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Biomedical subjects

K Taya

Publications and source records attributed to K Taya.

At least 163 records · Page 9Linked to original sources
PubMed1981

Postovulatory steroidogenesis after PMS-induced ovulation in immature female rats.

Thirty-day-old rats given a single subcutaneous injection of 5 IU pregnant mare serum gonadotropin (PMS) at 0900 h ovulated on the morning of day 33 (= estrus). However, the second ovulation did not occur until 9.4 days later. To determine the mechanism responsible for the delay in the second ovulation, in vivo and in vitro determinations of steroid and peptide hormones were compared between PMS-primed immature rats and adult cyclic rats. In PMS-primed rats, the corpora lutea (CL) produced progesterone for 2 days longer (until day 36) than the CL of the adult rat. Serum levels of 20 alpha-dihydroprogesterone, testosterone, and estradiol in PMS-primed rats were significantly lower than the corresponding values in adult rats. Serum LH was consistently lower in the PMS-primed rats. An increase in serum FSH occurred on days 36-37, which may be responsible for maturation of the follicles destined to ovulate at the second ovulation. On day 37, the nonluteal ovary of the PMS-primed rats also began to produce in vitro appreciable amounts of testosterone and estradiol. These findings suggest that the greater levels of prolactin and/or low levels of luteinizing hormone during estrus in PMS-primed rats may be responsible for the prolonged secretion of progesterone by the CL. This in turn inhibits follicular maturation, indirectly by lowering serum LH, which is reflected in reduced ability of the follicles in vitro to produce testosterone and estradiol until the CL regress.

20-alpha-Dihydroprogesterone↗
PubMed1981

Acute effects of exogenous progesterone on follicular steroidogenesis in the cyclic rat.

The effects of exogenous progesterone (P) on follicular steroidogenesis and serum gonadotropins in the cyclic rat were determined using in vivo and in vitro approaches. A single sc injection of 800 micrograms progesterone at 0900 h on diestrus II (day 0) consistently postponed ovulation by 24 h in 4-day cyclic rats, with no change in the ovulation rate. The preovulatory surges in serum LH and FSH were delayed by 1 day and occurred on day 2 in the P-treated animals. After the injection of 800 micrograms P at 0900 h on diestrus II, peak serum levels of P were reached 3 h later and thereafter decreased to basal levels by 1500 h on day 1. Within 1 h after injecting P, serum LH and FSH decreased to values below control levels; serum LH did not recover during the next 48 h, whereas serum FSH returned to basal levels within 6 h. An abrupt fall in serum 17 beta-estradiol occurred within 1 h after the administration of P. This drastic decline in serum estradiol was paralleled by temporally related decreases in serum LH and FSH but not by changes in serum testosterone. By 0900 h on day 1 (24 h after P injection), serum and estradiol returned to values within the range observed on diestrus II, then gradually increased to proestrous values by day 2. Within 3 h after the administration of P, the initial content and the in vitro production rate of P, testosterone, and 17 beta-estradiol by antral follicles decreased in the P-treated animals compared to that in follicles of control animals, whereas the follicular content the production rate of 20 alpha-dihydroprogesterone were unaffected. Thus, in the cyclic rat, the inhibitory effects of exogenous P on follicular steroidogenesis are mediated in this dose range through the hypothalamic-pituitary axis, especially via lowering serum LH.

20-alpha-Dihydroprogesterone↗
PubMed1981

Absence of prolactin surge during the period of premature ovulation induced by human chorionic gonadotropin or luteinizing hormone releasing hormone in diestrous rats.

The concentration of plasma prolactin during the period of premature ovulation induced by human chorionic gonadotropin (HCG) or luteinizing hormone releasing hormone (LH-RH) in diestrous rats was determined at 3 hr intervals from 1700 hr on the day of diestrus (day 0) to 2300 hr on the day of proestrus (day 1). Premature ovulation was induced by either a single injection of 10 IU HCG at 1700 hr on day 0 or three injections of 1 microgram LH-RH at 1 hr intervals from 1700 to 1900 hr on day 0. In saline-treated controls, the concentration of prolactin in plasma was low during diestrus but increased on the afternoon of proestrus with a peak value at 1700 hr, followed by an abrupt decline at 2300 hr on the same day. However, there was no significant rise in the plasma prolactin level throughout the period of observation in HCG-treated rats. In the LH-RH treated group, the prolactin level in plasma did not change until 1100 hr on day 1, but significantly increased at 1400 hr on the same day then declined by 2300 hr, though no significant difference was observed at any time when compared to HCG-treated rats. These results indicate that no prolactin surge occurred during the period of premature ovulation.

Animals↗
PubMed1981

Pituitary function during pseudopregnancy and lactation in the rat.

Plasma concentrations of FSH on Days 1, 2, 3, 8 and 9 of lactation (day of parturition = Day 0) were significantly higher than on the corresponding day of pseudopregnancy (day of vaginal plug = Day 1). Pituitary FSH content on Days 4-12 of lactation was also significantly higher than in pseudopregnant rats. However, pituitary LH content on Days 2-12 of lactation was significantly lower than in pseudopregnancy, whereas plasma concentrations of LH were almost similar. Two consecutive injections of LH-RH (100 ng/rat, i.v.), 60 min apart, resulted in a significant release of FSH in lactating rats (Days 3 and 15) in response to the second injection of LH-RH, but there was no increase in pseudopregnant rats on Day 3. The first and second injections of LH-RH produced significantly less release of LH on Days 3 and 15 of lactation than on Day 3 of pseudopregnancy. These results indicate that FSH secretion is not suppressed by suckling whereas the suckling stimulus is a potent inhibitor of LH.

Animals↗
PubMed1980

Mechanism of the selective surge of follicle-stimulating hormone in dioestrous rats during the induction of ovulation by human chorionic gonadotrophin.

A selective surge of FSH with a small concomitant rise in LH occurred invariably in rats when ovulation was induced by injecting human chorionic gonadtrophin (HCG) at various reproductive stages such as day 15 of lactation and in 29-day-old immature rats as well as in dioestrous animals. No FSH surge occurred on day 3 of lactation or in 26-day-old immature rats in which ovulation could not be induced by HCG. The FSH surge occurred 6-18 h after HCG treatment regardless of the time of day of injection of HCG. Ovulation began by 12 h and was completed by 18 h after injection of HCG. Pituitary responsiveness to luteinizing hormone releasing hormone (LH-RH) with respect to FSH release strikingly incresed at 01.00 h on day 1 after HCG injection at 17.00 h of dioestrus (day 0) to levels similar to those of the group at 01.00 h of oestrus, when the greatest response was noted during the normal cycle. With regard to LH release pituitary responsiveness to LH-RH at 01.00 h on day 1 markedly increased but the response was only about half of the response at 01.00 h of oestrus and one third of the response at 17.00 h of pro-oestrus when the greatest response was noted during the normal oestrous cycle. These results indicate that during ovulation the pituitary gland of the rat is highly responsive to LH-RH with respect to the release of FSH, for which secretory changes in the ovary after an ovulating dose of HCG may be responsible.

Animals↗
PubMed1980

Initiation of follicular maturation and ovulation after removal of the litter from the lactating rat.

In order to elucidate the mechanism of the resumption of follicular activity and ovulation in rats, levels of FSH, LH and prolactin in plasma and pituitary gland and ovarian follicular development were quantified after removal of the litter on day 3 of lactation (day of parturition = day 0 of lactation). Such removal resulted in ovulation of 13 oocytes 4 days later, a number comparable with that found in normal cyclic rats. Plasma levels of prolactin were high during lactation but markedly decreased after removal of the litter. Although plasma concentrations of FSH and LH did not change during days 3-7 of lactation, there was an FSH surge between 24 and 30 h after removal of the litter. Plasma concentrations of LH also increased slightly but significantly by 24 h after removal of the litter and this value persisted during the following 2 days. Surges of FSH, LH and prolactin occurred at 17.00 h 3 days after pups were removed. Removal of the litter did not increase pituitary contents of FSH, LH and prolactin and a marked reduction in pituitary levels of FSH and LH, but not of prolactin, occurred at 17.00 h 3 days after removal of the litter. A quantitative study of follicular development indicated that follicles larger than 401 micrometers in diameter were absent during days 3-7 of lactation. However, the number and size of antral follicles increased by 30 h after removal of the litter, probably due to the increases in plasma levels of FSH and LH, and follicles larger than 601 micrometers in diameter appeared 3 days after the young were removed. Although ovulation could not be induced by human chorionic gonadotrophin from days 3 to 5 of lactation, its administration 30 h after removal of the litter produced ovulation in all rats by the following morning. These results indicated that a moderate increase in FSH, although below the amounts released at the preovulatory surge, together with basal levels of LH which were within the range observed on the day of dioestrus during the normal cycle were responsible for the initiation of follicular maturation after removal of the litter.

Animals↗
PubMed1976

Purification and some properties of NADP+ -specific isocitrate dehydrogenase from an extreme thermophile, Thermus flavus AT-62.

Thermostable NADP+ -specific isocitrate dehydrogenase (EC 1.1.1.42) was purified from crude extract of an extremely thermophilic bacterium Thermus flavus AT-62 through DEAE-cellulose column, acetone fractionation, DEAE-Sephadex A-50 column and isoelectric focussing. The enzyme was purified about 500-folds in its specific activity and purity was found to be about 96%. The enzyme was not inactivated after 60 min at 70 degrees C, but 20 and 80% of the activity were lost after 60 min at 80 degrees and 90 degrees C, respectively. Oxalacetate plus glyoxylate (each 1 nM) demonstrated 75% inhibition of the activity in concerted manner. The degree of the inhibition and the affinity of the enzyme for isocitrate and NADP+ decreased with the rise of temperature, especially above 60 degrees C. The activation energy below and above 60 degrees C were 14,500 and 8,000 cal per mole respectively. In CD spectra negative bands at 210 and 220nm were observed and alpha-helix content was calculated to be about 26%. In the course of heating up to 60 degrees practically no change in CD bands are observed, but above 60 degrees the depth of CD bands decreased gradually and remarkably above 80 degrees C. The effect of temperature on kinetic parameters and secondary structures of the enzyme was discussed in relation to the temperature adaptation of the organism.

Circular Dichroism↗
PubMed1976

Studies on peroxisomes. VI. Relationship between the peroxisomal core and urate oxidase.

The peroxisomal core from the liver of rats was purified 450-fold as a marker of urate oxidase [EC 1.7.3.3.] activity. This preparation has a high specific activity of urate oxidase but not of other peroxisomal enzymes: D-amino acid oxidase [EC 1.4.3.3.], L-alpha-hydroxy acid oxidase [EC 1.1.3.15], or catalase [EC 1.11.1.6]. No activity of marker enzymes for other subcellular particles; cytochrome c oxidase [EC1.9.3.1] (mitochondria), acid phosphatase [EC 3.1.3.2] (lysosomes), or glucose-6-phosphatase [EC 3.1.3.9] (microsomes), was detected in this preparation. The core obtained showed a single protein band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis and the position of the band was found to correspond to a molecular weight 35,000. When the peroxisomal core was subjected to treatment at various pH's with 0.1 M carbonate buffer, urate oxidase was almost completely solubulized at pH 11.0, although approximately 35% of the core protein still remained in the pellet After solubilization of the core at pH 11.0, the specific activity of urate oxidase in the supernatant increased about 1.6 times; the density of the insoluble protein remaining in the pellet was identical with the that of the original core on sucrose density gradient centrifugation.

Animals↗
PubMed1975

Direct action of prostaglandins on the rat pituitary.

The purpose of this study is to ascertain whether or not prostaglandins (PGs) act directly on the pituitary. In the first experiment, the plasma LH levels were sharply decreased 24 hr after the production of hypothalamic lesions in ovariectomized mature rats. Ten min after the iv injection of PGE1, PGE2 or PGF2alpha, the plasma LH levels increased significantly as compared with the vehicle control. Also, the plasma LH levels were elevated following the iv injection of LH-releasing hormone (LH-RH). In the second experiment, after pretreatment of ovariectomized mature rats with estrogen and progesterone, animals received a SC injection of indomethacin, 2 mg in 0.2 ml of gelatin for 3 days. Twenty-four hr after the last injection, 100 ng of LH-RH were injected into the jugular vein. The response of the pituitary to the LH-RH was significantly lower in the indomethacin-treated rats than in the vehicle control rats. In the 3rd experiment, we tested several PGs for stimulatory effects on LH secretion by injecting them into the anterior pituitary. Following direct microinjection of PGE1 or PGE2 (50 or 100 mug/mul) into the rat pituitary, plasma LH was increased at 10 and 45 min after the injection. However, PGF2alpha at both 50 and 100 mug/5mul, failed to increase the plasma LH levels. In the last experiment, the effect of PGE1, PGE2 or PGF2alpha on in vitro rat anterior pituitary LH release was studied. Addition of PGE1, (2 or 20 mug), PGE2 (0.002 or 0.02 mug) or PGF2alpha (200 mug) to the incubation medium produced a significant increase in LH release into the incubation medium. These observations indicate that sufficient dosages of PGs can also stimulate LH secretion by acting directly on the pituitary.

Animals↗
PubMed1975

Effect of prostaglandin F2alpha upon ovulation and LH, FSH and prolactin secretion in chlorpromazine blocked rats.

The ovulation-inducing and LH, FSH and protein releasing activities of prostaglandin F2alpha (PG F2alpha) were investigated, using the female rats which had ovulation blocked by chlorpromazine (CPZ). Serum LH, FSH and prolactin concentrations were measured with NIAMD-rat-radioimmunoassay kits. The number of ova present in the fallopian tubes was investigated microscopically. Subcutaneous injection of 0.4-1.6 mg of PG F2alpha at 3:00 p.m. to CPZ-blocked proestrous rats induced ovulation in 80% of the animals during presumptive estrus. However, the percentage of ovulating rats was reduced in 40-60% of the animals when the same doses of PG F2alpha were injected intravenously. All control animals receiving the vehicle alone did not ovulate. The number of ova was not related to the dose of PG F2alpha, but the percentage of ovulating rats was. The serum LH peak was observed 10 min after the intravenous injection and 60-180 min after the subcutaneous injection of PG F2alpha. The peak in serum FSH and prolactin occurred simultaneously 180 min after both subcutaneous and intravenous injection of PG F2alpha. It is concluded from these data that PG F2alpha at dose levels used, may directly affect the hypothalamo-pituitary axis and consequently induce ovulation. These results further support the conception that the prostaglandins (PGs) have a central effect stimulating LH, FSH and prolactin release from the anterior pituitary.

Animals↗