Changes In Plasma LH Concentrations Research Articles

Does kisspeptin participate in GABA-mediated modulation of GnRH and GnRH receptor biosynthesis in the hypothalamic-pituitary unit of follicular-phase ewes?

The inverse relationship between GnRH transcript level and GABA neurons activity has suggested that GABA at the hypothalamic level may exert a suppressive effect on subsequent steps of the GnRH biosynthesis. In the present study, we analyzed the effects of GABA type A receptor agonist (muscimol) or antagonist (bicuculline) on molecular mechanisms governing GnRH/LH secretion in follicular-phase sheep. ELISA technique was used to investigate the effects of muscimol and/or bicuculline on levels of post-translational products of genes encoding GnRH ligand and GnRH receptor (GnRHR) in the preoptic area (POA), anterior (AH) and ventromedial (VMH) hypothalamus, stalk/median eminence (SME), and GnRHR in the anterior pituitary (AP). Real-time PCR was chosen for determination of the effect of drugs on kisspeptin (Kiss 1) mRNA level in POA and VMH including arcuate nucleus (VMH/ARC), and on Kiss1 receptor (Kiss1r) mRNA abundance in POA-hypothalamic structures. These analyses were supplemented by RIA method for measurement of plasma LH concentration. The study demonstrated that muscimol and bicuculline significantly decreased or increased GnRH biosynthesis in all analyzed structures, respectively, and led to analogous changes in plasma LH concentration. Similar muscimol- and bicuculline-related alterations were observed in levels of GnRHR. However, the expression of Kiss 1 and Kiss1r mRNAs in selected POA-hypothalamic areas of either muscimol- and bicuculline-treated animals remained unaltered. Our data suggest that GABAergic neurotransmission is involved in the regulatory pathways of GnRH/GnRHR biosynthesis and then GnRH/LH release in follicular-phase sheep conceivably via indirect mechanisms that exclude involvement of Kiss 1 neurons.

Melatonin Stimulates the Release of Gonadotropin-Inhibitory Hormone by the Avian Hypothalamus

Gonadotropin-inhibitory hormone (GnIH), a neuropeptide that inhibits gonadotropin synthesis and release, was first identified in quail hypothalamus. GnIH acts on the pituitary and GnRH neurons in the hypothalamus via GnIH receptor to inhibit gonadal development and maintenance. In addition, GnIH neurons express melatonin receptor and melatonin induces GnIH expression in the quail brain. Thus, it seems that melatonin is a key factor controlling GnIH neural function. In the present study, we investigated the role of melatonin in the regulation of GnIH release and the correlation of GnIH release with LH release in quail. Melatonin administration dose-dependently increased GnIH release from hypothalamic explants in vitro. GnIH release was photoperiodically controlled. A clear diurnal change in GnIH release was observed in quail, and this change was negatively correlated with changes in plasma LH concentrations. GnIH release during the dark period was greater than that during the light period in explants from quail exposed to long-day photoperiods. Conversely, plasma LH concentrations decreased during the dark period. In contrast to LD, GnIH release increased under short-day photoperiods, when the duration of nocturnal secretion of melatonin increases. These results indicate that melatonin may play a role in stimulating not only GnIH expression but also GnIH release, thus inhibiting plasma LH concentrations in quail. This is the first report describing the effect of melatonin on neuropeptide release.

Broiler breeders do not respond positively to photoperiodic increments given during the laying period

1. Broiler breeders were given a 3-h increase in photoperiod to 11 h at 20 week and then a series of increases to reach 16 or 17 h either immediately after the initial increment or in 30-min, 1- or 2-h increments starting at various ages after peak rate of lay. Controls were maintained on 11 h from 20 weeks. Changes in plasma LH concentration (after 7 d) were measured in birds that had been transferred to 11 or 16 h at 20 weeks and given further increases in photoperiod at 41 or 61 weeks of age. 2. Birds that were transferred to 16- or 17-h photoperiods, irrespective of when and how the maximum photoperiod was reached, had inferior rates of lay between 52 and 60 weeks of age to birds maintained on 11 h from 20 weeks. However, the 11-h birds laid more eggs on the floor and produced a larger number of cracked and dirty eggs, resulting in similar numbers of settable eggs. 3. Although transferring birds from 11- to 16-h photoperiods at 41 weeks of age significantly increased plasma LH concentration, there was no effect on egg production during the ensuing 12 d. None of the other increases in photoperiod significantly increased plasma LH, whether given at 41 or 61 weeks. 4. It is concluded in broiler breeders, that increases in photoperiod applied during the laying period, from 11 or 16 h, have little or no effect on LH secretion, do not compensate for age-related declines in egg production, and adversely affect rate of lay.

Hormonal and ovarian responses to a 5-day progesterone treatment in anoestrous dairy cows in the third week post-partum

Primiparous cows with low body condition at calving have an extended anovulatory period. Induction of ovulation and oestrus is possible with progesterone treatment but the response to this treatment differs between Friesian and Jersey breeds. The objective of this study was to describe changes in pulsatile LH secretion and the synchrony of developing ovarian follicles that occur during a progesterone treatment period of 5 days in primiparous anovulatory cows. The experimental model compared the progesterone treatment with spontaneous post-partum changes as well as a breed comparison in a factorial design. Thirty-six cows (Jersey n=19 and Friesian n=17) were managed to calve with a low body condition score (BCS<4.5). Daily changes in ovarian follicle size were observed with transrectal ultrasonography in each cow from 8 days post-partum. Thirty of these cows were diagnosed to be anovulatory at 12–18 days post-partum (day 0) and allocated to a treatment ( n=16) or a control group ( n=14), balanced for breed. Each treated cow had a progesterone-releasing controlled internal drug-releasing (CIDR) device inserted vaginally for 5 days while control cows were left untreated. Changes in plasma LH concentrations were measured with intensive blood sampling over 8 h on days −1, 1, and 4. Blood samples were also collected daily (06:00 h) for determination of plasma progesterone as well as oestradiol concentrations on days 6 and 8. Treatment with progesterone was associated with a transient initial decrease (day 1) in both LH pulse frequency and mean LH concentrations after device insertion, but both had returned to pre-treatment levels by day 4. Jersey cows had a greater pulse frequency, but there was no breed difference in mean LH concentrations. Patterns of ovarian follicle growth were affected by progesterone treatment with an increase in diameter of the dominant follicle (DF) identified after treatment initiation. This followed an earlier emergence of a new DF after device insertion. Follicular response to progesterone was dependent on the diameter of the DF present at treatment initiation. Those follicles ≥9 mm were replaced by a new DF during treatment such that the DF observed at the time of device removal was large (≥9 mm) and growing in 13/16 cases. Progesterone was not effective for the induction of an LH surge, ovulation and oestrus in anovulatory cows with a low BCS. However, treatment was associated with synchronous development of a DF so that it was large and growing at the end of the treatment period in most cases. This synchronous development may be due to the transient suppression of LH and the presence of an LH-dependent DF.

Effect of timing and size of photoperiod change on plasma FSH concentration and the correlation between FSH and age at first egg in pullets

1. ISA Brown pullets were transferred at 6, 9, 12, 15, 18 or 20.3 weeks of age from an 8 h photoperiod to an 8, 10, 13 or 16 h photoperiod. Plasma follicle stimulating hormone (FSH) concentration was measured at transfer at 7 and 14 d afterwards, and age at first egg (AFE) was recorded. 2. Plasma FSH concentration in pullets reared on constant 8 h photoperiods generally increased with age but with a trough at 12 weeks. Plasma FSH increased during the first 14 d of photostimulation to a significantly higher concentration, compared with constant 8 h controls, when the photoperiod was increased to 13 or 16 h at 9, 12 or 15 weeks; but for the increase from 8 h to 10 h photoperiods FSH was only significantly higher than controls when the change was made at 12 weeks. 3. The change in plasma FSH concentration 14 d after photostimulation was significantly correlated with mean AFE (reported in Lewis et al. , 1997) and appears to be a better predictor of gonadal development than concurrent changes in plasma LH concentration previously reported (Lewis et al. , 1994).

Effect of feed intake during lactation and after weaning on sow reproductive performance

To study the effects of feed intake during lactation and after weaning on reproductive performance, 89 second-parity Lacombe sows were allowed 6 kg feed d−1 (H) or were restricted to 3 kg feed d−1 (R) during lactation and during the weaning to estrus interval (WEI); this resulted in a 2 × 2 factorial design (groups HH, HR, RH and RR). To minimize the confounding effects of duration of WEI on sow performance, the experiment was terminated 10 d after weaning. The diet was formulated to provide 12.4 M J ME kg−1 and 16% crude protein. Restricted feeding during lactation resulted in a longer (P &lt; 0.05) WEI (7.3 d vs. 5.9 d). WEI was not affected by feed intake after weaning. Fewer (P &lt; 0.05) sows feed restricted during lactation exhibited estrus by 10 d from weaning (31.8% vs. 88.9%). Ovulation rate was not affected by lactation or postweaning feed intake. However, embryo survival at 25 d of gestation was influenced (P &lt; 0.05) by feed intake during both periods. The highest embryo survival (85%) was in HR sows, and the lowest (64%) was in RR sows. Blood samples were taken from 12 sows from each of the four treatments by means of indwelling vena cava cannulae at 6-h intervals from weaning until 24 h after mating or 10 d after weaning, whichever came first. Plasma gonadotrophin concentrations were reduced (P &lt; 0.05) by low feed intake during lactation but were unaffected by postweaning feed intake. Peak preovulatory LH surge concentrations were highest (9.5 ng mL−1) in HR sows and lowest (7.6 ng mL−1) in RR sows (P &lt; 0.05). These data confirm the adverse effects of restricted feeding during lactation on the reproductive performance of sows and indicate that such effects may be mediated through changes in plasma LH concentrations. No significant effect of post-weaning feed intake on any measured factor was observed. Key words: Sow, feed intake, reproductive performance

Photoperiodic requirements for LH release in juvenile broiler and egg-laying strains of domestic chickens fed ad libitum or restricted diets

Photoperiodic response curves for LH release were obtained for juvenile female domestic chickens at 8 weeks of age by measuring changes in plasma LH concentrations after increasing the daily photoperiod from 8 to 10.5, 12.75, 15.25, 17.75 or 20 h. The birds were bred either for meat production (broiler) or commercial egg-laying and were fed ad libitum or a restricted diet, similar to that used under commercial conditions. Ovarian and oviduct growth was stimulated by 2 weeks after transfer to 20 h light/day in the dwarf broiler strain, irrespective of the dietary treatment, but not in birds of the egg-laying strain. Baseline concentrations of plasma LH were higher in the egg-laying than in the dwarf broiler strain birds. A significant effect of dietary treatment was observed on the changes in concentration of plasma LH in the nonphotostimulated dwarf broiler, but not in the egg-laying bird. There was no significant interaction between dietary treatment and photoinduced LH release in birds of either strain. The shortest photoperiod needed to stimulate LH release (critical daylength) was less than 10.5 h in the dwarf broilers and between 10.5 and 12.75 h in the egg-laying birds. The shortest photoperiod needed to stimulate the maximum release of LH (saturation daylength) was between 10.5 and 12.75 h in the dwarf broiler strain. The saturation daylength in birds of the egg-laying strain was longer, being between 12.75 and 15.25 h.(ABSTRACT TRUNCATED AT 250 WORDS)

The Prepubertal Hiatus in Gonadotropin Secretion in the Male Rhesus Monkey (Macaca mulatto) Does not Appear to Involve Endogenous Opioid Pep tide Restraint of Hypothalamic Gonadotropin-Releasing Hormone Release*

To examine the possibility that the prepubertal hiatus in gonadotropin secretion in primates is occasioned by an endogenous opioid peptide (EOP)-dependent suppression of pulsatile GnRH release, the ability of an EOP receptor antagonist, naloxone (NAL), to elicit GnRH release was examined indirectly in the rhesus monkey. For this purpose, six castrated male monkeys, aged 18-24 months, first received an intermitten iv infusion of GnRH (0.1 micrograms/min for 3 min every h) to enhance the responsiveness of the gonadotroph to endogenous GnRH. Acute and chronic blockade of EOP receptors with single bolus injections of NAL at three doses (0.2, 2.0, and 10 mg/kg BW) and a continuous infusion of the antagonist (2 mg/h for 36 h), respectively, failed to elicit significant increments in circulating concentrations of mean LH. In addition, changes in plasma LH concentrations during a chronic intermitten iv infusion of NAL (2 mg/kg BW every 6 h for up to 16 days) were unremarkable. Unequivocal discharges of LH, however, were observed in response to small doses of GnRH (0.3 micrograms/monkey) administered iv after all modes of NAL administration. Taken together, these findings fail to provide evidence for the view that in primates, EOPs underlie the hiatus in pulsatile GnRH release, which in these species is responsible for the quiescence of the pituitary-testicular axis during the greater part of prepubertal development.

Pituitary and ovarian responses to prolonged administration of low doses of GnRH in prepubertal heifers

The responses of prepubertal heifers to continuous infusion of GnRH were examined in 4 experiments. Eighteen 4 month old beef heifers received 0.25, 0.5 or 2.5 μg GnRH/h for 48 h by continuous intravenous infusion. No significant changes in plasma LH concentrations were observed during infusion of the two lower GnRH doses. However, in all six heifers receiving 2.5 μg GnRH/h, jugular plasma LH concentrations were significantly increased within 2 h of the start of infusion. Preovulatory-type gonadotrophin surges occurred in three of the six animals receiving 2.5 μg/h GnRH during the period of infusion and elevated plasma progesterone concentrations were detected in these animals 4 and 6 days after the end of treatment. Heifers that exhibited preovulatory gonadotrophin surges had higher plasma oestradiol-17β concentrations before treatment than those that did not. In a second experiment, five heifers received 1.25 μg/h GnRH for 120 h. Mean LH and oestradiol-17β concentrations increased in all animals over the first 60 h and then returned to baseline. Two heifers exhibited preovulatory-type LH surges and some luteal function. In Experiment 3, osmotic infusion pumps implanted s.c. were used to deliver 5.0, 7.5 or 10.0 μG GnRH for 8 h and the LH responses compared with the responses to i.v. infusion of 2.5 μg GnRH for 8 h. The latin square design used four heifers and 4 treatment days. Significant effects of both GnRH-dose and day of GnRH treatment were detected, with subcutaneous infusion of 10.0 μg GnRH/h producing a significantly greater LH response than i.v. infusion of 2.5 μg GnRH/h, and the mean LH response to all treatments being greater during the first treatment period than on subsequent treatment days. In Experiment 4, 12 heifers received progesterone pretreatment for 14 days followed by 5.0 μg GnRH/h or saline, infusion s.c. for 120 h. A third group of five heifers received the GnRH infusion only. Mean LH concentrations were significantly elevated in response to GnRH over the first 8 h of the infusion period in progesterone pretreated heifers and over the first 16 h of infusion in animals receiving GnRH alone. Preovulatory LH surges were detected in four GnRH-treated heifers, two animals that were progesterone pretreated and two that received GnRH alone. Laparoscopy revealed corpora lutea in three of these four heifers, and plasma progesterone concentrations were elevated in two of these. It is concluded that GnRH infusion does not consistently induce ovulation in prepubertal heifers.

Effect of mouse epidermal growth factor on plasma concentrations of FSH, LH and progesterone and on oestrus, ovulation and ovulation rate in merino ewes.

The 24 h i.v. infusion of Merino ewes with 60 or 100 microgram mouse epidermal growth factor (EGF)/kg body weight on Days 4, 9 or 14 of the oestrous cycle decreased the strength of wool attachment and caused marked changes in subsequent reproductive performance. In ovaries removed 2 days after EGF treatment all follicles greater than or equal to 0.6 mm diameter were atretic. After 7 days either a normal pattern of atresia or no atresia was evident while after 12 days the pattern of follicular atresia was similar to that in controls. Irrespective of stage of cycle EGF caused dose-dependent increases in plasma FSH concentrations that persisted for up to 14 days. Changes in plasma LH concentrations were generally similar after infusion on Days 4 and 14, but were smaller and shorter-lived after infusion on Day 9. Irrespective of dose, the infusion of EGF on Days 4 and 14 caused immediate luteolysis then the formation of a luteinized follicle in many ewes. Most ewes treated on Day 4 returned to oestrus between Days 17 and 21 with the same ovulation rate (1.3) as the controls. Of those infused on Day 14 oestrus occurred about a cycle length later than expected and their ovulation rate then (1.9) was also similar to that of the controls (1.7). Luteal function was not affected in ewes infused on Day 9, and most returned to oestrus between Days 17 and 20 with an ovulation rate of 3.2. Fertile rams were not placed with the ewes until after the differences in ovulation rate had been observed. Mating occurred generally 2-4 weeks after treatment, and there were no differences between EGF-treated and control ewes in fertility or fecundity. The results are interpreted as indicating that mouse EGF induces ovarian follicular atresia but has differential effects on luteal function according to the stage of the oestrous cycle at which it is given. As a consequence of these two effects, which lead to differential changes in gonadotrophin secretion, ovarian function may be temporarily impaired, little affected or improved.

Multiunit activity in the anterior median eminence and adjacent areas of the hypothalamus of the ewe in relation to LH secretion.

Changes in multiunit activity (MUA) in the anterior median eminence and adjacent tissues just posterior to the optic chiasma were recorded in lightly anaesthetized, ovariectomized ewes after an i.m. injection either of oil (group I) or of 50 microgram oestradiol benzoate (ODB) in oil (group II). Changes in plasma LH concentration that occurred during the recording were determined by radioimmunoassay. In both groups, when the electrodes reached the correct site, the MUA showed a bursting pattern of firing with a frequency of 0.5-1.5 bursts/s. In group I (10 ewes), the MUA showed circhoral variations at intervals of 55.1 +/- 2.8 min similar to those for LH pulses. Plasma LH levels, measured every 10 min, for 2 h in 8 ewes, showed a total of 14 pulses which were always preceded by an increase in MUA. Hormonal values and bioelectrical activity were positively correlated (p < 0.01). When cumulated hourly, the mean MUA in group I remained stable, from 10.5 to 22.5 h after oil treatment. Then, intravenous injection of 100 microgram of ODB induced a rapid increase in MUA. During the 2 h after this injection, we observed only two pulses of LH in the 8 studied ewes. In animals injected i.m. with ODB before the recording (group II, n = 16), the mean MUA (cumulated every hour) from 10.5 to 22.5 postinjection was significantly higher (p < 0.001) than in animals from group I (control). Within group II, 5 ewes discharged an obvious peak of LH, 18-24 h after ODB injection and showed a shortening of the MUA circhoral period (which varied from 10 to 20 min, at the time of initiation of the surge) followed by an increase in the mean amplitude. These 5 ewes showed a significantly higher increase (p < 0.03) in the MUA per hour (from 10.5 to 22.5 h after ODB) than the 9 which did not show an LH peak. Thus, the changes in MUA were clearly related in time to changes in LH secretion whether occurring as spontaneous pulses or as peaks induced by ODB.

Effects of androgens, oestrogens and deoxycorticosterone acetate on plasma concentrations of luteinizing hormone in laying hens.

Testosterone, androstenedione, oestrone, oestradiol-17beta or deoxycorticosterone acetate (DOCA) were injected intramuscularly at several dose-levels and at various stages of the ovulatory cycle, and subsequent changes in plasma LH concentration were measured by radioimmunoassay. In 19 out of 24 hens, injection of 0.1, 0.5 or 1.0 mg DOCA/kg resulted in a mean maximal increase in plasma LH concentration of between 0.47 and 2.10 ng/ml. The magnitude of this response was not related to either the dose or the stage of the cycle at which the DOCA was injected. In the remaining five hens DOCA failed to stimulate LH secretion. Injection of either androstenedione, oestrone or oestradiol did not result in any increase in LH level in the circulation. In contrast, injection of 0.5, 1.0 or 2.0 mg testosterone/kg between 22 and 26 h after the terminal ovulation of a sequence resulted in mean maximal incremental changes in plasma LH level of 1.98 +/- 0.17, 2.17 +/- 0.21 and 2.41 +/- 0.31 (S.E.M.) ng/ml from pre-injection values of 1.38 +/- 0.16, 1.58 +/- 0.30 and 1.43 +/- 0.39 ng/ml (n=7, 6 and 5, respectively). The interval between the injection and the resulting rise in LH level was inversely proportional to the dose. The same doses of testosterone injected between 0 and 8 h after ovulation failed to stimulate LH secretion. There was also no significant increase in LH levels after injection of 0.5 and 1.0 mg testosterone/kg between 8 and 9 h after ovulation. However, injection of 2 mg testosterone/kg at this time resulted in a small but significant (P is less than 0.05) increase in LH levels. Since the largest ovarian follicle is more mature at 22-26 h after ovulation than at 0-9 h after ovulation, the ability of testosterone to cause the release of LH therefore appears to depend upon the degree of maturation of the ovarian follicle next due to ovulate.

Seasonal changes in plasma LH levels in domestic ducks.

Seasonal changes in plasma LH concentrations were measured by radioimmunoassay every month for 1 year in nine Khaki Campbell drakes kept under natural lighting conditions in Kiel, Germany. The LH levels rose in all the birds in March and April and reached a mean (+/-S.E.) maximum of 2-4 +/- 0-2 ng/ml early in May. Thereafter, LH levels remained high in three drakes, but decreased in the other six to between 0-9 and 0-4 ng/ml early in June and/or July and rose to about 2-5 ng/ml by the beginning of August. Plasma LH levels started to fall in all nine drakes in September and by early October had reached winter values of about 1-2 to 1-5 ng/ml. A small transient increase in the level of circulating LH was observed in most drakes during November or December.

Effects of gonadectomy on plasma LH concentration in the rhesus monkey.

The changes in plasma LH concentrations, as measured by a specific radioimmunoassay, were observed in 9 female and 3 male rhesus monkeys for a period of 20–35 days after gonadectomy. A 10-fold increase in plasma LH levels occurred during the first 3 weeks following castration. Hourly blood samples obtained from each of 3 chronically ovariectomized monkeys during a 24-hr period revealed major, seemingly random, peaks in plasma LH concentrations. (Endocrinology 87: 847, 1970)