The regulation of protein turnover in newborn rat heart cell cultures

Similar cardiovascular effects of growth hormone and insulin-like growth factor-I in rats after experimental myocardial infarction

Accumulating data show that growth hormone (GH) and insulin-like growth factor-I (IGF-I) have major effects on the cardiovascular system. In the present study we have directly compared GH and IGF-I in an in vivo rat model of experimental myocardial infarction. Four weeks after ligation of the left coronary artery, male rats were treated with recombinant human (rh) GH 1.1 mg/kg per day, rhIGF-I 3.0 mg/kg per day or saline s.c. for 2 weeks. Transthoracic echocardiography was performed before and after the treatment period. Both GH and IGF-I reduced total peripheral resistance (P< 0.01), end-systolic wall stress (P< 0.01) and end-systolic short-axis area (P< 0.001 and P< 0.05). GH also increased area fractional shortening (P< 0.05). Stroke volume (SV) and SV index were improved by IGF-I (P< 0.0001), and SV tended to be increased by GH (P= 0.12). In conclusion, GH and IGF-I had similar beneficial effects on systolic function and peripheral resistance after experimental myocardial infarction.

Anabolic and cardiovascular effects of recombinant human growth hormone in surgical patients with sepsis

The clinical and metabolic effects of 7 days of recombinant human growth hormone (rhGH) and total parenteral nutrition (TPN) in surgical patients with sepsis were determined in a randomized controlled trial. In patients with a mean(s.e.m.) pretreatment rate of net protein catabolism (NPC) of 1.5 g per kg per day or less rhGH treatment decreased NPC from 0.93(0.14) to -0.20(0.24) g per kg per day (n = 5; P < 0.0005) and rendered these patients anabolic. TPN alone decreased NPC from 1.12(0.11) to 0.61(0.11) g per kg per day (n = 5; P < 0.001). In patients with an initial NPC of more than 1.5 g per kg per day rhGH treatment decreased NPC from 2.72(0.12) to 1.08(0.24) g per kg per day (n = 5; P < 0.001) while TPN alone decreased it from 2.41(0.32) to 1.28(0.28) g per kg per day (n = 5; P < 0.005). Use of rhGH was not associated with any adverse effects or improvement in clinical course but did decrease the mean systolic and diastolic pressures during the study period. Thus rhGH is a useful anabolic agent and may have a role in the haemodynamic management of the catabolic patient with sepsis.

Contraction modulates the capacity for protein synthesis during growth of neonatal heart cells in culture

Neonatal ventricular myocytes that were incubated in a well-defined serum-free medium containing 50 mM KCl did not contract and maintained stable cell size, as assessed by the protein/DNA ratio. The present study utilized KCl-arrested cells to examine the effect of constant rates of synchronous contraction in normal [K+]o (4 mM) as a physiological stimulus for myocyte growth. Cell growth increased following the onset of contraction when measured over 3 days. The rate of protein synthesis was accelerated in parallel by contraction, but the rate of protein degradation remained similar to rates in noncontracting cells. The capacity for protein synthesis was estimated by total RNA content and was increased in contracting as compared with KCl-arrested cells. This increase was accompanied by faster rates of RNA synthesis as determined from the incorporation of [3H]uridine into RNA and the specific activity of the cellular UTP pool. The rate of RNA degradation was accelerated during contraction but the difference between the rates of RNA synthesis and degradation resulted in net RNA accumulation of 49% after 3 days. These data demonstrated that 1) contractile activity stimulated myocyte growth through an increased capacity for protein synthesis and 2) the increased capacity for protein synthesis involved acceleration of the rate of RNA synthesis. Since enhancement of protein synthetic capacity is a common feature of myocyte hypertrophy in vivo and in vitro, this model can be used to examine the regulation of ribosome synthesis during hypertrophic growth.

The effect of insulin and glucagon on systolic properties of the normal and septic isolated rat heart

Controversy exists in the literature concerning the effects of insulin and glucagon on cardiac muscle contractility, in particular during anoxia, ischemia or sepsis. The purpose of the present study was to determine the effects of insulin and glucagon on the systolic function of the normal and the dysfunctioning septic rat myocardium in the Langendorff preparation. In the normal isolated rat heart, neither insulin nor glucagon exhibited any lasting inotropic effect on systolic function or coronary flow. Sepsis (cecal ligation and puncture) resulted in a dramatic reduction of systolic function to 44% of control animals. All insulin-containing formulations tested improved systolic function in septic hearts by a mean of 85% compared to Krebs and glucose only. However, this improvement did not reach statistical significance compared to the use of Krebs and glucose only. Glucagon at 100 micrograms/l was doing as well as Krebs and glucose alone while at 1 mg/l glucagon was only able to maintain pre-perfusion contractility. Our results suggest that neither insulin nor glucagon seem to possess special inotropic properties for the isolated perfused normal or septic rat heart.

Effects of K+-deficiency and serum supplementation on protein turnover and nucleic acid synthesis in HeLa cells

When most of the K+ in a chemically defined medium was replaced with Rb+, cell growth of HeLa cells was strongly inhibited. The growth was partially but significantly restored by an addition of 5% dialyzed calf serum to the medium. The inhibition of cell growth in Rb+-substituted medium was partly due to suppression of protein synthesis by K+ deficiency, but the key mechanism of inhibition is still unknown. Rb+ substitution did not influence protein degradation or nucleic acid synthesis. The restoration of cell growth on addition of serum took place chiefly through stimulation of DNA synthesis. Protein and RNA syntheses were not affected by addition of serum, and serum-induced prevention of protein degradation was less in Rb+-substituted medium than in normal K+ medium.

Growth and differentiation of chicken embryo muscle cell cultures derived from fast- and slow-growing lines. Intrinsic differences in growth characteristics and insulin response

Primary myogenic cell cultures derived from 12-day embryos of genetically fast-growing chickens (fast cultures) and slow-growing chickens (slow cultures) were grown under identical conditions to examine differences in growth and differentiation at the cellular level. The two types of cultures exhibited significant (P less than 0.01) differences in proliferation, protein accumulation, response to the addition of insulin to the culture medium and the amount of insulin bound per nucleus. The fast cultures exhibited a larger number of both total nuclei and fused nuclei at 48, 72 and 96 h in culture, accumulated more protein per nucleus at 24, 48 and 72 h in culture and demonstrated a greater response to the addition of insulin to the culture medium, as reflected by increased fusion rate and protein accumulation at 24 h in culture. Maximal response to insulin in both types of cultures was obtained at 24 h to added insulin concentrations of 10(-10)-10(-9) M. Slow cultures bound more [125I]-insulin than fast cultures at 24 h in culture. These experiments suggest that different muscle growth potentials in animals of the same species are at least partly due to intrinsic cellular differences in the myogenic cells that give rise to adult muscle tissue.

Myocytes and fibroblasts exhibit functional synergism in mixed cultures of neonatal rat heart cells

Cardiac cells obtained from neonatal rat heart contain a mixed population of cell types that can be enriched in culture in either myocytes or fibroblast-like cells. A metabolic comparison of mixed heart cell cultures with enriched cultures of the same age-in-culture and initial cell density showed that mixed cultures used glucose more rapidly than either enriched myocytes or fibroblasts. Mixed cultures were shown to respond to deprivation of insulin and of serum with decreases in the rate of glucose usage and decreases in the protein content of cells, whereas enriched cultures did not respond in the expected manner to insulin deprivation. Mixed, 11-day-old cells also exhibited greater increases in cellular protein and greater resistance to the stress of starvation than enriched cultures. Palmitate usage, however, was similar in all cultures examined. We conclude that mixed cultures may serve as a better model system to study cardiac metabolism and to monitor the effects of drugs and hormones on the neonatal myocardium. In addition, it is clear from our results that myocytes and fibroblastic-like cells coexist in a metabolically functional synergism.

Measurement of steady state protein degradation in cultured human muscle cells

Double label techniques for measurement of protein turnover in cultured cells are described. In the isotope withdrawal method protein in cultured muscle is labeled with two isotopes of the same amino acid for 24 to 100 h, followed by exposure to fresh medium containing one isotope only at the same specific activity for an additional 24 to 48 h. In the isotope addition method the order of addition of single and double-labeled media is reversed. After incubation the ratio of the two isotopes in the cell protein is a function of the incubation time and the degradation rate constant KD; KD can readily be calculated using a graphical or iterative method. In mixed cultures of human muscle with initial incubation ranging 24 to 159 h, the KD's obtained from various incubation times were similar. Both the isotope withdrawal and the isotope addition methods gave a KD value of 0.018 h-1 similar to values obtained by two different single isotope methods which monitor the appearance of free isotope in the medium of previously labeled cells. There were no differences of KD values obtained in cultures of muscle from normal patients and those with denervation, inflammatory myopathies, or nonspecific myopathic biopsy changes. When proteins were separated by gel electrophoresis, those of molecular weight greater than 60,000 had higher average KD values as compared to lower molecular weight proteins. The double isotope labeling method has the advantage of being easily applied to cultures with small numbers of cells and is potentially useful in obtaining the degradation rates of individual cellular proteins. The major disadvantages are (1) in their present form the methods can be used only in steady state cultures and (2) they require rather long (24 h) labeling times.

Myocyte hypertrophy in neonatal rat heart cultures and its regulation by serum and by catecholamines

The role of hormones and other humoral factors in the regulation of myocardial hypertrophy has been difficult to evaluate. We asked whether myocardial cell hypertrophy could be demonstrated in cultures from the day-old rat ventricle and evaluated the effect of serum concentration and catecholamines on the growth process. Two single-cell preparations were used: serum-supplemented, bromodeoxyuridine-treated cultures and serum-free cultures with transferrin and insulin. Both preparations were characterized by myocardial cell predominance (about 75--80% of total cells) and constant cell numbers. Myocardial cell size was documented by photomicroscopy and quantified by volume (microscopic diameter of suspended cells), surface area (planimetry of attached cells), and total cell protein concentration (Lowry method and cell counts). Growth was also evaluated in pure nonmyocardial cell cultures. In cultures with 5% (vol/vol) serum, myocardial cell size increased 2- to 3-fold over 11 days in culture. Final volume, surface area, and protein concentration were about 3000 micrometer3/cell, 5000 micrometer2/cell, and 1500 pg/cell, respectively. Serum had a dose-related effect on myocardial cell hypertrophy; myocardial cell size increased about 4-fold when serum concentration was increased from 0% to 5% or 10%. Cells maintained in serum-free medium with transferrin and insulin (each 10 microgram/ml) did not hypertrophy, but did remain responsive to the growth-promoting activity of serum. Chronic exposure to isoproterenol or norepinephrine (1 microM) significantly stimulated myocardial cell hypertrophy. This stimulation was dose-related, was not blocked by equimolar propranolol, was not associated with a sustained chronotropic effect, and was more pronounced in the serum-free preparation. In pure cultures of nonproliferating (bromodeoxyuridine-treated) nonmyocardial cells, cell size also increased with time in culture, but variation in serum concentration and addition of norepinephrine had no significant effect on cell size. Myocardial cell hypertrophy occurs in culture and is regulated by variations in the culture medium, including serum, with its contained hormones and growth factors, and catecholamines. The culture preparation can be used to explore the regulation of myocardial cell hypertrophy by nonhemodynamic factors.

Insulin stimulation of protein synthesis in cultured skeletal and cardiac muscle cells

The effects of acute exposure to insulin on protein synthesis were examined in primary, differentiated cultures of embryonic chick heart and skeletal muscle cells. Synthetic rates were calculated using the specific activity of tRNA-bound leucine as precursor, a specific activity that was significantly less than that of extracellular leucine but greater than that of free, intracellular leucine at 0.2 mM external leucine. Insulin did not alter these relationships. Doses of insulin in the physiological range produced significant stimulation of protein synthesis in both cell types. Maximal responses, involving approximately 30% increases in both absolute and fractional rates, were observed at higher insulin concentrations. Significant stimulation by insulin was seen in cardiac cells after only 1 h of insulin treatment, and the effects of the hormone were observed both in the presence and absence of serum in the culture medium.