The blockade of LH release by indomethacin

Downregulation of Deiodinase 3 is the earliest event in photoperiodic and photorefractory activation of the gonadotropic axis in seasonal hamsters

In seasonal rodents, reproduction is activated by a long photoperiod. Furthermore, maintaining an inhibitory short photoperiod for over 20 weeks triggers a spontaneous reactivation of the gonadotropic axis called photorefractoriness. Photoactivation is proposed to involve melatonin, hypothalamic thyroid hormones (TH) and (Arg) (Phe)-amide peptides. The mechanisms involved in photorefractoriness are so far unknown. We analyzed the dynamic changes in long photoperiod- and photorefractory-induced activation of reproduction in both Syrian and Djungarian hamsters to validate the current model of photoactivation and to uncover the mechanisms involved in photorefractoriness. We detected a conserved early inhibition of expression of the TH catabolizing enzyme deiodinase 3 (Dio3) in tanycytes, associated with a late decrease of the TH transporter MCT8. This suggests that an early peak of hypothalamic TH may be involved in both photoinduced and photorefractory reactivation. In photoactivation, Dio3 downregulation is followed by an upregulation of Dio2, which is not observed in photorefraction. The upregulation of (Arg) (Phe)-amides occurs several weeks after the initial Dio3 inhibition. In conclusion, we uncovered a so far unreported early inhibition of Dio3. This early downregulation of Dio3 is reinforced by an upregulation of Dio2 in photoactivated hamsters. In photorefractoriness, the Dio3 downregulation might be sufficient to reactivate the gonadotropic axis.

Gliotransmission by prostaglandin e(2): a prerequisite for GnRH neuronal function?

Over the past four decades it has become clear that prostaglandin E(2) (PGE(2)), a phospholipid-derived signaling molecule, plays a fundamental role in modulating the gonadotropin-releasing hormone (GnRH) neuroendocrine system and in shaping the hypothalamus. In this review, after a brief historical overview, we highlight studies revealing that PGE(2) released by glial cells such as astrocytes and tanycytes is intimately involved in the active control of GnRH neuronal activity and neurosecretion. Recent evidence suggests that hypothalamic astrocytes surrounding GnRH neuronal cell bodies may respond to neuronal activity with an activation of the erbB receptor tyrosine kinase signaling, triggering the release of PGE(2) as a chemical transmitter from the glia themselves, and, in turn, leading to the feedback regulation of GnRH neuronal activity. At the GnRH neurohemal junction, in the median eminence of the hypothalamus, PGE(2) is released by tanycytes in response to cell-cell signaling initiated by glial cells and vascular endothelial cells. Upon its release, PGE(2) causes the retraction of the tanycyte end-feet enwrapping the GnRH nerve terminals, enabling them to approach the adjacent pericapillary space and thus likely facilitating neurohormone diffusion from these nerve terminals into the pituitary portal blood. In view of these new insights, we suggest that synaptically associated astrocytes and perijunctional tanycytes are integral modulatory elements of GnRH neuronal function at the cell soma/dendrite and nerve terminal levels, respectively.

The effect of nonsteroidal anti-inflammatory drugs on ovulation: a prospective, randomized clinical trial

OBJECTIVE

To assess the effect of ibuprofen, a nonspecific inhibitor of prostaglandin synthesis, on ovulation.

DESIGN

Prospective, randomized, double-blind, placebo-controlled cross-over study.

SETTING

University Medical Center.

PATIENT(S)

Twelve normally cycling women between ages 20 and 40.

INTERVENTION(S)

Subjects were randomized to either oral ibuprofen (800 mg) or placebo three times per day, beginning when the maximum diameter of the leading follicle reached 16 mm by ultrasound, and continuing for 10 days total. The second cycle was a washout period, and in the third cycle, the subjects were crossed over to the alternate regimen from the first cycle. The probability of delayed follicular collapse was determined using the binomial distribution, and changes in P levels were compared using the paired t test.

MAIN OUTCOME MEASURE(S)

Urinary LH surge, follicular collapse by serial transvaginal ultrasonography, and serum midluteal P levels.

RESULT(S)

Eleven of 12 subjects detected an LH surge with both ibuprofen and placebo. Five of 11 women demonstrated a >or=2-day increase in time interval from detection of the LH surge to follicular collapse, and 3 of those 5 had been randomized to ibuprofen. This represents a 27% (3 of 11; 95% confidence limits: 1%, 53%) rate of delay for follicular collapse for ibuprofen. There was no difference in average midluteal P levels for ibuprofen or placebo.

CONCLUSION(S)

If ibuprofen inhibits follicular collapse, this effect is seen in a small group of study subjects, and this information should be clinically reassuring to patients who take nonsteroidal anti-inflammatory drugs. Serum midluteal P levels were unaffected by administration of ibuprofen.

[Reproduction physiology and prostanoids]

Prostanoids, which consist of prostaglandins (PGs) and thromboxane, are produced from arachidonic acid by cyclooxygenases (COXs) as a rate-limiting step, and they exert various biological actions. Classically, prostanoids are suspected to be closely related to female reproductive processes such as ovulation, luteolysis and uterine contraction, as well as pathological processes such as fever generation and pain modulation. Recently the cDNA cloning of a series of prostaglandin-synthesizing enzymes and receptors enabled us to clarify which isoform or subtype is involved in each reproductive process by generating individual gene-deficient mice. In late pregnancy, PGF2 alpha synthesized by COX-1 is essential for induction of parturition via luteolysis. Furthermore, impaired induction of COX-2 in the myometrium of PGF2 alpha receptor-deficient mice is accompanied with loss of parturition, suggesting that COX-2 is presumably responsible for producing uterotonic PGs. In early pregnancy, PGE2 synthesized by COX-2 induces the expansion of cumulus cells through EP2 receptor and contributes to ovulation and fertilization. These results may be useful in not only developing novel drugs in the reproductive area but also understanding and overcoming harmful reproductive side effects of classical and novel drugs in non-reproductive areas.

Anovulation in cyclooxygenase-2-deficient mice is restored by prostaglandin E2 and interleukin-1beta

Mice carrying a null mutation for either of the two cyclooxygenase (COX) isoenzymes, necessary for prostanoid production, exhibit several isotype-specific reproductive abnormalities. Mice deficient in COX-1 are fertile but have decreased pup viability, whereas mice deficient in COX-2 fail to ovulate and have abnormal implantation and decidualization responses. The present study identifies the specific contribution of each COX isoenzyme in hypothalamic, pituitary, and ovarian function and establishes the pathology and rescue of the anovulatory syndrome in the COX-2-deficient mouse. In both COX-1- and COX-2-deficient mice, pituitary gonadotropins were selectively increased, whereas hypothalamic LHRH and serum gonadotropin levels were similar to those in wild-type animals (+/+). No significant differences in serum estrogen or progesterone were noted among the three genotypes. Exogenous gonadotropin stimulation with PMSG and hCG produced a comparable 4-fold increase in ovarian PGE2 levels in wild-type and COX-1(-/-) mice. COX-2(-/-) mice had no increase in PGE2 over PMSG-stimulated levels. Wild-type and COX-1(-/-) mice ovulated in response to PMSG/hCG; very few COX-2(-/-) animals responded to this regimen. The defect in ovulation in COX-2 mutants was attributed to both an abnormal cumulus oophorum expansion and subsequent stigmata formation. Gonadotropin stimulation and concurrent treatment with PGE2 or interleukin-1beta resulted in ovulation of COX-2(-/-) mice comparable to that in COX-2(+/+), whereas treatment with PGF2alpha was less effective. Collectively, these data demonstrate that COX-2, but not COX-1, is required for the gonadotropin induction of ovarian PG levels; that COX-2-related prostanoids are required for stabilization of the cumulus oophorum during ovulation; and that ovulation can be restored in the COX-2(-/-) animals by simultaneous treatment with gonadotropins and PGE2 or interleukin-1beta.

Noradrenaline affects secretory function of corpus luteum independently on prostaglandins in conscious cattle

The aim of this study was to examine whether prostaglandins are involved in the effects of noradrenaline on corpus luteum (CL) function. To establish an effective dose of indomethacin (INDO) to prevent prostaglandin synthesis, different doses (120, 180, 240 and 300 mg) of drug were infused for 30 min on days 17-18 of the estrous cycle in four heifers and followed with 50 IU of OT. Plasma concentrations of 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) were measured, both to illustrate the concentrations of all prostaglandins and to establish the effective dose of INDO that can effectively block prostaglandins synthesis. In Experiment 2, on days 10-12 of the cycle, heifers (n = 6) were infused in a Latin square design with 4 mg of noradrenaline (NA) and pre-treated with 120 mg of INDO or with saline. In both cases, NA did stimulate progesterone and ovarian oxytocin secretion. We conclude that NA affects secretory function of the CL independently of prostaglandins.

Lack of effects of indomethacin on estradiol feedback control of luteinizing hormone in ovariectomized ewes

We tested the hypothesis that indomethacin, a potent inhibitor of prostaglandin synthesis, would modify estradiol's effects on tonic and surge concentrations of LH in chronically ovariectomized ewes during the anestrous season. Ewes (n = 21) were assigned randomly to one of four treatments: Vehicle+Blank (n = 5); Indomethacin+Blank (n = 6); Vehicle+Estradiol (n = 5); or Indomethacin+Estradiol (n = 5). On d=0 (hr = 0), ewes began to receive i.m. injections of either indomethacin (4 mg/kg body weight) or corn oil every 8 hr for 9 d. Blood samples were collected every 12 min for 6 hr beginning at -6 hr, +18 hr, and on day 8 (relative to initial injections of indomethacin or vehicle) to assess tonic patterns of secretion of LH. At +24 hr, ewes received blank- or estradiol-containing Silastic implants and were bled hourly for 48 hr. On day 9, ewes received 50 micrograms of GnRH i.v. and were bled hourly for 8 hr. Serum samples were assayed for LH. Indomethacin had no effect on the following parameters of LH secretion: 1) mean concentrations (ng/ml; 8.4 +/- .7 vs 8.9 +/- .8; P > .1), 2) pulse frequency/6 hr (4.5 +/- .4 vs 4.1 +/- .4; P > .1) or 3) pulse amplitude (ng/ml; 15.3 +/- 1.1 vs 14.9 +/- 1.2; P > 1). Estradiol elicited a surge of LH which began 18.9 +/- 1.7 hr after implant insertion, reached a mean peak concentration of 95.3 +/- 20.1 ng/ml, and did not differ with respect to indomethacin treatment (P > .1).(ABSTRACT TRUNCATED AT 250 WORDS)

Prostaglandins and premenstrual syndrome

We examined plasma PGF2 alpha, PGE, PGE2, TXB2 and 6-keto-PGF1 alpha at intervals throughout 3 menstrual cycles in 20 patients with PMS. Similar measurements throughout 1 menstrual cycle were made in 12 age-matched control women. The plasma concentration of PGF2 alpha in the late luteal phase was significantly lower in patients with PMS compared with that in the control subjects. The plasma concentrations of PGE in the middle follicular phase and middle luteal phase, PGE2 alpha in the middle follicular phase and TXB2 in the middle and late luteal phase were significantly higher in 20 patients compared with the values in the controls. A disturbance of PG metabolism may contribute to the etiology of PMS.

Pre-menstrual syndrome--are gonadotropins the cause of the condition?

It is proposed that premenstrual syndrome results from the action of elevated gonadotropin levels in various tissues of body other than their natural target organs. These levels are derived from an increased sensitivity to estrogen after pregnancy, childbirth, etc., particularly with respect to the positive feedback on gonadotropin release from the pituitary. Estrogen in conjunction with gonadotropin-releasing hormone (GnRH) releases excessive amounts of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) at ovulation and in the premenstrual phase (post-menopausal patients have greatly elevated gonadotropins and can also demonstrate cyclic symptoms). Gonadotropin action via adenylate cyclase in the adrenal cortex elevates cortisol, while antagonism of parathyroid hormone action on bone gives rise to hypocalcemia. The physiological and psychological symptoms may thereby be explained.

Influence of certain prostaglandin synthetase inhibitors on cytoplasmic estrogen receptors in the uterus

Prostaglandin synthetase inhibitors are widely used in the treatment of primary dysmenorrhea. They are thought to act by inhibiting endometrial synthesis of prostaglandins and subsequently altering endometrial receptor concentration. Since prostaglandins are known to vary with the menstrual cycle in women, implicating an effect associated with sex steroid hormones, we examined the influence of certain prostaglandin synthetase inhibitors on specific estrogen binding capacity of uteri from rats. Ibuprofen (Motrin), 25 mg/kg, indomethacin (Indocin), 15 mg/kg, mefenamic acid (Ponstel), 25 mg/kg, and sulindac (Clinoril), 40 mg/kg, were evaluated at 6 and 24 hours after injection. Specific estrogen-binding capacity was elevated twofold by mefenamic acid; the other agents showed no statistically significant effect. No alteration in the dissociation constant values of the estrogen receptors was observed with these agents. These data suggest that prostaglandin synthetase inhibitors do not influence the estrogen response mechanism in rodents.

Effects of systemic administration of indomethacin to cyclic ewes on endometrial concentrations of prostaglandins effects on estrous cycle length and on progesterone, luteinizing hormone and prolactin patterns

Experiments were designed to evaluate in cyclic sheep the effects of systemic administration of a prostaglandin synthetase inhibitor (Indomethacin). Indomethacin (100 mg, 3 times daily, S.C.) was administered from day 7 of the estrous cycle for 16 days to five ewes in which the cycle was synchronized as well as the cycles of five control ewes. All control ewes had cycles of approximately 17 days duration, but three of five Indomethacin treated ewes showed no estrous behavior before their slaughter at 23 days after induced ovulation. Autopsy revealed normal corpora lutea which had not undergone luteolysis, as confirmed by progesterone determination in blood. The two remaining Indomethacin treated ewes showed an estrous behavior on day 19 and 20 respectively together with a "preovulatory surge" of luteinizing hormone and prolactin which was not followed by follicular rupture. These results show that inhibition of PGF2 alpha synthesis by systemic administration of Indomethacin to the ewe is able to prevent luteolysis. When luteolysis did occur however, it was not followed by an ovulation despite a normal gonadotropin surge, indicating that inhibition of prostaglandin synthesis by systemic administration of Indomethacin interferes with the luteolysis and follicle rupture processes.

LHRH test in Bartter's syndrome before and during treatment with prostaglandin synthesis inhibitors

LHRH tests were performed in two children with Bartter's syndrome before and during treatment with prostaglandin synthesis inhibitors. Before treatment, in patient 1 both basal and peak FSH and LH levels were elevated; in patient 2 basal and peak FSH levels were above the normal range, while basal and peak LH levels were normal. During treatment with an inhibitor of prostaglandin synthesis, abnormal values decreased into the normal range. These results support a possible role of endogenous prostaglandins in regulating gonadotrophin secretion in humans.

Clinical applications in the area of contraceptive development

The ovary is not necessarily a prime locus for regulating reproductive function but in the process of understanding various aspects of ovarian function, opportunities have arisen to test both the role of specific functions in the reproductive process and the possible use of a given function as a site for contraceptive regulation. Better understanding of corpus luteum physiology from receptor site-gonadotropin interaction to natural luteolytic processes still hold promise for contraceptive development.

Corpus luteum function in the ewe: effect of PGF2alpha and prostaglandin synthetase inhibitors

A series of experiments were conducted to evaluate the effects of mode and frequency of administration and estrous cycle stage on the response of the cycling ewe to PGF2alpha. The effects of dexamethasone, arachadonic acid and prostaglandin synthetase inhibitors on estrous cycle length and plasma progesterone levels were also determined. Intramuscular administration of 5 or 10 mg of PGF2alpha, on days 8 and 9 after estrus (5 ewes/group), significantly (p less than .01) shortened the mean length of the estrous cycle and the interval from the end of treatment to estrus. Mean plasma progesterone levels, 24 hours after initial injection, were significantly (p less than .01) lowered. When administered on day 8 only, these doses were considerably less effective in shortening estrous cycle length or lowering plasma progesterone levels. Intravaginal administration of PGF2alpha, by polyurethane tampon, was also largely ineffective. Treatment of ewes with 10 mg of PGF2alpha, by polyurethanetampon, was also largely ineffective. Treatment of ewes with 10 mg of PGF2alpha i.m., on days 3 and 4 of the estrous cycle, resulted in a return to estrus in 2 days in 25% of the treated animals. Plasma progesterone levels of PGF2alpha-treated ewes were significantly lower than controls on the second, third and fourth days after the start of dosing. It would appear that PGF2alpha exerts a retarding effect on developing CL functionality. The prostaglandin synthetase inhibitors, aspirin, flufenamic acid and 1-p-chlorobenzylidene-2-methyl-5-methoxy-3-indenylacetic acid, were administered orally or parenterally for 16 days beginning on day 8 of the estrous cycle. These compounds failed to prolong estrous cycle length. Parenteral administration of dexamethasone did not result in PGF2alpha release in the cycling ewe, at least not in quantities sufficient to induce luteolytis. The prostaglandin precursor, arachadonic acid, also was not luteolytic when given parenterally to cycling ewes.

Prostaglandins, possible mediators of the effects of oestrogens on luteinizing hormone output

A possible mechanism for the positive and negative feed-back effects of oestrogen on luteinizing hormone (LH) output is suggested. It is proposed that oestrogens may influence prostaglandin synthesis in the hypothalamus in relation to LH releasing hormone (LH.RH) synthesis and release. Changes in oestrogen level or in the oestrogen to progesterone ratio may alter the ratios of prostaglandin concentrations in the hypothalamus, and so modulate LH.RH output through effects on sympathetic neurotransmission, protein synthesis or LH.RH release.

Production of prostaglandin Falpha in ewes following luteal regression induced with a prostaglandin analogue, Estrumate (cloprostenol; I.C.I. 80996)

A single injection (100 mug i.m.) of Estrumate (I.C.I. 80996) was used to induce luteal regression on day 8 of the estrous cycle in 3 sheep. Progesterone levels in the utero-ovarian vein and femoral artery had fallen within 6 h to less than 50% of the concentrations seen before injection of the analogue. Luteolysis was not associated with endogenous production of PGF. The concentration of PGF in the uteroovarian vein began to increase 27-39 h after the administration of Estrumate, reaching a mean maximum concentration of 1455pg/ml 48 h after Estrumate. The mean concentration of PGF in the utero-ovarian vein between 36-69 h after Estrumate was significantly greater than during the 24 h before Estrumate (control period) or during the 0-30 h immediately after injection (both P less than 0.001). The maximum secretion of estradiol and the pre-ovulatory LH peak occurred during the period of elevated PGF concentrations in the utero-ovarian veins. The possible importance of endogenous PGF production at this time is discussed.

Increased blood LH and testosterone after administration of prostaglandin F2alpha in bulls

Two types of experiments were conducted to determine the relationship of changes in blood luteinizing hormone (LH) and testosterone in bulls given prostaglandin F2alpha (PGF2alpha). Episodic surges of LH and testosterone occurred in tandem, apparently at random intervals, on the average once during the 8-hr period after bulls were given saline. In contrast, after sc injection of 20 mg PGF2alpha, blood serum testosterone increased synchronously to a peak within 90 minutes four-fold greater than pre-injection values, and the testosterone surges were prolonged about three-fold compared to those in controls. Each of the PGF2alpha-induced surges of testosterone was preceded by a surge of blood serum LH which persisted for about 45 minutes and peaked at about 3 ng/ml. In a second experiment, PGF2alpha was infused (iv, 0.2 mg/min) for 20 hr; blood plasma testosterone increased from 7.0+/-0.6 to 16.0+/-1.5 ng/ml within 2.5 hr and remained near this peak for 10 hr. Then testosterone gradually declined to about 9 ng/ml at the conclusion of the 20-hr infusion. These changes in testosterone were paralleled by similar changes in blood plasma LH, although LH declined 3 hr earlier than testosterone. Random episodic peaks of blood plasma LH and testosterone typical of untreated bulls resumed within 8 hr after conclusion of PGF2alpha infusion. In both experiments, the surge of testosterone after PGF2alpha was preceded by increased blood LH. We conclude that increased LH after administration of PGF2alpha probably caused the increased testosterone. However the mechanisms of these actions of PGF2alpha remain to be determined.

Prostaglandin F2alpha production by the brain during estrogen-induced secretion of luteinizing hormone

The arteriovenous difference in the concentration of prostaglandin F2alpha (PGF2alpha) across the brain of the anestrous sheep was measured before and during the induction of luteinizing hormone secretion with 17 beta-estradiol. The results indicate that (i) the brain in vivo is a significant source of PGF2alpha, (ii) the release of PGF2alpha from the brain occurs in pulses with a circhoral rhythm, and (iii) the process through which estrogen exerts its negative and positive feedback effects on luteinizing hormone secretion may involve amplitude modulation of PGF2alpha output from the brain.

Prostaglandins in reproductive physiology

The role of prostaglandins in reproductive physiology is reviewed with particular emphasis on their possible importance in ovulation in humans. A possible interaction between gonadal steroids, biogenic amines and prostaglandins at hypothalamic-pituitary level, in relation to the release of luteinizing hormone releasing factor, and LH, is discussed. Anomalies regarding the role of oestrogens in LH release are noted, and it is suggested that high oestrogen levels may release prostaglandins from the uterus and/or centrally in humans, in connection with the mid-cycle LH surge and ovulation. A hypothetical role for prostaglandins in sexual behaviour and premenstrual changes is discussed.

The hypotheses open up new areas for clinical research to establish the role of prostaglandins in human endocrinology. The need for measurement of prostaglandin metabolites in blood and urine is emphasized.