Methylene-beta-phenylethylimine formation from 5-methyltetrahydrofolic acid and beta-phenylethylamine.

We have identified, by TLC, the product from the reaction between 5-methyltetrahydrofolic acid (5-MTHF) and β-phenylethylamine (βφEA) in rat brain extracts as methylene-β-phenylethylimine (MβφEI), a Schiff-base compound produced when formaldehyde, enzymatically formed from 5-MTHF, condenses with the amine. The formation of MβφEI in various brain regions, ranging from 517 ± 56 pmol formed per mg protein per hour in corpus striatum to 118 ± 9 pmol formed in hippocampus, is significantly correlated with that of 1,2,3,4-tetrahydro-β-carboline formed from 5-MTHF and tryptamine (r = 0.88; p < 0.01), which we reported elsewhere (1). In corpus striatum MβφEI formation is found nearly exclusively in cytosol, as was the β-carboline formation. We suspect that the enzyme involved in both reactions is methylenetetrahydrofolate reductase.     

Formation of 1,2,3,4-tetrahydro-β-carboline and methylene-β-phenylethylimine from 5-methyltetrahydrofolate and amines in tissues from developing rat brain

The rates of synthesis of 1,2,3,4-tetrahydro-β-carboline (THβC) and methylene-β-phenylethylimine (MβΦEI) from 5-methyltetrahydrofolate (5-MTHF) and tryptamine and β-phenylethylamine (βΦEA) respectively have been measured in cerebellum, corpus striatum, and the remainder of the brain from male and female rats at six specific ages after birth. With either substrate the specific activity of the reaction was higher in cerebellum than in corpus striatum until approximately 31 days after birth. The fluctuations in neonatal production of THβC and MβΦEI in cerebellum were nearly parallel except around six days, when THβC production peaked and MβΦEI production dropped considerably. The regional differences in the neonatal patterns of THβC and MβΦEI formation hint that the formaldehyde-forming enzyme (whether or not it is methylane-tetrahydrofolate reductase as we believe) might be related to structural and functional development in specific brain regions.     

Low [3H]Cytochalasin B Binding in the Cerebral Cortex of Newborn Rat

The concentrations of glucose transporter in the cerebral cortex and brainstem of neonatal (4–7 days old) and adult rats were measured using [³H]cytochalasin B binding. There was significantly lower binding in neonatal cortex (1.9 ± 0.7 pmol/mg protein) compared to adult (8.9 ± 2.5 pmol/mg protein). Scatchard analysis indicates this difference is due to a lower B_max (neonate, 9.7 pmol/mg protein; adult, 18.6 ± 1.3 pmol/mg protein). Measurement of [³H]cytochalasin B binding in microvessels prepared from cortex of adult (28.1 ± 3.5 pmol/mg protein) and neonate (12.8 ± 1.9 pmol/mg protein) indicates a lower binding in the microvasculature of neonates, whereas no such difference was seen in the binding in microvessels prepared from adult and neonatal brainstem (adult, 11.8 ± 2.3 pmol/mg protein; neonate, 9.4 ± 2.7 pmol/mg protein). In both adult and neonate brain, there is an enrichment of glucose transporters in the microvasculature.     

FACTORS INFLUENCING BRAIN AND TISSUE LEVELS OF TRYPTAMINE: SPECIES, DRUGS AND LESIONS

With a modification of the spectrophotofluorometric (SPF) method of HESS & UDENFRIEND (1959) (J. Pharmac. exp. Ther. 127 , 175-177), brain tryptamine levels in the rat (20.9 ng/g) and guinea-pig (20.7 ng/g) were found to be less than those in the dog (32.1 ng/g) and cat (52.2 ng/g). Regional distribution studies in the dog and cat showed that tryptamine was present in all major brain regions with highest concentrations in the spinal cord. Blood levels of tryptamine in the guinea-pig, dog and cat (6-7 ng/ml) were lower than brain levels. Pargyline significantly increased brain tryptamine in both the dog and cat; whereas, isocarboxazid (after 4 h) increased brain tryptamine levels in the dog but decreased brain levels in the cat. Reserpine (0.5-1.0 mg/kg per day for 1-4 days) did not significantly decrease brain, spinal cord or blood tryptamine levels in the dog. Spinal cord transection did not decrease tryptamine levels below the lesion in the chronic spinal dog.     

Identification, Development, and Regional Distribution of Ribonucleotide Reductase in Adult Rat Brain

The development and regional distribution of ribonucleotide reductase (EC 1.17.4.1) were determined in rat brain. Ribonucleotide reductase was partially purified by ammonium sulfate fractionation (20-40% saturation). Enzyme activity was measured by a specific radiochemical assay. This method involved the reduction of [¹⁴C]cytidine diphosphate (CDP) to [¹⁴C]deoxy-cytidine diphosphate with subsequent hydrolysis and separation of the product ([¹⁴C]deoxycytidine) from substrate ([¹⁴C]cytidine) by Dowex-1-borate ion-exchange chro-matography. The specific activity of ribonucleotide reductase in whole brain of newborn rats was 3.78 ± 0.55 units (pmol/h)/mg protein (SEM; n = 6) and declined to 0.17 ± 0.01 units/mg protein (n = 7) at 10-12 weeks of age, with a further decline to 0.11 ± 0.01 units/mg protein (n = 3) at 1 year. Ribonucleotide reductase activity in rat liver decreased from 4.58 ± 0.62 units/mg protein (n = 3) in newborn animals to 0.06 ± 0.01 units/mg protein (n = 7) at 10-12 weeks and was present at trace levels at 6 months of age. The decline in specific activity with age was not due to a change in the K_m for CDP. The K_m for CDP in brain of newborn and adult rats was 80-90 μM. In 10- to 12-week-old rats, the specific activity of ribonucleotide reductase was similar in the various regions of the brain tested except for the brainstem, which had 50% lower specific activity than the whole brain. These results indicate that ribonucleotide reductase activity is present and widely distributed in adult rat brain.     

Uptake of L-[3H] glutamic acid by crude and purified synaptic vesicles from rat brain

Rat brain synaptic vesicles suspended in a medium comprised of potassium tartrate displayed saturable accumulation of L-[³H] glutamic acid at 37° (Km 2.0 × 10^?4M; 311±13 pmol/mg protein), which was stable for periods up to 60 min. The accumulation was temperature sensitive and partially ATP-dependent, uptake levels being reduced to 18.7±0.8 pmol/mg protein at 4°, and to 141±4 pmol/mg protein in the absence of ATP. Fractionation of a crude vesicle preparation on a discontinuous sucrose gradient demonstrated the accumulation to be specifically associated with the synaptic vesicle fraction.     

EFFECTS OF LESIONS AND DRUGS ON BRAIN TRYPTAMINE

Abstract— The effects of various drugs and lesions on rat brain 5-hydroxytryptamine and tryptamine were determined. Monoamine oxidase inhibition caused a proportionately greater increase in tryptamine than in 5-hydroxytryptamine, reserpine depleted 5-hydroxytryptamine but had no effect on tryptamine while p -chlorophenylalanine lowered 5-hydroxytryptamine but increased tryptamine. α-Methyl- p -tyrosine reduced striatal dopamine with no effect on either 5-hydroxytryptamine or tryptamine. Increasing brain tryptophan by amphetamine administration. 24 h food deprivation or giving L-tryptophan did not increase brain tryptamine. However a high dose of ^L-tryptophan (100 or 200mg/kg) together with a monoamine oxidase inhibitor caused a proportionately much greater increase in tryptamine than in 5-hydroxytryptamine. Raphe lesions reduced 5-hydroxytryptamine by 64 per cent and tryptamine by only 29 per cent while intraventricular 6-hydroxydopamine lowered striatal dopamine (56 per cent), had no effect on 5-hydroxytryptamine but reduced tryptamine by 24 per cent, suggesting that tryptamine can be formed in both 5-HT and catecholaminergic neurones.
The results are discussed in relation to the formation, distribution, storage and possible transmitter function of tryptamine in rat brain.     

Properties of γ-aminobutyric acid synthesis by rat renal cortex

Substantial synthesis of γ-aminobutyric acid occurs in rat renal cortex. Renal glutamate decarboxylase activity (24.3±2.9 (S.E.) nmols/mg protein per h) is 15% of that in brain; renal γ-aminobutyric acid content (39.5±5.3 (S.E.) nmols/g wet wt.) is 5% of the whole brain concentration. Properties of glutamate decarboxylase were studied in homogenates of rat renal cortex and rat brain under conditions for which γ-aminobutyric acid formation from [2,3-³H]glutamate and CO₂ release from [1-¹⁴C]glutamate were equal. Several properties of renal glutamate decarboxylase distinguish it from the corresponding brain enzyme: (1) renal glutamate decarboxylase is selectively inhibited by cysteine sulfinic acid (K_i = 5·10^?5 M) ; (20 renal glutamate decarboxylase is less sensitive (K_i = 3–5·10^?5 M)_to inhibition by aminooxyacetic acid than is the brain enzyme (K_i = 1·10^?6 M); (3) brain but not renal glutamate decarboxylase activity can be substantially stimulated in vitro by the addition of exogenous pyridoxal 5′-phosphate; (4) renal glutamate decarboxylase is significantly decreased in renal cortex from rats on a low-salt diet. Proximal tubules are enriched in glutamate decarboxylase compared to the activity in whole renal cortex or glomeruli (42, 22 and 14 nmols/mg protein per h, respectively). We speculate that renal γ-aminobutyric acid synthesis does not reflect the presence of GABAergic renal nerves, but may serve a function in proximal tubular cells.     

EFFECT OF γ-AMINOBUTYRIC ACID ON BRAIN SEROTONIN AND CATECHOLAMINES

—Intraperitoneal injections of GABA (5 mg/kg) to rats lowered the level of norepinephrine in brain, heart and spleen but not suprarenals and raised that of serotonin in brain. Changes of these monoamines were most pronounced in the hypothalamic region after 20min. A reduction of hypothalamic norepinephrine was also observed 15min following the intracarotid administration of 0·5 mg/kg of GABA. In these experiments there was a concomitant increase in the level of free GABA in the anterior portion of the ventral hypothalamus. Brain dopamine level and 5-hydroxytryptophan decarboxylase, dihydroxyphenylalanine decarboxylase and monoamine oxidase activities were not affected. The 20 per cent increase of endogenous GABA observed in the midbrain 30 min following the administration of amino-oxyacetic acid was accompanied by a sharp fall in norepinephrine level (39 per cent) and an increase in serotonin (20 per cent). In in vitro studies 10–300 μg/ml of GABA were shown to release norepinephrine from cortical and hypothalamic slices, and to inhibit serotonin release without affecting 5-hydroxytryptophan uptake and to have no effect on the release of dopamine from slices of the region of the corpus striatum nor on the activity of the enzymes mentioned. Subcellular studies showed that the particulate:supernatant ratio for norepinephrine was reduced from a control value of 2·04 to 1·75 and that of serotonin was raised from 2·8 to 3·5. Following pretreatment with iproniazid, GABA reduced the raised level of brain norepinephrine to a greater extent than reserpine but not as intensively as amphetamine. The results obtained suggest that these monoamines may be involved in the mechanisms underlying the action of GABA in brain and that the effect of GABA on brain monoamines may be of certain significance in synaptic events.     

CYCLIC AMP AND PHOSPHODIESTERASE IN SYNAPTIC VESICLES FROM MOUSE BRAIN

The isolation of synaptic vesicles from mouse brain by a modification of previously reported methodology is described. Homogeneity of the preparations was ascertained by electron microscopy. Vesicles thus isolated contained cyclic AMP (365 ± 44 pmol/mg of protein; mean ± S.E.M.) and adenosine 3′,5′-monophosphate phosphodiesterase activity (500 pmol/mg of protein per 30 min). The number of vesicles in three of the vesicle preparations was determined by a visual count of grid fields under the electron microscope. The content of cyclic AMP in the vesicles was calculated at 5000-7500 molecules/vesiclc. The presence of cyclic AMP in the synaptic vesicles from presynaptic nerve endings would support a role for this nucleotide in nerve transmission.     

SODIUM-DEPENDENT EFFLUX AND EXCHANGE OF GABA IN SYNAPTOSOMES

Abstract— The influx and efflux of [³H]GABA were investigated in synaptosomes. Two efflux components were detected. The first, termed spontaneous efflux, was not affected by the external sodium chloride concentration. The second, termed GABA-stimulated efflux, was observed when low levels of GABA were added to the incubation medium and was found to require external sodium chloride. The rate of spontaneous efflux at 0°C was about 37 per cent of the rate at 27°C but both GABA-stimulated efflux and GABA influx were completely inhibited at 0°C. The stimulation of efflux by external GABA followed simple Michaelis–Menten kinetics with respect to external GABA. The concentration of external GABA required for half-maximal stimulation was 4·9 ± 1·4 μm and the V_max for efflux was 1·0 ± 0·6 nmol. min^-1.mg^-1 of protein. A similar stimulation of efflux was observed with GABA analogue l -2,4-diamino-butyric acid which is a competitive inhibitor of influx. The concentration of external l -2,4-diaminobutyric acid required for half-maximal stimulation of efflux was 51 ± 12 μm and the V_max for efflux was 0·8 ± 0·5 nmol.min^-1.mg^-1 of protein. Since the sodium-dependency, temperature sensitivity, and kinetic properties of the GABA-stimulated efflux system were similar to the influx system, GABA-stimulated efflux was attributed to carrier-mediated exchange diffusion. Measurement of efflux and influx in the same preparation showed there was a net efflux when total fluxes were considered and that the exchange ratio (influx to GABA-stimulated efflux) was 0·9 when carrier-mediated fluxes were considered. The effect of the temperature of the fluid used to rinse synaptosomes collected on filters in influx experiments was investigated. There was no detectable difference in measured values of influx between samples rinsed with cold fluid (0°C) and warm fluid (27°C). The endogenous GABA content of synaptosomes was found to be 20·3 ± 2·5 nmol GABA per mg of protein. From this value, the cytoplasmic concentration of GABA in synaptosomes was estimated to be a maximum of 40 mm . About 5 per cent of total cerebral cortical GABA was found in the synaptosomal fraction.     

微波辐射对小鼠脑内乙酰胆碱含量及胆碱乙酸转移酶活性的影响

用频率为2450MHz功率密度为10mW/Cm~2(WBASAR约11.4W/kg)的微波(连续波)对置于微波暗室内的昆明种雄性小鼠急性全身照射1小时后,立即按常规方法断头,取脑,制成样品,然后用放射免疫测定法测量小鼠脑内乙酰胆碱(ACh)含量及胆碱乙酰转移酶(ChAT)活性。结果表明:照射组的ACh含量为11.6±1.4pmol/mg(脑鲜重),ChAT活性为45.4±8.7pmolACh/min.mg(脑鲜重);而对照组的分别为16.0±2.1pmol/mg和61.0±13.8pmolACh/min.mg。证明微波照射后可引起动物脑内ACh水平和ChAT活性下降,提示微波辐射对中枢胆碱能系统确有不利影响。     

Evidence for cross-talk between atrial natriuretic peptide and nitric oxide receptors

Guanylyl cyclases (GCs), a ubiquitous family of enzymes that metabolize GTP to cyclic GMP (cGMP), are traditionally divided into membrane-bound forms (GC-A-G) that are activated by peptides and cytosolic forms that are activated by nitric oxide (NO) and carbon monoxide. However, recent data has shown that NO activated GC’s (NOGC) also may be associated with membranes. In the present study, interactions of guanylyl cyclase A (GC-A), a caveolae-associated, membrane-bound, homodimer activated by atrial natriuretic peptide (ANP), with NOGC, a heme-containing heterodimer (α/β) β1 isoform of the β subunit of NOGC (NOGCβ1) was specifically focused. NOGCβ1 co-localized with GC-A and caveolin on the membrane in human kidney (HK-2) cells. Interaction of GC-A with NOGCβ1 was found using immunoprecipitations. In a second set of experiments, the possibility that NOGCβ1 regulates signaling by GC-A in HK-2 cells was explored. ANP-stimulated membrane guanylyl cyclase activity (0.05 ± 0.006 pmol/mg protein/5 min; P < 0.01) and intra cellular GMP (18.1 ± 3.4 vs. 1.2 ± 0.5 pmol/mg protein; P < 0.01) were reduced in cells in which NOGCβ1 abundance was reduced using specific siRNA to NOGCβ1. On the other hand, ANP-stimulated cGMP formation was increased in cells transiently transfected with NOGCβ1 (530.2 ± 141.4 vs. 26.1 ± 13.6 pmol/mg protein; P < 0.01). siRNA to NOGCβ1 attenuated inhibition of basolateral Na/K ATPase activity by ANP (192 ± 22 vs. 92 ± 9 nmol phosphate/mg protein/min; P < 0.05). In summary, the results show that NOGCβ1 and GC-A interact and that NOGCβ1 regulates ANP signaling in HK-2 cells. The results raise the novel possibility of cross-talk between NOGC and GC-A signaling pathways in membrane caveolae.     

FATTY ACIDS,AMINO ACIDS,MINERAL CONTENTS,AND PROXIMATE COMPOSITION OF SOME BROWN SEAWEEDS1

This study was conducted to create a nutritional database on brown seaweeds and to popularize their consumption and utilization in Iran. The fatty acid contents, amino acids profiles, and certain mineral elements composition of some brown seaweeds, Padina pavonica (L.) Thivy, Dictyota dichotoma (Huds.) J. V. Lamour., and Colpomenia sinuosa (Mert. ex Roth) Derbés et Solier were determined. Total lipid content ranged from 1.46 ± 0.38 to 2.94 ± 0.94 g · 100 g^?1dry weight (dwt), and the most abundant fatty acids were C16:0, C18:1, C20:4 ω6, and C20:5 ω3. The unsaturated fatty acids predominated in all species and had balanced sources of ω3 and ω6 acids. Highest total polyunsaturated fatty acid (PUFA) levels occurred in C. sinuosa. The protein content of D. dichotoma was 17.73 ± 0.29 g · 100 g^?1dwt, significantly higher than the other seaweeds examined. Among amino acids essential to human nutrition, methionine (Met; in D. dichotoma and P. pavonica) and lysine (Lys; in C. sinuosa) were present in high concentrations. The crude fiber content varied by 9.5 ± 11.6 g · 100 g^?1dwt in all species. Chemical analysis indicated that ash content was between 27.02 ± 0.6 and 39.28 ± 0.7 g · 100 g^?1dwt, and that these seaweeds contained higher amounts of both macrominerals (7,308–9,160 mg · 100 g^?1dwt; Na, K, Ca) and trace elements (263–1,594 mg · 100 g^?1dwt; Fe, Ni, Mn, Cu, Co) than have been reported for edible land plants. C. sinuosa had the highest amount of Ca, Fe, and a considerable content of Na was measured in P. pavonica.     

FORMATION OF ASPARAGINE FROM ASPARTIC ACID IN RAT BRAIN

The synthesis of asparagine in rat brain was studied both in vitro and in vivo. A conversion in vitro of about 2 per cent of the added l -[¹⁴C]aspartic acid into asparagine was found after a 2 h incubation with the 100,000 g supernatant fraction from brain. This corresponded to a formation of 4·8 nmol of asparagine/mg of protein/h. The reaction required ATP and glutamine, and was linear with time during the 2 h incubation. When the crude mitochondrial fraction was added to the incubation mixture the reaction was inhibited, probably because of the presence of ATPase activity in the mitochondrial preparation. Inhibition by the reaction product seemed unlikely since removal of endogenous asparagine did not stimulate the reaction; only when asparagine was added at levels of 0·5 or 1·0 mm was significant inhibition found. Ammonium chloride was less effective than glutamine as an amide donor. Endogenous asparaginase (EC 3.5.1.1.) activity was low in the in vitro preparation and did not significantly affect the conversion. Synthesis of asparagine from aspartic acid did not occur in slices of brain nor was there a significant conversion of aspartic acid or glucose to asparagine after their intracerebral administration in vivo.     

A RAPID AND SIMPLE METHOD FOR THE DETERMINATION OF PICOGRAM LEVELS OF SEROTONIN IN BRAIN TISSUE USING LIQUID CHROMATOGRAPHY WITH ELECTROCHEMICAL DETECTION

A rapid and simple technique using solvent extraction and high pressure liquid chromatography with electrochemical detection has been developed for the determination of serotonin in small brain tissue samples (1-20 mg). The method has a reasonably good specificity and a very low experimental error (less than 3%s.e ., calculated from six samples processed and analysed from the same brain homogenate). The recovery of authentic 5-HT added is 80-90%. The 5-HT levels of rat whole brain was found with the present technique to be 690 ± 17.5 ng/g and of mouse neocortex 304 ± 16 ng/g. Monoamine oxidase inhibition with pargyline (2 h) increased 5-HT levels in mouse neocortex to 194 ± 15% (N = 5) of control, while reserpine depleted 5-HT to 13 ± 4% of control. The method has a sensitivity level of about 20 pg (0.1 pmol) per brain sample.     

EFFECT OF VITAMIN E SUPPLEMENTATION AND PARTIAL SUBSTITUTION OF POLY- WITH MONO-UNSATURATED FATTY ACIDS IN PIG DIETS ON MUSCLE,AND MICROSOME EXTRACT a-TOCOPHEROL CONCENTRATION AND LIPID OXIDATION

The experiment was organized in a 3×2 factorial arrangement with three dietary fat blends and a basal (20 mg kg^?1 diet) or supplemented (220 mg kg^?1) level of α-tocopheryl acetate. Dietary vitamin E and monounsaturated to polyunsaturated fatty acid ratio (dietary MUFA/PUFA) affected muscle α-tocopherol concentration (α-tocopherol [log μg g^?1]=0.18 (±0.105)+0.0034 (±0.0003)·dietary α-tocopherol [mg kg^?1 diet] (P<0.0001)+0.39 (±0.122)·dietary MUFA/PUFA (P<0.0036)). An interaction between dietary α-tocopherol and dietary MUFA/PUFA exists for microsome α-tocopherol concentration (α-tocopherol [log μg g^?1]=1.14 (±0.169) (P<0.0001)+0.0056 (±0.00099)·dietary α-tocopherol [mg kg^?1 diet] (P<0.0001)+0.54 (±0.206)·dietary MUFA/PUFA (P<0.0131)?0.0033 (±0.0011)·dietary α-tocopherol [mg kg^?1)]×dietary MUFA/PUFA (P<0.0067)), and hexanal concentration in meat (hexanal [ng·g^?1]=14807.9 (±1489.8)?28.8 (±10.6) dietary α-tocopherol [mg·kg^?1] (P<0.01)?8436.6 (±1701.6)·dietary MUFA/PUFA (P<0.001)+24.0 (±11.22)·dietary α-tocopherol·dietary MUFA/PUFA (P<0.0416)). It is concluded that partial substitution of dietary PUFA with MUFA lead to an increase in the concentration of α-tocopherol in muscle and microsome extracts. An interaction between dietary α-tocopherol and fatty acids exists, in which at low level of dietary vitamin E inclusion, a low MUFA/PUFA ratio leads to a reduction in the concentration of α-tocopherol in microsome extracts and a concentration of hexanal in meat above the expected values.     

Direct effect of the luteinizing hormone releasing hormone analog D-Trp6-Pro9-Net-LHRH on rat testicular steroidogenesis

The luteinizing hormone releasing hormone analog D-Trp⁶-Pro⁹-Net-LHRH (LHRH_a) inhibits rat testicular testosterone secretion. To determine whether LHRH_a decreases serum testosterone concentrations solely by inhibiting gonadotropin secretion or, in addition, by influencing directly testicular testosterone biosynthesis, we examined the effects of LHRH_a on the activities of 5 key testicular steroidogenic enzymes. Thirty hypophysectomized, hCG treated rats were given either LHRH_a (1 μg sc/day) or saline during 7 days. The LHRH_a treated animals exhibited a significant decrease of serum testosterone when compared to the control group (498 ± 37 ng/dl vs 2044 ± 105 ng/dl, mean ± SEM, P 〈0.001). 17-Hydroxyprogesterone serum levels were also decreased in the LHRH_a treated rats (61 ± 6 ng/dl vs 93 ± 7 ng/dl, P 〈0.005), while serum progesterone levels were similar in both groups of animals. These changes in steroid concentrations were associated with decreases in the musomal enzyme activities of 17-hydroxylase (37 ± 9 vs 654 ± 41 pmol/mg protein/min, P 〈0.001), 17, 20-desmolase (103 ± 9 vs 522 ± 47 pmol/mg protein/min, P 〈0.001), 3β-hydroxysteroid dehydrogenase (1.7 ± 0.02 vs 4.1 ± 0.1 nmol/mg protein/min, P 〈0.001), aromatase (95 ± 7 vs 228 ± 6 pmol/mg protein/ min, P 〈0.001) and 17-ketosteroid reductase (167 ± 9 vs 290 ± 18 pmol/mg protein/min, P 〈0.01) in the LHRH_a treated animals. These findings indicate that LHRH_a can inhibit directly rat testicular testosterone biosynthesis.     

Meal frequency differentially alters postprandial triacylglycerol and insulin concentrations in obese women

Objective:

The aim of this study was to compare postprandial lipemia, oxidative stress, antioxidant activity, and insulinemia between a three and six isocaloric high‐carbohydrate meal frequency pattern in obese women.

Design and Methods:

In a counterbalanced order, eight obese women completed two, 12‐h conditions in which they consumed 1,500 calories (14% protein, 21% fat, and 65% carbohydrate) either as three 500 calorie liquid meals every 4‐h or six 250 calorie liquid meals every 2‐h. Blood samples were taken every 30 min and analyzed for triacylglycerol (TAG), total cholesterol, high‐density lipoprotein cholesterol, low‐density lipoprotein cholesterol, oxidized low‐density lipoprotein cholesterol, myeloperoxidase, paraoxonase‐1 activity, and insulin.

Results:

The TAG incremental area under the curve (iAUC) during the three meal condition (321 ± 129 mg/dl·12 h) was significantly lower (P = 0.04) compared with the six meal condition (481 ± 155 mg/dl·12 h). The insulin iAUC during the three meal condition (5,549 ± 1,007 pmol/l^.12 h) was significantly higher (P = 0.05) compared with the six meal condition (4,230 ± 757 pmol/l^.12 h). Meal frequency had no influence on the other biochemical variables.

Conclusions:

Collectively, a three and six isocaloric high‐carbohydrate meal frequency pattern differentially alters postprandial TAG and insulin concentrations but has no effect on postprandial cholesterol, oxidative stress, or antioxidant activity in obese women.     

Effect of a test meal,duodenal acidification,and tetragastrin on the plasma concentration of β-endorphin-like immunoreactivity in man

The effects of various test materials on plasma β-endorphin-like immunoreactivity (β-EpLI) were investigated in man using a specific radioimmunoassay developed by the authors. Plasma β-EpLI was determined after extraction by the acid/acetone method (recovery 73±5%). The intraassay and interassay coefficients of variation were 5.0% and 7.6%, respectively. The plasma concentrations of human β-EpLI in normal subjects were 11.6±4.0 pmol/l for men (n=23) and 10.7±4.8 pmol/l for women (n=27). Ingestion of a test meal (150 g of Campbell's condensed meat soup) resulted in a biphasic rise in plasma β-EpLI from the basal level of 4.4±1.0 pmol/l to 29.2±1.9 pmol/l after 5 min and 24.8±6.7 pmol/l after 90 min. Intraduodenal infusion of 115 ml of 0.1 M HCl over 10 min increased the plasma β-EpLI level from 8.7±0.5 pmol/l to 15.5±0.4 pmol/l at 10 min after the start of infusion, but the level rapidly returned to the initial value after the end of the infusion. Intramuscular injection of 4 μg/kg body weight of tetragastrin markedly stimulated gastric acid output and β-EpLI release, but pretreatment with 10 mg of histamine H₂ receptor antagonist inhibited the gastric acid output and plasma β-EpLI release induced by tetragastrin.These results indicate that β-EpLI release is stimulated by ingestion of meat soup, duodenal acidification and tetragastrin administration. It is suggested that gastric acid participates, at least in part, in postprandial release of β-EpLI, probably from the gastrointestinal tract.