L. PITZEL and W. WUTTKE
J. Kronibus and W. Wuttke
Female rats were ovariectomized (ovx), adrenalectomized (adx) or both (adx-ovx) on day 8 after birth. The serum gonadotrophin concentrations on day 15 were higher in ovx and adx-ovx rats than in sham-operated or untreated controls of the same age. Intact animals on day 15 had higher LH and FSH levels compared with adult, dioestrous levels, and a number of LH peaks were observed. After partial separation of oestradiol (LH 20 column chromatography) from other lipid substances which interfere with the radioimmunoassay for oestradiol, levels of oestradiol were undetectable in ovx and in adx-ovx animals on day 15 but concentrations were relatively high in intact or adx rats.
To test whether the high gonadotrophin concentrations in 15-day-old intact rats were due to a positive feedback action of oestradiol, silastic tubes containing different amounts of oestradiol were implanted on day 8 at the time of adrenalectomy and ovariectomy. The mean serum LH and FSH concentrations were increased on day 15 in those animals in which silastic tube implantation resulted in physiological oestradiol levels. These elevated gonadotrophin values were due to a number of peak levels. Injection of 600 μg progesterone on day 15, 8 h before decapitation resulted in high FSH levels in all the implanted animals, whereas LH levels were still variable from one animal to another. This situation is very similar to that in intact control rats and it is concluded that the hypothalamo-pituitary axis in 15-day-old female rats reacts to an oestrogenic stimulus followed by a progestational reaction as does the adult "gonadostat". This would account for the premature, pre-ovulatory type of LH peaks.
W. Wuttke and M. Fenske
M. Fenske and W. Wuttke
Blood was collected from male rats of various ages under control conditions and after introduction of two stress factors. All animals were sacrificed between 15.00 and 16.00 h. Serum prolactin levels in immature male rats were found to be very low between birth and day 15 after birth. Neither exposure to a new environment, for example removal from the animal rooms for the duration of 10 min, nor exposure to concentrated ether vapour resulted in increased serum prolactin levels. Between day 20 and 35 basal serum prolactin levels were increased, they then fell at adult values. During this period of increasing serum prolactin levels pituitary prolactin release became stress-susceptable; i. e. elevated serum prolactin levels were observed after introduction of stress factors as in adult male rats. Serum TSH levels were found to be high between birth and day 10. Low TSH levels measured between day 15 and 40 and adult values were detected after day 40. Neither ether nor removal of the animals from their normal environment changed serum TSH levels at any age tested. These results indicate that the hypothalamo-pituitary in immature rats reacts in a similar way as that in adult animals from day 16–20 onwards. Serum TSH levels in these animals, however, are reduced, indicating that an increase in serum TSH is not necessary for normal processes of maturation.
J. W. Siebers, W. Wuttke and W. Engel
During pregnancy, binding of 125I-labelled HCG to the rat ovary increases markedly from the 3rd to the 17th day of pregnancy but is reduced drastically at the end of pregnancy and after delivery. At the 17th day of pregnancy the HCG-binding capacity of the rat ovary is raised 76-fold in comparison to oestrous rats (17th day of pregnancy: 128 × 10−15 mol/mg wet weight; oestrus: 1.67 × 10−15 mol/mg wet weight). It is assumed that only LH receptors not occupied by endogenous hormone are covered by our assay. The high number of "free" ovarian HCG receptors during pregnancy apparently represents "spare" receptors, the functional significance of which remains unclear. It is suggested that the metabolic activity of the ovarian luteal cells during pregnancy is not restricted by the number of HCG receptors present, but through the level of the endogenous gonadotrophic hormone and/or some unknown factors residing in the luteal cell.