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Biomedical subjects

N Miki

Publications and source records attributed to N Miki.

At least 181 records · Page 10Linked to original sources
PubMed1982

Interaction and electron transfer between cytochrome b5 and cytochrome P-450 in the reconstituted p-nitroanisole O-demethylase system.

The interaction and electron transfer between cytochrome b5 and cytochrome P-450B1 were investigated using the reconstituted p-nitroanisole O-demethylase system. Apocytochrome b5 was prepared from detergent-solubilized cytochrome b5 by the acid-butanone method. The apocytochrome b5 thus obtained has been substituted with several metalloporphyrin derivatives. The reconstituted system containing cytochrome b5 substituted with heme derivatives such as proto-, meso-, and deuteroheme exhibited demethylation activity at the maximum turnover rates of 94, 58, 30%, respectively, compared to that containing the native cytochrome b5, while neither apocytochrome b5 nor cobaltic protoporphyrin-cytochrome b5 displayed the activity. Kinetic analysis showed the formation of a 1:1 complex between cytochrome P-450B1 and each of these substituted cytochrome b5's, except for cobaltic protoporphyrin-cytochrome b5; the affinities differed with the cytochrome b5 species used. The synergistic effect with the addition of the NADH-linked electron transport system was more remarkable at the lower reduction levels of cytochrome b5 in the steady state. Interaction between the components involved in NADH- and NADPH-linked electron transport systems was modulated by the existence of Triton X-100. The optimal concentration in the reconstituted system for the demethylation was observed at around 0.03% of Triton X-100, where the reduction rates for cytochrome b5 and cytochrome P-450B1 by the respective reductases were maximal. These results indicate that the two electron transport systems are closely coupled and exhibit the demethylase activity.

Animals↗
PubMed1982

L-dopa restores amplitude of growth hormone pulses in old male rats to that observed in young male rats.

35 male Sprague-Dawley rats, 18 months old, were injected subcutaneously with the catecholamine precursor, L-dihydroxyphenylalanine (L-dopa) (100 mg/kg, twice daily), or vehicle alone, for 8 days in an attempt to increase the amplitude of growth hormone (GH) pulses in old male rats. 40% of young rats had at least one GH pulse greater than 600 ng/ml, over a 6.5 h sampling period, whereas only 22% of old vehicle-treated rats had pulses of similar amplitude. Treatment of old rats with L-dopa increased the number of animals showing elevated GH pulses to 53%. Young animals had mean GH concentrations of 136.5 +/- 14.0 ng/ml over the 6.5 h sampling period, whereas vehicle-treated old animals had mean GH levels of 95.2 +/- 7.7 ng/ml (p less than 0.05). Treatment of old animals with L-dopa increased mean plasma GH concentrations to 132.9 +/- 11.2 ng/ml (p less than 0.05) which was not significantly different from GH values in young rats. Pituitary GH concentration was less in old than in young rats (301 +/- 27.4 vs. 370 +/- 17.4 micrograms/mg protein, p less than 0.05). L-Dopa increased pituitary GH concentrations in old rats to 318 +/- 32.2 micrograms/mg protein, which was not significantly different from that in either young or old vehicle-treated animals. Hypothalamic somatostatin content in both rostral and caudal areas was lower in old than in young rats (p less than 0.01), and L-dopa had no significant effect on somatostatin content. These data indicate that L-dopa can increase the amplitude of GH pulses and elevate mean plasma GH in old male rats to levels present in young male rats, probably by increasing hypothalamic catecholamines.

Age Factors↗
PubMed1981

Ouabain binding to chick embryo neuroretina during development in ovo and in monolayer cultures.

Eight-day-old embryo neuroretinas (NR) were dissociated and cultured as monolayer. [3H]Ouabain binding was investigated during the culture period. [3H]Ouabain binding to NR increases continuously until around the tenth day of culture, but after that it gradually decreased. On the other hand, [3H]ouabain binding to NR during in ovo development continued to increase until the embryo was 20 days old. Na-K-ATPase activity was also compared with [3H]ouabain binding during development in ovo and in monolayer culture. It was found that changes in Na-K-ATPase activity of NR in vitro and in ovo were different from those of [3H]ouabain binding activity. Exposure of NR at the second day of culture to 0.1 mM ouabain for 8 h resulted in the degeneration of some differentiated neurons (rosette-formed cells), but new rosettes were soon re-formed after the withdrawal of ouabain, and [3H]ouabain binding to the ouabain-treated NR was decreased by 30%. Ouabain-treatment of NR in 10-day-old cultures completely destroyed the aggregated neurons, but did not apparently injure the glial cell layer. [3H]Ouabain binding decreased more than 90% in the ouabain-treated NR. These results suggest that [3H]ouabain binding activity of NR and the sensitivity to ouabain toxicity are useful indicators for differentiation and development of neurons in the cultured retinal cells.

Animals↗
PubMed1981

Activation of phosphodiesterase in frog rod outer segment by an intermediate of rhodopsin photolysis I.

Guanosine 3',5'-cyclic monophosphate phosphodiesterase (EC 3.1.4.1) in frog rod outer segment prepared by a sucrose stepwise density gradient method was activated by light in the presence of GTP. Rhodopsin in rod outer segment was solubilized with sucrose laurylmonoester and then purified by concanavalin A-Sepharose column. Addition of photo-bleached preparation of the purified rhodopsin to the crude rod outer segment, which had been prepared by 43% (w/w) sucrose floatation, caused the activation of phosphodiesterase in the dark, while each component of the photo-product eluted from the column (all-trans retinal and opsin) did not. Regenerated rhodopsin prepared from 11-cis retinal and purified opsin activated phosphodiesterase when it was bleached. From these facts it is suggested that an intermediate or a process of photolysis of rhodopsin causes activation of phosphodiesterase.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1981

Characterization of chick gizzard extract that promotes neurite outgrowth in cultured ciliary neurons.

Chicken gizzard extract contains a macromolecule(s) that promotes the neurite outgrowth of dissociated neurons from the ciliary ganglia (CG) of chick embryos. The factor in gizzard extract was partially purified and estimated to be about 12S (M.W. 200,000-300,000) on sucrose density gradient centrifugation. The neurite outgrowth of CG neurons by the factor strictly depends on the embryonal age. The maximal neurite outgrowth was observed when CG neurons were dissociated from the embryos younger than 10 days. After that time the response of CG neurons to the factor rapidly declined and was almost lost at day 14. The amount of factor in the gizzard began to increase rapidly from 12-day-old embryo and reached the maximal level at day 16, and thereafter a fairly steady level was maintained. When CG neurons were cocultured with rat myotubes, the ratio of muscle cells with synaptic responses (miniature end-plate potentials) was significantly higher in the presence of gizzard factor than its absence. The results suggest that this factor acts as an external signal on CG neurons to form synaptic connections in vivo.

Animals↗
PubMed1981

Effects of CNS active drugs and somatostatin antiserum on growth hormone release in young and old male rats.

The capacity of several potent pharmacological agents to increase growth hormone (GH) release was tested in young (3- to 4-month-old) and old (18- to 20-month-old) male Sprague-Dawley rats. Young and old animals were injected with alpha-methyl-p-tyrosine (250 mg/kg), a catecholamine synthesis inhibitor, followed 60 min later by the alpha-adrenergic receptor agonist, clonidine hydrochloride (150 micrograms/kg). Plasma GH levels increased to greater than 276 ng/ml by 30 and 50 min in young rats, whereas values never exceeded 130 ng/ml (p less than 0.01) in old rats. Piribedil methane sulfonate (1 mg/kg), a dopamine receptor agonist, significantly increased GH in young animals 60 min after injection (p less than 0.01), but had no effect in old rats. Morphine sulfate (5mg/kg) increased plasma GH concentration in young rats to greater than 400 ng/ml at 30, 50 and 70 min after injections, whereas values in old animals never exceeded 300 ng/ml (p less than 0.01). 15 min after injection of somatostatin antiserum No. 774 (5 ml/kg), plasma GH levels increased to greater than 750 ng/ml in both young and old rats. Administration of greater volumes of somatostatin antiserum (8 ml/kg) increased GH levels more in old than in young animals 30 and 45 min after injection (p less than 0.01). These results indicate that old male rats have less capacity to increase GH in response to agents that normally enhance GH release. This may be the result of a diminished number of affinity of post-synaptic neurotransmitter receptors, or to an increased release of somatostatin. Since somatostatin antiserum in creased H equally or to a greater extent on old that in young animals, aging rats may release more somatostatin or the pituitary may be more sensitive to the inhibitory effects of this hormone.

Aging↗
PubMed1981

[Neuropharmacology of cultured cells: studies on receptors, synapses and neuronal function of clonal cells (author's transl)].

This review concerns neuropharmacological properties of clonal cells from tumors in the nervous system and muscle, and/or somatic hybrid cells derived from these clonal preparations. These cells grow well under conditions of culture and show neuronal characteristics identical to those seen in normal cells. Observations of these clonal cells contribute to studies on development, differentiation, synaptogenesis and cellular recognition in the nervous system. Analysis of eukaryotic genes also enables investigations on genetic control mechanisms by which highly differentiated neuronal functions are expressed.

Adenylyl Cyclases↗
PubMed1980

Maintenance by L-DOPA treatment of estrous cycles and LH response to estrogen in aging female rats.

Nineteen, non-cycling female rats, 13-15 months of age, were fed 125 mg L-DOPA/15 g feed daily, and nineteen control rats of the same age were provided feed without L-DOPA. Sixteen of the L-DOPA fed rats each demonstrated 1-7 (average = 3) vaginal estrous cycles during the 75-day period of treatment, whereas no cycles were observed in the untreated controls. All animals were then ovariectomized and the post-castration rise in LH was monitored. Four weeks after ovariectomy, serum LH levels in the L-DOPA treated old female rats were significantly higher than in the non-treated old female rats. A single injection of 20 micrograms of estradiol benzoate (EB) significantly lowered serum LH in the L-DOPA treated rats, but no effect was observed in the non-treated controls. A second injection of EB three days later produced a significantly greater LH surge in the old rats given L-DOPA than in the non-L-DOPA treated controls. These results indicate that prolonged L-DOPA administration can partially prevent the decline in function of the hypothalamo-pituitary-ovarian system in aging female rats.

Aging↗
PubMed1980

NADH- and NADPH-dependent reconstituted p-nitroanisole O-demethylation system containing cytochrome P-450 with high affinity for cytochrome b5.

A reconstituted system containing a form of cytochrome P-450, cytochrome b5, NADPH-cytochrome P-450 reductase, and NADH-cytochrome b5 reductase, all purified from rabbit liver microsomes, could catalyze O-demethylation of p-nitroanisole in the presence of both NADPH and NADH. Omission of either cytochrome P-450 or cytochrome b5 from the system led to complete loss of the activity. The reconstituted activity was sensitive to carbon monoxide, metyrapone, phenyl isocyanide, and cyanide, indicating that the cytochrome P-450 used is cyanide-sensitive and is involved in the catalytic process. The maximal demethylase activity was attained when the system contained cytochrome P-450 and cytochrome b5 at a 1 : 1 molar ratio. Trypsin digestion of cytochrome b5 abolished the capacity of this cytochrome to reconstitute the demethylase activity. These results suggest that O-demethylation of p-nitroanisole by this particular form of cytochrome P-450 absolutely requires the intact form of cytochrome b5 and that the second electron needed for the demethylation may be donated to the cytochrome P-450 only by way of cytochrome b5.

Animals↗
PubMed1980

Effects of chlorpromazine and naloxone on growth hormone secretion in rats.

The present study was conducted to examine roles of brain monoamines and opioid peptides in growth hormone (GH) secretion in unanesthetized, freely behaving rats. The administration of chlorpromazine (CPZ, 300 microgram/100 g, i.v.), an antagonist of brain monoamines, to rats that were passively immunized with antiserum to somatostatin immediately lowered plasma GH levels and inhibited episodic GH secretion. An intraventricular injection of beta-endorphin (3.5 microgram) stimulated GH secretion. This effect was completely inhibited by the prior administration of naloxone (100 microgram/100 g, i.v.), a specific antagonist of opioid peptides, but not by CPZ. In addition, the administration of naloxone did not inhibit episodic GH secretion. The results suggest that CPZ inhibits episodic GH secretion via a factor(s) other than somatostatin. It is also inferred that brain monoamines, but not opioid peptides, play major roles in the regulation of episodic GH secretion in rats.

Animals↗
PubMed1980

Failure of naloxone to influence plasma growth hormone, prolactin, and cortisol secretions induced by insulin hypoglycemia.

The effect of naloxone, a specific antagonist of opioid peptides, on plasma, GH, PRL, and cortisol responses to insulin-induced hypoglycemia was studied in five healthy male subjects. The iv administration of regular insulin (0.15 U/kg) led to similar degrees of hypoglycemia on control and experimental days. Plasma GH, PRL, and cortisol levels rose significantly in response to insulin-induced hypoglycemia. A 2-h infusion of naloxone (0.8 mg/h) started 30 min before insulin injection did not alter either basal hormone levels or the hormone responses to insulin-induced hypoglycemia. These results suggest that endogenous opioid peptides do not play a major role in GH, PRL, or cortisol secretion induced by insulin hypoglycemia.

Adult↗
PubMed1980

Effects of oral befunolol on heart rate and systolic blood pressure during submaximal exercise in man.

For the purpose of determining exercise intensity required for evaluating the effect of beta-blocking agents, the multi-stage treadmill exercise was carried out up to intensity of 85% of maximal oxygen intake (VO2max) after administration of beta-blocking agents in 7 healthy men. To obtain a stable dose response in the inhibitory effect of beta-blocking agents on heart rate (HR) and systolic blood pressure (S-BP), the exercise intensity more than 65% of VO2max (75% of maximal heart rate) was needed. In order to evaluate the effect of befunolol (BFE), a submaximal treadmill exercise of 75% of the age adjusted predicted maximal heart rate was loaded in 6 healthy men at 1.5, 4, and 8 hours following a single oral administration of 10 mg, 20 mg or 40 mg of BFE and 20 mg or 40 mg of propranolol. Simultaneously, the plasma concentration of BFE was determined 1.5, 4, 6 and 8 hours after the administration of BFE at each dose. In human serum, BFE was detected together with its metabolite, revealing a significant correlation between BFE and metabolite (r = 0.94, p < 0.001). Almost a certain rate of metabolite (4--5 times) was detected against BFE. As for the biological half life, it was 1.79 +/- 0.13 hours with BFE and 3.67 +/- 1.33 hours with metabolite. The inhibitory effect of BFE on HR and S-BP during exercise exhibited a dose response with the oral dose and its plasma concentration, and was almost twice as much as that of propranolol at the same dose. Accordingly, the myocardial oxygen consumption which may be represented as rate pressure product was inhibited twice as much as propranolol. BFE is characteristic of its more rapid elimination of its effect compared to the other beta-blocking agents. The decrease in the inhibitory effect of BFE or HR during exercise was about 1.8 times quicker than that of propranolol.

Administration, Oral↗