Steroidogenic Effects of Luteinizing Hormone and Prolactin on the Rat Ovary in Vivo

Abstract

Progesterone and 20\g=a\-dihydroprogesterone were measured in the ovarian venous blood of rats in early pro-oestrus, late dioestrus, day 5 of pseudopregnancy, and in androgen-treated animals with persistent oestrus. Little progesterone was secreted in early pro-oestrus or persistent oestrus (0\m=.\1\ g=m\ g. / hr.), but the secretion rose in dioestrus (2\ m=. \ 1\g=m\g./hr.) and in pseudopregnancy (7 \g=m\g./hr.). The 20\g=a\-dihydroprogesterone secretion was low in the persistent oestrous group; in all the other groups it was 1\m=.\5\p=n-\3 \g=m\g./hr. Treatment with luteinizing hormone increased progesterone secretion within 30 min. in pro-oestrus and persistent oestrus, had no significant effect in dioestrus, and depressed it markedly in pseudopregnancy. It appeared to have no significant effect on 20\g=a\-dihydroprogesterone secretion except during pseudopregnancy, when it was depressed.Treatment with prolactin produced no effect within 30 min.in pro-oestrous, dioestrous or pseudopregnant animals.

Acute Effects of Various Gonadotropins and Other Pituitary Hormones on Preovulatory Ovarian Progestin Secretion in Hypophysectomized Rats

“…This coincides with the time of LH release from the pituitary which has been determined by Kobayashi et al (1968) using the same laboratory rats bred under the same conditions. This fact suggests that the increase of progesterone at proestrus is caused by LH, since there are evidences that LH causes an increase in rat ovarian progesterone synthesis in vivo (Marsh et al, 1966;Yoshinaga et al, 1967) and in vitro (Armstrong and Greep, 1962;Armstrong et al, 1964;Channing and Villee, 1966;Major et al, 1967;Chatterton et al, 1968). In this connection, the decrease of progesterone concentration in the ovarian tissues after the surge of gonadotropins on the evening of the day of proestrus was far too small to account for the observed increase of secretion (unpublished data).…”

“…Up to date, only prolactin in the pituitary hormones other than LH has been examined in regard to its effect on the rat ovarian progestin secretion and synthesis, but prolactin is ineffective either in vivo (Marsh et al, 1966;Yoshinaga et al, 1967) or in vitro (Marsh et al, 1966). On the other hand, Major and Armstrong (1968) (Galton, 1968) and in lactation (Grosvenor and Turner, 1958 Hilliard et al (1963) have shown that ACTH, oxytocin, and vasopressin are ineffective in stimulating the output of progestins in rabbits.…”

Further Studies on the Luteotropic Action of Estrogen in Rats

“…The maximal secretion of progesterone at 19.00 hr on Day 2 in the EB treated rats is brought by the acute steroidogenic action of LH (Armstrong et al, 1964;Marsh et al, 1966;Yoshinaga et al, 1967;Uchida et al, 1969b) released at this time (Table 2), and the long-lasting secretion of progesterone following its marked peak on Day 2 reflects the corpora lutea being functional. Since no ovulation occurs after the surge of LH on Day 2 (Uchida et al, 1972), there is no doubt that the prolonged secretion of progesterone originates from the corpora lutea formed after ovulation on Day 1 and exposed to the surge of LH on Day 2, suggesting that LH is not necessarily luteolytic.…”

Basic mechanisms of ovarian endocrine function

“…LH has long been known to stimulate steroidogenesis by luteal tissue acutely or chronically, in vitro (13) or in vivo (30). It is equally well known that prolactin is absolutely critical for maintenance of the CL in the rat, for example (30), but it is not steroidogenic in the acute sense in vivo (31) or in vitro (32). Yet PRL may somehow synergize with LH to maximize luteal progesterone secretion in vivo (25).…”