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  • Author: G. P. van Rees x
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G. P. van Rees

ABSTRACT

Levels of thyrotrophin were determined in the anterior pituitary glands and blood sera of thyroidectomized rats after treatment with triiodothyronine or thyroxine for two weeks. The effects of increasing doses of both hormones on pituitary TSH levels appeared to be of a biphasic nature: whereas lower doses caused an increase, higher doses did so to a smaller extent or even caused a decrease, while at the same time progressively depressing the serum TSH levels. The highest pituitary levels found in thyroid hormone treated thyroidectomized rats were similar to those found in untreated intact rats, and equal doses of thyroid hormone were necessary to normalize the increased serum levels as well as the decreased pituitary contents in thyroidectomized animals. These findings are interpreted as indicating that in thyroidectomized rats the rate of release of TSH is depressed by lower doses of triiodothyronine and thyroxine than the rate of synthesis. Triiodothyronine was about three times more active than thyroxine.

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G. P. van Rees

ABSTRACT

The hypothesis that steroid sex hormones influence pituitary F. S. H. by independent actions on its production and capacity of the gland to release it has been investigated by means of incubation experiments. During incubation, rat pituitary glands released considerable amounts of F. S. H. into the medium. Inactivation of F. S. H. during incubation could not be demonstrated; once (in females) some production of F. S. H. was even observed. The amount of F. S. H. which is released into the medium is influenced by the quantity of F. S. H. stored in the hypophyses.

Hypophyses from male rats pretreated with oestradiol released relatively more F. S. H. into the medium than hypophyses from control animals. On the other hand, pretreatment with testosterone caused the pituitary glands to release less F. S. H. into the medium. In agreement with these results, hypophyses from intact male rats released relatively less F. S. H. than hypophyses from intact female rats.

These facts support the hypothesis that androgens depress pituitary F. S. H.-secretion by inhibiting the capacity to release it, while oestrogens, which can even promote this property of the pituitary gland, also act by directly inhibiting its production.

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E. L. Noach and G. P. van Rees

It is well known that stimulation of the pituitary-adrenocortical axis results in a decrease in the ascorbic acid content of the adrenals, though the actual function of ascorbic acid in this gland is still obscure. Ascorbic acid might either be specifically involved in the production of corticoids or be of value in the formation of steroid hormones from their precursors. In the latter case a decrease of the ascorbic acid content of ovaries and testes might occur as a result of treatment with gonadotrophins in the same way as occurs in the adrenal following the administration of corticotrophin. A fall in the ascorbic acid content of ovaries due to gonadotrophin administration has been reported by Claesson et al. (1949).

According to Van Ravesteyn (1941) the ascorbic acid in the ovary is localized in the corpus luteum and interstitial tissue only. Coste et al. (1953 a) determined the ascorbic acid content

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G. P. van Rees and E. Gans

ABSTRACT

In female rats sterilized by an injection of testosterone propionate (TP) shortly after birth, the effects of gonadectomy and gonadectomy plus chronic treatment with oestradiol benzoate were studied.

Pituitary LH-contents were affected in a similar way as in normal females, although there was an indication that the sensitivity of the response of pituitary LH-content to oestradiol was slightly less in TP-sterilized than in normal rats.

The effect of oestradiol on uterine weights was definitely less in gonadectomized TP-sterilized rats than in gonadectomized controls. It was therefore concluded that negative feedback mechanisms between ovarian steroids and LH-secretion operate in a normal manner in TP-sterilized rats. The sensitivity of the uterus to oestrogen, however, is decreased.

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E. Gans and G. P. van Rees

ABSTRACT

The influence on the I. C. S. H.-content of the pituitary gland and the blood serum of long-term treatment of gonadectomized male and female rats with several low doses of oestradiol benzoate was investigated.

It was found that only in females treatment with 0.1 and 0.2 μg of oestradiol benzoate daily results in an increase of the pituitary I. C. S. H.-content, whereas in the serum content a (non-significant) decrease was observed. In male rats the pituitary I. C. S. H.-content was not influenced by treatment with these doses, but the serum content decreased.

Higher doses of oestradiol (0.5 and 2.0 μg daily) caused, both in males and in females, a decrease of the I. C. S. H.-content in the hypophysis as well as in the serum.

It is assumed that oestrogen, if chronically administered, exerts two different actions on pituitary I. C. S. H.: it depresses the production of I. C. S. H. and inhibits the release. In females, these two effects have different threshold levels, that for the release being the lower one. In males the threshold for the inhibition of production has to be lower.

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G. P. van Rees and O. L. Wolthuis

ABSTRACT

Hypophyses transplanted under the kidney capsule rapidly lose their F. S. H.-content. This decrease is counteracted by the administration of testosterone (17β-hydroxy-androst-4-en-3-one); an increase was even observed in the F. S. H.-content of the grafts. Treatment with progesterone (pregn-4-ene-3,20-dione) resulted in a non-significant increase in the F. S. H.-content of the grafts. Oestradiol was able to counteract to some extent the effect brought about by testosterone. These results point to a direct action on pituitary F.S.H.-release-capacity, at least for testosterone.

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E. Gans and G. P. van Rees

ABSTRACT

Augmentation of testis weight caused by the follicle stimulating hormone (FSH) was studied in hypophysectomized immature rats treated concomitantly with supramaximal amounts of human chorionic gonadotrophin (HCG). Using a rat pituitary homogenate, responses were found to increase linearly with the logarithm of the doses given. In assays of rat pituitary homogenate against purified sheep FSH no significant divergence was observed. The effect of a submaximally active dose of FSH was not significantly altered by the concomitant administration of purified growth hormone, thyrotrophin, corticotrophin, prolactin or luteinizing hormone (LH). Serum from intact male and female rats caused significant growth of the testis, while serum from male animals was more active than that of female rats. However, when serum from hypophysectomized male and female rats was given, some testis growth still occurred in one of the two experimental series. In this case, the responses were smaller than those caused by serum from intact males but not smaller than those caused by serum from intact females. No difference in testis growth-promoting effect could be demonstrated between the sera obtained from hypophysectomized male and female rats.

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J. A. M. J. van Dieten and G. P. van Rees

Abstract.

Ovariectomized (OVX) rats were treated for 24 h with pulses of LRH (1.25 ng/100 g b.w. every 20 min) or of saline. Moreover, the animals received 3 sc injections of oestradiol benzoate (EB) (50 μg) or oil during this period. At the end of this period all animals received phenobarbital (80 mg/kg ip) and the animals were given pulses of LRH (once every 20 min) containing 1.25, 2.5, 5.0 or 10 ng for 3 h. Pulsatile administration of 1.25 ng pulses for 24 h did not lead to pituitary insensitivity. Treatment with EB caused the development of an increased response to LRH (positive effect). When during the 24–27 h period 5.0 or 10.0 ng pulses of LRH were given, the positive response was the same whether LRH had been administered during the 0–24 h period or not. However, the response to 2.5 ng pulses of LRH was halved when the animals had been pre-treated with LRH. It is concluded that the presence of LRH can inhibit partly the development of the positive pituitary response to LRH as caused by EB.

When the dose of LRH was kept at 1.25 ng/pulse no clear positive effect developed. Chronic administration of phenobarbital for 24 h caused pituitary insensitivity, presumably through a direct toxic effect.