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  • 1
    Online Resource
    Online Resource
    SEX STEROIDS STIMULATE THE ACTIVITY OF HYPOTHALAMIC ARYLAMIDASES IN THE RAT
    Oxford University Press (OUP) ; 1974
    In:  Acta Endocrinologica Vol. 76, No. 1 ( 1974-05), p. 1-14
    Details
    In: Acta Endocrinologica, Oxford University Press (OUP), Vol. 76, No. 1 ( 1974-05), p. 1-14
    Abstract: The effect of steroid treatment on the activity of hypothalamic arylamidases in male and female rats was investigated. A new and improved method for the assay of arylamidase activity utilizing L-α-amino acid-p-nitroanilides as substrates is presented. The influence of varying experimental conditions on the activity of hypothalamic arylamidases hydrolyzing the p-nitroanilides of cystine, glutamic acid, alanine, tyrosine, leucine, and phenylalanine, such as changes of substrate and enzyme concentration, temperature, incubation time, and pH, were tested. There was a sex-dependent response in the activity of hypothalamic arylamidases to treatment of the rats with sex steroids. In female rats, the injection of 7 μg of ethinyloestradiol was followed 16 hours later by a significant rise of L-cystine and L-glutamic acid arylamidase activity. In male rats, the injection of testosterone and of ethinyloestradiol respectively brought about a general stimulation of all enzyme activities. This indicates that this enzyme system of the male and female rat hypothalamus responds to steroid treatment of the animals with a sex-specific pattern.
    Type of Medium: Online Resource
    ISSN: 0804-4643 , 1479-683X
    URL: Article
    DOI: 10.1530/acta.0.0760001
    RVK:
    WA 15000
    Language: Unknown
    Publisher: Oxford University Press (OUP)
    Publication Date: 1974
    detail.hit.zdb_id: 1485160-X
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  • 2
    Online Resource
    Online Resource
    THE REGULATORY FUNCTION OF A PITUITARY LH-RH-DEGRADING ENZYME SYSTEM IN THE FEEDBACK CONTROL OF GONADOTROPHINS
    Oxford University Press (OUP) ; 1977
    In:  Acta Endocrinologica Vol. 86, No. 1 ( 1977-09), p. 60-70
    Details
    In: Acta Endocrinologica, Oxford University Press (OUP), Vol. 86, No. 1 ( 1977-09), p. 60-70
    Abstract: It had previously been shown that a luteinizing hormone-releasing hormone (LH-RH)-inactivating enzyme in the rat hypothalamus, L-cystine arylamidase, is in all probability involved in the short-loop feedback mechanism of LH. Since this enzyme system was also shown to be present in the pituitary, the effect of the iv injection of several sex hormones upon its activity was investigated. The basal arylamidase activity was found to be considerably higher in the neurohypophysis as compared to the adenohypophysis. The injection of 10 μg LH brought about a significant rise in arylamidase activity (+60 %) only in the latter. There was a dose-dependent increase in the pituitary enzyme activity 2 h after the iv administration of LH, and 16 h after the injection of oestradiol and progesterone into dioestrous rats. Contrary to previous findings obtained with hypothalamic homogenates, the effect of LH upon the enzyme in the pituitary proved to be not dependent on the presence of sex steroids, as the iv application of 10 μg LH into ovariectomized rats resulted in an increase of pituitary L-cystine arylamidase by about 30 %. The injection of testosterone, oestradiol and - to a lesser degree - progesterone into adult male rats caused a significant increase of enzyme activity in the hypophysis. Progesterone proved to be ineffective in the hypothalamus. This indicates that in contrast to the hypothalamus there is no sex-specific response of the LH-RH-degrading enzyme in the pituitary. It is concluded that this enzyme system seems to play an important part in the mechanisms regulating gonadotrophin release in the pituitary.
    Type of Medium: Online Resource
    ISSN: 0804-4643 , 1479-683X
    URL: Article
    DOI: 10.1530/acta.0.0860060
    RVK:
    WA 15000
    Language: Unknown
    Publisher: Oxford University Press (OUP)
    Publication Date: 1977
    detail.hit.zdb_id: 1485160-X
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  • 3
    Online Resource
    Online Resource
    STIMULATION BY STEROIDS AND AGE-DEPENDENT CHANGES OF L-CYSTINE ARYLAMIDASE ACTIVITY IN THE HYPOTHALAMUS OF THE RAT
    Oxford University Press (OUP) ; 1974
    In:  Acta Endocrinologica Vol. 76, No. 1 ( 1974-05), p. 15-23
    Details
    In: Acta Endocrinologica, Oxford University Press (OUP), Vol. 76, No. 1 ( 1974-05), p. 15-23
    Abstract: L-cystine arylamidase activity was found to be high in hypothalamic homogenates from 10 day old rats, and then to decrease significantly until sexual maturity was reached ( P 〈 0.01). This enzyme activity could be stimulated by treating 10 to 35 day old male rats with 100 μg of testosterone. Contrary to this, L-cystine arylamidase activity could not be stimulated in female animals by the injection of 7 μg of ethinyl-oestradiol before Day 45 of life. These data are interpreted as meaning that the L-cystine arylamidase activity plays a rôle in the processes regulating sexual maturation.
    Type of Medium: Online Resource
    ISSN: 0804-4643 , 1479-683X
    URL: Article
    DOI: 10.1530/acta.0.0760015
    RVK:
    WA 15000
    Language: Unknown
    Publisher: Oxford University Press (OUP)
    Publication Date: 1974
    detail.hit.zdb_id: 1485160-X
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  • 4
    Online Resource
    Online Resource
    THE ACTIVITY OF AN LH-RH-DEGRADING ENZYME IN THE ANTERIOR PITUITARY DURING THE RAT OESTRUS CYCLE AND ITS ALTERATION BY INJECTIONS OF SEX HORMONES
    Oxford University Press (OUP) ; 1978
    In:  Acta Endocrinologica Vol. 87, No. 3 ( 1978-03), p. 476-484
    Details
    In: Acta Endocrinologica, Oxford University Press (OUP), Vol. 87, No. 3 ( 1978-03), p. 476-484
    Abstract: The basal activity of an LH-RH-degrading enzyme system, L-cystine arylamidase, was determined in the pituitary gland of female rats at 4 h intervals throughout the 4-day oestrus cycle. The activity of the enzyme was found to be fluctuating during the four stages of the cycle in a circadian rhythm with the highest values occurring at night and the lowest values at noon. The maximal activity for the whole cycle was measured at 04.00 h on the day of metoestrus, and the minimal activity between 12.00 h and 16.00 h on the day of pro-oestrus. The iv injection of various doses of oestradiol caused only a slight change in enzyme activity of the pituitary during oestrus, but considerable increases were observed during the other three stages. The stimulation of enzyme activity by progesterone was much more pronounced during dioestrus and pro-oestrus as compared with metoestrus and oestrus. Similarly the reaction to the injection with LH and prostaglandin E 2 , repectively, were not very pronounced during oestrus and metoestrus, whereas the enzyme activity rose by +50% and +100%, respectively, during dioestrus and pro-oestrus. The LH-RH-degrading enzyme system in the pituitary seems to be involved in the control of the tonic LH release, and in the maintenance and regulation of the sensitivity of the gonadotrophs to alterations in LH-RH release from the median eminence.
    Type of Medium: Online Resource
    ISSN: 0804-4643 , 1479-683X
    URL: Article
    DOI: 10.1530/acta.0.0870476
    RVK:
    WA 15000
    Language: Unknown
    Publisher: Oxford University Press (OUP)
    Publication Date: 1978
    detail.hit.zdb_id: 1485160-X
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  • 5
    Online Resource
    Online Resource
    TIME-DEPENDENT DECREASE OF PITUITARY RESPONSE TO LH-RH AFTER CHRONIC TREATMENT OF INTACT FEMALE RATS WITH ETHINYLOESTRADIOL AND NORETHINDRONE
    Oxford University Press (OUP) ; 1978
    In:  Acta Endocrinologica Vol. 89, No. 2 ( 1978-10), p. 240-250
    Details
    In: Acta Endocrinologica, Oxford University Press (OUP), Vol. 89, No. 2 ( 1978-10), p. 240-250
    Abstract: The effect of daily injections of 50 μg ethinyloestradiol and 1 mg norethindrone upon basal and LH-RH-stimulated LH release was investigated in intact adult female rats during a period of 30 days. Basal plasma LH was depressed by about 30 % during the whole time of steroid treatment, and returned to the level of the control values two weeks after discontinuation. The injection of 30 ng and 150 ng LH-RH into untreated rats resulted in a significant increase of plasma LH which was, however, not dose-dependent. After the treatment with ethinyloestradiol and norethindrone for 5 days, the pituitary response to 150 ng was approximately four times higher than that to 30 ng. The LH release after injection of 150 ng LH-RH decreased significantly with the duration of steroid treatment, and was totally abolished by 30 days; whereas two weeks after the termination of steroid application the pituitary responded to LH-RH in the same manner as in control rats. When 30 ng LH-RH were injected into oestrogen/norethindrone treated rats, no decrease in LH release was found until day 20 of the experiment. By 30 days of treatment no rise in plasma LH could be elicited. The activity of the LH-RH-degrading enzyme L-cystine arylamidase was stimulated during the treatment with ethinyloestradiol and norethindrone in the pituitary by approximately 100 %, whereas almost no effect on this enzyme was seen in the hypothalamus. It is concluded that the chronic treatment of intact female rats with ethinyloestradiol and norethindrone causes time-dependent and reversible alterations in the storage of LH in the pituitary. The elevated activity of the LH-RH-degrading enzyme in the pituitary is possibly involved in these processes and/or in the mechanism responsible for the depression of basal LH.
    Type of Medium: Online Resource
    ISSN: 0804-4643 , 1479-683X
    URL: Article
    DOI: 10.1530/acta.0.0890240
    RVK:
    WA 15000
    Language: Unknown
    Publisher: Oxford University Press (OUP)
    Publication Date: 1978
    detail.hit.zdb_id: 1485160-X
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