Biomedical subjects

K Taya

Publications and source records attributed to K Taya.

At least 55 records · Page 3Linked to original sources

PubMed2000

Follicle selection in cyclic guinea pigs with active immunization against inhibin alpha-subunit.

Experiments were conducted to elucidate the mechanisms of active immunization against inhibin on ovarian follicular development and selection in guinea pigs. Estrous cycle was synchronized in experimental guinea pigs by implanting progesterone containing tubes. Antibodies that bound 125I-labeled bovine inhibin were produced by all guinea pigs receiving the inhibin vaccine (recombinant ovine alpha-subunit in oil emulsion) without any effects on duration of the estrous cycle. Active immunization against inhibin increased the plasma concentrations of progesterone during the luteal phase and the plasma concentrations of estradiol but failed to increase the plasma concentration of follicle-stimulating hormone (FSH) during preovulatory period. The treatment also increased the number of corpora lutea (from 1.3+/-0.3 to 7.0+/-1.6 per each ovary), and preovulatory sized follicles (from 1.8+/-0.6 to 7.0+/-1.6 per each ovary), and follicles stained positively for inhibin alpha-subunit (from 2.3+/-0.5 to 6.3+/-1.3 per each ovary) significantly. The results indicate that active immunization against inhibin enhances ovulation rate by affecting the follicle selection and only dominant follicle can be stained for inhibin alpha-subunit in guinea pigs. This study is firstly to provide direct evidence that inhibins play important role in follicle selections in guinea pigs.

Animals↗

PubMed2000

Presynaptic L-type Ca(2)+ channels on excessive dopamine release from rat caudate putamen.

We investigated by means of behavioral and neurochemical studies the role of the nerve terminal L-type voltage sensitive Ca(2)+ channel on dopamine (DA) release. Microinjection of Bay K 8644 (BAYK), an L-type Ca(2)+ channel stimulant, into the rat caudate putamen increased locomotor activity and rearing behavior in a dose-dependent manner, whereas injections into the amygdala had no effect. DA receptor antagonists significantly blocked BAYK-induced hyperactivity. Significant increases of extracellular DA levels were detected by microdialysis 20 min after BAYK administration into caudate putamen and then declined. This increase was influenced by tetrodotoxin, an axonal Na(+) channel blocker. Pretreatment with nimodipine and nicardipine, but not nifedipine, which are 1, 4-dihydropyridine L-type Ca(2)+ channel antagonists, administered into the caudate putamen significantly blocked BAYK-induced hyperactivity and DA efflux. These results indicate that the extraordinary DA release in the caudate putamen was mediated by extreme stimulation of the nicardipine and nimodipine-sensitive L-type Ca(2)+ channel present in the nerve terminal of striatal DA neurons.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed2000

Changes in concentrations of plasma immunoreactive follicle-stimulating hormone, luteinizing hormone, estradiol-17beta, testosterone, progesterone, and inhibin in heifers from birth to puberty.

This study was designed to clarify the characteristics of changes in plasma concentrations of reproductive hormones in heifers from birth to puberty. Weekly or daily hormonal changes were observed in 39 heifers. Daily changes in the concentration of follicle-stimulating hormone (FSH) demonstrated a consistent cycle of hormone changes over a 7- to 8-day period in heifers from approximately 10 days to 9 months old. Weekly changes in reproductive hormones showed that there were three brief periods in heifers between birth and puberty in which dramatic changes occur. The first period was the first week after birth, during which a reciprocal relationship between steroid hormones and gonadotropins was observed. At birth, the concentrations of steroid hormones were higher than those at any other age. These hormone levels rapidly decreased within the first week after birth. Gonadotropin levels, however, increased from birth to 1 week of age. The second period of major change was at approximately 4 weeks of age when there was an increase in the concentrations of luteinizing hormone (LH), estradiol-17beta, testosterone, and immunoreactive inhibin. The third period was the last 5 weeks before the first ovulation, when there was an increase in the concentrations of estradiol-17beta followed by an increase in (LH). These results suggest that regular hormone changes start from 10 days after birth and that the periods from birth to 4 weeks of age and the last 5 weeks before the first ovulation in heifers are important to the development of reproductive functions before puberty.

Animals↗

PubMed2000

Immunohistochemical localization of inhibin and steroidogenic enzymes in the ovary of common tree shrew (Tupaia glis) and northern smooth-tailed tree shrew (Dendrogale murina).

To study the ovarian function of the Order Scandentia, the localization of inhibin and steroidogenic enzymes (3 beta-hydroxysteroid dehydrogenase/isomerase and aromatase) in the ovaries of common tree shrew (Tupaia glis) and northern smooth-tailed tree shrew (Dendrogale murina) was immunohistochemically analysed. As in the results reported for other mammals, inhibin alpha-chain was localized in the follicular epithelium of secondary or Graafian follicles in the two species. The localization of aromatase in the ovary of these two species, however, was different. In the common tree shrew, the aromatase was localized in the thecal cells, whilst in other mammals it is localized in the granulosa cells. These results indicate that in the ovary of the common tree shrew, the oestradiol may be synthesized in the thecal cells.

3-Hydroxysteroid Dehydrogenases↗

PubMed2000

Inhibin is an important factor in the regulation of FSH secretion in the adult male hamster.

We investigated the importance of inhibin and testosterone in the regulation of gonadotropin secretion in adult male golden hamsters (Mesocricetus auratus). After castration, plasma concentrations of inhibin and testosterone were reduced to undetectable, whereas plasma follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were increased. After hemicastration, plasma FSH and LH increased moderately and plasma inhibin decreased to one-half its initial level. Plasma testosterone levels in hemicastrated animals decreased 3 h after hemicastration but returned to those in sham-operated animals at 6 h. Plasma LH in the castrated hamster declined comparably to intact animals with testosterone treatment; plasma FSH also decreased but still remained at levels higher than those in intact animals. After treatment with inhibin in long-term-castrated animals, plasma FSH decreased, whereas plasma LH was not altered. Intact males treated with flutamide, an anti-androgen, showed a significant increase in plasma LH but not in FSH. On the other hand, treatment with anti-inhibin serum induced a significant elevation in plasma FSH, but not in LH. Using immunohistochemistry, we showed that the inhibin alpha-subunit was localized to both Sertoli and Leydig cells. The present study in adult male hamsters indicates that FSH secretion is regulated mainly by inhibin, presumably from Sertoli and Leydig cells, and that LH secretion is controlled primarily by androgens produced from the Leydig cells. This situation is more similar to that of primates than of rats.

3-Hydroxysteroid Dehydrogenases↗

PubMed2000

Development of embryos in superovulated guinea pigs following active immunization against the inhibin alpha-subunit.

Embryo recovery and subsequent embryonic development from guinea pigs treated with or without inhibin vaccines were compared to determine the effect of active immunization against the inhibin alpha-subunit. Twenty female guinea pigs of the Hartley strain were injected 3 times either with 1 ml inhibin vaccine (recombinant ovine inhibin a-subunit in oil emulsion: 50 microg/ml, inhibin-immunized group), or 1 ml placebo (saline in oil emulsion; control group) at 4 week intervals. After one estrous cycle following the last injection, females were naturally mated and embryos were collected at 11:00 hr of day 6 of pregnancy (Day 1: sperm in the vaginal smear) for culture in vitro. Active immunization increased the number of corpora lutea (12.6+/-3.0 vs. 4.6+/-0.2, P<0.05), recovered embryos (9.8+/-1.9 vs. 3.6+/-0.4, P<0.01) and normal embryos (7.8+/-1.4 vs. 3.6+/-0.4, P<0.05), although estrous cycle length was not affected (P>0.05). During subsequent 8 day culture in vitro, most of the recovered embryos formed trophoblast outgrowth; 100% (14/14) and 88.2% (15/17) in control and immunized groups, respectively. High levels of inhibin antibody titers were sustained in the inhibin-immunized guinea pigs at least for 5 months after the last injection while no antibody titer was detected in the control animals. These results indicate that active immunization against the inhibin a-subunit is a long-acting and efficient method to induce superovulation with normal embryonic development in the guinea pig.

Animals↗

PubMed2000

Effects of third ventricle injection of norepinephrine analogue on LH secretion of the non-laying SIJI goose.

The effect of norepinephrine analogue (NA) and norepinephrine antagonists on luteinizing hormone releasing hormone (LHRH) secretion in geese was investigated by monitoring serum levels of LH. Twenty non-laying geese were selected and randomly assigned to 4 groups of 5 each. The geese received a single intraventricular injection of saline (control), NA (12 microg/6 microl), phentolamine (1 microg/6l) plus NA or yohimbine (10 microg/6 microl). Phentolamine, a non-selective adrenoreceptor blocker was given 5 min before NA, but yohimbine, an alpha2-adrenoreceptor blocker, was delivered without NA injection. The results showed that serum levels of LH began to increase 20 min after injection of NA, and that high serum levels of LH were maintained until 105 min, followed by a decline to the basal level 125 min later. Significantly high levels of serum LH were observed at 50 and 105 min after the injection as compared with the respective control. Treatment with phentolamine completely blocked the stimulatory effect of NA on serum levels of LH in NA treated geese. Serum levels of LH increased by yohimbine treatment 5 min after the injection and the high levels of serum LH were maintained until 125 min later. Five out of 8 points were significantly high as compared with their respective control values. The present study also suggested that there is presynaptic modulation in the a-noradrenergic neural pathways which mediate the release of LHRH, and that this modulation may be carried out by alpha2-adrenoreceptor blocker.

Adrenergic alpha-Agonists↗

PubMed2000

Changes in plasma concentrations of inhibin A and inhibin B throughout sexual maturation in the male chimpanzee.

Profiles of circulating plasma inhibin A and inhibin B during sexual maturation in male chimpanzees were investigated by using two-site enzyme-linked immunoassay (ELISA). Plasma concentrations of testosterone and pituitary gonadotropins were also measured. Concentrations of inhibin B, testosterone, luteinizing hormone (LH) and prolactin increased with age throughout prepuberty to adulthood, whereas inhibin A level was low and there were no age-related changes in concentrations of either inhibin A and follicle-stimulating hormone (FSH). Inhibin B showed an inverse correlation with FSH in adult (7 years or order) but not in immature (6 years or younger) male chimpanzees. There was no correlation between plasma levels of FSH and testosterone throughout the period of sexual maturation. However, testosterone levels were positively correlated with inhibin B levels. These results suggest that circulating inhibin B is involved in the regulation of FSH secretion after puberty in adult male chimpanzees, and also that circulating inhibin B is an important form of inhibin as a marker of Sertoli cell function in adult male chimpanzees.

Aging↗

PubMed2000

Induction of superovulation by inhibin vaccine in cyclic guinea-pigs.

Experiments were conducted to determine whether neutralizing endogenous inhibin affects follicular development and ovulation rate in guinea-pigs. Eighteen female guinea-pigs bearing 4 week progesterone implants were divided into three groups. At 1 week after removal of the progesterone implants, the animals were given a s.c. injection of 1 ml placebo (saline in oil emulsion; control), or 25 or 50 micrograms inhibin vaccine three times at 4 week intervals. Blood samples were collected once a week throughout the experiment for measuring inhibin antibody titres. After the third injection of inhibin vaccine, blood samples and ovaries were collected on the morning of day 8 after the day of oestrus. Inhibin vaccine increased the ovulation rate in a dose-dependent manner (placebo: 4.2 +/- 0.4; 25 micrograms inhibin vaccine: 6.2 +/- 0.9; 50 micrograms inhibin vaccine: 9.8 +/- 0.9) without any effects on the duration of the oestrous cycle. The results also showed that active immunization against inhibin increased the number of atretic follicles of 300-399 microns in diameter on day 8 after ovulation. The present study is the first to show that the active immunization against inhibin may be a useful method for inducing multiple ovulation in guinea-pigs.

Analysis of Variance↗

PubMed1999

Plasma ACTH levels during early, two-way avoidance acquisition in high- and low-avoidance rats (Hatano strains).

Having successfully bred for high- and low-avoidance rats (HAA and LAA, respectively) on a shuttlebox task, we performed three experiments designed to identify factors which might be related to the phenotypic differences seen in avoidance behavior. In experiment 1, shuttlebox behavior was measured to determine whether the phenotypic difference was activity related. In terms of intertrial responses, there was no difference between HAA and LAA rats in locomotor activity during the conditioning process. Experiment 2 compared adrenal weights of HAA and LAA rats at 11 weeks of age. The observation that the adrenal glands were heavier in HAA than in LAA rats suggested that these strains might differ in aspects of endocrine response. In experiment 3, plasma levels of ACTH and corticosterone were determined during early escape/avoidance acquisition in the shuttlebox. Plasma levels of ACTH after the shuttlebox testing were higher in HAA than in LAA rats. There was no difference between the two strains in plasma levels of corticosterone after testing, possibly due to a ceiling effect. These results suggest that the phenotypic differences in the acquisition of avoidance behavior of HAA and LAA rats may be related to different endocrine responses, rather than to locomotor activity.

Adrenal Glands↗

PubMed1999

Immunohistochemical study of steroidogenic enzymes in the ovary and placenta during pregnancy in the dog.

Using the immunohistochemical technique, we attempted to identify the source of secretion of steroid hormones between the mid- and late-terms of gestation in dogs by investigating steroid converting enzymes such as cholesterol side-chain cleavage enzyme (SCC), 3 beta-hydroxysteroid dehydrogenase/isomerase (3 beta-HSD), 17 alpha-hydroxylase/C17, 20lyase (c17), and aromatase in the ovaries and placenta. Aromatase positive cells were slightly confirmed in luteal cells in the mid-term of gestation (day 40), whereas, in the late-stage (day 50 and 60), the number of aromatase positive cells had increased. However, the oestrogen precursor (c-17 positive cells), could barely be identified in the marginal regions of the corpora lutea (CL) and completely disappeared in the late-stage of gestation. The androgen precursors, convertase SCC and 3 beta-HSD, were confirmed in all regions of the CL during the mid-stage of gestation (day 40), showing particularly strong cell reactions in the marginal region of the CL. Yet, these positive reactions of SCC and 3 beta-HSD in the marginal region of the CL disappeared in the late-stage of gestation. Moreover, it was discovered that the number of SCC and 3 beta-HSD positive cells had decreased in all regions of the CL. None of the enzymes were detected in the placenta. The above results indicated that the source of oestrogen secretion in pregnant dogs is considered to be the CL, and that, compared with the mid-stage of gestation, there was an increased number of oestrogen synthesizing cells within the CL in the late-stage. However, the biosynthetic site of oestrogen precursors from the luteal cells during the late-stage of gestation is still unknown.

Animals↗

PubMed1999

Time-resolved fluoroimmunoassay (TR-FIA) of porcine relaxin.

We developed and validated a new assay system for porcine relaxin that overcame the drawbacks of RIA by adapting time-resolved fluoroimmunoassay (TR-FIA), which was recently introduced as a non-RIA format. The assay system was a solid-phase TR-FIA based on competition for a polyclonal anti-porcine relaxin antibody between europium (Eu)-labeled porcine relaxin and test samples. Antibody-relaxin complexes were then bound to the second antibody coated on the solid phase, achieving rapid and complete separation of bound and free antigen. A standard curve was produced over the range of 1 pg/well to 1000 pg/well. Serum and corpus luteum extracts from pigs in late pregnancy exhibited inhibition curves parallel to that of the relaxin standard, whereas male pig serum caused no displacement of the labeled hormone. No cross-reactivity was seen with other hormones, such as insulin, LH, and FSH, indicating a high specificity of the assay. The sensitivity was 4 pg/well (80 pg/ml), which was high and equivalent to that of the porcine relaxin RIA. The intra-assay and inter-assay coefficients of variation were less than 3.8% and 6.7%, respectively. Recovery of porcine relaxin added to male pig serum sample averaged 103%. The advantages of this TR-FIA were that addition of tyrosine was not necessary for labeling, unlike the RIA, Eu-labeled relaxin was stable enough to allow long-term storage for more than one year, the assay was completed in only 5 h versus two to seven days for the RIA, and no special safety precautions were needed. To validate this TR-FIA, the serum relaxin concentrations during late pregnancy, parturition and early lactation were investigated in pigs. Serum relaxin levels determined by this assay were similar to those obtained previously by RIA. In conclusion, this TR-FIA could replace RIA as the method of choice for assay of relaxin.

Animals↗

PubMed1999

Secretion of ovarian inhibin and its physiologic roles in the regulation of follicle-stimulating hormone secretion during the estrous cycle of the female guinea pig.

To characterize inhibin secretion during the estrous cycle in guinea pigs, the concentrations of plasma inhibin, estradiol, progesterone, and FSH were determined. A significant positive correlation was observed between inhibin and estradiol throughout the estrous cycle. Plasma inhibin and estradiol started to increase a few days before ovulation (Day 0 = day of estimated ovulation), and decreased after ovulation. These two hormones remained low during the luteal phase. The immunoreactivity of inhibin alpha, betaA, and betaB subunits was colocalized in the granulosa cells of one or two healthy large follicles in the ovary before ovulation. There was no positive reaction of inhibin alpha and beta subunits in the corpora lutea or other follicles. Ovariectomy resulted in an abrupt decrease in plasma inhibin and a significant increase in plasma FSH. Injection of anti-inhibin serum into adult female guinea pigs induced an elevation in plasma FSH in a dose-dependent manner. This report presents the first description of sequential changes in plasma inhibin and estradiol during the estrous cycle of guinea pigs. Results suggest that inhibin is secreted mainly by granulosa cells of a few healthy large follicles in the ovary and that it plays an important role in the regulation of FSH secretion during the estrous cycle in guinea pigs.

Animals↗

PubMed1999

Plasma adrenocorticotropin, cortisol and catecholamines response to various exercises.

The responses of plasma adrenocorticotropin (ACTH), cortisol, noradrenaline and adrenaline in 5 Thoroughbred horses to an incremental exercise and 2 relative workload exercises, at 105 and 80% maximal oxygen consumption (VO2max), on a treadmill were examined. These hormone concentrations increased (P < 0.05) with each exercise and the maximal plasma concentrations of ACTH, cortisol were observed between 5 and 30 min after the end of the exercise, while maximal catecholamine concentrations occurred just at exhaustion time. The plasma ACTH, noradrenaline and adrenaline responses during exercise were more sensitive to the intensity of exercise than that of cortisol and showed a significant correlation with blood lactate concentrations (r = 0.605, P < 0.001 for ACTH; r = 0.718, P < 0.001 for noradrenaline; r = 0.738, P < 0.001 for adrenaline). The plasma cortisol response appeared to be connected with the duration of exercise (r = 0.71, P < 0.05). The recovery of these hormones was related to the exercise styles. These results suggest that the autonomic nervous system and the pituitary-adrenal axis of the horse are efficiently stimulated by various treadmill exercises, and these hormones may be used in the evaluation of exercise-induced stress.

Adrenocorticotropic Hormone↗

PubMed1999

Effects of caffeine and promazine hydrochloride on plasma catecholamines in thoroughbreds at rest and during treadmill exercise.

Our aim was to investigate plasma catecholamine responses to so-called 'doping' drugs and exercise in Thoroughbreds. Plasma adrenaline (Ad) and noradrenaline (NA) were determined after the administration of caffeine and promazine hydrochloride (PRZ) using a high performance liquid chromatographic method. Caffeine or PRZ was administered i.m. to Thoroughbreds and its effects on plasma catecholamines at rest and during exercise were compared with the saline control. The treadmill exercise was performed 1 h after administration. A dose of 5.0 mg/kg bwt caffeine was found to significantly increase both plasma Ad and NA levels but this was not the case for the 2.5 mg/kg bwt dose and their peak levels at 1.5 h were about 3 and 2.5 times as compared with the control values at 1.5 h (Ad: mean +/- s.e. 21.2 +/- 2.8 pg/ml, NA: 55.5 +/- 4.1 pg/ml), respectively. Both 1.0 and 1.5 mg/kg bwt PRZ doses reduced the plasma Ad to below the detection limit (10 pg/ml) and significantly reduced the plasma NA. The 2.5 mg/kg bwt caffeine dose significantly increased plasma Ad and NA during exercise and approximately doubled their maximal values as compared with the saline control (Ad: mean +/- s.e. 12.328 +/- 4.733 ng/ml, NA: 9.997 +/- 4.146 ng/ml). The 1.5 mg/kg bwt PRZ dose decreased the plasma Ad during exercise but the effect was not significant. On the other hand, PRZ significantly increased the plasma NA as compared with the saline control. In conclusion, the present study demonstrates that the plasma catecholamine responses to caffeine and PRZ were modified by exercise. It is probable that the modification may be related to exercise-induced activation of the sympathetico-adrenal axis.

Animals↗

PubMed1999

A selective increase in circulating inhibin and inhibin pro-alphaC at the time of ovulation in the mare.

The relationship between a selective increase in circulating immunoreactive (ir)-inhibin and the time of ovulation was investigated in mares. Concentrations of plasma ir-inhibin were measured every 4 h during the periovulatory period. Inhibin pro-alphaC, a precursor protein of the inhibin alpha-subunit, was also measured. The changes in ir-inhibin and inhibin pro-alphaC in circulation were parallel. Concentrations of both ir-inhibin and inhibin pro-alphaC in the plasma increased at the same time when ovulatory follicles ruptured, and the peak levels of circulating ir-inhibin and inhibin pro-alphaC were maintained for 4-8 h. There was no selective increase in plasma concentrations of estradiol-17beta during the process of ovulation. These results suggest that the selective increase in ir-inhibin and inhibin pro-alphaC was caused by the absorption of follicular fluid after the rupture of ovulatory follicles. These results also suggest that the measuring of plasma concentrations of ir-inhibin or inhibin pro-alphaC in mares might be a useful method for detecting the time of ovulation.

Animals↗

PubMed1999

Regulations of gonadotropin secretion by circulating inhibin, estradiol, and progesterone in cyclic hamsters.

The physiological importance of gonadal hormones in feedback control of gonadotropin secretion during the estrous cycle in golden hamsters was investigated with immunoneutralization methods. Anti-inhibin serum (inhibin-AS) treatment always induced a drastic increase in follicle-stimulating hormone (FSH) secretion and occasionally raised luteinizing hormone (LH) secretion. Anti-estradiol-17beta serum (estradiol-AS) treatment increased LH secretion typically. Although estradiol-AS elevated FSH secretion occasionally, the elevation was much less than that by inhibin-AS. Plasma FSH reached ovariectomized levels by a synergistic effect of both antisera. Elevated plasma LH with both antisera was much less pronounced than in ovariectomized animals. Plasma LH increased dramatically to the levels in the ovariectomized group when antibody against progesterone (progesterone-AB) was given together with inhibin-AS and estradiol-AS, although progesterone-monoclonal antibody alone did not alter plasma gonadotropin levels. These results indicate that in hamsters FSH secretion is mainly regulated by inhibin and LH secretion is regulated by estradiol-17beta and progesterone during the estrous cycle.

Animals↗

PubMed1999

Morphological features of the spermatic cord in the musk shrew (Suncus murinus) with special reference to extratesticular Leydig cells.

Morphological features of the testicular artery and vein in the spermatic cord of the musk shrew (Suncus murinus) were evaluated by light microscopy, transmission electron microscopy, corrosion cast technique combined with scanning electron microscopy and immunohistochemistry. The vascular architecture in the spermatic cord of the musk shrew was simple. The testicular artery in the musk shrew was straight and accompanied by 1 to 3 branches of testicular vein. The testicular vein was also straight and anastomosed with each other in some points along its length, but it did not form a delicate pampiniform plexus. In the middle and distal portions of the spermatic cord, the tunica adventitia of the artery and vein was joined together to form a single connective tissue septum. Clusters of cells were found in this connective tissue septum in the middle portion of the cord. These cells were located close to the arterial wall and nerve endings, but they did not appear inside of neurium. They showed several typical characteristics similar to Leydig cells, and they were positive for 3beta hydroxysteroid dehydrogenase (HSD) antibody. Ultrastructural and immunohistochemical studies also indicated that the cells in cluster found in the vascular wall of the musk shrew spermatic cord may be equivalent to Leydig cells in testes. These extratesticular Leydig cells had characteristics of the active steroid-producing cell and seemed to be another source of testosterone.

3-Hydroxysteroid Dehydrogenases↗