Alterations in Steroid and Gonadotropin Release Resulting from Surgical Stress During the Morning of Proestrus in 5-Day Cyclic Rats

Abstract

The purpose of this experiment was to determine whether surgical stress on the morning of proestrus would elicit an early release of gonadotropin from the pituitary. Animals exhibiting 5-day estrous cycles underwent bilateral sham-ovariectomy under ether anesthesia at 0800 h of proestrus. These animals had high levels of progesterone and estradiol following the surgery. These steroids were thought to be adrenal in origin, since animals adrenalectomized at 0800 h of proestrus had low progesterone levels and estradiol comparable to unoperated controls. Subsequently, the sham-operated animals showed high FSH but not LH values at 1300 h, prior to the normal critical period for gonadotropin release. By 1400, the LH surge had begun, and progesterone was again being released. Adrenalectomized and unoperated controls showed no increase in any steroid or gonadotropin measured before 1400 h. These findings suggest that stress-induced release of adrenal estradiol and progesterone, rather than some other consequence of the surgical procedure, during the morning of proestrus, can advance the onset of release of FSH, prior to LH. Ovariectomy at 0800 h proestrus led to a rapid and dramatic increase in FSH but not LH secretion by 4 h after surgery. By 6 h after ovariectomy FSH had increased to six times control values and LH had increased to twice control values. Estradiol remained at control values for 6 h following surgery but 20alpha-hydroxypreg-4-en-3-one (20alpha-OHP) dropped quickly to baseline values. It is possible that a reduction in circulating 20 alpha-OHP may be responsible for the increases in FSH prior to LH in this group, but the absence of other negative feedback factors from the ovary or adrenal may also be involved.

Influence of Uterine Inflammation on the Estrous Cycle in Rats

“…The high P4 concentration and low GnRH as a result of metritis might be responsible for ovarian quiescence. However, Nequin et al [14] reported that E2 concentration also increased in addition to P 4 concentration under a surgical stress condition, although this was not observed in this study.…”

“…This shows that the lifespan of the corpus luteum was not prolonged and that pseudopregnancy was not induced. Alternatively, stress stimulates progesterone secretion from the adrenal cortex in rats [7,14] and this secretion depends on corticotrophin releasing hormone (CRH) from the hypothalamus [22] . CRH also acted on cells directly producing GnRH and suppressed secretion of GnRH [9,13].…”

Evidence for ovarian “inhibin”: Suppression of the secondary rise in serum follicle stimulating hormone levels in proestrous rats by injection of porcine follicular fluid

“…Recent evidence has indicated that control of pituitary secretion of follicle stimulating hormone (FSH, follitropin) may differ from that of pituitary secretion of luteinizing hormone (LH, lutropin) (1)(2)(3)(4)(5), in spite of the failure to find more than one hypothalamic decapeptide releasing factor acting on the pituitary-LH/FSH-RF (6). FSH is secreted in high amounts without LH, beginning [5][6][7][8][9][10][11][12] hr after ovariectomy in the rat (3,4) or following hypothalamic electrochemical stimulation in the specific locus (5).…”

“…FSH is secreted in high amounts without LH, beginning [5][6][7][8][9][10][11][12] hr after ovariectomy in the rat (3,4) or following hypothalamic electrochemical stimulation in the specific locus (5).…”

Stimulation of the Hippocampus and Ovulation in the Rat: Specific or Nonspecific Effects

“…Although there were no significant differences between the group that underwent ECS at 13.00 h and the controls, there was an ap parent reduction in the mean ova per rat in this group. This could be due to the possibility that some of the rats in this group may have not fully recovered from the stressful ef- fects of stereotaxic surgery by the time that the critical peri od started (14.00h) and this may have had an effect on the preovulatory LH surge and ovulation [18,29]. Only when bilateral ECS was followed by the procedure for blood sam pling from the external jugular vein under ether anesthesia were the LH surge and ovulation significantly inhibited (ta ble II, fig-2).…”