Biomedical subjects

K Taya

Publications and source records attributed to K Taya.

At least 127 records · Page 7Linked to original sources

PubMed1990

Involvement of the adrenal gland in the suckling-induced decrease in LH and FSH secretion and the concomitant increase in prolactin secretion in the rat.

The role of the adrenal gland in the regulation of gonadotrophin and prolactin secretion in the lactating rat was investigated. Changes in secretion of LH, FSH, prolactin, ACTH, beta-lipotrophin (beta-LPH), inhibin, corticosterone and progesterone after adrenalectomy were examined during the second half of lactation. Follicular maturation was determined by the ability of the follicles to ovulate in response to 10IU human chorionic gonadotrophin (hCG). Adrenalectomy on day 10 of lactation prevented an increase in plasma concentrations of LH and FSH in response to ovariectomy performed at the same time as adrenalectomy, and markedly stimulated secretion of ACTH, beta-LPH and prolactin. Adrenalectomy reduced the number of follicles capable of ovulating in response to hCG. Concentrations of inhibin and progesterone in the plasma significantly decreased after adrenalectomy, indicating that development of ovulatory follicles and luteal function had been suppressed. Abolishing the increase in plasma concentrations of LH and inducing a decrease in FSH in the plasma by adrenalectomy therefore prevented maturation of a new set of follicles usually seen during the second half of lactation in rats. The decrease in plasma concentrations of LH also inhibited the ability of the corpus luteum to secrete progesterone, although high concentrations of plasma prolactin were maintained in adrenalectomized lactating rats. These results indicate that the pituitary-adrenal system is capable of influencing the maintenance of a normal secretion of gonadotrophin and prolactin as well as the maintenance of ovarian function during lactation in the rat.

Adrenal Glands↗

PubMed1990

Dynamics of ovarian inhibin secretion during the oestrous cycle of the rat.

Plasma and ovarian concentrations of inhibin were determined at 3-h intervals throughout the 4-day oestrous cycle of rats by a radioimmunoassay (RIA) based on a bovine RIA. Plasma concentrations of LH, FSH, progesterone, testosterone, oestradiol-17 beta, and pituitary contents of FSH and LH were also determined during the cycle. Plasma levels of inhibin showed a marked increase on the morning of oestrus and the afternoon of metoestrus, and a further increase was noted on the morning of pro-oestrus. These increases in plasma levels of inhibin were probably due to the following three events in the ovary, follicular recruitment on the morning of oestrus, selection of follicles on the day of metoestrus, and final maturation of follicles for ovulation on the morning of pro-oestrus with an increase in oestradiol-17 beta secretion. A striking decrease in inhibin secretion occurred during the process of ovulation after the preovulatory gonadotrophin surge on the afternoon of pro-oestrus. Basal levels of plasma FSH gradually decreased from metoestrus to pro-oestrus as plasma levels of inhibin increased. There was a significant inverse relationship between plasma levels of FSH and inhibin throughout the oestrous cycle (r = -0.51). The present findings suggest that changes in the plasma levels of inhibin during the oestrous cycle provide a precise indicator for follicular recruitment, selection and ovulation, and that changes in concentrations of oestradiol-17 beta in the plasma are associated with follicular maturation.

Animals↗

PubMed1989

[Experimental studies on bile acid metabolism after extended hepatectomy, with special reference to mechanism of an early increase of bile acids in the serum].

The purpose of this study was to evaluate an early increase of bile acids in the serum after the extended hepatectomy, namely 84% hepatectomy in normal dogs and 70% hepatectomy in dimethylnitrosamine-induced cirrhotic dogs. Many dogs died due to hepatic insufficiency caused by severe intrahepatic cholestasis and functional disturbance of the remnant liver within 7 days after extended hepatectomy. Serum total bile acids increased with the peak at 12 hours after surgery, accompanied by an increase of taurine-conjugated bile acids, and each concentration of them was higher in the hepatic vein than in the portal vein. These results suggested that an early increase of bile acids in the serum after the extended hepatectomy resulted from the reflux to systemic circulation from the remnant liver due to disturbance of bile excretion into biliary tract and the decrease of hepatic functional mass with decrease of blood perfusion.

Animals↗

PubMed1989

Relationship between the production capacity of ovarian 13,14-dihydro-prostaglandin F2-alpha and the process of ovulation in immature female rats pretreated with gonadotropin.

The purpose of this work was to investigate the effects of gonadotropin on the production capacity of ovarian 13,14-dihydro-prostaglandin F2-alpha (13,14H2-PGF2 alpha) and whether or not this capacity had any relation to the process of ovulation in rat. To induce the first ovulation, immature rats were injected subcutaneously with PMSG (5 IU/rat) at 8:00 at 26 days of age and some of these rats were followed by an intraperitoneal injection of hCG (10 IU/rat) at 57 hrs after PMSG treatment. The 13,14H2-PGF2 alpha production capacity was unchanged as compared with vehicle control until 57 hrs after PMSG treatment. However, the capacity showed a striking increase at 60 hrs after PMSG treatment. A maximal increase of about 7 fold was observed at 9 hrs after hCG injection just before ovulation. The production capacity of the Graafian follicle (GF) and the part (WO-GF) of the whole ovary (WO) from which the GF is removed at 2:00 on day 29 and the capacity of early corpus luteum at 8:00 on day 29 was greater than that of GF and WO-GF at 0:00 on day 29. These results suggest that the 13,14H2-PGF2 alpha production capacity in rat ovary is regulated by gonadotropin and is closely associated with the process of ovulation.

Animals↗

PubMed1989

Effect of hCG on the 13,14-dihydro-prostaglandin F2-alpha forming capacity of the ovary after ovulation in PMSG-primed immature female rats.

We have examined the change in the ovarian 13,14-dihydro-prostaglandin F2 alpha (13,14H2-PGF2 alpha) forming capacity after the first ovulation induced by injection of pregnant mare serum gonadotropin (PMSG 5 IU, sc) at 26 days of age. After ovulation, the 13,14H2-PGF2 alpha forming capacity in the whole ovary (WO) and in non-luteal ovarian tissues (WO-CL) gradually decreased, whereas a rapid decrease of the synthesizing capacity was observed in corpus luteum (CL). The capacity in WO 4 days after ovulation (33 days of age) was markedly stimulated by human chorionic gonadotropin (hCG 10 IU, ip) administration, whereas CL at 33 days of age did not respond to the stimulatory effect of hCG. A single injection of hCG on day 7 after hypophysectomy resulted 12 hrs later in a significant increase in the forming capacity of 13,14H2-PGF2 alpha in WO-CL. These results indicate that the 13,14H2-PGF2 alpha forming capacity in CL rapidly decreases after the first ovulation and the WO-CL, but not CL, retain the ability to form 13,14H2-PGF2 alpha in response to exogenous gonadotropin for a long time.

Animals↗

PubMed1989

Initiation of follicular maturation during mid-pregnancy by the administration of LH in the rat.

Pregnant rats were injected twice daily for 1-3 days (Days 13-16 of pregnancy) with various doses of ovine LH. Follicular maturation was determined by the ability of the follicles to ovulate in response to 10 i.u. hCG as well as by endogenous production of oestradiol-17 beta and inhibin. In control animals, no ovulation was induced by hCG given on Day 16 of pregnancy. An injection of hCG on Day 16 of pregnancy, however, induced ovulation in LH-treated animals (6.25-50.0 micrograms LH per injection, s.c. at 12-h intervals from Days 13 to 16). Concentrations of oestradiol-17 beta and inhibin activity in ovarian venous plasma increased after the administration of LH, indicating that development of ovulatory follicles had been induced. Abolishing the decline in plasma LH values therefore induced maturation of a new set of follicles or prevented the atresia of large antral follicles usually seen at this time of pregnancy. Plasma and pituitary concentrations of FSH decreased in LH-treated animals compared with those in control animals. Concentrations of progesterone, testosterone and oestradiol-17 beta in the peripheral plasma were not significantly different between the two groups. These results suggest that the increase in inhibin secretion from the ovary containing maturing follicles after LH treatment may suppress the secretion of FSH from the pituitary gland. These findings indicate that (1) the development of ovulatory follicles can be induced by the administration of exogenous LH during mid-pregnancy in the rat and (2) basal concentrations of FSH are enough to initiate follicular maturation even in the presence of active corpora lutea of pregnancy, when appropriate amounts of plasma LH are present.

Animals↗

PubMed1989

Inhibitory effects of corticotrophin-releasing factor and beta-endorphin on LH and FSH secretion in the lactating rat.

The roles of corticotrophin-releasing factor (CRF) and beta-endorphin in the suppression of LH and FSH secretion during lactation were investigated using ovariectomized lactating rats separated from their litters overnight. Within 1 h of returning the pups to their mothers a marked fall in plasma LH concentration and a large increase in plasma prolactin were noted. However, resuckling caused no significant change in plasma concentration of FSH until 12 h after the return of the litter but a significant decline occurred thereafter. Twenty-four hours after removal of the litter, a single i.v. injection of 200 microliters anti-LHRH serum caused similar changes in plasma concentrations of LH and FSH observed in nursing rats during suckling. These results suggest that the suckling stimulus itself is responsible for the suppression of LH as well as FSH, via inhibition of the secretion of LHRH. Twenty-four hours after removal of the litter, a single intracerebroventricular (i.c.v.) injection of either 10 micrograms CRF or beta-endorphin resulted in a rapid decrease in plasma LH. Only beta-endorphin caused a marked increase in plasma levels of prolactin within 1 h whereas FSH was less affected by either hormone. Repeated i.c.v. administration of 10 micrograms CRF or beta-endorphin at 6-h intervals caused a prolonged inhibition of LH as well as FSH secretion during 48 h, with beta-endorphin being less effective than CRF. These results demonstrate that the suckling stimulus alone suppressed the secretion of both LH and FSH, and suggest that this effect may be mediated by the inhibition of LHRH secretion from the hypothalamus.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Peripheral blood levels of immunoreactive inhibin during pseudopregnancy, pregnancy and lactation in the rat.

Concentrations of inhibin in peripheral blood were determined by radioimmunoassay in pseudopregnant, pregnant and lactating rats and correlated with the status of follicular development, luteal function in the ovaries and placental function. In pseudopregnant rats, plasma concentrations of inhibin remained relatively high from days 2 to 12 of pseudopregnancy and no significant changes occurred throughout pseudopregnancy. In pregnant rats, a marked decline in plasma concentrations of inhibin occurred between days 6 and 14 followed by an abrupt increase on days 20 and 21. In lactating rats, plasma concentrations of inhibin were consistently lower in dams nursing eight pups than in dams nursing two pups. Plasma concentrations of inhibin remained low during the early stages of lactation followed by a significant increase during the late stages in dams nursing eight pups. These changes in inhibin during the period of lactation correlated with those of plasma concentrations of LH, but not with those of oestradiol-17 beta, testosterone and progesterone. Throughout pseudopregnancy, pregnancy and lactation, on the other hand, plasma concentrations of FSH were within the range of dioestrous levels. These findings indicate that concentrations of inhibin in peripheral plasma vary with the number of healthy antral follicles and no positive correlation was observed with luteal function during the luteal phase in rats. The results also suggest that inhibin is a more direct index of follicular development than oestradiol-17 beta in rats.

Animals↗

PubMed1989

Radioimmunoassay of inhibin in various mammals.

A sensitive radioimmunoassay (RIA) for the determination of inhibin in peripheral plasma and tissue homogenates of different species has been developed using antisera to partially purified bovine follicular fluid (bFF) inhibin and 125I-labelled bFF 32 kDa inhibin. Antisera were produced by immunization of rabbits with partially purified bFF inhibin prepared by immunoaffinity chromatography. Increasing doses of a high titre antiserum could neutralize the suppressing effect of bFF, porcine follicular fluid and rat ovarian homogenate on FSH secretion from rat anterior pituitary cells in culture. Sensitivity of the assay was 3.1 ng International Research Standard of porcine inhibin per tube. Parallel inhibition curves were obtained for inhibin preparations from female and male animals of ten species, i.e. cattle, goats, sheep, cats, dogs, monkeys, pigs, horses, rats and man. Inhibin subunits and related proteins cross-reacted minimally with the antiserum used in the study. Plasma concentrations of inhibin in adult male and female rats were measured by the RIA before and at various times after gonadectomy. Inhibin levels in peripheral plasma before gonadectomy were significantly higher in adult female than in adult male rats. Inhibin levels decreased abruptly after gonadectomy in both sexes and they correlated negatively with plasma concentrations of FSH. This inhibin RIA will facilitate studies of the physiology of inhibin in various species of animals.

Animals↗

PubMed1989

[Validity of estimating left ventricular relaxation and filling dynamics by Doppler trans-mitral flow].

To evaluate the validity of estimating left ventricular (LV) diastolic function using the Doppler transmitral flow profile, the relationship of transmitral flow to LV relaxation and LV filling dynamics was observed. A total of 54 subjects, including patients with ischemic heart disease, idiopathic cardiomyopathy, and normal persons were examined. LV filling dynamics were assessed in 20 of them who had no regional wall motion abnormality or irregular LV geometry. Peak velocity of rapid filling (R) and acceleration of rapid filling (AR) at the mitral annular level were measured as indices of transmitral flow during the rapid filling period. LV relaxation was evaluated according to the time constant of LV isovolumic pressure decline (T) using the method of Weiss et al. The correlation coefficient between R and T was -0.27 and that between AR and T was -0.16, indicating lack of correlations. The v-wave of pulmonary wedge pressure (PWPv) was measured as an index for left atrial driving pressure during the rapid LV filling period. Multiple regression analyses of R or AR as dependent variables and T and PWPv as independent variables revealed significant correlations (r = 0.66 and r = 0.59). The peak transit rate (PTR = R/TVI) and atrial transit fraction (ATF = TVIa/TVI) were determined from the time integral of the transmitral flow velocity (TVI = time velocity integral during diastole, TVIa = time velocity integral during the atrial contraction phase). Also, the peak filling rate (PFR) during the rapid filling and atrial filling fraction (AFF) were determined by left ventriculography.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1988

A new male hypogonadism mutant rat (hgn/hgn): concentrations of testosterone (T), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) in the serum and the responsiveness of accessory sex organs to exogenous T, FSH, human chorionic gonadotropin, and luteinizing hormone-releasing hormone.

To determine the etiology of male hypogonadism in a newly found mutant rat (hgn/hgn, with a single autosomal recessive trait), concentrations of testosterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) were measured, and the responsiveness of the urogenital organs, hypothalamus, and pituitary gland to testosterone (1 mg/kg s.c. for 7 days), FSH (0.3 AU/kg s.c. for 7 days), human chorionic gonadotropin (hCG) (40 IU/kg s.c. for 7 days), and luteinizing hormone-releasing hormone (LHRH) (0.5 or 5.0 micrograms/kg s.c. for 7 days) were tested. Treatment with testosterone only increased the weights of all of the accessory sex organs, whereas treatment with FSH, hCG, or LHRH did not. Levels of serum FSH and LH were extremely higher and testosterone was lower in hgn/hgn males than in normal males. Serum FSH and LH decreased to levels found in intact animals after treatment with testosterone, suggesting that hypothalamic responsiveness to exogenous testosterone is present in the hgn/hgn males. Thus, the status of the hgn/hgn males was indicated to be due to primary Leydig cell dysfunction.

Animals↗

PubMed1988

Age-related changes in the secretory pattern of FSH and LH in response to LH-RH in prepubertal female rats.

Developmental changes in the pituitary responsiveness and the secretory pattern of FSH and LH in response to a single injection of LH-RH (100 ng/rat, s.c.) as estimated by increases in plasma concentrations of FSH and LH 10, 30 and 60 min after the injection were studied in female rats at 5, 10, 15, 20, 25 and 30 days of age. The pituitary responsiveness to LH-RH for both FSH and LH release increased from 5 to 15 days of age, reached a maximum on 15 days of age and declined thereafter, whereas a marked increase in the amount of these hormones in the pituitary occurred between 15 and 20 days of age. An apparent change in the secretory pattern of both FSH and LH was observed from 20 days of age onward. In groups up to 15 days of age, plasma concentrations of FSH and LH remained elevated 60 min after the injection of LH-RH, though the plasma concentration of these hormones returned to preinjection concentrations in groups at 20 days of age or later. These results indicate that the age-related changes in the secretory pattern of LH and FSH in response to LH-RH as well as changes in the pituitary responsiveness were apparent during the prepubertal period.

Age Factors↗

PubMed1988

A new male pseudohermaphrodite rat mutant with androgen deficiency.

A male pseudohermaphrodite rat mutant showing a blind-ending vagina, small undescended testes, rudimentary male sex accessory organs and XY karyotype was investigated. Genetic analysis revealed an autosomal single recessive transmission of this defect and indicated that the gene action is restricted to males. Microscopic examination showed an absence of typical Leydig cells in testes of the mutant. Plasma concentrations of testosterone were extremely low and the values were comparable to those of castrated male rats and did not change after castration and/or after administration of hCG. Plasma concentrations of LH and FSH were remarkably high and the values were comparable to those of long-term castrated normal male rats which declined to basal levels after administration of exogenous testosterone. Weights of thymus and adrenal glands decreased and weights of preputial glands, kidneys and male accessory sex organs increased in response to exogenous testosterone. These results indicate that the primary defect in the mutant is an androgen deficiency probably due to a Leydig cell agenesis in the testes.

Androgens↗

PubMed1988

Suprainguinal ectopic scrota of TS inbred rats.

A new rat line (TS inbred rats) showing uni- or bilateral ectopic scrota in about 70% of the males was established. Ectopic scrota were elongated pouches of the thin muscle layer under the suprainguinal body skin, in which hypoplastic testes and epididymides were seen. Genetic analysis revealed that the ectopic scrotum was controlled by multiple genes. Groups of 5 normal, uni- and bilaterally affected rats were killed at 25 weeks of age. Histologically, ectopic testes of uni- and bilaterally affected rats showed arrest of spermatogenesis at the primary spermatocyte stage. Contralateral testes of unilaterally affected rats were normally descended and showed normal spermatogenesis. No abnormality was seen in the urinary system. Plasma concentrations of FSH were significantly elevated in bilaterally affected rats but plasma concentrations of testosterone and LH were unchanged in uni- and bilaterally affected rats. Pituitary contents of LH and FSH were significantly elevated in bilaterally affected rats. The endocrinological status of TS inbred rats was therefore similar to that of experimentally induced cryptorchid rats.

Animals↗

PubMed1988

Induced development of ovulatory follicles during the early stages of lactation by the administration of LH in the rat.

To determine whether failure of follicular maturation during the early stages of lactation in rats is due to inadequate LH stimulation, lactating rats nursing eight pups were injected twice daily for 1-3 days (days 2-5 of lactation) with various doses of ovine LH. Follicular maturation was determined by the ability of the follicles to ovulate in response to 10 IU human chorionic gonadotrophin (hCG), endogenous oestradiol-17 beta and inhibin production. Ovulation was not induced in control animals in response to 10 IU hCG given between days 2 and 5 of lactation. On the other hand, an injection of 10 IU hCG could induce ovulation in LH-treated animals, in which 25 and 50 micrograms LH per injection were given s.c. from days 2 to 5 of lactation. Concentrations of oestradiol-17 beta and inhibin activity in ovarian venous plasma increased progressively after the administration of LH, indicating that induced development of ovulatory follicles had occurred. Plasma concentrations of FSH declined in LH-treated animals compared with those in control animals. The decrease in plasma concentrations of FSH was not observed when lactating rats were ovariectomized before the first injection of LH, indicating that ovarian products, probably inhibin, from developing follicles may suppress the secretion of FSH from the pituitary gland. In both LH-treated and control animals, concentrations of prolactin and progesterone remained increased during the period of LH administration. The present results, therefore, suggest that the plasma levels of LH are an important determinant of follicular maturation during lactation in rats.

Animals↗

PubMed1988

Selective release of FSH in lactating rats during the period of follicular atresia induced by the administration of antiserum to LH-releasing hormone.

Passive immunoneutralization of LHRH by injecting a caprine antiserum to LHRH (LHRH-AS) in lactating rats nursing two pups on day 5 of lactation resulted in an immediate decline in concentrations of LH in the plasma during the 24-h study period, followed by a gradual increase to control levels 30 h later. Concentrations of oestradiol-17 beta and inhibin activity in ovarian venous plasma also decreased abruptly in LHRH-AS treated animals and recovered to control levels 36 h later. These changes were correlated with changes in concentrations of LH in the plasma. On the other hand, plasma concentrations of FSH increased abruptly in the LHRH-AS treated animals within 3 h after injection, but the concentrations declined gradually to control levels 48 h later. The ability of follicles to ovulate in response to human chorionic gonadotrophin (hCG) began to decrease within 6 h after treatment with LHRH-AS, and further decreased until 18 h after injection of LHRH-AS, when hCG induced ovulation (with two oocytes) in only one of five animals. A gradual increase in ovulation rate to control levels was noted by 36 h after injection of LHRH-AS. These results indicate that Graafian follicles present at the time of LHRH-AS injection had become atretic and that a new set of follicles had then begun to mature. Selective release of FSH could not be induced by injection of LHRH-AS in ovariectomized animals. Treatment with inhibin (porcine follicular fluid) suppressed the selective release of FSH, whereas treatment with oestradiol-17 beta had no inhibitory effect on the selective release of FSH. These findings indicate (1) that tonic secretion of LH is an important factor in normal follicular maturation and maintenance in lactating rats, (2) that selective release of FSH after injection of LHRH-AS is attributed to the removal of a negative influence of inhibin from antral follicles during the period of follicular atresia and (3) that a selective surge of FSH is responsible for initiation of new follicular maturation.

Animals↗

PubMed1988

Secretion of inhibin by chicken granulosa cells in vitro.

Inhibin activity was investigated using chicken granulosa cell culture medium. Chicken granulosa cells were collected individually from the largest follicle (F1 follicle) and the third largest follicle (F3 follicle) of the ovary, dispersed using enzyme and incubated in a suspension method or cultured in a monolayer method in vitro. Culture medium was assessed for follicle-stimulating hormone (FSH) inhibiting (inhibin) activity using the rat anterior pituitary cell culture method. The FSH secretion from cultured rat pituitary cells was suppressed by experimental increasing of the amounts of granulosa cell culture medium in a dose-dependent manner, though luteinizing hormone (LH) secretion was not affected in a dose-dependent manner. Inhibin activity of the granulosa cell culture medium derived from F1 follicles was higher than that from F3 follicles. These results suggest that chicken granulosa cells secrete inhibin-like substance(s) and that the F1 follicle may secrete a larger amount of inhibin than the F3 follicle.

Animals↗

PubMed1987

Changes in the secretion of inhibin and steroid hormones during induced follicular atresia after hypophysectomy in the rat.

Sequential changes in the function of antral follicles during the period of follicular atresia were investigated after hypophysectomy (Hypox) at 1100 hr on proestrus. Within 6 hours after Hypox, concentrations of progesterone (P), testosterone (T) and estradiol-17 beta (E) decreased abruptly in ovarian venous plasma (OVP) and follicles showed a reduced ability to ovulate. Six hours after Hypox, ovulation was still induced by human chorionic gonadotropin (hCG) in all animals but with significantly fewer number of oocytes compared to the group given hCG at 1100 hr on the day of proestrus. Nine hours after Hypox, several granulosa cells of all large follicles (greater than 400 microns in diameter) exhibited morphological signs of atresia. Twelve hours after Hypox, all large and medium sized (200-400 microns in diameter) follicles showed advanced stages of atresia and almost all follicles failed to ovulate in response to hCG. Inhibin activity in OVP declined more slowly compared to the profiles of steroid hormones and 53% of the initial inhibin activity was still maintained at 18 hours after the operation. Inhibin activity further decreased to 7% of the initial level at 24 hours and was undetectable by 48 hours after Hypox. These results suggest that fully developed Graafian follicles gradually lose their ability to secrete inhibin in contrast to the rapid decrease in secretion of steroid hormone during the process of atresia.

Animals↗