Growth hormone inhibits growth hormone secretion from the rainbow trout pituitary in vitro

Growth hormone (GH) secretion in salmonids and other fish is under the control of a number of hypothalamic factors, but negative feed-back regulation by circulating hormones can also be of importance for the regulation of GH secretion. Mammalian studies show that GH has a negative feed-back effect on its own secretion. In order to elucidate if GH levels present a direct ultra-short negative feedback loop at the pituitary level GH secretion was studied in intact pituitaries from 50 g fish in an in vitro perifusion system. Following an initial equilibrium period pituitaries were exposed to five increasing concentrations (1-1,000 ng ml(-1)) of ovine GH (oGH) in 20-min steps, before being returned to a GH-free perifusion. Ovine GH caused a significant dose-dependent inhibition of GH secretion and it is concluded that GH can exert a direct negative feedback control on GH secretion at the pituitary level.     

Cholecystokinin octapeptide: Vesicular localization and calcium dependent release from rat brain in vitro

Sub-cellular fractionation tissue from rat hypothalamus and cerebral cortex in sucrose gradients indicated a concentration of cholecystokinin-like peptides in synaptosomal fractions. Lysis of synaptosomes yielded a vesicle rich fraction which was further enriched in cholecystokinin-like peptides, particularly the octapeptide (CCK-8). In vitro release experiments carried out using rat cerebral cortex tissue slices showed a calcium dependent release of cholecystokinin (primarily as CCK-8). The demonstration of a vesicular localization and calcium evoked release of cholecystokinin is consistent with a role for cholecystokinin as a neurotransmitter/neuromodulator in the CNS.     

Cholecystokinin octapeptide purified from brains of Australian marsupials

Cholecystokinin octapeptides (CCK8s) have been purified from methanol extracts of two brains from each of two Australian marsupials, Tammar Wallaby and Eastern Quoll, containing 3 nmol and 2 nmol of the peptides, respectively. Immunoreactive CCK was concentrated on QMA SepPak cartridges and purified by two successive HPLC steps on Nova C18 radial-pak cartridges. The sequence of each of the peptides is identical with that previously reported for Old World mammals (DYMGWMDF). This is in contrast to the previously reported sequence for CCK8 from the South American hystricomorphs, guinea pig and chinchilla, which differs in a substitution of valine for methionine in position 3 from the NH2-terminus. Although evolutionary history suggests that marsupials migrated from South America into Australia before the two continents separated, this peptide resembles that found in Old World mammals rather than that of South American hystricomorphs. Such molecular data are useful in assessing phylogenetic relationships among taxa.     

Effects of TRH and somatostatin on releases of prolactin and growth hormone in vitro by the pituitary of Poecilia latipinna

Summary Pituitary glands from a teleost fish were incubated in the presence of the synthetic hypophysiotropic peptides, thyrotrophin-releasing hormone and somatostatin, in two media of different osmotic pressure.The effects on prolactin and growth hormone cells were detected by electron-microscopic morphometry with the aid of an image analyser. Thyrotrophin-releasing hormone caused changes in prolactin cell ultrastructure consistent with stimulated hormone release and, in the low osmotic pressure medium, appeared to increase synthetic activity. There was no effect on growth hormone cells. After somatostatin treatment, both synthesis and release in prolactin cells appeared to be inhibited, and there was an obvious inhibition of synthesis and release in growth hormone cells. The response of both cell types to somatostatin did not appear to be dependent on the osmotic pressure of the medium.     

Galanin stimulates rat pituitary growth hormone secretion in vitro

The effect of galanin on growth hormone (GH) secretion was investigated in monolayer cultures of rat anterior pituitary cells. Galanin caused a gradual increase in GH concentrations into the culture medium that was maximal at 90 minutes and sustained after 180 minutes. The ED50 for galanin-stimulated GH secretion was approximately 200 nM compared to an ED50 for rat GH-releasing factor (rGRF)-stimulated GH secretion of 10pM. Galanin and rGRF were additive in increasing GH release into the incubation medium. These data indicate that porcine-derived galanin has a direct effect on pituitary GH secretion in vitro.     

Luteinizing hormone secretion from the quail pituitary in vitro

An enzymatically dispersed pituitary preparation from Japanese quail (Coturnix coturnix) was used to study the dynamics of gonadotropin release. After an 18-h incubation, the cells were challenged with different luteinizing hormone-releasing hormones (LHRH) for 90 min. Using pituitary cells from mature males, mammalian and chicken LHRH I (Gln8-LHRH) had approximately equal luteinizing hormone (LH)-releasing activity whereas chicken LHRH II (His5, Trp7, Tyr8-LHRH) was 8-9 times more potent. The LHRH agonist (Trp6, Pro9-NEt-LHRH) had 15 times greater potency than chicken LHRH I. Pre-incubation with an LHRH antagonist (D-Phe2, D-Trp6-LHRH) significantly suppressed LH release. Acid extracts of median eminence released LH from pituitary cells, extracts from short-day and long-day males had equal activity, while tissue extracts from castrated males had significantly greater LH-releasing activity. Pituitary cells from sexually immature males released LH in response to chicken LHRH I in a similar profile to cells from mature males. These data indicate that the quail LHRH receptor in the male recognizes several different molecular species of LHRH and the response to LHRH is comparable between short- and long-day males. Pituitary cells from ovulating females were variably sensitive to LHRH peptides, possibly due to changes in pituitary sensitivity during the ovulatory cycle. Pituitary cells from immature females did not release LH in response to chicken LHRH I. However, pituitary cells from immature females photostimulated for 1 wk displayed a response to chicken LHRH I and II similar to that of pituitary cells from males.(ABSTRACT TRUNCATED AT 250 WORDS)     

In vivo and in vitro effects of cholecystokinin octapeptide on the release of growth hormone in rats

The effect of cholecystokinin octapeptide (CCK-8) on the release of growth hormone (GH) in rats was studied in vivo and in vitro. Intravenous injection of 5 micrograms/100 g BW of CCK-8 resulted in significant increase in the plasma GH level after 10 and 20 min. CCK-8 at concentrations of 10(-11)M to 10(-7)M also caused dose-dependent stimulation of GH release from dispersed cells of rat anterior pituitary. On the other hand, somatostatin (SRIF) inhibited GH release from dispersed cells of rat anterior pituitary in a dose-related manner at concentrations of 10(-7)M to 10(-9)M. Release of GH from the cells was increased by addition of K+ at high concentration (50 mM) in a Ca++-dependent manner. Addition of 10(-3)M verapamil to the incubation medium inhibited CCK-8-induced GH release from the cells. Addition of SRIF (10(-7)M) to the incubation medium inhibited GH release from the cells induced by CCK-8 or high K+ (50 mM). These results indicate that CCK-8 acts directly on the anterior pituitary cells to stimulate GH release and that calcium ion is involved in the mechanism of this effect.     

Myelin basic protein: a substance that releases immunoreactive growth hormone in vitro.

A protein has been isolated from ovine hypothalamus on the basis of its ability to stimulate release of growth hormone by $\text{in}$$\text{vitro}$ cultures of dispersed pituitary cells. This protein has been identified as being myelin basic protein. With no similar biological activity $\text{in}$$\text{vivo}$, myelin basic protein is thus to be recognized as a potentially interfering substance in any search for the physiological growth hormone releasing factor using $\text{in}$$\text{vitro}$ assay systems.     

八肽胆囊收缩素对大鼠颈动脉窦压力感受器反射的抑制作用

在36只隔离灌流颈动脉窦区的麻醉大鼠上,观察了八肽胆囊收缩素(cholecystokinin octapepide,CCK-8)对颈动脉窦压力感受器反射的影响。其结果如下：(1)以CCK-8(0．1、0．5、1．0μmol／L)隔离灌流颈动脉窦区时,压力感受器机能曲线向右上方移位,曲线最大斜率(peak slope,PS)减小,反射性血压下降幅度(reflex decrease,RD)减少,阈压(threshold pressure,TP)和饱和压(saturation pressure,SP)均增高。其中RD、PS和TP呈明显的剂量依赖性;(2)用CCK-8的非特异性受体拮抗剂丙谷胺(100μmol／L)预处理后,能明显减弱CCK-8(0．50mol/L)对压力感受器反射的抑制;(3)预先灌流一氧化氮合酶(nitric oxide synthase,NOS)阻断剂(L-NAME,100μmol／L),不能阻断CCK-8(0．5μmol/L)对压力感受器反射的影响;(4)用Ca^2 通道激动剂Bay K 8644(500nmol／L)预处理后,也能明显减弱CCK-8(0．5μmol／L)对压力感受器反射的抑制作用。以上结果提示,CCK-8是通过作用于颈动脉窦压力感受器神经元末梢上的受体而起到抑制作用的,其机制可能为抑制了牵张敏感性通道,致使Ca^2 离子内流减少,而与内皮细胞释放NO无关。     

Cholecystokinin octapeptide immunoreactivity in the nucleus tractus solitarius of the cat

The nucleus tractus solitarius possessed distinct patterns of cholecystokinin immunoreactive fibers and cell bodies within its various subdivisions. The commissural, medial, intermediate, parvocellular, dorsolateral and interstitial subdivisions contained relatively dense amounts of CCK immunolabelled fibers. In contrast, CCK immunoreactivity within the ventrolateral subdivision consisted of a few scattered fibers and small neurons. The commissural, intermediate, medial, dorsolateral and parvocellular subdivisions contained CCK immunoreactive neurons following colchicine treatment. The presence of CCK in the NTS suggest that it may be involved as a neuromodulator and/or neurotransmitter in circuitry that mediate cardiovascular, respiratory, gastrointestinal and taste functions.     

Cholecystokinin octapeptide decreases intake of solid food in man

Cholecystokinin octapeptide (CCK-OP) was reported to decrease the intake of liquid food in lean and in obese man. This study investigated the effect of CCK-OP on the consumption of real life food, i.e., of standardized sandwiches. Sixteen young non-obese females and males participated, after an overnight fast, each in two experiments. After a basal 30 min, saline or CCK-OP, 1.5 or 3.0 Ivy Dog Units/kg body weight/15 min, was infused in random double blind fashion, while sandwiches were placed in front of the subjects. For the next three 15-min periods, the subjects were instructed to eat as much as they liked. In the first 15 min after 3.0 as well as 1.5 U CCK-OP/kg/15 min significantly fewer sandwiches (50 and 17 percent) were eaten than after saline (p less than 0.01 and p less than 0.05) and less hunger was reported (p less than 0.02 and p less than 0.05). Self-reported activation decreased only with 3.0 U CCK-OP (p less than 0.005). Reports of well-bring , electroencephalogram, heart rate, and respiration were not altered. The results support the notion that CCK is involved in the regulation of food intake.     

Rat milk stimulates pituitary growth hormone secretion of neonatal pituitaries in vitro

Aqueous extracts of rat milk stimulated growth hormone (GH) secretion from superfused pituitaries of two-day old rats. The GH stimulatory effect of milk increased with the time elapsed postpartum; growth hormone releasing hormone and thyrotropin releasing hormone seem to be the major milk borne GH releasing factors. These results indicate that milk intake may play a role in maintaining the high plasma GH levels observed in the neonatal period.     

Cholecystokinin octapeptide induces both proliferation and apoptosis in the rat pancreas

Cholecystokinin-8 (CCK-8) causes exocrine pancreatic hypertrophy and hyperplasia. High doses of the CCK analogue cerulein causes necrosis and an inflammatory response in the pancreas. We have studied the pancreatic growth response in rats after administration of CCK-8 for 3 days, given either intermittently (20-80 microg/kg) twice a day, or continuously (2.4-48 microg/kg per 24 h). Plasma CCK-8 levels, pancreatic wet weight, water, protein and DNA contents and the pancreatic caspase-3 activity were measured. Cell proliferation was visualized by [3H]thymidine incorporation and apoptosis by TUNEL reaction. Continuous administration of CCK-8 dose-dependently increased the plasma CCK levels, the pancreatic wet weight, protein and DNA contents as well as thymidine labeling index, apoptotic index and caspase-3 activity. Intermittent injections of CCK-8 caused transient raises in plasma CCK, increased apoptotic index and caspase-3 activity, a dose-dependent increase in thymidine labeling but caused a dose-dependent reduction of pancreatic wet weight, protein, and DNA contents. It is concluded that CCK-8 causes both increased proliferation and apoptosis in the pancreas. In case of continuous administration of CCK-8, the proliferation outweighs the apoptosis causing hyperplasia but in the case of intermittent administration the opposite effect is seen.     

Cholecystokinin octapeptide, proglumide, and passive avoidance in rats

Rats were conditioned to avoid a darkened chamber using electric footshock (0.25 mA for 2 sec). Cholecystokinin octapeptide (CCK-8), a CCK-8 antagonist proglumide, or 0.9% NaCl solution was injected immediately following the footshock to study the effect upon passive avoidance behavior. The passive avoidance behavior was observed one day following the conditioning footshock and treatment. CCK-8 produced a reduction of the passive avoidance latency of rats at doses ranging from 30 micrograms/kg to 500 micrograms/kg. Proglumide (5 mg/kg) was able to block the CCK-8 effect on rat passive avoidance conditioning. Proglumide by itself at a dose of 2 mg/kg decreased the latency to enter the darkened chamber. Endogenous CCK-8 activity may be involved in passive avoidance conditioning in rats.     

Identification and purification of factor B-GHRH from hypothalami which releases growth hormone

Exploratory purifications and assays of fractions for release of growth hormone (GH) revealed two separable entities each of which unambiguously released GH by radioimmunoassay. They are provisionally designated factor A-GHRH and factor B-GHRH until they are chemically and biologically characterized. After initial steps of isolation from porcine hypothalami, factor B-GHRH was extensively purified by stepwise chromatography using Bio-Gel P-2, Sephadex LH-20, Sephadex G-25 with a partition system of acetic acid-butanol-pyridine, DEAE-Sephadex A-25, and Bio-Gel CM-2. Assays showed that certain fractions were active, $\text{in vitro}$, at levels of $\text{ca}$. 15 μg. Factor B-GHRH is inhibited by somatostatin.     

Cholecystokinin antagonist,proglumide, stimulates growth hormone release in the rat

Previous studies have revealed a stimulatory action of cholecystokinin on growth hormone release in the rat. To evaluate the physiologic significance of these effects we employed the cholecystokinin antagonist, proglumide and injected it intravenously and intraventricularly (third cerebral ventricle, 3V) to determine its actions on growth hormone. The experiments were performed in conscious, freely moving rats with indwelling cannulae in the 3V and/or external jugular vein. Intraventricular injection of 2 or 10 □g of proglumide significantly elevated plasma growth hormone concentrations in intact and castrated male rats and in ovariectomized females. Intravenous injections of 10 or 100 □g of proglumide were also effective in elevating growth hormone in a dose-related manner. Surprisingly, the response to the lower dose given intraventricularly was somewhat greater than that of the higher dose. We speculate that these stimulatory effects of proglumide given intraventricularly are due to the agonist action of proglumide at these doses since action of cholecystokinin itself is to increase plasma growth hormone following its intraventricular injection. The studies therefore do not establish a physiologically significant growth hormone-releasing action of brain cholecystokinin but provide more evidence that activation of cholecystokinin receptors in the brain can induce a stimulation of growth hormone release either by activation of the release of growth hormone-releasing hormone or by inhibition of the release of somatostatin or by a combination of these two actions.     

Characterization of human growth hormone from acromegalic pituitary tumors

Human growth hormone (HGH) was extracted from acromegalic pituitary tumors at pH 10.5 and precipitated with ammonium sulfate at 20-40% saturation. It was purified on a Sephadex G-100 column to yield monomeric HGH. The tumor-HGH was indistinguishable from the authentic one in polyacrylamide gel electrophoresis at pH 8.3 or in the presence of sodium dodecyl sulfate, high-performance liquid chromatography, radioimmunoassay, peptide map, amino acid composition and N-terminal partial amino acid sequence. The tumor-HGH is active in the tibia assay and bodyweight gain test in hypophysectomized rats with comparable potency to that of the authentic sample.     

Synthesis and secretion of phosphorylated growth hormone by rat pituitary glands in vitro

Rat anterior pituitary glands were incubated in buffered medium, pH 7.4, containing 32Pi. After incubation the tissue and medium were separated and a post-mitochondrial supernate (PMS) of the tissue homogenate was prepared. Gel filtration of the PMS and medium resulted in a radioactive peak which coincided with the elution volume of authentic rat growth hormone (rGH). Polyacrylamide gel electrophoresis of the radioactive peak under denaturing condition resulted in a protein-staining band having the same mobility as authentic rGH. Autoradiography of the gels revealed radioactivity precisely at the position of growth hormone as well as elsewhere. The specific radioactivity of the PMS [32P]GH was estimated to be 5 to 10 times greater than that of tissue [32P]GH. These results indicate that phosphorylated GH is synthesized and secreted by pituitary glands in vitro.     

Limited effects of placental and pituitary growth hormone on cytokine expression in vitro

The hypothesis that growth hormone (GH) can affect immune responses in man has been evaluated by monitoring cytokine expression in cultures from peripheral blood mononuclear cells, by enzyme-linked immunosorbent assay (ELISA) and ribonuclease protection assay, and in tonsillar cells by ELISA. In addition to pituitary GH (GH-N), the placental form (GH-V), differing from pituitary GH by 13 amino acids has also been tested. Only few effects reached statistical significance and were in no case greater than 15%. Pituitary GH slightly reduced IL-5 production and stimulated IFN-gamma production. The latter effect was also observed with prolactin and could thus be induced through the prolactin receptor. It is proposed that GH has no strong effects on the parameters investigated, possibly as a result of redundancy in the cytokine network. Alternatively, effects on leukocytes are mediated by other tissues such as the liver or are clear only in response to stronger challenges.