In vivo detoxification of cyanide by cystathionase gamma-lyase

The results of several in vitro studies have suggested that the enzyme cystathionase gamma-lyase (EC 4.4.1.1) may function in the endogenous detoxification of cyanide; however, this possibility has not been investigated in vivo. If cystathionase gamma-lyase in involved in the endogenous detoxification of cyanide, it logically follows that inhibiting cystathionase gamma-lyase should increase the toxicity of cyanide. To test this hypothesis, the activity of cystathionase gamma-lyase was inhibited with a suicide inhibitor, 2-amino-4-pentynoic acid (propargyl-glycine). The activity of liver cystathionase gamma-lyase activity was decreased 96.8% by administration of propargylglycine, indicating that the propargylglycine treatment was effective. The propargylglycine treatment did not alter the activity of thiosulfate:cyanide sulfurtransferase (EC 2.8.1.1) or 3-mercaptopyruvate:cyanide sulfurtransferase (EC 2.8.1.2), two other enzymes that have been proposed to be involved in the detoxification of cyanide. The LD50 of cyanide in rats treated with propargylglycine was 5.14 +/- 0.029 mg NaCN/kg, which was significantly (P < 0.05) lower than the 5.98 +/- 0.008 mg NaCN/kg LD50 of cyanide determined in control rats. The results of these studies suggest that cystathionase gamma-lyase may participate in the detoxification of cyanide in vivo.

The effect of three alpha-keto acids on 3-mercaptopyruvate sulfurtransferase activity

3-Mercaptopyruvate sulfurtransferase catalyzes the transfer of sulfur from 3-mercaptopyruvate to several possible acceptor molecules, one of which is cyanide. Because the transsulfuration of cyanide is the primary in vivo mechanism of detoxification, 3-mercaptopyruvate sulfurtransferase may function in the enzymatic detoxification of cyanide in vivo. Three alpha-keto acids (alpha-ketobutyrate, alpha-ketoglutarate, and pyruvate) have previously been demonstrated to be cyanide antidotes in vivo, and it has been suggested that this is due to the nonenzymatic binding of cyanide by the alpha-keto acid. However, it has also been proposed that alpha-keto acids may increase the activity of enzymes involved in the transsulfuration of cyanide. Thus, the effect of these three alpha-keto acids on the enzyme 3-mercaptopyruvate sulfurtransferase was examined. All three alpha-keto acids inhibited 3-mercaptopyruvate sulfurtransferase in a concentration-dependent manner and were determined to be uncompetitive inhibitors of MST with respect to 3-mercaptopyruvate. The inhibitor constant Ki was estimated by two methods for each inhibitor and ranged from 4.3 to 6.3 mM. The I50, which is the inhibitor concentration that produces 50% inhibition, was calculated for all three alpha-keto acids and ranged between 9.5 and 13.7 mM. These observations add further support to the hypothesis that the mechanism of the alpha-keto acid antidotes is the nonenzymatic binding of cyanide, not stimulation of enzymes involved in the transsulfuration of cyanide to thiocyanate.

Specificity studies of 3-Mercaptopyruvate sulfurtransferase

3-Mercaptopyruvate sulfurtransferase (E.C. 2.8.1.2; MST) is an enzyme believed to function in the endogenous cyanide (CN) detoxification system because it is capable of transferring sulfur from 3-mercaptopyruvate (3-MP) to CN, forming the less toxic thiocyanate (SCN). To date, 3-MP is the only known sulfur-donor substrate for MST. In an effort to increase the understanding of what chemical properties of 3-MP affect its utilization as a substrate, in vitro enzyme kinetic studies of MST were conducted using two mercaptic acids that are structurally related to 3-MP. Neither of these compounds was able to serve as a sulfur-donor substrate for MST. Inhibitor studies determined that 3-mercaptopropionic acid did not affect the Km of MST for 3-MP but did decrease Vmax and, thus, was determined to be a noncompetitive inhibitor. Alternatively, 2-mercaptopropionic acid 2-MPA decreased Km and Vmax and was determined to be an uncompetitive inhibitor of MST with respect to 3-MP. These data indicate that the alpha-keto group of 3-MP is necessary for its utilization as a substrate, and the inhibitor studies suggest that the position of the sulfur may also affect the binding of these compounds to the enzyme. These observations increase the understanding of what factors can affect the utilization of a compound as a sulfur-donor substrate for MST and may aid in the development of alternative sulfur-donor substrates for MST.

Rapid effect on suckling of an oxytocin antisense oligonucleotide administered into rat supraoptic nucleus

Suckling in the lactating rat (days 6-10 of lactation) was used to characterize the effects of intracerebral oxytocin (Oxt) antisense oligonucleotide treatment on the hypothalamo-neurohypophysial system. Vehicle, mixed bases, Oxt antisense, or vasopressin antisense oligonucleotides (2.5 micrograms/0.5 microliter each) were infused directly into the left and right supraoptic nucleus (SON), 4 h before a litter of 10 pups was allowed to suckle for 30 min. In the Oxt antisense group, there was a significant reduction in the number of milk ejection reflexes (to 34.6 +/- 4.88%, P < 0.001), as well as in the weight gain of the litter (to 18.8 +/- 6.98%, P < 0.03) compared with vehicle (100%)-, mixed base-, or vasopressin antisense-treated animals, which did not differ from each other. The time to onset of suckling, however, was unchanged. Compared with presuckling values, plasma Oxt was significantly increased in all four groups 30 min after onset of suckling (vehicle, to 325 +/- 117%; mixed bases, to 258 +/- 48.2%; vasopressin antisense, to 330 +/- 55.7%), but this increase was less pronounced in Oxt antisense-treated rats (to 157 +/- 20.5%; P < 0.05 vs. vasopressin antisense). In contrast to these changes in neuroendocrine functions during suckling, Oxt as well as vasopressin content and Oxt immunoreactivity in posterior pituitaries and the SON, respectively, did not differ among groups. Our data indicate rapid and specific effects of an Oxt antisense oligonucleotide infused into the SON on neuroendocrine, suckling-related parameters that are not due to depleted stores of Oxt in the hypothalamo-neurohypophysial system.

Neuropeptide-Y stimulates pituitary-adrenal activity in fetal and adult sheep

Corticotrophin-releasing factor (CRF) and arginine vasopressin (AVP) are the primary neuropeptides regulating the secretion of ACTH from the anterior pituitary gland during fetal and adult life. However, a number of other neuropeptides including neuropeptide-Y (NPY) appear to modulate the activity of this system. The potential role of NPY in the regulation of pituitary-adrenal function was examined in fetal and adult sheep. Administration of NPY (6.5 micrograms) as a bolus injection into the third cerebral ventricle of adult ewes elicited a significant (P < 0.05) increase in plasma concentrations of ACTH. In fetal sheep at day 125 gestation (term = 145 days) a five-fold higher dose (30 micrograms) of NPY injected into the lateral cerebral ventricles also caused a significant increase in plasma concentrations of ACTH. The potential of NPY to influence ACTH secretion directly from the pituitary gland was investigated using primary cultures of fetal (day 130 gestation) and adult pituitary cells. CRF (10(-10)-10(-7) M) caused a significant (P < 0.01) dose-related increase in ACTH secretion from both fetal and adult pituitary cells. Furthermore, the secretion of ACTH from adult cells was significantly greater (P < 0.05) than that from fetal cells. NPY (10(-10)-10(-7) M) had no effect on basal or CRF-stimulated ACTH secretion from fetal or adult pituitary cells. Pre-incubation of pituitary cells with cortisol (10(-9) and 10(-7) M) for three days significantly inhibited CRF-stimulated ACTH secretion but had no effect on basal ACTH release. The simultaneous addition of NPY did not alter the ability of cortisol to inhibit CRF-stimulated ACTH secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Taurine regulation of Ca2+ uptake and (Ca(2+)+Mg2+)-ATPase in developing chick B-cells

1. The objective of the present study was to determine the effect of age and taurine on chick B cell calcium uptake and membrane (Ca(2+)+Mg2+)-ATPase activity in 1-4-week-old chicks. 2. The calcium uptake rate decreased with age (P < 0.05) and was further decreased by taurine (P < 0.05). 3. (Ca(2+)+Mg2+)-ATPase activity increased with age (P < 0.05) and was stimulated by taurine (P < 0.05). 4. The data demonstrate that the flux of calcium across the B-cell membrane changes during early post-hatch development, and that taurine regulates both the influx and efflux of calcium in chick B-cells.

The effect of taurine on the incorporation of thymidine by chick B cells

1. This study was conducted to determine the effect of extracellular taurine on chick B cell proliferation as measured by the incorporation of [3H] thymidine. 2. B cells were cultured in RPMI-1640 media containing bacterial lipopolysaccharide and either 0 or 100 microM taurine. 3. Thymidine incorporation was significantly increased in the presence of 100 microM extracellular taurine. 4. These results suggest a role for taurine in the chick B cell proliferation process.

Endocrine actions of central neuropeptide Y in the ewe: activation of the hypothalamo-pituitary-adrenal axis by exogenous neuropeptide Y and role of endogenous neuropeptide Y in the secretion of luteinizing hormone during the oestrous cycle

Neurons immunoreactive for neuropeptide Y (NPY) are abundant in the hypophysiotrophic areas of the brain. In particular, there is considerable anatomical evidence for the influence of this neuropeptide on the reproductive and hypothalamo-pituitary-adrenal axes. We therefore investigated whether central administration of NPY can alter the activities of the reproductive and hypothalamopituitary-adrenal axes in the ewe, and whether ovarian steroids are involved in the modulation of these events. We also attempted to investigate whether endogenous NPY is important in the control of luteinizing hormone-releasing hormone/luteinizing hormone (LHRH/LH) secretion in the sheep oestrous cycle. Central injection of NPY (0.15 and 1.5 nmol in 50 microliters saline), delivered by gravity flow into the third cerebral ventricle, had no effect on LH levels in ovariectomized (OVX) ewes (n = 6) or OVX ewes implanted with oestradiol (OVX/E2) (n = 7), nor was LH secretion altered by central NPY (1.5 nmol) in intact cycling animals in either the follicular or the luteal phase (n = 5). However, central administration of 1.5 nmol NPY to intact ewes during both the follicular (P < 0.05) and the luteal phase (P < 0.01), and in OVX/E2 ewes (P < 0.05) caused a large and significant increase in plasma cortisol levels. High titre antibodies were raised to NPY in sheep and the effects of peripheral and central (intracerebroventricular) administration of anti-NPY antibodies on the timing and/or characteristics of the E2-induced LH surge in anoestrous ewes and of the preovulatory surge of LH in cycling ewes were determined. Intravenous administration of anti-NPY antibodies (n = 6) had no effect on the oestradiol benzoate-induced LH surge, compared with the control injection of non-immune plasma (n = 6). Likewise, passive systemic immunization against NPY (n = 10) was without effect on the characteristics of the preovulatory LH surge, compared with the control group (n = 10). However, central (intracerebroventricular) administration of anti-NPY antibodies (n = 4) delayed or abolished the preovulatory LH surge when compared with non-immune plasma treatment in the same animals. In summary, tonic LHRH/LH secretion is unaffected by centrally administered NPY at the doses used in this study. However, the same doses of NPY activate the hypothalamo-pituitary-adrenal axis, thus lending clear support to the hypothesis that NPY is involved in the multifactorial regulation of adrenocorticotrophin and cortisol secretion in this species, probably by stimulating corticotrophin-releasing hormone and/or arginine vasopressin secretion within the hypothalamus.(ABSTRACT TRUNCATED AT 400 WORDS)

Estrogen enhancement of Ca-, Mg-, and Ca-Mg-stimulated adenosine triphosphatase activity in the chick shell gland

The effect of 17 beta-estradiol (E2) on Ca-, Mg-, and Ca-Mg-ATPase activity was investigated in the shell gland of 6-week-old chicks. In the first study, each of 42 birds was implanted with three E2 (Compudose-200) pellets. An additional 6 sham-implanted birds served as controls for measurements of body weight and concentrations of E2 and Ca in plasma. The activities of Mg-, Ca-, and Ca-Mg-ATPase peaked coincident with maximum plasma E2 concentrations 8 days after implantation and then progressively declined in concert with the decline in plasma E2. By 29 days after implantation, the ATPase activities were similar to those measured in birds whose E2 pellets had been removed for 11 days. Concentrations of plasma E2 dropped from peak values of 1676 +/- 317 at Day 8 to 611 +/- 180 pg/ml at Day 29. When birds whose E2 pellets had been removed were reimplanted with three pellets per bird, plasma E2 again increased to 1637 +/- 227 pg/ml. ATPase activity in these reimplanted birds also was greater (P < 0.05) than activities measured in E2-removed or E2-maintained birds. In a second study the Ca-ATPase Km and Vmax were determined in E2-implanted chicks (three pellets per bird) and compared to E2-withdrawn chicks. Five days after reimplantation of chicks with E2, there was a significant increase in both Vmax (3.38 +/- 0.21 vs 2.37 +/- 0.28 micrograms Pi/mg protein/min; P < 0.05) and Km (0.31 +/- 0.02 vs 0.25 +/- 0.01 mM Ca; P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Taurine flux in chicken erythrocytes

1. The intracellular taurine concentration in chick erythrocytes increased with age. 2. Erythrocyte taurine influx and efflux rates increased with age. 3. Erythrocyte taurine influx decreased when the extracellular sodium concentration was below normal physiological concentrations. 4. Under hypo-osmotic conditions, taurine efflux from erythrocytes increased. 5. The data suggest that chick erythrocyte taurine metabolism changes during early post-hatch development and that one taurine function may be as an osmoregulator.

Taurine Uptake into Chick B Cells

The objective of the present study was to determine whether chick B cells possess a specific transport system for taurine. The Bursa of Fabricius was isolated from newly hatched to 6-week-old chicks and an enriched fraction (86.2%) of B cells was isolated. The chick B cells maintained a high intracellular taurine concentration (0.8-1.12 mM) that decreased with age. The B cells exhibited carrier-mediated and simple diffusion uptake components, but only the carrier-mediated component increased with age. Inhibitor studies indicated taurine uptake was sodium and energy dependent. The data demonstrate that chick B cells possess a specialized taurine transport system and the activity of this system changes during posthatch B cell development.

Taurine uptake in chicken leukocytes and erythrocytes

1. The intracellular taurine concentration and rate of taurine uptake of chicken erythrocytes and two leukocyte populations were determined from one to six weeks of age. 2. Plasma taurine concentrations increased significantly from the time of hatching to week 2 and remained constant thereafter. 3. Intracellular taurine concentrations in both leukocyte populations increased significantly with age without any significant change in the erythrocytes. 4. Taurine uptake rate for erythrocytes was significantly higher at weeks 1-3 while both leukocyte populations showed no significant change during the six week period studied.

Taurine content of isolated rat alveolar type I cells

1. Rat alveolar type I cells were isolated by enzymatic digestion and purified by centrifugal elutriation and specific surface adsorption. 2. The identity of the harvested cells was confirmed using electronic cell sizing and transmission electron microscopy. 3. Purified cell preparations contained 4.6 +/- 2.3 x 10(6) type I cells/rat lung with a purity of 79 +/- 3%. 4. Isolated type I cells exhibited the following characteristics: mean cell volume = 716 +/- 48 microns 3; diameter = 11.1 +/- 0.7 microns; and cell water content = 0.50 +/- 0.03 microliter/10(6) cells. 5. Taurine content of these alveolar type I cells was measured by HPLC. 6. The intracellular taurine concentration of type I cells was 0.14 +/- 0.07 mM, a value close to that of plasma (0.1 mM).

Effects of in vitro ozone exposure on peroxidative damage, membrane leakage, and taurine content of rat alveolar macrophages

Rat alveolar macrophages (AM) were isolated by pulmonary lavage, allowed to adhere to a tissue culture flask, and then exposed to 0.45 +/- 0.05 ppm ozone. After exposures ranging from 0 to 60 min, the medium was decanted and cells were harvested. Cells were assayed for oxidant damage and media analyzed for leakage of intracellular components. Increasing length of exposure to ozone resulted in a decreased number of adherent AM and decreased cell viability. Resting and zymosan-stimulated chemiluminescence increased immediately after ozone exposure and reached a maximum at 15-30 min, then declined to initial levels after 60 min of ozone exposure. Lipid peroxidation and leakage of protein and K+ ions increased with increasing length of exposure to ozone, while leakage of reduced and oxidized glutathione increased through 30 min, then declined (reduced) or leveled off (oxidized). Activity of the Na+/K+ ATPase decreased with time while intracellular taurine concentration exhibited an initial rise, peaked at 30 min, and then returned to the untreated level. Leakage of taurine into the medium increased with time of exposure, suggesting that exposure of AM to ozone results in a shift from bound to free intracellular taurine. These data indicate that in vitro exposure of AM to ozone results in a time-dependent alteration of cell function, membrane integrity, and viability.

Plasma cortisol is increased during the inhibition of LH secretion by central LHRH in the ewe

The delayed and sustained suppression of LH secretion induced by the administration of LHRH into the third cerebral ventricle of the ovariectomized ewe suggests the activation of a neuroendocrine mechanism involving components separate from the LHRH system. Endogenous opioid peptides are involved in regulating LHRH secretion but our recent work shows they do not mediate this inhibition. There is, however, clear evidence for a role for each of the components of the hypothalamopituitary-adrenal axis in the suppression of LHRH/LH secretion. Thus, the relationship between the central administration of LHRH, changes in plasma cortisol and LH secretion was investigated. Injection of LHRH (21 pmol) into the third cerebral ventricle of ovariectomized ewes caused a significant and rapid rise in plasma cortisol to a maximum of 4-5 times pre-injection values, followed by a delayed but sustained reduction in LH secretion. There was a high correlation (r = -0.902) between the increase in cortisol and the reduction in LH. Both the stimulatory effect of central LHRH on plasma cortisol and the inhibitory effect on plasma LH were blocked by prior central treatment with an LHRH antagonist. Intravenous infusion of cortisol, to reach levels observed after central LHRH administration, reduced LH secretion (although not to the levels which followed central LHRH) due in part to a reduction in pituitary responsiveness to LHRH. These experiments provide evidence that cortisol, either alone or in combination with another component(s) of the hypothalamopituitary-adrenal axis, may play a role in the LHRH-induced inhibition of LHRH/LH secretion in the sheep.

Calcium transport in chicken leukocytes and erythrocytes

1. In the present study, Ca2+ uptake and Ca2(+)-ATPase activity of two different chicken leukocyte populations and erythrocytes isolated from 1- to 6-week-old chickens were determined. 2. The Ca2(+)-ATPase activity of the two leukocyte populations significantly increased at 3 weeks of age. Erythrocyte Ca2(+)-ATPase activity significantly increased at 2 weeks of age. 3. Calcium transport activities into the two leukocyte populations did not differ significantly with age.

Central administration of corticotrophin-releasing factor in the sheep: effects on secretion of gonadotrophins, prolactin and cortisol

Stress interferes with the normal secretion of LH and FSH from the anterior pituitary gland and therefore exerts a deleterious effect on reproductive function. Evidence suggests that the stress-induced disruption of gonadal function is due to a central action of corticotrophin-releasing factor (CRF) to inhibit the release of LHRH into the hypophysial-portal circulation. The following studies were undertaken to investigate further the role of CRF in regulating gonadotrophin release in the sheep and to determine whether central administration of this peptide can alter the secretion of other hormones (e.g. prolactin and cortisol) known to be released under conditions of stress. In contrast to other species, injection of CRF into the third ventricle of the sheep brain caused a dose-related stimulation of LH secretion. The pulse frequency and mean levels of LH were increased significantly following central administration of CRF. In contrast to this effect, central administration of CRF did not alter the plasma concentration of FSH but caused a marked and dose-related stimulation of prolactin and cortisol secretion. The stimulatory effect of CRF on prolactin secretion was reversed by i.v. administration of the opioid antagonist naloxone, suggesting that endogenous opioid peptides mediate the central effect of CRF on the release of prolactin, but not cortisol. In conclusion, these data demonstrate that administration of CRF causes a dose-related stimulation of LH and prolactin release from the anterior pituitary gland and cortisol from the adrenal gland. In the case of prolactin, endogenous opioid peptides are likely to mediate this response.(ABSTRACT TRUNCATED AT 250 WORDS)

Naloxone does not Affect the Luteinizing Hormone-Releasing Hormone-Induced Inhibition of Luteinizing Hormone Secretion in Sheep

Abstract Injection of luteinizing hormone-releasing hormone (21 pmol) into the third cerebral ventricle of long-term ovariectomized ewes caused a marked inhibition of luteinizing hormone secretion. Mean luteinizing hormone levels and luteinizing hormone pulse frequency were reduced significantly when compared with the control responses to saline (50 mul). A notable characteristic of the response was the delayed and sustained nature of the luteinizing hormone-releasing hormone-induced inhibition. In the presence of the opioid antagonist naloxone (4 +/- 25 mg iv), the central administration of luteinizing hormone-releasing hormone still produced a marked inhibition of luteinizing hormone secretion. Again, mean luteinizing hormone levels and luteinizing hormone pulse frequency were reduced significantly. When naloxone was injected iv, there was a significant rise in mean luteinizing hormone levels as a consequence of an increase in pulse frequency (in four out of five ewes) and a significant increase in luteinizing hormone pulse amplitude. In conclusion, these data suggest that central opioid pathways sensitive to blockade by naloxone are not involved in the luteinizing hormone-releasing hormone-induced inhibition of luteinizing hormone release. Furthermore, in the long-term ovariectomized ewe, endogenous opioid peptides exert a tonic inhibitory influence on luteinizing hormone-releasing hormone/luteinizing hormone secretion.

Inhibitory effect of central LHRH on LH secretion in the ovariectomized ewe

The role of central luteinizing hormone releasing hormone (LHRH) in the control of pulsatile LHRH and luteinizing hormone (LH) secretion was investigated in ovariectomized adult ewes. Injection of LHRH (2.1-21 pmol) into the third cerebral ventricle caused a delayed but sustained inhibition of LH secretion. Pulse frequency, pulse amplitude and mean LH levels were reduced significantly when compared with the responses to the control injection of saline (50 microliters). The inhibitory effect of centrally administered LHRH was not accompanied by a reduction in the pituitary responsiveness to intravenous LHRH. In contrast to the effect on LH, plasma levels of follicle-stimulating hormone (FSH) and prolactin were unaffected by central LHRH. The inhibitory action of LHRH was antagonized by prior injection of an LHRH antagonist ([N-Ac-D-Nal(2)1, D-p-Cl-Phe2, D-Trp3, D-hArg (Et2)6, D-Ala10] LHRH, 69 pmol) into the third ventricle. Central injection of the LHRH antagonist alone (at the same concentration) did not influence any characteristic of pulsatile LH secretion. In conclusion, these data indicate that exogenous administration of LHRH into the brain exerts a dose-related and receptor-mediated inhibition of LHRH pulse generator activity. However, the physiological significance of endogenous LHRH in the regulation of the LHRH pulse generator remains unresolved.

Reversed-phase high-performance liquid chromatography technique for taurine quantitation

Taurine (2-aminoethanesulfonic acid) was quantitated by reversed-phase chromatography on a C18 Resolve column using a linear gradient of 9-11% methanol in water. Glutamine was used as the internal standard. Pre-column derivatization of the amino acid with o-phthalaldehyde allowed the detection of as little as 0.1 pmol taurine. Dual ion-exchange column chromatography was employed to remove other amino acids and metabolic precursors of taurine from the samples. Cysteic acid and cysteine sulfinic acid did not interfere with taurine analysis by the high-performance liquid chromatographic method. For sample deproteinization, boiling and picric acid precipitation were used. Recovery of taurine averaged 93.5 +/- 5.0% (means +/- standard error of the mean) from standard solutions and was not affected by the method of deproteinization. Using this procedure, plasma taurine concentrations for the rat and chick were determined to be 100.7 +/- 13.1 microM and 108.0 +/- 0.3 microM, respectively. Recovery of taurine from plasma samples averaged 97.2 +/- 4.7%.

Nature of the multiple forms of sweet-potato glucose phosphate isomerase

The previously reported isoenzymes of sweet-potato glucose 6-phosphate isomerase were resolved by DEAE-cellulose chromatography. The multiple forms exhibited identical electrophoretic properties and electrofocused as a single component with an apparent isoelectric pH of 4.0. Chromatographic studies also suggest that the multiple forms do not represent true isoenzymes.