William B. Wehrenberg

Molecular characterization of fibroblast growth factor: distribution and biological activities in various tissues.

Publisher Summary This chapter provides an overview of molecular characterization and the distribution and biological activities of fibroblast growth factor (FGF) in various tissues. FGF in the pituitary plays a nonmitogenic role in the maintenance of prolactin and thyrotropin responsiveness, while the same molecule in macrophages may promote wound healing and in the corpus luteum angiogenesis. It is based on the diverse biological activities of somatostatin in brain, hypothalamus, stomach, and pancreas and the wide distribution of numerous neuropeptides in both the central nervous system and the gastrointestinal tract. The concept is equally applicable to FGF and perhaps other growth factors that show a wide distribution in many tissues. The results presented in the chapter suggest that heretofore unidentified biologic activities may be related if not identical to acidic and basic FGFs. These would include ovarian growth factor, macrophage-derived growth factor, cartilage growth factor, tumor angiogenic factor, eye-derived growth factor, retina-derived growth factor, corpus luteum angiogenic peptide, follicular angiogenic factor, adrenal vascularizing factor, and endothelial cell growth factors.

Physiological roles of somatocrinin and somatostatin in the regulation of growth hormone secretion

Abstract Somatocrinin, a 44 amino acid peptide with potent growth hormone (GH) releasing activity in anesthetized rats, was tested in conscious freely-moving rats. When high doses of 1 to 10 μg were administered (iv) at random times between spontaneous GH pulses, the responses were inconsistent. When similar doses were tested under identical conditions but in rats pretreated with antibodies against somatostatin, all animals demonstrated a marked and immediate increase in plasma GH of 5 to 10 fold. Similarly, a 1 μg dose of somatocrinin was also ineffective in increasing plasma GH when administered to rats subjected to a 72 h fast, a paradigm known to enhance endogenous somatostatin secretion. However, plasma GH increased over 20 fold if rats were pretreated with antibodies against somatostatin. These results demonstrate the dynamic and opposite roles exerted by somatocrinin and somatostatin in regulating GH secretion.

Somatocrinin, growth hormone releasing factor, stimulates secretion of growth hormone in anesthetized rats.

The synthetic replicate of a 44 amino acid peptide isolated from a human pancreatic tumor which had caused acromegaly possesses high specific activity to release growth hormone (GH) in anesthetized male rats. The GH secretion induced by this peptide is dose-dependent from 50 ng to 1 μg, with plasma GH concentrations increasing more than 10-fold within 5 min of iv administration at the higher doses. Two enzymatic degradation products of the 44 residue peptide were also isolated and consist of the first 37 and 40 amino acids. All three peptides appear to possess similar potency, on a molar basis, invivo, contrary to invitro results. The specificity of these peptides on GH release was shown by their failure to alter plasma concentrations of prolactin (PRL), thyroid-stimulating hormone (TSH), luteinizing hormone (LH), follicle-stimulating hormone (FSH) and corticosterone. Based on these invivo results, the three peptides with serve as powerful tools with which to investigate the mechanisms of GH secretion.

characterization of A 40 residue peptide from a human pancreatic tumor with growth hormone releasing activity

Abstract Structural characterization of a 40 amino acid peptide with high intrinsic growth hormone releasing activity isolated from a human pancreatic tumor which had caused acromegaly was accomplished by gas phase sequence analyses of the intact peptide and its carboxy terminal cyanogen bromide digestion fragment. High pressure liquid chromatography of the native peptide and synthetic replicates showed that the molecule possessed a free acid rather than an amidated carboxy terminus. The structure of the peptide was established as: Tyr-Ala-Asp-Ala-Ile-Phe-Thr-Asn-Ser-Tyr-Arg-Lys- Val-Leu-Gly-Gln-Leu-Ser-Ala-Arg-Lys-Leu-Leu-Gln-Asp-Ile-Met-Ser-Arg-Gln-Gln-Gly- Glu-Ser-Asn-Gln-Glu-Arg-Gly-Ala-OH using 1.8 nmoles of material. The structural identity of this material with a previously characterized fragment of a larger growth hormone releasing peptide isolated from a different human tumor is discussed.

The role of glucocorticoids in the regulation of Growth Hormone secretion: mechanisms and clinical significance.

Glucocorticoids are well known to inhibit growth and GH secretion in humans and animals, yet in vitro these steroids stimulate GH synthesis and secretion. These opposite actions appear to be mediated at different sites. The inhibition involves modulation of hypothalamic somatostatin and the stimulation involves direct actions on the pituitary. Current evidence suggests that the predominant action in vivo is through the inhibitory influences of somatostatin.

A Physiological Role for Neuropeptide Y in Regulating the Estrogen/Progesterone Induced Luteinizing Hormone Surge in Ovariectomized Rats

To test the hypothesis that neuropeptide Y (NPY) is involved in the regulation of the estrogen/progesterone-induced luteinizing hormone (LH) surge in ovariectomized rats, we passively immunized animals against NPY by administering purified immunoglobulins raised against the peptide directly into the central nervous system. Ovariectomized rats were prepared with an intracerebroventricular (i.c.v.) guide cannula and an intravenous catheter prior to experimentation. On day 1 of the experiment the animals received a 5-microliters i.c.v. injection of a highly specific immunoglobulin against NPY (NPY-ab) and a 50-micrograms injection of estradiol benzoate. The antibody injection was repeated on days 2 and 3 of the experiment. On day 3, animals received a 2.5-mg injection of progesterone. Control animals were treated in exactly the same fashion except that a nonspecific control immunoglobulin was injected i.c.v. rather than the NPY-ab. As expected, the steroid-primed animals treated with the control antibodies exhibited large surges in LH secretion approximately 4 h following the progesterone injection. Concentrations rose from 4.2 +/- 1.0 to 27.9 +/- 9.9 ng/ml. In marked contrast, the NPY-ab-treated animals demonstrated no increase in LH concentrations. Baseline values were 3.1 +/- 0.3 ng/ml and remained unchanged (maximum concentrations were 3.8 +/- 1.9 ng/ml) following the progesterone injection. These results demonstrate that hypothalamic NPY plays a role in mediating the estradiol/progesterone-induced gonadotropin surge and suggests that this neuropeptide plays a physiological role in normal ovulatory surges of LH and FSH.

Growth hormone-releasing factor from ovine and caprine hypothalamus: isolation, sequence analysis and total synthesis.

Peptides with high intrinsic growth hormone releasing activity (growth hormone-releasing factor, GRF) were isolated from 2100 ovine and 2600 caprine (goat) hypothalami by means of acid extraction, immunoaffinity chromatography, gel filtration and reverse phase HPLC. Structural characterization of the 44 amino acid ovine peptide by gas-liquid phase sequencing and peptide mapping established its primary structure as Tyr-Ala-Asp-Ala-Ile-Phe-Thr-Asn-Ser -Tyr-Arg-Lys-Ile-Leu-Gly-Gln-Leu-Ser-Ala-Arg-Lys-Leu-Leu-Gln-Asp-Ile-Met -Asn -Arg-Gln-Gln-GLy-Glu-Arg-Asn-Gln-Glu-Gln-Gly-Ala-Lys-Val-Arg-Leu-NH2. Caprine GRF was found to possess the same sequence except for the replacement of the isoleucine residue in position 13 with valine and thus is identical to bovine GRF.

Synthesis and invitro bioactivity of C-terminal deleted analogs of human growth hormone-releasing factor

Abstract A series of C-terminal deleted analogs of human growth hormone-releasing factor (hGRF) with either an amidated or a free carboxylic acid C-terminus were synthesized by solid phase methodology. Their capacity to re;ease growth hormone was tested on rat anterior pituitary cells in monolayer culture. A gradual decrease of bioactivity down to 23% relative to hGRF was noted when the C-terminal amino acids were deleted to hGRF(1–34)OH. Further deletions, however, did not decrease the bioactivity because the potencies of the fragments, hGRF(1–31)NH 2 , (1–30)NH 2 and (1–29)NH 2 remained at about 50% of that of hGRF. Continual deletion of residues to hGRF(1–23)NH 2 , (1–22)NH 2 and (1–21)NH 2 still yielded bioactive fragments with full intrinsic activity despite very low potency. Only with the deletion down to hGRF(1–19)NH 2 did the bioactivity completely disappear. Thus, together with the data published in a previous paper (1), the minimal biologically active core of hGRF with full intrinsic activity comprises the fragment (3–21).

Invivo biological potency of rat and human growth hormone-releasing factor and fragments of human growth hormone-releasing factor

The biological potency of the synthetic replicates of three peptides isolated from a human pancreatic tumor with growth hormone releasing activity and rat hypothalamic growth hormone-releasing factor was evaluated in conscious freely-moving rats and anesthetized rats. All 4 peptides are equipotent on a molar basis in their ability to stimulate GH secretion. Studies with synthetic fragments of the human derived material indicated that the amino-terminal amino acid is required for activity. Deletion of as many as 13 amino acids from the carboxy-terminal failed to decrease GH-releasing activity; however, deletion of 16 amino acids resulted in a significant decrease and deletion of 20 amino acids resulted in complete loss of bioactivity.

Somatocrinin, the growth hormone releasing factor

Publisher Summary This chapter discusses the isolation of tumor-derived and hypothalamic GRFs, structure-activity relationships of synthetic replicates of GRFs, in vitro studies on the mechanism of action of GRF, and antagonism between GRF and somatostatin. Clinical interest in GRF extends over its use as a diagnostic tool and a treatment of hypothalamic dwarfism. GRF helps to promote anabolism in chronic debilitating diseases, as long as the dietary intake is adequate, and to promote the healing of wounds and bone fractures. The availability of GRF with its highly specific effect in stimulating GH secretion should permit investigations of the proposed role of GH in diabetic retinopathy. Structural analogs of GRF acting as competitive antagonists may be of major clinical significance in the treatment of accidents of juvenile diabetes.