Regulation of ovine pituitary function with estrogen alone and in combination with progresterone Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/cr56n358j

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  • Five experiments were conducted to study the activity of the pituitary gland in sheep as influenced by estrogen administered alone or in combination with progesterone. Particular emphasis was given to the study of gonadotropic activity. Mature wethers (experiments I, III, IV and V) or ewes (experiment II) were utilized as experimental subjects. Blood samples were drawn from the sheep before hormone treatment to provide control samples, and during and after treatment to study sequential changes of pituitary secretion. The cavernous sinus collection technique was utilized to obtain pituitary venous blood which contains assayable gonadotropic activity. The plasma obtained was pooled for each collection period of a specific experiment and administered to immature, female, hypophysectomized rats. Responses in the recipient animals were used for a determination of the qualitative and quantitative changes of the donor animal's pituitary secretion. Total gonadotropic activity was measured by weight responses of the ovarian and oviductuterine structures. FSH and ICSH activities were indicated by ovarian histological changes in the follicles and interstitial cells, respectively. Other pituitary activities were indicated by weight responses of the adrenal and thyroid glands, and by measurement of the tibial epiphyseal plate width. The first two experiments involved wethers (I) and anestrous ewes (II) which were administered 0.005 mg. of estradiol benzoate daily for 10 consecutive days. The hormonal activity of plasma from wethers was not found to be significantly affected by the estrogen treatment although a trend of inhibition seemed apparent. Assays of plasma from the anestrous ewes revealed a significant decrease in the rat oviduct-uterine weight response both during and following the 10-day estrogen treatment. Stimulation of plasma FSH activity and inhibition of plasma ICSH activity were significantly indicated after withdrawal of estrogen injections in the ewe experiment. A single injection of 0.025 mg. of estradiol benzoate was given to wethers in experiments III and IV. The bioassays indicated that such estrogen treatment caused a significant rise of plasma gonadotropic activity. The FSH activity approached being significantly increased and the ICSH activity was significantly increased, especially on the fifth and sixth days after cessation of hormone therapy. The gonadotropic activity decreased to a point comparable to the control level on the eighth and tenth day after estrogen treatment. Significantly increased plasma activity, as indicated by weight responses of the adrenal and thyroid glands, was observed after estrogen administration. A significant increase in epiphyseal plate width was observed, also indicating an increase in plasma activity after estrogen therapy. Experiment V involved wethers injected daily with 0.025 mg. of estradiol benzoate and 20 mg. of progesterone for 10 consecutive days. Significant and prolonged inhibition of pituitary secretion was clearly indicated by the bioassay. FSH and ICSH inhibition were most pronounced on the fifth and sixth days after withdrawal of treatment.
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