Somatotroph Hyperplasia

309

114

The mitogenic effect of the hypothalamic peptides growth hormone-releasing factor (GRF) and somatostatin on cultured growth hormone (GH)-producing cells (somatotrophs) was studied. Using autoradiographic detection of [3H]thymidine uptake and immunocytochemical identification of GH-producing cells, we show that 5 nM GRF causes a 20-fold increase in the percentage of somatotrophs labeled with [3H]thymidine. The total number of somatotrophs in GRFtreated cultures was increased by 60%. Somatostatin had no measurable effect on the labeling index by itself, but it partly inhibited the GRF-induced increase in both the labeling index and the total number of cells. Forskolin caused an increase in both the percentage of somatotrophs with a [3H]thymidinelabeled nucleus and the somatotroph number similar to that caused by GRF. GH secretion as well as cellular GH content in the GRF-or forskolin-treated cells increased with culture time over the entire period, whereas secretion and content of GH gradually decreased in control or somatostatin-treated cultures during the entire culture period. These data suggest that GRF and somatostatin regulate the mitotic activity of GH-producing cells and that the effect of GRF is possibly mediated by cyclic AMP.The biosynthesis and secretion of growth hormone (GH) in the anterior pituitary gland is under complex hormonal regulation. The hypothalamic peptide growth hormone-releasing factor (GRF) stimulates both release (1-3) and synthesis (4, 5) of GH, as well as transcription of the GH gene (6, 7), whereas somatostatin depresses GH secretion (8). Patients with GRF-producing tumors (9-12) and transgenic mice expressing large amounts of GRF (13) have chronically increased plasma GRF with resulting high levels of plasma GH, pituitary enlargement, increased somatic growth, and acromegaly. This suggests but does not establish that GRF stimulates the growth ofpituitary somatotrophs, the cells that secrete GH. Not only might the effects ofGRF in these in vivo studies be indirect or require the interaction of other mitogenic substances, but also other products of the GRFproducing cells might be involved. We therefore chose to explore the effect of long-term GRF administration on the growth and function of cultured rat somatotrophs. The results show that GRF stimulates the mitotic activity in somatotrophs as measured by cell counts in pituitary cultures treated with [3H]thymidine and immunohistochemically stained for GH. The specificity of this response was indicated by the observation that somatostatin attenuates the growth-promoting effect of GRF, whereas prepro-GRF-(75-104) had no measurable influence. MATERIALS AND METHODSCell Culture. Rat anterior pituitary cells from male Sprague-Dawley rats (Holtzmann, Madison, WI) were prepared as described (14) and seeded in two-well slides, coated with an extracellular matrix from bovine pituitary endothelial cells. Cells were cultured in 1.5 ml of minimal essential medium containing D-valine instead of L-valine (GIBCO) and supplemented with 5 nM ...

Section: Resultsmentioning

confidence: 99%

Growth hormone-releasing factor stimulates proliferation of somatotrophs in vitro.

Billestrup¹,

Swanson²,

Vale³

1986

309

114

“…G rowth hormone-releasing hormone (GHRH), also known as growth hormone-releasing factor, was initially isolated from pancreatic tumors causing acromegaly (1,2), and hypothalamic human GHRH was shown to be identical to the one isolated from the pancreas tumor (3). Thereafter, the sequences of GHRHs were determined in various vertebrate species and in protochordates (4).…”

mentioning

confidence: 99%

Discovery of growth hormone-releasing hormones and receptors in nonmammalian vertebrates

Lee¹,

Siu²,

Tam³

et al. 2007

112

In mammals, growth hormone-releasing hormone (GHRH) is the most important neuroendocrine factor that stimulates the release of growth hormone (GH) from the anterior pituitary. In nonmammalian vertebrates, however, the previously named GHRH-like peptides were unable to demonstrate robust GH-releasing activities. In this article, we provide evidence that these GHRH-like peptides are homologues of mammalian PACAP-related peptides (PRP). Instead, GHRH peptides encoded in cDNAs isolated from goldfish, zebrafish, and African clawed frog were identified. Moreover, receptors specific for these GHRHs were characterized from goldfish and zebrafish. These GHRHs and GHRH receptors (GHRHRs) are phylogenetically and structurally more similar to their mammalian counterparts than the previously named GHRH-like peptides and GHRH-like receptors. Information regarding their chromosomal locations and organization of neighboring genes confirmed that they share the same origins as the mammalian genes. Functionally, the goldfish GHRH dose-dependently activates cAMP production in receptor-transfected CHO cells as well as GH release from goldfish pituitary cells. Tissue distribution studies showed that the goldfish GHRH is expressed almost exclusively in the brain, whereas the goldfish GHRH-R is actively expressed in brain and pituitary. Taken together, these results provide evidence for a previously uncharacterized GHRH-GHRH-R axis in nonmammalian vertebrates. Based on these data, a comprehensive evolutionary scheme for GHRH, PRP-PACAP, and PHI-VIP genes in relation to three rounds of genome duplication early on in vertebrate evolution is proposed. These GHRHs, also found in flounder, Fugu, medaka, stickleback, Tetraodon, and rainbow trout, provide research directions regarding the neuroendocrine control of growth in vertebrates. molecular evolution ͉ genome duplication ͉ pituitary adenylate cyclase-activating polypeptide

“…Many investigators have reported the presence of GH-releasing activity in human carcinoid tumors (13)(14)(15) and pancreatic islet cell tumors removed from patients with acromegaly (15)(16)(17). Recently, human pancreatic GRF (hpGRF) was isolated and structurally characterized from two pancreatic islet cell tumors in patients with acromegaly (9,18,19).…”

mentioning

confidence: 99%

“…In addition, the NH2-terminal 29 amino acids of hpGRF maintain full intrinsic activity and potency in vitro (18), and recently amino acids [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] tion was stirred on a rotary mixer for 1 hr at room temperature, then dialyzed in spectapor 3 membrane tubing (Spectrum Medical Industries, Los Angeles) against a 1-liter 10 mM phosphate buffer (pH 7.4) for 2 hr at room temperature with constant stirring. The dialyzed complexes were emulsified with complete Freund's adjuvant (GIBCO) and normal saline (1:1:1) in the presence of 10 mg of active charcoal (Fisher), using two glass syringes connected by a three-way stopcock until the emulsion was firm.…”

mentioning

confidence: 99%

Levels of human and rat hypothalamic growth hormone-releasing factor as determined by specific radioimmunoassay systems.

Audhya¹,

Manzione²,

Nakane³

et al. 1985

Polyclonal antibodies to synthetic human pancreatic growth hormone-releasing factor )NH2] and rat hypothalamic growth hormone-releasing factor [rhGRF(1-43)OHJ were produced in rabbits by injecting these weak immunogens, coupled to thyroglobulin and emulsified with complete Freund's adjuvant in the presence of activated charcoal, directly into the spleen. A subsequent booster in-jection by the conventional intramuscular route resulted in high-titer antibodies, which at a 1:20,000 dilution were used to develop highly sensitive and specific radioinmunoassays for these peptides. By using antibodies with an apparent K. of 3.3x 10-12 (human) and 7.7 x 10-11 (rat), the sensitivity of these assays in both human and rat was found to be <1 fmol. The antibody to hpGRF(1-44)NH2 is directed against the COOHterminal region of the molecule, as shown by its crossreactivity with various hpGRF analogues: 140% with hpGRF(30-44)NH2; 1%-2% with hpGRF(1-37)OH, hpGRF(140)OH, and hpGRF(1-40)NH2; and none with hpGRF(1-29)NH2. Serial dilutions of human and rat hypothalamic extracts demonstrated parallelism with the corresponding species-specific standard and 12,5-labeled tracer. There was no crossreactivity with other neuropeptides, gastrointestinal peptides, or hypothalamic extracts of other species. The hypothalamic content in fmol/mg (wet weight) of tissue was 3.6 ± 0.2 for the human and 11.1 ± 5.5 for the rat. Age-related changes in hypothalamic GRF content were present in rats, with a gradual increase from 2 to 16 weeks and a correlation between increasing body weight and GRF content. These radioimmunoassays winl serve as important tools for understanding the regulation of growth hormone secretion in both human and rat.Since 1959 (1), it has been known that the hypothalamus is involved in the control of growth hormone (GH) secretion. Experimental and clinical evidence has since indicated that the hypothalamus performs a dual function in the regulation of GH secretion from the anterior pituitary (2-4). Inhibition of GH release is accomplished by an inhibitory peptide, somatostatin (SRIF), which in 1972 was isolated from ovine hypothalami, purified, and characterized as a tetradecapeptide (5). In contrast, as suggested by physiological evidence (2-4) and GH-releasing activity in hypothalamic extracts (6-8), stimulation of GH release is accomplished by a stimulatory peptide, GH-releasing factor (GRF). Until 1982, howev-er, the isolation and characterization of GRF remained elusive. The difficulty in its characterization had been due to the minute quantities of the peptide in hypothalamic tissue, the large quantities of SRIF that interfere in the bioassay, and the fact that the methodology used for peptide sequencing and purification has only recently become available (9-12).The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. 2970Many investigators have reported the presenc...