Effect Of MT Research Articles

Meta‐topolin, an alternative to benzyladenine in tissue culture?

The metabolism and the in vitro effects of the cytokinin N6‐(3‐hydroxybenzyl)adenine (meta‐topolin, mT) were compared with those of N6‐benzyladenine (BA), N6‐benzyl‐9‐(2‐tetrahydropyranyl)adenine (BPA) and N6‐benzyladenine‐9‐riboside ([9R]BA) in micropropagated Spathiphyllum floribundum Schott cv. Petite. In vitro, BA, BPA and [9R]BA were mainly converted into the stable derivative N6‐benzyladenine‐9‐glucoside ([9G]BA), located at the basal part of the plant. N6‐(3‐O‐β‐D‐glucopyranosyl)benzyladenine‐9‐riboside {(OG)[9R]mT} was the main derivative of mT. This new cytokinin‐O‐glucoside, which was present in all plant parts, was metabolized much faster than [9G]BA during acclimatization. The effect of BA and mT on in vitro shoot and root production and post vitro rooting was compared. Only mT combined a good shoot production with in vitro root formation. The plants that developed on medium with 10 µM or more mT rooted better during acclimatization than those developed on medium with equimolar concentrations of BA.

Transgenic Mice That Overexpress Metallothionein-I Are Protected from Cadmium Lethality and Hepatotoxicity

The purpose of this study was to determine whether metallothionein-I (MT-I) transgenic female mice (MT-TG) are resistant to cadmium (Cd) hepatotoxicity. Female MT-TG mice have 10- to 20-fold higher MT concentrations in liver than control mice and are more resistant to Cd-induced lethality than control mice. CdCl2 (3.7 mg Cd/kg, iv) was lethal to 73% of control mice, but only to 13% of MT-TG mice. Cd administration (3.1 mg/kg, iv) to control mice produced extensive liver injury as evidenced by 20- and 70-fold increases in serum enzyme activities of sorbitol dehydrogenase and alanine aminotransferase, respectively. MT-TG mice are considerably more resistant to Cd-induced hepatotoxicity than control mice, as evidenced by only about one-tenth the elevation in serum enzymes observed in control mice and a lower incidence of hepatocyte necrosis in MT-TG mice. To ascertain the mechanism of this protection, the distribution of Cd to various organs and the subcellular distribution of Cd in liver were determined 2 hr after Cd injection (109CdCl2, 3.5 mg Cd/kg, iv). The hepatic subcellular distribution of Cd was altered markedly in MT-TG mice, with much less Cd distributing to nuclei, mitochondria, and microsomes (25, 42, and 24% of controls, respectively), and more Cd to the cytosol (240% of controls). The increased cytosolic Cd was bound primarily to MT, as determined by G-75 gel chromatography. In addition, primary hepatocyte cultures from MT-TG mice maintained higher levels of MT than hepatocytes from control mice and were more resistant to Cd cytotoxicity than control hepatocytes. In conclusion, studies using MT-I transgenic mice demonstrate that MT protects against Cd lethality and hepatotoxicity, and this hepatoprotective effect of MT is also observed in hepatocyte cultures from MT-TG mice.

Sex differentiation in the European eel: histological analysis of the effects of sex steroids on the gonad

The effects of sex steroids on sex differentiation in the European eel were studied. The steroids, 17α‐methyltestosterone (MT) and 17α‐ethynylestradiol (EE), were given in the diet to 6–8 cm elvers and to 15–18 cm and 22–25 cm yellow eels. In our rearing conditions a very large percentage of the untreated eels developed as males. No masculinizing effect of MT could be demonstrated. The EE, administered at a dose of 10 mg kg‐1 of diet to 6–8 cm elvers and 15–18 cm eels, induced ovarian differentiation in about 90 and 65% of eels respectively, while in the control <5% of females was recorded. In 22–25 cm yellow eels a moderated feminizing effect was observed.Histological analysis of the gonads of treated eels showed that sex steroids affect the gonadal structure. The androgen stimulates hypertrophy of compact connective tissue, early differentiation of Leydig cells, Sertoli cells and early formation of the spermatic duct. Oestrogen inhibits the differentiation of these structural components and stimulates the differentiation of follicular cells and an ovarian structure.The involvement of gonadal structural components is discussed in relation to the effect of steroid treatment and to the peculiarities of sex differentiation in the European eel.

Metoprolol monotherapy in the treatment of mild hypertension

AbstractMetoprolol tartrate (MT) as monotherapy was administered orally in 17 patients with mild hypertension. All other drugs were discontinued 2 weeks prior to MT therapy. The present study group consisted of 10 men and 7 women within the age range of 42 to 71 years (mean ± S.D. = 55.8 ± 8). MT was administered at an initial dose of 50 mg twice daily. Subsequently, the dose of MT was titrated on a biweekly basis for a period of 12 weeks until the diastolic blood pressure was < 90 mmHg or a maximum daily dose of 300 mg was administered. The blood‐pressure‐lowering effect of MT was found to be clinically satisfactory and statistically significant (P < 0.05). Mild fatigue and swelling of the extremities were seen in two patients each. Mild headache, transient diarrhea, and mild cloudiness of mind were seen in one patient. From this study it is concluded that MT is a safe and effective first‐step antihypertensive agent. The long‐term effect of MT as a monotherapy in the treatment of mild hypertension needs further clinical evaluation.

Inhibitory effects of 17α-methyltestosterone and estradiol-17β on smoltification of sterilized amago salmon ( Oncorhynchus rhodurus)

Underyearling amago salmon parr, previously sterilized by 17α-methyltestosterone (MT) treatment, were fed either MT (1 or 10 μg/g diet), estradiol-17β (E 2; 1 or 10 μg/g diet), or no hormone (control), in late autumn for 60 days. The occurrence of smolts in the different treatment groups, as judged by body silvering and dorsal fin-margin darkening at the end of the experiment, was as follows: control, 80%; MT − 1 ppm, 0%; MT − 10 ppm, 0%; E 2 − 1 ppm, 33%; E 2 − 10 ppm, 2%. A seawater challenge test indicated a lower hypoosmoregulatory ability of fish treated with both doses of MT and with the higher dose of E 2. The histological activity of the gill chloride cells was lower in the hormone-treated fish than in the control animals. MT and E 2 stimulated pituitary gonadotrophs. The pituitary somatotrophs of the control fish showed the most active features among the experimental groups, while the cells of the fish treated with the high dose of E 2 showed pathological changes. These results indicate that both MT and E 2 inhibit smoltification of amago salmon, morphologically and physiologically. The inhibitory effect of MT on smoltification was greater than that of E 2. Thus the present experiment suggests that androgens and estrogens, which are synthesized in the gonad of sexually maturing amago salmon parr, prevent parr-smolt transformation of the fish.

Lack of Evidence that the Central Serotoninergic System Plays a Role in the Activation of Prolactin Secretion following Inhibition of Dopamine Synthesis or Blockade of Dopamine Receptors in the Male Rat

Administration of alpha MT to inhibit catecholamine synthesis or dopamine (DA) receptor blockade with spiroperidol had no effect on the hypothalamic concentration of 5HT or 5HIAA. Fluoxetine to block serotonin uptake had no influence on the elevation of serum prolactin levels induced by alpha MT or DA receptor blockers and conversely alpha MT did not influence the prolactin-releasing action of 5HTP alone or in combination with fluoxetine. Depletion of brain serotonin stores with p-chlorophenylalanine did not affect the prolactin-releasing action of alpha MT or DA receptor blockers. In contrast, the serotonin blocker methysergide, but not cyproheptadine, inhibited the prolactin-releasing effect of alpha MT or alpha-flupentixol, a DA receptor blocker, but not of spiroperidol, another DA receptor blocker. The intensity of the inhibition induced by methysergide paralleled the intensity of inhibition induced by apomorphine. Methysergide conspicuously lowered serum prolactin in animals with electrolytic destruction of the median eminence, whereas cyproheptadine had only a slight effect. The prolactin-inhibiting effect of methysergide could be prevented by pretreatment of the lesioned rats with spiroperidol. It is concluded (1) that elimination of the influence of the DA system does not activate the central serotoninergic system; (2) that activity of the serotoninergic system has no role in the activation of prolactin secretion induced by suppression of the inhibitory dopaminergic influence, and (3) that the inhibiting action of methysergide on the prolactin-releasing effect of alpha MT or alpha-flupentixol is due to its dopamine receptor agonist activity rather than to blockade of serotonin receptors.

Role of Catecholamines in Photoperiodically-Induced Gonadal Development in Coturnix Quail1

The involvement of central biogenic amines in the mechanisms controlling photoperiodically-induced testicular development in Coturnix quail were studied employing pharmacological approaches. Daily administration of alpha-methyltyrosine (MT), which blocks catecholamine (CA) biosynthesis, to 6-week-old quail exposed to long daily photoperiods markedly depleted brain dopamine (DA), norepinephrine (NE) and epinephrine (E). This was associated with a partial suppression of testicular growth 7 days after light stimulation. Combined treatment with MT and L-dihydroxyphenylalanine (L-DOPA), a precursor of DA, NE and E, elevated the monoamine levels in the brain and prevented the blocking effect of MT on testicular growth. Selective blockade of NE and E biosynthesis with diethyl-dithiocarbamate (DDC) depleted both NE and E, while it elevated DA level. Furthermore, such treatment reduced testicular weight. In DDC-treated birds, D,L-dihydroxyphenylserine (DL-DOPS) administration, which bypasses the DDC block, restored only brain NE level and reversed the blocking action of DDC on testicular weight. It is concluded that central NE plays a role in transformation of the photoperiodic information affecting gonadal development in Coturnix quail.

Effects of methimazole and propylthiouracil on blood disappearance and urinary excretion of iodide in the rat.

SummaryRegardless of the dose of MT administered, MT decreased the rate of disappearance of radioiodide from the blood for at least 25 hr by depressing urinary excretion of iodide in thyroidectomized, thyroxine-maintained rats fed LID. This effect of MT was lessened in rats fed HID. In contrast, PTU augmented disappearance of blood iodide during the first 60 min after radioiodine injection. This effect was apparently related to the dose of PTU administered. It is concluded that MT and PTU have different mode of action on extrathyroidal iodine metabolism in the rat.