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M Bernier

Publications and source records attributed to M Bernier.

At least 91 records · Page 5Linked to original sources
PubMed1989

Ischemia-induced and reperfusion-induced arrhythmias: importance of heart rate.

The relationship between heart rate and ischemia-induced and reperfusion-induced arrhythmias was studied using 573 isolated rat hearts. Hearts (12/group), subjected to 7 min of coronary occlusion and 10 min reperfusion, were paced at 300, 330, 360, 390, 420, 480, or 540 beats/min. Pacing either throughout the experiment or during ischemia alone led to a rate-dependent increase in the incidence of reperfusion-induced ventricular fibrillation (VF) from 25% in the unpaced hearts to greater than 90% when the rate was 420 beats/min or higher. However, pacing during reperfusion alone did not increase the incidence of reperfusion-induced VF. In separate hearts, the right atrium was removed to permit examination of both low and high rates (167 +/- 2, 240, 336 +/- 3, or 480 beats/min throughout the experiment) over a wide range of durations of occlusion (3, 5, 7, 10, 15, 20, or 40 min). Ischemia-induced VF incidence was critically dependent on heart rate, low rates being protective. During reperfusion, the incidence of VF was also highly rate dependent if reperfusion was initiated within 10 min of the onset of ischemia (ranging from 8% when rate was 167 +/- 2 beats/min to 100% when rate was 480 beats/min) but was unrelated to heart rate when reperfusion occurred at later times (ranging from 33 to 50% when ischemia duration was 40 min). Heart rate can therefore influence susceptibility to ischemia- and reperfusion-induced arrhythmias, probably as a result of an effect on the rate of development of ischemic injury.

Animals↗
PubMed1989

Reperfusion arrhythmias: dose-related protection by anti-free radical interventions.

Isolated rat hearts (n = 15 per group) were subjected to regional ischemia (10 min) and reperfusion. Superoxide dismutase (SOD; 8 X 10(3), 2 X 10(4), 4 X 10(4), 6 X 10(4), 8 X 10(4), 1.2 X 10(5), or 1.6 X 10(5) IU/l) given early (i.e., throughout the experiment) reduced the incidence of reperfusion-induced ventricular fibrillation (VF), the dose-response characteristics describing an asymmetric U-shaped curve. The optimal dose of SOD (8 X 10(4) IU/l) reduced VF incidence from its control value of 87 to 27% (P less than 0.05). Given late (i.e., 2 min before reperfusion), this dose of SOD exerted a reduced but nonetheless significant antifibrillatory effect. Early administration of catalase (1 X 10(3), 1 X 10(4), 2.5 X 10(4), 5 X 10(4), 1 X 10(5), 1.5 X 10(5), or 1 X 10(6) IU/l) reduced VF incidence in a linear dose-dependent manner, from its control value of 87 to 7% with 1 X 10(6) IU/l (P less than 0.05). Late administration of this dose reduced VF incidence from its control value of 87 to 27% (P less than 0.05). Allopurinol (0.07, 0.15, 0.37, 0.73, 1.10, or 1.47 mM added to the perfusate throughout the experiment) significantly reduced VF incidence over a wide range of doses, but low and high doses were ineffective. Pretreatment with allopurinol (0, 0.01, 0.02, 0.05, 0.10, 0.20, or 0.50 g.kg-1.day-1 per os 48, 24, and 1 h before study) reduced VF incidence from its control value of 93 to less than 50% at several doses.(ABSTRACT TRUNCATED AT 250 WORDS)

Allopurinol↗
PubMed1989

Singlet oxygen-induced arrhythmias. Dose- and light-response studies for photoactivation of rose bengal in the rat heart.

In a study of aerobically perfused rat hearts, the in situ photoactivation (530-590 nm) of rose bengal (a process that leads to the production of singlet oxygen and superoxide) has been shown to lead to the rapid development of electrocardiographic abnormalities and arrhythmias. With rose bengal concentrations of 1,000, 500, 250, 100, and 50 nmol/l (n = 6/group), photoactivation (3,600 lx) led to electrocardiographic changes (inversion of the T wave, Q-T prolongation, or both) after 3.8 +/- 0.9, 4.5 +/- 0.7, 11.8 +/- 2.1, 24.8 +/- 3.9, and 65.3 +/- 6.0 seconds), respectively; ventricular premature beats occurred in 100% of hearts after 0.5 +/- 0.2, 1.1 +/- 0.3, 2.2 +/- 0.7, 4.4 +/- 0.8, and 6.6 +/- 1.2 minutes, respectively. Ventricular tachycardia occurred in 83%, 83%, 83%, 67%, and 50% of hearts after 2.1 +/- 0.2, 2.1 +/- 0.4, 2.8 +/- 0.7, 5.7 +/- 2.0, and 11.2 +/- 1.9 minutes, respectively, and complete atrioventricular block in 100%, 100%, 100%, 100%, and 67% of hearts after 3.8 +/- 0.7, 6.5 +/- 1.0, 5.5 +/- 0.9, 13.8 +/- 1.0, and 14.1 +/- 0.9 minutes, respectively. With a fixed concentration (250 nmol/l) of rose bengal, similar light-response relations were observed. Photoactivation of rose bengal had no effect on heart rate but caused a transient (0-4 minutes) vasodilation followed by a progressive vasoconstriction. In further studies in which rose bengal was washed out for 10 minutes before photoactivation, several arrhythmias still developed, indicating that rose bengal binds strongly to tissue and acts as a cellular level rather than in the vascular compartment. To assess the reversibility of rose bengal-induced effects, hearts (n = 6/group) were perfused with rose bengal (250 nmol/l) for 1, 2, 4, 6, and 20 minutes followed by perfusion in the dark for 19, 18, 16, 14, and 0 minutes, respectively. During dark perfusion, the incidence of arrhythmias declined and any decrease in coronary flow was reversed. However, analysis of contents of adenosine triphosphate, creatine phosphate, lactate, and creatine kinase leakage indicated the occurrence of severe injury that did not abate on termination of photoactivation. Finally, although many arrhythmias developed before the onset of vasoconstriction, the reduction in flow with consequent ischemia was shown to exacerbate vulnerability to arrhythmias. In conclusion, short-lived reactive oxygen intermediates such as singlet oxygen and superoxide, which are produced during the photoactivation of rose bengal, can cause rapid and major damage to the heart and its function.

Animals↗
PubMed1989

Rapid electrophysiological changes leading to arrhythmias in the aerobic rat heart. Photosensitization studies with rose bengal-derived reactive oxygen intermediates.

The objective of this study was to determine whether reactive oxygen intermediates (e.g., singlet oxygen and the superoxide radical) can rapidly induce electrophysiological disturbances leading to the genesis of arrhythmias, even in the absence of ischemia and reperfusion. Rat hearts (n = 6 per group) were perfused aerobically at 37 degrees C for 10 minutes without rose bengal and for 5 minutes with rose bengal (250 nmol/l), during which time no changes in coronary flow or heart rate were observed. Hearts were then uniformly illuminated for 20 minutes with green light (530-590 nm) from 200 fiber optic cables. With light and without rose bengal, or vice versa, all hearts remained stable. However, in the illuminated rose bengal group, electrophysiological changes (inversion of the terminal portion of the T wave and an increase in Q-T interval) were observed within 11.8 +/- 2.1 seconds (i.e., less than 60 beats). All hearts exhibited ventricular premature beats (within 2.2 +/- 0.7 minutes) and ventricular tachycardia (within 2.8 +/- 0.7 minutes) before the occurrence of complete atrioventricular block (within 5.5 +/- 0.9 minutes). During the illumination period, coronary flow progressively fell in the rose bengal-perfused hearts from 11.6 +/- 0.5 ml/min to 2.0 +/- 0.4 ml/min (p less than 0.05 when compared with any control group). When a similar progressive reduction in coronary flow was mimicked (with or without rose bengal), no arrhythmias occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerobiosis↗
PubMed1988

Effect of vanadate on the cellular accumulation of pp15, an apparent product of insulin receptor tyrosine kinase action.

The possible involvement of a 15-kDa phosphotyrosyl protein, pp15, in insulin action was investigated by using the insulin-mimetic agent, vanadate. Vanadate, a phosphotyrosine phosphatase inhibitor, was found to mimic insulin in 3T3-L1 adipocytes by three criteria. First, kinetic and concentration-dependence studies verified the insulin-like effect of vanadate in activating 2-deoxyglucose uptake. Insulin had an additive activating effect at a submaximal vanadate concentration, but showed no further activation at a saturating vanadate concentration. The trivalent arsenical, phenylarsine oxide (PAO) which forms complexes with vicinal dithiols, markedly inhibited vanadate-activated hexose transport in agreement with our previous studies in which PAO abolished the insulin-activated component of sugar uptake. Second, in situ phosphorylation experiments showed that vanadate activated tyrosine phosphorylation of the insulin receptor's beta-subunit. Exposure of vanadate-treated cells to PAO further increased the level of beta-subunit phosphorylation. The increased level of phosphorylation in the presence of PAO occurred only on tyrosyl residues. Third, vanadate caused the accumulation of a phosphorylated 15-kDa protein in the presence of PAO, but not in its absence. The characteristics of this protein were identical to those of pp15: 1) both proteins behaved identically by two-dimensional gel electrophoresis, 2) digestion of both proteins with trypsin gave rise to apparently identical phosphopeptides, and 3) both proteins contained phosphotyrosine as the only phosphoamino acid. The results indicate that both vanadate and insulin stimulate the accumulation of pp15 in the presence of PAO. The dithiol,2,3-dimercaptopropanol, but not a monothiol, reversed the effects of PAO on the inhibition of vanadate-induced hexose transport and the accumulation of pp15, thus implicating a vicinal dithiol in these actions of vanadate and insulin. Our results support the hypothesis that turnover of the phosphoryl group of pp15, a product of insulin receptor tyrosine kinase action, is coupled to signal transmission to the glucose transport system.

Adenosine Triphosphate↗
PubMed1988

Inhibition of hormonal-induced cAMP and steroid production by inhibitors of pregnenolone metabolism in adrenal and Leydig cells.

The effects of inhibitors of pregnenolone metabolism, WIN-24540 and spironolactone, on adrenocorticotropic hormone (ACTH)- and human chorionic gonadotropin (hCG)-induced cAMP and steroid production by bovine (BAC) and ovine (OAC) adrenal cells and pig Leydig cells (PLC) were investigated. The inhibitors reduced cAMP production by adrenal and Leydig cells by about 75% and 60%, respectively (P less than 0.001). Further, the inhibitors also reduced the cholera toxin- and forskolin-induced cAMP production by pig Leydig cells. In the presence of the inhibitors, corticosterone and testosterone production by BAC and PLC, respectively, following hormonal stimulation was reduced by more than 90%. However, pregnenolone production by BAC and PLC under these conditions represented only 12% and 42% of the corticosterone and testosterone production, respectively, in the absence of inhibitors. Moreover, the inhibitors also reduced the steroidogenic response of PLC to 8-Br-cAMP and the conversion of 22(R)-hydroxycholesterol to pregnenolone by BAC and PLC. The reduced production of pregnenolone in the presence of inhibitors was in part due to the weak inhibition of 17 alpha-hydroxylase by spironolactone. However, when OAC cells were incubated in the presence of WIN-24540 and SU-10603, a potent 17 alpha-hydroxylase inhibitor, the amount of pregnenolone produced in response to ACTH or 22(R)-hydroxycholesterol was only 10% and 19%, respectively, of the steroids (corticosterone plus cortisol) secreted in the absence of inhibitors. The results show that the inhibitors of pregnenolone metabolism reduced, in both adrenal and Leydig cells, the response of adenylate cyclase to several effectors and the activity of the cholesterol side-chain cleavage.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗
PubMed1988

Reperfusion-induced arrhythmias: a study of the role of xanthine oxidase-derived free radicals in the rat heart.

We have assessed whether oxygen-derived free radicals produced by xanthine oxidase may be an important trigger mechanism in the genesis of reperfusion-induced arrhythmias. We have examined (i) the effects of inhibition of xanthine oxidase by both folic acid solution and amflutizole; (ii) the effects of the inhibitor of xanthine dehydrogenase to xanthine oxidase conversion, soybean trypsin inhibitor; (iii) the effects of administration of superoxide dismutase and catalase, both singly and in combination and (iv) in an isolated rat heart preparation we have investigated the ability of free radical scavengers to reduce reperfusion arrhythmias caused by the infusion of xanthine oxidase and hypoxanthine. The prior administration of folic acid solution, amflutizole, superoxide dismutase, catalase, and superoxide dismutase plus catalase all reduced the incidence of reperfusion-induced arrhythmias and resultant mortality, caused by reperfusion after a transient period of coronary artery occlusion in the anaesthetised rat. Prior administration of soybean trypsin inhibitor significantly reduced mortality. In an isolated, perfused rat heart preparation with temporary coronary artery occlusion, addition of xanthine oxidase-hypoxanthine to the perfusion medium increased the incidence of reperfusion arrhythmias and decreased the total duration of sinus rhythm during reperfusion. Further addition of superoxide dismutase or L-methionine increased significantly the total duration of sinus rhythm. These results suggest that in the rat heart xanthine oxidase may be involved in the genesis of reperfusion-induced arrhythmias.

Allopurinol↗
PubMed1988

Identification of phosphorylated 422(aP2) protein as pp15, the 15-kilodalton target of the insulin receptor tyrosine kinase in 3T3-L1 adipocytes.

[32P]pp15, the [32P]phosphorylated form of a specific cytosolic substrate of the insulin receptor tyrosine kinase, was purified to homogeneity from mouse 3T3-L1 adipocytes incubated with 32Pi. Evidence presented here and previously indicates that pp15 contains a single phosphotyrosine residue. Alkylated [32P]pp15 was subjected to limited digestion with trypsin, after which three incompletely digested tryptic [32P]phosphopeptides were purified for analysis. Amino acid and radiochemical sequence analysis of the [32P]phosphopeptides revealed that pp15 is the phosphorylation product of 422(aP2) protein, a 15-kDa adipocyte protein previously sequenced in this laboratory from the corresponding cDNA.

Adipose Tissue↗
PubMed1988

Inhibition by phenylglyoxal of the sodium-coupled fluxes of glucose and phosphate in renal brush-border membranes.

The coupling of phosphate and glucose transport to sodium in brush-border membrane vesicles from rat kidney cortex was studied after chemical modification of arginine residues by phenylglyoxal. Phosphate (10 mM) and sodium (20 mM) uptakes were linear for 6 s and stimulated in the presence of their cosubstrate. The sodium:phosphate stoichiometry measured by a direct method was 1.74. Sodium-independent phosphate and glucose influx were found to be unaffected by phenylglyoxylation. Phosphate- or glucose-independent sodium influx also remained unaltered by the treatment. However, phosphate influx measured with sodium was inhibited by 69% and sodium influx measured with phosphate was inhibited by 40%. When these values were corrected for uncoupled fluxes, the sodium influx coupled to phosphate and the phosphate influx coupled to sodium were inhibited by 93 and 95%, respectively. Glucose influx measured in the presence of sodium was inhibited by 36% and sodium influx in the presence of glucose was reduced by 39%. When the values were corrected for diffusion, these inhibitions were 95 and 100%, respectively. We conclude that the coupling of phosphate and glucose to sodium fluxes by the renal carriers requires the participation of arginine residue(s) in the translocation process. Modification of this arginine by phenylglyoxal leads to a marked inhibition of coupling. These results suggest the implication of arginine residues in the molecular coupling for both glucose and phosphate sodium symporters.

Aldehydes↗
PubMed1988

Reperfusion-induced arrhythmias: mechanisms of protection by glucose and mannitol.

Isolated rat hearts (n = 15/group) were subjected to regional ischemia (10 min) and reperfusion (3 min). Mannitol (5, 11, 25, 50, 55, 61, or 75 mM included in the perfusate throughout) reduced reperfusion-induced sustained ventricular fibrillation (VF) from its control incidence of 93% (14/15) to 80, 80, 40, 27, 47, 80, and 80%, respectively. Addition of glucose (11 mM) potentiated this effect, VF now fell to 87, 47, 33, 7, 7, 7, 13, and 13%, respectively. However, 11 mM glucose alone exerted no antiarrhythmic effects. When hearts (n = 15/group) were perfused with identical osmotic loads of mannitol plus glucose (11 + 50, 50 + 11, 61 + 0, or 0 + 61 mM, respectively), very different antiarrhythmic effects were observed. When given throughout the experimental period, glucose alone (0, 11, 25, 50 or 61 mM) had no effect on the incidence of VF (93, 87, 47, 53, and 20%, respectively), but when glucose was added 2 min before reperfusion, improved protection was observed (VF: 93, 87, 40, 27, and 13%, respectively). Our results suggest that the osmotic and free-radical scavenging properties of hexoses are relatively unimportant in relation to their antiarrhythmic effects. The metabolic effects are complex, suggesting that low concentrations of glucose may be beneficial, whereas high concentrations may be detrimental.

Animals↗
PubMed1988

Mannitol and reperfusion-induced arrhythmias: possible mechanisms of action in the isolated rat heart.

Mannitol has been shown to exert a dose-dependent, antiarrhythmic effect in the rat heart during reperfusion following a brief period of regional myocardial ischemia. Isolated perfused rat hearts were used to determine whether this protective effect is direct (ie, operative during reperfusion) or indirect (ie, due to an action during ischemia). Hearts (12 in each group) were subjected to 5, 10, 20, 30 or 40 mins of regional ischemia which was induced by ligation of the left anterior descending coronary artery. Upon reperfusion 25%, 100%, 83%, 33% and 17%, respectively, of the hearts fibrillated and 8%, 92%, 58%, 17% and 17% remained in irreversible fibrillation for the duration of the reperfusion period. Addition of mannitol (50 mM, the optimal antiarrhythmic dose) to the perfusion fluid throughout the experiment (early administration) caused a shift of this 'bell-shaped' time-vulnerability curve to the right such that the highest incidence of arrhythmias occurred after 20 mins rather than 10 mins of ischemia. Similar shifts were seen in other indices of electrical instability. Regional ischemia caused a 40 to 45% reduction in coronary flow in all groups of hearts, with no significant difference between the control and the mannitol-treated series. Heart rate fell by a mean of 10 to 15% in all control hearts and by a similar extent in mannitol-treated hearts. In additional studies, mannitol (50 mM) was administered 2 mins before reperfusion and throughout the reperfusion period (late administration studies). In the mannitol-free control group 100% of the hearts exhibited fibrillation and 92% remained in fibrillation for the duration of the reperfusion period.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Decreased production of IL-6 by peripheral blood mononuclear cells of patients with chronic lymphocytic leukemia and related disorders.

The present study has shown a decreased production of IL-6 by LPS-stimulated mononuclear cells of B-CLL blood. This decrease with attributed to an abnormality of either monocytes or T lymphocytes. A similar decrease was seen in HCL and NHL. Experiments with mixtures of normal and CLL cells suggest that the decreased IL-6 production in CLL is due neither to an inhibition of normal blood mononuclear cells IL-6 production by B-CLL lymphocytes nor to the absence in CLL blood of cell(s) or cytokine(s) needed for IL-6 production.

Humans↗
PubMed1987

Stimulatory and inhibitory effects of protein kinase C activation and calcium ionophore on cultured pig Leydig cells.

The acute and the long-term (24 h) effects of protein kinase C activators, phorbol 12 myristate 13-acetate (PMA) and 1-oleoyl-2-acetyl-sn-glycerol, and the calcium ionophore A23187 on cultured pig Leydig cell functions were investigated. None of these drugs modified basal cAMP production, but they induced a small (3-4-fold) increase in testosterone secretion. The stimulatory effects of human choriogonadotropin (hCG; 1 nM) on both cAMP and testosterone productions were inhibited by short-term incubation with these drugs. In addition, they suppressed the stimulation of testosterone output by forskolin and 8-bromo-adenosine 3',5'-monophosphate, whereas the forskolin-dependent cAMP production was unaffected. The inhibitory effects of PMA on hCG stimulation of both cAMP and testosterone were due mainly to a decrease of the Vmax without modification of the ED50. Moreover, PMA did not modify the binding of 125I-hCG. Pretreatment of Leydig cells with the three drugs for 24 h induced more pronounced modifications, such as a reduction in the number of hCG binding sites and a decreased responsiveness to hCG and forskolin, the testosterone production being drastically reduced. The effects of PMA were dose- and time-dependent; however, the concentration of PMA required to induce half-maximal effects on hCG receptors (10 nM) was about one order of magnitude higher than those required to reduce cAMP and testosterone productions. Further, the inhibitory effects on cAMP and testosterone secretions appeared within the first 3 h, whereas the hCG receptor number remained constant for at least 8 h. It appears therefore, that the main alteration responsible for the steroidogenic refractoriness of PMA-treated Leydig cells is located beyond cAMP formation. Moreover, since conversion of exogenous pregnenolone to testosterone by control and PMA-treated cells was similar, the alteration was probably located before pregnenolone formation. Kinetic studies with 125I-hCG showed that the rate of internalization of the hormone-receptor complexes was similar in control cells and in PMA-treated cells, suggesting that the decline in receptor number observed in the latter group after an 8-h delay is not due to an increased rate of internalization nor to sequestration of the internalized receptors inside the cells. Since cycloheximide blocked the effects of PMA on hCG down-regulation, it is likely that the phorbol esters and 1-oleoyl-2-acetyl-sn-glycerol induce the synthesis of some proteins which blocked the recycling of internalized receptors. A similar hypothesis has been put forward recently to explain the hCG-induced down regulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Insulin-activated tyrosine phosphorylation of a 15-kilodalton protein in intact 3T3-L1 adipocytes.

Insulin stimulates phosphorylation of a tyrosine residue(s) on a 15-kDa protein (p15), and the cytosolic phosphorylated protein (pp15) accumulates only when 3T3-L1 adipocytes are treated with phenylarsine oxide. It has been shown previously that phenylarsine oxide, an agent that complexes vicinal dithiols, interrupts signal transmission from the insulin receptor to the glucose transport system. Several lines of evidence presented here indicate the involvement of pp15 in insulin receptor-initiated signal transduction to the glucose transport system. The reciprocal effects of phenylarsine oxide on the insulin-activated accumulation of pp15 and on insulin-stimulated hexose uptake are reversed by the vicinal dithiol 2,3-dimercaptopropanol but not by the monothiol 2-mercaptoethanol. Thus, a cellular dithiol appears to function in the signal transmission pathway downstream from pp15. Like the insulin-activated autophosphorylation of the receptor's beta subunit (on tyrosine), activation of phosphorylation of p15 is specific, with insulin-like growth factors 1 and 2, epidermal growth factor, and platelet-derived growth factor being inactive. Moreover, both processes exhibit identical insulin concentration dependence. The temporal kinetic relationship of insulin-activated receptor beta-subunit phosphorylation, followed by the phosphorylation of p15 and then increased hexose uptake rate, is consistent with an intermediary signaling role for pp15 in insulin-stimulated glucose uptake.

Adipose Tissue↗
PubMed1986

Processing of human choriogonadotropin and its receptors by cultured pig Leydig cells. Role of cyclic AMP and protein synthesis.

We have examined the process by which human choriogonadotropin/luteinizing hormone (hCG/LH) receptors are regulated in cultured porcine Leydig cells. Treatment of Leydig cells with human choriogonadotropin, cholera toxin, forskolin and cyclic 8-bromoAMP (8-BrcAMP) produced a loss of surface receptors without modification of the binding affinity. This negative regulation of the number of receptors mediated by maximal concentrations of hCG was higher than that induced by the other agents. The extent of receptor loss in cells treated with increasing concentrations of hCG was highly correlated with their capacity to stimulate cAMP production. However, there was little correlation between down-regulation and cAMP production of these cells treated by hCG plus forskolin or cholera toxin plus forskolin, where a synergistic cAMP production was obtained. Following exposure of Leydig cells to both hCG and 8-BrcAMP, the surface receptor disappearance began after an initial lag period of about 6-8 h. Thereafter a 50% loss of surface receptor was observed in the next 8-h incubation. Monensin with hCG shortens this lag period before initiation of receptor loss. Kinetic studies with 125I-hCG, in the presence or absence of monensin, showed that the half-life of the receptor-bound hormone complexes at the cell surface was 10.5 h and 8 h respectively. Therefore, the steady state of the surface receptor during the lag phase of 8 h is probably related to recycling of internalized receptors and/or translocation of performed receptors. Cycloheximide and actinomycin D inhibit hCG-mediated and 8-BrcAMP-mediated down-regulation. Cycloheximide lengthens ligand-receptor complexes at the surface by slowing down the rate of internalization (half-life of 20 h), but this mechanism is not enough per se to explain the effect of cycloheximide. Pulses of hCG or 8-BrcAMP for 4 h and 8 h sufficed to induce nearly maximal down-regulation. However, it was possible to attenuate this triggering effect by adding cycloheximide after pulse of the cells. Thus, even after removal of the triggering agent (hCG or 8-BrcAMP), the loss of surface receptor could be triggered by a protein-sensitive signal. Taken as a whole these results indicate that a coordinated interaction is involved in the cell-surface hCG/LH receptor regulation. The apparent steady state of the number of receptors during the first hours of stimulation passed through a reuptake of internalized receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1986

Regulation of gonadotropin receptors, gonadotropin responsiveness, and cell multiplication by somatomedin-C and insulin in cultured pig Leydig cells.

We have investigated the effects of insulin and somatomedin-C/insulinlike growth factor I(Sm-C) in purified porcine Leydig cells in vitro on gonadotrophins (hCG) receptor number, hCG responsiveness (cAMP and testosterone production), and thymidine incorporation into DNA. Leydig cells cultured in a serum-free medium containing transferrin, vitamin E, and insulin (5 micrograms/ml) maintained fairly constant both hCG receptors and hCG responsiveness. When they were cultured for 3 days in the same medium without insulin, there was a dramatic decline (more than 80%) in both hCG receptor number and hCG responsiveness. However the cAMP but not the testosterone response to forskolin was normal. Both insulin and Sm-C at nanomolar concentrations prevent the decline of both hCG receptors and hCG-induced cAMP production. This effect of both peptides was dose dependent with an ED50 of about 1 ng/ml and 5 ng/ml for SM-C and insulin, respectively. Insulin and Sm-C had no additive effect on these parameters. At nanomolar concentrations, Sm-C and insulin enhanced hCG-induced testosterone production but the effect of Sm-C was significantly higher than that of insulin. However, the effect of insulin at higher concentrations (5 micrograms/ml) was significantly higher than that of Sm-C at 50 ng/ml. In contrast, at nanomolar concentrations only Sm-C stimulated [3H]-thymidine incorporation into DNA and cell multiplication, the stimulatory effect of insulin on these parameters, was seen only at micromolar concentrations. These results indicate that both Sm-C and insulin acting through their own receptors increase Leydig cell steroidogenic responsiveness to hCG by increasing hCG receptor number and improving some step beyond cAMP formation. In contrast, the mitogenic effects of insulin are mediated only through Sm-C receptors.

Animals↗
PubMed1986

Normothermic ischemic cardiac arrest and reperfusion of the isolated working rat heart: effect of carbocromene pretreatment on functional and metabolic recovery.

Normothermic Ischemic Cardiac Arrest and Reperfusion of the Isolated Working Rat Heart: Effect of Carbocromene Pretreatment on Functional and Metabolic Recovery. This paper describes the effect of carbocromene pretreatment on the functional recovery of the isolated rat heart submitted to ischemic cardiac arrest and reperfused. In a previous study we showed that hearts isolated from rats which had been pretreated for 8 days with a daily oral administration of carbocromene at 15 mg/kg body weight, exhibit higher mechanical performances (aortic output, coronary flow, cardiac work) than hearts isolated from untreated animals. This was associated with a greater tissue content of high energy phosphates and glycogen. In the present work, carbocromene-pretreated hearts are submitted to 30 minutes of normothermic no-flow ischemia after being arrested by a 2 min high potassium, substrate-free perfusion, containing 2 mg/l carbocromene (cardioplegic solution). After reperfusion, post-ischemic recovery of function is significantly better in treated hearts as compared to control untreated preparations submitted to a similar protocol. Although no significant difference can be demonstrated in the metabolic status of either groups of preparations after 30 min of reperfusion, lactate dehydrogenase release, taken as an index of myocardial cell damage, is significantly reduced in the carbocromene-treated group. In view of these results it is suggested that carbocromene pretreatment and/or the addition of carbocromene to cardioplegic solutions could be beneficial in improving functional recovery after temporary ischemic cardiac arrest.

Animals↗