LH Episodes Research Articles

Endocrine patterns of the post-partum cow

Summary. Milked dairy cows generally have a shorter post-partum interval to ovarian cyclicity than suckling dairy or beef cows. In milked and suckling cows, there is a strong seasonal influence with spring-calving cows remaining anoestrous longer. Increasing the suckling intensity further delays the onset of ovarian cyclicity, probably by increasing the frequency or strength of its inhibitory influence on hypothalamic activity. Plasma FSH levels rise in most cows 5–10 days after calving and thereafter the random changes observed have little relationship to the onset of cycles. Recovery of FSH release therefore occurs earlier post partum than recovery of LH release. Hyperprolactinaemia is not a cause of reproductive failure in milked or suckling cows because there is no correlation between plasma prolactin levels and the onset of ovarian cycles. Plasma LH concentrations undergo significant changes directly related to the initiation of ovarian cycles, with low plasma levels immediately post partum, followed by an increase in basal secretion and the development of clear LH episodes. This pulsatile pattern appears earlier in dairy than in beef cows and is further delayed by suckling compared to milking. Before the first ovulation there is an increased frequency and peak height of LH episodes leading to a rise in plasma LH levels and eventually to a preovulatory-type LH surge which results in the first ovulation. These changes in the pattern of LH release appear definitive in the initiation of ovarian activity in post-partum cows.

Frequency of low serum LH is associated with increased early pregnancy loss in IVF/ICSI cycles

The role of LH during ovarian stimulation remains uncertain. Previous studies defined the low LH group using a single LH measurement on a predefined day of stimulation possibly not reflecting the entire follicular phase. This study retrospectively collected data from 619 IVF/ICSI cycles with GnRH antagonist and recombinant FSH. The low LH group was defined as LH concentration ≤0.8 mIU/ml at any time during the cycle. Pregnancy results were compared between patients with one episode of low LH or more than two episodes of low LH (study group) and those without low LH (control group). There was no difference in fertilization rates between the two groups (67.5 ± 1.7% versus 68.8 ± 1.0%, respectively). The implantation rates (20.4% versus 25.2%), clinical pregnancy rates (43.9% versus 45.2%) and live-birth rates (LBR) (23.7% versus 30.4%) appeared lower in the study group, but the differences were not significant. In the study group, there were significantly increased early pregnancy loss rates (31.1% versus 16.3%, P = 0.012). The odds of early pregnancy loss increases by 1.55 fold for increased episodes of low serum LH (P = 0.029). Whether the adverse outcome is due to impaired oocyte quality or an endometrial component deserves further investigation.

Effects of metformin on inappropriate LH release in women with polycystic ovarian syndrome and insulin resistance

The role of hyperinsulinaemia in neuroendocrine abnormalities in polycystic ovarian syndrome (PCOS) is controversial. The present study applied frequent blood sampling to assess the response of LH to metformin treatment in insulin-resistant women with PCOS. Thirteen predominantly overweight women with PCOS were studied before and after treatment with 1.5 g/day metformin for 3 months. Serum LH and testosterone were measured every 10 min for 10 h; LH was measured for an additional 2 h after gonadotrophin-releasing hormone (GnRH) administration. LH pulses were characterized by cluster analysis, secretory LH episodes by a deconvolution procedure, and synchronicity of paired LH-testosterone concentrations by lag-specific cross-correlation. After treatment, basal LH concentrations, amplitude of LH pulses, LH secretory amplitude, response to exogenous GnRH, and basal testosterone concentrations significantly decreased in seven patients, whereas in the remaining women these parameters remained unaltered. Before treatment, decreased coordinate LH and testosterone release was manifested by all patients; metformin treatment led to re-establishment of the feed-back control of testosterone on LH secretory rates by −20 to 0 min. Treatment did not modify the glucose:insulin ratio or serum insulin concentrations. In conclusion, administration of metformin allowed the identification of two subsets of PCOS women in whom neuroendocrine abnormalities may improve independently of the presence of insulin resistance or hyperinsulinaemia.

Episodic gonadotropin secretion in the mature fowl: serial blood sampling from unrestrained male broiler breeders (Gallus domesticus).

Forty-week-old male broiler breeders were used in two experiments. Males were reared as recommended by the breeder, housed in individual cages, and cannulated to facilitate blood sampling. In experiment 1, blood samples were collected at 10- min intervals for 4 h commencing the day of cannulation (Day 0) and for 12 h on each of Days 1 and 2. In experiment 2, blood samples were collected at 10-min intervals for 8 h on Day 1. After centrifugation, plasma was stored at -20 degrees C until LH, FSH (experiment 1 and 2), testosterone, and corticosterone (experiment 1) concentrations were determined by RIA. Different statistical methods used to identify hormone secretion profiles revealed a characteristic pulsatile pattern of LH and FSH in plasma. However, LH pulses were more frequent and had greater amplitude than FSH pulses. Less than 32% of the FSH pulses were associated with LH episodes. Conversely, the association between LH and testosterone pulses averaged 83% in birds with testis weight greater than 10 g. Concentrations of corticosterone tended to increase after cannulation and remained elevated for only 3-4 h. Our data indicate that LH, FSH, and testosterone secretion is pulsatile in male broiler breeders. Additionally, LH pulses are associated with testosterone episodes but not with FSH pulses. The pulsatile pattern of FSH secretion, which is unique from those of LH, in adult males suggests that FSH secretion is independently regulated in the adult male fowl.

Effects of ovarian input on GnRH and LH secretion immediately postovulation in pony mares

The potential involvement of ovarian factors in regulating GnRH and LH postovulation was studied in ovarian intact (Group 1; n=3) and ovariectomized (OVX; Group 2; n=3) mares (OVX within 12 hr of ovulation). Blood samples were collected every 10 min for 6 hr from jugular vein (JV) and intercavernous sinus (ICS) during estrus and on Day 8 postovulation for LH and GnRH analysis. Additionally, JV samples were collected twice daily (12-hr intervals) for 30 days for LH and progesterone (P 4) analysis. A significant treatment × day effect (P<0.0001) describes declining plasma LH concentration in intact mares, and regression analysis indicated that response curves were not parallel (P<0.001). Plasma LH concentrations remained elevated in OVX mares. LH increased further in OVX mares by Day 8 post-OVX (P<0.06), reflecting the increased (P<0.07) LH episode amplitude. GnRH decreased from estrus to Day 8 in both groups reflecting an effect of sampling period (P<0.03). GnRH episode amplitude declined (P<0.08) from estrus (62.8±3.1 pg/mL) to Day 8 (46.3±3.1 pg/mL) in OVX mares, but not in control mares (intact estrus, 36.5±6.4; intact Day 8, 37.5±7.3; OVX estrus, 62.8±3.1; OVX Day 8, 46.3±3.1 pg/mL). In conclusion, we propose that postovulatory LH decline requires ovarian feedback in mares, and that OVX alters GnRH secretory dynamics such that LH concentrations does not decline postovulation and, in fact, is further elevated with time after OVX.

Effect of stress-like concentrations of cortisol on the feedback potency of oestradiol in orchidectomized sheep

The effect of stress-like concentrations of cortisol on oestradiol-induced change in LH secretion and GnRH receptor expression was evaluated in orchidectomized sheep (wethers). Twenty-four wethers were assigned at random to one of the four treatment groups in a 2x2 factorial design (n=6 wethers/group). Wethers received cortisol (90 microg/kg/h; groups 2 and 4) or a comparable volume of cortisol delivery vehicle (groups 1 and 3) by continuous infusion for 48 h. During the final 24 h of infusion, wethers received oestradiol (6 ng/kg/h; groups 3 and 4) or oestradiol delivery vehicle (groups 1 and 2). The pattern of LH secretion was assessed during a 3-h period of intensive blood collection beginning 21 h after initiation of oestradiol infusion. Although neither cortisol nor oestradiol alone affected (P>0.05) mean serum concentration of LH or LH pulse frequency, serum LH and the frequency of secretory episodes of LH were significantly reduced (P<0.05) in wethers receiving cortisol and oestradiol in combination. Anterior pituitary tissue was collected at the end of the infusion period. Oestradiol increased (P<0.05) tissue concentrations of GnRH receptor and GnRH receptor mRNA. Although cortisol alone did not affect (P>0.05) basal concentrations of receptor or receptor mRNA, the magnitude of oestradiol-induced increase in GnRH receptor and GnRH receptor mRNA was significantly reduced in wethers receiving cortisol and oestradiol concurrently. Conversely, steady-state concentrations of mRNA encoding the LHbeta and FSHbeta subunits were increased (P<0.05) in wethers receiving cortisol. These observations demonstrate that stress-like concentrations of cortisol act in concert with oestradiol to suppress LH secretion. In addition, cortisol blocks oestradiol-dependent increase in pituitary tissue concentrations of GnRH receptor and GnRH receptor mRNA.

Effect of stress-like concentrations of cortisol on gonadotroph function in orchidectomized sheep.

The effect of stress-like concentrations of cortisol (C) on the feedback potency of estradiol (E2) was assessed using 32 orchidectomized sheep (wethers) assigned at random to 1 of 4 treatment groups in a 2 x 2 factorial design. Wethers received C (3. 6 mg/50 kg per hour; groups 2 and 4) or a comparable volume of C delivery vehicle (groups 1 and 3) as a continuous infusion for 7 days. During the final 48 h of infusion, wethers received E2 (0.3 microg/50 kg/h; groups 3 and 4) or E2 delivery vehicle (groups 1 and 2). The pattern of LH secretion was assessed during a 4-h period of intensive blood collection beginning 44 h after initiation of E2 infusion. Gonadotroph responsiveness (LH secretion induced by GnRH challenge [500 ng, i.v.]) was determined 48 h after E2 delivery was begun. Although the frequency of secretory episodes of LH was not affected (p > 0.05) by infusion of C or E2 alone, LH pulse frequency was significantly decreased in wethers receiving C and E2 in combination. In contrast, neither the magnitude of basal gonadotroph responsiveness nor the extent of E2-dependent augmentation of responsiveness was significantly affected by stress-like concentrations of C. In a second experiment, the effect of C on the magnitude of E2-induced increase in pituitary concentration of GnRH receptor and GnRH receptor mRNA was assessed using 32 additional wethers. Continuous infusion of E2 for 48 h increased (p < 0.05) tissue concentrations of GnRH receptor and GnRH receptor mRNA. Concurrent delivery of C did not affect (p > 0.05) E2-induced increase in GnRH receptor mRNA but significantly reduced the magnitude of the E2-dependent increase in pituitary concentration of GnRH receptor. Collectively, these data indicate that stress-like concentrations of C enhance the negative feedback potency of E2 and reduce estrogen-dependent augmentation of the concentration of GnRH receptor in pituitary tissue.

The corpus luteum insufficiency: a multifactorial disease.

The pulsatile release pattern of LH during the entire menstrual cycle is well defined; however, the response of corpora lutea to these LH pulses in patients suffering from corpus luteum insufficiencies (CLI) is largely unknown. Patients suffering from CLI were selected from infertile patients on the basis of low progesterone (P < 25 nmol/L) in a blood sample withdrawn during a monitoring cycle. During the next cycle, nine blood samples were collected during the follicular and luteal phase and follicular development was assessed by vaginal sonography. Of 109 patients who had a CLI in the monitoring cycle, 55 had a CLI again, and 38 women agreed to undergo assessment of pulsatile hormone secretion. These women again had P < 25 nmol/L at days 6 and 7 of the luteal phase and blood samples were withdrawn through antecubital vein catheters from 0900-1700 h at 10-min intervals on days 7, 8, or 9 following ovulation. From 38 patients with such defined CLI, 16 (42%) had no LH episode and significantly lower basal LH levels in comparison with 14 control subjects. Thirteen (34%) of the patients had normal appearing LH episodes despite too low P and E2 concentrations, but their CL did not react to the LH episodes. The remaining 9 patients (24%) had normal LH episodes; their CL reacted to these episodes, but their basal P levels were too low. In all blood samples LH was not only determined using an immunoassay but also by the mouse Leydig cell testosterone production bioassay. It could be established that no CLI exists, which is due to the release of bioinactive LH. It is anticipated that the differentiation of three different types of CLI, one of hypothalamic and two of ovarian origin, may allow the development of differential diagnostic and therapeutic tools in the future.

Effects of pulsatile pituitary adenylate cyclase activating polypeptide (PACAP) on gonadotropin secretion and subunit mRNA levels in perifused rat pituitary cells.

The effects of pituitary adenylate cyclase activating polypeptide (PACAP) administered intermittently on gonadotropin secretion and subunit mRNA levels in anterior pituitary cells from 7wk old intact and orchidectomized rats were studied. Cells were perifused for 9 h with hourly pulses of 2.5 nM GnRH or 10 nM PACAP, or with medium alone. Pulsatile PACAP initiated episodes of LH, FSH and alpha-subunit secretion, but was much less effective than GnRH. Responsiveness declined with repeated pulses of PACAP, although interpulse secretion increased gradually throughout the experiment. PACAP was a slightly more effective stimulator of LH release by pituitary cells from castrated than intact rats. At the completion of perifusion, pituitary RNA from castrated rats was extracted for measurement of gonadotropin subunit mRNA levels. Pulsatile PACAP stimulated alpha-subunit and LHbeta mRNA levels but did not affect FSHbeta mRNA. By contrast, continuous PACAP increased alpha-subunit mRNA levels, but suppressed FSHbeta mRNA without affecting LHbeta mRNA. We conclude that pulsatile PACAP is a relatively ineffective stimulator of gonadotropin secretion when administered alone, and regulates gonadotopin subunit gene expression quite differently than continuous PACAP. We propose that the mode of PACAP secretion in vivo may be a determinant of the differential expression of the gonadotropin subunit genes.

Gonadotropin secretion in ovariectomized Chinese Meishan and hybrid large white gilts; responses to challenges with estradiol benzoate, gonadotropin-releasing hormone, or porcine follicular fluid.

Castrated Meishan (MS) and hybrid Large White (hLW) gilts were used in a series of challenge experiments to establish differences in the control of gonadotropin secretion. Acutely ovariectomized gilts (72 h) were injected i.m. with 10 micrograms/kg estradiol benzoate (EB) and serially bled for evaluation of estradiol clearance from the blood and patterns of LH and FSH release. Estradiol was more rapidly metabolized from the circulatory system of the acutely ovariectomized MS gilts than from the hLW gilts; as a consequence, hLW gilts had higher concentrations of estradiol than MS gilts at 24-32 h (p < 0.05) and 48-60 h (p < 0.01) post-EB treatment. The hLW but not the MS gilts exhibited a classic negative/positive LH response to EB; MS gilts responded with a random release of large episodes of LH. Plasma FSH concentrations were consistently greater (p < 0.05) in acutely ovariectomized MS gilts than in hLW gilts. Both breeds demonstrated a slight negative FSH response to EB and then exhibited increased variability in plasma FSH with time after treatment. Mean plasma LH was immediately elevated in chronically ovariectomized (> 14 days) hLW and MS gilts given 1 microgram/kg of GnRH i.m., but the magnitude of the LH response was greater (p < 0.01) in the hLW gilts. Comparable differences (p < 0.01) in FSH secretion were also observed, indicating the presence of greater pools of releasable FSH and LH in the hLW gilts, or a greater sensitivity to GnRH.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of pituitary adenylate cyclase-activating polypeptide on gonadotropin secretion and subunit messenger ribonucleic acids in perifused rat pituitary cells.

Pituitary adenylate cyclase-activating polypeptide-38 (PACAP38) is a neuropeptide related to vasoactive intestinal peptide-secretin-glucagon which stimulates adenylate cyclase in cultured rat pituitary cells and stimulates LH and FSH release in vitro and in vivo. Because the cAMP-protein kinase-A pathway regulates the gonadotropin subunit messenger RNAs (mRNAs) and modulates GnRH-stimulated gonadotropin secretion in vitro, we examined the effects of PACAP38 on gonadotropin secretion and subunit mRNA levels. Anterior pituitary cells were prepared from 7-week-old male rats castrated at 5 weeks of age. In monolayer cultures stimulated with GnRH, 0.1-10 nM PACAP38 decreased (P < 0.05) the EC50 for GnRH dose-dependently without affecting the maximum LH secretory response. Cells were next stimulated with 1-min pulses of 2.5 nM GnRH every hour for 9 h in the absence or presence of 10 nM PACAP38, which was perifused continuously. The amplitude of GnRH-induced LH, FSH, and alpha-subunit secretory episodes from PACAP38-treated cells rose (P < 0.01) gradually to 233 +/- 54%, 197 +/- 44%, and 378 +/- 104%, respectively (mean +/- SEM; n = 5 experiments), of the value for control cells lacking PACAP38. This enhancement was sustained for at least 3 h after PACAP38 was removed from the perifusion medium. With PACAP treatment, interpulse secretion of LH and alpha-subunit increased gradually (P < 0.01) to 174 +/- 21% and 212 +/- 64% of the value for chambers stimulated with GnRH alone (control), respectively, whereas interpulse secretion of FSH declined (P < 0.001) to 75 +/- 7% of the control value. In contrast to the gradual effect of PACAP38 to enhance GnRH-induced hormone secretion, PACAP38 alone produced a transient burst of gonadotropin secretion. At the completion of the perifusions, total RNA was extracted and gonadotropin subunit mRNA levels were determined by Northern analysis. GnRH increased (P < 0.01) FSH beta mRNA to 438 +/- 52% of the level in cells stimulated with medium alone (control). Adding PACAP38 to the perifusion medium partially blocked (P < 0.01) the effect of GnRH (178 +/- 20% of the control value), and PACAP38 alone reduced (P < 0.01) FSH beta mRNA levels to 31 +/- 3% of the control value. By contrast, alpha-subunit mRNA levels were increased by both PACAP38 (143 +/- 4% of the control value; P < 0.01) and GnRH (121 +/- 2% of the control value; P < 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)

Intrinsic secretory characteristics of luteinizing hormone and prolactin episodic release during pubertal development

The intrinsic characteristics of LH and prolactin (PRL) episodic secretion were evaluated in a group of 18 children (8M and 10F). The children were divided into two groups according to the Tanner stage: Group A (Tanner < or = 1, N = 7, 3M and 4F, 6-10 years of age) and group B (Tanner 2-3, N = 11, 5M and 6F, 9-11 years of age). A pulsatility study of 4 h, sampling every 10 min, was carried out in all children. LH and PRL plasma levels were assayed by IFMA and RIA respectively. LH and PRL secretory episodes were then identified on plasma determinations using the program DETECT. Instantaneous secretory rates (ISR) were then computed for both LH and PRL using the specific algorithm within the DETECT program. Plasma LH levels were different between the two groups of children. Group A children showed undetectable LH plasma levels (below the minimal detectable dose of 0.1 mIU/ml), while group B demonstrated LH plasma levels in the normal range of values for age and sexual development (1.5 +/- 0.3 mIU/ml, mean +/- SEM). LH pulse frequency for group B was 3.2 +/- 0.4 peaks/4 h. No significant differences in mean plasma PRL levels, pulse frequency and pulse amplitude were observed between the two groups of children. Computation of ISR for LH (group B only) and PRL (both groups) identified the intrinsic episodic characteristics of the two hormones. No significant differences in LH and PRL pulse frequencies were observed when comparing the results estimated on ISR with those estimated on plasma concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of galanin in stimulation of pituitary luteinizing hormone secretion as revealed by a specific receptor antagonist, galantide.

In this study, a specific galanin (GAL) receptor antagonist, galantide, was employed to evaluate the role of endogenous GAL in episodic basal and phasic LH release in rats. To assess the specificity of galantide, a series of experiments was performed. In the first experiment, we observed that administration of GAL (0.62 nm) intracerebroventricularly (icv) in ovarian steroid-primed ovariectomized (ovx) rats rapidly increased plasma LH levels between 10-30 min, and prior injection of galantide icv (5 nm) blocked the GAL-induced LH release. In the second experiment, galantide inhibited the GAL-evoked in vitro release of LHRH from the median eminence-arcuate nucleus (ME-ARC) of ovarian steroid-primed ovx rats. In addition, galantide on its own significantly decreased the basal efflux of LHRH from the ME-ARC of similarly treated rats, thereby suggesting that even the basal LHRH secretion may be a GAL-dependent event. In the third experiment, the effects of galantide on the phasic LH surge elicited by progesterone (P) in estradiol benzoate-primed ovx rats and that occurring spontaneously on proestrus were examined. Ovx rats bearing icv cannulae were primed with estradiol benzoate (30 micrograms/rat, sc) and 2 days later received a P (2 mg/rat, sc) injection at 1000 h to evoke a LH surge in the afternoon. Galantide (1 or 5 nm) in 3 microliters saline or saline was injected icv at 1300, 1400, and 1500 h. The results showed that the two dosages of galantide suppressed the LH surge in the afternoon. On the other hand, only a very high dose of galantide (15 nm) injected iv at 1300, 1400, and 1500 h blunted the P-induced LH hypersecretion. Central injections of galantide (1 or 5 nm) at 1300, 1400, and 1500 h on proestrus also inhibited the preovulatory LH surge and significantly reduced the numbers of rats ovulating the following day. In the final experiment, the role of GAL receptors in modulation of episodic LH release was analyzed in ovx rats. The results showed that an injection of galantide (5 nm, icv) significantly decreased both the mean LH levels and the amplitude of LH episodes during the 3-h observation period. Cumulatively, these results show that normally GAL stimulates LHRH release by activation of a specific receptor located in the ME-ARC, and that GAL may be a key excitatory signal in the hypothalamic neural circuitry involved in the regulation of basal episodic and phasic LHRH secretion in cycling female rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of galanin in stimulation of pituitary luteinizing hormone secretion as revealed by a specific receptor antagonist, galantide

In this study, a specific galanin (GAL) receptor antagonist, galantide, was employed to evaluate the role of endogenous GAL in episodic basal and phasic LH release in rats. To assess the specificity of galantide, a series of experiments was performed. In the first experiment, we observed that administration of GAL (0.62 nm) intracerebroventricularly (icv) in ovarian steroid-primed ovariectomized (ovx) rats rapidly increased plasma LH levels between 10-30 min, and prior injection of galantide icv (5 nm) blocked the GAL-induced LH release. In the second experiment, galantide inhibited the GAL-evoked in vitro release of LHRH from the median eminence-arcuate nucleus (ME-ARC) of ovarian steroid-primed ovx rats. In addition, galantide on its own significantly decreased the basal efflux of LHRH from the ME-ARC of similarly treated rats, thereby suggesting that even the basal LHRH secretion may be a GAL-dependent event. In the third experiment, the effects of galantide on the phasic LH surge elicited by progesterone (P) in estradiol benzoate-primed ovx rats and that occurring spontaneously on proestrus were examined. Ovx rats bearing icv cannulae were primed with estradiol benzoate (30 micrograms/rat, sc) and 2 days later received a P (2 mg/rat, sc) injection at 1000 h to evoke a LH surge in the afternoon. Galantide (1 or 5 nm) in 3 microliters saline or saline was injected icv at 1300, 1400, and 1500 h. The results showed that the two dosages of galantide suppressed the LH surge in the afternoon. On the other hand, only a very high dose of galantide (15 nm) injected iv at 1300, 1400, and 1500 h blunted the P-induced LH hypersecretion. Central injections of galantide (1 or 5 nm) at 1300, 1400, and 1500 h on proestrus also inhibited the preovulatory LH surge and significantly reduced the numbers of rats ovulating the following day. In the final experiment, the role of GAL receptors in modulation of episodic LH release was analyzed in ovx rats. The results showed that an injection of galantide (5 nm, icv) significantly decreased both the mean LH levels and the amplitude of LH episodes during the 3-h observation period. Cumulatively, these results show that normally GAL stimulates LHRH release by activation of a specific receptor located in the ME-ARC, and that GAL may be a key excitatory signal in the hypothalamic neural circuitry involved in the regulation of basal episodic and phasic LHRH secretion in cycling female rats.

Role of neuropeptide-Y in episodic luteinizing hormone release in ovariectomized rats: an excitatory component and opioid involvement.

We tested the hypothesis that hypothalamic neuropeptide-Y (NPY) is an excitatory signal in the episodic secretion of LH in ovariectomized (ovx) rats and that the suppression of LH secretion that consistently follows intracerebroventricular administration of NPY is due to concurrent release of opioids or CRH, both previously shown to readily inhibit LH release. In the first experiment, ovx rats received continuous intraventricular infusion of either serum containing NPY antibodies (NPY-Ab) or normal rabbit serum (control) at dilutions of 1:5 or 1:1. NPY-Ab infusion at a 1:5 dilution significantly decreased mean plasma LH levels and LH pulse amplitude without affecting LH pulse frequency over a 3-h period of observation. However, infusion of relatively more concentrated NPY-Ab (1:1) markedly decreased not only mean plasma LH levels and LH pulse amplitude, but also the frequency of LH episodes. In the next experiment, we observed that intraventricular administration of NPY (0.2 nmol) suppressed LH release for 60 min. However, blockade of opiate receptors with iv infusion of naloxone (2 mg/h) before and after NPY injection completely counteracted the NPY-induced inhibition of LH release. On the other hand, prior blockade of the CRH receptors with alpha-helical CRH-(9-41) (25 or 100 micrograms/rat) was ineffective in reversing the inhibitory LH response of NPY (0.125 nmol). These results together with our previous demonstration of morphological communication between NPY and beta-endorphin neurons, show that suppression of LH by exogenous NPY in ovx rats may result from concurrent stimulation of opioids, primarily beta-endorphin. However, diminution of all parameters of episodic LH secretion by NPY-Ab affirms the notion that the NPY network is a physiologically important excitatory component of the hypothalamic pulse generator circuitry that regulates episodic LH secretion in rats.

Role of neuropeptide-Y in episodic luteinizing hormone release in ovariectomized rats: an excitatory component and opioid involvement

We tested the hypothesis that hypothalamic neuropeptide-Y (NPY) is an excitatory signal in the episodic secretion of LH in ovariectomized (ovx) rats and that the suppression of LH secretion that consistently follows intracerebroventricular administration of NPY is due to concurrent release of opioids or CRH, both previously shown to readily inhibit LH release. In the first experiment, ovx rats received continuous intraventricular infusion of either serum containing NPY antibodies (NPY-Ab) or normal rabbit serum (control) at dilutions of 1:5 or 1:1. NPY-Ab infusion at a 1:5 dilution significantly decreased mean plasma LH levels and LH pulse amplitude without affecting LH pulse frequency over a 3-h period of observation. However, infusion of relatively more concentrated NPY-Ab (1:1) markedly decreased not only mean plasma LH levels and LH pulse amplitude, but also the frequency of LH episodes. In the next experiment, we observed that intraventricular administration of NPY (0.2 nmol) suppressed LH release for 60 min. However, blockade of opiate receptors with iv infusion of naloxone (2 mg/h) before and after NPY injection completely counteracted the NPY-induced inhibition of LH release. On the other hand, prior blockade of the CRH receptors with alpha-helical CRH-(9-41) (25 or 100 micrograms/rat) was ineffective in reversing the inhibitory LH response of NPY (0.125 nmol). These results together with our previous demonstration of morphological communication between NPY and beta-endorphin neurons, show that suppression of LH by exogenous NPY in ovx rats may result from concurrent stimulation of opioids, primarily beta-endorphin. However, diminution of all parameters of episodic LH secretion by NPY-Ab affirms the notion that the NPY network is a physiologically important excitatory component of the hypothalamic pulse generator circuitry that regulates episodic LH secretion in rats.

Mode of action of interleukin-1 in suppression of pituitary LH release in castrated male rats

These studies were undertaken to elucidate the mechanisms whereby the cytokine, Interleukin (IL-1) suppresses pituitary LH release in orchidectomized rats. Since LH secretion in pulsatile in castrated rats, the effects of IL-1 on the components of the LH pulsatility were assessed. Intracerebroventricular (i.c.v.) administration of IL-1α or IL-1β suppressed LH release, but IL-1β was relatively more effective than IL-1α in terms of the onset (IL-1β = 30min; IL-1α = 105min) as welk as the magnitude and duration of LH suppression. Further, the marked suppression of LH secretion in IL-1β-treated rats was found to be due to significant reductions both in the frequency and amplitude of LH episodes. We next evaluated whether the IL-1β-induced suppression of LH release was mediated by either of the two inhibitory hypothalamic peptidergic systems, corticotrophin releasing hormone (CRH) and endogenous opioid peptides (EOP). Passive immunoneutralization of CRH by i.c.v. administration of a specific CRH-antibody, either once at 15 min or twice at 75 and 15 min before IL-1β injection, failed to block the suppressive effects of IL-1β on LH release. Similarly, pharmacological blockade of CRH by i.c.v. injection of the CRH receptor antagonist, α-helical CRH 9–41 15 min before IL-1β was ineffective. However, i.v. infusion of the opiate receptor antagonist, naloxone, which on its own had no effect on LH secretion, counteracted the inhibitory effects of IL-1β. To further identify the opiate receptor subtype involved, we utilized specific opiate receptor subtype antagonists. We observed that neither blockade of δ receptors with naltrindole, nor blockade of κ receptors with nor-binaltorphimine dihydrochloride, altered the course of LH suppression seen after IL-1β injection. However, prior blockade ofμ 1 opiate receptors wit β-funaltrexamine hydrochloride, completely reversed the inhibitory effects of IL-1β on LH release. These results show that IL-1β suppresses both the frequency and amplitude of LH discharge in two-week castrated rats. Further pharmacologic evidence shows that IL-1ß-induced suppression of LH secretion may involve stimulation of hypothalamic endogenous opioids which presumably act via the hypothalamicμ 1 opiate receptor subtype, and that stimulation of hypothalamic CRH release may not be essential in manifestation of the inhibitory effects of IL-1ß on LH release.

Analysis of the Copulsatility of Anterior Pituitary Hormones*

We have used combinatorial algebra and computer simulations to calculate expected means, variances, and probabilities of hormone-peak coincidences in 2 or more endocrine pulse series. We illustrate application of this conditional probability analysis to pulsatile LH, FSH, and/or PRL data. We observed that 1) serum LH and FSH pulses in 14 young men were randomly associated on different days (P greater than 0.10), but highly synchronized on any given day (P less than 0.0001); 2) serum LH and FSH (P less than 0.0001), LH and PRL (P = 0.023), and FSH and PRL (P = 0.0003) peaks were significantly coupled in healthy postmenopausal women; and 3) the number of triple coincidences among LH, FSH, and PRL release episodes in postmenopausal women significantly exceeded chance expectations (P less than 0.0001). We conclude that suitable statistical coincidence analysis can offer an informative tool with which to evaluate nonrandom event concordance in endocrine investigations, such as clinical studies of the temporally coordinated release of anterior pituitary hormones.

Manipulation of plasma FSH concentrations by administration of bFF affects LH secretion in seasonally anoestrous ewes

Changes in the secretion of LH, both endogenous and in response to injections of gonadotrophin releasing hormone (GnRH), were monitored in seasonally anoestrous ewes in which FSH secretion had been suppressed by treatment with bovine follicular fluid (bFF). Groups of five animals received GnRH (250 ng per injection given intravenously at 2 h intervals) alone, or in conjunction with bFF (1.5 ml per injection given subcutaneously at 8 h intervals). Mean LH and FSH concentrations were assessed from blood samples collected at 2 h intervals from 12 h before the start until 48 h after the end of the 72 h treatment period. Appraisal of episodic LH secretion was based on three periods of frequent blood sampling (at 15 min intervals) undertaken 12–18, 64–70 and 84–90 h after the star of treatment. In ewes treated with bFF, plasma FSH concentrations fell immediately from a mean pretreatment level of 23.8 ± 2.37 ng ml −1 to reach a mean concentration of 9.4 ± 0.42 ng ml −1 8 h later, and remained low for the next 72 h (mean ± s.e.m. 8.1 ± 0.35 ng ml −1). After the end of bFF treatment, FSH concentrations increased rapidly to reach a mean maximum concentration of 60.4 ± 7.58 ng ml −1 by 36 h after the last bFF injection and then returned to pretreatment levels. Mean LH concentrations were unchanged from pretreatment values throughout the period of bFF administration, but increased ( P < 0.01) coincident with the post-treatment elevation in FSH concentrations. The pattern of episodic LH secretion was also affected by bFF treatment. The mean magnitude of GnRH-induced LH episodes recorded after 64 h of bFF treatment (8.72 ± 0.94 ng ml −1), was greater ( P < 0.01) than that recorded early (12–18 h) in the treatment period (5.04 ± 0.71 ng ml −1). In addition, after the end of the treatment period, both the frequency of endogenous LH episodes (mean interpulse interval of 2.31 h for bFF-treated and 10.00 h for control ewes; P< 0.01) and their amplitude (9.44 ± 1.79 ng ml −1 for bFF-treated and 5.05 ± 0.41 ng ml −1 for control ewes; P < 0.05), were significantly greater in animals that had previously been treated with bFF. Apart from the occurrence of a pre-ovulatory LH surge (all five of the control ewes and none of the five bFF-treated ewes ovulated), mean LH concentrations in ewes treated with GnRH alone did not change significantly throughout the 132 h period of blood sampling. Similarly, the magnitude of GnRH-induced LH episodes did not change significantly. These results demonstrate that treatment with bFF influences LH secretion by increasing the LH response to a standard dose of GnRH, and also by increasing the frequency with which endogenous LH episodes occur.

Efficacy of intermittent or continuous administration of GnRH in inducing ovulation in early and late seasonal anoestrus in the Pere David's deer hind (Elaphurus davidianus)

Père David's deer hinds were treated with GnRH, administered as intermittent i.v. injections (2.0 micrograms/injection at 2-h intervals) for 4 days, or as a continuous s.c. infusion (1.0 micrograms/h) for 14 days. These treatments were given early (February-March) and late (May-June) in the period of seasonal anoestrus. The administration of repeated injections of GnRH increased mean LH concentrations from pretreatment values of 0.54 +/- 0.09 to 2.10 +/- 0.25 ng/ml over the first 8 h of treatment in early anoestrus, and from 0.62 +/- 0.11 to 2.73 +/- 0.49 ng/ml in late anoestrus. The mean amplitude of GnRH-induced LH episodes was greater (P less than 0.01) in late (4.03 +/- 0.28 ng/ml) than in early (3.12 +/- 0.26 ng/ml) anoestrus, but within each replicate (early or late anoestrus), neither mean LH episode amplitude nor mean plasma LH concentrations differed significantly between the four periods of intensive blood sampling. On the basis of their progesterone profiles, 6/12 hinds had ovulated in response to treatment with injections of GnRH (1/6 in early anoestrus and 5/6 in late anoestrus), and oestrus and a preovulatory LH surge were recorded in all of these animals. Oestrus and a preovulatory LH surge were also recorded in one other animal treated in early anoestrus in which progesterone concentrations remained low. The mean times of onset of oestrus (91.0 +/- 1.00 and 62.4 +/- 0.98 h) and of the preovulatory LH surge (85.8 +/- 3.76 and 59.4 +/- 0.25 h) both occurred significantly earlier (P less than 0.001) in animals treated in late anoestrus. Continuous infusion of GnRH to seasonally anoestrous hinds resulted in an increase in mean plasma LH concentrations, but this response did not differ significantly between early (2.15 +/- 0.28 ng/ml) and late (2.48 +/- 0.26 ng/ml) anoestrus. Ovulation, based on progesterone profiles, occurred in 2/7 hinds in early anoestrus and in 4/6 hinds in late anoestrus. Oestrus was detected in all except one of these hinds. The mean time of onset of oestrus occurred earlier in animals treated in late anoestrus (66.2 +/- 0.32 h and 46.7 +/- 0.67 h, P less than 0.01). The administration of GnRH, given either intermittently or continuously, will induce ovulation in a proportion of seasonally anoestrous Père David's deer. However, more animals ovulate in response to this treatment in late than in early anoestrus (75% compared with 23%).