Histochemical responses in the retina after acute blood loss

Adult albino mice were bleed through the hearts by cardiac puncture under Nembutal anesthetic. 0.3 ml of blood was withdrawn form every animal. The retinae were then studied on a timed basis with succinic dehydrogenase histochemistry and alkaline phosphatase histochemistry. In control retinae, high SDH activities were localized in the inner segments, outer plexiform, inner plexiform, and ganglion cells layers and high alkaline phosphatase activities were localized in the ganglion cell layers and the vessels of the plexiform layers. Decrease in the enzymatic activities of both SDH and alkaline phosphatase in these layers were most evident 5h after bleeding. 9 to 24 h after bleeding, a compensatory increase was detected. 48 to 72 h after, the enzymatic activities decreased again. Reperfusion of experimental animals with 5% dextrose would increase the retinal enzymatic activities back to normal, even if the reperfusion was carried out as late as 48 h after bleeding.     

Relative changes in the function of muscle ribosomes and mitochondria during the early phase of steroid-induced catabolism

1. Five glucocorticoids, when administered daily to rats for 5-7 days at a dosage of 5mg/kg, were in the following order of effectiveness with respect to their ability to decrease the weight gain of whole animals and the vastus lateralis, vastus medialis and gluteus medius muscles: corticosterone相似文献   

A critical period of progesterone withdrawal precedes menstruation in macaques

Macaques are menstruating nonhuman primates that provide important animal models for studies of hormonal regulation in the uterus. In women and macaques the decline of progesterone (P) at the end of the cycle triggers endometrial expression of a variety of matrix metalloproteinase (MMP) enzymes that participate in tissue breakdown and menstrual sloughing. To determine the minimal duration of P withdrawal required to induce menses, we assessed the effects of adding P back at various time points after P withdrawal on both frank bleeding patterns and endometrial MMP expression. Artificial menstrual cycles were induced by treating the animals sequentially with implants releasing estradiol (E2) and progesterone (P). To assess bleeding patterns, P implants were removed at the end of a cycle and then added back at 12, 24, 30, 36, 40, 48, 60, or 72 hours (h) after the initial P withdrawal. Observational analysis of frank bleeding patterns showed that P replacement at 12 and 24 h blocked menses, replacement at 36 h reduced menses but replacement after 36 h failed to block menses. These data indicate that in macaques, a critical period of P withdrawal exists and lasts approximately 36 h. In other similarly cycled animals, we withdrew P and then added P back either during (12-24 h) or after (48 h) the critical period, removed the uterus 24 h after P add back and evaluated endometrial MMP expression. Immunocytochemistry showed that replacement of P during the critical period suppressed MMP-1, -2 and -3 expression along with menses, but replacement of P at 48 h, which failed to suppress mense, suppressed MMP-1 and MMP-3 but did not block MMP-2. We concluded that upregulation of MMPs is essential to menses induction, but that after the critical period, menses will occur even if some MMPs are experimentally blocked.     

Effect of ethanol on the concentration of serotonin in the brain of the rat and the excretion of 5-hydroxyindoleacetic acid

It is found that serotonin content in the brain areas and heart of rats with low alcohol motivation decreases after 5 months of chronic consumption of 48% ethanol solution in a dose of 4 g/kg; in animals with high alcohol motivation serotonin content decreases only in the hypothalamus. Under chronic alcoholization for 1 and 12 months no considerable changes were found in serotonin level of the studied tissues. 60 min after intraperitoneal administration of 20% ethanol solution in a dose of 3 g/kg in intact animals there occurs an increase of serotonin content in the brain hemispheres and heart and its decrease in the hypothalamus; in rat with low alcohol motivation after taking ethanol for 5 months this administration evokes a decrease of serotonin content in the hypothalamus and truncus cerebri; in rats with high alcohol motivation--its decrease in the hypothalamus. Excretion of 5-oxyindoleacetic acid with urine decreases 10 months after alcohol intoxication. When rats were not given ethanol after its chronic taking for 3 months serotonin oxidation was intensified for the first day, which was not observed after 7-month alcoholization of animals.     

Effect of the spleen cells from partially splenectomized and partially hepatectomized mice on the proliferation of hepatocytes in the regenerating liver of syngeneic recipients

Cells of mouse spleen obtained 48 h after foster splenectomy, foster hepatectomy, resection of 2/3 of spleen or 36 h after resection of 2/3 of liver were introduced intravenously into partially hepatectomized (resection of 2/3 or 1/4 of liver) syngeneic recipients. Cells of regenerating spleen sharply inhibited the mitotic activity of cells of the recipient liver following resection of 1/4 of liver 48 h after the operation and introduction of cells. Inhibition proved to be dose-dependent: it became apparent when 30 million cells were introduced, increased at a dose of 60 million cells and remained at the same level at higher doses. Division of hepatocytes after resection of 1/4 of liver was inhibited by spleen cells taken in the donors 36 h after partial hepatectomy. Spleen cells of intact and pseudo-operated donors had no such ability. Introduction of 60 million of cells of the regenerating spleen and of the spleen of partially hepatectomized animals into recipients with resection of 2/3 of liver did not inhibit reliably the division of hepatocytes, thus indicating the dependence of inhibition on the level of suppressors in the organism. Resection of a major part of liver was accompanied by a greater decrease in the activity of endogenous suppressors which could not be recovered by the introduced cells. Inhibition of cell division by suppressors was not organ specific. Suppressors inhibited proliferation in liver irrespective of the site of operation.     

Regulation of Na channels of the rat cortical collecting tubule by aldosterone

The activity of apical membrane Na channels in the rat cortical collecting tubule was studied during manipulation of the animals' mineralocorticoid status in vivo using a low-Na diet or the diuretic furosemide. Tubules were isolated and split open to expose the luminal membrane surface. Induction of Na channel activity was studied in cell- attached patches of the split tubules. No activity was observed with control animals on a normal diet. Channel activity could be induced by putting the animals on the low-Na diet for at least 48 h. The mean number of open channels per patch (NPo) was maximal after 1 wk on low Na. Channels were also induced within 3 h after injection of furosemide (20 mg/kg body wt per d). NPo was maximal 48 h after the first injection. In both cases, increases in NPo were primarily due to increases in the number of channels per patch (N) at a constant open probability (Po). With salt depletion or furosemide injection NPo is a saturable function of aldosterone concentration with half-maximal activity at approximately 8 nM. When animals were salt repleted after 1- 2 wk of salt depletion, both plasma aldosterone and NPo fell markedly within 6 h. NPo continued to decrease over the next 14 h, while plasma aldosterone rebounded partially. Channel activity may be dissociated from aldosterone concentrations under conditions of salt repletion.     

Uterine contractility and plasma levels of steroid hormones after intravaginal treatment of pregnant Japanese monkeys (Macaca fuscata fuscata) with 16,16-dimethyl-trans-delta2-prostaglandin E-1 methyl ester.

Intravaginal treatment with a PGE-1 analogue (ONO-802) resulted in strong uterine contractions with a high frequency which lasted for more than 3 h. When 20-50 microgram ONO-802/kg were administered intravaginally 5 times every 3 h in 5 pregnant animals, vaginal bleeding started by 6 h and abortion occurred by 26 h after the initial treatment. There were no significant side effects. Plasma levels of steroid hormones, especially progesterone and 20alpha-dihydroprogesterone, fluctuated initially and then finally dropped to undetectable levels within 24 h.     

Semistarvation and exercise

Nutritional intake plays an important role in determining metabolic and respiratory demands during both rest and exercise. This study examines the effects in normal subjects of 4 days of semistarvation with 440 kcal/day of intravenously infused dextrose followed by the infusion of 480 kcal/day of amino acids for 48 h on the metabolic and ventilatory response to exercise (1.25, 2.50, and 5.0 kg . m/s.). After 4 days of the dextrose infusion, arterial PCO2 (P less than 0.05), and the ventilatory equivalent for CO2 (VE/VCO2, P less than 0.05) were decreased at rest compared with control measurements made prior to the dextrose infusion. During all three levels of steady-state exercise, arterial PCO2 was significantly lower (P less than 0.05) than observed before the start of the dextrose infusion. The subsequent infusion of amino acids resulted in increases in O2 consumption (V02; P less than 0.05) and minute ventilation (VE; P less than 0.05), a decrease in arterial PCO2 (P less than 0.05), and little change in CO2 production (VCO2) at rest. During low levels of exercise, compared with the values obtained following the 4 days of dextrose infusion, there were larger increases in VE and VO2, whereas VCO2 changed little. Mechanical efficiency (kcal work/kcal energy utilized) during exercise increased after 4 days of dextrose and returned to near control levels with the amino acid infusion. The adaptive response characteristic of semistarvation with dextrose appears to be altered when isocaloric amounts of amino acids are subsequently administered for short periods.     

Mianserin-Induced Down-Regulation of Human 5-Hydroxytryptamine2A and 5-Hydroxytryptamine2C Receptors Stably Expressed in the Human Neuroblastoma Cell Line SH-SY5Y

Abstract: We have assessed the ability of the serotonergic antagonist mianserin to modulate the number and functional activity of human 5-hydroxytryptamine_2A (5-HT_2A) and 5-HT_2C receptors stably expressed in the human neuroblastoma cell line SH-SY5Y. Incubation of cells expressing the 5-HT_2A receptor with mianserin (100 n M ) for 24 h caused a significant decrease (48%) in the binding capacity of [³H]ketanserin. This receptor down-regulation was associated with a corresponding decrease in the maximal production of inositol phosphates induced by 5-HT but not by carbachol. Exposure of cells expressing the 5-HT_2C receptor to mianserin (100 n M ) for 72 h but not for 24 h similarly resulted in a significant reduction (44%) in [³H]mesulergine binding. Corresponding analysis of inositol phosphate production by 5-HT at the 5-HT_2C receptor after incubation with mianserin showed no change in maximal response after 24 h. No change in the binding capacity of either radioligand was seen after incubation with mianserin for 1 h. A decrease in the binding affinity of both radioligands was also observed after mianserin treatment, but this decrease was similar after 1 h of incubation to that seen after 24 or 72 h, and was probably due to the retention of mianserin within the tissue. We conclude that antagonist down-regulation is evident at human 5-HT_2A and 5-HT_2C receptors stably expressed in a human neuroblastoma cell line and is probably mediated by a direct action of mianserin at the receptor.     

Hyperbaric oxygen treatment: the influence on the hippocampal superoxide dismutase and Na+,K+-ATPase activities in global cerebral ischemia-exposed rats

The influence of hyperbaric oxygen (HBO) treatment on the activities of superoxide dismutase (SOD) and Na⁺,K⁺-ATPase was determined during different time periods of reperfusion in rats exposed to global cerebral ischemia. Ischemic animals were either sacrificed or exposed to the first HBO treatment 2, 24, 48 or 168 h after ischemic insult (for SOD activities measurement) or immediately, 0.5, 1, 2, 6, 24, 48, 72 or 168 h after ischemic procedure (for Na⁺,K⁺-ATPase activities measurement). Hyperbaric oxygenation procedure was repeated for seven consecutive days. The results of presented experiments demonstrated the statistically significant increase in the hippocampal SOD activity 24 and 48 h after global cerebral ischemia followed by a decrease in the enzymatic activity 168 h after ischemic insult. In the ischemic rats treated with HBO the level of hippocampal SOD activity was significantly higher after 168 h of reperfusion in comparison to the ischemic, non HBO-treated animals. In addition, it was found that global cerebral ischemia induced a statistically significant decrease of the hippocampal Na⁺,K⁺-ATPase activity starting from 1 to 168 h of reperfusion. Maximal enzymatic inhibition was obtained 24 h after the ischemic damage. Decline in Na⁺,K⁺-ATPase activity was prevented in the animals exposed to HBO treatment within the first 24 h of reperfusion. Our results suggest that global cerebral ischemia induces significant alterations in the hippocampal SOD and Na⁺,K⁺-ATPase activities during different periods of reperfusion. Enhanced SOD activity and preserved Na⁺,K⁺-ATPase activity within particular periods of reperfusion, could be indicators of a possible benefitial role of HBO treatment in severe brain ischemia.     

Role of protein degradation in the growth of livers after a nutritional shift.

Fractional rates of synthesis and degradation of liver porteins were estimated during the rapid restoration of liver mass observed in protein-depleted mice when they are fed with an adequate diet. 1. Net protein gain was fastest 12h after the nutritional shift, when it reached a rate of 48% per day. 2. The RNA/protein ratio in livers of protein-depleted animals was essentially the same as in normal livers; it increased by a maximum of 13% 12h after the nutritional shift. 3. Rates of protein synthesis in vivo were measured by the incorporation into liver protein of massive amounts of L-[1-14C]leucine. In protein-depleted animals, the rate of synthesis per mg of RNA was 72% of that in normal livers. Normal rates were recovered within 12h of the nutritional shift. 4. The fraction of newly synthesized protein retained by the liver was studied after they were pulse-labelled by the intravenous injection of radioactive leucine, and, 5 min later, pactamycin (an inhibitor of the initiation of protein synthesis); 3h later the livers in both experimental situations retained 58% of the newly synthesized protein. 5. Fractional rates of protein degradation were estimated either from the difference between the synthesis of stable liver proteins and the net protein increase, or by the disappearance of radioactivity from the liver protein previously labelled by the administration to the mice of NaH14CO3. Both procedures demonstrated a large decrease in the rate of protein degradation during liver growth.     

Changes in peripheral inhibin levels and follicular development following treatment of buffalo with PMSG and Neutra-PMSG for superovulation

Fourteen buffalo were synchronized by administration of a prostaglandin (PG) salt Lutalyse in a double injection schedule, with a single intramuscular (im) injection of 25 mg at Day -13, followed by 30 mg and 20 mg im 12 h apart on Day 0 of the experiment. The 30-mg PG injection was designated as 0 h of the experiment. Group I animals (n = 4) received saline and served as the controls, while animals in Groups II and III (n = 5 each) received PMSG (2500 IU im at -48 h. Group III animals were administered 5 ml Neutra-PMSG intravenously at 60 h. Blood samples were collected every 48 h from Day -12 to Day -4, every 24 h from Day -4 to Day 0, every 3 h from Day 1 to Day 4 and every 24 h from Day 5 to Day 10 of experiment for the measurement of peripheral plasma inhibin concentrations by RIA. The number of large follicles (> 10 mm diameter) in animals of Groups II and III was assessed by ultrasonography on Days -2, -1, 0, 1, 2, 5 and 7 of the experiment. Treatment with PMSG of Group II animals resulted in a significant increase (P < 0.05) in plasma inhibin concentrations over that of control animals of Group I at 24 to 99 h, with a peak inhibin concentration of 1.01 +/- 0.31 ng/ml at 48 h. Treatment with Neutra-PMSG in Group III animals caused a significant reduction (P < 0.05) in the peripheral inhibin concentrations at 84 to 120 h and in the number of large unovulated follicles at 168 h compared with that in Group II animals. Peripheral inhibin levels in Group III animals came down to those of Group I after 21 h of Neutra-PMSG treatment. These results suggest that treatment of buffalo with PMSG for superovulation causes a marked rise in peripheral inhibin concentrations. Administration of Neutra-PMSG after PG treatment reduces the peripheral inhibin concentrations and the number of large unovulated follicles.     

Growth hormone stimulates the peripheral conversion of thyroxine into triiodothyronine by increasing the liver 5'-monodeiodinase activity in the fasted and normal fed chicken

Normal fed and 2 days fasted Warren chickens were injected intravenously with 100 micrograms of ovine growth hormone (GH) and ovine prolactin and plasma concentrations of thyroid hormones were assayed prior and up to 2 h after injection. Fasting alone decreases T3, but increases T4. An injection of GH resulted in increases of plasma T3 concentrations in two fasting experiments by 40% (after 3/4 h) and 104% (after 1 h). In normal fed animals no increase is observed in the first experiment, whereas a 35% increase occurs in the second one. An injection of 100 micrograms prolactin does not influence T3 in normal fed or fasting animals. Both GH and prolactin, however, may decrease plasma concentrations of T4. In a separate experiment 50 micrograms and 200 micrograms of GH raised the decreased T3 levels after fasting by 39% and 60% respectively 1 h after injection and by 24 and 61% respectively in normal fed chicken, whereas prolactin was ineffective in this regard. Using Hisex chickens, the influence of an injection of 100 micrograms GH on plasma concentrations of thyroid hormones could be confirmed. At the same time GH increases the liver 5'-monodeiodinase activity by 330% after 1 h and by 147% after 2 h. The peroxidase activity is not influenced in normal fed chickens, but GH decreases this activity in food deprived animals after 1 h and 2 h. It is concluded that ovine GH, but not prolactin, stimulates the peripheral conversion of T4 into T3 in both normal fed and food deprived chicken and that this effect is dose dependent.     

Mutagenic activity of the organophosphorus insecticide chloracetophon

Chloracetophone (0,0-dimethyl-2,2,2-trichloro-1-(1-chloroacetoxy)phosphonate) is a new organophosphorus insecticide. The LD50 for male rats is 420 mg/kg b.w. The mutagenic activity was evaluated with the method of cytogenetic analysis of rat bone marrow after acute and short-term oral exposure. In the acute study groups of male and female animals were treated with chloracetophone at a dose of 1/5 LD50 and then examined at periods of 6, 12, 24, 48 and 72 h following administration. Separate groups of animals were examined 24 h after single administration of the doses 1/5, 1/10 and 1/20 LD50. In the short-term study groups of male animals were treated for 5 successive days. The slides were prepared 6 or 24 h after the last administration. Concurrent negative and positive (cyclophosphamide 20 mg/kg b.w.) control groups were used. 50 cells at metaphase per animal were scored for chromosomal aberrations. The results did not show significant increase in the frequency of chromosomal breaks in the groups with chloracetophone.     

Modulation of myocardial mitochondrial mechanisms during severe polymicrobial sepsis in the rat

Background

We tested the hypothesis that 5-Hydroxydecanoic acid (5HD), a putative mitoK_ATP channel blocker, will reverse sepsis-induced cardiodynamic and adult rat ventricular myocyte (ARVM) contractile dysfunction, restore mitochondrial membrane permeability alterations and improve survival.

Methodology/Principal Findings

Male Sprague-Dawley rats (350–400 g) were made septic using 400 mg/kg cecal inoculum, ip. Sham animals received 5% dextrose water, ip. The Voltage Dependent Anion Channels (VDAC1), Bax and cytochrome C levels were determined in isolated single ARVMs obtained from sham and septic rat heart. Mitochondria and cytosolic fractions were isolated from ARVMs treated with norepinephrine (NE, 10 µmoles) in the presence/absence of 5HD (100 µmoles). A continuous infusion of 5HD using an Alzet pump reversed sepsis-induced mortality when administered at the time of induction of sepsis (−40%) and at 6 hr post-sepsis (−20%). Electrocardiography revealed that 5HD reversed sepsis-induced decrease in the average ejection fraction, Simpsons+m Mode (53.5±2.5 in sepsis and 69.2±1.2 at 24 hr in sepsis+5HD vs. 79.9±1.5 basal group) and cardiac output (63.3±1.2 mL/min sepsis and 79.3±3.9 mL/min at 24 hr in sepsis+5HD vs. 85.8±1.5 mL/min basal group). The treatment of ARVMs with 5HD also reversed sepsis-induced depressed contractility in both the vehicle and NE-treated groups. Sepsis produced a significant downregulation of VDAC1, and upregulation of Bax levels, along with mitochondrial membrane potential collapse in ARVMs. Pretreatment of septic ARVMs with 5HD blocked a NE-induced decrease in the VDAC1 and release of cytochrome C.

Conclusion

The data suggest that Bax activation is an upstream event that may precede the opening of the mitoK_ATP channels in sepsis. We concluded that mitoK_ATP channel inhibition via decreased mitochondrial membrane potential and reduced release of cytochrome C provided protection against sepsis-induced ARVM and myocardial contractile dysfunction.     

Testicular torsion and its effects on the spermatogenic cycle in the contralateral testis of the rat

The aim of the present study was to evaluate the effects of unilateral testicular torsion on the contralateral testis with respect to the stages of the cycle of the seminiferous epithelium (CSE). Fifty-five male Wistar rats, 60 days old, were used. The animals were divided into 11 groups. Groups 1-5 were subjected to unilateral testicular torsion from 3 to 48 h, followed by detorsion. Groups 6-10 had unilateral orchiectomies after unilateral testicular torsion for 3 to 48 h. Animals constituting group 11 served as the control sham-operated group. All animals were killed after 2 months. The percentage of affected tubules (tubules showing pathological changes) in the contralateral testis was estimated based on the CSE stages. In the torsion/detorsion group, the percentage of affected tubules was significantly greater (58.6%) than in torsion/orchiectomy group (48.0%). Stages VI-XI of the spermatogenic cycle were the most affected when compared with the rest of the stages in each experimental group (P <0.05). These results show that stages VI-XI of the spermatogenic cycle, the stages associated with low antioxidant capacities, are the most sensitive to the effects of testicular torsion on the contralateral testis.     

Persistence of drug-induced chromosome aberrations in peripheral blood lymphocytes of the rat

We have studied the persistence of pre-clastogenic lesions, detected as induced chromosomal aberrations, in rat peripheral lymphocytes at various time intervals after acute treatment with 3 different antineoplastic drugs: cyclophosphamide (CPA), 5-fluorouracil (5-FU) and adriamycin (AM). Single i.p. doses were administered to groups of rats and heart blood samples from each group were taken after 3, 12, 24 or 48 h or weekly up to 20 weeks later. The cytogenetic analysis was performed on lymphocytes cultured for 33 h after sampling. The results for CPA exposure (10 mg/kg) show that the yield of chromosome aberrations is maximal 3 h after the treatment (20 times the control level). For up to 8 weeks the values remain about 6 times the baseline; afterwards a decrease is observed and the control level is reached after 20 weeks. For 5-FU (50 mg/kg) a remarkable increase (13-fold) in chromosomal damage is observed at the first sampling time. Within 48 h the effect is drastically reduced but persistent (3 times the control level), and the level returns to spontaneous values 1 week later. AM treatment (2 mg/kg) induced an increase of about 8 times the control level at 3 h post exposure. The clastogenic effects remained at a detectable level for 1 week (about 6 times the control level at all sampling times); 2 weeks after the treatment the control level was found. A parallel analysis was performed on bone marrow cells. In this tissue the clastogenic effects of the treatments were maximal, as in lymphocytes, at the first sampling time (20-25 times the control level) and were no longer detectable within 72 h after exposure, irrespective of the administered drug.     

The role of leucine in ketogenesis in starved rats.

The quantitative significance of the conversion in vivo of L-[U-14C]leucine to ketone bodies was determined in rats starved for 3 or 48 h. In animals starved for 3 h, 4.4% of ketone-body carbon is derived from the metabolism of leucine, and in rats starved for 48 h the corresponding value is 2.3%. This conversion occurs rapidly, and the specific radioactivity of ketone bodies in blood is maximal at 2 min after the intravenous injection of labelled leucine for both periods of starvation. The flux of leucine in the blood is 1.01 and 1.04 mumol/min per 100 g body wt. respectively for animals starved for 3 and 48 h. The specific radioactivity of blood ketone bodies was compared at 2 min after the injection of labelled leucine, lysine and phenylalanine. The specific radioactivity was 4-5 fold higher with leucine than with lysine or phenylalanine.     

Effect of hysterectomy on the short life-cycle corpus luteum produced after GnRH-induced ovulation in the anoestrous ewe

Anoestrous Romney Marsh ewes were treated with small-dose (250 ng) multiple injections of GnRH. Ewes in Groups 1 and 3 were hysterectomized 2 weeks before treatment, while those in Groups 2 and 4 were intact controls. Groups 1 and 2 were primed with progesterone (+P) and treated with 2 h injections of GnRH (250 ng) for 36 h, while Groups 3 and 4 were not pretreated (-P) but were given 2 h injections of GnRH (250 ng) for 18 h. Both treatment regimens were terminated with a bolus injection of GnRH (125 micrograms), given to synchronize the timing of the LH surge and subsequent luteal progesterone production. The plasma progesterone profiles of 5/5 animals in Group 2 (+P controls) and 2/5 animals in Group 4 (-P controls) were indicative of normal luteal function, while the remaining 3/5 animals in Group 4 produced plasma progesterone profiles typical of abnormal luteal function. However, in all the hysterectomized animals (Groups 1 and 3) peripheral plasma progesterone concentrations rose to reach a mean peak value of 1.3 ng/ml plasma on Day 8 which was maintained in all animals irrespective of progesterone pretreatment. The absence of a fall in progesterone concentrations precluded the identification of any animal in Group 4 showing abnormal luteal function. It was also noted that, after hysterectomy, although the corpus luteum was maintained, it was with reduced secretory capacity. The prevention of the expected proportion (70%) of -P animals from displaying a decline in plasma progesterone concentration after hysterectomy provides firm evidence that the uterus is involved in the premature regression of the short-cycle corpus luteum.     

Changes in the proportion of acetyl-CoA carboxylase in the active form in rat liver. Effect of starvation, lactation and weaning

1. The activity of acetyl-CoA carboxylase (EC 6.4.1.2) in extracts of freeze-clamped liver samples from fed or 24 h-starved virgin, pregnant, lactating and weaned rats was measured (i) immediately after preparation of extracts (;I activity'), (ii) after incubation of extracts with partially purified preparations of either rabbit muscle protein phosphatase 1 [Antoniw, Nimmo, Yeaman & Cohen (1977) Biochem. J.162, 423-433] or rabbit liver phosphatase [Brandt, Capulong & Lee (1975) J. Biol. Chem.250, 8038-8044] (;A activity') and (iii) after incubation with 20mm-potassium citrate before or after incubation with phosphatases (;C activity'). 2. Incubation of liver extracts at 30 degrees C without any additions resulted in activation of acetyl-CoA carboxylase that was shown to be due to dephosphorylation of the enzyme by endogenous protein phosphatase activity. This latter activity was not stimulated by Ca(2+) and/or Mg(2+) but was stimulated by 1 mm-Mn(2+). Incubation of extracts with either of the partially purified phosphatases (0.2-0.5 unit) resulted in faster dephosphorylation and activation. The activity achieved after incubation with either of the exogenously added phosphatases was similar. 3. The A and C activities increased during late pregnancy, were lower than in the virgin rat liver during early lactation and increased by 2-fold in liver of mid-lactating rats. Weaning of mid-lactating rats for 24 h resulted in no change in A and C activities but after 48 h weaning they were significantly lower than those in livers from suckled mothers. 4. The I activity followed a similar pattern of changes as the A and C activities during pregnancy and lactation such that, although the I/A and I/C activity ratios tended to be lower during late pregnancy and early lactation, there were no significant changes in I/A and I/C ratios between lactating and virgin animals. However, these ratios were significantly higher in liver from fed 24 h-weaned animals. 5. Starvation (24 h) resulted in a marked decrease in I activity for all animals studied except early-lactating rats. This was due to a combination of a decrease in the concentration of acetyl-CoA carboxylase in liver of starved animals (A and C activities) and a decrease in the fraction of the enzyme in the active form (lower I/C and I/A ratios). The relative importance of the two forms of regulation in mediating the starvation-induced fall in I activity was about equal in livers of virgin, pregnant and lactating animals. However, the decrease in I/A and I/C ratios was of dominating importance in livers of weaned animals. The A/C activity ratios were the same for livers from all animals studied. 6. The maximal activity of fatty acid synthase was also measured in livers and was highly and positively correlated with the A and C activities of acetyl-CoA carboxylase, suggesting that the concentrations of the two enzymes in the liver were controlled coordinately. 7. It is suggested that the lack of correlation between plasma insulin levels and rates of lipogenesis in the transition from the virgin to the lactating state may be explained by different effects of insulin and prolactin on the concentration of acetyl-CoA carboxylase in the liver and on the fraction of the enzyme in the active form.