Peak Serum Luteinizing Hormone Research Articles

THU193 Clinical Usefulness Of Repetitive GnRH Stimulation Test For The Diagnosis Of Central Precocious Puberty

Abstract Disclosure: S. Heo: None. Y. Shim: None. H. Lee: None. J. Hwang: None. J. Lim: None. Objective In girls, breast development under 8 years of age and peak serum luteinizing hormone (LH) is 5 IU/L or higher in gonadotropin releasing hormone (GnRH) stimulation tests is a standard method for diagnosing central precocious puberty (CPP). Although breast development and bone age progress rapidly compared to chronological age, repeated GnRH stimulation tests do not exceed 5 IU/L in some cases. We aimed to analyze the clinical characteristics of girls who repeatedly examined the GnRH stimulation test. Methods We retrospectively reviewed the medical records of 988 girls under 9 years of age who visited our hospital due to breast development more than Tanner stage II and whose bone age was more than a year advanced than the chronological age and examined GnRH stimulation test twice or more. According to peak luteinizing hormone (LH) at first GnRH stimulation test, patients were divided into 5 groups that < 1.0 IU/L (group 1, n=34), ≥1.0 to < 2.0 IU/L (group 2, n=219), ≥2.0 to < 3.0 IU/L (group 3, n=297), ≥3.0 to < 4.0 (group 4, n=252) and ≥4.0 to < 5.0 (group 5, n=186). We analyzed the incidence of CPP through the repetitive GnRH stimulation test and factors associated with the outcomes using a Cox proportional hazard model. Results Mean age of total of 988 girls was 7.68 ± 0.67 years and the period between the first and last GnRH stimulation test was 216.40 ± 145.14 days. CPP was diagnosed in 138 patients. Incidence of CPP were differed by groups that 0%, 1.4%, 6.1%, 20.6%, 34.9% each groups. When group 1 and each groups were compared using the Cox proportional hazard regression model, difference between bone age and chronological age (95% CI, 1.27-2.35, p<0.001) (BA-CA) and basal follicle-stimulating hormone (95% CI, 1.01-1.48, p=0.039) showed a statistically significant positive correlation when stratifying the peak LH at GnRH stimulation test. Conclusion In the diagnosis of CPP, the GnRH stimulation test is gold standard. But the lower the peak LH in GnRH stimulation test, the more other factors such as difference between bone age and chronological age, basal FSH should be considered in the possibility of CPP. Presentation: Thursday, June 15, 2023

Mid-Luteal Progesterone Is Inversely Associated with Premenstrual Food Cravings.

It is not clear whether progesterone and estradiol associate with premenstrual food cravings, which significantly contribute to cardiometabolic adverse effects associated with obesity. We sought to investigate this question in the present study based on the prior literature showing a protective effect of progesterone on drug craving and extensive neurobiological overlaps between food and drug cravings. We enrolled 37 non-illicit drug- or medication-using women in the study to provide daily ratings of premenstrual food cravings and other symptoms across two-three menstrual cycles, based on which we classified them as premenstrual dysphoric disorder (PMDD) or control participants. In addition, the participants provided blood samples at eight clinic visits across the menstrual cycle. We aligned their mid-luteal progesterone and estradiol using a validated method which relies upon the peak serum luteinizing hormone and analyzed estradiol and progesterone using ultraperformance liquid chromatography tandem mass spectrometry. Hierarchical modeling, adjusted for BMI, showed a significant inverse effect of progesterone (p = 0.038) but no effect of estradiol on premenstrual food cravings. The association was not unique to PMDD or control participants. Results of research to date in humans and rodents showing that progesterone has dampening effects on the salience of the reinforcer translate to premenstrual food cravings.

Relationship between GnRH-induced LH increase profiles in the serum and vaginal mucus of Japanese Black beef cows.

This study aimed to investigate the relationship between increases in the luteinizing hormone (LH) profiles in the serum and vaginal mucus of cows induced by gonadotropin-releasing hormone (GnRH). Samples for LH determination were collected from Japanese Black beef cows during estrus, which was induced with a controlled internal progesterone-releasing device and the administration of cloprostenol immediately before GnRH administration and every 30 min from the start of GnRH administration until 6.5 h. The peak serum LH concentration was clearly identified at 2.5 h post-GnRH administration, with serum concentrations returning to near-pre-GnRH-administration values after 6.5 h, whereas the peak vaginal mucus LH concentration was identified 4.5 h after GnRH administration. These results indicate that the LH secretion peak in vaginal mucus appeared about 2 h after peak LH secretion in the serum.

Factors that predict a positive response on gonadotropin-releasing hormone stimulation test for diagnosing central precocious puberty in girls.

PurposeThe rapid increase in the incidence of precocious puberty in Korea has clinical and social significance. Gonadotropin-releasing hormone (GnRH) stimulation test is required to diagnose central precocious puberty (CPP), however this test is expensive and time-consuming. This study aimed to identify factors that can predict a positive response to the GnRH stimulation test.MethodsClinical and laboratory parameters, including basal serum luteinizing hormone (LH), follicle-stimulating hormone (FSH), and estradiol (E2), were measured in 540 girls with clinical signs of CPP.ResultsTwo hundred twenty-nine of 540 girls with suspected CPP had a peak serum LH level higher than 5 IU/L (the CPP group). The CPP group had advanced bone age (P<0.001), accelerated yearly growth rate (P<0.001), increased basal levels of LH (P=0.02), FSH (P<0.001), E2 (P=0.001), and insulin-like growth factor-I levels (P<0.001) compared to the non-CPP group. In contrast, body weight (P<0.001) and body mass index (P<0.001) were lower in the CPP group. Although basal LH was significantly elevated in the CPP group compared to the non-CPP group, there was considerable overlap between the 2 groups. Cutoff values of basal LH (0.22 IU/L) detected CPP with 87.8% sensitivity and 20.9% specificity.ConclusionNo single parameter can predict a positive response on the GnRH stimulation test with both high sensitivity and specificity. Therefore, multiple factors should be considered in evaluation of sexual precocity when deciding the timing of the GnRH stimulation test.

Changes in serum luteinizing hormone (LH) concentrations in response to luteinizing hormone releasing hormone (LHRH) in bull calves that attained puberty early or late

The objectives of this study were to determine if the response to luteinizing hormone releasing hormone (LHRH) could be used to select bull calves capable of early sexual maturation and to establish the optimum route and dose of LHRH. In Trial 1, at 4, 10 and 20 week of age, 20 calves were treated iv with 2μg/kg body weight of LHRH 1 and 5h after commencing a 9-h period of blood sampling. Bulls were separated into early and late maturing (n=10), based on age at puberty (scrotal circumference (SC) of ≥28cm). At 4 and 20 week of age, peak serum LH concentrations and area under the LH response curve in response to LHRH were lower (P<0.05) in early- versus late-maturing bulls. In Trial 2, calves at 20 week of age were given LHRH as follows: 2μg/kg body weight iv (n=6), im (n=6) or sc (n=6); 5μg/kg im (n=6), or ischio-rectally (ir, n=6) or sc (n=6); and 10μg/kg im (n=6) or sc (n=6). Serum LH concentrations were at a plateau from 30 to 165min after treatment with 5μg/kg of LHRH (im or ir; P>0.05). We concluded that the LH responses to LHRH in calves at 4 and 20 week of age could facilitate the development of a simple test (one blood sample prior to treatment with LHRH and a second during the period of sustained response to LHRH) to select early-maturing bulls.

Spontaneous serum gonadotropin concentrations in the evaluation of precocious puberty

Objective: We assessed the utility of spontaneous and gonadotropin-releasing hormone (GnRH)-stimulated serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels measured by new immunochemiluminometric assays in the evaluation and monitoring of precocious puberty. Methods: We evaluated serum gonadotropin values from intravenous GnRH stimulation tests in 49 girls with clinical signs suggesting central precocious puberty (CPP). Because GnRH-stimulated LH has been considered the standard for diagnosing CPP, we used it as the basis for comparison with GnRH-stimulated FSH levels and spontaneous LH and FSH measured by immunochemiluminometric assay. Results: Twenty-six patients had a peak serum LH value above the +2 SD threshold for normal prepubertal female subjects (LH > 5 IU/L). The GnRH-stimulated FSH values had a narrow range and did not discriminate patients with CPP. In contrast, elevations in spontaneous LH and FSH were found to be specific for CPP. Spontaneous LH levels correlated strongly with peak stimulated LH levels in subjects with precocious puberty ( r = 0.79) or in control subjects ( r = 0.93, both p < 0.0001). Spontaneous LH levels in excess of 0.1 IU/L detected true puberty with 94% sensitivity and 88% specificity. Random LH levels in excess of 0.3 IU/L had 100% specificity for CPP. Conclusions: The GnRH-stimulated FSH levels do not adequately differentiate children with and without CPP and have limited utility in the evaluation of precocious puberty. Spontaneous FSH levels are elevated in CPP with fair sensitivity and marked specificity. Elevated random LH, measured by third-generation assay such as immunochemiluminometric assay, is strongly correlated with and highly predictive of elevated peak GnRH-stimulated LH, and is a useful screening tool for CPP. (J P EDIATR 1995;127:47-52)

Self-limiting reflex luteinizing hormone release and sexual behavior during extended periods of unrestricted copulatory activity in estrous domestic cats.

Estrous female cats (queens) were permitted 36-h periods of unrestricted mating activity; they then were injected with various doses of gonadotropin-releasing hormone (GnRH) at 36 h and allowed single copulations at 48 or 72 h of study. Serum luteinizing hormone (LH) levels were determined in samples collected prior to and 2 h after the initial copulation, before and 30 min after selected copulations during the next 10 h, and before and 30 min after copulations occurring at 20-24, 36, and 48-72 h, as well as 0, 15, and 30 min after the GnRH injections (0.3-3.0 micrograms/kg) at 36 h of study. Copulations occurred 14-20 times in 12 h and 20-36 times in 36 h. Copulation frequency (mean +/- SEM) decreased (p less than 0.05) from 5.5 +/- 0.6/2 h initially to 1.5 +/- 0.6/2 h during the subsequent 2-h period, and was 1.4 +/- 0.2/2 h at 12-36 h of study. Intromissions lasted 1-27 (8 +/- 0.3) s. Variation in durations of mounting by males (1.7 +/- 0.1 min; range, 0.3-10 min) or of the postcoital behavioral reactions displayed by the queens (2.5 +/- 0.1 min; range, 1-17 min) could not be related to animals or time of study. Peak serum LH levels (11-280 ng/ml; mean, 112 +/- 30 ng/ml) were observed at 2-4 h after the first mating. Mean LH steadily declined thereafter, reached basal values (less than or equal to 3 ng/ml) by 20-24 h, and remained low at 36 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Steroid hormone feedback on LH in prepubertal holstein heifers

A significant dose-response relationship between gonadotropin-releasing hormone (GnRH) and time to luteinizing hormone (LH) peak, peak serum LH and total serum LH was obtained in prepubertal Holstein heifers (28 weeks of age) (Experiment 1). For the second experiment, the effect of steroid feedback on the anterior pituitary was determined. A steady infusion of saline, estradiol-17β or progesterone was maintained for 24 h while GnRH, in various schemes, was administered 8 h after the beginning of steroid infusion. Estradiol-17β infusion (2.08 μg/h), although it did not affect peripheral concentrations of estrogen, caused an LH release 24 to 30 h later in 37.5% of the heifers. This amount of exogenous estrogen did not affect the LH response to a single GnRH (4 μg) challenge. When the same GnRH dosage (4 μg) was administered 6 times at hourly intervals, the heifers infused with estradiol had a lower response after the first 2 injections of GnRH and a greater response after the last 4 injections than heifers infused with saline. When GnRH was infused (4 μg/h) for 6 h, beginning 8 h after steroid infusion, estradiol infusion caused a significantly higher peak LH and total LH release than an infusion of either saline or progesterone (7.3 μg/h). The progesterone infusion had no effect on the GnRH-stimulated LH release. We conclude that prepubertal dairy heifers have an anterior pituitary capable of responding to the feedback effect of estrogen in a positive manner.

Isosexual precocious puberty in girls.

This paper reviews the clinical findings, pituitary gonadotrophin reserve and plasma oestradiol, neurological findings and pelvic ultrasound appearance in 47 girls with precocious puberty starting before the age of 7 years. Of the 39 girls who had air encephalograms or cranial CT scans, 19 showed intracranial abnormalities (hamartomas 11; hydrocephalus 5; optic glioma 2; arachnoid cyst 1). There was no significant difference in the peak serum luteinizing hormone and follicle-stimulating hormone responses to intravenous gonadotrophin stimulating hormone in girls with and without intracranial lesions. Pelvic ultrasound examination showed development of the ovaries, uterus, and vagina similar to that seen in normal puberty. Treatment with cyproterone acetate (50-100 mg/day) in 26 girls resulted in arrest of breast development and suppression of menstruation, but a definite effect on growth was not documented.

Correlation of luteinizing hormone surges with estrogen nuclear and progestin cytosol receptors in the hypothalamus and pituitary gland. I. Estradiol dose response effects.

The present studies were designed to answer three questions: (1) how will a progressive increase in serum estradiol (E2) in ovariectomized (OVX) rats affect progesterone (P4)-induced luteinizing hormone (LH) surge concentrations? (2) Can steroid-induced LH surges be correlated with estrogen nuclear receptor (E2Rn) and progestin cytosol receptor (PRc) levels in brain regions known to regulate LH secretion, and (3) do differences in pituitary responsiveness to LHRH in E2- or E2P4-treated OVX rats parallel changes in E2Rn and PRc concentrations in this gland? 1 week after ovariectomy of adult cyclic rats (day 0), Silastic E2 capsules were placed subcutaneously at 09.00 h and produced serum E2 levels of 6-8 (low), 12-19 (medium) and 27-37 (high) pg/ml, respectively. 2 days later (day 2), some rats also received Silastic P4 capsules subcutaneously which elevated serum P4 concentrations to 10-12 ng/ml. In rats with low serum E2, P4 treatment induced peak serum LH levels of 913 ng/ml. When serum E2 was increased to the medium or relatively high physiologic range, P4 treatment resulted in LH surge levels of 4,686 and 5,030 ng/ml. OVX controls and E2-treated OVX rats were sacrificed at 10.00 h on day 2 and E2Rn and PRc were measured concurrently in the preoptic area (POA), mediobasal hypothalamus (MBH), corticomedial amygdala (CMA) and pituitary gland (PIT). Raising serum E2 from OVX levels to the low range significantly increased both E2Rn and PRc in MBH and PIT, but not in the POA or CMA.(ABSTRACT TRUNCATED AT 250 WORDS)

Cortisol and luteinizing hormone after adrenocorticotropic hormone administration to postpartum beef cows.

Cortisol and luteinizing hormone (LH) were measured in serum after the administration of adrenocorticotropic hormone (ACTH) to suckled (S) and nonsuckled (NS) beef cows. Blood was sampled on 2 consecutive days every 2 weeks for four bleeding periods starting 14 days after calving. Cows were injected with 200 IU ACTH or saline in a 2-day switchback design. Serum was collected before ACTH or saline injection and at 30-min intervals thereafter for 8 hours. Average cortisol concentrations in serum were similar in S and NS cows (6.4 +/- .6 and 6.1 +/- .8 ng/ml, respectively) after saline. Average cortisol concentrations in serum collected during an 8-hr period after ACTH on days 14, 28, 42 and 56 postpartum were 24.7 +/- 2.4, 31.8 +/- 3.5, 36.4 +/- 4.2 and 40.7 +/- .5 ng/ml, respectively, for S cows, and 31.1 +/- 2.9, 44.7 +/- 5.2, 45.0 +/- 5.7 and 46.0 +/- 5.4 ng/ml, respectively, for NS cows. Cortisol response to ACTH, measured as area under the response curve, was greater (P less than .05) in NS than in S cows. Amount of cortisol released by 200 IU ACTH was maximal by days 28 to 29 postpartum in NS cows, but the response increased gradually between days 14 to 15 and days 56 to 57 in S cows. overall, LH in serum averaged .55 +/- .08 ng/ml for S cows and .92 +/- .06 ng/ml for NS cows after saline, and .49 +/- .07 ng/ml for S cows and .94 +/- .06 ng/ml for NS cows after ACth. Although mean and peak serum LH concentrations did not differ between cows given ACTH and those given saline, the number of LH peaks and the number of cows having LH after saline. Mean serum LH concentrations were lower (P less than. 05) in S than in NS cows at 28 days postpartum. The number of LH peaks was lower (P less than .05) and the magnitude of the largest LH peak tended to be lower (P less than .06) in S cows at all sampling periods.

Relationship of Reproductive Behavior, Serum Luteinizing Hormone and Time of Ovulation in the Bitch

This study was performed to define the relationship betweed luteinizing hormone (LH), reproductive behavior and time of ovulation in the domestic bitch. Laparoscopy was effective for distinguishing ovarian follicular development and the morphological alterations indicative of ovulation and corpus tuteum (CL) formation. The actual moment of follicular rupture was observed in 2 animals. An LH surge was detected in all animals and mean LH values did not differ between bitches subjected to laparoscopy at 48 h intervals and those bitches which did not undergo laparoscopy during the experiment. During the proestrous-estrous period, baseline LH concentrations before and after the LH surge averaged 1.7 ± 0.1 ng/ml (S.E.). The major preovulatory LH surge ranged from 11.0-90.3 ng/ml with an average of 45.1 ± 4.4 ng/ml (S.E.) The duration of the LH surge was prolonged and occurred over a 3.5-4 day period. In 52% of the cycles examined, an episodic burst of LH (mean 6.1 ± 0.9 ng/ml) was detected 3-9.5 days prior to peak preovulatory concentrations of LH. This early release of gonadotropin may be associated with preovulatory luteinization and early progesterone secretion by the follicle. Evidence of ovulation was found in 9 3.5% of the follicles by 96 h after the LH peak, with the greatest incidence (77.2%) of follicular rupture occurring over the interval of 24-72 h following the LH peak. Wide variations in the physical and behavioral signs of estrus were observed. The mean length of proestrus was 8.7 days (range 3-17 days) and the mean duration of estrus was 11.4 days (range 3-21 days). The LH peak or the onset of ovulation could not be correlated with a specific day of proestrus or estrus. However, 22/25 LH peaks were detected within ±3 days of the first day of estrus. These results, employing direct ovarian examination and frequent blood sampling, suggest that 1) the duration of the LH surge in the bitch is prolonged in comparison to most common domestic animals; 2) most ovulations in the bitch occur 24-72 h following peak serum LH concentrations; 3) a specific day of standing estrus is not precisely related to the onset of the LH surge in the bitch and therefore cannot be used as an accurate estimate of time of ovulation in this species.

Estradiol treatment and luteinizing hormone (LH) response of prepubertal Holstein heifers.

Twenty-one prepubertal Holstein heifers 29 ± 1 weeks of age (188 ± 9kg) were given estradiol (E2) at various dosages, in different forms and by different routes of administration. Response was measured by changes in blood serum LH. Estrous behavior was not induced in any of the heifers treated with E2. Priming with progesterone had no effect on the LH response in heifers given 4 mg 17 -estradioI intramuscularly. An LH surge was observed at all dosages of E2 (62.5-4000 i g’ but not in all heifers treated. The failure of heifers to respond was not related to dosage of E2, to pretreatment serum progesterone levels or to the size or age of the heifers. However, pretreatment serum LH levels tended to be higher (1.7 ± 0.2 vs 0.9 ± 0.1 ng/ml;P=0.07) m heifers which failed to respond. Over all experiments, a slight relationship (b=0.002, P=0.06) was observed between the dosage of E2 and the quantity of LH released. Peak serum LH, time to peak serum LH and total serum LH released were equally effective in measuring the responsiveness of the heifers to E2. An LH release was observed in 80% of the heifers at 18 ± 0.8 h following E2 treatment. Peak serum LH levels averaged 42.5 ± 8.8 ng/mi and were highest following i.m. injection of 17#{216}-estradiol-3benzoate (74 ± 22 ng!ml). A 24 h i.v. infusion of E2 (2.6-41.7 Mg/h) also induced an LH release. We conclude that the prepubertal heifer, similar to the mature cow, has a functional hypothalamic-pituitary-gonadal feedback system.

Serum LH concentrations and ovarian activity in cows with repetitive administration of LH-RH/FSH-RH.

The effect of luteinizing hormone-releasing hormone/follicle stimulating hormone (LH-RH/RSH-RH) on serum luteinizing hormone (LH) concentrations was studied in Angus heifers and cows. The animals received 150 mcg LH-RH/FSH-RH in acidified saline intravenously via an indwelling catheter every 4 hours for 96 hours on Days 16 through 19 of the estrous cycle. Mean serum LH vaues were significantly higher in treated heifers compared with controls (p <.01). During the 1st half of the treatment period peak serum LH values were significantly higher than those observed during the 2nd half (p <.01). LH values returned to near basal concentrations within 4 hours of treatment. Cows ovariectomized at the end of the treatment period did not show any marked differences in follicular fluid volume or corpora lutea weight compred with controls. The results indicate that the regimen failed to stimulate ovarian activity in the cow though the decline and subequent rise in peak serum LH during treatment is not yet understood.

Secretion of alpha subunits of luteinizing hormone (LH) by the anterior pituitary.

Free alpha subunit chains of the glycopeptide pituitary hormones have been found in the sera of normal subjects and postmenopausal women. To ascertain whether the alpha subunit of LH is directly secreted by the pituitary or formed as a result of degradation of intact LY in the periphery, alpha subunits and intact LH were measured by radioimmunoassay in human volunteers after LRF stimulation and purified LH infusion. In 4 subjects a loading dose of 90 IU, followed by the infusion of 22.5 IJ of purified human LH over 30 min, produced peak serum LH levels of 41 mIU/ml but no change in alpha subunit levels of 35 IU of purified human LH to an additional 4 subjects, produced peak LH levels of 8* mIU/ml, but again, no change in alpha subunits. In the same two groups of subjects 100 mug of LRF produced peak LH levels of 25 mIU/ml and 75 mIU/ml, respectively, with significant alpha subunit elevations at 20 min of 1.7 ng/ml and 2.7 ng/ml, respectively. In separate groups of men LRF was administered over a wide dose range of 1 to 3,000 mug and LH and the alpha subunit measured. A dose-response curve existed over the entire LRF dose range for blood LH; no minimum or maximum plateaus were observed over the range studied. However, the alpha chain response appeared to reach a maximal plateau at a dose of 100 mug of LRF. The results are compativle with the hypothesis that the alpha subunits appearing in the peripheral circulation in response to LRF are due to secretion by the anterior pituitary and not due to peripheral degradation of intact secreted LH.

Absorption of antibodies from the baboon vagina.

The ability of the baboon vagina and cervix to absorb antibodies was studied by measuring luteinizing hormone (LH) estrogen and progestin l evels after the intravaginal instillation of bovine milk immunoglobulin (Ig) (1 gm immunoglobulin/day). Daily treatment resulted in a significant (p less than .01) decrease in mean peak serum LH and progestin levels. The administration of anti-LH did not affect the mean peak estrogen level. There was no apparent effect of control antibodies on LH estrogen or progestin levels in 2 animals studied. The immunological response was confirmed by serological tests in 6 of 9 animals as evidenced by the appearance of antibodies against bovine immunoglobulin. The results emphasize that extreme caution should be taken when introducing potentially toxic or antigenic compounds into the vagina for therapeutic prophylactic or hygienic purposes.

FACTORS INFLUENCING THE SECRETION OF LUTEINIZING HORMONE AND OVULATION IN RESPONSE TO ELECTROCHEMICAL STIMULATION OF THE PREOPTIC AREA IN RATS

SUMMARY Factors affecting luteinizing hormone (LH) secretion in response to stimulation of the preoptic area (POA) of the forebrain in rats were explored by determining serum LH levels after electrochemical stimulation of the POA. In rats made anovulatory by exposure to constant light (CLA rats), peak concentrations of LH in serum were found 2 h after stimulation with 5–15 mC, and 1 h after stimulation with 0·5–1 mC. The peak levels increased with increasing doses between 0·5 and 15 mC. The incidence of rats ovulating and the mean number of ovulations/rat were roughly proportional to the stimulating dose, but a plateau was reached between 5 and 10 mC. A threshold level of serum LH seemed to be necessary for ovulation, and the incidence of ovulations of six ova or more/rat increased with the increase in peak serum LH level. Preoptic-roof section, which cuts dorsal afferents to the POA, enhanced the increase in serum LH in response to POA stimulation in CLA rats, while sodium pentobarbitone anaesthesia decreased the response. In both cases, the incidence of ovulation and the number of ovulations/rat were not different from values found in POA-stimulated control CLA rats showing the same peak serum LH level. In normal cyclic rats the response of serum LH to stimulation was much greater on the morning of pro-oestrus than on that of oestrus; at prooestrus a second rise occurred between 17.00 and 19.00 h. Three days after ovariectomy the basal level of LH increased; these ovariectomized rats showed a small increase in response to a dose of 5 mC. Treatment with 20 μg oestradiol benzoate at the time of ovariectomy, however, resulted in a lowered basal LH level, but the peak response to 5 mC was almost as great as that found in similarly stimulated intact CLA rats. In intact males and in neonatally androgen-treated females the peak levels of serum LH in response to doses of 5 or 15 mC were equivalent to those in CLA females in response to doses of only 1–5 mC.

Human luteinizing hormone in serum during the menstrual cycle: determination by radioimmunoassay.

Human luteinizing hormone (LH) has been quantitated by radioimmunoassay in sera obtained daily from 11 subjects during 16 menstrual cycles. In each cycle, a brief surge in LH was found prior to the rise in basal body temperature. Peak serum LH concentrations, expressed in terms of the Second International Reference Preparation of Human Menopausal Gonadotropin, have ranged from 0.027 to 0.054 IU/ml. The concentration of serum LH was usually lowest at the onset of menstruation, followed by somewhat higher, relatively constant levels throughout the follicular phase. More variable LH levels were found in the luteal phase following the midcyclic peak. Sera were obtained throughout 5 cycles from 3 subjects who had a history of abdominal pain at midcycle. In each cycle, the pain was reported prior to, rather than after, the surge in LH.