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Biomedical subjects

R Hirota

Publications and source records attributed to R Hirota.

At least 19 recordsLinked to original sources
PubMed1995

Visible light-sensitized oxidation of arachidonic acid in the presence of inperatorin.

To understand the mechanism of the phototoxic effects of inperatorin, a psoralen derivative used as a pigmentation agent, we have investigated the photosensitized oxidation of arachidonic acid (ARA) by irradiation with visible light (> 400 nm) in the presence of inperatorin. HPLC and GC/MS analyses of the products showed the formation of many hydroperoxyeicosatetraenoic acids (HPETEs) including the products of lipoxygenase-catalyzed reactions such as 5- and 15-HPETEs, which are the precursors of chemical mediators such as leukotrienes and lipoxins, during the reaction. Active oxygen scavening agents such as D-mannitol, superoxide dismutase, and beta-carotene inhibited the formation of the oxidation products, indicating that the oxidation reaction was mediated by various active oxygen species. These results suggest that the phototoxic effects of inperatorin could also be induced by visible light and could be explained at least partially in terms of inflammation initiated by the biologically active HPETEs arising from photosensitized oxygenation reactions of ARA with the drug.

Arachidonic Acid↗
PubMed1991

Production of corticosterone and testosterone in scorbutic mutant rats: difference of in vivo production between adrenal gland and testis.

Effects of deficiency in ascorbic acid on in vivo production of corticosterone and testosterone were examined using a mutant strain of rats unable to synthesize ascorbic acid. The adrenal weight of scorbutic rats was larger, and corticosterone levels in plasma and adrenal tissues were higher than those of ascorbic acid-supplied (ascorbutic) rats. Acute and chronic stimulation with ACTH increased corticosterone levels in both ascorbutic and scorbutic rats. In contrast, weights of seminal vesicles and ventral prostates in unstimulated scorbutic rats were smaller, and testosterone levels in plasma and testicular tissues were lower than those in ascorbutic rats. Acute stimulation with hCG increased testosterone levels only slightly in plasma and not in testicular tissues of scorbutic rats, when testosterone levels in ascorbutic rats reached a maximum. Chronic stimulation with hCG increased testosterone levels remarkably in both ascorbutic and scorbutic rats. These findings seem to indicate that ascorbic acid is not essential for the synthesis of steroid hormones. The scurvy seems to increase plasma ACTH levels secondary to the stress, resulting in the stimulation of the adrenals. In contrast, a prolonged deficiency in ascorbic acid appears to decrease plasma gonadotropin levels, and may reduce the sensitivity of testes to gonadotropins.

Adrenal Glands↗
PubMed1989

Effect of physical training on thrombotic tendency in rats: decrease in thrombotic tendency measured by the He-Ne laser-induced thrombus formation method.

The effect of physical training on thrombotic tendency was assessed in rats. Exercise was done on a flat treadmill for 30 min at a rate of 1,400 m/h (submaximal speed), 5 times a week for either 1.5 or 3 months. The thrombotic tendency was measured by the He-Ne laser-induced thrombus formation method in microvessels of mesentery, i.e. measurement of the number of laser irradiations necessary to induce stasis of blood flow by occlusive thrombus formation. An increase in the number of irradiations necessary to induce occlusive thrombus formation was observed in arterioles, but not in venules after physical training for 1.5 and 3 months.

Animals↗
PubMed1982

Effect of cholecystokinin octapeptide and vasoactive intestinal polypeptide on adrenocortical secretion in the rat.

Intraperitoneal (i.p.) injection of C-terminal octapeptide of cholecystokinin (CCK-8) produced a dose-related increase in plasma corticosterone levels in intact rats, but not in vagotomized ones. Intracerebroventricular (i.c.v.) injection of CCK-8 was ineffective in stimulating the secretion of corticosterone, and in vitro experiment on ACTH release indicated that CCK-8 could not affect pituitary tissue directly. Since i.p. injection of non-sulfated CCK-8 failed to elevate plasma corticosterone levels, sulfated tyrosine residue in the CCK molecule is assumed to be indispensable for the stimulation of visceral organs. On the other hand, vasoactive intestinal polypeptide (VIP) was found to cause a dose-dependent increase in plasma corticosterone levels when administered centrally, but not after i.p. injection. However, VIP could not stimulate the release of ACTH from the pituitary tissue directly. The results suggest that VIP, but not CCK, stimulates the hypothalamic CRF neurons either directly or indirectly.

Adrenal Cortex↗
PubMed1982

Effect of intraventricular administration of vasoactive intestinal polypeptide on body temperature in the rat.

Intracerebroventricular injection of vasoactive intestinal polypeptide (VIP) into rat caused a temporary elevation of body temperature followed by a decrease to below the control level. Hypothermia induced by cholecystokinin octapeptide was abolished by simultaneous administration of VIP. Hypothermia following pentobarbital administration was reduced by successive injections of VIP. The results suggest that multiple interactions of neuropeptides are involved in central thermoregulation.

Animals↗
PubMed1981

Cholecystokinin-induced hypothermia in the rat.

Cholecystokinin-octapeptide (CCK-8) was shown to cause hypothermia after intracerebroventricular administration in the rat, and the hypothermic effect of CCK-8 was antagonized by simultaneous injection of TRH.

Animals↗
PubMed1980

Effect of neonatal hydrocortisone treatment on brain monoamines in developing rats.

In our previous study, neonatal treatment with hydrocortisone was shown to produce a marked retardation of pituitary-adrenocortical development in infant rats. The present investigation was an attempt to determine whether or not the retarded activity is caused by functional changes in brain monoamine systems. In rats treated with hydrocortisone (0.5 mg/rat, s.c.) on the 2nd day of life, the development of whole brain was suppressed significantly. However, norepinephrine, dopamine and serotonin contents in the brain were higher in these rats than controls. These changes of monoamine contents were apparent in the hypothalamus, diencephalon and pons-medulla oblongata. Our data suggest that monoaminergic nervous systems are potentiated with hydrocortisone in these brain regions, although the results do not necessarily explain the retarded hypothalamo-pituitary function.

Animals↗
PubMed1980

Conditioned circadian rhythm of plasma corticosterone in the rat induced by food restriction.

Earlier observations that food restriction for a short period of time in the morning produced an altered circadian rhythm of plasma corticosterone having the peak just before feeding time, and that the elevated plasma corticosterone levels declined promptly immediately after food presentation were confirmed. After a 14-day restricted feeding schedule, where food was given from 11:00 to 13:00, if food was not given, elevated levels of plasma corticosterone were sustained for at least 1 hr and then declined gradually. On the other hand, if food was given 2 hr earlier than the scheduled time, the peak at 11:00 disappeared. The conditioned peak of plasma corticosterone was maintained for at least 3 days after the restricted feeding schedule if hypertonic saline, but not tap water, was given without food in male rats and ovariectomized female ones. When female rats were treated with lysine vasopressin for 5 days 10 min before the food presentation, highly elevated levels of plasma corticosterone were found at the time of food presentation. However, administration of cortisol 2 hr before the feeding time blocked the effect of vasopressin. The results suggest that vasopressin is involved in the acquisition and consolidation of the conditioned circadian rhythm of plasma corticosterone induced by restricted feeding.

Animals↗
PubMed1980

The rate of phase shift of plasma corticosterone circadian rhythm during early developmental stages in neonatally blinded rats.

The phase shift of circadian periodicity of pituitary-adrenocortical activity was studied in neonatally blinded infant rats. The phase shift of the rhythm was surprisingly rapid during the early stage of prepubertal period, while changes in the rhythm pattern were rather small after puberty, as indicated by a slight shift of the acrophase. Low amplitude was observed in the group data of blinded rats after puberty.

Age Factors↗
PubMed1980

Effect of a cholecystokinin preparation on brain monoamines in the rat.

In order to elucidate the central action mechanism of cholecystokinin (CCK), effects of this peptide on norepinephrine, dopamine and serotonin contents in the brain were observed in saline control, alpha-methyl-p-tyrosine-, L-DOPA- and pargyline-pretreated rats. Intraperitoneal injection of CCK in a dose of 40 U/kg did not produce any significant changes in the monoamine contents. However, since a tendency to increase in norepinephrine turnover rate after CCK injection was noticed, the possibility that brain monoamines are involved in the central action of CCK could not be excluded.

Animals↗
PubMed1979

Suppressive effect of pentagastrin on pituitary-adrenocortical secretion.

The effect of pentagastrin on the pituitary-adrenocortical secretion was examined in male rats. In the morning the intraperitoneal injection of this peptide produced a slight, but significant, decrease in the plasma corticosterone levels, but it had no effect on the evening rise due to circadian periodicity and the stress-induced elevation of the plasma corticosterone level. Following intracerebroventricular administration of pentagastrin, plasma corticosterone tended to decrease and in in vitro incubation of rat pituitary tissue the addition of pentagastrin elicited a suppressive effect on the ACTH release from the tissue into the medium. It was suggested that gastrin-like peptide might control the secretion of ACTH.

Adrenocorticotropic Hormone↗
PubMed1978

[Postnatal development of adrenocortical circadian rhythm in neonatally cortisol- and estriol-treated rats (author's transl)].

The effect of a single neonatal administration of cortisol and estriol on the development of the adrenocortical circadian rhythm was investigated in immature rats. In normal control rats of both sexes, the plasma corticosterone rhythm was discernible on day 21. In male rats the adult pattern was observed on day 28, but in females as the plasma corticosterone level elevated progressively during puberty, the rhythm increased in amplitude and the adult pattern was established at 8 weeks of age. In neonatally cortisol-treated rats, the plasma corticosterone rhythm appeared at 4 weeks of age, but the plasma level was significantly lower than that of the controls until 6 weeks and attained a level similar to the controls at 8 weeks. Neonatally estriol-treated rats exhibited the rhythm as early as 2 weeks of age, but this was temporary. It disappeared at 3 weeks and reappeared a 4 weeks. Although 5-week-old males showed normal rhythm as seen in the controls, in females the plasma corticosterone level remained low for weeks and approached the control level at 8 weeks of age. The development of circadian periodicity of adrenal corticosterone content almost paralleled that of plasma corticosterone not only in the controls but also in steroid-treated groups, but the rhythm was occasionally equivocal. In neonatally estriol-treated rats, stress response of plasma and adrenal corticosterone to ether was similar to that of the controls, but the response to exposure to a strange environment was significantly small.

Adrenal Cortex↗