Professional knowledge among Swedish and Saudi healthcare practitioners regarding oro-facial pain in children and adolescents.

Oro-facial pain (OFP) and temporomandibular disorders (TMD) in children and adolescents are a growing problem. To meet patients' healthcare needs, professionals must perform their work intuitively and with quality. Therefore, a high degree of professional knowledge is necessary. To investigate the professional knowledge regarding OFP/TMD in children and adolescents among Swedish and Saudi Arabian dental and medical specialists compared with Swedish OFP specialists. One questionnaire including the four domains Chronic pain and behaviour; Aetiology; Diagnosis and classification; Treatment and prognosis was distributed to 383 potential participants, that is physicians and dentists in Sweden and Saudi Arabia. The Swedish OFP/TMD specialists were used as a reference group. The response rates from Sweden and Saudi Arabia were 49% and 86%, respectively. The degree of agreement was highest in the domain Chronic pain and behaviour, especially for the Swedish groups. Regarding the other three domains, the agreement was modest to poor. In general, Swedish groups showed a higher agreement with Swedish OFP/TMD specialists than Saudi Arabian groups. This study shows that professional knowledge regarding OFP/TMD in children and adolescents is limited among Swedish and Saudi Arabian dental and medical professionals compared to Swedish OFP/TMD specialists. In Swedish groups, the professional knowledge is more accurate than in the corresponding Saudi Arabian. With these results in mind, and the frequent prevalence of OFP/TMD in children and adolescents, one can draw the conclusion that there is a need for modern medical education regarding OFP/TMD among both physicians and dentists, especially in Saudi Arabia.

Effect of carbon starvation and proteolytic activity on stationary-phase acid tolerance of Streptococcus mutans.

Previous research with Streptococcus mutans and other oral streptococci has demonstrated that the acid shock of exponential-phase cells (pH 7.5 to 5.5) resulted in the induction of an acid tolerance response (ATR) increasing survival at low pH (3.5-3.0). The current study was designed to determine whether two fresh isolates, H7 and BM71, and two laboratory strains, Ingbritt and LT11, were capable of a stationary-phase ATR as estimated by a survival test at pH 3.5 for 3 h. All four strains were unable to generate a stationary-phase ATR under control conditions at pH 7.5, with the exception of a burst of survivors in the transition between the exponential and stationary phases when the carbon source (glucose) was depleted. Adaptation at pH 5.5 resulted in the expected pH-dependent exponential-phase ATR, but only the fresh isolates exhibited a stationary-phase ATR at this pH. Glucose starvation of cells in complex medium was shown to enhance acid tolerance for the fresh isolates, but not the laboratory strains. This tolerance was, however, greatly diminished for all strains in a defined medium with a low concentration of amino acids. Growth of strain H7 in complex medium resulted in the formation of at least 56 extracellular proteins, nine of which were degraded in the early stationary phase following the induction of proteolytic activity during the transition period. No proteolytic activity was observed with strain LT11 and only 19 extracellular proteins/peptides were apparent in the medium with only one being degraded in the early stationary phase. Strain H7 was also shown to have two- to fourfold higher levels of intracellular glycogen in the stationary phase than strain LT11. These results suggest that S. mutans H7 possessed the required endogenous metabolism to support amino acid/peptide uptake in the early-stationary phase, which resulted in the formation of basic end products that, in turn, contributed to enhanced intracellular pH homeostasis.

A retrospective study of patients with retained nuclear fragments after cataract extraction.

PURPOSE: A registration and follow-up of patients who underwent pars plana vitrectomy after dislocated nuclear fragments to the vitreous following cataract extraction. MATERIAL AND METHODS: A retrospective study of 125 patients referred to The National Hospital during the years 1991 to 1998. Phacoemulsification and extracapsular technique were used in 115 eyes and 10 eyes, respectively. A pars plana vitrectomy was performed within an average of 13 days (1-99 days) after cataract extraction. Average follow-up period was 9 months (0.5-35 months). RESULTS: The visual acuity at follow-up was > or = 0.5 in 67 eyes (55.4%), <0.5->0.1 in 32 eyes (26.4%), and < or = 0.1 in 22 eyes (18.2%). The total number of retinal detachments was 26 (21.5%). CONCLUSION: Retained nuclear fragments in the vitreous is a serious complication and most eyes achieve acceptable visual results.

Varying very low-density lipoprotein secretion of rat hepatocytes by altering cellular levels of calcium and the activity of protein kinase C.

BACKGROUND: Calcium antagonists lower plasma levels of lipoproteins and suppress hepatic very low-density lipoprotein (VLDL) secretion. Similar effects have been observed with the calcium ionophore A23187. We studied further the effect of calcium on VLDL metabolism. METHODS: Hepatocytes from male Wistar rats were isolated and cultured in the presence or absence of calcium-mobilizing hormones, or compounds that either stimulate or inhibit the activity of protein kinase C. Secreted VLDL (d < 1.006 g mL-1) was isolated by centrifugation (145,000 x g), and lipids and apolipoprotein B were analysed. RESULTS: VLDL secretion reached maximum in hepatocytes cultured in medium containing calcium 0.8-2.4 mmolL-1. Depleting the cells of calcium by incubating in calcium-free medium or by treating the cells with the Ca(2+)-ATPase inhibitor thapsigargin (5 x 10-7 molL-1) suppressed lipid secretion to less than 15% of control, and this was accompanied by an increase in cellular levels of triacylglycerol. Calcium loading (medium calcium > 2.4 mmolL-1) suppressed both lipoprotein secretion and cellular levels of lipids, suggesting a reduced overall rate of lipid synthesis. At an extracellular calcium concentration of 0.8 mmolL-1, angiotensin II, vasopressin, endothelin-1 (10(-7) molL-1) or phenylephrine (10(-4) molL-1) suppressed VLDL secretion (maximum to 37% of control), and elevated medium calcium attenuated this effect. The protein kinase C inhibitor chelerythrine (5 x 10(-5) molL-1) and the protein kinase C activator phorbol 12-myristate 13-acetate (PMA) (10(-6) molL-1), suppressed VLDL secretion to 18% and 60% of control, respectively, whereas the protein kinase C-inactive 4 alpha-PMA was without an effect. No effect on ketogenesis was observed by these compounds, indicating that suppressed lipid secretion was not due to an enhanced oxidation of lipids. CONCLUSIONS: Hepatic VLDL secretion can be related to changes in hepatocyte levels of calcium and the activity of protein kinase C.

Acute bacterial meningitis in adults. A 20-year overview.

BACKGROUND: Most clinical overviews of acute bacterial meningitis have either focused on children or all age groups combined, although the disease poses serious problems in the adult population. OBJECTIVE: To study the clinical and microbiological features of adult bacterial meningitis in Iceland, as a representative of the average European or North American community. PATIENTS AND METHODS: Data on a total of 132 cases in 127 patients (age, > or = 16 years) who were diagnosed as having acute bacterial meningitis in Iceland during the years 1975 to 1994 were collected from patient and laboratory records. Complete hospital records were found for 119 of the 132 cases identified. RESULTS: The annual incidence was 1.7/100,000 to 7.2/ 100,000 inhabitants (mean, 3.8/100,000). The most common causative organisms were Neisseria meningitidis (56%), Streptococcus pneumoniae (20%), Listeria monocytogenes (6%), and Haemophilus influenzae (5%). Neisseria meningitidis caused 93% of the infections in the 16- to 20-year-old age group, but it caused only 25% of the infections in patients aged 45 years or older. Listeria monocytogenes caused 14% of these cases. Cases of nosocomial and recurrent meningitis were rare. A significant underlying illness or condition was present in 39% of the patients. The mean mortality was 19.7%, and it did not change during the study period. CONCLUSIONS: In a study that involved all adult patients with bacterial meningitis in a single country for 2 decades, meningococci and pneumococci were the most frequent causative agents. However, meningococci were responsible for only one fourth of the cases among adult patients aged 45 years or older, most of these cases were caused by pneumococci and Listeria. Despite modern medical developments, approximately 20% of adult patients with bacterial meningitis died.

[The weight of the thyroid in Icelanders. A study based on 197 accidentally dead individuals.].

OBJECTIVE: The objective of the present study was to ascertain whether the weight of the thyroid gland had increased in comparison with older studies. The thyroid in Icelanders has been considered small, an opinion based on two different studies, one from 1939 and the other from 1967-1976. MATERIAL AND METHODS: The thyroids of 197 individuals who died accidentally in the period from March 1984 to September 1985. The thyroids were weighed fresh. CONCLUSION: The weight of the thyroid in Icelanders has increased. In this study no attempt was made to speculate on what might be the most likely cause for the increased weight of the thyroid in Icelanders.

[Acute bacterial meningitis in adults, a 20 year overview.].

INTRODUCTION: Although acute bacterial meningitis is most common among children, the disease nevertheless poses serious problems in the adult population. However, most clinical overviews of the disease have either focused on children or all age groups combined. SUBJECTS AND METHODS: Information on all patients 5=16 years of age diagnosed in Iceland during the years 1975-1994 was collected from patient records from 10 hospitals and the records of the Dept. of Microbiology at the University Hospital which processes all bacterial isolates from the CSF identified in the country. RESULTS: One hundred thirty six patients were identified, but complete records were found for 123 patients. Yearly incidence ranged from 1.7-7.2/100,000 inhabitants with a mean of 3.8/100,000. The most common causative organisms were Neisseria meningitidis (54%), Streptococcus pneumoniae (20%), Listeria monocytogenes (6%) and Haemophilus influenzae (5%). The relative incidence of N. meningitidis was dependent on age, the organism caused 93% of infections in the 16-20 year age group, whereas only 25% of infections in subjects 3=45 years of age were due to meningococci. On the other hand, the relative incidence of S. pneumoniae did increase from 2% in the younger age group to 37% in the older subjects. L. monocytogenes caused 14% of cases among patients 3=45 years of age. The mean mortality was 19.1% and did not change significantly during the study period. A significant underlying illness or condition was present in 39% of the patients. During the first third of the study period penicillin or ampicillin alone or in combination with chloramphenicol were used as initial empiric therapy in 76% of cases, wheras during the last third of the period these agents were used initially in 24% of patients. The third generation cephalosporins either alone or in combination were instead employed for empiric treatment in almost two-thirds of the patients. CONCLUSIONS: Meningococci were the most common cause of bacterial meningitis in adults in Iceland during the study period, albeit age dependent, and causing only a fourth of infections in patients 3=45 years of age. Mortality did not change during the period. The third generation cephalosporins are now the most commonly used agents for empiric therapy.

Regulation of VLDL secretion in primary culture of rat hepatocytes: involvement of cAMP and cAMP-dependent protein kinases.

When hepatocytes were cultured for 24 h in the presence of forskolin (10(-4) mol l-1) or isobutylmethylxanthine (IBMX, 10(-3) mol l-1), the intracellular cAMP concentration peaked (320-380 pmol mg-1 protein) after 10-20 min of culture. This increase was accompanied by a decrease in the secretion of triacylglycerol, cholesterol and apoprotein B associated with VLDL. After 4 h cAMP levels had returned almost to basal values but the inhibition of VLDL secretion persisted. There was a small intracellular accumulation of triacylglycerol but not of apoprotein B. Addition of forskolin and IBMX together led to a further increase in intracellular cAMP and a further suppression of VLDL output. Similar effects on the secretion of VLDL were also observed after addition of Bt2cAMP. Exposure of cell cultures to glucagon (10(-7) mol l-1) for only 10 min raised cellular cAMP levels to > 200 pmol mg-1 protein, and suppressed VLDL secretion during the next 24 h to < 40% of control. All of the substances tested inhibited de novo synthesis of fatty acids but had little or no effect on cholesterol synthesis and did not inhibit oleate esterification to triacylglycerol. The cAMP-dependent protein kinase antagonist Rp-cAMPS prevented suppression of VLDL triacylglycerol secretion induced by glucagon (10(-7) mol l-1) and abolished glucagon-induced ketogenesis. Rp-cAMPS also inhibited Bt2cAMP (7.5 x 10(-6) mol l-1)-induced suppression of VLDL secretion and enhancement of ketogenesis. It is concluded that rat hepatic VLDL metabolism can be regulated by cAMP and cAMP-dependent protein kinases, and that the initial transient rise in cellular cAMP levels induced by glucagon is sufficient to maintain a long-term inhibitory effect on assembly and secretion of VLDL.

Prostaglandins suppress VLDL secretion in primary rat hepatocyte cultures: relationships to hepatic calcium metabolism.

In primary cultures of rat hepatocytes, prostaglandin E2 and prostaglandin D2 (PGE2 and PGD2) inhibited the secretion of very low density lipoprotein (VLDL)-associated apoB, triacylglycerol, and cholesterol. These effects were concentration-dependent and remained apparent for at least 3 days of culture without an effect on the apoB/triacylglycerol ratio of the secreted VLDL. Prostaglandins had no effect on the overall synthesis of triacylglycerol but triacylglycerol accumulated within the cells, without intracellular accumulation of apoB. PGE2, when added to the medium together with glucagon, increased the inhibition of VLDL secretion, compared to that observed with glucagon alone. However, PGE2 did not increase the stimulatory effect of glucagon on ketogenesis. Unlike glucagon, the prostaglandins did not inhibit fatty acid synthesis nor did they stimulate ketogenesis or production of cAMP. Thus, of all the parameters of hepatic lipid metabolism studied, PGE2 and PGD2 selectively affected VLDL. Selective inhibition of VLDL secretion was also observed with the calcium antagonist verapamil. The divalent cation ionophore A23187 also inhibited VLDL release but, in contrast, also inhibited fatty acid and cholesterol synthesis. The results suggest that VLDL secretion is modulated at some optimal cell calcium concentration that may be mediated selectively by agents such as prostaglandins.

The role of pancreatic hormones in the regulation of lipid storage, oxidation and secretion in primary cultures of rat hepatocytes. Short- and long-term effects.

Exposure of cultured rat hepatocytes to a high concentration of insulin (78 nM) for 24 h in the presence of extracellular oleate (0.75 mM) resulted in a decrease in the secretion of apoprotein B (apoB) and triacylglycerol associated with very-low-density lipoprotein (VLDL). However, continuous exposure of the cells to insulin for longer periods (72 h) stimulated the secretion of apoB and triacylglycerol. Treatment of hepatocytes with glucagon (0.1 microM) for 24 h also suppressed the secretion of VLDL apoB, cholesterol and triacylglycerol. The cells remained responsive to the inhibitory effect of glucagon for at least 3 days. In contrast with insulin, however, exposure of the cells to glucagon for a continuous period of 72 h did not lead to a reversal of the initial inhibition. Glucagon also stimulated ketogenesis, and in this regard the cells were responsive for at least 3 days in culture. These changes were accompanied by a transient increase in intracellular cyclic AMP (cAMP) concentration, which reached a peak 10 min after addition of glucagon. Between 12 h and 24 h after glucagon addition, cAMP levels had returned almost to normal, but the secretion of VLDL remained suppressed during this period.

Fourier analysis of biliary and pancreatic excretion in man based on data obtained by a duodenal perfusion/aspiration technique.

A standard duodenal perfusion/aspiration technique was used to continuously monitor biliary and pancreatic excretion in young healthy human subjects, and the excretory patterns were examined by Fourier power spectral analysis. Experiments were carried out in the fasting state, either without or during a continuous parenteral (i.v.) stimulation by secretin and the cholecystokinin analogue ceruletide. The duodenal content aspirated was either discarded after sampling or reinfused into the jejunum. In the fasting state, significant biliary and pancreatic excretion was detected, fluctuating with a periodicity of about 60 min. During parenteral infusion with ceruletide/secretin, to simulate a postprandial state, the rate of biliary and pancreatic excretion increased as compared with fasting levels alone (basal levels). A dominant period of about 60 min was still detected but second periods of approximately 45 min and approximately 95 min, respectively, were also observed. The peak power and the total power of the biliary excretion signals were reduced. Reinfusion of aspirated duodenal fluid into the intestine (jejunum) led to a further decrease in peak power and total power of the known biliary signals. Trypsin excretion into the duodenum revealed mainly insignificant changes in peak and total power upon hormone stimulation despite a definite increase in total amount of trypsin excreted. The results indicate that parenteral ceruletide/secretin stimulation has a stabilizing effect on biliary excretion in man, and that reinfusion of aspirated duodenal content into the intestine further stabilizes the excretion.

Identification of P2Y purinoceptors associated with voltage-activated cation channels in cardiac ventricular myocytes of the rat.

Extracellular ATP has vasodilatory and inotropic effects in the heart. We have demonstrated that extracellular ATP, in a concentration-dependent manner (10 nM-0.1 mM), increased [Ca2+]i in suspensions of isolated fura-2-loaded rat cardiac ventricular myocytes (maximum 96 +/- 10% increase over basal levels, SEM, n = 12, P less than 0.01). The increase in [Ca2+]i was often biphasic, with an initial fast phase (less than 1 s) of low amplitude, followed by a slower phase of higher amplitude. A second application of ATP had little effect, and ATP abolished the effect of subsequent electrical stimulations, even through the cells were still able to respond with an increase in [Ca2+]i to KCl-induced depolarization or stimulation by caffeine. Pretreatment of cells with nifedipine, verapamil, caffeine, ryanodine, or 8-(N,N-diethylamino)octyl 3,4,5-trimethoxybenzoate hydrochloride attenuated the effect of extracellular ATP on [Ca2+]i, and binding of extracellular free calcium by excess EGTA completely abolished the effects of extracellular ATP and electrical stimulation. Extracellular ATP increased bisoxonol fluorescence in ventricular myocytes, indicating depolarization of the sarcolemma. Pretreatment of the myocytes with tetrodotoxin (50 microM), or replacement of NaCl in the incubation buffer with the impermeant cation N-methyl-D-glucamine, suppressed the extracellular ATP effect on [Ca2+]i. ADP and AMP had smaller effects on [Ca2+]i than ATP; adenosine had no effect. ATP analogues showed the following rank order of potency in increasing [Ca2+]i or bisoxonol fluorescence: ATP greater than or equal to 2-methylthioATP much greater than adenosine 5'-O-[3-thio]triphosphate greater than adenosine 5'-[alpha, beta-methylene]triphosphate approximately adenosine 5'-[beta, gamma-methylene]triphosphate approximately adenosine 5'-[beta, gamma-imino]triphosphate greater than adenosine. These data are consistent with the presence of purinoceptors (P2Y subtype) on the sarcolemma of cardiac ventricular myocytes of the rat, which upon activation lead to depolarization and activation of cation channels of the sarcolemma and flux of extracellular Ca2+ into the cells. This may result in further flux of Ca2+ into the cytosol from intracellular stores. The effects of extracellular ATP on [Ca2+]i in rat cardiac ventricular myocytes may, in part, explain the direct inotropic effects of extracellular ATP on the mammalian heart.

Modulation of coronary flow rate and cardiac contractility by the divalent cation ionophore A23187 and inhibitors of the cyclooxygenase and 5-lipoxygenase pathways: development of heterogeneous patterns of myocardial ischemia.

In the present studies, we demonstrate in buffer-perfused isolated working guinea pig hearts that indometacin reduces coronary flow rate in a dose-dependent manner (max 56.7 +/- 5.5%, SEM, n = 6, of control at 5 x 10(-6) mol/l of indometacin, P less than 0.01), and that this leads to a development of heterogeneous patterns of myocardial ischemia (elevated myocardial levels of reduced pyridine nucleotide, NADH) and depressed cardiac work (64.7 +/- 11.7%, SEM, of control at 5 x 10(-6) mol/l of indometacin, P less than 0.05). The effect of indometacin on coronary flow rate and consequently on myocardial tissue oxygenation was completely prevented by the preferential 5-lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA) (1 x 10(-6) mol/l), or the sulfidopeptide leukotriene receptor antagonist FPL 55712 (2 x 10(-5) mol/l), indicating that the isolated working guinea pig heart, even when deprived of blood, is able to produce vasoactive sulfidopeptide leukotrienes at significant levels. At higher concentrations of indometacin (5 x 10(-5) mol/l, 1 x 10(-4) mol/l), coronary flow rate returned to initial levels while cardiac work became further depressed despite normoxic levels of NADH. These data support that indometacin also has a direct suppressive effect on the myocardium independent of its coronary vascular effect. This conclusion is supported by the observation that addition of sodium arachidonate (6 x 10(-5) mol/l) completely inhibited the vascular effect of indometacin, but not the depressive effect on the myocardium. The divalent cation ionophore A23187 (6 x 10(-6) mol/l) had a strong positive chronotropic effect on the heart and a biphasic effect on coronary flow rate. After a brief period of increased coronary flow rate, presumably due to coronary vasodilatation, the ionophore caused a sustained reduction in coronary flow, and this was accompanied by high myocardial levels of NADH fluorescence of characteristically heterogeneous pattern. This is presumably caused by vasoconstrictory effects of elevated levels of intracellular Ca2+ of vascular smooth muscle, independent of stimulation of 5-lipoxygenase or cyclooxygenase pathways, since neither indometacin nor nordihydroguaiaretic acid modified the effect of A23187.

Inducers of adenylate cyclase reverse the effect of leukotriene D4 in isolated working guinea pig heart.

The recovery of coronary flow and cardiac work was studied in isolated guinea pig hearts (working-heart preparation) after successive bolus injections of leukotriene D4 (LTD4) at increasing doses (0.01-1,000 ng). LTD4 caused an immediate (within 1 min) reduction in coronary flow and cardiac work and an increase in myocardial NADH fluorescence. There was limited spontaneous recovery at any dose and at the end of the cumulative LTD4 study, coronary flow recovered only from 41.4 +/- (SE) 3.5 (n = 10) to 53.5 +/- 4.7% of initial values, and cardiac work recovered from 21.2 +/- 4.1 to 33.1 +/- 5.6% (P less than 0.05). Adenosine (1 X 10(-6) M) or iloprost (1 X 10(-7) M) restored coronary flow but not cardiac work after LTD4 injections, in contrast to full recovery of cardiac work observed in hearts subjected to a similar degree of ischemia induced by reducing the coronary flow by a peristaltic pump, or hypoxia caused by reducing PO2 of the perfusion fluid. Adenosine (1 X 10(-6) M) and forskolin (1 X 10(-6) M) in combination, or iloprost (1 X 10(-7) M) and isoproterenol (1 X 10(-8) M) in combination, restored both coronary flow and cardiac work to control levels. Myocardial NADH levels, which increased immediately after LTD4 injections, returned to normal after perfusion with adenosine or iloprost. The data suggest that LTD4 has a prolonged vasoconstrictive effect on the heart. Reversal of this effect by compounds that stimulate adenylate cyclase of the vascular tissue (adenosine, prostacyclin) revealed a direct suppressive effect on the myocardium independent of the vascular effect and myocardial ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction between leukotriene D4 and adenosine or iloprost in the isolated working guinea-pig heart: prevention of the leukotriene D4 effect.

The interaction between leukotriene D4 and adenosine or the prostacyclin analogue iloprost was studied in isolated guinea-pig hearts. Adenosine (1 X 10(-6) M) or iloprost (5 X 10(-8) M) abolished or greatly attenuated the vasoconstrictive effect of leukotriene D4 over a wide dose range of leukotriene D4 (0.01-1000 ng), and myocardial ischemia as a consequence of coronary insufficiency completely disappeared. Comparison of myocardial levels of reduced pyridine nucleotide fluorescence in hearts treated with leukotriene D4 and in hearts subjected to varying degrees of high-flow hypoxia, or the calcium agonist BAY-K 8644, revealed low levels of reduced pyridine nucleotides in the leukotriene D4-treated hearts, suggesting that leukotriene D4 directly suppressed myocardial contractility. These findings were supported by full restoration of cardiac work by the receptor antagonist FPL 55712 following leukotriene D4 treatment. It is concluded that adenosine and iloprost are potent inhibitors of leukotriene D4-induced reduction in coronary flow in guinea-pig hearts, and that myocardial ischaemia and suppressed cardiac work are prevented during leukotriene D4 study in adenosine or iloprost perfused hearts. Low levels of myocardial-reduced pyridine nucleotides during leukotriene D4 treatment and restoration of cardiac work by FPL 55712 indicate that leukotriene D4 may also have a direct suppressive effect on myocardial contractility.

Effect of drugs, peptide hormones and lipogenic precursors on the relative incorporation of [3H]H2O and carbon into hepatic cholesterol.

Measurement of the weight of desmosterol produced during its biosynthesis in the presence of tritiated water and triparanol has permitted a direct determination of the relative flux of carbon and tritium (the H/C ratio) into sterol in hepatocytes. The H/C ratio increased with time of incubation irrespective of the nutritional state of the donor animals. This increase was more marked in hepatocytes from starved animals. Pyruvate and lactate increased, and glucagon decreased, the sterol H/C ratio. Addition of pyruvate to incubations containing glucagon resulted in a 32-67% increase in the H/C ratio depending upon nutritional status. Insulin had no effect whilst (-)-hydroxycitrate decreased the ratio by 25%.

Diurnal changes in the rate of cholesterogenesis in hepatocytes from fed and starved rats: effects of precursors and pancreatic hormones in vitro.

The activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) varied with a diurnal periodicity in hepatocytes prepared at different times from rats accustomed to a controlled feeding and lighting schedule. The rates of sterol synthesis varied in a similar manner but the maximum rate was not synchronous with maximum HMG-CoA reductase activity. The diurnal increase in HMG-CoA reductase activity and sterol synthesis rate started before food was offered to donor animals. Neither insulin nor glucagon had any effect on the diurnal pattern of hepatic sterol synthesis in vitro. Pyruvate inhibited sterol synthesis in hepatocytes prepared during the feeding period but had no effect at other times of day. When food was withheld from donor animals at the beginning of the normal feeding period both HMG-CoA reductase activity and the rate of sterol synthesis rapidly decreased. During this period neither insulin nor lipogenic substrates, alone or in combination, were able to restore the rates of sterol synthesis to normal values. In hepatocytes prepared from animals starved for a longer period (43 h) the decrease in the activity of HMG-CoA reductase was much less than that in the rate of sterol synthesis. In contrast to hepatocytes from fed or short-term-starved animals, the rate of sterol synthesis in these hepatocytes could be increased by glucose or pyruvate.

Evidence that changes in hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase activity are required partly to maintain a constant rate of sterol synthesis.

The effects of insulin, glucagon, pyruvate, and lactate on the rate of sterol synthesis and 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase activity were determined in hepatocytes obtained at different times of the day from rats maintained on a controlled lighting and feeding schedule. In hepatocytes from animals killed immediately before the start of the feeding period (D0 hepatocytes), the initially low activity of HMG-CoA reductase increased during incubation while that in hepatocytes prepared 6 h later (D6 hepatocytes) remained constantly high. The rates of sterol synthesis followed similar patterns of change. In both D0 and D6 cells, insulin stimulated HMG-CoA reductase but had little or no effect on the rates of sterol synthesis. In both types of cell preparation glucagon maximally suppressed HMG-CoA reductase activity at a concentration of 10(-7) M, but there was relatively little change in the rates of sterol synthesis. Both pyruvate and lactate mitigated the glucagon-mediated inhibition of HMG-CoA reductase. Each of these lipogenic precursors alone suppressed the rate of sterol synthesis in a dose-dependent manner. These changes were more apparent in the simultaneous presence of insulin and were greater in the D0 compared to the D6 hepatocytes. In the presence of lactate or pyruvate, the activity of HMG-CoA reductase was elevated, and the increase was greater when insulin was simultaneously present. In general, changes in the rate of fatty acid synthesis were positively correlated with changes in the activity of HMG-CoA reductase. These observations suggest that the latter changes are required to compensate for variations in the availability of simple precursors for sterol synthesis.