Plasma Luteinizing Hormone Concentrations Research Articles

Concentrations of plasma melatonin and luteinizing hormone in domestic gilts reared under artificial long or short days.

Plasma melatonin concentrations were measured every 1-2 h over 24 h and plasma luteinizing hormone (LH) concentrations every 15 min over 12 h in domestic gilts reared under artificial light regimens that had previously been used to demonstrate photoperiodic effects on puberty. In Expt 1, the light regimens both commenced at 12 h light: 12 h dark (12L:12D) and either increased (long-day) or decreased (short-day) by 15 min/week until the long-day gilts were receiving 16L:8D and the short-day gilts 8L:16D at sampling. In Expt 2, both light regimens commenced at 12L:12D and either increased (long-day) or decreased (short-day) by 10 or 15 min/week to a maximum of 14.5L:9.5D or a minimum of 9.5L:14.5D before being reversed. Sampling took place when daylength had returned to 14L:10D (long-day) or 10L:14D (short-day). In immature gilts housed at 12L:12D (Expt 1) and in postpubertal (Expt 1) and prepubertal (Expt 2) gilts reared under long-day or short-day light regimens, mean plasma melatonin concentrations were basal (3.6 pg/ml) when the lights were on and increased to peak concentrations greater than 15 pg/ml within 1-2 h after dark, before declining gradually to basal concentrations at or near the end of the dark phase. In prepubertal gilts bearing subcutaneous melatonin implants and reared under long-days (Expt 2), mean plasma melatonin concentration in the 6 h before dark was 91.9 +/- 5.26 pg/ml and 125.0 +/- 6.66 pg/ml 1 h after dark, but this increase was not statistically significant. In Expt 2, the short-day gilts had fewer LH pulses (2.6 +/- 0.25 vs. 4.6 +/- 0.24; P less than 0.01) in the 12-h sampling period than the long-day gilts, but the amplitude of the pulses (2.28 +/- 0.23 vs. 1.26 +/- 0.16 ng/ml; P less than 0.01) and the area under the LH curve (78.8 +/- 5.60 vs. 47.3 +/- 6.16; P less than 0.01) was greater in the short-day gilts. In the short-day, but not in the long-day, gilts LH pulses were more frequent (2.0 +/- 0.0 vs. 0.6 +/- 0.25; P less than 0.01), but had a smaller area (61.9 +/- 7.2 vs. 120.2 +/- 23.6; P less than 0.05) in the 6 h of dark than in the 6 h of light, which together made up the 12-h sampling period.(ABSTRACT TRUNCATED AT 400 WORDS)

Requirement of thyroid function for the expression of seasonal reproductive and related changes in red deer (Cervus elaphus) stags.

The effect of thyroid function on regulation of seasonal reproduction was investigated in three red deer stags thyroidectomized (THX) in summer (January 1988) in comparison with five thyroid-intact controls. Responses of luteinizing hormone (LH) and testosterone to a bolus injection of 10 micrograms gonadotrophin-releasing hormone (GnRH) were tested in July, October, December, February and April. Blood samples were collected at weekly intervals from December 1987 to June 1989 for measurement of testosterone, triiodothyronine (T3) and prolactin concentrations. Testis diameters were measured every 2 weeks. In October 1988 (spring), plasma LH concentrations of control stags were less responsive (P less than 0.01) to stimulation by GnRH than those of THX stags; plasma testosterone concentrations and testis diameters were low and there was no increase in plasma testosterone concentrations after injection of GnRH in control stags during October or December (spring, early-summer). In contrast, THX stags maintained a testosterone response (P less than 0.01) in these 2 months and did not exhibit any signs of a seasonal lack of reproductive activity at this time of year. Control stags cast antlers in spring whereas THX stags maintained hard antlers throughout the study. Concentrations of plasma T3 were not detected in THX stags from June 1988 onwards, but exhibited a seasonal pattern in control stags, with low concentrations during autumn and winter (April to July) and high concentrations in spring and summer (August to February). There was no effect of thyroidectomy on the seasonal pattern of prolactin secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Endocrinology of nutritional flushing in gilts

As part of a nutritional flushing study, the endocrine status of gilts was compared to gain further knowledge of the mechanism(s) that mediate the restoration of ovulation rate. From 45.3 kg BW to puberty, 42 gilts were fed 2.0 kg d−1 (L) or ad libitum (H). From puberty to second estrus, one-half of the L gilts had their feed allowance increased to 2.8 kg d−1 (LH). Gilts in the H group continued to be fed ad libitum (HH). Gilts in the LH and H groups showed a greater increase in ovulation rate between first and second estrus than LL gilts (P < 0.05). Based on sampling every 4 h through the peri-estrous period of 28 gilts, feeding level did not affect mean plasma follicle-stimulating hormone (FSH), luteinizing hormone (pLH), estradiol-17β or progesterone concentrations (P > 0.05). During the follicular phase, however, LH and HH gilts had not only a greater proportion of samples > 1 ng mL−1 but also showed an increased mean pLH daily sample variance compared with LL gilts (P < 0.05). The latter parameters were interpreted as indicators of an increased frequency of episodic pLH release. Furthermore, HH gilts had greater (P < 0.05) plasma insulin concentrations through the peri-estrous period and greater insulin-like growth factor I (IGF-I) concentrations during the pLH-surge period than LL gilts. These results confirm that increased plasma insulin may be an important metabolic cue, which in an independent or synergistic action with gonadotropins and IGF-I mediates the ovulatory response to flush-feeding. Key words: Gilt, flushing, ovulation, gonadotropins, insulin, IGF-I.

Effect of daylength on the rate of recovery of photosensitivity in male starlings (Sturnus vulgaris)

Four groups of castrated photorefractory starlings were transferred from a photoperiod of 18 h light/day (18 L) to photoperiods of 6 L, 8 L, 11 L or 12 L. A control group was kept on 18 L. Plasma concentrations of luteinizing hormone (LH) were low in all groups initially. The first significant increase in LH, which signals the recovery of photosensitivity, occurred after 4 weeks in the groups on 6 L and 8 L, after 8 weeks in the 11 L group and after 13 weeks in the 12 L group. There was no increase in the group on 18 L. The rate of recovery of photosensitivity is therefore inversely proportional to daylength, for daylengths between 8 L and 12 L.

Social control of reproduction in breeding and non-breeding male naked mole-rats (Heterocephalus glaber)

Eight male naked mole-rats, from three colonies were studied in captivity. When non-breeding male naked mole-rats were removed from their colonies and paired with a non-breeding female, or removed and housed singly for 6 weeks before pairing with a female, concentrations of urinary testosterone and plasma luteinizing hormone (LH) increased significantly (P less than 0.05). Concentration of these hormones were highest while the males were singly housed: urinary testosterone (mean +/- s.e.m.) increased from 8.2 +/- 1.3 ng/mg urinary creatinine (Cr) in a non-breeder in a colony to 49.1 +/- 5.5 ng/mg Cr when singly housed and 21.8 +/- 2.5 ng/mg Cr when paired with a female. Plasma LH concentrations increased from 4.7 +/- 1.0 miu/ml when a non-breeder in a colony to 19.8 +/- 4.0 miu/ml when singly housed and 9.9 +/- 1.1 miu/ml when paired with a female. After pairing with a female, the pattern of urinary testosterone secretion in the male was synchronized with the ovarian cycle of the female mate, such that urinary testosterone concentrations were significantly higher during the early follicular phase of the female's cycle (P less than 0.05). These results suggest that active suppression of reproductive physiology by social cues occurs in non-breeding male naked mole-rats, and that this is readily reversible if social cues are removed and males are housed singly. When a male was subsequently paired with a female, endocrine suppression was partially reimposed on the reproductively active males, such that urinary testosterone concentrations were suppressed to values similar to those in non-breeding males, except for periods prior to mating.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of medial preoptic GABA neurones in regulating luteinising hormone secretion in the ovariectomised rat

The role of GABA neurones in the medial preoptic area (MPOA) in regulating the activity of the luteinising hormone-releasing hormone (LHRH) neurones projecting to the median eminence was investigated in the conscious ovariectomised rat. Plasma luteinising hormone (LH) concentrations were measured while (1) endogenous GABA release from the MPOA was monitored with the technique of microdialysis, or (2) activity at the GABA receptor was modulated by local infusions into the MPOA. Microdialysis studies revealed a fluctuating level of GABA release in the MPOA which did not correlate with pulsatile LH secretion. Infusion of 10 microM GABA (n = 8) or bicuculline methiodide (BMI, n = 6) into the MPOA, at a rate of 1 microliter/30 min, significantly inhibited mean LH concentrations (P less than 0.05-0.001) and LH pulse frequency (P less than 0.05-0.001) compared with controls (n = 8). LH pulse amplitude was not significantly altered by infusion of GABA (P greater than 0.05) while too few pulses were found after BMI treatment to enable statistical analysis. Infusions of GABA into the ventral half of the MPOA had a more significant inhibitory effect upon LH secretion compared with dorsal infusions (P = 0.012). A similar relationship did not exist for BMI infusions. These results show that acute changes in preoptic GABA receptor occupancy result in disruption of pulsatile LH secretion in the ovariectomised rat. This suggests that GABA neurones provide a tonic input important for the functional integrity of the neural network controlling LH secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Various Types of Hypothalamic Deafferentation on Luteinizing Hormone Pulses in Ovariectomized Rats

Abstract The pulsatile luteinizing hormone (LH) secretion in chronically ovariectomized rats bearing various types of hypothalamic deafferentation was examined. Ovariectomized rats were subjected to complete, anterolateral or anterior hypothalamic deafferentation and bled every 6 min for 3 h through an indwelling atrial cannula 5 days after the brain surgery. Another group of ovariectomized animals was subjected to posterior-anterior hypothalamic deafferentation (PAD), which cut off the anterior part of the arcuate nucleus from the mediobasal hypothalamus, and bled 1, 3 or 5 weeks after the deafferentation. Coronal sections of the brain were immunostained with anti-LH-releasing hormone (LHRH) serum. The pulsatile LH secretion was observed in rats bearing anterior, anterolateral or complete hypothalamic deafferentation and these types of deafferentation did not affect the frequency of LH pulses. The mean LH level during the 3-h sampling period and the amplitude of LH pulses decreased as the incision extended postero-laterally. Rats bearing PAD showed an irregular fluctuating pattern in plasma LH concentration 1 week after PAD. Parameters of LH pulses were restored with time after PAD. This suggests that the system generating LHRH pulses severed by PAD had been reorganized. LHRH-immunopositive neuronal fibres were found in the external layer of the median eminence in the rats bearing any type of deafferentation. The present results suggest that the frequency of LH pulses could be controlled by the LHRH pulse generator, which consists of non-LHRH neurons and is located in the mediobasal hypothalamus.

Plasma progesterone and luteinizing hormone concentrations and the role of the corpus luteum and LH gonadotrophs in the control of delayed implantation in Schreibers' long-fingered bat (Miniopterus schreibersii)

In Schreibers' long-fingered bat from South Africa (approximately 33 degrees S) copulation, ovulation and fertilization occurred in April and May, implantation was delayed until August, and parturition occurred in December. Delayed implantation coincided with winter, during which the bats remained active, only entering prolonged periods of torpor during particularly cold spells. Plasma progesterone concentration was low during non-pregnancy (1.54 ng/ml) and during delayed implantation (1.67 ng/ml), and thereafter increased to reach a peak mean of 64.82 ng/ml in late pregnancy. Changes in size and ultrastructure of the luteal cells indicated periods of steroidogenesis just after formation of the corpus luteum, and for about 2 months after implantation; reduced steroidogenic activity during delayed implantation; and luteolysis in the last 2 months of pregnancy. Plasma luteinizing hormone (LH) concentration and pituitary LH-beta immunoreactivity were highest during follicular development and peaked just before ovulation. During early delayed implantation, plasma LH concentration was low, and both plasma LH and pituitary LH-beta immunoreactivity increased from July, reaching peaks in late pregnancy. LH may be required to activate the corpus luteum and terminate delayed implantation, or, as in some small carnivores, it may be required for luteal maintenance.

Plasma concentrations of luteinising hormone and body weights during somatic maturation in intact and castrated Australorp cockerels from a line of hens selected for increased ovulation rate

1. Plasma concentrations of luteinising hormone (LH), comb size and body weight were measured between 46 and 208 d of age in intact and castrated cockerels from lines of selected and control Australorp domestic chickens. The selected line had been selected for increased rate of lay by reducing oviposition intervals within sequences. The cockerels were reared and maintained on 15.25 h light/d. 2. Concentrations of plasma LH in the intact control cockerels were low in the 'immature' phase (less than 100 d old) and increased during the 'mature' phase (older than 175 d) with a peak occurring when the testes are beginning to grow at the onset of the 'mature' phase. In comparison with the control line of cockerels, the selected line had significantly higher plasma LH concentrations at the onset of the 'mature' phase. Selection had no effect on the mean concentration of plasma LH in either the immature phase or a few weeks after the onset of the mature phase. 3. There was no effect of selection in sibling females for higher rates of lay on changes in comb size or body weight during sexual maturation in the intact cockerels. 4. Castration at 45-46 d of age resulted in increased plasma LH concentrations and no comb growth. Plasma LH concentration increased progressively between 40-208 d. There was no difference between the two lines of cockerels in plasma LH concentration or rate of body growth after castration. 5. It is concluded that selection of females for a change in the rate of egg production has resulted in increased plasma LH concentrations in sibling males around the onset of sexual maturation. Selection appears to have caused this effect by altering an unidentified component of the inhibitory feedback mechanism which controls the tonic secretion of LH.

Effect of castration on plasma concentrations of luteinizing hormone and follicle-stimulating hormone in adult Merino rams which were homozygous carriers or non-carriers of the Booroola fecundity gene

Before castration, the mean plasma concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) did not differ between FF and ++ Booroola rams. After castration, mean LH and FSH concentrations increased after 8 h, and for the next 14 days the rate of increase in FSH, but not LH, secretion was significantly faster in FF than in ++ rams (P less than 0.05). Mean FSH concentrations over this period were significantly higher in FF than in ++ rams (P less than 0.05). In both genotypes, the ranked FSH values did not significantly change their order over time, i.e. a significant within-ram effect was noted (P less than 0.05). Repeated-measures analysis of variance indicated a significant effect of genotype on mean FSH secretion (P less than 0.05) and a significant effect of sire in the FF (P less than 0.05), but not the ++ (P = 0.76), genotype. From Day 28 to Day 58 after castration, FSH and LH concentrations were variable and no overall increases in concentrations were observed. The mean concentrations of both hormones over this period were not related to genotype. There were no gene-specific differences in pulsatile LH secretion 14 weeks after castration. However, the mean LH, but not FSH, response to a bolus injection of 25 micrograms of gonadotrophin-releasing hormone (GnRH) was significantly higher in FF than in ++ rams (P less than 0.05) and this was not significantly affected by sire. These studies support the hypothesis that the F gene is expressed in adult rams, in terms of pituitary responsiveness to an injection of GnRH and to the removal of the testes, but it is not clear from this study whether the influence of sire is related to or independent of the apparent gene-specific differences.

Effects of Ethane Dimethane Sulphonate and Orchidectomy on Luteinizing Hormone Secretion

Abstract The aim of this study was to determine whether testicular products of non-Leydig cell origin modulate rat luteinizing hormone (LH) secretion in vivo. We therefore compared the effects of ethane dimethane sulphonate (EDS), a toxin regarded as highly selective for Leydig cells, with that of bilateral orchidectomy on LH secretion in mature male Wistar rats. The intention was thereby to compare the effects of selective removal of Leydig cells with that of removing both Leydig cells and seminiferous tubules, respectively. Following a single dose of EDS (75 mg/kg, ip), plasma LH concentrations rose equally with those of castrated rats for the first 3 days. After that time, however, plasma LH concentrations in the EDS-treated rats fell progressively below those of the orchidectomized rats despite the continuing castrate level of circulating testosterone until Day 17. The effects of EDS treatment or orchidectomy on pulsatile LH secretion were then compared after 11 days to castrate levels of testosterone. EDS-treated rats demonstrated reduced LH pulse amplitude, mean plasma LH levels and net LH secretion compared with castrate rats, although LH pulse frequency was unaltered. However, a further group of rats treated with EDS and orchidectomized failed to demonstrate that these changes were fully reversed by the castration and therefore EDS may have direct effects upon pituitary LH secretion. In order to determine the mechanism of the reduced LH pulse amplitude after EDS treatment, a further study was conducted to determine whether EDS treatment resulted in reduced pituitary sensitivity to gonadotropin-releasing hormone (GnRH). Responsiveness of pituitary LH to exogenous GnRH (0.01 to 10 mug/kg body wt) was studied 11 days after removal of testicular testosterone feedback by either EDS or castration. Plasma LH response was linearly related to the log of the GnRH dose. At 10 min after GnRH administration, the plasma LH response in EDS-treated rats was less sensitive than in castrate rats. We conclude that the lesser augmentation of LH secretion between Days 3 and 17 after EDS treatment compared with castrate rats cannot be explained solely by changes in Leydig cell secretion but may involve direct effects of EDS on pituitary LH secretion or non-Leydig cell testicular products. Dampening of LH pulse amplitude without change in LH pulse frequency together with the reduced sensitivity to GnRH in EDS-treated rats suggests that this toxin may have direct effects on pituitary LH secretion independent of its effects on Leydig cell function.

Plasma luteinizing hormone bioactivity and immunoactivity in ovariectomized rats treated with a long-acting agonist of luteinizing hormone releasing hormone.

The dose response of a luteinizing hormone releasing hormone (LHRH) agonist in rats with high endogenous gonadotrophin levels was determined. Female rats were ovariectomized and injected with 0.3 microgram (group B), 3.2 micrograms (group C), 32 micrograms (group D) and 320 micrograms (group E) of a slow-releasing microcapsule preparation of the LHRH agonist D-Trp 6-LHRH. Control ovariectomized rats (group A) remained untreated. Plasma luteinizing hormone (LH) concentrations were measured by radioimmunoassay (RIA) before the LHRH agonist injection as well as 5, 15 and 30 days thereafter. Furthermore, LH bioactivity was determined by an in vitro rat LH bioassay in order to evaluate changes in bioactivity after administration of LHRH agonist. In control rats, plasma LH concentrations increased to 4.8 +/- 1.3 ng/ml on day 5, reaching peak levels of 9.9 +/- 1 ng/ml on day 30. In contrast to the control group, those rats which received 320 micrograms of LHRH agonist did not show any increase. Rats which received intermediate doses (groups C and D) tended to maintain levels of LH halfway between group A and group E during the first 15 days of treatment. Thereafter LH concentrations were similar to the untreated control group. The course of the LH concentrations during treatment measured by bioassay (BA) showed a similar pattern to the LH concentrations measured by RIA. The BA/RIA ratio was similar in all groups.

Monoamine Content of the Stalk‐Median Eminence and Hypothalamus in Adult Female Sheep as Affected by Daylength

Abstract In the ewe, plasma luteinizing hormone and prolactin concentrations exhibit seasonal variations. During long days, inhibition of pulsatile luteinizing hormone secretion is mediated by monoamines. In a model of ovariectomized ewes bearing a subcutaneous oestradiol implant, we previously showed that the steroid-dependent inhibition of luteinizing hormone involves the A15 dopaminergic nucleus of the retrochiasmatic area. In the present work, we compared the aminergic activities of tele-diencephalic structures in groups of ovariectomized ewes under artificial illumination for short versus long days (8 versus 16 h/day of light, respectively). Half the animals in each group were bearing a subcutaneous oestradiol implant. Using high-performance liquid chromatography and electrochemical detection, we measured the levels of amines and amine metabolites in 'punches' of tissues from regions containing luteinizing hormone-releasing hormone axon terminals or cell bodies and catecholaminergic structures. Concurrently, we checked the pulsatile luteinizing hormone release and plasma prolactin concentration to assess the ability of our model to mimic seasonal changes in the hormonal status. As expected, ovariectomized ewes with a subcutaneous oestradiol implant showed an inhibition of the pulsatile luteinizing hormone release under long days. A higher concentration of plasma prolactin was also observed under long days, without any effect of the steroid treatment. Under this light regimen, statistically significant higher contents of dopamine than under short days were found in the stalk-median eminence. Larger contents of homovanillic acid, a dopamine metabolite, and 4-hydroxy-3-methoxyphenylethyleneglycol (MHPG), a noradrenaline metabolite were observed in the infundibular nucleus, while the catechola-mines themselves remained unchanged. Furthermore, oestradiol also significantly increased the content of MHPG in the latter structure. During long days, animals without oestradiol treatment exhibited a significant lower content of noradrenaline in the A15 nucleus, without any alteration of the dopamine content. Daylength or oestradiol treatment had no significant effects on the levels of amines or amine metabolites in the preoptic or septal areas. Thus, our results in the ewe underline the role played by the medial basal hypothalamus in the catecholaminergic regulation of seasonal changes in hormone release and suggest modifications in the turnover of the neurotransmitters in some structures.

Plasma Luteinizing Hormone, Steroid Hormones, Behavioral Role, and Nest Stage in Cooperatively Breeding Harris' Hawks (Parabuteo unicinctus)

We measured plasma levels of testosterone (T), estradiol 17β (E), corticosterone, and luteinizing hormone (LH) in adult breeders, adult-plumaged helpers, and juvenal-plumaged helpers of the cooperatively breeding Harris' Hawk (Parabuteo unicinctus) in southeastern Arizona. In the males, both adult breeders and most adult-plumaged helpers had elevated T and LH during February and March, when nest building occurs, whereas most juvenal-plumaged helpers showed no change in LH, T, or E throughout the year. Thus adult-plumaged helpers, usually not related to the breeders, are hormonally ready to breed in the spring. We suggest that these helpers attain breeding readiness because potential benefits they can derive from either occasional successful copulations or possible attainment of the breeding position make reproductive readiness advantageous. In contrast, most juvenal-plumaged helpers are aiding their own parents on their natal territory and are not hormonally ready to breed, and thus they physiologically avoid the potential for inbreeding. An exception to this was a juvenal-plumaged male helper with elevated testosterone levels who was not helping his parents. The female breeders we examined had elevated T, LH, and E during the nest-building period, whereas the helpers (both adult- and juvenal-plumaged) did not show elevations at any time of the year. During the early part of the nesting cycle, the adult-plumaged female helpers weighed significantly less (ca. 10%) than the breeders. It is possible that poor body condition, subordinate status to the breeding females, or both were related to their lack of breeding readiness. In all birds, corticosterone levels increased with handling time, and were higher during the nesting periods than during non-nesting periods, but showed no consistent relation with helper or breeder status. As in other species that are relatively social, maintain long-term pair bonds, or are tropical in distribution, plasma concentrations of LH and sex steroids in Harris' Hawks, even when elevated, were relatively low.

Effects of reducing the remating interval after parturition on the fertility and plasma concentrations of luteinizing hormone, prolactin, oestradiol-17 and progesterone in lactating domestic rabbits

Primiparous crossbred does were remated on Day 1 (n = 15) or 14 (n = 25) post partum and killed on Day 10 post coitum to assess their fertility. Blood samples were taken during the pre- (0-12 h post coitum) and post- (1-10 days post coitum) ovulatory periods and plasma was assayed for luteinizing hormone (LH), prolactin, oestradiol-17 beta and progesterone. Ovulation response was significantly greater (P less than 0.01) and ovulation rate significantly lower (P less than 0.001) in does mated on Day 1 than in those mated on Day 14 post partum. Does failing to ovulate on Day 14 post partum exhibited no preovulatory LH surge and had significantly lower (P less than 0.05) premating concentrations of oestradiol-17 beta and prolactin than those ovulating at this time. No significant differences in hormone concentrations were observed during the preovulatory period between does ovulating on Days 1 and 14 post partum, with the exception of oestradiol-17 beta. Concentrations of this hormone were significantly lower (P less than 0.01) in does mated on Day 1, at 1 h post coitum. We conclude that (i) fertility was affected by the remating interval after parturition, (ii) ovulation failure was associated with an absence of the preovulatory LH surge and a reduction in premating concentrations of oestradiol-17 beta and prolactin and (iii) the lower ovulation rate in early lactation was apparently caused by a reduction in ovarian competence to respond to the gonadotrophic stimulus.

Pulsatile immunoreactive and bioactive luteinizing hormone secretion in adolescents with chronic renal failure

Delayed or arrested pubertal development is common in children with chronic renal failure (CRF). Normal puberty is initiated by the onset of episodic nocturnal secretion of luteinizing hormone (LH) containing an increasing proportion of bioactive hormone. To test the functional integrity of the hypothalamo-pituitary axis in CRF we measured immunoreactive (i-LH) and bioactive (bio-LH) plasma LH concentrations at 15-min intervals from 2000 to 0700 hours in 65 pubertal patients aged 10-23 years [46 boys/19 girls; 20 on conservative treatment (CT), 13 on dialysis (D), 32 with transplants (TP)]. i-LH was determined by radio-immunoassay and bio-LH by a mouse Leydig cell assay. Peak detection was performed by the cluster analysis computer programme. The mean (+/- SD) number of i-LH (in both sexes) and bio-LH pulses (in boys) per profile, and the mean peak area of i-LH (in both sexes) and bio-LH (in girls) were higher in TP than in CT or D patients. The ratio of bio-LH to i-LH increased during puberty in CT (G1 vs G4/5, 0.3 +/- 0.5 vs 1.8 +/- 0.,4) and TP (0.6 +/- 0.7 vs 1.8 +/- 0.7) but remained low in male D patients (0.4 +/- 0.7 vs 1.1 +/- 0.8). The ratios were subnormal, however, even in mature TP patients compared with healthy adults. The bio-LH/i-LH ratio and the bio-LH peak area best predicted integrated nocturnal testosterone concentrations in TP but not in uraemic male patients.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of the GnRH analogue buserelin for IVF—does it improve fertility?

To determine the effect of a short course of the GnRH analogue buserelin and human menopausal gonadotrophin (hMG), for ovarian stimulation in our IVF programme, on reproductive endocrinology and pregnancy rates compared with conventional clomiphene citrate and hMG treatment. Prospective randomized allocation to one of two ovulation stimulation regimens. Fertility clinic. 373 infertile couples with various factors associated with their subfertility. All the women were less than 46 years of age and had normal menstrual cycles. The first group (n = 151) was given clomiphene citrate (CC) from days 2-6 of the menstrual cycle and hMG from day 5 onwards (CC/hMG). The second group (n = 222) was given buserelin from days 1-3 and hMG from day 2 (buserelin/hMG). Concentration of plasma luteinizing hormone (LH), oestradiol (E2) and progesterone, number of ovulatory follicles induced and the occurrence of pregnancy. Plasma LH, E2 and progesterone concentrations were reduced in the late follicular phase after buserelin/hMG compared with CC/hMG. Buserelin/hMG promoted the development of more follicles than CC/hMG. The overall pregnancy rate after buserelin/hMG was not significantly different from that following CC/hMG treatment. The chance of pregnancy is not improved by the short-term use of buserelin with hMG, provided adequate follicular phase management is maintained.

Inhibitory feedback action of oestradiol on tonic secretion of luteinizing hormone in pre-and postpubertal gilts

Experiments were performed in gilts to test whether the inhibitory feedback action of oestradiol-17β on tonic luteinizing hormone (LH) secretion decreases around puberty and whether a stimulus to tonic LH secretion occurs which is independent of ovarian steroid control. Fifty-eight German Landrace gilts were either ovariectomized (OVX), OVX and treated with oestradiol-17β via subcutaneous silastic implants to maintain chronic low levels of oestradiol-17β, or served as controls. Treatments began at either 130, 180 or 210 days of age. All 130- and 180-day-old gilts providing data used for analysis were prepubertal, while 210-day-old gilts were OVX between Days 9–15 of their first oestrous cycle. Blood samples for analysis of LH were taken over a 4 h period at 10 min intervals 1 day before OVX and on Days 2, 7, 14, 21 and 28 after OVX. Intact controls were sampled on corresponding days. Mean LH, nadir LH levels, LH pulse frequency and amplitude were calculated for each 4 h sampling period. Mean plasma LH levels were not affected by age in intact controls. Within 2 days of ovariectomy plasma LH concentrations increased rapidly and then further increased only marginally without any difference between the three age groups. In the youngest age group which received a 3 cm oestradiol-17β implant resulting in oestradiol levels and uterine weights below those of respective controls ( P < 0.05), plasma LH was suppressed until 145 days of age when circulating LH increased ( P < 0.01). Between 180 and 210 days of age oestradiol-17β implants of 6 cm length (producing oestradiol levels and uterine weights similar to those of respective controls) suppressed LH to levels of controls. In postpubertal gilts oestradiol-17β implants of the same length and with similar effects on plasma oestradiol levels were unable to suppress LH until 21 days after ovariectomy when LH returned to pretreatment levels. Changes in mean LH in all age and reproductive status groups reflected changes in LH pulse frequency and nadir LH levels, whereas LH pulse amplitude was not affected. Since the postovariectomy levels of LH did not differ between pre- and postpubertal animals, it appears that in the gilt a stimulus to tonic LH secretion which is independent of ovarian steroid control does not occur during puberty. A major part of the reduction in the sensitivity to oestradiol negative feedback became apparent after first ovulation, which does not support the view that a resetting of the “gonadostat” initiates ovarian cyclicity. The transition from high to low oestradiol feedback sensitivity may be temporary or not complete even after first ovulation and a return to the hypersensitive state may occur.

Secretion of LH and progesterone after intravenous administration of GnRH in the camel ( Camelus dromedarius)

Five multiple intravenous injections of GnRH (50 μg every 2 h) to non-pregnant female-camels resulted in a significant increase in the peripheral plasma concentration of luteinizing hormone (LH) compared with saline-treated animals. Gonadotrophin releasing hormone (GnRH) treatment also resulted in oestrus and the formation of a short-lived corpus luteum (indicated by rectal palpation and progesterone secretion). The level of oestrogen was not affected by GnRH or saline injection during the treatment period.

The effect of alternating months of “long days” and “short days” on plasma luteinising hormone and testosterone concentrations in Welsh Mountain Pony stallions

The hypothesis to be tested was whether the highly seasonal Welsh Mountain Pony stallion can be transformed into an animal potentially able to reproduce all the year round by exposing it to alternating months of “long days” (16L:8D) and “short days” (8L:16D). Two Welsh Mountain Pony stallions were kept under natural daylight from January (8L:16D) until 4 July (16L:8D) and thereafter on alternating four-week periods of short days and long days. Plasma samples were collected hourly over 12-hour periods in February, May and June, and again at the end of every four-week artificial photoperiod. Luteinising hormone (LH) and testosterone concentrations were determined by radio-immunoassay. Plasma LH and testosterone concentrations rose from 0.34 ng ml −1 and 2.52 nmol l −1 respectively in February to maximum values of 2.66 ng ml −1 and 4.97 nmol l −1 in June (all values expressed as geometric means). Each subsequent period of short days suppressed both LH and testosterone concentrations (greatest mean = 1.03 ng ml −1 and 3.16 nmol l −1) whereas each period of long days stimulated them (smallest mean = 1.49 ng ml −1 and 3.64 nmol l −1). It was concluded that alternating months of long and short days did not transform the highly seasonal Welsh Mountain Pony into an animal capable of reproducing all the year round.