Direct demonstration of insulin-like growth factor-I-induced nitric oxide production by endothelial cells

Growth hormone and the heart

Impaired cardiovascular function has recently been demonstrated to potentially reduce life expectancy both in GH deficiency and excess. Experimental and clinical studies have supported the evidence that GH and IGF-I are implicated in cardiac development. In most patients with acromegaly a specific cardiomyopathy, characterized by myocardial hypertrophy with interstitial fibrosis, lympho-mononuclear infiltration and areas of monocyte necrosis, results in biventricular concentric hypertrophy. In contrast, patients with childhood or adulthood-onset GH deficiency (GHD) may suffer both from structural cardiac abnormalities, such as narrowing of cardiac walls, and functional impairment, that combine to reduce diastolic filling and impair left ventricular response to peak exercise. In addition, GHD patients may have an increase in vascular intima-media thickness and a higher occurrence of atheromatous plaques, that can further aggravate the haemodynamic conditions and contribute to increased cardiovascular and cerebrovascular risk. However, several lines of evidence have suggested that the cardiovascular abnormalities can be partially reversed by suppressing GH and IGF-I levels in acromegaly or after GH replacement therapy in GHD patients. Recently, much attention has been focussed on the ability of GH to increase cardiac mass suggesting its possible use in the treatment of chronic nonendocrine heart failure. In fact, GH administration can induce an improvement in haemodynamic and clinical status in some patients. Although these data need to be confirmed in more extensive studies, such promising results seem to open new perspectives for GH treatment in humans.

Treatment with a growth hormone secretagogue in a model of developing heart failure: effects on ventricular and myocyte function

BACKGROUND

Exogenous administration of growth hormone (GH) and subsequently increased production of insulin-like growth factor-1 can influence left ventricular (LV) myocardial growth and geometry in the setting of congestive heart failure (CHF). This study determined the effects of an orally active GH secretagogue (GHS) treatment that causes a release of endogenous GH on LV function and myocyte contractility in a model of developing CHF.

METHODS AND RESULTS

Pigs were randomly assigned to the following treatment groups: (1) chronic rapid pacing at 240 bpm for 3 weeks (n=11); (2) chronic rapid pacing and GHS (CP-424,391 at 10 mg x kg(-1) x d(-1), n=9); and (3) sham controls (n=8). In the untreated pacing CHF group, LV fractional shortening was reduced (21+/-2% versus 47+/-2%) and peak wall stress increased (364+/-21 versus 141+/-5 g/cm(2)) from normal control values (P:<0.05). In the GHS group, LV fractional shortening was higher (29+/-2%) and LV peak wall stress lower (187+/-126 g/cm(2)) than untreated CHF values (P:<0.05). With GHS treatment, the ratio of LV mass to body weight increased by 44% from untreated values. Steady-state myocyte velocity of shortening was reduced with pacing CHF compared with controls (38+/-1 versus 78+/-1 microm/s, P:<0.05) and was increased from pacing CHF values with GHS treatment (55+/-7 microm/s, P:<0.05).

CONCLUSIONS

The improved LV pump function that occurred with GHS treatment in this model of CHF was most likely a result of favorable effects on LV myocardial remodeling and contractile processes. On the basis of these results, further studies are warranted to determine the potential role of GH secretagogues in the treatment of CHF.

Membrane estrogen receptor engagement activates endothelial nitric oxide synthase via the PI3-kinase-Akt pathway in human endothelial cells

17beta-Estradiol (E(2)) is a rapid activator of endothelial nitric oxide synthase (eNOS). The product of this activation event, NO, is a fundamental determinant of cardiovascular homeostasis. We previously demonstrated that E(2)-stimulated endothelial NO release can occur without an increase in cytosolic Ca(2+). Here we demonstrate for the first time, to our knowledge, that E(2) rapidly induces phosphorylation and activation of eNOS through the phosphatidylinositol 3 (PI3)-kinase-Akt pathway. E(2) treatment (10 ng/mL) of the human endothelial cell line, EA.hy926, resulted in increased NO production, which was abrogated by the PI3-kinase inhibitor, LY294002, and the estrogen receptor antagonist ICI 182, 780. E(2) stimulated rapid Akt phosphorylation on serine 473. As has been shown for vascular endothelial growth factor, eNOS is an E(2)-activated Akt substrate, demonstrated by rapid eNOS phosphorylation on serine 1177, a critical residue for eNOS activation and enhanced sensitivity to resting cellular Ca(2+) levels. Adenoviral-mediated EA.hy926 transduction confirmed functional involvement of Akt, because a kinase-deficient, dominant-negative Akt abolished E(2)-stimulated NO release. The membrane-impermeant E(2)BSA conjugate, shown to bind endothelial cell membrane sites, also induced rapid Akt and consequent eNOS phosphorylation. Thus, engagement of membrane estrogen receptors results in rapid endothelial NO release through a PI3-kinase-Akt-dependent pathway. This explains, in part, the reduced requirement for cytosolic Ca(2+) fluxes and describes an important pathway relevant to cardiovascular pathophysiology.

Effects of homocysteine on endothelial nitric oxide production

Hyperhomocysteinemia (HHCy) is an independent and graded cardiovascular risk factor. HHCy is prevalent in patients with chronic renal failure, contributing to the increased mortality rate. Controversy exists as to the effects of HHCy on nitric oxide (NO) production: it has been shown that HHCy both increases and suppresses it. We addressed this problem by using amperometric electrochemical NO detection with a porphyrinic microelectrode to study responses of endothelial cells incubated with homocysteine (Hcy) to the stimulation with bradykinin, calcium ionophore, or L-arginine. Twenty-four-hour preincubation with Hcy (10, 20, and 50 microM) resulted in a gradual decline in responsiveness of endothelial cells to the above stimuli. Hcy did not affect the expression of endothelial nitric oxide synthase (eNOS), but it stimulated formation of superoxide anions, as judged by fluorescence of dichlorofluorescein, and peroxynitrite, as detected by using immunoprecipitation and immunoblotting of proteins modified by tyrosine nitration. Hcy did not directly affect the ability of recombinant eNOS to generate NO, but oxidation of sulfhydryl groups in eNOS reduced its NO-generating activity. Addition of 5-methyltetrahydrofolate restored NO responses to all agonists tested but affected neither the expression of the enzyme nor formation of nitrotyrosine-modified proteins. In addition, a scavenger of peroxynitrite or a cell-permeant superoxide dismutase mimetic reversed the Hcy-induced suppression of NO production by endothelial cells. In conclusion, electrochemical detection of NO release from cultured endothelial cells demonstrated that concentrations of Hcy >20 microM produce a significant indirect suppression of eNOS activity without any discernible effects on its expression. Folates, superoxide ions, and peroxynitrite scavengers restore the NO-generating activity to eNOS, collectively suggesting that cellular redox state plays an important role in HCy-suppressed NO-generating function of this enzyme.

Low serum insulin-like growth factor-binding protein-1 is associated with an unfavourable cardiovascular risk profile in elderly men

Serum insulin-like growth factor-binding protein-1 (IGFBP-1) is regulated by insulin and has been suggested to be a marker of the insulin resistance syndrome. The aim of this study was to investigate whether serum IGFBP-1 is associated with cardiovascular risk factors. Serum insulin-like growth factor-I and IGFBP-3 were also determined. 331 men aged 70-89 years were examined from the Finnish cohort of the Seven Countries Study. Serum IGFBP-1 concentrations were measured by immunofluorometric assay, and the results were analysed with respect to markers of cardiovascular risk, insulin resistance, and insulin secretion that were determined by using the homeostasis model assessment. Fasting serum IGFBP-1 correlated inversely with fasting serum insulin, serum insulin 2 h after oral glucose challenge test, body mass index, and serum triglycerides, and it correlated positively with age and serum high-density lipoprotein (HDL) cholesterol. After adjustment for age, fasting serum IGFBP-1 correlated positively with HDL cholesterol and inversely with fasting serum insulin and triglycerides. Serum IGFBP-1 correlated positively with insulin sensitivity and negatively with beta-cell function. In conclusion, low serum IGFBP-1 levels in elderly men are associated with a number of cardiovascular risk factors.

Effects of cardiotrophin-1 on hemodynamics and endocrine function of the heart

Cardiotrophin-1 (CT-1), a member of the interleukin-6 superfamily of cytokines, possesses hypertrophic actions and atrial natriuretic peptide (ANP)-producing activity in vitro. The goal of our study is to elucidate whether CT-1 affects the cardiovascular system in vivo. Intravenous injection of CT-1 (4-100 microg/kg) in conscious rats evoked significant declines in blood pressure and reflex increases in heart rate (HR) in a dose-dependent manner. CT-1 induced no significant change in cardiac output (from 260.7 +/- 11.0 to 264.7 +/- 26.6 ml. min(-1). kg(-1), P = not significant), which was compatible with the results from isolated perfused rat hearts; HR, change in pressure over time, left ventricular developed pressure, and perfusion pressure were unaffected. Northern blot and RT-PCR analyses revealed that CT-1 increased expression of inducible nitric oxide synthase (iNOS) in lung and aorta but not in heart or liver. Pretreatment with aminoguanidine, a specific iNOS inhibitor, inhibited both iNOS mRNA production and the depressor effect of CT-1. Interestingly, CT-1 increased ventricular expression of ANP and brain natriuretic peptide (BNP). The data demonstrate that CT-1 elicits its hypotensive effect via a nitric oxide-dependent mechanism and that CT-1 induces ANP and BNP mRNA expression in vivo.

Selective neuroprotective effects with insulin-like growth factor-1 in phenotypic striatal neurons following ischemic brain injury in fetal sheep

Severe perinatal asphyxia can lead to injury and dysfunction of the basal ganglia. Post insult administration of insulin-like growth factor-1 is neuroprotective, particularly in the striatum. Insulin-like growth factor-1 is also known to be a neuromodulator of several types of striatal neurons. The striatum comprises various phenotypic neurons with a complex neurochemical anatomy and physiology. In the present study, we examined the specificity of neuronal rescue with insulin-like growth factor-1 on different striatal neurons. Bilateral brain injury was induced in near term fetal sheep by 30 min of reversible carotid artery occlusion. A single dose of 3 microg of insulin-like growth factor-1 was infused over 1 h into the lateral ventricle 90 min following ischemia. The histological and immunohistochemical outcome were examined after 4 days recovery using paraffin tissue preparations. Insulin-like growth factor-1 treatment (n = 11) significantly reduced the percentage of neuronal loss in the striatum compared with the vehicle treated group (n = 10, 28.3+/-5.1% vs 55.5+/-17.3%, P < 0.005). Immunohistochemical studies showed that ischemia resulted in a significant loss of calbindin-28kd, choline acetyltransferase, parvalbumin, glutamate acid decarboxylase, neuronal nitric oxide synthase and neuropeptide Y immunopositive neurons, compared with sham controls. Insulin-like growth factor-1 markedly prevented the loss of calbindin-28kd (n = 7, P < 0.05), choline acetyltransferase (n = 7, P < 0.05), neuropeptide Y (n = 7, P < 0.05), neuronal nitric oxide synthase (n = 8, P < 0.05) and glutamate acid decarboxylase (n = 9, P < 0.05) immunopositive neurons, but failed to protect parvalbumin (n = 6) immunopositive neurons. The present study indicates that the therapeutic effect of insulin-like growth factor-1 in the basal ganglia is selectively associated with cholinergic and some phenotypic GABAergic neurons. These data suggest a potential role for insulin-like growth factor-1 in preventing cerebral palsy due to perinatal asphyxia.

Enhanced electron flux and reduced calmodulin dissociation may explain "calcium-independent" eNOS activation by phosphorylation

Bovine endothelial nitric oxide synthase (eNOS) is phosphorylated directly by the protein kinase Akt at serine 1179. Mutation of this residue to the negatively charged aspartate (S1179D eNOS) increases nitric oxide (NO) production constitutively, in the absence of agonist challenge. Here, we examine the potential mechanism of how aspartate at 1179 increases eNOS activity using purified proteins. Examination of NO production and cytochrome c reduction resulted in no substantial changes in the K(m)/EC(50) for L-arginine, calmodulin, and calcium, whereas there was a 2-fold increase in the rate of NO production for S1179D and a 2-4-fold increase in reductase activity (based on cytochrome c reduction). The observed increase in activity for both assays of NOS function indicates that a faster rate of electron flux through the reductase domain is likely the rate-limiting step in NO formation from eNOS. In addition, S1179D eNOS did show an increased resistance to inactivation by EGTA compared with wild type eNOS. These results suggest that a negative charge imposed at serine 1179, either by phosphorylation or by replacement with aspartate, increases eNOS catalytic activity by increasing electron flux at the reductase domain and by reducing calmodulin dissociation from activated eNOS when calcium levels are low.

Regulation of endothelial constitutive nitric oxide synthase gene expression in endothelial cells and in vivo : a specific vascular action of insulin

BACKGROUND

The vasodilatory effect of insulin can be acute or increase with time from 1 to 7 hours, suggesting that insulin may enhance the expression of endothelial nitric oxide synthase (eNOS) in endothelial cells. The objective of the present study was to characterize the extent and signaling pathways by which insulin regulates the expression of eNOS in endothelial cells and vascular tissues.

METHODS AND RESULTS

Physiological concentrations of insulin (10(-10) to 10(-7) mmol/L) increased the levels of eNOS mRNA, protein, and activity by 2-fold after 2 to 8 hours of incubation in cultured bovine aortic endothelial cells. Insulin enhanced eNOS gene expression in microvessels isolated from Zucker lean rats but not from insulin-resistant Zucker fatty rats. Inhibitors of phosphatidylinositol-3 kinase (PI-3 kinase) decreased the effect of insulin on eNOS gene expression, but a general protein kinase C (PKC) inhibitor, GF109203X or PKCbeta isoform inhibitor, LY333531 enhanced eNOS expression. In contrast, PKC activators inhibited both the activation by insulin of PI-3 kinase and eNOS mRNA levels. Overexpression of PKCbeta isoform in endothelial cells inhibited the stimulation by insulin of eNOS expression and PI-3 kinase activities in parallel.

CONCLUSIONS

Insulin can regulate the expression of eNOS gene, mediated by the activation of PI-3 kinase, in endothelial cells and microvessels. Thus, insulin may chronically modulate vascular tone. The activation of PKC in the vascular tissues as in insulin resistance and diabetes may inhibit PI-3 kinase activity and eNOS expression and may lead to endothelial dysfunctions in these pathological states.

Insulin and insulin-like growth factor-I cause vasorelaxation in human vessels in vitro

BACKGROUND

Insulin and insulin-like growth factor-I (IGF-I) are endogenous peptides with vasoactive activities.

OBJECTIVE

To evaluate the vasodilatory effects of insulin and IGF-I on human vessels taken from patients with and without noninsulin-dependent diabetes mellitus (NIDDM) and to elucidate their mechanisms of action.

METHODS

Vascular rings of human internal mammary artery (IMA) and saphenous vein harvested from 54 patients with and without NIDDM undergoing coronary bypass surgery were studied in vitro.

RESULTS

For samples from patients without NIDDM both insulin and IGF-I (10(-12)-10(-7) mol/l) evoked greater relaxation in IMA rings (30 +/- 4 and 29 +/- 6%, maximal relaxation +/- SEM, respectively) than they did in saphenous-vein rings (43 +/- 4 and 42 +/- 5%, respectively, P < 0.05 both for insulin and for IGF-I). Similar results were obtained with vessels from patients with NIDDM. Relaxation was not affected by the removal of the endothelium and by inhibition of the production of nitric oxide. However, the vascular relaxation caused by insulin and IGF-I was completely abolished by KCI, and was attenuated by the nonspecific potassium-channel blocker tetraethylammonium (for IMA rings, to 77 +/- 8 and 66 +/- 4% with insulin and IGF-I, respectively; for saphenous vein rings, 73 +/- 2 and 77 +/- 1% for insulin and IGF-I, respectively, P < 0.001).

CONCLUSIONS

Both insulin and IGF-I induced endothelial-independent, nitric oxide-independent vasorelaxation of rings from human IMA and saphenous veins, through a mechanism involving activation of potassium channels. This response remained intact in vessels from patients with NIDDM. This result supports the hypothesis that insulin and IGF-I play roles in the regulation of vascular tone in human vessels.

IGF-I inhibitors reduce compensatory hyperfiltration in the isolated rat kidney following unilateral nephrectomy

BACKGROUND

A role for insulin-like growth factor-I (IGF-I) as a mediator of renal hyperfiltration and hyperperfusion following unilateral nephrectomy (UNx) has been examined.

METHODS

Adult male Wistar rats were subjected to either left UNx or sham operation. Twenty one days after surgery, the right kidney was removed under barbiturate anaesthesia, and renal function was measured ex vivo using an isolated rat kidney perfusion system. The glomerular filtration rate was assessed from the renal clearance of [(14)C]inulin.

RESULTS

UNx stimulated renal growth as shown by a significantly higher (P<0.02) tissue dry weight in kidneys from UNx (0.45+/-0.02 g) than from sham-operated rats (0.31+/-0.02 g). Compensatory hyperfiltration could be detected ex vivo; kidneys obtained from UNx rats having a significantly higher (P<0.05) [(14)C]inulin clearance (0.75+/-0.08 ml/min, n=8) than kidneys obtained from sham-operated animals (0.39+/-0.05 ml/min, n=8). Compensatory hyperperfusion was also detected ex vivo; kidneys obtained from UNx rats having a significantly higher (P<0.05) renal perfusate flow (28.2+/-2.7 ml/min) than kidneys obtained from sham-operated rats (22.5+/-0.8 ml/min). Following perfusion with either 50 microg monoclonal IGF-I antibody (n=4) or 6.5 microM genistein (n=4), an inhibitor of tyrosine kinase, no significant difference in [(14)C]inulin was observed between kidneys obtained from either UNx or sham-operated rats. In contrast to hyperfiltration, renal hyperperfusion remained unaffected by the IGF-I antibody and was only reduced by 30% following genistein administration.

CONCLUSIONS

The results suggest a role for renal IGF-I as a mediator of compensatory hyperfiltration in the rat.

The autoinhibitory control element and calmodulin conspire to provide physiological modulation of endothelial and neuronal nitric oxide synthase activity

NO production by the endothelial and neuronal isoforms of nitric oxide synthase (cNOS) is regulated on a moment-to-moment basis by calmodulin binding, triggered by transient elevations in intracellular-free calcium levels. Nonetheless, additional modes of cNOS regulation are implicit in the discoveries of stimuli that elicit a sustained increase in cNOS activity despite undetectable or transient increases in intracellular Ca2+ in endothelial cells; such stimuli include shear-stress, oestrogen, insulin or insulin-like growth factor treatment of endothelial cells. Recently, we identified a peptide insertion within the FMN-binding domain of mammalian NOSs that is unique to calcium-dependent isoforms, and not shared with inducible NOS or ancestral flavoproteins. Evidence suggests that this insertion serves as a fundamental control element, analogous to intrinsic autoinhibitory peptides that have been demonstrated to regulate activity of other calmodulin-dependent enzymes. Thus, the peptide insertion of cNOSs appears to function as structural element that is displaced upon calmodulin binding, resulting in dysinhibition of NO synthesis. Once displaced, the peptide may also be subject to transient chemical modifications and protein-protein interactions that modulate autoinhibitory function. Herein we summarize our present knowledge and speculate on mechanisms by which calmodulin and the autoinhibitory peptide conspire to regulate cNOS activity.

Influence of age on contractile response to insulin-like growth factor 1 in ventricular myocytes from spontaneously hypertensive rats

Evidence suggests a pathophysiological role of insulin-like growth factor 1 (IGF-1) in hypertension. Cardiac function is altered with advanced age, similar to hypertension. Accordingly, the effects of IGF-1 on cardiac myocyte shortening and intracellular Ca(2+) were evaluated in hypertension at different ages. Ventricular myocytes were isolated from Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR), aged 12 and 36 weeks. Mechanical and intracellular Ca(2+) properties were examined by edge-detection and fluorescence microscopy. At 12 weeks, IGF-1 (1 to 500 ng/mL) increased peak twitch amplitude (PTA) and FFI changes (DeltaFFI) in a dose-dependent manner in WKY myocytes, with maximal increases of 27.5% and 35.2%, respectively. However, IGF-1 failed to exert any action on PTA and DeltaFFI in the age-matched SHR myocytes. Interestingly, at 36 weeks, IGF-1 failed to exert any response in WKY myocytes but depressed both PTA and DeltaFFI in a dose-dependent manner in SHR myocytes, with maximal inhibitions of 40.5% and 16.1%, respectively. Myocytes from SHR or 36-week WKY were less sensitive to norepinephrine (1 micromol/L) and KCl (30 mmol/L). Pretreatment with nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 micromol/L) did not alter the IGF-1-induced response in 12-week WKY myocytes but unmasked a positive action in 12-week SHR and 36-week WKY myocytes. L-NAME also significantly attenuated IGF-1-induced depression in 36-week SHR myocytes. In addition, the Ca(2+) channel opener Bay K8644 (1 micromol/L) abolished IGF-1-induced cardiac depression in 36-week SHR myocytes. Collectively, these results suggest that the IGF-1-induced cardiac contractile response was reduced with advanced age as well as with hypertension. Alterations in nitric oxide and intracellular Ca(2+) modulation may underlie, in part, the resistance to IGF-1 in hypertension and advanced age.

Myocyte death in the failing human heart is gender dependent

Cardiovascular disease is delayed and less common in women than in men. Myocyte death occurs in heart failure, but only apoptosis has been documented; the role of myocyte necrosis is unknown. Therefore, we tested whether necrosis is as important as apoptosis and whether myocyte death is lower in women than in men with heart failure. Molecular probes were used to measure the magnitude of myocyte necrosis and apoptosis in 7 women and 12 men undergoing transplantation for cardiac failure. Myocyte necrosis was evaluated by detection of DNA damage with blunt end fragments, whereas apoptosis was assessed by the identification of double-strand DNA cleavage with single base or longer 3' overhangs. An identical analysis of these forms of cell death was performed in control myocardium. Heart failure showed levels of myocyte necrosis 7-fold greater than apoptosis in patients of both sexes. However, cell death was 2-fold higher in men than in women. Heart failure resulted in a 13-fold and 27-fold increase in necrosis in women and men, respectively. Apoptosis increased 35-fold in women and 85-fold in men. The differences in cell death between women and men were confirmed by the electrophoretic pattern of DNA diffusion and laddering of isolated myocytes. The lower degree of cell death in women was associated with a longer duration of the myopathy, a later onset of cardiac decompensation, and a longer interval between heart failure and transplantation. In conclusion, myocyte necrosis and apoptosis affect the decompensated human heart; each contributes to the evolution of cardiac failure. However, the female heart is protected, at least in part, from necrotic and apoptotic death signals.

Growth hormone and hexarelin prevent endothelial vasodilator dysfunction in aortic rings of the hypophysectomized rat

The endothelial vasodilation mechanism(s) has been investigated in aortic rings of hypophysectomized male rats as well as hypophysectomized rats treated for 7 days with growth hormone (GH, 400 microg/kg, s.c.) or hexarelin (80 microg/kg, s.c.). Tissue preparations from intact animals were taken as controls. The results obtained indicate that the release of 6-keto-prostaglandin F1alpha (6-keto-PGF1alpha) from aortic rings of hypophysectomized rats was markedly reduced (51%; p<0.01) as compared with that of control preparations; the peak response to cumulative concentration of endothelin-1 (ET-1, from 10(-11) to 10(-5) M) was increased 2.4-fold (p<0.01) versus controls; the relaxant activity of acetylcholine (ACh, from 10(-10) to 10(-4) M) in norepinephrine-precontracted aortic rings was reduced by 39.5+/-4.4%. Pretreatment of hypophysectomized rats with GH or hexarelin markedly antagonized the hyperresponsiveness of the aortic tissue to ET-1 and allowed a consistent recovery of both the relaxant activity of ACh and the generation of 6-keto-PGF1alpha. Collectively these findings support the concept that dysfunction of vascular endothelial cells may be induced by a defective GH function. Because a replacement regimen of GH restored the somatotropic function and increased plasma insulin-like growth factor-I (IGF-I) concentrations in the hypophysectomized rats, it is suggested that IGF-I may have protected the vascular endothelium acting as a biologic mediator of GH action. In contrast to GH, hexarelin replacement neither increased body weight nor affected the plasma concentrations of IGF-I, indicating that its beneficial action on vascular endothelium was divorced from that on somatotropic function and was likely due to activation of specific endothelial receptors.

Thyrotropin-releasing hormone stimulates nitric oxide release from GH3 cells

Constitutive nitric oxide synthase (NOS) is expressed in the rat adenohypophysis but the mechanisms regulating its activity at the cellular level remain to be elucidated. The effect of TRH on nitric oxide release from GH3 cells was studied by means of reverse-phase HPLC to measure NO-2 and NO-3 concentrations in the incubation medium, and by polarography using electrodes specific for NO. Medium NO-2 concentrations in the incubation medium were dependent on the incubation time, and were further increased by sodium nitroprusside (SNP) or high potassium. NO-3 was detectable only in the presence of 100 microM SNP. Addition of L-arginine increased medium NO-2 concentrations. Diamino-hydroxypyrimidine decreased medium NO-2 concentrations, which were restored by the addition of (6R)-5, 6, 7, 8-tetrahydro-L-biopterin (THB). TRH elicited dose-related increases in medium NO-2 concentrations and in nitric oxide-specific currents, which were abolished by Nomega-nitro-L-arginine methyl ester. TRH failed to increase medium NO-2 concentrations in cells loaded with an intracellular Ca2+-chelating agent. The findings suggest that mobilization of intracellular Ca2+ by TRH stimulation activates Ca2+-dependent NOS in GH3 cells.

Insulin-like growth factor-1 attenuates the detrimental impact of nonocclusive coronary artery constriction on the heart

Coronary artery narrowing (CAN) induces tissue injury, which may involve myocyte necrosis and apoptosis. Insulin-like growth factor (IGF)-1 may counteract cell death, modifying the detrimental effects of myocardial ischemia. On this basis, CAN was produced in female FVB.Igf+/- mice and nontransgenic littermates, and the animals were euthanized 7 days later. CAN consisted of an 82% reduction in the vessel luminal cross-sectional area in both groups of mice. Severe left ventricular dysfunction was present in CAN nontransgenic and transgenic mice, but heart and left ventricular weights increased more in littermates than in FVB.Igf+/- mice. Similarly, the changes in chamber volume and diastolic wall stress were greater in nontransgenic mice. Subacute tissue injury, represented by foci of replacement fibrosis, was 2.6-fold higher in CAN littermates than in FVB.Igf+/- mice. Ongoing myocyte necrosis was 5-fold greater in nontransgenic mice, whereas apoptosis was low and did not differ in the 2 groups of mice. In CAN nontransgenic mice, myocyte necrosis was 12-fold more frequent than apoptosis but, in CAN transgenic mice, these 2 types of cell death were comparable. alpha-Myosin and beta-myosin isoform mRNAs were affected by CAN, but alpha-myosin mRNA was reduced more in nontransgenic mice. In conclusion, myocyte necrosis and replacement fibrosis are the prevailing forms of myocardial damage induced by CAN. Constitutive overexpression of IGF-1 attenuates myocyte necrosis and tissue injury, having no effect on cell apoptosis. These factors limit ventricular dilation, myocardial loading, cardiac hypertrophy, and alterations in alpha- and beta-myosin isoform expression.

Growth hormone (GH) and atherosclerosis: changes in morphology and function of major arteries during GH treatment

Patients with hypopituitarism have increased carotid artery intima-media thickness and reduced arterial distensibility. The effect of 2 years of growth hormone (GH) replacement therapy on these parameters was studied in 11 GH-deficient men (age range, 24-49 years) with hypopituitarism and compared with 12 healthy, age-matched men with no evidence of pituitary or vascular disease. Before treatment the intima-media of the common carotid arteries and the carotid bifurcations were significantly thicker in patients (P < 0.001) than in the control group. Treatment with GH normalized the intima-media thickness of the common carotid artery within 6 months and of the carotid bifurcation within 3 months. The changes in intima-media thickness of the carotid artery were negatively correlated with changes in serum levels of insulin-like growth factor I during treatment. There was a significant improvement in flow-mediated, endothelium-dependent dilation of the brachial artery at 3 months, which was sustained at 6, 18 and 24 months of GH treatment (P < 0.05). Thus, GH replacement therapy in GH-deficient men reverses early morphological and functional atherosclerotic changes in major arteries, and may reduce rates of vascular morbidity and mortality.

Decrease in carotid intima-media thickness after one year growth hormone (GH) treatment in adults with GH deficiency

An increased carotid arterial intima-media thickness (IMT) has been reported in hypopituitary adults untreated for GH deficiency. In the present study, the effect of GH replacement on IMT and cardiovascular risk factors was prospectively investigated, in GH deficiency patients treated at a mean dose of 1 UI/day during 1 yr (n = 22) and 2 yr (n = 11). The IMT measurements were performed by the same experienced physician, and the coefficient of variation (calculated in two control groups) was below 6.5%. IMT at baseline was related to conventional risk factors. After 1 yr GH treatment, IMT decreased from 0.78 +/- 0.03 mm to 0.70 +/- 0.03 mm (P < 0.001). The decrement was observed in 21 of 22 patients. After 2 yr GH treatment, IMT had stabilized at 0.70 +/- 0.04 mm and remained significantly different from baseline values (P < 0.003). GH treatment resulted in a moderate decrease in waist circumference and body fat mass and an increase in VO2 max. Conventional cardiovascular risk factors were unmodified except for a transient 10% decrease in low-density lipoprotein cholesterol at 6 months. The contrast between the limited metabolic effect of treatment and the importance and precocity of the changes in IMT suggests that the decrease in IMT was not exclusively attributable to a reversal in the atherosclerotic process. A direct parietal effect of GH replacement on the arterial wall might also be involved. The consequences, in terms of cardiovascular risk, should be established by randomized prospective trials.

Endothelial dysfunction in hypopituitary adults with growth hormone deficiency

OBJECTIVES

Adult hypopituitarism with growth hormone deficiency (GHD) results in reduced exercise capacity, detrimental changes in body composition and lipid profiles and may be associated with an excess cardiovascular mortality. Endothelial dysfunction is an early event in the pathogenesis of atherosclerosis and predisposes to the deposition of unstable atherosclerotic plaques. We have used a noninvasive method to assess endothelial function in the brachial arteries of a group of treated hypopituitary adults with GHD, and a group of healthy age- and sex-matched controls.

PATIENTS

Seventeen hypopituitary adults with GHD (13 male, 4 female) aged 26-54 years were studied. Each patient was receiving standard replacement therapy for all other hormonal deficiencies such that all target hormones were maintained in the normal reference range. All observations obtained were compared with those made in age- and sex-matched control subjects. All study subjects had no identifiable risk factors for endothelial dysfunction.

MEASUREMENTS

Using an ultrasound vessel wall tracking system, the diameter of the left brachial artery was measured at rest, in response to reactive hyperaemia (endothelium-dependent dilation) and following sublingual glyceryl trinitrate (GTN) (endothelium-independent vasodilatation). We also measured fasting lipids, insulin, plasma glucose, glycated haemoglobin (HbA1c) and IGF-1, and studied the relationship of these parameters to endothelial function.

RESULTS

Flow mediated endothelium-dependent dilatation (FMD), expressed as a percentage change from resting base-line diameter, was significantly impaired in the GHD group (3.70 +/- 2.36% vs. 7.30 +/- 2.42%, P < 0.001). In contrast, GTN-mediated dilatation was similar in both groups. There were no differences in total cholesterol, HDL cholesterol, LDL cholesterol or plasma triglyceride between the groups. Both fasting insulin (27.1 +/- 18.1 vs. 15.89 +/- 6.65 mU/l, P < 0.05) and glycated haemoglobin (HbA1c) levels (5.29 +/- 0.43 vs. 4.91 +/- 0.43%, P < 0.05) were significantly higher in the GHD group. FMD in both groups showed an inverse relationship with total cholesterol (r = -0.58, P < 0.05, GHD and r = -0.55, P < 0.05 controls). However, in the GHD subjects, there was a strong inverse relationship between FMD and LDL-cholesterol (r = -0.81, P < 0.0001). No other relationships were noted between FMD and any other metabolic parameters, or characteristics of GHD.

CONCLUSIONS

Endothelial dysfunction is present in GH deficient adults prior to the onset of overt atherosclerotic disease. The similar glucose yet elevated fasting insulin levels imply a state of relative insulin insensitivity. The strong inverse correlation between endothelial dysfunction and LDL-cholesterol suggests a possible aetiological role for LDL-cholesterol in the pathogenesis of any excess cardiovascular risk associated with adult hypopituitarism.

Insulin-like growth factor-1 (IGF-1) and growth hormone (GH) in immunity and inflammation

In recent years many efforts have been undertaken to elucidate the complex interactions between mediators of the endocrine system and the immune system. The main effector of growth hormone (GH) is insulin-like growth factor-1 (IGF-1), an endocrine mediator of growth and development under physiological conditions. Besides this important function, IGF-1 also plays a prominent role in the regulation of immunity and inflammation. This article will address the involvement of IGF-1 in innate as well as acquired immunity and host-defense. We also discuss the role of IGF-1 in the course of inflammatory disorders, including sepsis and sepsis-induced catabolism as well as degenerative arthritis. Based on recent insights, we finally examine the pathophysiological background, potential pitfalls and perspectives of IGF-1 suppletion therapy in these conditions.

The effects of the N-terminal tripeptide of insulin-like growth factor-1, glycine-proline-glutamate in different regions following hypoxic-ischemic brain injury in adult rats

Insulin-like growth factor-1 has pleiotropic effects in the central nervous system and can act both as a survival and a differentiation factor. Insulin-like growth factor-1 can be proteolytically cleaved into des-N-(1-3)-insulin-like growth factor-1 and a N-terminal tripeptide fragment, glycine-proline-glutamate. Both insulin-like growth factor-1 and des-N-(1-3)-insulin-like growth factor-1 can improve neuronal survival after hypoxic-ischemic brain injury in vivo. The present study investigates the effects of glycine-proline-glutamate on different brain regions and neuronal populations after hypoxic-ischemic injury. Unilateral hypoxic-ischemic injury was induced in adult rats. Glycine-proline-glutamate (3 microg) was administered centrally 2 h after the injury and the extent of brain damage determined five days later. In a separate trial immunohistochemical techniques were used to determine the effects of glycine-proline-glutamate on specific populations of neurons in the striatum after the injury. Compared to the vehicle treatment, glycine-proline-glutamate (n=19) treatment reduced the extent of cortical damage and neuronal loss in the CA1-2 subregions of the hippocampus (P<0.05). In the striatum, there was a trend towards a reduction in neuronal loss after glycine-proline-glutamate treatment (P=0.053) compared to the vehicle (n=21)-treated animals. In a separate study, glycine-proline-glutamate (n=8) treatment prevented the loss of choline acetyltransferase (P<0.05), glutamate acid decarboxylase (P<0.05) and somatostatin (P<0.05) containing neurons in the ipsilateral striatum following hypoxic-ischemic brain injury and also increased the numbers of neuronal nitric oxide synthase (P<0.05) containing neurons in the contralateral side. These studies suggest that in addition to neuroprotective effects, glycine-proline-glutamate can influence neuronal activity after hypoxic-ischemic injury.

Mean arterial blood pressure and serum levels of the molar ratio of insulin-like growth factor-1 to its binding protein-3 in healthy centenarians

OBJECTIVE

Healthy centenarians have a greater molar ratio of plasma insulin-like growth factor-1 to insulin-like growth factor binding protein-3 than that of aged subjects. We investigated the question of whether differences in mean arterial pressure and in this plasma ratio were related in healthy centenarians.

SUBJECTS AND METHODS

We studied 52 subjects in total, 30 aged subjects (70-99 years) and 22 healthy centenarians (> 100 years) to determine differences in mean arterial pressure, endothelial function and intracellular cation levels.

RESULTS

In the healthy centenarians, the molar ratio of fasting plasma insulin-like growth factor-1 to its binding protein-3 was significantly correlated with mean arterial pressure (r = -0.66, P < 0.001). Baseline (19.3 +/- 1.5 versus 27.6 +/- 2.2 mumol/l, P < 0.05) and L-arginine-stimulated percentage increases in the plasma total nitrate: nitrite ratio (67 +/- 3.4 versus 48 +/- 4.5%, P < 0.03) were greater in the healthy centenarians than in the aged subjects. An L-arginine bolus elicited an increase in forearm blood flow which was correlated with the percentage increase in the plasma total nitrate: nitrite ratio (r = 0.79, P < 0.001) and with the fasting erythrocyte magnesium concentration (r = 0.80, P < 0.001) in healthy centenarians. Both correlations remained significant (P < 0.01) after adjustment for sex, body mass index and the waist: hip ratio. Moreover, the fasting plasma molar ratio of insulin-like growth factor-1 to its binding protein-3 was correlated with the percentage increase in forearm blood flow (r = 0.59, P < 0.005) and with the percentage increase in the plasma total nitrate: nitrite ratio (r = 0.54, P < 0.009) in healthy centenarians. The centenarians had higher baseline total erythrocyte magnesium and lower calcium concentrations than the aged subjects. The addition of insulin growth factor-1 to the incubation medium increased the total intracellular erythrocyte magnesium content and decreased the calcium content in both groups of subjects. Nevertheless, the percentage increase in total erythrocyte magnesium (33 +/- 3.8 versus 12 +/- 3.4%, P < 0.03) and decline in intracellular calcium (17 +/- 2.8 versus 8 +/- 3.1%, P < 0.02) concentrations were greater in the healthy centenarians than the aged subjects.

CONCLUSION

In healthy centenarians, insulin-like growth factor-1 may preserve endothelial function and modulate the intracellular cation content, thus contributing to a lower mean arterial pressure than that in aged subjects.

Altered inotropic response to IGF-I in diabetic rat heart: influence of intracellular Ca2+ and NO

Normally, insulin-like growth factor I (IGF-I) exerts positive effects on cardiac growth and myocardial contractility, but resistance to its action has been reported in diabetes. This study was designed to determine whether IGF-I-induced myocardial contractile action is altered in diabetes as a result of an intrinsic alteration of contractile properties at the cellular level. Contractile responses to IGF-I were examined in left ventricular papillary muscles and ventricular myocytes from normal and short-term (5-7 days) streptozotocin-induced diabetic rats. Mechanical properties of muscles and myocytes were evaluated using a force transducer and an edge detector, respectively. Preparations were electrically stimulated at 0.5 Hz, and contractile properties analyzed include peak tension development (PTD) or peak twitch amplitude (PTA), time to peak contraction/shortening, and time to 90% relaxation/relengthening. Intracellular Ca2+ transients were measured as fura 2 fluorescence intensity changes. IGF-I (1-500 ng/ml) caused a dose-dependent increase in PTD and PTA in preparations from normal but not diabetic animals. IGF-I did not alter time to peak contraction/shortening or time to 90% relaxation/relengthening. Pretreatment with the NO synthase inhibitor Nomega-nitro-L-arginine methyl ester (100 microM) attenuated IGF-I-induced increases in PTD in normal myocardium but unmasked a positive inotropic action in diabetic animals. Pretreatment with Nomega-nitro-L-arginine methyl ester blocked IGF-I-induced increases in PTA in single myocytes. Consistent with its inotropic actions on muscles and myocytes, IGF-I induced a dose-dependent increase in Ca2+ transients in normal but not diabetic myocytes. These results suggest that the IGF-I-induced inotropic response is depressed in diabetes because of an intrinsic alteration at the myocyte level. Mechanisms underlying this alteration in IGF-I-induced myocardial response may be related to changes in intracellular Ca2+ and/or NO production in diabetes.

Insulin and insulin-like growth factor-I cause coronary vasorelaxation in vitro

Insulin and insulin-like growth factor-I (IGF-I) may play a role in the modulation of coronary artery tone, yet there are few data regarding their vasoactive effects on the coronary vascular bed. We evaluated the vasorelaxation effects of insulin and IGF-I on porcine coronary epicardial vessels in vitro and elucidated possible mechanisms. Porcine epicardial arteries were contracted with 10(-7) mol/L endothelin-1 and relaxed with cumulative concentrations of either insulin or IGF-I (10(-12) to 10(-7) mol/L). The above experiments were repeated in vessels without endothelium. Vessels were also incubated with the nitric oxide synthase inhibitor NG-monomethyl-L-arginine (L-NMMA; 10(-4) mol/L) with and without 10(-3.5) mol/L L-arginine, the potassium channel blocker tetraethylammonium (TEA; 10(-2) mol/L), and the guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3,-alpha]quinoxalin-1-one (ODQ; 10(-5.5) mol/L); vessels were then contracted with endothelin-1 and relaxed with insulin or IGF-I. Insulin and IGF-I were also added after contraction with 60 mmol/L KCl. Insulin and IGF-I caused a similar decrease in coronary epicardial tension after contraction with endothelin-1 (relaxation of 28+/-4% [n=7] and 25+/-3% [n=8] with insulin and IGF-I, respectively; P<0.0001 for both peptides). Removal of the endothelium did not affect these responses. Incubation with L-NMMA, but not ODQ, attenuated the vasorelaxation response to insulin and IGF in vessels without endothelium. L-Arginine did not reverse this effect of L-NMMA. KCl and TEA attenuated the vasorelaxation effect of both insulin and IGF-I. Thus, both insulin and IGF-I caused non-endothelium-dependent coronary vasorelaxation in vitro, probably through a mechanism involving the activation of potassium channels. These findings suggest that insulin and IGF-I participate in the regulation of coronary vasomotor tone.

Serum total IGF-I, free IGF-I, and IGFB-1 levels in an elderly population: relation to cardiovascular risk factors and disease

Recently, a method to measure free insulin-like growth factor-I (IGF-I) levels has been developed. Free IGF-I levels may have greater physiological and clinical relevance than total (bound and free) IGF-I. The associations between the circulating IGF-I/IGF binding protein (IGFBP) system and cardiovascular disorders was studied. In a cross-sectional study of 218 healthy persons (103 men, 115 women) aged 55 to 80 years, fasting serum (total and free) IGF-I and IGFBP-1 levels, lipid profile, insulin, and glucose were measured. In addition, blood pressure, body mass index (BMI), and waist-hip ratio (WHR) were measured. Ultrasonography of both carotid arteries was performed to investigate the presence of atherosclerotic lesions. A history of angina pectoris, the presence of a possible or definite myocardial infarction on the ECG, and plaques in the carotid arteries were used as indicators of presence of cardiovascular signs and symptoms. Free IGF-I was inversely related to serum triglycerides (P=.04, adjusted for age and sex). Mean free IGF-I levels in subjects without signs or symptoms of cardiovascular diseases were significantly higher than in those with at least one cardiovascular symptom or sign (P=.002, adjusted for age and sex). Free IGF-I levels were also higher in subjects who had no atherosclerotic plaques in the carotid arteries (P=.02, adjusted for age and sex) and who had never smoked (P=.02, adjusted for age and sex). IGFBP-1 showed an inverse relation with insulin, BMI, and WHR and a positive relation with HDL cholesterol. The associations between IGFBP-1 levels and HDL cholesterol, WHR, and BMI remained significant after adjustment for fasting insulin levels. High fasting serum free IGF-I levels are associated with a decreased presence of atherosclerotic plaques and coronary artery disease and lower serum triglycerides, whereas high fasting IGFBP-1 levels are associated with a more favorable cardiovascular risk profile. The findings suggest that the IGF-I/IGFBP system is related to cardiovascular risk factors and atherosclerosis.

Untreated growth hormone deficiency explains premature mortality in patients with hypopituitarism

Untreated growth hormone deficiency (GHD) might explain the increased mortality reported in patients with hypopituitarism. These statistics appear to be largely attributable to cardiovascular disease. Differences in fibrinolytic activity regulators, together with dyslipidaemias, abdominal obesity and raised blood pressure in hypopituitarism might explain this increased risk. There is growing evidence that treatment with growth hormone (GH) can rectify most of the cardiovascular abnormalities associated with GHD. The reported improved psychosocial well-being in response to GH treatment may also be important in lowering risk in this group of patients.

Podokinesis in endothelial cell migration: role of nitric oxide

Previously, we demonstrated the role of nitric oxide (NO) in transforming epithelial cells from a stationary to locomoting phenotype [E. Noiri, T. Peresleni, N. Srivastava, P. Weber, W.F. Bahou, N. Peunova, and M. S. Goligorsky. Am. J. Physiol. 270 (Cell Physiol. 39): C794-C802, 1996] and its permissive function in endothelin-1-stimulated endothelial cell migration (E. Noiri, Y. Hu, W. F. Bahou; C. Keese, I. Giaever, and M. S. Goligorsky, J. Biol: Chem. 272: 1747-1753, 1997). In the present study, the role of functional NO synthase in executing the vascular endothelial growth factor (VEGF)-guided program of endothelial cell migration and angiogenesis was studied in two independent experimental settings. First, VEGF, shown to stimulate NO release from simian virus 40-immortalized microvascular endothelial cells, induced endothelial cell transwell migration, whereas NG-nitro-L-arginine methyl ester (L-NAME) or antisense oligonucleotides to endothelial NO synthase suppressed this effect of VEGF. Second, in a series of experiments on endothelial cell wound healing, the rate of VEGF-stimulated cell migration was significantly blunted by the inhibition of NO synthesis. To gain insight into the possible mode of NO action, we next addressed the possibility that NO modulates cell matrix adhesion by performing impedance analysis of endothelial cell monolayers subjected to NO. The data showed the presence of spontaneous fluctuations of the resistance in ostensibly stationary endothelial cells. Spontaneous oscillations were induced by NO, which also inhibited cell matrix adhesion. This process we propose to term "podokinesis" to emphasize a scalar from of micromotion that, in the presence of guidance cues, e.g., VEGF, is transformed to a vectorial movement. In conclusion, execution of the program for directional endothelial cell migration requires two coexisting messages: NO-induced podokinesis (scalar motion) and guidance cues, e.g., VEGF, which imparts a vectorial component to the movement. Such a requirement for the dual signaling may explain a mismatch in the demand and supply with newly formed vessels in different pathological states accompanied by the inhibition of NO synthase.

Effects of insulin-like growth factor I on the renal juxtamedullary microvasculature

To characterize the effects on the rat renal preglomerular microvasculature of insulin-like growth factor I (IGF-I), experiments were performed using the in vitro blood-perfused juxtamedullary nephron preparation. IGF-I induced a reversible vasodilation of pre- but not postglomerular microvessels in a dose-dependent manner (10(-9)-10(-7) M). The IGF-I-induced vasodilation was similar in all preglomerular vascular segments: interlobular artery, 11.5 +/- 1.2% of control (n = 16); mid-afferent arterioles, 11.6 +/- 1.7% (n = 24); and juxtaglomerular afferent segments, 16.1 +/- 2.8% (n = 19). Renal autoregulatory capacity was not reduced by IGF-I. Pretreatment with the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine methyl ester (10(-4) M) completely inhibited the vasodilatory response to IGF-I. IGF-I induced a rapid increase of NO concentration in intact renal microvessels, monitored by a NO-selective voltametric microelectrode. Pretreatment with the cyclooxygenase inhibitor indomethacin (10(-5) M) not only abrogated the IGF-I-induced dilation, but, moreover, IGF-I elicited a small but significant (approximately 10%) vasoconstriction in all preglomerular vessels. These results indicate that the renal vascular effects of IGF-I involve activation of two endogenous vasodilators (NO and vasodilatory prostaglandins). In addition, IGF-I may also release an undefined vasoconstrictor.

Elevated D-glucose induces insulin insensitivity in human umbilical endothelial cells isolated from gestational diabetic pregnancies

1. The effects of human insulin and elevated D-glucose on L-arginine transport and synthesis of nitric oxide (NO) and prostacyclin (PGI2) have been investigated in human umbilical vein endothelial cells isolated from gestational diabetic pregnancies. 2. The increase in the Vmax for L-arginine transport (9.0 +/- 1.1) pmol (micrograms protein)-1 min-1) in diabetic endothelial cells cultured in 5 mM D-glucose was unaffected following 24 h exposure to 25 mM D-glucose. 3. Gestational diabetes-induced increases in basal intracellular cGMP and L-citrulline levels (inhibitable by L-NAME) and [Ca2+], were unaffected by elevated D-glucose. In contrast, PGI2 release was inhibited in diabetic cells exposed to either 5 or 25 mM D-glucose. 4. Elevated D-glucose attenuated histamine (10 microM, 5 min)-stimulated accumulation of cGMP and L-citrulline in endothelial cells isolated from gestational diabetic pregnancies. 5. The membrane hyperpolarization (-79 +/- 0.9 mV) sustained in diabetic endothelial cells in culture was insensitive to elevated D-glucose. 6. Elevated D-glucose abolished the stimulatory effect of human insulin (1 nM, 8 h) on L-[3H]leucine incorporation in diabetic endothelial cells cultured in 5 mM D-glucose. 7. Human insulin reduced the elevated rates of L-arginine transport and cGMP accumulation in diabetic cells cultured in 5 mM D-glucose but failed to reduce increased rates of transport or NO production in cells exposed to 25 mM D-glucose or cycloheximide. 8. Our findings demonstrate that hyperglycaemia impairs the actions of human insulin on umbilical vein endothelial cells isolated from gestational diabetic pregnancies. Changes in insulin sensitivity and/or its signalling cascade may be affected by hyperglycaemia associated with gestational diabetes, resulting in insulin resistance in endothelial cells derived from the fetal vasculature.

Nitric oxide production contributes to the angiogenic properties of vascular endothelial growth factor in human endothelial cells

Vascular endothelial growth factor (VEGF) is a regulator of vasculogenesis and angiogenesis. To investigate the role of nitric oxide (NO) in VEGF-induced proliferation and in vitro angiogenesis, human umbilical vein endothelial cells (HUVEC) were used. VEGF stimulated the growth of HUVEC in an NO-dependent manner. In addition, VEGF promoted the NO-dependent formation of network-like structures in HUVEC cultured in three dimensional (3D) collagen gels. Exposure of cells to VEGF led to a concentration-dependent increase in cGMP levels, an indicator of NO production, that was inhibited by nitro-L-arginine methyl ester. VEGF-stimulated NO production required activation of tyrosine kinases and increases in intracellular calcium, since tyrosine kinase inhibitors and calcium chelators attenuated VEGF-induced NO release. Moreover, two chemically distinct phosphoinositide 3 kinase (PI-3K) inhibitors attenuated NO release after VEGF stimulation. In addition, HUVEC incubated with VEGF for 24 h showed an increase in the amount of endothelial NO synthase (eNOS) protein and the release of NO. In summary, both short- and long-term exposure of human EC to VEGF stimulates the release of biologically active NO. While long-term exposure increases eNOS protein levels, short-term stimulation with VEGF promotes NO release through mechanisms involving tyrosine and PI-3K kinases, suggesting that NO mediates aspects of VEGF signaling required for EC proliferation and organization in vitro.

Insulin-like growth factor I reverses interleukin-1beta inhibition of insulin secretion, induction of nitric oxide synthase and cytokine-mediated apoptosis in rat islets of Langerhans

We have previously observed that treatment of rat islets of Langerhans with interleukin-1beta for 12 h results in nitric oxide-dependent inhibition of insulin secretion, while 48 h treatment increased rates of islet cell death by apoptosis. Here, we demonstrate that interleukin-1beta-mediated nitric oxide formation and inhibition of insulin secretion are significantly reduced by 24 h pretreatment of rat islets of Langerhans with insulin-like growth factor I (IGF-I). IGF-I decreased cytokine induction of nitric oxide synthase in islets. Use of an arginine analogue in culture or IGF-I pretreatment of islets were also effective in protecting islets against cytokine-mediated apoptotic cell death. We conclude that IGF-I antagonises inhibitory and cytotoxic effects of cytokines in rat islets.

17 beta-estradiol regulation of human endothelial cell basal nitric oxide release, independent of cytosolic Ca2+ mobilization

Estradiol retards the development of atherosclerosis. Animal models have suggested that NO may be a critical effector molecule in this cardiovascular protection. In this study, female human umbilical vein endothelial cells (HUVECs) were propagated in phenol red-free gonadal hormone-free medium and pretreated with 17 beta-estradiol (E2). Reduced NO2- and NO3- (NOx) concentration, determined by chemiluminescence, demonstrated a rapid increase in basal HUVEC NO release in response to physiological concentrations of E2. The estrogen receptor (ER) antagonist ICI 164,384 inhibited the augmented NO release, demonstrating an ER-mediated component of this response. Because endothelial NO synthase (eNOS) activity is largely regulated by cytosolic Ca2+, relative [Ca2+]i in response to E2 was determined in a fluorometric assay. E2 did not promote HUVEC Ca2+ fluxes. Furthermore, eNOS activity in E2-pretreated endothelial whole-cell lysates was not dependent on additional Ca2+. Despite involving the ER, this is a nongenomic effect E2, as demonstrated by maintained responses in transcriptionally inhibited cells and by the rapidly (10 minutes) of cGMP formation in an NO bioassay. We demonstrate, for the first time, that independent of cytosolic Ca2+ mobilization, there is augmentation of eNOS activity with a resultant increase in HUVEC basal NO release in response to short-term estradiol exposure. Implications for the cardiovascular protective role of estrogen are discussed.

Insulin-like growth factor-1 retinal microangiopathy in the pig eye

OBJECTIVE

Human recombinant insulin-like growth factor-1 (hrIGF-1), a ubiquitous angiogenic growth factor, was injected into the vitreous cavity of pigs to investigate the clinical and histopathologic consequences of supraphysiologic levels of this angiogenic growth factor on the retinal vasculature.

DESIGN

Young male pigs were injected with 600 microg hrIGF-1 into the vitreous cavity and were observed with serial examinations by ophthalmoscopy, fundus photography, and fluorescein angiography for varying periods up to 6 months. In a separate set of experiments, a dose-response relation was explored in animals injected with varying doses of IGF-1.

MAIN OUTCOME MEASURES

Histopathologic analysis included light and transmission electron microscopy and modified elastase digestion. Quantitative morphometric measurements were made of capillary basement membrane thickness and endothelial cell and pericyte densities of the retinal capillaries.

RESULTS

Early clinical features of IGF-1-injected eyes included marked arteriolar tortuosity, vitreitis, and retinal vessel and optic nerve head vascular fluorescein leakage. By 4 weeks, hyperfluorescent dots consistent with microaneurysms appeared and increased in number until 8 weeks postinjection. Clinical findings did not change appreciably after 8 weeks. Elastase digestion showed microaneurysms of the retinal capillaries and no ischemia or pericyte ghosts. Quantitative analysis of the digested specimens showed increased endothelial density by 1 month after injection (P < 0.05). Transmission electron microscopic cross-sections of capillaries showed significant basement membrane thickening by 3 months (P < 0.05). Lower doses of IGF-1 showed fewer clinical and histopathologic changes, and no significant changes were noted with a single 6 microg injection. Suspending hrIGF-1 in acidic buffer produced less intraocular inflammation than use of bovine serum albumin at neutral pH.

CONCLUSIONS

A single intravitreous injection of a large dose of hrIGF-1 produces a retinal microangiopathy that has a prolonged time of onset and remains stable from 2 to 6 months after injection. Some aspects of this angiopathy resemble diabetic retinopathy, suggesting growth factor effects in the morphologic vascular changes of diabetes.

Production and physiological actions of anandamide in the vasculature of the rat kidney

The endogenous cannabinoid receptor agonist anandamide is present in central and peripheral tissues. As the kidney contains both the amidase that degrades anandamide and transcripts for anandamide receptors, we characterized the molecular components of the anandamide signaling system and the vascular effects of exogenous anandamide in the kidney. We show that anandamide is present in kidney homogenates, cultured renal endothelial cells (EC), and mesangial cells; these cells also contain anandamide amidase. Reverse-transcriptase PCR shows that EC contain transcripts for cannabinoid type 1 (CB1) receptors, while mesangial cells have mRNA for both CB1 and CB2 receptors. EC exhibit specific, high-affinity binding of anandamide (Kd = 27.4 nM). Anandamide (1 microM) vasodilates juxtamedullary afferent arterioles perfused in vitro; the vasodilation can be blocked by nitric oxide (NO) synthase inhibition with L-NAME (0.1 mM) or CB1 receptor antagonism with SR 141716A (1 microM), but not by indomethacin (10 microM). Anandamide (10 nM) stimulates CB1-receptor-mediated NO release from perfused renal arterial segments; a similar effect was seen in EC. Finally, anandamide (1 microM) produces a NO-mediated inhibition of KCl-stimulated [3H]norepinephrine release from sympathetic nerves on isolated renal arterial segments. Hence, an anandamide signaling system is present in the kidney, where it exerts significant vasorelaxant and neuromodulatory effects.

Nitric oxide-mediated vasorelaxation induced by sodium polyoxyethylene laurylether sulfate

Ingestion of surfactants is known to cause hemodynamic changes with decreased total vascular resistance. Motivated by this clinical observation, we investigated the direct effects of a common anionic surfactant, sodium polyoxyethylene laurylether sulfate (LES), on isolated ring segments of rat thoracic aorta. LES did not produce any vasocontractile responses, but relaxed ring segments precontracted with 10(-6) M phenylephrine in a concentration-dependent manner. This LES-induced vasorelaxation was significantly reduced by the removal of endothelium or pretreatment with N(G)-nitro-L-arginine methylester hydrochloride, methylene blue, or oxyhemoglobin to the same degree, but was not affected by pretreatment with indomethacin. A further study measuring NO2- plus NO3- (NO(x), total metabolites of NO) in the medium of calf pulmonary artery endothelial (CPAE) cells, a cultured cell line, revealed that LES caused a significant increase in NO(x) production. On the other hand, in a study measuring intracellular Ca2+ in fura-2-loaded CPAE cells, LES caused a significant increase in intracellular Ca2+. These results suggest that LES causes endothelium-dependent vasorelaxation via a NO-mediated signaling pathway, which might be due to Ca2+ mobilization.

Modulation of renal hemodynamics by IGF-1 is absent in spontaneously hypertensive rats

We recently reported that attenuation of vasoactive agent-induced calcium signal and cell contraction of mesangial cell by insulin-like growth factor 1 (IGF-1), observed in normal mesangial cells, is totally abolished in spontaneously hypertensive rat (SHR) mesangial cells. This phenomenon might be related to the well-known aberrant regulation of SHR glomerular hemodynamics. Since it has been reported that in vivo IGF-1 infusion increases renal plasma flow (RPF) and glomerular filtration rate (GFR), we examined whether the modulation of renal function by IGF-1 is altered in SHR. We performed in vivo renal clearance studies using eight-week-old SHR and control Wistar Kyoto rats (WKY) before and after IGF-1 (5 micrograms/kg) infusion into the left renal artery for 20 minutes. Mean arterial pressure was not affected by IGF-1 in both WKY and SHR. In WKY, IGF-1 increased GFR and RPF, and decreased renal vascular resistance (RVR). However, GFR, RPF, and RVR were not altered by IGF-1 in SHR, while systemic infusion of angiotensin II antagonist, CV-11974, increased GFR and RPF. The present data show that the modulation of renal hemodynamics by IGF-1 is absent in SHR. This might be related the pathophysiology of the development of hypertension.

Evaluation of an electrochemical microprobe for direct NO measurement in the rat gastric fundus

Nitric oxide (NO) is an inhibitory nonadrenergic, noncholinergic (NANC) neurotransmitter in the rat gastric fundus and is released upon electrical or pharmacological stimulation of the inhibitory NANC neurons. In this study, it was attempted to measure the release of NO from the rat gastric fundus upon electrical stimulation or administration of nicotine directly via an electrochemical probe (ISO-NO). The system was evaluated by adding exogenous NO. Addition of exogenous NO induced concentration-dependent relaxation of the rat gastric fundus and an increase in the ISO-NO probe baseline current. The concentration of NO detected by the ISO-NO probe was lower than the concentration of NO administered. When no tissue was present, higher concentrations of NO were detected than in the presence of a tissue. In the absence of 95% O2/5% CO2 the concentration of NO detected was highest. Electrical stimulation induced relaxations of the rat gastric fundus which were reduced by NG-nitro-L-arginine methylester (L-NAME). An increase in the ISO-NO probe baseline current was also observed, but this was duc to nonspecific effects as the response also occurred without a tissue present and was not sensitive to L-NAME. Nicotine induced relaxations, which were reduced by L-NAME, but the ISO-NO probe baseline current remained unaltered, even in the presence of L-arginine plus superoxide dismutase. It can be concluded that it is not possible to detect directly the NO release from the rat gastric fundus upon electrical or pharmacological stimulation of the NANC neurons with the ISO-NO probe.

Nutritional modulation of somatotropic axis-cytokine relationships in cattle: a brief review

The objective of this review is to summarize data on the interrelationships that exist between nutrition, the endocrine system and their modulation of plasma tumor necrosis factor-alpha responses to endotoxin in cattle. During stress, intake of nutrients often is compromised and a percentage of available nutrients are diverted away from growth processes to stabilize other physiological processes of a higher survival priority. Management practices that minimize the magnitude and duration of disease stress will aid in speeding the return to homeostatic equilibrium. However, the shift away from growth during stress is almost inevitable as a mechanism to survive. Some degree of control and management of the metabolic cost of disease stress involves understanding the integration of nutritional, endocrine and immune signals by cells and working with the natural homeostatic processes. Endocrine hormones and immune system cytokine signals participate in redirecting nutrient use during disease stress. In an intricate interplay, hormones and cytokines regulate, modify and modulate each other's production and tissue interactions to alter metabolic priorities. Levels of dietary protein and energy intake affect patterns of hormones and cytokines in the blood after endotoxin challenge and further modulate the biological actions of many of these regulatory effectors. In vivo, administration of growth hormone to young calves has significant effects to decrease the many specific physiological responses to endotoxemia. Many aspects of nutrition can attenuate or facilitate this effect.

Permissive role of nitric oxide in endothelin-induced migration of endothelial cells

Endothelin (ET) synthesis is enhanced at sites of ischemia or in injured vessels. The purpose of this study was to explore the possibility of autocrine stimulation of endothelial cell migration by members of the endothelin family. Experiments with microvascular endothelial cell transmigration in a Boyden chemotactic apparatus showed that endothelins 1 and 3, as well as a selective agonist of ETB receptor IRL-1620, equipotently stimulated migration. Endothelial cell migration was unaffected by the blockade of ETA receptor, but it was inhibited by ETB receptor antagonism. Based on our previous demonstration of signaling from the occupied ETB receptor to constitutive nitric oxide (NO) synthase (Tsukahara, H., Ende, H., Magazine, H. I., Bahou, W. F., and Goligorsky, M. S. (1994) J. Biol. Chem. 269, 21778-21785), we next examined the contribution of ET-stimulated NO production to endothelial cell migration. In three independent cellular systems, 1) migration and wound healing by microvascular endothelial cells, 2) wound healing by Chinese hamster ovary cells stably expressing ETB receptor with or without endothelial NO synthase, and 3) application of antisense oligodeoxynucleotides targeting endothelial NO synthase in human umbilical vein endothelial cells, an absolute requirement for the functional NO synthase in cell migration has been demonstrated. These findings establish the permissive role of NO synthesis in endothelin-stimulated migration of endothelial cells.

Temporal activation of Ca2+-calmodulin-sensitive protein kinase type II is obligate for adipogenesis

Differentiation of 3T3-L1 embryonic fibroblasts to adipocytes in response to induction by dexamethasone and isobutylmethylxanthine is blocked by inhibitors of Ca2+-calmodulin-sensitive protein kinase type II, but not by inhibitors of protein kinase A or protein kinase C. CaM kinase II displays a biphasic increase in autonomous activity, rising after an initial transient peak from 1 to 15 h, declining at 24 h, followed by a sustained rise from 24 to 48 h, which is 2. 5-fold greater than basal values at induction of adipogenesis. Adipogenesis was blocked effectively by CaM kinase II inhibitors, either KN-62 or KN-93, if the inhibitors are introduced at 6 h and maintained until 12 h of induction of adipogenesis. Equally effective, however, is inhibition of CaM kinase II activity at 24-48 h after induction, during the later phase of autonomous CaM kinase activity. Inhibition of cultures with KN-62 or KN-93 either for 0 to 6 h or for 12 to 24 h failed to influence adipogenesis. Two temporally-distinct phases of CaM kinase II activation, either 6 to 12 h or 24 to 48 h, if inhibited with either KN-62 or KN-93, blocked the conversion to adipocytes. Thus, a biphasic activation of CaM kinase II is obligate for the progression of the embryonic fibroblasts to adipocytes. Inhibition of either phase of CaM kinase activity blocks adipogenesis and expression of several intermediate early gene products.

Insulin like growth factor 1 increases vascular smooth muscle nitric oxide production

Insulin like growth factor 1 (IGF-1) vasodilates, increases blood flow and lowers blood pressure; nitric oxide (NO) has been suggested to mediate some of these effects. We studied the role of IGF-1 in the regulation of NO production in vascular smooth muscle cells (VSMC). IGF-1 induced a concentration and time-dependent increase in NO release from endothelium-denuded aortic rings. Pre-incubation with cycloheximide or aminoguanidine blocked IGF-1-stimulated NO release. In addition, a six-fold increase in NO production by VSMC was seen upon incubation with IGF-1. These results suggest that IGF-1 induces NO release in VSMC through a process that involves new protein synthesis and the inducible isoform of nitric oxide synthase.