Prostaglandin E2の下垂体性GonadotropinおよびProlactinの放出作用について

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Numerous reports concerning the mechanism by which pituitary gonadotropin and prolactin are released by prostaglandins (μg) have been made since the experimental work of Orczyk & Behrman et al (1972). Nonetheless, it is still uncertain whether the location of this effect is in the hypothalamus, higher centers or in the pituitary gland. In this paper, we report an investigation of the effects of μgE2 on the vaginal smear in rats and observation of central nervous system changes based upon the recording of multiple unit activity (MUA). Furthermore, we have measured the effects of μgE2 on these locations by determining the amounts of gonadotropin and prolactin in the blood and the pituitary gland. Experiment I. First we observed the changes in the vaginal smear following a single subcutaneous injection of 10μg, 100μg or 500μg of μgE2 in the DI period of mature, female Wistar strain rats undergoing normal 4 day (reproductive) cycles. Almost no changes were seen in the groups injected with 10μg or 100μg of μgE2, but in the 500μg group, all animals showed disorder. From these results, we concluded that the 500μg μgE2 subcutaneous injection had some sort of effect upon the rat's endocrine environment. Experiment II. MUA recording electrodes were stereotaxically placed following the brain atlas of Albe-Fessard et al (1966) under the administration of Nembutal (anesthesia). After more than 2 weeks following the stereotaxy and after ascertaining that the normal reproductive cycle had recurred at least twice, 500μg of μgE2 was administered in a single dose at 2 P.M. during the DI period, and the changes in the MUA of the medial preoptic area (MPO) and the medial amygdala (m-AMYG) were observed. A remarkable decrease in the level of activity at both locations was seen approximately 10 minutes after the μgE2 administration, and this low level was maintained for approximately 60 minutes. These results were clearly due to the effects of the μgE2 administration and indicate distinct changes in the electrical activity of the MPO and m-AMYG. Experiment III. The rats having been castrated, 3 to 5 weeks later 500μg or 1000μg of μgE2 was subcutaneously injected in a single dose following pretreatment with 100μg of estradiol benzoate and 10mg of progesterone. Blood samples were obtained by decapitation from both groups 10, 30 and 60 minutes later, and simultaneously the adenohypophysis was excised. Radioimmunoassay was performed using the method of Monroe et al (1968). Blood LH was found to have increased significantly 10 minutes after the administration of 500μg of μgE2, returning to a resting level after 30 to 60 minutes. Significant changes in FSH levels were not found in either the blood or the pituitary. Blood prolactin increased significantly 10 minutes after the administration of a large dose of μgE2 (1000μg) and showed a significantly high level after 30 minutes. By contrast, pituitary prolactin decreased significantly 10 minutes after the administration of 1000μg of μgE2 and returned to a resting level after 30 to 60 minutes. From the above experiments, it is apparent that there are notable similarities between the MUA rhythm patterns of the MPO and m-AMYG and the pattern of changes of LH and prolactin in the blood and pituitary following μgE2 administration. It has been previously suggested that the release mechanism of gonadotropin and prolactin by μgE2 works by way of LHRH, PIF and PRF. From the results we have obtained in this experiment, it is indicated that gonadotropin and prolactin secretions are enhanced by the action of LHRH, PIF and PRF on the higher nerve centers, the medial preoptic area and the medial amygdala.

Prostaglandin E<SUB>2</SUB>の下垂体性GonadotropinおよびProlactinの放出作用について

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