SECRETION DE LA PROGESTERONE PAR LES CORPS JAUNES DE LA BREBIS APRES HYPOPHYSECTOMIE, SECTION DE LA TIGE PITUITAIRE ET HYSTERECTOMIE

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Abstract
The purpose of these experiments was to investigate the part played by the pituitary gland and the uterus in the control of sheep corpus luteum. Six experiments were carried out, as follows: 1. Hypophysectomy early and late in the estrous cycle : on days 2-5 hypophysectomy allowed the corpus luteum to continue secreting normal amounts of progesterone for up to 9 days, therafter the secretion declined; on days 9-10 hypophysectomy caused progesterone secretion to fall within 4 days, as the corpus luteum has a limited functional life span, and normally requires the presence of a pituitary luteotropin during the 2nd half of the estrous cycle if it is to secrete normally for 15 days, 2. Pituitary stalk section early and late in the estrous cycle: regardless of the time of stalk section, the corpus luteum behaves as it would during a normal cycle; pituitary stalk section does not produce the same effect as hypophysectomy, and seems to allow the severed pituitary gland to continue secreting luteotropin. 3. Hypophysectomy and hysterectomy carried out simultaneously early in the cycle: results were similar to those in 1, progesterone secretion having declined significantly by days 12-15, thus confirming that the declining secretory activity is due to a deficiency of pituitary luteotropin, and not to any uterine luteolytic effect in this experiment. 4. Pituitary stalk section and hysterectomy carried out simultaneously early in the cycle: in striking contrast to 3, some corpora lutea were still secreting progesterone normally on day 18, thus substantiating that the isolated pituitary gland can continue to secrete luteotropin; different responses in this experiment and 2 emphasise the fact that the uterine luteolytic effect is normally dominant to the pituitary luteotrophic stimulus, and it would be impossible to demonstrate leuteotropic activity if the uterus were still present. 5. Hysterectomy carried out at mid cycle, followed by hypophysectomy 20-30 days later: while hysterectomy alone prolongs the secretory activity of the corpus luteum, subsequent hypophysectomy results in a rapid decline in progesterone secretion, commencing 48 hr. after the operation; the corpora lutea prolonged by hysterectomy, unlike those of the normal cycle, require daily pituitary luteotropin secretion for their continued existence. 6. Hysterectomy carried out at mid cycle, followed by pituitary stalk section 20-30 days later: allows the corpora lutea to continue to secrete progesterone in large amounts for at least 15 days after the operation; this experiment, together with 2 and 4, emphasises that the stalk-sectioned pituitary gland can continue to secrete luteotropin. These experiments support the view that the cyclical corpus luteum of the sheep is under the dual control of a pituitary luteotropin, whose secretion continues after stalk section, and a uterine luteolysin that is dominant to the luteotropic stimulus, and can still function normally after pituitary stalk section. The fact that the corpus luteum of the hysterectomized animal cannot function for more than about 15 days after stalk section suggests that the luteotropic stimulus may be complex, possibly envolving more than one hormone.