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J. PRESL, J. HERZMANN and J. HORSKý

Morphological and sexual differentiation extending far into postnatal life in the rat, a species with short gestation, is influenced in the female first by the absence and later by the presence of ovarian oestrogens. Therefore, in the present study the total oestrogen concentration was determined in the blood of normal female rats from the early postnatal critical period of hypothalamic sexual differentiation until sexual maturity.

Wistar rats aged 5–7 days were used. The animals were given heparin s.c. (5- and 10-day-old animals receiving 500 i.u., all others 1000 i.u.) and were killed by decapitation 45 min. later. At each age studied, blood from groups of 6–120 animals (Table 1) was pooled and replicate samples of 5 ml. were taken from each pool. The oestrogens were extracted and purified according to the method described in detail by Herzmann, Presl, Horský & Vrchlabská (1967) and were measured fluorimetrically (Ittrich, 1960).

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J. PRESL, J. JIRÁSEK, J. HORSKÝ and M. HENZL

Female rats treated during the early postnatal period with a sufficient amount of oestrogen develop a severe disorder of the regulatory mechanisms of the oestrous cycle with subsequent anovulation and sterility (Greene, Burrill & Ivy, 1939; Greene & Burrill, 1941; Turner, 1941; Wilson, Hamilton & Young, 1941). We have studied the cytological changes in the anterior pituitary of such animals.

Ten female rats of our laboratory strain, aged 5 days, received a single s.c. injection of 1·25 mg. oestradiol dipropionate in 0·1 ml. peanut oil. The animals were killed at the age of 200 days and their ovaries and pituitaries were removed.

Histological investigation of the ovaries showed numerous large vesicular follicles and hypertrophied interstitial cells in the interfollicular spaces. Corpora lutea were absent. The animals were persistently in oestrus in agreement with the findings of Takasugi (1952) who reported that short-term injections of oestrogens given to female rats during

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J. PRESL, J. HORSKÝ, M. HENZL and J. JIRÁSEK

SUMMARY

With the object of obtaining basic information concerning the establishment of the feedback mechanism between the ovaries and the diencephalic-hypophysial system (DHS), changes in the gonadotrophic activity and histological structure of the anterior pituitary lobe were determined in groups of rats 21 days following ovariectomy on the day of birth or at 5, 10, 15, 20, 30 and 50 days.

It was shown that the gonadotrophic activity of the hypophysis of spayed females and non-spayed controls differed using the criterion of uterine weight of the recipient, following ovariectomy at birth. After spaying at the age of 5 days the difference was also statistically significant using the criterion of ovarian weight. Histological investigation showed that in animals ovariectomized at days 1 and 5 there was an increase in PAS-positive mucoid cells in the adenohypophysis with a distinct PAS-positive Golgi zone in the pale centre of the cytoplasm.

The results of these experiments show that a feedback mechanism between the ovaries and the DHS becomes established at an age between (21–x) and (26–x) days, where x is the period necessary for the development of demonstrable post-castration changes in the anterior lobe. In view of the reported initiation of ovarian oestrogen production, the hypothesis is discussed that the feedback mechanism begins to function during very early post-natal life.

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J. PRESL, J. HORSKÝ, J. HERZMANN, I. MIKULÁŠ and M. HENZL

The development of characteristic castration changes in the anterior pituitary of rats ovariectomized at the age of 1 and 5 days (Presl, Horský, Henzl & Jirásek, 1963) means that the feedback mechanism between the ovaries and the diencephalohypophysial system becomes established early postnatally, before sexual maturity. The observed changes suggested that the ovaries already produce oestrogens during this period. The purpose of the present work was to obtain direct evidence of oestrogen production in 10-day-old female rats, i.e. when steroid-3β-ol dehydrogenase is already present in the ovaries (Presl, Jirásek, Horský & Henzl, 1965).

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Wistar rats bred in our laboratory were used. The animals were given heparin s.c. (10-day-old animals received 500 i.u., all others 1000 i.u.) and were killed by decapitation 45 min. later. Ovariectomized animals were killed 4 weeks after the operation. Adrenalectomy was performed 3 weeks after ovariectomy and the animals were killed 10 days later. For each