Changes In Luteinizing Hormone Concentrations Research Articles

The effects of intracerebroventricular infusion of prolactin on luteinizing hormone, testosterone and growth hormone secretion in male sheep

This study tested a hypothesis that the enhancement of the prolactin (PRL) concentration within the central nervous system (CNS) disturbs pulsatile luteinizing hormone (LH) and growth hormone (GH) secretion in rams that are in the natural breeding season. A 3 h long intracerebroventricular (icv.) infusion of ovine PRL (50 μg/100 μl/h) was made in six rams during the daily period characterized by low PRL secretion in this species (from 12:00 to 15:00 h); the other six animals received control infusions during the same time. Blood samples were collected from 9:00 to 18:00 h at 10 min intervals. A clear daily pattern of LH secretion was shown in control animals, with the lowest concentration at noon and an increasing basal level around the time of sunset ( P<0.001). No significant changes in LH concentration occurred in PRL-infused animals and the concentration noted after infusion of PRL was significantly ( P<0.05) lower than after the control infusion. The frequency of LH pulses tended to decrease in rams after PRL treatment. The changes in LH secretion clearly carried over to the secretion of testosterone in the rams of both groups. The GH concentrations changed throughout the experiment in both groups of rams, being higher after the infusions ( P<0.001). However, the mean GH concentration and GH pulse amplitude noted after PRL infusion were significantly lower ( P<0.001 and P<0.05, respectively) from those recorded in the control. The continued fall in PRL secretion observed in rams following PRL infusion ( P<0.05 to P<0.001) indicates a high degree of effectiveness of exogenous PRL at the level of the CNS. In conclusion, maintenance of an elevated PRL concentration within the CNS leads to disturbances in the neuroendocrine mechanisms responsible for pulsatile LH and GH secretion in sexually active rams.

Effects of female pheromones on gonadotropin-releasing hormone gene expression and luteinizing hormone release in male wild-type and oestrogen receptor-alpha knockout mice.

Pheromones are an important class of environmental cues that affect the hypothalamic-pituitary-gonadal axis in a variety of vertebrate species, including humans. When male mice contact female-soiled bedding, or urine, they display a reflexive luteinizing hormone (LH) surge within 30 min. Aside from the requirement that males have gonads to show this response, the physiological mechanisms that underlie this pituitary response are unknown. In this experiment, we asked if female pheromones acted at the level of gonadotropin-releasing hormone (GnRH) gene expression to affect this hormone response. In addition, we also examined the contribution of one of the oestrogen receptors (ERalpha) by studying this neuroendocrine reflex in wild-type and oestrogen receptor-alpha knockout (ERalphaKO) males. Both ERalphaKO and wild-type males showed the expected LH surge, 45 and 90 min after contact with female pheromones. Males housed in clean bedding or bedding soiled by another adult male did not display the LH elevation. Interestingly, this dramatic change in LH concentrations was not accompanied by any alterations in GnRH mRNA expression or levels of primary transcript in the preoptic area-anterior hypothalamus. The one exception to this was a significant increase in GnRH mRNA expression in tissue collected from wild-type males exposed to bedding from another male. This is particularly intriguing since LH was not elevated in these males. These data replicate and extend our previous finding that ERalphaKO males do exhibit an LH surge in response to female pheromones. Thus, this neuroendocrine response is regulated by a steroid receptor other than ERalpha and does not require alterations in GnRH mRNA expression.

Profiling of urinary testosterone and luteinizing hormone in exercise-stressed male athletes, using gas chromatography-mass spectrometry and enzyme immunoassay techniques.

Knowledge of the effects of episodic or short-term exercise-stress on endogenous testosterone and luteinizing hormone levels still remains fragmentary and inconclusive. In this study, an approach based on the absolute concentrations of urinary total testosterone (T), luteinizing hormone (LH) and the T/LH concentration ratios, was used to profile short-term exercise-stress responses in healthy drug-free male athletes. Testosterone and luteinizing hormone concentrations were measured using gas chromatography-mass spectrometry (GC-MS) and microparticle enzyme immunoassay (MEIA) techniques, respectively. Stress profiles derived from exercise-stress at VO2max, 68.1% VO2max and 51.6% VO2max were plotted using the concentrations of T, LH and the ratios of T/LH found under non-stressed and stressed conditions. Significant changes in LH concentrations (p < 0.005) and T/LH ratios (p < 0.005) levels were observed between the pre-stress and post-exercise conditions during acute exercise-stress at VO2max but the T concentration did not show any marked change relative to the non-stressed condition. Whilst exercise-stress appeared to reduce the change in T concentrations between the pre- and post-exercise states compared to that in the non-stressed control condition, the change in LH concentrations showed a moderate increase at submaximal oxygen uptake values. The stress profiles derived from this study facilitated an assessment of the relationship between the endogenous T, LH and T/LH ratio stress-responses over a short period of applied exercise-stress.

From basal luteinizing hormone (LH) concentrations to the pre-ovulatory LH surge: titration of the physiological effect of gonadotrophin surge-inhibiting/attenuating factor.

Pulsatile luteinizing hormone (LH) release is thought to be controlled by the functional antagonism between gonadotrophin-releasing hormone (GnRH) and the putative ovarian factor gonadotrophin surge-inhibiting/attenuating factor (GnSIF/AF). Our experiments were designed to titrate the input of endogenous basal and follicle stimulating hormone (FSH)-stimulated GnSIF/AF in this system. The effects were studied of five consecutive pulses of GnRH administration (10-250 pmol/pulse/kg rat), 1 h apart, on the self-priming effect in pro-oestrus phenobarbital-blocked rats injected with FSH or saline. In response to the two high pulses of GnRH, a clear GnRH self-priming was demonstrated. However, pulses of 25 pmol GnRH induced only a minor self-priming effect and the LH blood concentrations were within the physiological range. Pulses of 10 pmol GnRH had no effect. FSH suppressed the unprimed LH response and delayed GnRH self-priming by approximately 1 h. Increasing the GnRH pulse frequency of the 25 pmol GnRH pulses from one to three per hour induced pre-ovulatory-like LH surges. The effect was facilitated by ovariectomy to eliminate GnSIF/AF. Thus, the results are consistent with relative inputs of GnRH and GnSIF/AF being responsible for the changes in LH concentration during the ovarian cycle, including the generation of the mid-cycle LH surge.

Prolactin, Growth Hormone, and Luteinizing Hormone-β Subunit Gene Expression in the Cephalic and Caudal Lobes of the Anterior Pituitary Gland during Embryogenesis and Different Reproductive Stages in the Chicken

Messenger RNA (mRNA) levels of prolactin (PRL), growth hormone (GH), and luteinizing hormone (LH)-β subunit in the cephalic and caudal lobes of the anterior pituitary gland of the chicken during embryonic development and different reproductive stages were determined by Northern blot analysis and are related to hormone levels in plasma and each lobe. Steady-state levels of 1.4-kb transcript of PRL of the cephalic and caudal lobes increased on Days 18 and 20 of incubation, respectively. The levels were greater in the cephalic lobe than in the caudal lobe on Days 18 and 20 of incubation. Levels of PRL in each lobe show similar changes to those of mRNA levels. GH mRNA levels of both lobes started to increase on Day 16 of incubation but the levels were higher in the caudal lobe than in the cephalic lobe on Days 16-20 of incubation. Levels of GH in the cephalic lobe increased discontinuously, while those in the caudal lobe increased continuously on days of incubation. LH-β mRNA was not detected in embryos. Levels of PRL mRNA increased approximately 18-, 20-, and 3-fold in hens at 1 and 3 weeks of egg incubation and brooding stages in the hen, relative to prelaying, respectively. These levels were higher in the cephalic lobe than in the caudal lobe at all stages except for prelaying stages. Levels of PRL in each lobe displayed essentially similar changes to the mRNA levels. GH mRNA levels did not significantly vary during the cycle but were higher in the caudal lobe than in the cephalic lobe. There was no difference in LH-β mRNA levels between the two lobes but the levels were higher at prelaying and laying stages than at incubation and brooding stages. The same changes in LH concentrations in plasma as those of LH-β mRNA were found at the stages. This study shows regional differences between PRL and GH mRNA levels in the anterior pituitary gland in relation to embryogenesis and different reproductive stages.

Changes in luteinizing hormone concentrations after abortion, parturition, and weaning in primiparous sows

This study compared the endocrine changes associated with the capacity of gilts to return to estrus following mid-gestation abortion, removal of piglets at birth (zero weaned), during lactation, and following the removal of piglets after lactation (weaned). Serum concentrations of luteinizing hormone (LH), estradiol-17β (E 2), and progesterone (P 4) were determined in aborted gilts (Group 1; n = 5), zero-weaned gilts (Group 2; n = 6), and gilts (Group 3; n = 6) weaned after a 3 week lactation. In addition, postpartum endocrine changes were compared between Group 2 and Group 3 gilts during lactation. The day of abortion, parturition and weaning was considered Day 0. Blood samples were collected at 6 h intervals from Day —2 to Day 21 and at 15-min intervals for 8 h on Days —2, 1, 4, 7, 10 and 14. Following each 8 h sampling period, gilts were treated i.v. with gonadotropin releasing hormone (GnRH) at 0.5 μg kg −1 body weight (BW) and blood samples collected at 10-min intervals for 3 h. Estrus was detected using twice daily boar exposure. The number of gilts exhibiting estrus were four, four and one at 4.5 ± 0.3 days, 14.8 ± 0.5 days and 9 days for aborted, zero-weaned, and weaned groups, respectively. Gilts exhibited increasing LH concentrations with time following abortion, while GnRH-induced LH release was not affected by group or time. Changes in E 2 and P 4 concentrations reflected the endocrine changes associated with gestation or the return to estrus for each group. In addition, LH, E 2 and P 4 concentrations were similar in lactating and zero-weaned gilts for 7 days following parturition. It was evident that gilts aborted during mid-gestation have an increased ability to return to estrus than zero-weaned gilts, and that pituitary responsiveness to exogenous GnRH did not differ between groups nor was affected by the termination of pregnancy or lactation.

Inhibin and gonadotrophin secretion in physically active males after acute exercise

Serum concentrations of luteinizing hormone (LH) follicle stimulating hormone (FSH), testosterone and inhibin were measured in six physically active male volunteers after heavy exercise on a treadmill. Hormone measurements were made before exercise, immediately after exercise and at 30-min intervals for 3 h after exercise. Serum concentrations of LH fell after exercise reaching nadir values between 60 and 180 min post-exercise. The nadir value of LH for the group as a whole occurred 90 min after exercise. Serum testosterone concentrations paralleled the changes in LH concentrations. Serum FSH and inhibin concentrations did not show any appreciable change from baseline values. The data suggest that acute exercise does not significantly lower serum concentrations of FSH or inhibin. Whether repetitive and prolonged heavy exercise, as in competitive runners, produces alterations in serum inhibin concentrations remains to be determined.

Effects of pulsatile and continuous luteinizing hormone (LH) infusions on testosterone responses to LH in rams actively immunized against gonadotropin-releasing hormone.

Yearling rams actively immunized against GnRH were used as a hypogonadotropic model for studies of the significance of the pulsatility of LH secretion in determining the trophic actions of the hormone on testicular steroidogenesis. GnRH-immunized rams, in which testicular regression was complete, were infused iv for 12-20 days with ovine LH (NIDDK oLH 24) in three different regimens, delivering a total daily dose of 60 micrograms/100 kg: 1) 1-min pulses of 5 micrograms/100 kg every 2 h (low amplitude, high frequency), 2) 1-min pulses of 30 micrograms/100 kg every 12 h (high amplitude, low frequency), or 3) continuous infusion of 2.5 micrograms/100 kg.h. Serum testosterone levels and acute responses to LH challenges were monitored at intervals throughout the infusion periods. Acute responses to LH were evaluated in terms of the area under the curve for serum testosterone vs. time after LH and the lag time between the infusion of LH and attainment of maximum serum testosterone levels. At the beginning of the experiments, serum testosterone was at castrate values, and testosterone responses to LH were of low magnitude with a long lag time. LH infusion in the low amplitude, high frequency regimen consistently increased the magnitude and decreased the lag time of acute responses to LH; these effects were significant by the sixth day of treatment and persisted for the duration of the experiments. This regimen also had positive effects on morphological features of testes and Leydig cells. Infusion of the high amplitude, low frequency regimen, however, had neither of the positive effects on responsiveness to LH, but did seem to improve testicular and Leydig cell morphology. Continuous infusion of LH also increased the magnitude and decreased the lag time of responses to low amplitude pulses of LH, at least as well as the high frequency infusion regimen did. These results suggest that the high frequency, low amplitude pattern of LH secretion characteristic of reproductively active animals has trophic actions on the testes, increasing their responsiveness to acute gonadotropic stimulation, but the pulsatility of that pattern of LH secretion is not necessary for its trophic actions. The efficacy of high frequency LH secretion may depend only on the elevation of basal or mean LH concentrations, rather than on the low amplitude peaks or the dynamic changes in LH concentrations to which the testes are exposed.

Influences of season and artificial photoperiod on stallions: luteinizing hormone follicle-stimulating hormone and testosterone.

Influence of day length on seasonal endocrine responses were studied using stallions (seven per group). Treatments included 1) control, with natural day length; 2) 8 h light and 16 h dark (8:16) for 20 wk beginning July 16, 1982 then 16:8 from December 2, 1982 until March 5, 1984 (S-L); or 3) 8:16 from July 16, 1982 until March 5, 1984 (S-S). Blood was sampled hourly for 5 h every 4 wk; sera were pooled within horse, and luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone were quantified. Blood was collected every 20 min for 24 h every 8 wk and 2 wk before and after the December light shift. Samples were assayed for LH. Stallions in all groups underwent seasonal changes (P less than .05) in concentrations of LH, FSH, testosterone and basal concentrations of LH and amplitude of LH pulses. Season X treatment (P less than .05) reflected on early recrudescence of LH, FSH and testosterone concentrations in S-L stallions followed by earlier regression. Except for FSH hormone concentrations were depressed in S-S stallions. Number of LH pulses per 24 h was unaffected by season, treatment or their interaction. Mean amplitude of LH pulses was affected (P less than .05) by season X treatment; maximal values occurred in April vs February for control and S-L stallions, and minimal values occurred in December vs April. The season X treatment interaction (P less than .05) similarly affected basal concentrations of LH. Thus, seasonal changes in concentrations of LH, FSH and testosterone can be driven by photoperiod. Increased peripheral concentrations of LH during seasonal recrudescence of reproductive function apparently results from more LH secreted per discharge without an increased frequency of LH discharges.

Compensatory response of the luteinizing-hormone (LH)-releasing hormone (LHRH)/LH pulse generator after administration of a potent LHRH antagonist in the ram.

It is established that the blockade of the pituitary LHRH receptor by an LHRH antagonist will suppress pituitary LH secretion and reduce serum concentrations of gonadal steroids. Little is known, however, about the activity of the LHRH/LH pulse generator during this inhibitory period or during the recovery phase. To investigate this, a potent LHRH antagonist [N-Ac-D-pCl-Phe1,D-pCl-Phe2,D-Trp3,D-hArg(Et2)6, D-Ala10 LHRH was injected iv into sexually active rams and the changes in the blood plasma concentrations of LH, FSH, testosterone, and PRL were measured in samples collected every 15 min for 24-48 h. The treatment induced an immediate blockade of pulsatile LH secretion and a parallel decline in blood levels of testosterone. Plasma levels of FSH were not suppressed by treatment with the LHRH antagonist and there was no consistent effect on plasma levels of PRL. The duration of the inhibition of LH was dose dependent lasting 4.3 +/- 0.4 h, 18.0 +/- 1.0 h, and 31.8 +/- 1.3 h for the low (6 micrograms/kg), medium (36 micrograms/kg), and high (365 micrograms/kg) doses of LHRH antagonist, respectively. During the recovery period there was an approximate 2-fold increase in the frequency of LH pulses. These results suggest a compensatory response to the decline in the negative feedback effect of testosterone secretion. Even the lowest dose of antagonist elicited a decrease in the level of testosterone and an increase in LH pulse frequency. At this dose, the decline in testosterone was very transitory indicating an acute sensitivity of the hypothalamus to changes in the negative feedback signal. These results suggest that the suppression of LH and testosterone secretion in the ram by LHRH antagonist is associated with a compensatory increase in the activity of the LHRH pulse generator.

LHRH receptor, LH and FSH concentrations in anterior pituitaries of cycling, noncycling and early pregnant heifers.

In domestic animals limited data are available concerning levels of pituitary luteinizing hormone-releasing hormone (LHRH) receptors during various physiological states. The objectives of this study were to quantify anterior pituitary gonadotropin and LHRH receptor concentrations in cycling, noncycling and early pregnant beef heifers. To accomplish these objectives, five heifers each were slaughtered, after synchronization with prostaglandin F2 alpha (PGF2 alpha), on d 0 (estrus), 7 and 14 of the estrous cycle and d 40 of pregnancy. Four heifers determined to be noncycling were also slaughtered. Pituitaries were collected and analyzed for LHRH receptor and gonadotropin concentrations. Pituitary luteinizing hormone (LH) concentrations were low on d 0 (1.4 +/- .2 micrograms/mg pituitary, mean +/- SE) and remained low on d 7 (1.4 +/- .1 micrograms/mg pituitary) before increasing (P less than .01) on d 14 (2.6 +/- .5 micrograms/mg pituitary). Luteinizing hormone concentrations, compared with d 0, were also elevated (P less than .01) in noncycling (NC; 2.6 +/- .2 micrograms/mg pituitary) animals and in 40-d pregnant (PG; 2.5 +/- .2 micrograms/mg pituitary) heifers. Pituitary follicle stimulating hormone (FSH) concentrations, though similar (P greater than .05) for all groups, paralleled changes in LH concentration. Pituitary LHRH receptor binding affinity did not differ (P greater than .05) among groups, with an overall Kd = .64 +/- .02 X 10(-9) M. Luteinizing hormone-releasing hormone receptor concentrations were highest on d 0 (1.09 +/- .12 fmol/mg pituitary) and fell (P less than .01) to low levels on d 7 (.75 +/- .11 fmol/mg pituitary).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of a single oral dose of phenobarbital on prolactin, growth hormone and luteinizing hormone in normal women.

The effects of a single oral dose of phenobarbital (PB) on the 24 h secretion of prolactin, growth hormone and luteinizing hormone have been evaluated in normal women. An EEG record was taken and barbiturate levels assayed in serum. A statistically significant decrease of growth hormone 24 h mean levels was observed and growth hormone and prolactin values during sleep were diminished. No changes in luteinizing hormone concentrations were observed. After PB the EEG showed no important alterations in sleep pattern, but on the power analysis an increase above 16 Hz absolute power was detected during the waking period.

Luteinizing hormone in blood plasma of post-partum buffaloes (Bubalus bubalis)

The changes in luteinizing hormone concentration were measured by heterologous double-antibody radioimmunoassay in blood plasma of 28 Murrah buffaloes. The LH concentration fluctuated between 0.22 to 0.78 ng/ml during first 21 days post-partum. The level increased significantly (P < 0.001) at estrus. The basal LH concentration of second and third week post-partum was inversely related to the first post-partum ovulation interval.

Variable sensitivity of prepubertal male rats to inhibin-like activity of bull seminal plasma and to testosterone propionate.

Bull seminal plasma (bSP) contains inhibin-like activity that can suppress the rise of serum concentrations of follicle stimulating hormone (FSH) and luteinizing hormone (LH) that otherwise occurs 24 h after castration in the male rat. The sensitivity of prepubertal rats to the, activity in bSP extract varied with the time of the year. In intact rats of the same age, bSP extract could always suppress serum FSH levels, but only sometimes did it affect serum LII; LH suppression occurred during times of greater sensitivity on the part of the acutely castrated rats. These variations in the response of 5-week-old rats to bSP extract may arise from seasonal changes that were observed in the sensitivity of acutely castrated rats to testosterone propionate. The concomitant changes in serum concentrations of LH and testosterone in intact animals indicated that the age of puberty did vary in our colony of rats. Despite the marked changes in the sensitivity of acutely castrated rats to bSP extract and testosterone propionate, serum concentrations of FSH and LH in intact rats showed little change throughout the year.

Alterations in the number of ovine luteal receptors of LH and progesterone secretion induced by homologous hormone.

To study the events associated with down-regulation of receptors for luteinizing hormone (LH) in the ovine corpus luteum, normally cycling ewes were injected i.v. with 1 mg LH on Day 10 of the estrous cycle. Changes in concentrations of LH and progesterone in serum, luteal concen trations of progesterone and numbers of luteal receptors for LH were measured up to 72 h after LH injection. Serum levels of LH increased more than 1000-fold (P<0.01) from a control level of 298 ±23 pg/ml (mean ±SEM) to 327 ±22 ng/ml at 10 mm, then returned to control levels by 24 h. Progesterone concentrations in serum increased (P<0.05) from 2.63 ±0.29 (least squares mean ±SEM) to 4.09 ±0.29 ng/ml within 10 mm after administration of LH, remained elevated for 2 h, decreased to control levels within 4 h, but never decreased below control levels. Proges terone content of the corpus luteum was correlated (r = 0.78, P<0.05) with progesterone concen trations in serum. The number of unoccupied receptors decreased (P<0.05) by 66% from control levels of 2.63 ±0.48 X 1012 mol/corpus luteum to 0.90 ±0.48 X 1012 mol/corpus luteum by 12 h. Recovery to control levels had occurred between 24—48h. Within 10 mm the total number of receptors for LH increased 260% while the number of occupied receptors increased 13-fold from control levels of 0.41 ±0.66 X 1012 mol/corpus luteum to 5.43 ±0.73 X 1012 mol/corpus luteum. The number of receptors occupied by LH decreased rapidly until 6 h and had returned to control values by 24 h. Serum concentrations of progesterone were correlated (r = 0.80, P<0.05) with the number of occupied receptors during the first 24 h after LH injection. In addition, there was good correlation between the number of receptors occupied by LH at 10 min (5.43 X 10-12 mol/corpus luteum) and the number of total receptors lost from 10 min to 24 h (6.75 X 10-12 mol/corpus luteum) after LH injection. These data suggest that down-regulation of ovine luteal receptors forLH involves thelossofoccupiedreceptors, perhapsviainternalization ofhormone receptor complexes. In addition, a mechanism for the replacement of receptors is proposed.

Seasonal variations in blood luteinizing hormone and testosterone levels in rams.

SUMMARY Three adult Suffolk rams were bled at weekly intervals for 14 months, and at hourly intervals for 24 h during the summer (one ram) and autumn (two rams). Luteinizing hormone (LH) was measured by radioimmunoassay, and testosterone by a competitive protein binding assay. There were episodic bursts of LH secretion during the 24 h period in both the summer and the autumn; the frequency of discharge was lower in the summer, but the amplitude (0·1–8·0 ng/ml) did not appear to change. It was not always possible to detect seasonal changes in LH concentration in single blood samples taken once a week throughout the year. The blood testosterone levels also showed marked fluctuations throughout the 24 h, and the frequency of the peaks was lower in the summer. But in contrast to LH, the magnitude of the testosterone peaks also changed throughout the year; from January to September the testosterone concentration ranged from 0·5 to 10 ng/ml plasma, whereas from October to December it ranged from 3 to 28 ng/ml. Thus in temperate regions the ram, like the ewe, shows seasonal changes in gonadal endocrine activity, although some degree of spermatogenesis continues throughout the whole year.

Relationship between the plasma levels of luteinizing hormone and progesterone during the normal menstrual cycle.

Abstract The temporal relationship between the concentrations of luteinizing hormone (LH) and progesterone in peripheral plasma has been determined during the course of the normal human menstrual cycle. Daily plasma samples were assayed, in duplicate, for progesterone by the competitive protein-binding method of Murphy (0.5 ml aliquots of plasma) and for LH by a radioimmunologic procedure (0.1 ml aliquots of plasma). Plasma progesterone levels remained consistently low (<0.2-1.8 mμg/ml) during the first half of the cycle and did not begin to rise until after the midcycle surge of LH became fully evident. Following the decline in plasma LH concentrations, the plasma progesterone levels increased rapidly, reaching maximal concentrations of 10–19 mμg/ml in 3–5 days. Progesterone concentrations remained elevated for 4–6 days and then fell abruptly to the initial low levels approximately 24 hr before the onset of menstruation without concomitant changes in LH concentration.