PROGESTERONE AND 20α-Hydroxypregn-4-en-3-One LEVELS IN OVARIAN VEIN BLOOD OF THE RAT THROUGHOUT LACTATION

Abstract

Changes in the rate of progesterone and 20\g=a\-hydroxypregn-4-en-3-one (20\g=a\-OH-P) secretion by the rat ovary during the course of lactation were investigated. The level of progesterone in the ovarian vein blood, which was very low on day 1 of lactation, increased progressively up to day 8 (355 \ g=m\ g. / 100 ml. blood), then declined to day 18 (45\m=.\5 \g=m\g./100ml.) and day 21 of lactation. A high concentration of 20\g=a\-OH-Pin blood was observed on day 1 and day 21 of lactation, but from day 4 to day 18 the secretion of this steroid was relatively low. The ratio of progesterone to 20\g=a\-OH-Pexceeded unity from day 4 to day 16, and in the middle of lactation the concentration of progesterone in ovarian venous blood was about four times greater than that of 20\g=a\-OH-P. These changes in the secretory pattern of progestins during lactation are discussed in connexion with the effects of the suckling stimulus on prolactin and gonadotrophin secretion from the anterior pituitary gland.

Variations of Serum Estradiol and Progesterone Levels during Consecutive Reproductive States in Mongolian Gerbils (Meriones unguiculatus)

“…The serection of estrogen is eventually restrained, but the physiological estrogen level is stimulative for lactation maintenance. The Mongolian gerbil displays a postpartum ovulation phenomenon [18], and the suckling stimulus during early lactation allows the corpus luteum that is formed after ovulation to become functional and secrete progesterone [7,10,25,31]. Prolactin (PRL) induced by the suckling stimulus maintains the corpus luteum function and induces continuous P4 secretion [28,34].…”

Duration of Diestrous Period and Secretion of Progestins during Prolonged Lactation in the Rat

“…Therefore, the fact that the level of progesterone during the 1st diestrous period as reported previously (Tomogane et al, 1969) was higher than that during the 2nd diestrous period might be due to the higher levels of prolactin secreted under the influence of suckling stimulus and exteroceptive stimuli originated from young pups (Grosvenor et al, 1970;Mena & Grosvenor, 1972) in the former period. The stimulative effect of the suckling on prolactin secretion in rats has been well demonstrated by many workers (Amenomori et al, 1970;Terkel et al, 1972;Ford & Melampy, 1973;Yanai & Nagasawa, 1973).…”

“…Lactation was prolonged beyond the normal period by replacing pups at appropriate intervals (Nicoll & Meites, 1959;Bruce, 1961;Kurz, 1967;Thatcher and Tucker, 1968). However, only a few papers have appeared concerning the ovarian function during a prolonged lactating period (Selye We have been working on the maintenance of luteal function during lactation with special reference to the luteotropic action of prolactin and have reported the pattern of progestin secretion (Tomogane et al, 1969) and the effect of ergocornine, a specific inhibitor of the release of prolactin, on progestin secretion (Tomogane et al, 1975) in normal lactating animals. Therefore, it was of interest to study the pattern of progestin secretion in prolonged lactating rats showing fairly long diestrous periods (Selye & McKeown, 1934;Bruce, 1961 were given ad libitum.…”

“…Therefore, blood samples were collected 1, 4, 7, and 11 days after the day of the 1st estrus (21-28days of lactation) and on the day of the 2nd estrus. The methods of collection of blood samples from the ovarian vein and of determination of progestins in the sample were similar to those described in the previous paper (Tomogane et al, 1969 …”

Luteinizing hormone, prolactin and ovarian 20 alpha-hydroxysteroid dehydrogenase activities during pregnancy or pseudo-pregnancy in the rat

“…Interconversion of progesterone and 20ri-hydroxyprogesterone is medi ated by 20a-OH-SDH, and a positive correlation between peripheral plasma levels of 20a-hydroxyprogesterone and ovarian 20a-OH-SDH activity has been demonstrated during pregnancy (Wiest, et al, 1968) and probably exists during lactation (Tomogane, Ota, and Yokoyama. 1969;Kuhn and Briley, 1970).…”