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Biomedical subjects

N Ling

Publications and source records attributed to N Ling.

At least 271 records · Page 15Linked to original sources
PubMed1984

Isolation and characterization of caprine corticotropin-releasing factor.

The hypophysiotropic peptide, corticotropin-releasing factor (CRF) was isolated from caprine hypothalamic median eminence tissue by means of acid extraction, immunoaffinity chromatography, gel filtration and two steps of reverse-phase high-performance liquid chromatography (RPLC). Amino acid sequence determination using a gas-phase sequencer established the primary structure of the first 39 residues from the NH2-terminus. The nature of the COOH-terminal dipeptide was elucidated by Staphylococcus aureus V8 protease digestion of the native peptide, dansylation of the digest and comparative RPLC studies with the dansylated dipeptides Ile-Ala-NH2, Ile-Ala-OH, Ala-Ile-NH2 and Ala-Ile-OH. The complete structure of the peptide was established as: H-Ser-Gln-Glu-Pro-Ile-Ser-Leu-Asp-Leu-Thr-Phe-His-Leu-Leu-Arg-Glu- Val-Leu-Glu-Met-Thr-Lys-Ala-Asp-Gln-Leu-Ala-Gln-Gln-Ala-His-Ser-Asn- Arg-Lys-Leu-Leu-Asp-Ile-Ala-NH2, which is identical to that of ovine CRF.

Amino Acid Sequence↗
PubMed1984

Synthesis and in vitro bioactivity of human growth hormone-releasing factor analogs substituted at position-1.

Eight position-1 analogs of the 40-amino acid fragment and two position-1 analogs of human growth hormone-releasing factor were synthesized by solid phase methodology and their capacity to release growth hormone was determined using rat anterior pituitary cells in monolayer culture. Relative to hGRF(1-40)OH, which was arbitrarily assigned a potency value of 1, [D-Tyr1]hGRF(1-40)OH, [Phe1]hGRF(1-40)OH, [Trp1]hGRF(1-40)OH, [His1]hGRF(1-40)OH, [Ala1]hGRF(1-40)OH, [(-Ac)Tyr1]hGRF(1-40)OH, Arg0-hGRF(1-40)OH and Ala0-hGRF(1-40)OH have potencies of 0.022, 0.038, 0.003, 0.351, 0.010, 0.032, 0.002 and 0.007 respectively. Relative to hGRF(1-44)NH2 = 1, [(3-Me)His1]hGRF(1-44)NH2 and [(O-Me)Tyr1]hGRF(1-44)NH2 have potencies of 0.132 and 0.001 respectively. These results demonstrate the prerequisite for an aromatic residue at position-1 for potent biological activity and also suggest that the capacity for hydrogen bond formation with the first residue is required for full receptor-ligand interaction.

Amino Acids↗
PubMed1984

Effects of forskolin and cholera toxin on cyclic AMP release in a neurotensin-secreting rat C-cell line.

The effects of forskolin and cholera toxin on the regulation of cAMP release were studied in a neurotensin-secreting rat C-cell line. The interaction of these agents with norepinephrine, a potent neurotensin secretagogue, was also investigated. Forskolin stimulated cAMP release 10(2)-10(3) fold while it increased neurotensin release 2-3 fold. Cholera toxin caused a 10(2)-10(3) fold increase in cAMP release and had no effect on neurotensin release. We conclude that the 44-2 C-cells provide a new model for studying the regulation of the concomitant (via forskolin) or independent (via cholera toxin) secretion of cyclic AMP and/or neurotensin.

Adenylyl Cyclases↗
PubMed1984

Corticotropin-releasing factor in the amacrine cells of the chicken retina.

The distribution of ovine corticotropin-releasing factor (CRF)-like immunoreactivity (CRFI) in the chicken retina was investigated by means of immunohistochemistry. The observations from frozen sections show that CRFI is localized in the stratified amacrine cells of the fourth sublayer . Whole-mount preparations revealed that these amacrine cells are moderately concentrated in the inferior part of the retina.

Animals↗
PubMed1984

The distribution and projection of gamma-melanocyte stimulating hormone in the rat brain: an immunohistochemical analysis.

The distribution and projection of immunoreactive gamma-melanocyte-stimulating hormone (gamma-MSHI) in the rat brain was examined by indirect immunofluorescence using an antiserum against synthetic rat gamma-MSH. The present study confirmed the presence of gamma-MSHI neurons in the arcuate nucleus and further demonstrated that the n. commissuralis is a new gamma-MSHI neurons-containing site. We also found a gamma-MSHI fiber network in the hypothalamus, thalamus, amygdala, central gray matter of the midbrain and upper pons, and further demonstrated a much more extensive distribution of these fibers particularly in the medulla oblongata, an area previously thought not to contain gamma-MSHI structures. The present observation on the normal distribution of gamma-MSHI suggested the existence of two different systems: one is the arcuatofugal gamma-MSH system and the other n. commissuralis gamma-MSH system. Using experimental manipulations, we clearly established that gamma-MSHI fibers in the forebrain, diencephalon, midbrain and upper pons originate from gamma-MSHI neurons in the arcuate nucleus and those in the medulla oblongata from the n. commissuralis .

Animals↗
PubMed1984

Subcellular distribution of somatostatin-14, somatostatin-28 and somatostatin-28 (1-12) in rat brain cortex and comparisons of their respective binding sites in brain and pituitary.

Subcellular distribution and binding characteristics of the three endogenous peptides somatostatin-14 (SRIF-14), somatostatin-28 (SRIF-28) and somatostatin-28(1-12) (SRIF-28(1-12] derived from preprosomatostatin were investigated in the rat brain cortex. The three peptides are predominantly recovered from a crude mitochondrial pellet (P2), containing the pinched off nerve endings. Specific high affinity binding sites for 125I-N-Tyr-SRIF-14 and 125I-N-Tyr-SRIF-28 are present on pituitary and brain membranes. Under the same conditions, 125I-N-Tyr-SRIF-28(1-12) binding is undetectable. Moreover, SRIF-28(1-12) does not displace 125I-N-Tyr-SRIF-14 or 125I-N-Tyr-SRIF-28 binding. SRIF-28 is more potent than SRIF-14 to displace 125I-N-Tyr-SRIF-28 binding to brain and pituitary membranes, while both peptides are equipotent to displace 125I-N-Tyr-SRIF-14 binding. Finally, the regional distribution of 125I-N-Tyr-SRIF-14 and 125I-N-Tyr-SRIF-28 binding sites in the brain is identical. In conclusion, the present results are consistent with a neurotransmitter and neurohormonal role for SRIF-14 and SRIF-28. The function of SRIF-28(1-12) in brain remains to be elucidated. Additionally, a differential role for SRIF-14 and SRIF-28 both in adenohypophysis and brain cannot be ascertained at the present time.

Animals↗
PubMed1984

Pituitary response to growth hormone-releasing factor in rats with functional or anatomical lesions of the central nervous system that inhibit endogenous growth hormone secretion.

The pituitary growth hormone (GH) response to the growth hormone-releasing factor, hpGRF-44, was evaluated in male rats with various lesions of the central nervous system. These included an electrical lesion of the ventromedial hypothalamus, a chemical lesion of the arcuate nucleus induced by neonatal treatment with monosodium glutamate, a functional lesion of catecholamine synthesis with alpha-methyl-p-tyrosine or a functional lesion of catecholamine storage with reserpine. The first three lesions appear to partially inhibit normal somatostatin secretion since in every instance hpGRF-44 administration induced a significant increase in plasma GH concentrations. In contrast, reserpine blocked the GH response to hpGRF-44, presumably by stimulating somatostatin secretion. The pituitary GH response to hpGRF-44 in the above described models was enhanced by pretreatment of the rats with antibodies against somatostatin. The pituitary GH response to repeated injections of hpGRF-44 was also evaluated in rats with an anatomical lesion of the arcuate nucleus or a functional lesion of catecholamine synthesis. The maximum GH response did not vary over time to the repeated injections of hpGRF-44 in rats with lesions of the arcuate nucleus; however, interruption of catecholamine synthesis resulted in a significant decrease in the GH response to hpGRF-44 over time.

Animals↗
PubMed1984

Topographical and ontogenetic study of the neurons producing growth hormone-releasing factor in human hypothalamus.

Neurons producing growth hormone-releasing factor have been characterized and analyzed by immunohistochemistry in the hypothalami of human fetuses, neonates, infants and adults, using two antibodies against human pancreatic GRF (hpGRF). One of the antibodies recognized both the hpGRF(1-40)OH and hpGRF(1-44)NH2 in the mid portion (between the 28th and 39th amino acid), the other one specifically recognized the C-terminal end of hpGRF(1-44)NH2. These two antibodies stain a single neuronal system with cell bodies mainly located in the infundibular (arcuate) nucleus, and in the ventromedial and lateralis tuber nuclei. These neurons project to the median eminence where they give numerous endings in contact with portal vessels. These neurons are distinct from those containing LH-RH, somatostatin, CRF or pro-opiocortin. In fetuses, neurons immunoreactive with hpGRF antibodies are first detected at the 29th week. They display a neuroblastic aspect which persists after birth. Immunoreactive fibers are detectable in the median eminence after the 31st week. These results demonstrate that the infundibular nucleus plays a major role in control of GH secretion in man and that secretion of GRF appears late during fetal life; this suggests that the first stages of differentiation and development of GH producing cells in the human fetus do not depend on hypothalamic GRF secretion.

Adult↗
PubMed1984

Ontogeny of the response to growth hormone-releasing factor.

Primary cell cultures were prepared from fetal, neonatal and adult rat pituitaries and evaluated for their ability to secrete growth hormone (GH) in response to growth hormone-releasing factor (GRF). Pituitary cells prepared from fetuses at days 19 and 21 of gestation, neonatal animals at the day of birth (day 0) or the following day (day 1) and peripubertal male rats showed full dose response curves to GRF with maximal GH release when stimulated with 1 X 10(-10) M rat GRF. At this concentration of GRF, the amount of GH released was not different from that elicited by activation of adenylate cyclase with 1 X 10(-5) M forskolin. In contradistinction, a preparation of cells from fetuses at day 18 of gestation did not show the same release of GH when challenged with 1 X 10(-10) M GRF and forskolin (0.057 +/- 0.001, compared to 0.076 +/- 0.003 micrograms/10(5) cells per 4.5 h), although the cells clearly responded to both secretagogues (basal levels of GH, 0.029 +/- 0.002 micrograms/10(5) cells per 4.5 h). While cells prepared from fetuses at day 21 of gestation or from animals after birth released 5-10% of their total cellular GH content, those prepared from 18- and 19-day fetuses released as much as 40% of their total GH suggesting there is a maturation of intracellular GH processing that occurs late in gestation. The results show that, in late pregnancy, the rat fetal pituitary is highly responsive to growth hormone-releasing factor and suggest that this peptide participates in regulating GH levels during the perinatal period.

Aging↗
PubMed1984

Distribution of six neuropeptides in the nucleus tractus solitarii of the rat: an immunohistochemical analysis.

Distribution of substance P-, [Leu]enkephalin-, cholecystokinin-8-, neurotensin-, avian pancreatic polypeptide- and gamma-melanocyte stimulating hormone-like immunoreactive structures were investigated in the nucleus tractus solitarii of the rat by means of the indirect immunofluorescence method. The density of the immunoreactive structures varied markedly according to neuropeptides or subnuclei, with the medial and commissural nuclei containing the highest density. This suggests that the peptides examined play a role in cardiovascular function. However, as seen in the substance P- and [Leu]enkephalin-like immunoreactive structures, these peptides were widely distributed in the nucleus tractus solitarii in addition to the commissural and medial nuclei; a high density of immunoreactive fibers in the ventral, dorsolateral and intermediate subnuclei. In addition to the immunoreactive fiber plexus, a group of immunoreactive cells was also identified in the subnuclei mentioned above. These findings strongly suggest that substance P- and [Leu]enkephalin-like immunoreactive structures are involved not only in cardiovascular function but also in other functions such as respiration, at least in the rat. Finally, the present study demonstrated that the area postrema, particularly its lateral portion, contains various neuropeptide-like structures, both neurons and fibers, substance P-, [Leu]enkephalin-, cholecystokinin-8- and neurotensin-like immunoreactive neurons and fibers, and avian pancreatic polypeptide- and gamma-melanocyte stimulating hormone-like immunoreactive fibers.

Animals↗
PubMed1984

Isolation, primary structure, and synthesis of human hypothalamic somatocrinin: growth hormone-releasing factor.

The hypophysiotropic peptide, growth hormone-releasing factor (GRF), was isolated from human hypothalamic-hypophysial tissues by means of acid extraction, immunoaffinity chromatography, gel filtration, and two steps of reverse-phase high-performance liquid chromatography. Amino acid sequence determination using a gas-phase sequencer and reverse-phase liquid chromatography of the native peptide and its synthetic replicates showed its primary structure to be as follows: H-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-Arg-Ala-Arg-Leu-NH2, which is identical to that of the GRF recently isolated and characterized from a human pancreatic tumor that had caused acromegaly. Human hypothalamic GRF shows major homologies (93%, 89%, and 86%, respectively) when its primary structure is compared to that of the hypothalamic GRF from the porcine, bovine, caprine, and ovine species.

Amino Acid Sequence↗
PubMed1984

Isolation and partial molecular characterization of pituitary fibroblast growth factor.

Fibroblast growth factor (FGF) has been purified to homogeneity from bovine pituitaries by two methods. Starting material for both methods was an FGF preparation partially purified as described by Gospodarowicz [Gospodarowicz, D. (1975) J. Biol. Chem. 250, 2515-2520]. Purification procedure I involved cation-exchange and reversed-phase HPLC, while procedure II employed gel filtration and ion-exchange chromatography. Isolation was monitored by testing column fractions for their capacity to stimulate the proliferation of vascular endothelial cells in vitro. The growth factor has an approximate molecular weight of 16,000. Its amino-terminal sequence was determined as Pro-Ala-Leu-Pro-Glu-Asp-Gly-Gly-Ser-Gly-Ala-Phe-Pro-Pro-Gly. Sequence and amino acid composition indicate that the structure of pituitary FGF is different from that of other known growth factors. Pituitary FGF, as isolated under nonacidic conditions (procedure II), has high potency and intrinsic activity to stimulate adult bovine aortic endothelial cells (half-maximal proliferation at 2 pM). Acidic conditions as in procedure I, however, lead to about 90% loss of potency while the intrinsic activity remains intact (identical maximal stimulation values). By all other criteria (molecular weight, amino acid composition, amino-terminal sequence), the two preparations are indistinguishable. Antibodies were raised in rabbits against a synthetic peptide representing the first nine residues of the amino-terminal sequence of the pituitary FGF. The polyclonal antibodies recognize the synthetic peptide and the purified growth factor on an equimolar basis and are capable of inhibiting mitogenic activity in vitro. This report describes a partial chemical characterization of a pituitary FGF and demonstrates rigorously that the characterized protein possesses the mitogenic activity commonly referred to as "basic pituitary FGF."

Amino Acid Sequence↗
PubMed1984

Pituitary growth hormone response in rats during a 24-hour infusion of growth hormone-releasing factor.

The pituitary GH response during a 24-h iv infusion of GH-releasing factor (hpGRF-44; 15 micrograms/h) and to a subsequent bolus injection of hpGRF-44 (2 micrograms) was studied in conscious, freely moving male rats pretreated with antiserum against somatostatin. Within 2 h of the initiation of the hpGRF-44 infusion, plasma GH concentrations rose from 169 +/- 16 to 2465 +/- 307 (+/- SE) ng/ml. By 6 h, plasma GH concentrations began to fall. They decreased slowly and reached a nadir of 490 +/- 107 ng/ml by 12 h. Rats infused for 24 h with hpGRF-44 failed to respond to a 2-micrograms bolus injection (iv) of hpGRF-44, whereas rats infused for 24 h with saline responded with a normal increase in plasma GH. The pituitary GH content of rats treated with saline was significantly greater than that of rats treated with hpGRF-44. These results demonstrate that the capacity of the pituitary to respond to GRF can be exhausted after the chronic administration of hpGRF-44 and that this lack of response appears to be due, in part, to a depletion of pituitary stores of GH.

Animals↗
PubMed1984

Multiple stimulation of the adenohypophysis by combinations of hypothalamic releasing factors.

We have investigated the in vitro and in vivo interactions of the four hypothalamic releasing factors, LHRH, corticotropin-releasing factor, TRH, and GH-releasing factor on anterior pituitary hormone secretions, using a 2 X 2 X 2 X 2 factorial experimental design. This experimental design allows for the evaluation of both the main treatment effects of the hypothalamic releasing factors as well as all of the possible interactions between them. Significant main treatment effects were: LHRH on LH and FSH, corticotropin-releasing factor on ACTH and beta-endorphin, TRH on TSH, and GH-releasing factor on GH. These results confirm the specificity of the four releasing factors on their respective target cells. There were no significant interactions between any of the releasing factors on anterior pituitary hormone secretions. These results suggest that the changes in pituitary secretion that are observed under physiological conditions are not due to interactions between the hypothalamic releasing factors at the level of the pituitary, but rather to other secondary interactions that modify pituitary activation or response. These results also indicate that the clinical pituitary reserve tests can be expanded to include all four hypothalamic releasing factors, since any lack of response will reflect a specific pituitary defect and not a failure to respond owing to interaction of the secretagogues administered.

Adrenocorticotropic Hormone↗
PubMed1984

Growth hormone (GH)-releasing factor does not regulate GH release or GH mRNA levels in GH3 cells.

Previous studies have shown that GH-releasing factor (GRF) regulates both GH production and GH mRNA levels in primary cultures of rat pituitary cells. Investigations were carried out to ascertain the ability of GRF to regulate GH production or mRNA levels in a clonal strain of rat pituitary tumor (GH3) cells. Incubation of the cells with GRF at 1-1000 nM for 4 h to 10 days did not result in a stimulation of GH or PRL production, nor did it affect the cytoplasmic levels of the corresponding mRNAs. The lack of response to GRF was not affected by dexamethasone, T3, or serum. We conclude that GH3 cells do not provide a useful model system for studies of the mechanism(s) of action of GRF on either GH release or GH gene expression.

Animals↗
PubMed1984

The interrelationship of growth hormone (GH)-releasing factor and somatostatin in generation of the ultradian rhythm of GH secretion.

To further delineate the relationship between GH-releasing factor (GRF) and somatostatin (SRIF) in generation of the ultradian rhythm of GH secretion, we used two GRF peptides, human pancreas (hp) GRF-44 and rat hypothalamic (rh) GRF, and studied their interaction with SRIF by passive immunization with a specific antiserum (AS) to SRIF. Freely moving, chronically cannulated male rats were given 10 micrograms of either hpGRF-44 or rhGRF, iv, during peak (1100 h) and trough (1300 h) periods of the GH rhythm. Six-hour plasma GH profiles were obtained after pretreatment with either SRIF AS or normal sheep serum (NSS) as a control. In NSS-treated rats, the plasma GH responses to both hpGRF-44 and rhGRF were significantly greater when the peptides were administered during peak than during trough periods. Immunoneutralization with SRIF AS eliminated these differences and permitted marked GH release in response to both peptides at 1300 h. In addition, SRIF AS augmented the GRF-induced GH response at 1100 h compared with that in NSS controls. The rhGRF peptide caused significantly more GH release than hpGRF under both conditions. These results demonstrate that 1) the GH-releasing abilities of the GRF peptides vary markedly according to the time of injection; 2) the weak GRF-induced GH response observed during trough periods of the GH rhythm is due to antagonization by endogenous circulating SRIF; and 3) the rat-derived GRF may be a more potent GH secretagogue than the human-derived peptide in the rat. The findings reported here together with the available evidence provide support for the hypothesis that GRF and SRIF are secreted tonically from the hypothalamus into the hypophyseal portal blood, and that superimposed upon this steady state release is an additional 3- to 4-h rhythmic surge of each peptide, providing for integration of the ultradian rhythm of GH secretion, as observed in peripheral blood.

Animals↗
PubMed1984

Age-related changes in plasma growth hormone response to growth hormone-releasing factor in man.

The response of plasma growth hormone to synthetic growth hormone-releasing factor (hpGRF-44) administered intravenously was examined in normal men of various ages ranging from 20 to 75 years. Most of the subjects who were over forty years old had either no or much lower response of plasma growth hormone to hpGRF-44. In contrast plasma growth hormone increased markedly after hpGRF-44 injection in all men in their twenties and thirties. The mean peak level of plasma GH following hpGRF-44 administration was 29.6 +/- 20.4 (SD) ng/ml in men in their twenties, 30.2 +/- 26.5 ng/ml in their thirties, 9.7 +/- 5.2 ng/ml in their forties, 10.9 +/- 5.4 ng/ml in their fifties, 8.4 +/- 4.8 ng/ml in their sixties and 8.1 +/- 7.5 ng/ml in their seventies. These results suggest that somatotroph cells become less sensitive to growth hormone-releasing factor with aging.

Adult↗