Stimulation of DNA synthesis in rat A10 vascular smooth muscle cells by threonine-59 insulin-like growth factor I

Does paced breathing improve the reproducibility of heart rate variability measurements?

The effects of paced breathing (PB) on the reproducibility of heart rate variability (HRV) measurements were examined in 55 male subjects (age range: 20-54 years). Spectral components of HRV were measured under a combination of two respiratory conditions (spontaneous and 4s PB) and two postures (standing and supine). The procedures were repeated 3 weeks after the first measurement. Log-transformed low-frequency (lnLF) and high-frequency (lnHF) components of HRV were calculated from a 205s electrocardiography (ECG) recording. The coefficients of interindividual variations of lnHF and lnLF (ca. 13-16%) and the intraindividual variations of the frequency components (5-6%) were not significantly affected by PB. The coefficients of intraindividual variation of heart rate, ln HF and ln LF did not correlate with age in either posture. Effect sizes of PB on the intraindividual variation ranged from -0.04 to 0.13. Although intraclass correlation coefficients (ICCs) were slightly improved by PB in some cases, the differences were negligible. The above results suggest that PB provides a limited improvement in the reproducibility of HRV measurements, and metronome-guided respiration is not necessarily required for HRV measurement if subjects are reminded to avoid irregular respiration.

Unpleasantness and physiological responses in using sanitary napkins

This study investigated the physiological and psychological effects of sanitary napkins (SN) on women in hemorrhage treatment during the menstrual phase. Mesh and non-woven napkins were employed, and the effects were studied during the follicular and menstrual phases; mesh SN presented a higher textural surface-roughness. In both phases, the increases in systolic and diastolic blood pressure were significantly dependent on the application intervals. The low-frequency component of systolic blood pressure variability significantly increased, while the salivary secretion rate decreased with the use of mesh SN during the follicular phase compared with non-woven SN. In addition, the heart rate during the menstrual phase significantly increased in subjects after the replacement of mesh SN compared with non-woven SN. In cases of wearing the unpleasant mesh SN, electroencephalography (EEG) manifested bilateral enhancements in beta and alpha2 waves in the frontal areas increased arousal level during both phases. From the above findings, napkin use increased physiological loading and wearing napkins with higher textural surface-roughness tended to increase activities of the autonomic nervous system and brain arousal level.

Specific Physiological Responses in Women with Severe Primary Dysmenorrhea during the Menstrual Cycle

This study examined the specific physiological responses of women with primary dysmenorrhea during the severely painful menstrual (days 1-2 of menstruation) and the non-painful follicular phases (days 5-8 after the onset of menstruation). Subjects consisted of 10 severe primary dysmenorrheic (Group P) and 10 non-dysmenorrheic women (Group C) with regular menstrual cycles. However, only 9 out of 10 and 8 out of 10 subjects of Groups P and C participated during the follicular phase. Physiological measures were taken in a resting state for 60 min. In the menstrual phase, the pain ratings and secretory immunoglobulin A (s-IgA) concentrations of Group P were significantly higher than those of Group C, with relatively significant decreases in the leg-skin temperature in the former as well. In addition, the systolic (SBP) and diastolic blood pressure (DBP) at 45 min after rest in Group P were significantly higher than those found in Group C. These reactions strongly suggest activation of the sympathetic-adrenal-medullary axis (SAM axis) by painful stress. Furthermore, the low-frequency (LF) component of the SBP variability (SBPV) was significantly higher in Group P than Group C, even during the follicular phase. These findings imply that Group P may well have elevated activities of the SAM axis throughout the whole menstrual cycle. As such, it suggests that dysmenorrheic women may be affected by certain stressors other than pain per se and pain-derived emotions throughout the whole menstrual cycle. The findings also indicate that women with dysmenorrhea have more sensitive responses to the SAM system than non-dysmenorrheic women during stress. Moreover, the high-frequency (HF) component of heart rate variability (HRV), or the index for the vagus nerve activity, displayed a consistently higher value in Group P than C. It is postulated that the human body may have responded to pain in an attempt to maintain the homeostatic state by enhancing vagus nerve activity.

Effects of laughing and weeping on mood and heart rate variability

We investigated the effects of laughing and weeping induced by watching comedy and tragedy videos on mood and autonomic nervous function. Ten healthy female subjects volunteered for the experiment. Chest electrocardiogram and respiration curve were recorded before, after, and during watching a comedy or a tragedy video. We also asked them to fill out profiles of mood states (POMS) to evaluate their mood states while watching videos. Autonomic nervous function was estimated by spectral analysis of heart rate variability (HRV). All subjects more or less laughed and wept while watching comedy and tragedy videos, respectively. Anger-hostility score of the POMS decreased and vigor score increased significantly after watching comedy videos, while depression-dejection score increased significantly after watching tragedy ones. Although both contents tended to increase a low to high frequency component ratio (LF/HF ratio) of HRV, the time course of responses was different. The LF/HF ratio which reflects cardiac sympathovagal balance increased immediately after they started watching comedy videos, and returned to the basal level right after they stopped watching, whereas the LF/HF ratio increased gradually to a lesser extent while watching tragedy videos. In contrast, the high-frequency component which reflects cardiac parasympathetic nerve activity gradually decreased while watching both videos but did not return to the basal level after watching tragedy ones. These results suggest that laughing has strong but transient effects on the autonomic nervous system, while weeping or feeling sad has moderate but sustained effects on it.

Differential regulation of Na+/H+ exchange and DNA synthesis in vascular smooth muscle cells

Na+/H+ exchange has been proposed to be involved in the regulation of cell growth. However, little is known about the regulatory pathway and relationship between Na+/H+ exchange and DNA synthesis. In vascular smooth muscle cells, platelet-derived growth factor (a tyrosine kinase-coupled receptor agonist) and thrombin (a G protein-coupled receptor agonist) stimulate both activation of Na+/H+ exchange and DNA synthesis. In this study, we compared the effect of platelet-derived growth factor (PDGF) and thrombin on the signal transduction pathway leading to the activation of these responses in A10 cells, clonal rat thoracic aortic smooth muscle cells. To investigate the role of mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3-kinase as potential mediators, we examined the effect of pharmacological kinase inhibitors on these responses. The Na+/H+ exchange activity induced by thrombin was inhibited by a specific inhibitor of MAPK kinase, 2'-amino-3'-methoxyflavone (PD98059), but was not affected by a specific phosphatidylinositol-3-kinase inhibitor, 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002). Thrombin-induced DNA synthesis was inhibited by LY294002, but not by PD98059. In contrast, the Na+/H+ exchange activity induced by PDGF was inhibited by neither LY294002 nor PD98059, but PDGF-induced DNA synthesis was inhibited by both LY294002 and PD98059. These data suggest that, in A10 cells, Na+/H+ exchange activation and DNA synthesis are differently regulated by the two extracellular stimuli.

Cyclic stretch regulates autocrine IGF-I in vascular smooth muscle cells: implications in vascular hyperplasia

Vascular smooth muscle cells (VSMC) subjected to acute or chronic stretch display enhanced growth rates in vitro and in vivo. Clinical examples of vascular hyperplasia (e.g., systolic hypertension and postinjury restenosis) suggest that local insulin-like growth factor I (IGF-I) expression is enhanced. Therefore, we investigated the role of in vitro cyclic stretch on rat VSMC IGF-I secretion and cellular growth. In serum-free medium, cyclic stretch (1 Hz at 120% resting length for 48 h) stimulated thymidine incorporation approximately 40% above that seen in nonstretched cells. Graded stretch magnitude (100-125% resting length) yielded graded increases in VSMC growth. Exogenous IGF-I increased growth of serum-starved, nonstretched VSMC in a dose-dependent manner, with maximal growth seen with 10(-7) M. IGF-I secretion from stretched cells was 20- to 30-fold greater than from those cells cultured in a static environment. Stretch-induced increases in growth were completely blocked on addition of anti-IGF-I and partially blocked with platelet-derived growth factor (PDGF) antibodies and with a tyrosine kinase inhibitor (tyrphostin-1). Finally, blockade of stretch-activated cation channels with GdCl3 profoundly inhibited stretch-induced growth. We conclude that stretch increases VSMC IGF-I secretion and that such autocrine IGF-I is required for stretch-induced growth. PDGF and stretch-sensitive cation channels are likely additional components of a complex pathway that regulates stretch-induced VSMC seen in systolic hypertension and postinjury restenosis.

Enhanced secretion of insulin plays a role in the development of atherosclerosis and restenosis of coronary arteries: elective percutaneous transluminal coronary angioplasty in patients with effort angina

OBJECTIVES

We investigated the relation between insulin and coronary atherosclerosis and restenosis of the coronary arteries, by performing elective percutaneous transluminal coronary angioplasty (PTCA).

BACKGROUND

Insulin is known to promote atherosclerosis of the arteries and has been implicated in the development of restenosis after PTCA.

METHODS

Of 210 angina patients who underwent PTCA, newly detected lesions in 35 consecutive nondiabetic subjects without previous intervention on the same main coronary arteries were analyzed after a 75-g oral glucose tolerance test (OGTT) and follow-up coronary angiography. Atherosclerotic lesions were evaluated by pattern, severity and extent. Restenosis was defined as loss of gain, the percentage of loss of the initial gain in the coronary diameter achieved by PTCA > or = 50%.

RESULTS

Patients with restenosis had a significantly higher extent index (a marker of atherosclerosis), insulin area, ratio of insulin area to glucose area, insulinogenic index and minimal lumen diameter after PTCA than those without restenosis (p=0.001, 0.011, 0.002, 0.016 and 0.041, respectively). Simple regression analysis revealed that only the ratio of insulin area to glucose area (a relative marker of enhanced insulin secretion) significantly correlated with the extent index (p=0.035). Extent index, insulin area, the ratio of insulin area to glucose area and insulinogenic index significantly correlated with loss of gain (p=0.001, 0.010, 0.002 and 0.032, respectively). Stepwise multiple regression analyses revealed that extent index and the ratio of insulin area to glucose area significantly correlated with loss of gain.

CONCLUSIONS

Enhanced secretion of insulin during the OGTT might be useful as a predictor of coronary atherosclerosis and of restenosis after elective PTCA in nondiabetic patients with effort angina.

Normalization of respiratory sinus arrhythmia by factoring in tidal volume

The amplitude of respiratory sinus arrhythmia (RSA) was measured in eight healthy young male students with special reference to the effect of tidal volume (Vt). Under simultaneously controlled respiratory frequency and Vt, the heart rate variability (HRV) of the subjects was measured. While the respiratory frequency was adjusted to either 0.25 or 0.10 Hz, the Vt was controlled at 13 different volumes for each frequency. Linear relationships between RSA amplitude and Vt were observed and close correlations were obtained for 0.25 Hz compared with 0.10 Hz. However, regression equations showed a marked variation among subjects. Furthermore, RSA amplitude was related to vital capacity. Subjects who had lower vital capacity tended to show higher RSA amplitudes at the same Vt. Therefore, the ratio (% Vt) of Vt to vital capacity is a more effective index in normalizing RSA than raw tidal volume. From these results, we have proposed a normalized RSA (RSA amplitude/% Vt) as a new index of autonomic activity that provides a constant value regardless of Vt.

Insulin is required for angiotensin II-mediated hypertrophy of smooth muscle cells

The prevalence of hypertension and atherosclerosis among subjects with hyperinsulinemia supports the premise of a direct metabolic link between insulin and angiotensin II at the cellular level. In the present study, the effect of insulin on the angiotensin II-induced growth of A10 smooth muscle cells (SMC) was investigated. Treatment of quiescent A10 cells with angiotensin II caused an increase in RNA synthesis, proto-oncogene c-fos mRNA levels and cell size dependent upon pretreatment with insulin. The insulin requirement was independent of its actions as a growth factor, since a pre-treatment of at least 24 h with insulin was essential for growth stimulation by angiotensin II. Using RT-PCR, insulin was shown to regulate AT2 receptor expression in both quiescent and differentiating cells. These data suggest the AT2 receptor, which mediates the growth effects of angiotensin II in A10 cells, may be the critical target for the effect of insulin.

Somatostatin, growth hormone, insulin-like growth factor-1, and diabetes: friends or foes?

Major findings with regard to the somatostatin-growth hormone (GH)-insulin-like growth factor (IGF-1) axis and diabetes are summarized. GH hypersecretion and reduced circulating IGF-1 levels are prevalent in insulin-dependent diabetes. Somatostatin improves metabolism in insulin-dependent diabetics. Insulin resistance and poor metabolic regulation, which may partly be due to hypersecretion of GH, are believed to accelerate the development of diabetic angiopathy. Diabetic hypersomatotrophinemia may be due to hepatic resistance to GH and increased hepatic production of IGF-1-binding protein-1 (IGFBP-1), leading to reduced levels of circulating IGF-1 and further stimulation of GH production. Studies in vitro and in diabetics suggest a causal link between diabetic hypersomatotrophinemia and diabetic angiopathy. In vitro evidence for the involvement of IGF-1 in diabetic angiopathy is reviewed. Also reviewed is evidence, from rat and human studies, of the possible involvement of GH and IGF-1 in diabetic nephropathy. The role of somatostatin in late diabetic vascular complications remains to be elucidated.

Postural effect on respiratory sinus arrhythmia with various respiratory frequencies

Heart rate variations during steady state respiration with various frequencies were studied on seven healthy male students at two different body positions. Respiration was controlled at four different frequencies (0.083, 0.100, 0.200, 0.250Hz), and the tidal volume was simultaneously controlled at 1500ml (0.083, 0.100Hz) or 1000ml (0.200, 0.250Hz). A tilting bed was used for changing body position, and the measurements were conducted at horizontal and vertical position. RSA (respiratory sinus arrhythmia) amplitude at 0.250Hz was significantly decreased at vertical position compared with horizontal position. At 0.200Hz the significant decrease could not be obtained although some tendency of decrease appeared. Contrary to these high frequencies, the amplitudes at low frequencies (0.083, 0.100Hz) were significantly increased (p < 0.01) during vertical position. This postural effect on the low frequency RSA could be regarded as a similar result on MWSA (Mayer wave relate sinus arrhythmia) which reflects sympathetic nervous activity. Furthermore, the ratio between the amplitude at 0.100Hz and that at 0.250Hz was significantly correlated with mean heart rate (n = 56, r = 0.73). From these results it was assumed that the RSA amplitude at low frequency associate a with not only parasympathetic nerves but also sympathetic nerves whereas the amplitude at high frequency was solely mediated by parasympathetic nerves.

Regulation of alternative splicing of protein kinase C beta by insulin

Insulin regulates a diverse array of cellular signaling processes involved in the control of growth, differentiation, and cellular metabolism. Insulin increases glucose transport via a protein kinase C (PKC)-dependent pathway in BC3H-1 myocytes, but the function of specific PKC isozymes in insulin action has not been elucidated. Two isoforms of PKC beta result via alternative splicing of precursor mRNA. As now shown, both isoforms are present in BC3H-1 myocytes, and insulin induces alternative splicing of the PKC beta mRNA thereby switching expression from PKC beta I to PKC beta II mRNA. This effect occurs rapidly (15 min after insulin treatment) and is dose-dependent. The switch in mRNA is reflected by increases in the protein levels of PKC beta II. High levels of 12-0-tetradecanoylphorbol-13-acetate, which are commonly used to deplete or down-regulate PKC in cells, also induce the switch to PKC beta II mRNA following overnight treatment, and protein levels of PKC beta II reflected mRNA increases. To investigate the functional importance of the shift in PKC beta isoform expression, stable transfectants of NIH-3T3 fibroblasts overexpressing PKC beta I and PKC beta II were established. The overexpression of PKC beta II but not PKC beta I in NIH-3T3 cells significantly enhanced insulin effects on glucose transport. This suggests that PKC beta II may be more selective than PKC beta I for enhancing the glucose transport effects of insulin in at least certain cells and, furthermore, that insulin can regulate the expression of PKC beta II by alternative mRNA splicing.

Mechanism of anti-proliferation caused by YC-1, an indazole derivative, in cultured rat A10 vascular smooth-muscle cells

An indazole derivative, YC-1, was identified in this study to be capable of reversibly and effectively inhibiting proliferation of rat A10 vascular smooth-muscle cells (VSMCs) in vitro. YC-1 (1-100 microM) dose-dependently inhibited [3H]thymidine incorporation into DNA in rat A10 VSMCs that were synchronized by serum depletion and then restimulated by addition of 10% foetal calf serum (FCS), whereas FCS-induced [3H]thymidine incorporation into rat synchronized endothelial cells was unaffected by this agent. The dose of YC-1 required to cause inhibition of FCS-induced proliferation was similar to that necessary for the formation of cellular cyclic GMP (cGMP). Guanylate cyclase activity in soluble fractions of VSMCs was activated by YC-1 (1-100 microM), whereas cGMP-specific phosphodiesterase activity was unaffected by this compound. The anti-proliferative effect of YC-1 was mimicked by 8-bromo-cGMP, a membrane-permeable cGMP analogue, and was antagonized by KT 5823 (0.2 microM), a selective inhibitor of protein kinase G. The anti-proliferative effect of YC-1 was also antagonized by Methylene Blue (50 microM), a guanylate cyclase inhibitor, and was potentiated by 3-isobutyl-1-methylxanthine (500 microM), a phosphodiesterase inhibitor. These results verified that YC-1 is a direct soluble guanylate cyclase activator in A10 VSMCs, and the anti-proliferative effect of YC-1 is mediated by cGMP. YC-1 still inhibited FCS-induced DNA synthesis even when added 10-18 h after restimulation of the serum-deprived A10 VSMCs with 10% FCS. Flow cytometry in synchronized populations revealed an acute blockage of FCS-inducible cell-cycle progression at a point in the G1/S-phase in YC-1 (100 microM)-treated cells. The inhibition of proliferation by YC-1 was demonstrated to be independent of cell damage, as documented by several criteria of cell viability. In conclusion, YC-1 reversibly and effectively inhibited the proliferation of VSMCs, suggesting that it has potential as a therapeutic agent in the prevention of vascular diseases.

Synergistic interactions between selective pharmacological inhibitors of phosphodiesterase isozyme families PDE III and PDE IV to attenuate proliferation of rat vascular smooth muscle cells

The interaction between selective inhibitors of 3',5'-cyclic-nucleotide phosphodiesterase (PDE) III (cyclic GMP inhibited phosphodiesterase) and selective inhibitors of PDE IV (Ro 20-1724 inhibited phosphodiesterase) to attenuate fetal bovine serum-stimulated incorporation of [3H]thymidine into DNA and cell proliferation was studied in a line (A10) of vascular smooth muscle cells (VSMC). The nonselective PDE inhibitors 3-isobutyl-1-methylxanthine (IBMX) and papaverine attenuated DNA synthesis with EC50 values (16 and 18 microM, respectively) in the same range as their published IC50 values (2-50 and 2-25 microM, respectively) as PDE inhibitors. The selective PDE III inhibitors CI-930 and cilostamide used alone attenuated DNA synthesis with EC50 values (> 300 and 5.3 microM, respectively) that were much higher than published IC50 values (0.15-0.46 and 0.005-0.064 microM, respectively) for inhibition of PDE III. In the presence of the PDE IV inhibitor rolipram (10 microM), their EC50 values were shifted (0.66 and 0.16 microM, respectively) much closer to their respective IC50 values. When the selective PDE IV inhibitors rolipram and Ro 20-1724 were used alone, they attenuated DNA synthesis with EC50 values (111 and > 100 microM, respectively) much higher than their IC50 values (0.6-2.6 and 2-13 microM, respectively) as inhibitors of PDE IV, but 10 microM CI-930 (PDE III inhibitor) shifted their EC50 values (0.56 and 1.5 microM, respectively) much closer to their IC50 values. In experiments that assessed VSMC proliferation using the MTT [3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide] method, IBMX and papaverine attenuated proliferation with EC50 values (27 and 58 microM, respectively) close to their IC50 values. CI-930 and cilostamide used alone did not cause 50% attenuation of proliferation at the highest concentrations tested (100 and 10 microM, respectively). In the presence of 5 microM rolipram, however, their effects were enhanced greatly with EC50 values (0.86 and 0.23 microM, respectively) that were close to their IC50 values as PDE III inhibitors. Similarly, rolipram and Ro 20-1724 attenuated VSMC proliferation with EC50 values close to their IC50 values in the presence (2.1 and 4.6 microM, respectively) but not in the absence (> 100 and > 10 microM, respectively) of 2 microM CI-930. The interactions between PDE III inhibitors and PDE IV inhibitors to attenuate DNA synthesis and VSMC proliferation were synergistic as determined by the combination index. The data demonstrate that the synergistic interactions that attenuate incorporation of [3H]thymidine into DNA are accompanied by synergistic attenuations of VSMC division.(ABSTRACT TRUNCATED AT 400 WORDS)

Relation of restenosis after excimer laser angioplasty to fasting insulin levels

Several studies have shown that diabetes mellitus increases the risk of restenosis after coronary intervention, but the role of insulin in restenosis has not been defined. The relation between fasting insulin levels and restenosis was evaluated prospectively at 6-month angiographic follow-up in 70 patients undergoing excimer laser coronary angioplasty of 75 lesions. Restenosis (> 50% diameter narrowing on quantitative angiography) was observed at 37 of 75 treated sites (49%). Although patients with glucose intolerance and noninsulin-dependent diabetes mellitus showed a trend toward increased restenosis (restenosis rate 69%; odds ratio for restenosis 2.7 [95% confidence interval 0.76, 9.82]; p = 0.124), those with increased fasting insulin levels > 15 muU/ml had reduced restenosis (restenosis rate 24%; odds ratio 0.22 [0.07, 0.67]; p = 0.008). Other factors including fasting serum glucose, glycated hemoglobin and lipoprotein fraction were not predictive of restenosis. The relation between insulin levels and restenosis after excimer laser angioplasty may provide insights into the biology of vascular injury and repair after coronary intervention.

In vivo proliferation of rat vascular smooth muscle in relation to diabetes mellitus insulin-like growth factor I and insulin

The roles of diabetes mellitus, insulin-like growth factor I and insulin in vascular smooth muscle proliferation in vivo were studied. Proliferation was induced by endothelial injury (balloon catheterization) of rat aorta, and was measured as 3H-thymidine incorporation into DNA. Levels of insulin-like growth factor I mRNA and insulin-like growth factor I receptor mRNA were measured with a solution hybridization assay. The increase in DNA synthesis was most pronounced 2 days after injury in both normal and diabetic rats and declined thereafter, but DNA synthesis in aortas from diabetic rats was lower throughout the time period studied. Levels of insulin-like growth factor I mRNA and the receptor mRNA were both increased in balloon catheterized aortas, and time-course studies showed an increase in receptor mRNA prior to the increase in insulin-like growth factor I mRNA. Diabetic rats were treated with equimolar concentrations of insulin (35 nmol/day) or insulin-like growth factor I (31 nmol/day) for 5 days. Insulin-like growth factor I increased DNA synthesis in injured aortas 2 days after injury without improving blood glucose, whereas the effect of insulin was associated with a decrease in blood glucose levels. In conclusion, vascular smooth muscle proliferation is impaired by diabetes and stimulated by insulin treatment. Insulin-like growth factor I infusion stimulates vascular smooth muscle proliferation without affecting blood glucose, and gene expressions of insulin-like growth factor I and its receptor are increased in proliferating vascular smooth muscle, indicating that insulin-like growth factor I and involved in vascular smooth muscle proliferation in vivo.

Prolactin induces proliferation of vascular smooth muscle cells through a protein kinase C-dependent mechanism

The effects of prolactin (PRL) on A10 (aortic smooth muscle) cell proliferation were examined by measuring both [3H]thymidine incorporation and increases in cell number. PRL induced a significant proliferative response from 10(-11) to 10(-7) M, with optimal activity at 10(-10) M. PRL also enhanced platelet-derived growth factor (PDGF)-induced proliferation. The possibility that PRL induces proliferation through a protein kinase C (PKC)-mediated mechanism was also examined. PRL caused activation of PKC from 10(-12) to 10(-8) M. Antiserum to PRL, a monoclonal antibody directed against the PRL receptor and the immunosuppressive agent cyclosporine A, were able to inhibit PRL-induced proliferation and activation of PKC. The PKC inhibitors, staurosporine, sphingosine, and 1-(-5-iso-quinoline-sulfonyl)-2-methylpiperazine (H-7) also antagonized both proliferation and PKC activation. These data strongly suggest that PRL-induced A10 cell proliferation is mediated through the PKC pathway and that this may play a role in vascular smooth muscle cell hyperplasia, characteristic of the pathogenesis of cardiovascular diseases such as hypertension and atherosclerosis.

Binding and biological effects of insulin, insulin analogues and insulin-like growth factors in rat aortic smooth muscle cells. Comparison of maximal growth promoting activities

Binding and growth promoting effects of insulin, insulin analogues modified in the B chain, proinsulin, insulin-like growth factor-I and -II were studied in cultured rat aortic smooth muscle cells. Specific binding of 125I-insulin was 0.9 +/- 0.2% of total 125I-insulin added, and the IC50-value was estimated to 8.9 pmol/l. The insulin analogue B10 Asp tended to be more potent than insulin in displacing 125I-insulin, B28 Asp was equipotent, B9 Asp/B27 Glu was approximately 100 times less potent and insulin-like growth factor-I more than 1000 times less potent than insulin. Specific binding of 125I-insulin-like growth factor-I after 4 h incubation at 10 degrees C was five times higher than the specific binding of insulin (4.4 +/- 0.4% of total 125I-insulin-like growth factor-I added), and the IC50-value was 0.3 nmol/l. Insulin was approximately 500 times less potent than insulin-like growth factor-I in displacing 125I-insulin-like growth factor-I. The insulin analogue B10 Asp was slightly more potent and analogue B28 Asp was equipotent with insulin. Analogue B9 Asp/B27 Glu was ten times less potent and proinsulin was more than ten times less potent than insulin. The order of potency was similar for 3H-thymidine incorporation into DNA: insulin-like growth factor-I greater than B10 Asp greater than insulin-like growth factor-II greater than insulin greater than or equal to B28 Asp greater than B9 Asp/B27 Glu greater than proinsulin. The maximal effect of insulin-like growth factor-I on 3H-thymidine incorporation was 71 +/- 16% higher than the maximal effect of insulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium influx modulates DNA synthesis and proliferation in A7r5 vascular smooth muscle cells

In A7r5 vascular smooth muscle cultures basal Ca2+ influx was higher in growing versus quiescent cells (P less than 0.05), due primarily to a five-fold increase in dihydropyridine-inhibitable Ca2+ influx (P less than 0.005). Verapamil decreased [3H]thymidine incorporation in a concentration dependent fashion with a significant 6 +/- 2% inhibition at 0.1 microM and a maximal inhibition of 67 +/- 2% at 100 microM. Similarly, nitrendipine inhibited fetal calf serum-stimulated [3H]thymidine incorporation with a threshold concentration of 1 nM and a maximal inhibition of 79 +/- 12% at 10 microM. In quiescent cells, verapamil (10 microM) inhibited the increases in [3H]thymidine incorporation stimulated by fetal calf serum, serotonin, vasopressin or 12-0-tetradecanoyl phorbol-13-acetate by 37-43% (P less than 0.001 vs. control for all). Finally, verapamil (100 microM) and nitrendipine (10 microM) inhibited proliferation by 39 +/- 10 and 20 +/- 6%, respectively (P less than 0.01 and 0.02 vs. control, respectively). Thus in A7r5 cells, proliferation is associated with increased Ca2+ influx via dihydropyridine-sensitive Ca2+ channels and organic Ca2+ channel antagonists inhibit DNA synthesis and cell proliferation.

Characterization of the increased biological potency in BALB/C 3T3 cells of two analogs of human insulinlike growth factor I which have reduced affinity for the 28 K cell-derived binding protein

We have characterized the biological activity of two analogs of insulinlike growth factor I (IGF I) which have significantly reduced affinity for the soluble 28 K binding proteins which are secreted by various cell types. The analogs, which were made by site-directed mutagenesis of a synthetic gene encoding for IGF I, are [Gln 3, Ala 4, Tyr 15, Leu 16] IGF I and an analog in which the first 16 amino acids of IGF I were replaced with the first 17 amino acids of insulin (B-chain mutant). These two peptides have 100-fold and greater than 1,000-fold lower affinity, respectively, than IGF I for the 28 K binding protein present in the conditioned medium of two cell types, the clonal rat vascular smooth muscle line A10, and BALB/C 3T3 cells. The 28 K protein secreted by BALB/C 3T3 cells has fivefold-lower apparent affinity for both IGF I and [Gln 3, Ala 4, Tyr 15, Leu 16] IGF I than does the 28 K protein secreted by A 10 cells. Conditioned medium from these two cell types has similar amounts of unoccupied 28 K protein as evidenced by the ability of 125I-IGF I to specifically bind to and be covalently bound to the protein after treatment with the bifunctional cross-linking reagent disuccinimidyl suberate. In the presence of 0.1% calf serum, IGF I and [Gln 3, Ala 4, Tyr 15, Leu 16] IGF I stimulate DNA synthesis in A10 cells with ED50 = 0.4 nM, and in BALB/C 3T3 cells with ED50 = 10 nM and 1.3 nM, respectively. Thus, these peptides are equipotent in A10 cells, but the mutant peptide is ten times more active than IGF I in BALB/C 3T3 cells. A10 cells can be made ten times less sensitive to IGF I by performing the incubation in the presence of conditioned media from BALB/C 3T3 cells but not from A10 cells. The activity of [Gln 3, Ala 4, Tyr 15, Leu 16] IGF I is not altered under these conditions. Thus, the conditioned media, which contain 28 K proteins secreted by A10 cells and BALB/C 3T3 cells, have different effects on the biological action of IGF I. These data suggest that the 28 K binding proteins can have important effects on the sensitivity of tissues to IGF I and that the B-chain mutant and [Gln 3, Ala 4, Tyr 15, Leu 16] IGF I will be useful in assessing the biological role of these proteins.

Expression, purification and characterization of recombinant human insulin-like growth factor I in yeast

Insulin-like growth factor I (IGF-I) is a 70 amino acid (aa) protein that is structurally similar and functionally related to insulin. We have inserted a synthetic gene coding for human IGF-I into a Saccharomyces cerevisiae expression vector utilizing the MF alpha 1 promoter and pre-pro leader peptide. This vector directs the expression and secretion of native, biologically active growth factor. Cleavage of the pre-pro alpha factor leader sequence in vivo results in the secretion of a 70-aa recombinant IGF-I molecule with the native N-terminal glycine residue. Human IGF-I purified from yeast culture supernatant is equipotent to serum-derived IGF-I in inhibiting [125I]IGF-I binding to type-I IGF receptors and crude human serum-binding proteins. Recombinant IGF-I is also equipotent to human IGF-I in the stimulation of DNA synthesis in rat aortic smooth-muscle cells. In contrast, yeast recombinant IGF-I is less potent than serum-derived IGF-I in binding to type-2 IGF receptors. The ability to produce native, biologically active IGF-I in yeast will allow the elucidation of binding domains through the expression and characterization of specific structural analogs.

Receptors for and effects of insulin and IGF-I in rat glomerular mesangial cells

Receptors for and biological effects of insulin and insulin-like growth factor I (IGF-I) were studied in cultured rat renal mesangial cells. Specific binding of 125I-IGF was over 200-fold greater (5.8%/0.2 mg cell protein) than the specific binding of 125I-insulin (0.2%/2 mg cell protein). Fifty percent inhibition of 125I-insulin binding was obtained with 8 x 10(-9) M unlabeled insulin. For 125I-IGF-I, 50% inhibition required 1.8 x 10(-9) M unlabeled IGF-I. 125I-IGF-I was also displaced by IGF-II and insulin but at 10-and 100-fold lower potencies, respectively, than IGF-I. Cross-linking of 125I-insulin and 125I-IGF-I to their receptors, using disuccinimidyl suberate (DSS), and identification of the receptor with sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography showed a band with a molecular mass of 135 kDa, probably corresponding to the alpha-subunit of the insulin receptor and a major band with a molecular mass of 145 kDa for the alpha-subunit of the IGF-I receptor. Both insulin and IGF-I stimulated the incorporation of [3H]thymidine into DNA. A half-maximal effect was obtained at 1.6 x 10(-8) M for insulin and 1.2 x 10(-9) M for IGF-I. No additive effect on DNA synthesis was observed. Insulin at 8 x 10(-10) M increased the accumulation of [14C]glucose in mesangial cells, whereas IGF-I was 10-fold less potent.

Expression of a synthetic gene encoding human insulin-like growth factor I in cultured mouse fibroblasts

A synthetic gene encoding human insulin-like growth factor I (hIGF-I) was assembled and inserted into an expression vector containing the cytomegalovirus immediate early (CMV-IE) transcriptional regulatory region and portions of the bovine growth hormone gene. The recombinant plasmid encodes a 97 amino acid fusion protein containing the first 27 amino acids of the bovine growth hormone precursor and the 70 amino acids of hIGF-I. This plasmid, when transiently introduced into cultured mouse fibroblasts, directs synthesis of the fusion protein, subsequent proteolytic removal of the bovine growth hormone signal peptide, and secretion of hIGF-I into the culture medium. Conditioned medium from transfected cells inhibits binding of 125I-labeled IGF-I to type I IGF receptors on human placental membranes and to acid-stable human serum carrier proteins. The recombinant hIGF-I produced is biologically active, as monitored by the stimulation of DNA synthesis in vascular smooth muscle cells.