OVARIAN ASCORBIC ACID AS AN ENDOGENOUS AND EXOGENOUS ASSAY FOR CYCLIC PROESTROUS LH RELEASE¹

Abstract

Cyclic proestrous LH release was investigated by endogenous and exogenous assay in rats exposed to light from 5:00 A.M. to 7:00 P.M. daily. Pituitaries were removed from proestrous rats at 10:00-11:00 A.M. and 4:00-5:00 P.M., injected into immature, primed recipient rats and tested for ovarian ascorbic acid depleting ability (exogenous assay). "Morning" pituitaries were significantly more potent than "afternoon" pituitaries, confirming the finding of drug and hypophysectomy studies that LH is released from the pituitary between 2:00 and 3:00 P.M. Ovaries removed from the proestrous donor rats showed no consistent ascorbic acid depletion on the afternoon of proestrus (endogenous assay). There was, however, a cyclic variation in ovarian ascorbic acid, the highest values occurring in metestrus, the lowest in proestrus. I N RECENT years Everett and his co-workers (1,2) have accumulated indirect evidence suggesting that when cyclic female rats are exposed to light daily between 5:00 A.M. and 7:00 P.M., LH is released from the pituitary starting at 2:00 P.M. and completed in 90% of animals by 3:30 P.M. on the day of proestrus. Ovulation then occurs around midnight. This timing of LH release was demonstrated by injecting a variety of centrally-acting blocking drugs (1) or hypophysectomizing (2) at the critical time in the afternoon and looking for presence or absence of ovulation the following morning.The use of endogenous ovulation as a criterion of LH release necessitates the presence of prepared follicles, limiting the variety of experiments which might be utilized to elucidate the factors triggering LH release. In order to avoid the need for a prepared ovary, changes in LH content must be measured directly, either in the anterior pituitary or in the body fluids. Acute decreases in pituitary gonadotrophin content have been demonstrated following coitus-induced ovulation in the rabbit (3, 4), following the onset of heat in the ewe (5) and sow (6), and following post-partum ovulation in the mouse (7). This encouraged us to look for acute decreases

The Lactational Anoestrus of the Sow: The Status of the Anterior Pituitary-Ovarian System During Lactation and After Weaning

“…Decreases in the pituitary content of FSH during cyclic oestrus or immediately preceding it have been reported in the ewe (Santalucito, Clegg & Cole, 1960;Robertson & Hutchinson, 1962) and sow (Day, Anderson, Hazel & Melampy, 1959;Parlow et al 1964) and decreases in LH have been observed in the rat (Mills & Schwartz, 1961;Gorski & Barraclough, 1962;Schwartz & Bartosik, 1962), ewe (Santalucito et al 1960;Robertson & Hutchinson, 1962) and sow . These decreases were considered to represent release of the hormones to produce ovulation and the follicular growth immediately preceding it.…”

Timing of Lh Release and Ovulation in the Cyclic Mouse

“…The small number of such mice available prevented the testing of this hypothesis. Both the time of lh release and the time of ovulation in the mice with a longer cycle (and at least the time of ovulation in the mice with a shorter cycle) are later than that found in the rat with a shorter cycle; lh is released between 14.00 and 16.00 hours at pro-oestrus and the rat ovulâtes close to 02.00 hours at oestrus (Everett, 1961;Mills & Schwartz, 1961;Schwartz & Bartosik, 1962;Schwartz & Caldarelli, 1965). An exact comparison of mice exhibiting 5-day cycles with rats exhibiting this cycle length, awaits further investigation in the rat.…”

“…In the rat exhibiting either 4-or 5-day oestrous cycles, the surge of lh responsible for ovulation is released from the anterior pituitary after 14.00 hours on the day of pro-oestrus (lights on from 05.00 to 19.00 hours) (Mills & Schwartz, 1961;Schwartz & Bartosik, 1962;Schwartz & Caldarelli, 1965). Untreated 4-day cyclic rats housed under conditions of 14 hr light and 10 hr darkness (L14:D10; 24.00 hours = midpoint of the dark period) ovulate at about 02.00 hours on the morning of oestrus (Everett, 1961).…”

Anterior Pituitary Ovulating Capacity in the PMSG-Primed Immature Female Rat

“…The data from the PMSG-primed females compare favourably with the pituitary lh information on the adult cycling rat (Mills & Schwartz, 1961;Schwartz & Bartosik, 1962) where pituitary lh decreased during the critical period, but lowest lh values were seen on the morning of oestrus. However, no pituitary change was seen between 14.00 and 19.00 hours in PMSG-ovulated 27-day-old females, but a significant fsh decrease occurred (Rennels & O'Steen, 1967 (Ramirez & Sawyer, 1965a) have shown an increase in the lh-rf in prooestrus, continuing for some time after the critical period, and followed by a decrease which is maintained into the morning of oestrus.…”

“…Progesterone administration on the day before pro-oestrus in 5-day cycling adult female rats causes ovulating hormone release 24 hr earlier than normal (Everett & Sawyer, 1949b (Ramirez & McCann, 1964;Schwartz & Calderelli, 1965). Phénobarbital blocked the lh increase in the afternoon of pro-oestrus (Schwartz & Calderelli, 1965 (Cole, 1936;Strauss & Meyer, 1962 (Mills & Schwartz, 1961;Schwartz & Bartosik, 1962;Rennels & O'Steen, 1967) have been shown to decrease during the critical period and both exogenous lh and fsh can cause ovulation (Zarrow, Caldwell, Hafez & Pincus, 1958;Zarrow & Gallo, 1966 0/9 0/9 0/9 0/9 0/9 0/9 0/9 0/9 0/9 0/9 0/9 9/9 9/9 9/9 9/9Î 9/9t 9/9Î 9/9Î 0/9 0/9 0/9 0/9 0/9 9/9 9/9 9/9 9/9Í 0/12 11/11 12/12 9/9 10/llt 10/llt 13/13Î 12/12J (5/9)t (6/8) (4/9) (4/9) (4/9) (4/9) (7/9) (3/9) (4/9) (3/9) (0/9) (0/9) (0/9) (0/9) (0/9) (0/9) (0/9) (0/9) (7/9) (4/9) (3/9) (3/8) (1/9) (0/9) (0/9) (0/9) (0/9) (3/12) (1/ ) (1/12) (1/9) (1/11) (1/11) (0 (7/9) (9/9) (9/9) (9/9) (8/9) (8/9) (8/9) (8/9) (9/9) (8/9) (6/9) (0/9) (1/9) (1/9) (2/9) (4/9) (1/9) (3/9) (9/9) (9/9) (7/9) (9/9) (2/9) (0/9) (1/9) (0/9) (1/9) (8/12) (4/11) (7/12) (8/9) (7/11) (10/11) (6/13) (7 (Bogdanove, 1964). Therefore, in the 16.30 PB rat oh synthesis occurs.…”