Regulation of TRH and TRH-related peptides in rat brain by thyroid and steroid hormones.

To investigate the possibility that TRH (pGlu-His-Pro-NH(2)) and EEP (pGlu-Glu-Pro-NH(2)) contribute to the behavioral and mood changes attending hypothyroidism, hyperthyroidism and hypogonadism, we have treated young, adult, male Sprague-Dawley rats (5/group, 250 g bw at time of sacrifice) for one week with either daily ip injections of saline, 5 microg T(4), 3 mg PTU or castration. Immunoreactivity for TRH (TRH-IR), TRH-Gly (pGlu-His-Pro-Gly, a TRH precursor), EEP and Ps4 (prepro-TRH-derived TRH-enhancing peptide) was measured in 8 brain regions by RIA. Castration reduced the Ps4-IR levels in hippocampus by 80%. High pressure liquid chromatography revealed that in many brain regions EEP-IR and TRH-IR consisted of a mixture of TRH and other TRH-like peptides including EEP, Val(2)-TRH, Tyr(2)-TRH, Leu(2)-TRH and Phe(2)-TRH. Transition from the hyperthyroid to the hypothyroid state increased the Val(2)-TRH and Tyr(2)-TRH levels in the accumbens by 10-fold and 15-fold, respectively, and the corresponding ratios for the pyriform cortex increased 9-fold and 12-fold, respectively. Hypothyroidism and castration reduced the levels of TRH and the majority of other TRH-like peptides in the entorhinal cortex. This is the first report that thyroid and steroid hormones alter the levels of TRH, prepro-TRH-derived peptides, and a newly discovered array of TRH-like neuropeptides in limbic brain regions.     

Lactate delivery (not oxygen) limits hepatic gluconeogenesis when blood flow is reduced

The purpose of this study was to determine, using the isolated liver perfusion technique, whether the limiting factor for hepatic gluconeogenesis (GNG) from lactate was precursor delivery or oxygen availability during reduced flow rates of 0.85 or 0.60 ml.min(-1).g liver(-1). After a 24-h fast, three different experimental protocols were employed. Protocol 1 examined the impact on GNG when reservoir lactate concentration was maintained but oxygen delivery was elevated via increases in hematocrit (Hct). Elevating the Hct from 22.5+/- 0.8% to 30.9+/- 0.4% at a blood flow of 0.89+/- 0.01 ml.min(-1).g liver(-1) increased the oxygen consumption (Vo(2)) but did not augment GNG. Similarly, when the Hct was elevated from 22.5+/- 0.8% to 41.5+/- 0.7% at 0.59+/- 0.04 ml.min(-1).g liver(-1), Vo(2) was increased, but GNG was unaffected. Protocol 2 examined the impact on GNG when Hct was maintained but precursor delivery was elevated via increases in reservoir lactate concentration ([LA]). Specifically, elevating the [LA] from 2.31+/- 0.07 to 3.61+/- 0.33 mM at a flow rate of 0.82+/- 0.04 ml.min(-1).g liver(-1) significantly increased GNG. Similarly, elevating the [LA] from 2.31+/- 0.07 to 4.24+/- 0.37 mM at a flow rate of 0.58+/- 0.02 ml.min(-1).g liver(-1) increased GNG. Finally, we examined the impact of increasing both the oxygen and lactate delivery (Protocol 3). Again, Vo(2) was elevated with increased oxygen delivery, but GNG was not augmented beyond that observed with elevations in lactate delivery alone, i.e., Protocol 2. The results indicate that, during decrements in blood flow, GNG is limited primarily by precursor delivery, not oxygen availability.     

Synthesis, biological activity, and tritiation of L-3, 4-dehydroproline-containing peptides

A series of analogs of thyroliberin (TRH) ([L-delta3Pro3]-TRH, [D-delta3Pro3]-TRH, [L-3-MeHis2, L-delta3Pro3]-TRH) in which proline was replaced by L- or D-3, 4-dehydroproline was synthesized. The analogs exhibited approximately the same biological activity as the corresponding proline-containing peptides. These analogs and others in which 3, 4-dehydroproline is present at the NH2-terminal, COOH-terminal or internal positions in the peptide were successfully reduced with deuterium or tritium to provide the 3, 4-2H2-proline or 3,4-3H2-proline analogs, respectively, with near theoretical values of substitution. A novel procedure for the chemical resolution of DL-3, 4-dehydroproline is also described.     

Central nervous system action of TRH to stimulate gastric emptying in rats

The effects of intracisternal injection of TRH on gastric emptying of a liquid meal was investigated in 24 h fasted rats using the phenol red method. Intracisternal injection of TRH, RX 77368, or [N-Val2]-TRH, an analog devoid of TSH-releasing activity, 5 min prior to a meal, stimulated gastric emptying measured 20 min later. TRH action was dose dependent (1-100 ng), and rapid in onset. The calculated time for emptying half of the meal was decreased from 16 +/- 3 min (control group) to 4 +/- 1 min (TRH 30 ng). The stable analog, RX 77368, unlike TRH, stimulated gastric emptying when the meal was given 60 min after peptide injection. Intravenous injection of atropine (2.5 micrograms) inhibited and that of carbachol (1 microgram) stimulated gastric emptying whereas i.v. injection of TRH (0.1-1 microgram) had no effect. Vagotomy but not adrenalectomy reversed the increase in gastric emptying induced by intracisternal TRH. Atropine blocked the stimulatory effect of TRH and carbachol. These results demonstrate that TRH acts within the brain to stimulate gastric emptying through vagus-dependent and cholinergic pathways whereas alterations of adrenal and pituitary-thyroid secretion do not play an important role.     

Postprandial body protein synthesis and amino acid catabolism measured with leucine and phenylalanine-tyrosine tracers

Whether phenylalanine-tyrosine (Phe-Tyr) tracers yield estimates of postprandial protein synthesis comparable to those of the widely used leucine (Leu) tracer is unclear. We measured Leu oxidation (Ox), Phe hydroxylation (Hy), and their disposal into whole body protein synthesis before and after the administration of a mixed meal (62 kJ/kg body wt, 22% of energy as protein), over 4 h in healthy subjects. Both plasma and intracellular precursor pools were used. The amino acid data were extrapolated to body protein by assuming a fixed ratio of Leu to Phe in the proteins. In the postabsorptive state, whole body protein synthesis (expressed as mg. kg(-1). min(-1)) was similar between Leu and Phe-Tyr tracers irrespective of the precursor pool used. After the meal, Leu Ox, Phe Hy, and body protein synthesis increased (P < or = 0.01 vs. basal). With the use of intracellular precursor pools, the increase of protein synthesis with Phe-Tyr (+0.51 +/-0.21 mg. kg(-1). min(-1)) and Leu tracers (+0.57 +/- 0.14) were similar (P = not significant). In contrast, with plasma pools the increase of protein synthesis was more than twofold greater with Phe-Tyr (+1.17 +/- 0.19 mg. kg(-1). min(-1)) than that with Leu (0.50 +/- 0.13 mg. kg(-1). min(-1), P < 0.01). Direct correlations were found between Leu and Ox [using both plasma and intracellular pools (r < or = 0.65, P < or = 0.01)] but not between Phe and either plasma or intracellular Hy. In conclusion, 1) Phe-Tyr and Leu tracers yield comparable estimates of body protein synthesis postprandially, provided that intracellular precursor pools are used; 2) both Leu Ox and Phe Hy are stimulated by a mixed meal; 3) Phe does not correlate with Hy, which might be better related to the (unknown) portal Phe.     

Effects of severity of dystocia on cold tolerance and serum concentrations of glucose and cortisol in neonatal beef calves

Effects of dystocia on rectal temperature and serum cortisol and glucose concentrations, were studied in neonatal calves exposed to 0 degree C. Primiparous dams were observed continuously during parturition and if Stage II (labor) was not completed within 2 h after appearance of the allantochorion, delivery was completed with obstetrical assistance. Parturitions were scored (CDS) for difficulty and obstetric assistance required: CDS 1, no assistance (n = 8); CDS 2, minor manual assistance (n = 7); CDS 3, use of a mechanical calf puller (n = 5); CDS 4, cesarean section (n = 6). A blood sample, rectal temperature, and body weight were obtained within 30 min after birth. Calves were then fed 38 degrees C pooled colostrum, muzzled to prevent suckling, and placed back with their dam in a heated (22 degrees C) barn. At 4 h of age an indwelling jugular catheter was inserted. At 5 h of age calves were placed in a 0 degree C room for 140 min and blood samples and rectal temperatures were obtained every 10 or 20 min. A shivering score (1 = no shivering; 2 = moderate shivering; 3 = intense shivering) was assigned at each sampling time. Rectal temperatures were higher (P < 0.01) in CDS 1, 2 and 4 calves (39.0, 39.3, and 39.0 +/- .02 degrees C, respectively) than in calves with CDS 3 (38.3 +/- 0.02 degrees C) and were affected by duration of cold exposure (time; P < 0.01). Shivering was not affected by CDS but was affected by time (P < 0.01). Glucose concentrations were higher (P < 0.01) in CDS 3 calves (110.1 +/- 1.6 mg/dL) than in CDS 1, 2, or 4 calves (77.2, 86.4, and 89.0 +/- 1.3 mg/dL, respectively) and changed over time (P < 0.01). Cortisol concentrations were higher in CDS 1 calves (80.0 +/- 1.7 ng/mL) than in CDS 2, 3 or 4 calves (62.7, 58.2, and 57.7 +/- 2.0 ng/mL, respectively) and were affected by time (P < 0.01). We conclude that severe dystocia (CDS 3) resulted in lower calf rectal temperature, reduced serum cortisol, and increased serum glucose which could affect the ability of the calf to withstand cold stress. Minor dystocia did not cause and timely cesarean delivery prevented, the physiological aberrations encountered in severe dystocia.     

Potent and selective tools to investigate neuropeptide Y receptors in the central and peripheral nervous systems: BIB03304 (Y1) and CGP71683A (Y5)

We have evaluated 3 newly developed neuropeptide Y receptor antagonists in various in vitro binding and bioassays: BIBO3304 (Y1), T4[NPY33-36]4 (Y2), and CGP71683A (Y5). In rat brain homogenates, BIBO3304 competes for the same population of [125I][Leu31,Pro34] peptide YY (PYY) binding sites (75%) as BIBP3226, but with a 10 fold greater affinity (IC50 of 0.2 +/- 0.04 nM for BIBO3304 vs. 2.4 +/- 0.07 nM for BIBP3226),while CGP71683A has high affinity for 25% of specific [125I][Leu31,Pro34]PYY binding sites. Both BIBO3304 and CGP71683A (at 1.0 microM) were unable to compete for a significant proportion of specific [125I]PYY3-36/Y2 sites. The purported Y2 antagonist T4[NPY33-36]4 competed against [125I]PYY3-36 binding sites with an affinity of 750 nM. These results were confirmed in HEK 293 cells transfected with either the rat Y1, Y2, Y4, or Y5 receptor cDNA. BIBO3304, but not CGP71683A, competed with high affinity for [125I][Leu31,Pro34]PYY binding sites in HEK 293 cells transfected with the rat Y1 receptor cDNA, whereas the reverse profile was observed upon transfection with the rat Y5 receptor cDNA. Additionally, both molecules were inactive at Y2 and Y4 receptor subtypes expressed in HEK 293 cells. Receptor autoradiographic studies revealed the presence of [125I][Leu31,Pro34]PYY/BIBO3304-insensitive sites in the rat brain as reported previously for BIBP3226. Finally, the selective antagonistic properties of BIBO3304 were demonstrated in a Y1 bioassay (rabbit saphenous vein; pA2 value of 9.04) while being inactive in Y2 (rat vas deferens) and Y4 (rat colon) bioassays. These results confirm the high affinity and selectivity of BIBO3304 and CGP71683A for the Y1 and Y5 receptor subtypes, respectively, while the purported Y2 antagonist, T4[NPY33-36]4 possesses rather low affinity for this receptor.     

Radiolabeling and biodistribution of methyl 2-(methoxycarbonyl)-2-(methylamino) bicyclo[2.1.1] -hexane -5-carboxylate,a potential neuroprotective drug

Methyl 2-(methoxycarbonyl) -2-(methylamino) bicyclo[2.1.1] -hexane -5-carboxylate (MMMHC) is developed as a potential neuroprotective drug. It was labeled with C-11 from the desmethyl precursor methyl 2-(methoxycarbonyl)-2-amino bicyclo[2.1.1]-hexane-5-carboxylate with [11C]methyl triflate in acetone solution at 60 degrees C with labeling yield of 69% and with radiochemical purity of >99%. Positron Emission Tomography (PET) studies in a normal rat showed that Methyl 2-(methoxycarbonyl)-2-([11C]methylamino)bicyclo[2.1.1]-hexane-5-carboxylate ([11C] MMMHC) accumulated mainly in the cortical brain areas after iv administration. Frontal cortex/cerebellum ratios in a rat brain were 8.0/6.0, 6.8/4.2, 6.3/4.3, 5.5/4.2 and 5.2/4.5 percent of the injected dose in 100 ml at 2 min, 5 min, 10 min, 20 min and 40 min respectively after i.v. injection. During 20-40 min, 2.9+/-0.4% of the total activity stayed in the brain. These results showed that MMMHC could be labeled with C-11 with high yield, and it passed the brain-blood barrier and accumulated in several brain regions.     

Brain-to-blood efflux transport of estrone-3-sulfate at the blood-brain barrier in rats

Efflux transport of estrogens such as estrone-3-sulfate (E1S), and estrone (E1) across the blood-brain barrier (BBB) was evaluated using the Brain Efflux Index (BEI) method. The apparent BBB efflux rate constant (Keff) of [3H]E1S, and [3H]E1 was 6.63 x 10(-2) +/- 0.77 x 10(-2) min(-1), and 6.91 x 10(-2) +/- 1.23 x 10(-2) min(-1), respectively. The efflux transport of [3H]E1S from brain across the BBB was a saturable process with Michaelis constant (Km) of 96.0 +/- 34.4 microM and 93.4 +/- 22.0 microM estimated by two different methods. By determining [3H]E1S metabolites using high performance liquid chromatography (HPLC) after intracerebral injection, significant amounts of [3H]E1S were found in the jugular venous plasma, providing direct evidence that most of [3H]E1S is transported from brain across the BBB in intact form. To compare the apparent efflux clearance across the BBB of E1S with that of E1, the brain distribution volume of E1S and E1 was estimated using the brain slice uptake method. The apparent efflux clearance of [3H]E1S was determined to be 74.9 +/- 3.8 microl/(min x g brain) due to the distribution volume of 1.13 +/- 0.06 ml/g brain. By contrast, the apparent efflux clearance of E1 was more than 227 +/- 3 microl/(min x g brain), since the distribution volume of [3H]E1 at 60 min was 3.28 +/- 0.13 ml/g. The E1S efflux transport process was inhibited by more than 40% by coadministration of bile acids (taurocholate, and cholate), and organic anions (sulfobromophthalein, and probenecid), whereas other organic anions did not affect the E1S efflux transport. The [3H]E1S efflux was significantly reduced by 48.6% after preadministration of 5 mM dehydroepiandrosterone sulfate. These results suggest that E1S is transported from brain to the circulating blood across the BBB via a carrier-mediated efflux transport system.     

Biochemical and Autoradiographical Determination of Protein Synthesis in Experimental Brain Tumors of Rats

The rate of leucine incorporation into brain proteins was studied in rats with experimental brain tumors produced by intracerebral transplantation of the glioma clone F98. Incorporation was measured with [14C]leucine using a controlled infusion technique for maintaining constant specific activity of [14C]leucine in plasma, followed by quantitative autoradiography and biochemical tissue analysis. After 45 min the specific activity of free [14C]leucine in plasma was 2.5-3 times higher than in brain and brain tumor, indicating that the precursor pool for protein synthesis was fueled both by exogenous (plasma-derived) and endogenous (proteolysis-derived) amino acids. Endogenous recycling of amino acids amounted to 73% of total free leucine pool in brain tumors and to 60-70% in normal brain. Taking endogenous amino acid recycling into account, leucine incorporation was 78.7 +/- 16.0 nmol/g of tissue/min in brain tumor, and 17.2 +/- 4.2 and 9.7 +/- 3.3 nmol/g/min in normal frontal cortex and striatum, respectively. Leucine incorporation within tumor tissue was markedly heterogeneous, depending on the local pattern of tumor proliferation and necrosis. Our results demonstrate that quantitative measurement of leucine incorporation into brain proteins requires estimation of recycling of amino acids derived from proteolysis and, in consequence, biochemical determination of the free amino acid precursor pool in tissue samples. With the present approach such measurements are possible and provide the quantitative basis for the evaluation of therapeutic interventions.     

A macromolecule which gives rise to thyrotropin releasing-hormone.

Chemical and enzymatic treatment of a high-molecular weight fraction from a frog brain extract resulted in formation of a “TRH-Like material” (TRH-i). Sequential treatment with trypsin and carboxypeptidases A and B, acetic acid and then chemical amidation generated a quantity of TRH-i equivalent to 25% of the endogenous TRH. TRH-i was similar to TRH (pGlu·His·ProNH₂) as assessed by molecular weight estimations, radioimmunoassay and susceptibility to serum inactivation. TRH and TRH-i also competed with [³H]-TRH for binding to TRH receptors, stimulated prolactin synthesis and uridine uptake, and “down-regulated” TRH receptors in pituitary cells. These results suggest the possibility that TRH may be processed from a macromolecular precursor.     

17O-NMR studies of the conformational and dynamic properties of enkephalins in aqueous and organic solutions using selectively labeled analogues

The synthesis of Leu-enkephalin selectively 17O-enriched in Gly2 and Gly3 is reported. The 17O-nmr chemical shifts of [17O-Gly2, Leu5]- and [17O-Gly3, Leu5]-enkephalins in H2O are almost identical and independent of the pH. Since hydrogen bonding is the dominant factor governing the chemical shifts of the peptide oxygen, it can be concluded that the hydration state of both oxygens is identical and independent of the pH. The 17O chemical shifts of the [17O-Leu5]-enkephalin terminal carboxyl group at pH approximately 1.9 and 5.6 are very different in H2O but very similar in CH3CN/DMSO (4:1) solution. This suggests that the protonation state of the carboxyl group at both pH values in CH3CN/DMSO solution is the same and consequently that Leu-enkephalin exists in the neutral form at pH approximately 5.6. In this organic mixed solvent system both Gly2 and Gly3 oxygen resonances exhibit a significant shift to high frequency by the same extent (delta delta approximately 30 ppm). It is concluded that both peptide oxygens are not hydrogen bonded to an appreciable extent and that no specific 2----5 hydrogen bonding exists to an appreciable extent. This conclusion is in agreement with the energy of activation for molecular rotation, as determined from T1 measurements, which was found to be almost identical for both [17O-Gly2, Leu5]- and [17O-Gly3, Leu5]-enkephalins in CH3CN/DMSO (4:1) mixed solvent.     

Neuropeptide Y-Y1 receptor modulates nitric oxide level during stroke in the rat

In a rat endovascular middle cerebral artery occlusion (MCAO) stroke model, we previously showed that intracerebroventricular (ICV) injection of neuropeptide Y (NPY) or an Y1 receptor agonist, [Leu(31),Pro(34)]-NPY, increased the infarct volume, that an Y1 receptor antagonist, BIBP3226, reduced the infarct volume, and that an Y2 receptor agonist, NPY3-36, had no effect. In this study, we used electron paramagnetic resonance (EPR) spectroscopy to measure nitric oxide (NO) and examined how ICV administration of NPY or its receptor analogs would modulate the brain NO level between the bregma levels +2 and -4 mm during MCAO, since excessive NO mediates ischemic damage. The relative brain NO concentration was increased to 131.94 +/- 7.99% (mean +/- SEM; n = 8) at 15 min of MCAO. NPY treatment further increased the relative brain NO concentration to 250.94 +/- 50.48% (n = 8), whereas BIBP3226 significantly reduced the brain NO concentration to 69.63 +/- 8.84% (n = 8). [Leu(31),Pro(34)]-NPY (137.61 +/- 14.54%; n = 7) or NPY3-36 (129.23 +/- 21.77%; n = 8) did not affect the brain NO concentration at 15 min of MCAO. Our results suggest that the NPY-Y1 receptor activation mediates ischemic injury via NO overproduction and that inhibition of the Y1 receptor may confer protection via suppression of excessive NO production during ischemia.     

Large alkyl side-chains of isoleucine and leucine in the NPIRL region constitute the core of the vacuolar sorting determinant of sporamin precursor

The N-terminal propeptide of the sporamin precursor contains vacuolar targeting information within the Asn-26/Pro-27/Ile-28/Arg-29/Leu-30 (NPIRL) sequence. An Agrobacterium-mediated transient expression assay with tobacco BY-2 cells was employed to investigate the role of each amino acid of the NPIRL region in vacuolar targeting. Replacement of Asn-26, Pro-27, Ile-28 and Leu-30 with several amino acids caused secretion of the mutant prosporamin. Leu was the only amino acid that could be substituted for Ile-28 without affecting transport. Exchange of Leu-30 for amino acids with small side-chains abolished vacuolar delivery. These results indicate that the consensus composition of the NPIRL sequence is [preferably Asn]-[not acidic]-[Ile or Leu]-[any amino acid]-[large and hydrophobic] and suggest that the large alkyl side-chains of Ile-28 and Leu-30 constitute the core of the vacuolar sorting determinant.     

Synthesis and in vivo evaluation of [11C]SN003 as a PET ligand for CRF1 receptors

Synthesis and evaluation of [O-methyl-11C](4-methoxy-2-methylphenyl)[1-(1-methoxymethylpropyl)-6-methyl-1H-[1,2,3]triazolo[4,5-c]pyridin-4-yl]amine or [11C]SN003 ([11C]6), as a PET imaging agent for CRF1 receptors, in baboons is described. 4-[1-(1-Methoxymethylpropyl)-6-methyl-1H-[1,2,3]triazolo[4,5-c]pyridin-4-ylamino]-3-methylphenol (5), the precursor molecule for the radiolabeling, was synthesized from 2,4-dichloro-6-methyl-3-nitropyridine in seven steps with 20% overall yield. The total time required for the synthesis of [11C]SN003 is 30 min from EOB using [11C]methyl triflate in the presence of NaOH in acetone. The yield of the synthesis is 22% (EOS) with >99% chemical and radiochemical purities and a specific activity of >2000 Ci/mmol. PET studies in baboon show that [11C]6 penetrates the BBB and accumulates in brain. No detectable specific binding was observed, likely due to the rapid metabolism or low density of CRF1 receptors in primate brain.     

Hydroxyurea transport across the blood-brain and blood-cerebrospinal fluid barriers of the guinea-pig

Hydroxyurea is used in the treatment of HIV infection in combination with nucleoside analogues, 2'3'-didehydro-3'deoxythymidine (D4T), 2'3'-dideoxyinosine or abacavir. It is distributed into human CSF and is transported from the CSF to sub-ependymal brain sites, but its movement into the brain directly from the blood has not been studied. This study addressed this by a brain perfusion technique in anaesthetized guinea-pigs. The carotid arteries were perfused with an artificial plasma containing [14C]hydroxyurea (1.6 microm) and a vascular marker, [3H]mannitol (4.6 nm). Brain uptake of [14C]hydroxyurea (8.0 +/- 0.9%) was greater than [3H]mannitol (2.4 +/- 0.2%; 20-min perfusion, n = 8). CSF uptake of [14C]hydroxyurea (5.6 +/- 1.5%) was also greater than [3H]mannitol (0.9 +/- 0.3%; n = 4). Brain uptake of [14C]hydroxyurea was increased by 200 microm hydroxyurea, 90 microm D4T, 350 microm probenecid, 25 microm digoxin, but not by 120 microm hydroxyurea, 16.5-50 microm D4T, 90 microm 2'3'-dideoxyinosine or 90 microm abacavir. [14C]Hydroxyurea distribution to the CSF, choroid plexus and pituitary gland remained unaffected by all these drugs. The metabolic half-life of hydroxyurea was > 15 h in brain and plasma. Results indicate that intact hydroxyurea can cross the brain barriers, but is removed from the brain by probenecid- and digoxin-sensitive transport mechanisms at the blood-brain barrier, which are also affected by D4T. These sensitivities implicate an organic anion transporter (probably organic anion transporting polypeptide 2) and possibly p-glycoprotein in the brain distribution of hydroxyurea and D4T.     

Generation of Arachidonic Acid and Diacylglycerol Second Messengers from Polyphosphoinositides in Ischemic Fetal Brain

Intracerebral administration of [3H]arachidonic acid ([3H]ArA) into 19-20-day-old rat embryos, resulted in a rapid incorporation of label into brain lipids. One hour after injection, 55.6 +/- 8.2, 18.0 +/- 3.4, and 13.7 +/- 1.3% of the total radioactivity was associated with phosphatidylcholine, phosphatidylinositol, and phosphatidylethanolamine, respectively. Approximately 10% of radioactivity was found acylated in neutral lipids of which free ArA comprised only 1.5 +/- 0.2% of the total radioactivity. Complete restriction of the maternal-fetal circulation for < or = 40 min did not affect the rate of [3H]ArA incorporation (t1/2 = 2 min) into fetal brain lipids, suggesting an effective acylation mechanism that proceeds irrespective of the impaired blood flow. After a short restriction period (5 min), the radioactivity in diacylglycerol was elevated by 50%. After a longer restriction period (20 min), the radioactivity in the free fatty acid and diacylglycerol fractions increased to values of 130 and 87%, respectively. Polyphosphoinositides prelabeled with either [3H]ArA or 32P were rapidly degraded after 5 min of ischemia. After 20 min, the decrease in phosphatidylinositol-4-phosphate and phosphatidylinositol-4,5-bisphosphate radioactivity was 47 and 70%, respectively. Double labeling of phospholipids with [14C]palmitic acid and [3H]ArA indicated a preferential loss of [3H]ArA within the polyphosphoinositide species after 20 min, but not after 5 min of ischemia. The specific activity of [14C]palmitate remained unchanged. The current data suggest phospholipase C-mediated diacylglycerol formation at the beginning of the insult followed by a phospholipase A2-mediated ArA liberation at a later time, both enzymes presumably acting preferentially on polyphosphoinositide species.     

4-Aminobutyraldehyde as a precursor convertible to gamma-aminobutyric acid in vivo

It was found that 4-aminobutyraldehyde (ABAL) is a precursor convertible to gamma-aminobutyric acid (GABA) in vivo. [2,3-3H]ABAL was synthesized from [2,3-3H]putrescine. After the subcutaneous administration of [3H]ABAL at the dose of 1 mumol/g body weight, [3H]GABA was produced in the mouse brain in an amount of about 350 nmol/g brain in 10 min. After oral administration of [3H]ABAL at the dose of 2 mumol/g body weight, [3H]GABA was also produced in the brain in an amount of about 530 nmol/g brain in 30 min. It seems that peripherally administered ABAL penetrates the blood-brain barrier into the central nervous system and is rapidly metabolized to GABA in the brain.     

Leucine pools in normal and dystrophic chicken skeletal muscle cells in culture

The specific radioactivity of [3H]Leu in the extracellular, intracellular, and Leu-tRNA pools of normal (white leghorn) and dystrophic (line 307) embryonic chick breast muscle cultures was analyzed as a function of equilibration time and extracellular Leu concentration (0.05-5 mM). The primary results were the following 1) [3H]Leu equilibrated to a constant specific radioactivity in the intracellular and Leu-tRNA pools within 2 min after addition to both normal and dystrophic cultures. 2) After equilibration, the extracellular [3H] Leu specific radioactivity in dystrophic cell culture medium was lower than that of medium exposed to normal cells (especially at low Leu concentrations), probably because of increased release of unlabeled Leu from the dystrophic cells as a result of faster protein breakdown. Accordingly, the specific radioactivities in the intracellular and the Leu-tRNA pools were also lower in dystrophic cells. 3) At 5 mM extracellular Leu, the specific radioactivity in the Leu-tRNA pool was approximately 40% lower than the specific radioactivity in the intracellular pool in both normal and dystrophic cells. Thus, high concentrations of extracellular Leu cannot be used to "flood out" reutilization of unlabeled Leu (released by protein degradation) during protein synthesis. 4) At 5.0 mM extracellular Leu, the specific radioactivity of [3H]Leu in the intracellular pool was comparable to that in the extracellular pool in normal and dystrophic cells; however, the specific radioactivity of Leu-tRNA (i.e. the immediate precursor to protein synthesis) was only 55-65% of the extracellular specific radioactivity in normal and dystrophic cells. In conclusion, reutilization of Leu from protein degradation is higher in dystrophic muscle cell cultures than in normal muscle cell cultures, and accurate rates of protein synthesis in cell cultures can only be obtained if specific radioactivity of amino acid in tRNA is measured.     

Total plasmalogens and O-(acylalkylglycerophosphoryl) ethanolamine from labelled hexadecanol and palmitate during hypoxia and anoxia in rat heart.

By the use of the Langendorff technique, surviving isolated rat hearts were perfused with [1-14 C] palmitate, [1-14C] hexadecanol or [1-14C,1-3H] hexadecanol under normal or anoxic conditions. After perfusion for 30min with either precursor, when oxygenated or in an hypoxic condition, or when 1mM-KCN was included in the system, the heart tissues showed no significant chemical changes in their content of total lipids, total phospholipids or total ethanolamine-containing phospholipids. Changes were observed in the ratio of alkyl-to alk-1-enyl-glycerophosphorylethanolamine in the tissue perfused with N2+CO1 plus CN-. A slight increase from 4.0+/-0.3 to 4.9+/-0.2% in alkyl derivatives and a decrease from 11.2+/-0.4 to 9.4+/-0.3% in alk-1-enyl derivatives was observed. The incorporation of the [14C] palmitate and the [14C] hexadecanol into the recovered phospholipids and plasmalogens was severely decreased in the tissues perfused with CN-: in the hypoxic state only a mild inhibition was observed compared with the oxygenated systems. Considerable 3H from [1-14C, 1-3H] hexadecanol was retained (25-35%) in the alk-1-enylether chains of plasmalogens under both the oxygenated conditions and with CN-, suggesting that the same mechanism of incorporation is operational at high or low O2 concentrations. The results are consistent with an O2-dependent, CN-sensitive step in the biosynthesis of plasmalogens in the rat heart.