf1rb) were detected in the zebrafish ovary. GH was exclusively expressed in the full-grown oocytes, while its receptors were detectable in both the follicle cells and oocytes. The IGFs and their receptors were all expressed in both compartments except igf3, which was expressed in the follicle cells only. During folliculogenesis, there was a sharp decrease of gh expression at follicle activation; however, the expression of its receptors increased significantly. The expression profiles of igf1, igf2a, and igf2b were similar to that of fshr, whereas igf3 expression was close to lhcgr, suggesting differential roles for different forms of IGFs in follicle development. To examine if the ovarian GH–IGF system is regulated by gonadotropins (e.g., hCG) and GH, we performed in vitro experiments using cultured zebrafish follicle cells. The expression of igf1 and igf1ra, but not others, was down-regulated by hCG (LH analog), whereas recombinant zebrafish GH stimulated igf1 expression. In addition, GH also increased the expression of activin βA subunit (inhbaa). In agreement with this, the stimulatory effect of GH but not IGF-I on oocyte maturation could be abolished by follistatin. In conclusion, the present study revealed an intrafollicular network involving GH–IGF mini-axis in the zebrafish ovary; however, it might not work in the same way as that of the systemic somatotrophic axis.

Naloxone decreases the inhibitory effect of somatostatin on GH release induced by cigarette smoking in man

To establish whether somatostatin (SRIH) exerts its inhibitory effect on the nicotine-induced release of GH by interacting with an opioid pathway, normal volunteers were treated with naloxone during (2 no-filter) cigarettes smoking and with SRIH. Nicotine significantly increased serum GH levels about 3.5 fold. Naloxone alone did not change GH rise induced by cigarette smoking. The stimulatory effect of GH by nicotine was completely blocked by SRIH. In the presence of both SRIH and naloxone, GH levels rose 1.5 fold in response to nicotine. Since naloxone only partially reversed the inhibiting action of SRIH, only a partial involvement of opioid peptides in SRIH action might be supposed. Alternatively, SRIH and naloxone-sensitive opiates might produce this inhibiting effect on GH rise in response to cigarette smoking through independent pathways.

OR3,17 Acromegaly is associated with enhanced renal and extrarenal epithelial sodium channel (ENaC) activity in humans

Context: GH exerts a direct stimulatory effect on ENaC-dependent transport both in vitro and in vivo (Kamenicky et al. Endocrinology. 2008, 149(7):3294–305). Objectives: To investigate the effect of GH excess on renal and extrarenal ENaC activity in acromegalic patients before (P1) and after (P2) treatment by assessing 1) the natriuretic and kaliuretic responses to amiloride (an ENaC blocker) and to furosemide (a loop diuretic that acutely increases Na delivery to distal tubule) and 2) intranasal amiloride sensitive potential (ASP) reflecting ENaC activity in nasal epithelium. Study protocol: 16 acromegalic patients (11M/5F) aged 46 yrs [27; 75] were randomly assigned to receive in a crossover study a single dose of amiloride (20mg po) or furosemide (5mg IV bolus + 2h infusion of 10mg) at 2–7 days interval. Na and K daily intakes were maintained at 150 and 80mmol/day. Urinary Na/K ratio was measured before and after diuretic administration. ASP was measured before first drug administration. Investigations were repeated before (P1) and after (P2) medical and/or surgical treatment of acromegaly. Results: Serum IGF-1 concentration normalized in all subjects after acromegaly treatment (798 [387; 1445] vs 180ng/mL [72.0; 265.0], P < 0.0001). Daily Na and K intakes were similar between P1 and P2. The post-amiloride UNa/K ratio was significantly higher on P1 than on P2 (16.8mmol/mmol [7.0; 36.0] vs 8.1mmol/mmol [5.0; 20.6], P < 0.001). In contrast, UNa/K ratio during furosemide administration was significantly lower on P1 than on P2 (6.8mmol/mmol [4.6; 10.8] vs 9.3mmol/mmol [2.7; 12.9], P < 0.05). ASP was significantly higher on P1 than on P2 (5.5mV [3.5; 14.7] vs 4.1mV [8.2; 19.0], P < 0.05). Conclusion: Our data suggest enhanced renal and extrarenal ENaC activity in acromegaly as attested before acromegaly treatment by (1) higher response to amiloride and lower response to furosemide, supporting stimulatory effect of GH on ENaC activity in distal renal tubule; (2) higher amiloride sensitive-nasal potential. These observations provide first evidence in humans that ENaC stimulation might contribute to volume expansion and arterial hypertension in acromegalic patients.

OR3,18 Clinical, genetic and molecular characterisation of patients with familial isolated pituitary adenomas (FIPA), especially GH-secreting adenomas

Context: GH exerts a direct stimulatory effect on ENaC-dependent transport both in vitro and in vivo (Kamenicky et al. Endocrinology. 2008, 149(7):3294–305). Objectives: To investigate the effect of GH excess on renal and extrarenal ENaC activity in acromegalic patients before (P1) and after (P2) treatment by assessing 1) the natriuretic and kaliuretic responses to amiloride (an ENaC blocker) and to furosemide (a loop diuretic that acutely increases Na delivery to distal tubule) and 2) intranasal amiloride sensitive potential (ASP) reflecting ENaC activity in nasal epithelium. Study protocol: 16 acromegalic patients (11M/5F) aged 46 yrs [27; 75] were randomly assigned to receive in a crossover study a single dose of amiloride (20mg po) or furosemide (5mg IV bolus + 2h infusion of 10mg) at 2–7 days interval. Na and K daily intakes were maintained at 150 and 80mmol/day. Urinary Na/K ratio was measured before and after diuretic administration. ASP was measured before first drug administration. Investigations were repeated before (P1) and after (P2) medical and/or surgical treatment of acromegaly. Results: Serum IGF-1 concentration normalized in all subjects after acromegaly treatment (798 [387; 1445] vs 180ng/mL [72.0; 265.0], P < 0.0001). Daily Na and K intakes were similar between P1 and P2. The post-amiloride UNa/K ratio was significantly higher on P1 than on P2 (16.8mmol/mmol [7.0; 36.0] vs 8.1mmol/mmol [5.0; 20.6], P < 0.001). In contrast, UNa/K ratio during furosemide administration was significantly lower on P1 than on P2 (6.8mmol/mmol [4.6; 10.8] vs 9.3mmol/mmol [2.7; 12.9], P < 0.05). ASP was significantly higher on P1 than on P2 (5.5mV [3.5; 14.7] vs 4.1mV [8.2; 19.0], P < 0.05). Conclusion: Our data suggest enhanced renal and extrarenal ENaC activity in acromegaly as attested before acromegaly treatment by (1) higher response to amiloride and lower response to furosemide, supporting stimulatory effect of GH on ENaC activity in distal renal tubule; (2) higher amiloride sensitive-nasal potential. These observations provide first evidence in humans that ENaC stimulation might contribute to volume expansion and arterial hypertension in acromegalic patients.

Isolated porcine ovarian follicles as a model for the study of hormone and growth factor action on ovarian secretory activity.

The aim of our in vitro experiments with isolated porcine ovarian follicles was to study the effects of gonadotropins, GH, IGF-I and oxytocin (OT) on release of ovarian steroid, OT, IGF-I, insulin-like growth factor-binding protein-3 (IGFBP-3), prostaglandin F (PGF), prostaglandin E (PGE) and cAMP. It was found that quarters of ovarian follicles cultured for 8 days produced significant amounts of progesterone, estradiol-17 beta, OT and IGFBP-3 with peaks of accumulation from the 3rd to the 8th day of culture. Addition of serum promoted progesterone, estradiol and OT release, whilst accumulation of IGFBP-3 was maintained to a greater extent in serum-free medium. GH (10 ng/ml or above) was able to inhibit androstenedione, OT, PGF and IGFBP-3, to stimulate IGF-I and cAMP, and to alter testosterone and PGE release by follicles cultured in serum-supplemented and/or serum-free medium. IGF-I (10 ng/ml or more) inhibited androstenedione and PGF secretion, stimulated testosterone, estradiol, OT and cAMP production, but did not influence progesterone, IGFBP-3 or PGE output in these conditions. OT (100 ng/ml) was able to inhibit androstenedione and to stimulate testosterone, IGF-I, PGF and PGE, but not estradiol or IGFBP-3 release. A stimulatory effect of LH on progesterone and OT and an inhibitory influence of LH on estradiol secretion in the serum-supplemented medium were observed. FSH in these conditions stimulated OT, but not progesterone or estradiol secretion. The use of this experimental model suggests the involvement of gonadotropins, OT, GH and IGF-I in the control of ovarian steroid and nonapeptide hormone, growth factor, growth factor-binding protein, prostaglandin and cyclic nucleotide production. The stimulatory effect of GH on IGF-I, and the stimulatory influence of IGF-I on OT, as well as coincidence of the majority of effects of IGF-I and OT, suggest the existence of a GH-IGF-I-OT axis. On the other hand, the different patterns of action of GH and IGF-I on OT, estrogen and IGFBP-3 suggest that part of the GH effect on ovarian cells is IGF-I independent.

Stimulatory effect of growth hormone on in vitro maturation of bovine oocytes is exerted through cumulus cells and not mediated by IGF-I.

A previous study reported that the addition of bovine growth hormone (bGH) during in vitro maturation of bovine oocytes accelerates nuclear maturation and stimulates subsequent embryonic development. The aim of this study was to investigate whether bovine cumulus oocyte complexes (COCs) contain growth hormone receptor (GHR), and whether the stimulatory effect of GH on oocyte maturation is cumulus-dependent and mediated by insulin-like-growth factor (IGF-I). The expression of growth hormone receptor mRNA in mural granulosa cells, in cumulus cells, and in the oocyte was studied using reverse transcriptase polymerase chain reaction (RT-PCR). To investigate the importance of cumulus cells for GH-promoted maturation, COCs and denuded oocytes were cultured for 16 hr in M199 with or without bGH s(NIH-GH-B18). To investigate whether GH action is mediated by IGF-I, COCs were cultured in 1) 100 ng/ml bGH, 2) 100 ng/ml bGH plus anti-IGF-I, 1:100 dilution, 3) 100 ng/ml h-IGF-I, 4) 100 ng/ml h-IGF-I plus anti-IGF-I, 1:100 dilution, and 5) anti-IGF-I, 1:100 dilution. Culture was performed at 39 degrees C in a humidified atmosphere with 5% CO2 in air, and the nuclear stage of oocytes was assessed using 4,6-diamino-2-phenyl-indole (DAPI) staining. PCR on cDNA of mural granulosa cells, cumulus cells, and oocytes revealed that mRNA for GHR was present in all cell types. Addition of GH (100 ng/ml) to the culture medium of denuded oocytes did not affect the number of metaphase II oocytes after 16 hr, while a significant (P < 0.001) increase was observed, when COCs were cultured in the presence of GH. Addition of the antibody against IGF-I to the culture medium completely suppressed the stimulatory effect of IGF-I on oocyte maturation and cumulus expansion, while stimulation by GH was not affected by the antibody. It is concluded that bovine cumulus cells, mural granulosa, and oocytes express mRNA for the GH receptor. The stimulatory effect of GH on bovine oocyte maturation is dependent on the cumulus cells and is not mediated by IGF-I.

The action of GH/IGF-I/IGFBP in osteoblasts and osteoclasts.

Bone remodelling is a cyclical phenomenon consisting of osteoclastic bone resorption followed by osteoblastic bone formation. Although recent evidence suggests that GH participates in bone remodelling, the exact mechanism remains unclear. The present series of in vitro studies aimed to clarify how GH affects bone formation and resorption. GH binding sites were found to be present in osteoblastic MC3T3-E1 cells. Bovine GH (bGH) increased DNA synthesis, stimulated alkaline phosphatase activity and enhanced both type I procollagen mRNA expression and collagen synthesis. GH also increased the expression of both IGF-I and IGF-binding protein-5 mRNA as well as the release of IGF-I from these cells. The addition of IGF-I or recombinant IGFBP-5 alone significantly increased ALP activity and type I procollagen mRNA expression. These findings indicate that GH acts directly on osteoblasts to stimulate bone formation and that IGF-I and IGFBP-5 are involved in GH-stimulated bone formation. GH also stimulated pit formation on dentine slices and osteoclast differentiation in stromal cell-containing mouse bone cell cultures, whereas it did not affect the bone-resorbing activity of isolated rabbit osteoclasts. The addition of IGF-I or rIGFBP-5 alone exhibited similar effects. These stimulatory effects of GH on pit formation and osteoclast differentiation were significantly blocked in the presence of neutralizing anti-IGF-I antibody. PCR products corresponding in size to the mouse GH receptor were detected in osteoclast precursor cells. GH stimulated osteoclast-like cell formation from these cells in the absence of stromal cells, and these osteoclast-like cells formed pits on dentine slices in the presence of MC3T3-G2/PA-6 stromal cells. These findings indicate that GH stimulates osteoclastic bone resorption through both its direct and indirect action on the maturation of osteoclast precursor cells and through its indirect activation of mature osteoclasts, possibly via stromal cells. In conclusion, GH stimulates osteoclastic bone resorption as well as osteoblastic bone formation in vitro, and locally produced IGF-I and/or IGFBP-5 are involved in the stimulation of bone remodelling by GH.

Effect of bovine GH and ovariectomy on mammary tissue sensitivity to IGF-I in prepubertal heifers

Sixteen prepubertal Holstein Friesian heifers were used to study the effect of long-term administration of bovine GH (bGH; 15 mg/day for 15 weeks) and ovariectomy (at 2.5 months of age) on GH and IGF-I receptors in mammary and liver parenchymal tissue. Heifers were slaughtered on the day after the last injection of bGH or excipient. Mammary and liver parenchymal tissue was collected for preparation of crude membranes for ligand-binding assays. Specific binding of [125I]IGF-I to mammary membranes increased linearly with increasing membrane protein concentration and was displaced by IGF-I, less effectively by IGF-II and least effectively by insulin. Linear Scatchard plots were obtained showing the presence of a single class of high-affinity binding sites for IGF-I in prepubertal mammary tissue. Specific binding of IGF-I was unaffected by bGH treatment but tended to be higher (P < 0.10) in membranes from ovariectomized heifers. Hepatic binding of GH and IGF-I was unaffected by bGH treatment and ovariectomy. However, specific binding of GH tended to be lower (P < 0.06) in liver tissue from bGH-treated intact heifers compared with control heifers. The present study confirms the presence of IGF-I receptors in prepubertal mammary tissue in agreement with the suggested involvement of IGF-I in the mechanism of action of GH on mammary glands in this period. The results, however, indicate that the stimulatory effect of GH on mammary growth is mediated via increased serum concentration of IGF-I and not by increased IGF-I binding to its mammary receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of growth hormone on steroidogenesis, insulin-like growth factor-I (IGF-I) and IGF-binding protein-1 production and DNA synthesis in cultured human luteinized granulosa cells.

Numerous clinical and experimental observations have suggested that GH is important in ovarian function. We have investigated the effect of GH alone and GH in combination with FSH on the secretion of oestradiol, progesterone, insulin-like growth factor-I (IGF-I) and IGF-binding protein-1 (IGFBP-1) and on [3H]thymidine incorporation in cultured human luteinized granulosa cells. Granulosa cells from patients undergoing treatment for in vitro fertilization were isolated and cultured for 2 days in culture medium with 10% serum. After this preincubation, the medium was removed and the cells were incubated with GH (1, 10 and 100 micrograms/l) with or without FSH in serum-free medium and in the presence of [3H]methylthymidine (2 microCi/ml). GH alone resulted in a significant dose-dependent increase of oestradiol (P < 0.05) and in IGFBP-1 (P < 0.002) in the medium. The release of IGF-I was undetectable and there was no increase in [3H]thymidine incorporation with GH alone. Neither GH nor FSH alone stimulated granulosa cell proliferation or progesterone release, while the combination induced increases (P < 0.001) in both. The stimulatory effect of GH on steroidogenesis, IGFBP-1 production and granulosa cell proliferation supports a putative role for GH in the regulation of ovarian function.

In vivo and in vitro effect of growth hormone on estradiol secretion by human granulosa cells.

GH therapy increases the ovarian response to gonadotropin stimulation in women presenting with ovaries that are relatively resistant to conventional gonadotropin therapy. As it is not completely certain whether GH modulates the actions of FSH on granulosa cells directly or via insulin-like growth factor-I (IGF-I) production, we studied its effect on steroid release by human granulosa cells obtained from subjects affected by unexplained or male factor infertility. In all subjects, superovulation for in vitro fertilization/embryo transfer was induced by treatment with gonadotropins or GH plus gonadotropins combined. The effects of the different in vivo treatments were evaluated in the conditioned medium obtained after the first 24 h of incubation; granulosa cells from patients treated with GH released higher amounts of estradiol and progesterone into the medium than did granulosa cells from patients treated with gonadotropins alone. When the release of steroid due to the in vivo treatment was exhausted, cells were subjected to increasing concentrations of GH in the presence or absence of 200 nmol anti-IGF Sm 1.2 monoclonal antibody (MoAb) or the antitype I receptor alpha IR3 MoAb. The results revealed that GH stimulates estradiol production in a dose-dependent fashion, and the presence of the MoAbs drastically reduces the GH effect. These data demonstrate that the established stimulatory effect of GH on ovarian function is dependent not only on the increased levels of circulating IGF-I, but also on a direct effect of GH on granulosa cells, which seems to be mediated at least in part by the autocrine action of IGF, particularly IGF-II. In fact, chromatographic analysis of medium conditioned by human granulosa cells revealed that these cells clearly produce IGF-II and IGF-binding proteins and only small amounts of IGF-I. Since GH appears to be able to increase the in vitro effect of both IGF-I and IGF-II, we can hypothesize a sensitization of the granulosa cells to the IGF-II produced by the cells themselves, which acts through the IGF-I receptor.

Growth hormone and insulin-like growth factor-I stimulate hormonal function and proliferation of thymic epithelial cells.

We have investigated the role of GH and insulin-like growth factor-I (IGF-I) in controlling the secretion of thymulin, a hormone produced by thymic epithelial cells (TEC). Thymulin plasma concentrations (mean +/- SD) were increased in 21 patients with acromegaly compared to those in 30 controls, as assessed by bioassay (4.24 +/- 0.97 vs. 2.67 +/- 0.87; P less than 0.001) and RIA (561 +/- 241 vs. 315 +/- 113 pg/L; P less than 0.01). Good correlations were observed between plasma levels of thymulin and IGF-I (P less than 0.001). In vitro experiments demonstrated that both recombinant human GH and IGF-I significantly increased thymulin production in culture supernatants of normal human TEC and a rat TEC line. In parallel, IGF-I also significantly stimulated the proliferation of human TEC, as measured by bromodeoxyuridine incorporation. Additionally, the stimulatory effect of GH on thymulin production was abrogated by both an anti-IGF-I antibody and an anti-IGF-I receptor antibody. These results support a role for GH and IGF-I in the control of thymic hormonal function in man and suggest that the effect of GH may be mediated by local secretion of IGF-I within the thymus.

The Stimulatory Effect of Growth Hormone, Prolactin, and Placental Lactogen on β-Cell Proliferation Is not Mediated by Insulin-Like Growth Factor-I

The effects of GH, PRL, and placental lactogen (PL) on the proliferation of pancreatic beta-cells in vitro were studied as well as the possible effect of insulin-like growth factor-I (IGF-I) in mediating this effect. Proliferating beta-cells were identified by staining with a monoclonal antibody to bromodeoxyuridine (BrdU) after cells were incubated for 1 h in the presence of 10 microM BrdU. By double staining with insulin antibodies it was found that 6.3% of the beta-cells had incorporated BrdU when cultured for 7 days in the presence of 1 microgram/ml human GH (hGH) compared to 0.6% when cultured in the absence of hGH. Similar results were obtained using rat GH. The half-maximal effect of hGH on beta-cell proliferation was observed at 10 ng/ml, and the maximal effect at 100 ng/ml. Islet cells cultured in the presence of PRL or PL caused a dose-dependent increase in beta-cell proliferation similar to that caused by hGH. GH, PRL, and PL had no effect on the proliferation of glucagon- or somatostatin-producing cells. The addition of 100 ng/ml IGF-I to either control or GH-stimulated islet cells did not affect the labeling index. When GH-stimulated proliferation of beta-cells was measured in the presence of neutralizing concentrations of a rabbit IGF-I antiserum, the percentage of beta-cells incorporating BrdU was unaffected. Using Northern blot analysis, no IGF-I transcripts could be detected in RNA from GH-stimulated islets, whereas IGF-I transcripts were readily detected in RNA isolated from rat liver tissue. These data suggest that the stimulatory effect of GH, PRL, and PL on beta-cell proliferation is not mediated by IGF-I, but, rather, is a direct mitogenic effect on the beta-cell.

Effects of human growth hormone on peripheral nerve regeneration

Systemic administration of human growth hormone (hGH) to intact or hypophysectomized rats was found to stimulate regeneration of the crush-lesioned sciatic nerve. The IGF-I levels of serum of the treated rats did not correlate with regeneration of the nerve but hGH treatment increased the IGF-I content of the nerve. The results suggest that a GH-mediated increase of IGF-I in the sciatic nerve could be involved in the stimulatory effect of GH on neurite outgrowth.

Effects of hypopituitarism and growth hormone replacement therapy on the production and utilization of glucose in childhood.

Glucose metabolism during fasting was investigated in 10 children aged 1.5 month-11.5 yr with deficiency of GH with or without other pituitary hormone deficiencies. After 10-16 h of fasting, mean plasma glucose was 56 +/- 4 (SEM) mg/dl, the result of decreased hepatic production of glucose (3.3 +/- 0.3 mg kg-1 min-1) insufficient to match glucose utilization (3.6 +/- 0.4 mg kg-1 min-1). The diminution of plasma glucose and of glucose production was similar whether ACTH deficiency was present (3.2 +/- mg kg-1 min-1) or not (3.5 +/- 0.6 mg kg-1 min-1). These results indicate that the lack of GH was the primary cause of hypoglycemia. Fasting plasma alanine (212 +/- 41 mumol/liter) and lactate (1222 +/- 136 mumol/liter), the main gluconeogenic substrates, were normal and did not correlate with the decrease of hepatic glucose release. Both plasma FFA (552 +/- 35 microM) and beta-hydroxybutyrate (654 +/- 158 microM) were in the low normal range, and neither correlated with the rate of glucose utilization. hGH replacement therapy resulted in a normalization of fasting plasma glucose concentration (78.5 +/- 6 mg/dl, P less than 0.005) and hepatic glucose production (6.1 +/- 1.2 mg kg-1 min-1). No significant changes occurred in the plasma concentrations of gluconeogenic or lipid substrates. These results, together with the known stimulatory effects of GH on carbohydrate-induced insulin secretion and storage of hepatic glycogen, suggest that the changes in glucose production in untreated and GH treated patients reflect the degree of hepatic glycogen replenishment.

Cerebral myelinogenesis in theSnell dwarf mouse: Stimulatory effects of GH and T4 restricted to the first 20 days of postnatal life

We attempted to define the critical time period during early postnatal life when GH and T4 are essential for myelination. We administered bGH and T4 to Snell dwarf mice during the first and second 20 days after birth. Positive results were obtained only when hormones were given during the first 20 days of postnatal life. We observed a distinct increase in brain weight, DNA content, CNPase activity and a remarkably increased level of spontaneous locomotion activity with a diurnal periodicity. Morphological observations of brain sections stained for myelin basic protein (MBP) correlated the biochemical findings. The later administration of hormones was ineffective. Our interpretation is that the administration of exogenous hormones led to increased myelinogenesis through their stimulatory effects on glial proliferation, as evidenced by the increase in cerebral DNA content.

Use of Antibodies to Modify the Effect of Growth Hormone on Sugar Transport in Rat Diaphragm Muscle*

GH stimulates sugar transport into diaphragm muscle of hypophysectomized rats, but this effect subsides in 2–3 h and a period of refractoriness follows in which the cells do not respond to further stimulation with the hormone. To determine the briefest period of in vitro GH-tissue interaction required to induce 1) the early stimulatory effect of GH on the transport of 3-O-methylglucose (30MG) and 2) the delayed refractory response, the GH-tissue interaction was interrupted at various times with antibodies against GH. Diaphragms isolated from hypophysectomized rats were incubated with rat GH (rGH), 0.4 μg/ml for 30 min at 0-2 C, to permit binding of the hormone to the cells in the absence of metabolism. Next, the muscles were warmed to 37 C for various times in the presence of rGH, then cooled again to 2 C and exposed for 1 h to either monkey serum or monkey anti-rGH antibodies (ArGH). The muscles were then washed in buffer and again warmed to 37 C for various times. Their ability to transport 30MG was ass...