Differential effects of estradiol on the adrenocorticotropin responses to interleukin-6 and interleukin-1 in the monkey.

Endotoxin and the inflammatory cytokines interleukin (IL)-1 and IL-6 are potent activators of the hypothalamic-pituitary-adrenal (HPA) axis. Although estradiol (E(2)) has been shown to enhance the HPA response to certain types of stress, previous studies in the rodent have shown that HPA responses to endotoxin and to IL-1 were enhanced by ovariectomy and attenuated by E(2). The mechanisms underlying these observations are unclear, but there is evidence that E(2) may have direct inhibitory effects on IL-6 synthesis and release. Because endotoxin and IL-1 both stimulate IL-6, it is possible that the E(2)-induced suppression of the HPA response to endotoxin and IL-1 results from decreased IL-6 release. We have therefore examined the ACTH response to IL-6 and IL-1beta in six ovariectomized rhesus monkeys with and without 3 weeks of E(2) replacement. In the first study, plasma ACTH levels peaked at 60 min after iv injection of 6 microg recombinant human IL-6. Both the ACTH response, over time, and the area under the ACTH response curve were significantly higher in the E(2)-treated animals (P < 0.05). The peak ACTH level was 66 +/- 16 pg/ml without E(2) vs. 161 +/- 69 pg/ml with E(2). In the second study, iv infusion of recombinant human IL-1beta (400 ng) produced plasma IL-6 levels comparable with those seen after IL-6 injection in the first study. In the IL-1 study, however, there was a significant attenuation of the ACTH response, over time, in the E(2)-treated animals (P < 0.001); the peak ACTH level was 83 +/- 34 pg/ml vs. 13 +/- 4.4 pg/ml after E(2). The IL-6 response was similarly attenuated (P < 0.001); the peak IL-6 level was 614 +/- 168 pg/ml vs. 277 +/- 53 pg/ml after E(2) treatment. Our results demonstrate that physiological levels of E(2) enhance the ACTH response to IL-6 but attenuate the ACTH response to IL-1. The attenuated ACTH response to IL-1 was accompanied by a blunted IL-6 response. Our results suggest that the blunted HPA response to IL-1 can be explained, at least in part, by E(2)-induced alterations in IL-6 release. It remains to be determined whether E(2) affects other inflammatory mediators that also participate in this process.

Inhibitory effects of endotoxin on LH secretion in the ovariectomized monkey are prevented by naloxone but not by an interleukin-1 receptor antagonist.

Endotoxin (lipopolysaccharides, LPS), the pathogenic moiety of gram-negative bacteria, is a well-known trigger for the central release of cytokines. The objective of this study is to evaluate the effects of systemic endotoxin administration on LH and cortisol secretion in a non-human primate model and to investigate whether these endocrine effects are mediated by centrally released interleukin-1 (IL-1) using the receptor antagonist to IL-1 (IL-1ra). An additional objective is to investigate whether endogenous opioid peptides mediate these endocrine effects of LPS, using the opiate antagonist naloxone. The experiments were performed in long-term-ovariectomized rhesus monkeys. Blood samples for hormone determination were obtained at 15-min intervals for a period of 8 h, which included a 3-hour baseline period. Since the effective central dose of IL-1ra in the monkey was unknown, in the first experiment we tested the potency of several doses of this antagonist in preventing the effects of centrally administered IL-1alpha, a cytokine which is known to inhibit LH and stimulate cortisol release. Rhesus monkeys received a 30-min intracerebroventricular infusion of IL-1alpha (4.2 microg/30 min) alone or together with various doses of IL-1ra (30-180 microg/h i.c.v.). IL-1ra infusion was initiated 1 h before IL-1 and extended over the experimental period. As previously reported, IL-1alpha induced a significant inhibition of LH, to 36.5 +/- 3.3% (mean +/- SE) by 5 h as a percentage from the 3-hour baseline. This inhibitory effect was reversed by cotreatment with the 180 microg/h dose of IL-1ra (to 82.5 +/- 3.8% by 5 h; NS vs. saline) but not with the lower doses. IL-1 stimulated cortisol release to 165.9 +/- 7.7%, but this increase was prevented by IL-1ra (66.6 +/- 8.9%; p < 0.05 vs. IL-1, NS vs. saline). In the second experiment, LPS (50 microg) was administered intravenously, alone or in combination with intracerebroventricular IL-1ra infusion. LPS induced a significant decrease in LH secretion (to 57.1 +/- 5.2%). These effects were not reversed by intracerebroventricular administration of IL-1ra (52.5 +/- 9.6%). Cortisol secretion increased in response to LPS, but this stimulatory effect was not affected by IL-1ra (178.3 +/- 13.4 vs. 166.9 +/- 5.7%). There were no effects of IL-1ra alone. In experiment 3, we investigated whether the opiate antagonist naloxone reverses the endocrine effects of endotoxin. Both LPS (50 microg) and naloxone (5-mg bolus + 5 mg/h) were infused intravenously. Naloxone was effective in preventing the inhibitory effect of LPS on LH (to 124.6 +/- 22.1%, NS vs. saline) but not the increase in cortisol (to 166.7 +/- 16.7%; p < 0.05 vs. saline, NS vs. LPS). Naloxone alone has no significant effect on LH or cortisol secretion. These data demonstrate that, in the ovariectomized monkey, a systemic inflammatory/immune- like stress challenge acutely inhibits tonic LH secretion while concomitantly stimulating cortisol release. Although endotoxin is known to affect central cytokine release, these endocrine effects do not require a mediatory role of central IL-1 in the primate. In contrast, endogenous opioid pathways appear to be involved in this process.

Stress and the menstrual cycle: short- and long-term response to a five-day endotoxin challenge during the luteal phase in the rhesus monkey.

Previously, we reported that in the rhesus monkey a 5-day inflammatory-like stress during the early-mid follicular phase acutely stimulates the hypothalamic-pituitary-adrenal axis and exerts effects on the hypothalamic-pituitary-gonadal axis, delays folliculogenesis and in some animals decreases luteal function in the post-treatment cycle. Because the endocrine environment at the time of the stress may influence the response to the stress, we now investigate the acute and long-term responses to a similar stress challenge during the luteal phase of the menstrual cycle, at a time of progesterone dominance. Nine monkeys with normal cycles were injected with endotoxin (lipopolysaccharide; LPS, 150 microg i.v.) twice a day for 5 days starting on days 4-8 after the LH peak. Blood samples were taken at hour 3 and hour 8 after each morning LPS injection to monitor the acute gonadotropin and cortisol responses. To verify cyclicity, menses were checked every day, and daily blood samples were taken for estradiol and progesterone measurement. Two control cycles, the LPS treatment cycle, and two post-treatment cycles were documented. Endotoxin activated the adrenal axis: mean (+/-SE) cortisol secretion was significantly increased at hour 3 after the first morning LPS injection (74.1 +/- 4.9 vs. 24.1 +/- 1.8 microg/dL in the control; P < 0.05) and remained elevated at hour 8. This response decreased progressively with time: on day 5 of LPS treatment, the cortisol level was still significantly higher than control at hour 3 (38.5 +/- 5.0 microg/dL; P < 0.05) but had returned to the control concentration by hour 8 (days 3-5 of LPS). Mean integrated progesterone through the luteal phase of the LPS treatment cycle was significantly decreased (33.5 +/- 3.3 ng/ml vs. 48.9 +/- 3.7 and 54.0 +/- 4.9 in the two control cycles; P < 0.05), but luteal phase length remained unchanged. When compared with control levels on the same day of the luteal phase, about one third of LH and FSH values were lower than one SD below mean control levels. LPS administration had no effect on the two post-treatment cycles, except that integrated luteal progesterone in 3 out of 9 monkeys was still reduced in post-treatment cycle 1. There were no differences in follicular phase length and preovulatory estradiol peaks between control cycles and post-treatment cycles. When compared with our previous study, the results illustrate specific responses to stress at different phases of the menstrual cycle and support the notion that a moderate short-term inflammatory-like stress episode has the potential to subtly alter critical aspects of cyclicity.

Stress and the menstrual cycle: relevance of cycle quality in the short- and long-term response to a 5-day endotoxin challenge during the follicular phase in the rhesus monkey.

The notion that stress activates central and peripheral pathways to inhibit the menstrual cycle is well accepted, but the initial processes through which this occurs have not been investigated. This study uses a relevant nonhuman primate model to document the cyclic endocrine effects imposed by a moderate short-term stress episode in the follicular phase. The stress paradigm is a 5-day inflammatory/immune-like challenge produced by the administration of bacterial endotoxin [lipopolysaccharide (LPS)], which, through the release of endogenous cytokines and other mediators, induces a physiopathological response similar to a bacterial infection. LPS was administered iv twice daily for 5 days starting on days 2-8 of the follicular phase. The stress challenge resulted in a significant lengthening of the follicular phase in all monkeys. Two distinct groups were observed. In group 1 (n = 5), the mean (+/- SE) length of the follicular phase in the LPS-treated cycle was significantly increased, from 10.2 +/- 0.2 in control cycle 2 to 30.8 +/- 4.3 days (except in one monkey that had a 4-month amenorrheic interval). In group 2 (n = 5), the length of the follicular phase significantly increased but not to exceed the duration of the LPS treatment (9.7 +/- 1.1 vs. 13.6 +/- 1.2). Estradiol concentrations decreased significantly after LPS in group 1 (34.8 +/- 5.5 vs. 16.2 +/- 6.5 pg/mL) and remained suppressed after the challenge. In group 2, estradiol levels remained stationary throughout the 5-day LPS treatment (26.0 +/- 6.5 vs. 25.6 +/- 3.9). Compared with control values at a similar stage of the follicular phase, most LH and FSH values during LPS treatment were higher than controls. Estradiol and gonadotropin surges were delayed by LPS treatment for a varying length of time according to each grp. Significant differences in integrated luteal progesterone concentrations characterized control cycles of groups 1 and 2 (group 1: 36.5 +/- 1.5, group 2: 47.5 +/- 2.6). In group 1, there were no further effects of LPS on luteal progesterone during the treatment and two post-LPS cycles. In contrast, in group 2, integrated luteal progesterone concentrations were significantly decreased in post-LPS cycle 1 (to 36.0 +/- 4.4). Cortisol significantly increased at hour 3 after each morning LPS injection but the amplitude of the response decreased over the 5-day period. Progesterone increased significantly by hour 3 after the first LPS injection but remained unchanged after subsequent LPS administration. Our data demonstrate that a 5-day inflammatory-like episode during the follicular phase can delay folliculogenesis and that damage to this process is intensified in individuals who already demonstrate a subtle cyclic degradation, in the form of decreased progesterone secretion in the luteal phases preceding the stress episode. Long-term endocrine effects, in the form of decreased luteal secretory activity in the first poststress cycle, are observed in normally cycling individuals, suggesting that inadequacy of the luteal phase may represent the first stage in the damage that a stress episode can inflict upon the normal menstrual cycle.

Tonic support of luteinizing hormone secretion by adrenal progesterone in the ovariectomized monkey replaced with midfollicular phase levels of estradiol.

Although it is known that progesterone facilitates the estradiol-induced gonadotropin surge at midcycle, its effect on LH secretion at other times of the follicular phase remains to be investigated. In this study, we investigate the role of progesterone on tonic LH secretion in the ovariectomized primate replaced with estradiol at levels representative of the follicular phase. The experiments were performed in nine ovariectomized rhesus monkeys, either unreplaced with estradiol or after a 5-day estradiol therapy to mimic early follicular (10-36 pg/mL; low dose) and midfollicular (medium dose; 40-75 pg/mL) concentrations. We used two antiprogesterone compounds, RU-486 (5 mg) and ORG-31806 (1 mg), to antagonize endogenous progesterone activity and studied their acute effects on LH secretion in each group. LH concentrations were measured at 15-min intervals for a 3-h baseline period and during a 5-h period after antagonist administration. LH concentrations remained unchanged after either antiprogesterone compound or diluent (ethanol) administration in the estrogen-unreplaced monkeys or after low dose estradiol replacement. However, both antiprogesterone compounds significantly decreased LH secretion in monkeys pretreated with the medium dose of estradiol; by 5 h, the mean (+/-SE) areas under the LH curve were 54.8 +/- 4.1% and 64.0 +/- 4.2% after RU-486 and ORG-31806, respectively (P < 0.05 vs. unreplaced and low dose estrogen-replaced groups). To exclude the possibility that the LH response reflects an agonist action of the progesterone antagonist, LH responses to progesterone infusions (at three doses to reproduce preovulatory, luteal, and pharmacological levels) were also examined in monkeys pretreated with midfollicular levels of estradiol. In none of these was there a decrease in LH; rather, progesterone infusions resulted in an increase in LH secretion in all three groups (to 115-194% of baseline in seven of eight monkeys). Finally, we determined that at the dose used in our protocol, neither of the two progesterone antagonists was able to prevent dexamethasone-induced cortisol suppression, thus excluding the possibility that results after progesterone antagonist administration may reflect a putative antiglucocorticoid activity of these compounds. When the doses of the antiprogesterone compounds were increased 6 times, only RU-486 counteracted the effect of dexamethasone on cortisol. In summary, our data indicate support by progesterone of tonic LH secretion in the nonhuman primate under estrogenic conditions similar to the midfollicular phase of the menstrual cycle. Significantly, because the experiments were performed in ovariectomized monkeys, and endogenous progesterone was most probably of adrenal origin, the data also demonstrate a role of the hypothalamo-pituitary-adrenal axis in support of gonadotropin secretion.

The luteinizing hormone but not the cortisol response to arginine vasopressin is prevented by naloxone and a corticotropin-releasing hormone antagonist in the ovariectomized rhesus monkey.

In the primate, arginine vasopressin (AVP) is known to activate the hypothalamo-pituitary-adrenal axis and to inhibit LH secretion. In the present study, we investigate the role of the endogenous opioid peptides and corticotropin-releasing hormone (CRH) in these processes. Adult ovariectomized rhesus monkeys bearing a chronic cannula in the lateral ventricle for intraventricular (i.c.v.) infusion were used. In experiment 1, the effects of 5-hour i.c.v. infusions of saline (n = 7), AVP (50 micrograms/h, n = 7), naloxone (2 mg bolus + 2 mg/h i.v., n = 4) and AVP plus naloxone (n = 4) on LH and cortisol secretion were investigated. As compared to saline and naloxone alone, LH pulse frequency was significantly decreased by AVP (p < 0.05) and by 5 h, the mean LH expressed as a percentage from the 3-hour baseline was also significantly reduced (saline 100.9 +/- 5.1%; naloxone 112.3 +/- 2.9%; AVP 63.3 +/- 8.2%). Coadministration of naloxone abolished the effects of AVP on LH (107.3 +/- 12.1% of baseline). AVP increased cortisol secretion (p < 0.05 vs. baseline), but naloxone did not prevent the increase. In experiment 2, the LH and cortisol responses to AVP were compared in the absence and presence of a CRH antagonist. The antagonist was infused intraventricularly at two doses: 60 and 180 micrograms/h. At both doses, the inhibitory effect of AVP on LH was significantly attenuated (at 4 h, 86.9 +/- 3.2% of baseline; NS vs. saline). However, the CRH antagonist did not block the AVP-induced increase in cortisol. The results confirm previous evidence in the primate of a role of vasopressin in inhibiting the hypothalamo-pituitary-gonadal axis and demonstrate a role of hypothalamic opioid peptides in this process. They also demonstrate that, although CRH is a prerequisite for AVP's action on the hypothalamo-pituitary-gonadal axis, AVP can stimulate the adrenal axis in the primate in the presence of decreased CRH activity.

Interleukin-1 stimulates luteinizing hormone release during the midfollicular phase in the rhesus monkey: a novel way in which stress may influence the menstrual cycle.

We previously demonstrated an inhibitory effect of an inflammatory/immune-like stress challenge, as simulated by intracerebroventricular interleukin-1 alpha (IL-1 alpha) administration, on LH secretion in the ovariectomized rhesus monkey. This was shown to be the result of activation of the hypothalamo-pituitary-adrenal axis by the cytokine. In the present experiments, we have investigated LH and cortisol responses to IL-1 alpha administration in intact monkeys during the follicular phase of the menstrual cycle. Eleven adult rhesus monkeys, bearing an intraventricular cannula for cytokine administration, were used. Cycle parameters were monitored in the preceding control cycles, during the experimental cycles, as well as in subsequent cycles by daily measurements of estradiol and progesterone concentrations and daily menstruation checks. The experiments were performed according to estradiol concentrations: estradiol, 5-38 pg/mL, group 1, early follicular; and estradiol, 50-64 pg/mL, group 2, midfollicular. The effects of intracerebroventricular saline (30 microL/30 min) or IL-1 alpha (4.2 micrograms/30 min) infusions on LH, FSH, and cortisol were compared. After saline infusion, there was no significant change in LH secretion. No significant acute change in LH occurred after IL-1 alpha administration in group 1 (to 0.98 +/- 0.12 ng/mL by 5 h from a baseline of 0.85 +/- 0.12); however, the length of the follicular phase was significantly prolonged in these early follicular phase animals. IL-1 significantly increased LH release in monkeys during the midfollicular phase (group 2; to 2.45 +/- 0.45 ng/mL by 5 h from a baseline of 0.88 +/- 0.11; P < 0.05 vs. baseline and all other groups). FSH was also increased in the latter group. When the experimental observation period was extended to 18 h after IL or saline treatment in eight monkeys, LH and FSH consistently increased after IL administration in three of four animals (to 4.3 +/- 0.7 ng/mL), and in one animal, a surge-like gonadotropin release occurred, whereas no further changes occurred after saline. IL-1 alpha, but not saline, significantly increased cortisol and progesterone release. In conclusion, our results demonstrate that dependent on estradiol concentrations, an acute inflammatory/immune-like stress challenge can affect the hypothalamo-pituitary-ovarian axis differently, either by stimulating gonadotropin release in the presence of significant estradiol concentrations or by inhibiting follicular maturation when given in the presence of low estradiol levels.

A 5-day estradiol therapy, in amounts reproducing concentrations of the early-mid follicular phase, prevents the activation of the hypothalamo-pituitary-adrenal axis by interleukin-1 alpha in the ovariectomized rhesus monkey.

In a previous report, we have shown that intracerebroventricular (icv) administration of the cytokine interleukin-1 alpha (IL-1 alpha) in the ovariectomized (OVX) rhesus monkey results in the acute activation of the hypothalamo-pituitary-adrenal (HPA) axis and the inhibition of LH and FSH secretion. Here, we compare the cortisol response to IL-1 alpha administration in OVX monkeys and in OVX animals replaced with estradiol (E) to reproduce E concentrations typical of the early-mid follicular phase. Cortisol, LH and FSH were measured after an icv infusion of physiological saline or IL-1 alpha (2.1 or 4.2 micrograms/30 min) in both groups. E-containing capsules were implanted sc 5 days prior to the experiment. In OVX, E concentrations were < 5 pg/ml. Cortisol concentrations decreased throughout the afternoon after saline infusion (to 49.7 +/- 5.1% of baseline at 5 h; n = 7), but increased significantly after IL-1 alpha to 158.3 +/- 13.8% (n = 7). In OVXE, cortisol also declined after saline (to 76.4 +/- 16.2%; n = 5). There were 2 types of response to IL-1 alpha: in grp 1 (mean E: 18.0 +/- 0.7 pg/ml), the cortisol response was similar to that in OVX (160.8 +/- 17.0%; n = 5), while in grp 2 (E: 30.7 +/- 3.1 pg/ml), the cortisol response was absent (66.6 +/- 7.2% of baseline at 5 h; NS vs saline in OVXE; n = 7). The cortisol response to IL-1 alpha was restored in 2 monkeys when E was increased to > 100 pg/ml, confirming our previous observations.(ABSTRACT TRUNCATED AT 250 WORDS)