Gonadotrophin and Steroid Levels Around the Time of First Ovulation in the Rat

Abstract

Luteinizing hormone, FSH, prolactin, oestradiol and progesterone concentrations were measured by radioimmunoassay in the blood of female rats from 7 days before the first ovulation (the day of first ovulation is designated day 0) until the day after the second ovulation. Serum LH concentrations varied between 29 and 59 ng NIAMDD-rat-LH RP-1/ml from days -7 to -2. On the day preceding first ovulation (day -1) a steep increase in serum LH was found between 13.00 h and 15.00 h reaching a maximal value of 2100 ng/ml at 17.00 h. Thereafter LH levels decreased to undetectable values (less than 15 ng/ml). Serum FSH concentrations from days -7 to -2 varied between 108-154 ng NIAMDD-rat-FSH RP-1/ml; increased concentrations were found on the afternoon of day -1 and on the morning thereafter (first oestrus) with a maximal value of 1150 ng/ml at 19.00 h on day -1. On the day preceding the second ovulation (day +4) LH and FSH peaks were again found. Prolactin concentrations on the days preceding first ovulation were generally low. A small rise was found nearing first ovulation (12-7 ng/ml, day -6; 23-9 ng/ml, day -2). On day -1 a peak (118 ng/ml) was found at 15.00 h, similar to that found on day +4 in adult pro-oestrous rats. Plasma progesterone concentrations also reached a peak value (50 ng/ml) on day -1, at 17.00 h, preceded by concentrations between 3-5 ng/ml from days -6 to -2. Progesterone concentrations after the first ovulation showed a pattern characteristic of the adult cycle. Plasma oestradiol levels were un-etectable (less than 10 pg/ml) from days -6 to -2; a clearly increased oestradiol concentration was found on day -1, reaching a value of 98 pg/ml. One and two days before the second ovulation, oestradiol levels rose again. The differences and similarities between pubertal and adult pro-oestrous hormone peaks are discussed.

Reflections on the attainment of puberty in the rat: have circadian signals a role to play in its onset?

“…In the female, neonatal levels are high in comparison with those of the adult ; they increase between 7 and 25 days of age and then return to adult dioestrous values before vaginal opening. On the evening of first pro-oestrus the rise in FSH concentrations is equivalent to that observed during subsequent preovulatory surges (Meijs-Roelofs et al, 1975b;Parker & Mahesh, 1976;Ojeda et al, 1976 . In our colony, serum LH concentrations Text- fig.…”

“…An investigation of the effects of PMSG treatment on immature rats showed that, rather than increasing the numbers of large follicles, the hormone altered the balance between large and atretic follicles (Peters, Byskov, Lintern-Moore, Faber & Anderson, 1973 (McNatty, Hunter, McNeilly & Sawers, 1975) supported the previous findings and showed that an increase in FSH stimulated the granulosa cells to secrete oestradiol which in turn affected the growth of subsequent follicles (Baird, Baker, McNatty & Neal, 1975 fig. 4), whereas after 21 days of age values decrease and remain consistently low until the first preovulatory rise (Cheng & Johnson, 1974;Meijs-Roelofs et al, 1975b;Ojeda et al, 1976 (Text-fig. 4).…”

Tamoxifen but Not Other Selective Estrogen Receptor Modulators Antagonizes Estrogen Actions on Luteinizing Hormone Secretion while Inducing Gonadotropin-Releasing Hormone Self-Priming in the Rat

“…In the rat, rising estrogen levels during diestrus are critical for the preovulatory release of GnRH and LH in proestrus and, consequently, the release of eggs during the early hours of estrus [2]. Both basal and GnRH-stimulated LH secretion are strictly dependent on estrogen action on the pituitary [26]. All SERMs used in these experiments reduced both basal and stimulated LH secretion, as did the ‘pure’ anti-estrogen ICI.…”

Neuroendocrine Mechanisms Controlling the Onset of Female Puberty:The Rat as a Model

“…On the day of first proestrus, and under the influence of ele vated estrogen levels (1, 50,62] the responsiveness to LHRH increases again and the LHRH 'priming' effect becomes ap parent (20,75]. This facilitatory effect of estradiol (E2) on gonadotropin release can be demonstrated as early as 5 days after birth (86] and the priming effect of LHRH by day 26 [27], Thus, it seems evident that the pituitary gland can re spond to LHRH stimulation with substantial increases in LH release very early in life.…”