A high-protein diet induces dissociation between plasma concentrations of growth hormone and ghrelin in wethers

High-carbohydrate or high-fat diets have been demonstrated to change ghrelin concentrations in plasma; however, there remains a need to clarify the effects of dietary protein on the interaction between circulating GH and ghrelin concentrations in the ruminant. In this study, we investigated the postprandial changes in plasma concentrations of GH and ghrelin and their interactions when wethers were fed either a high-protein (HP; 40% CP) or a low-protein (LP; 10% CP) diet for 2 wk. The wethers were divided into 2 groups and fed once a day for 2 wk in a randomized crossover design. Each diet contained the same level of ME. Blood was collected from the animals at specific times over 24 h to measure hormones and metabolites. Feeding once a day caused a prompt reduction in the GH and ghrelin concentrations regardless of the type of diet that the wethers consumed. The preprandial concentrations (P = 0.04), area under the curve (AUC; P = 0.04), and incremental AUC (iAUC; P = 0.06) for ghrelin in HP-fed wethers were or tended to be greater than those in LP-fed wethers although concentrations for GH were the same for both diets (P = 0.23). In addition, the time it took for the postprandial ghrelin concentrations to recover to the preprandial concentrations was greater in HP-fed wethers than in LP-fed wethers although this was not true for GH concentrations. Similarly, as for ghrelin, postprandial increase (P < 0.001) and AUC (P = 0.03) for insulin concentration was greater in the HP-fed wethers than in the LP-fed wethers. From these findings, we concluded that dietary proteins (or some other derived metabolites) may dissociate the interaction between plasma concentrations of GH and ghrelin in wethers.

Apelin is involved in postprandial responses and stimulates secretion of arginine-vasopressin, adrenocorticotropic hormone, and growth hormone in the ruminant

Apelin and its mRNA are expressed in several tissues, including the supraoptic and paraventricular nuclei in the hypothalamus. Although apelin is reported to be involved in the regulation of fluid homeostasis, little is known about the postprandial dynamics of apelin in plasma and its regulatory effects on the anterior pituitary hormones of ruminants. Therefore, the aims of this study were to investigate the following: (1) changes in plasma apelin concentrations in response to food intake under conditions of hydration (free access to water) or dehydration (water restriction), and (2) the effects of intravenous administration of apelin on plasma concentrations of arginine-vasopressin (AVP), ACTH, GH, and insulin. In Experiment 1 with the use of goats, the postprandial plasma apelin concentration was significantly increased under the dehydration condition compared with the hydration condition, and this increase was accompanied by increased plasma concentrations of AVP and ACTH after 24 h of dehydration. In Experiment 2 with the use of sheep and hydration conditions, the intravenous administration of apelin ([Pyr(1)]-apelin-13; 0.5 mg/head) caused a tendency to increase or caused a significant increase in plasma concentrations of AVP, ACTH, GH, insulin, and glucose. On the basis of these findings, we concluded that apelin is involved in the feeding process, and it regulates endocrine functions in the anterior pituitary gland via AVP in ruminant animals.

Effects of long-chain fatty acids on cytosolic triacylglycerol accumulation and lipid droplet formation in primary cultured bovine mammary epithelial cells

Mammary epithelial cells have recently been shown to express and secrete leptin into milk and to accumulate triacylglycerol (TAG) in cytosol. We examined the effects on the accumulation of cytosolic TAG of free fatty acid addition to the medium bathing bovine mammary epithelial cells (bMEC). Both saturated (palmitic and stearic) and unsaturated (oleic and linoleic) fatty acids stimulated the accumulation of TAG in a concentration-dependent manner from 50 to 400 microM and the expression of mRNA expression for CD36, which is involved in the uptake and secretion of long-chain fatty acids. However, leptin mRNA expression and lipid droplet formation were significantly increased only by the addition of unsaturated, but not saturated, fatty acids. Interestingly, both types of fatty acids stimulated alphas1-casein mRNA expression. These data suggest that the expression of leptin is related to droplet formation, whereas CD36 is related to cytosolic TAG accumulation, and that fatty acids or cytosolic TAG accumulation also have a role to accelerate differentiation of bMEC as shown by casein synthesis.

IGF-I-induced apoptosis in LM2d6 cultured at a low concentration of fetal bovine serum

We examined the effects of IGF-I (1-1000 ng/ml) on cell proliferation in LM2d6 mouse fibroblast cells at 0.1, 1.0 and 5.0% fetal bovine serum (FBS). In medium containing 0.1% FBS, treatment of LM2d6 cells with IGF-I significantly reduced the cell number in a dose- and time-dependent manner, whereas no effects were seen at 1 or 5% FBS. Treatment of the cells with 0.1% FBS for 72 h caused DNA laddering and nuclear condensation. However, Scatchard analysis for IGF-I binding sites on the cells revealed that both the number and the affinity of IGF-I receptors were not greater than that of Balb/3T3 cells. Furthermore, the apoptotic action of Long (R(3))-IGF-I, an analogue of IGF-I that has a reduced affinity for IGF binding proteins, was not greater than that of IGF-I. Taken together, we conclude that IGF-I reduces cell proliferation at low levels of FBS due to the induction of apoptosis. This effect is probably not caused by an excess production of IGF binding proteins in LM2d6 cells.

Effects of adenosine 5'-triphosphate and growth hormone on cellular H+ transport and calcium ion concentrations in cloned bovine mammary epithelial cells

The present experiment was carried out to investigate the effects of exogenous adenosine 5'-triphosphate (ATP) and growth hormone (GH) on cellular H(+) efflux rate (extracellular acidification rate) and Ca(2+) concentration ([Ca(2+)](c)) in cloned bovine mammary epithelial cells (bMEC) raised from the mammary gland of a 26-day-pregnant Holstein heifer. Perifusion of 2-day cultured cells with a medium containing ATP (10, 100 and 1000 micromol/l) for 30 min caused a significant and concentration-dependent increase in the cellular H(+) efflux rate. ATP application (100 micromol/l) caused a transient and large increase in [Ca(2+)](c) in all cells. In contrast, perifusion with a medium containing bovine GH at 10, 50 and 250 ng/ml for 30 min caused a significant decrease in the cellular H(+) efflux rate in a concentration-dependent manner. However, bovine GH application (50 ng/ml) caused a small decrease followed by an increase, in some cases, in [Ca(2+)](c). In bMEC treated with lactogenic hormones (1 microgram/l prolactin, 1 nmol/ml dexamethasone and 5 microgram/ml insulin) for 2 days, the increased H(+) efflux rate induced by ATP was significantly reduced, whereas the negative response induced by GH was inversely and significantly changed to the positive. Treatment of the cells with lactogenic hormones reduced the increase in [Ca(2+)](c) induced by ATP stimulation, while it enhanced the increase in [Ca(2+)](c) induced by GH stimulation. Application of ATP or GH did not cause any significant changes in [pH](c). Treatment with lactogenic hormones enhanced GH receptor (GHR) transcription that was determined by RT-PCR. From these results, we conclude that exogenous application of ATP and GH causes prompt and significant responses in H(+) transport and [Ca(2+)](c) that were significantly changed in the opposite direction by the treatment with lactogenic hormones. The lactogenic hormone treatment also enhanced GHR transcription, which may change post-receptor signal transduction systems for both agents in the bMEC.

Nerve growth factor-induced transient increase in the phosphorylation of ribosomal protein S6 mediated through a mechanism independent of cyclic AMP-dependent protein kinase and protein kinase C

Treatment of PC12h cells with nerve growth factor (NGF) induced a transient increase in the phosphorylation of a 35,000-dalton protein. This transient increase was observed also when extracts of NGF-treated cells were incubated with [gamma-32P]ATP. In the intact-cell phosphorylation system, treatment with N,2'-dibutyryladenosine 3',5'-cyclic monophosphate (dBcAMP) or 12-O-tetradecanoylphorbol 13-acetate (TPA) also induced a transient increase in the phosphorylation of the 35,000-dalton protein, but the effect was less than that of NGF. An effect comparable to that of NGF was obtained by the combination of dBcAMP and TPA. Pretreatment of PC12h cells with dBcAMP plus TPA for 3 days, which deprived the cells of their ability to respond to a rechallenge with dBcAMP, TPA, or dBcAMP plus TPA by increasing the rate of 35,000-dalton protein phosphorylation, caused only a slight attenuation of the NGF effect, directly indicating a minimal role of cyclic AMP (cAMP)-dependent protein kinase and protein kinase C in the mechanism of the NGF action. Pretreatment of the cells with K-252a, a protein kinase inhibitor, at a concentration of 300 nM almost completely blocked the action of NGF, but scarcely affected the action of dBcAMP, TPA, or dBcAMP plus TPA in intact-cell phosphorylation experiments. This NGF-sensitive 35,000-dalton protein was a ribosomal protein and identified as ribosomal protein S6. The results lead us to conclude that NGF activates some NGF-sensitive component(s), probably some specific protein kinase(s) other than cAMP-dependent protein kinase or protein kinase C, which is suppressed by K-252a and directly or indirectly activates a 35,000-dalton protein kinase(s) [S6 kinase(s)] to increase the rate of phosphorylation of the 35,000-dalton ribosomal protein (S6).

Fibroblast growth factor-induced decrease in the phosphorylation of Nsp100 mediated through a calcium-dependent mechanism and blocked by lectins

Separate treatment of PC12h cells with basic fibroblast growth factor (bFGF) and with epidermal growth factor (EGF) induced a selective decrease in the incorporation of radioactive phosphate into a 100,000-dalton soluble protein during phosphorylation with (gamma-32P)ATP of soluble extracts from the cells, as was seen previously with nerve growth factor (NGF). This 100,000-dalton soluble protein was designated in earlier studies as nerve growth factor-sensitive protein 100 (Nsp100). The inhibitory effects of bFGF and EGF on Nsp100 phosphorylation were prevented by pretreatment of PC12h cells with the calcium chelator, EGTA. Treatment of PC12h cells with the plant lectin wheat germ agglutinin (WGA), which binds to N-acetylglucosamine and sialic acid residues on glycoconjugates, blocked the inhibitory effects of bFGF, EGF, and NGF on Nsp100 phosphorylation. The blockage by WGA was reversed by the addition of the lectin-specific sugar N-acetylglucosamine to the PC12h cultures. Although pretreatment of PC12h cells with succinylated WGA, which has the ability to bind to N-acetylglucosamine but not to sialic acid residues, failed to block the inhibitory effect of NGF on Nsp100 phosphorylation as described previously, it did prevent the inhibitory effect of bFGF on this phosphorylation. These data suggest that in PC12h cells bFGF and EGF induce a decrease in the phosphorylation of Nsp100 mediated through a Ca2(+)-dependent mechanism, as in the case of NGF. Furthermore, the blockage of the bFGF-induced inhibition of Nsp100 phosphorylation by WGA and its succinylated form indicates that N-acetylglucosamine residues of bFGF receptor molecules might be involved in the mechanism by which bFGF inhibits the phosphorylation.(ABSTRACT TRUNCATED AT 250 WORDS)

Blockage of nerve growth factor action in PC12h cells by staurosporine, a potent protein kinase inhibitor

Staurosporine, which has a structure similar to that of K-252a, a potent protein kinase inhibitor that blocks nerve growth factor (NGF) action in PC12 and PC12h cells, is also known as a potent inhibitor of several protein kinases. This study shows that in PC12h cells staurosporine has a dual action: at lower concentrations than that required by K-252a, it is an inhibitor of NGF induction of neurite formation and of changes in the phosphorylation of specific proteins, whereas at concentrations higher than that required to inhibit NGF-induced neurite outgrowth, it rapidly enhances outgrowth by itself.

Staurosporine-induced neurite outgrowth in PC12h cells

Treatment of PC12h cells with staurosporine (100 nM), a potent inhibitor of protein kinases, promoted rapid outgrowth of neurites. The mechanism of neurite formation elicited by staurosporine is different from that elicited by nerve growth factor or by dibutyryl cyclic AMP, based on the independence from transcription or from activation of cyclic AMP-dependent protein kinase, respectively. Comparative experiments showed that of these three neurite-promoting agents, staurosporine was the most effective in eliciting neurite initiation.

Wheat germ agglutinin, concanavalin A, and lens culinalis agglutinin block the inhibitory effect of nerve growth factor on cell-free phosphorylation of Nsp100 in PC12h cells

It has been shown that in PC12 and its subclone PC12h treatment of the cells with nerve growth factor (NGF) induces a selective decrease in the incorporation of radioactive phosphate into a 100,000-dalton protein, designated in an earlier study as Nsp100, in the subsequent phosphorylation of soluble extracts from cells with (gamma-32P)ATP. In the present study, we show that plant lectins, wheat germ agglutinin (WGA), concanavalin A (Con A), and lens culinaris agglutinin (LCA), inhibit the action of NGF on Nsp100 phosphorylation in PC12h cells. Treatment of the cells with WGA, which binds to N-acetylglucosamine and sialic acid residues on glycoproteins, strongly blocked the inhibitory action of NGF on the protein phosphorylation. Con A and LCA, both of which recognize the same specific sugars (mannose, glucose), displayed only a moderate blocking effect. Unlike the native lectin, succinylated WGA, which has the ability to bind to N-acetylglucosamine but not to sialic acid residues, and other lectins examined in this study did not inhibit the action of NGF on Nsp100. WGA-mediated inhibition of NGF action was reversed by the addition of N-acetylglucosamine and by the addition of a much lower concentration of a sialoglycoprotein, mucin, into the culture. Since the binding of succinylated WGA to N-acetylglucosamine residues of cell-surface glycoconjugates is not sufficient to prevent the action of NGF, WGA might act on sialic acid residues of the NGF receptor molecule to effect the inhibition of biological actions of NGF.

Adrenergic modulation of pancreatic glucagon and insulin secretion in sheep

The effect of intravenous infusion of epinephrine, either alone or together with various doses of phentolamine or propranolol, on the secretion of both glucagon and insulin was determined in six sheep. Intravenous infusion of epinephrine alone caused increases in plasma glucagon and glucose concentrations and produced a slight but significant decrease in plasma insulin concentration. The concomitant infusion of propranolol and epinephrine augmented glucagon release and inhibited insulin secretion. Combined propranolol plus epinephrine infusion also caused a marked hyperglycemia. The concomitant infusion of phentolamine and epinephrine produced slight inhibition of glucagon secretion and markedly promoted insulin secretion. Epinephrine-induced hyperglycemia was eliminated by phentolamine infusion. The effects of isoproterenol infusion on plasma glucagon, insulin, and glucose concentrations were similar to that caused by the concomitant infusion of phentolamine and epinephrine. The effects of isoproterenol were abolished by the infusion of propranolol. It is concluded that an alpha-receptor mechanism is the most important component of adrenergic modulation of pancreatic glucagon secretion, whereas beta-receptor activation stimulates and alpha-receptor activation inhibits insulin secretion in sheep.

Insulin response to glucose and glucose tolerance following feeding in sheep

Sheep offered a roughage diet for 4 h daily were injected intravenously with glucose before and at various times after feeding. The insulin secretory response to glucose and the rate of disappearance of injected glucose were determined. While the basal concentration of plasma insulin was unchanged, the base-line plasma glucose concentration tended to decrease during the meal. The glucose load brought about an increase in the plasma insulin concentration at each injection, but the insulin response to glucose and the rate of glucose disposal were increased during the meal. On varying the time of feeding between 08.00 and 16.00 hours, the increase in the insulin response to glucose and in the rate of glucose disposal always appeared to be related to the giving of food, independent of the time food was offered. It is concluded that feeding increases the insulin response to an intravenous glucose load even when the increase in the basal level of plasma insulin on feeding is very modest in sheep given a roughage diet. The increased insulin response and glucose disposal rate following feeding did not appear to be related to diurnal rhythms in insulin secretory activity or glucose metabolism.