Low serum levels of FSH, LH and prolactin in luteal phase inadequacy

In order to elucidate the relationship between prolactin (PRL) levels and corpus luteum function in humans, assessment of temporal relationship between levels of PRL, LH, FSH, estradiol and progesterone was made in eleven normal cycling women and six short luteal women. All hormones were determined by specific radioimmunoassay. The mean PRL level in the luteal phase was higher than that in the follicular phase in normal women. On the other hand, no difference mean was seen between the PRL levels of follicular and luteal phases in short luteal women. In addition, follicular and luteal phase secretion of PRL in the short luteal phase (SLP) was lower than that in the normal control. LH and FSH in the follicular and luteal phases, estradiol secretion in the late follicular and early to mid-luteal phases in SLP were also lower than those in the control. These observations were consistent with the hypothesis that SLP is a sequel to aberrant folliculogenesis. In addition, it is inferred that low PRL levels in the SLP might be due to inadequate augmentation by estrogen, rather than giving PRL any positive controlling role in the maintenance of corpus luteum function.     

LH release and luteal function in post-partum acyclic ewes after the pulsatile administration of LH-RH

The administration of LH-RH in a pulsatile regimen (100 ng i.v./h for 48 h) to acyclic ewes 26-30 days post partum increased plasma LH concentrations, and both the frequency and amplitude of plasma LH pulses. In 12/14 ewes these increases were followed by plasma LH surges similar to the preovulatory surges observed in 10 control cyclic ewes. Subsequent luteal function in the post-partum ewes was deficient. Plasma progesterone was detected in 7/12 post-partum ewes showing plasma LH surges. The concentrations were lower (1.3 +/- 0.2 ng/ml) and detected for shorter periods (3-10 days) than in cyclic ewes (2.4 +/- 0.2 ng/ml, 12/15 days). In the post-partum ewes the increases in plasma LH concentrations before the LH surge were higher but of shorter duration than in the cyclic ewes. The inadequate luteal function in the post-partum ewes could therefore have been due to inappropriate LH stimulation of the ovary before the LH surge.     

Influence of naloxone and yohimbine administration on pulsatile LH secretion in luteal phase beef cows

This study examined the effects of two specific neurotransmitter receptor antagonists, naloxone (NAL; mu-opioid) and yohimbine (YOH; alpha(2)-adrenergic), on pulsatile luteinizing hormone (LH) release during the luteal phase (Day 10; Day 0 = estrus) of beef cows. Treatments were saline i.m. (C; n = 4); 1mg/kg NAL i.m. followed 3 h later by two 0.5 mg/kg injections spaced 2.5 h apart (N; n = 4); 0.2 mg/kg YOH i.v. (Y; n = 3); or combined N and Y regimens, with Y preceding N by 30 min (NY; n = 4). Blood samples were collected for 8 h before (Period I) and after (Period II) initiation of treatment. Respiration rates of Y cows were similar to C cows during Period II. However, respiration rates of N and NY animals increased 70% within 30 min of the first NAL injection. Acute LH release was not observed in response to either NAL or YOH. Pulsatile LH secretion was unchanged in N, Y and NY cows during Period II when compared with Period I. In contrast, basal and pulsatile LH secretion was inhibited in C cows during Period II. The inhibition of LH secretion in C animals following NAL indicate that the cows were under stress during Period II. Thus, these data suggest that the inhibition of LH release in stressed animals can be overcome by pharmacologic attenuation of inhibitory (N) or accentuation of stimulatory (Y) signals to LHRH-containing neurons.     

Progesterone and LH variations after LH-RH administration in the luteal phase of the menstrual cycle

We have investigated the pituitary and luteal responses to LH-RH and their related changes. 11 normal women were studied during the luteal phase (day +4/+11). Blood samples were collected every 15 min for a basal period of 180 and 120 min after the intravenous administration of 25 micrograms of LH-RH. Progesterone (P) and LH were assayed by radioimmunoassay. Data were analyzed as maximum peak and its percent increase (delta max), integrated secretory area (ISA) and percent increase of ISA (delta A) in respect to basal values for both P and LH. LH-RH elicited a secretory response of both hormones in all cases. ISA of LH was significantly greater after LH-RH administration in respect to basal values (p less than 0.001) and delta max accounted to 475 +/- (SE) 36% of the basal concentration. Luteal responsiveness varied from about 115-130% to more marked increments. ISA of P differed from basal to stimulated conditions (p less than 0.05) and delta max was 166 +/- (SE) 14%. The analysis of temporal relationship between P and LH secretion showed that LH promptly rose after LH-RH, while the enhancement of P plasma levels occurred within 31 +/- 19 min after LH rise. Then P levels reached a plateau, values of which were statistically different from those observed before LH-RH administration. In two cases where luteal function was blunted or absent, in spite of marked increments of LH, P secretion did not occur. These data are consistent with the presence of close relationships between hypothalamic, pituitary and luteal functions and strengthen the contention about the usefulness of LH-RH during luteal phase for the lifespan and maintenance of corpus luteum.     

Comparative effects of LHRH agonist and ovine LH administration on testicular steroidogenesis in intact adult rat

In order to better understand the effects of LHRH administration on testicular function in adult rat, we compared the inhibitory effects of LH and the LHRH analogue [D-Ser-(TBU)⁶, des-Gly-NH₂ ¹⁰]LHRH ethylamide upon testicular steroidogenesis and LH, FSH and prolactin receptor contents. Administration of LH as well as LHRH analogue resulted in a marked decrease of LH receptor levels, accompanied by a blockage at the level of 17-hydroxylase activity. We have been able to demonstrate that multiple LH administration can achieve a testicular desensitization comparable to that observed after LHRH agonist treatment.     

Oestradiol and progesterone: soluble receptor levels and metabolism in the uterus of the ovariectomized ewe

Ovariectomized ewes received injections designed to mimic to some extent oestradiol and progesterone secretion during early pregnancy (maintenance progesterone), during oestrus (oestrous oestradiol) and during the luteal phase of the previous cycle (priming progesterone). The animals were killed at times equivalent to 1, 4 or 7 days after oestrus in those animals which had received oestrous oestradiol. The level of soluble oestradiol and progesterone receptors in whole uterus, and [3H]oestradiol and [3H]progesterone metabolism by uterus minces were measured. Oestradiol receptor level was highest on day 1 in those animals receiving oestrous oestradiol with no significant effect at any stage of the inclusion or omission of priming or maintenance progesterone. Progesterone receptor level was also high on day 1 in those animals receiving oestrous oestradiol with high levels maintained to day 4. Again, inclusion of priming or maintenance progesterone was without effect. In animals not receiving oestrous oestradiol the level of both receptors was uniformly low. Metabolism of [3H]oestradiol was low and not affected by treatment. [3H]Progesterone metabolism, although more variable, was also low and not affected by treatment.     

Effect of GnRH administration on blood polyamines and LH levels in normal and obese children

Blood polyamines (spermidine and spermine) and LH levels have been studied after acute GnRH injection both in obese and normal weight children. In both groups LH values significantly increased after stimulation but reached higher peaks in normal children than in obese ones (P less than 0.05). On the contrary, polyamine levels increased significantly only in the normal weight children. LH peaked at 30 min and polyamines at 60 min after GnRH injection. On the basis of the proposed role of polyamines in hormone action and of our results, we suggest that polyamines may play a pivotal role in hormone responsiveness of hypothalamic-hypophyseal axis.     

Effects of endocannabinoid 1 and 2 (CB1; CB2) receptor agonists on luteal weight, circulating progesterone, luteal mRNA for luteinizing hormone (LH) receptors, and luteal unoccupied and occupied receptors for LH in vivo in ewes

Thirty to forty percent of ruminant pregnancies are lost during the first third of gestation due to inadequate progesterone secretion. During the estrous cycle, luteinizing hormone (LH) regulates progesterone secretion by small luteal cells (SLC). Loss of luteal progesterone secretion during the estrous cycle is increased via uterine secretion of prostaglandin F(2α) (PGF(2α)) starting on days 12-13 post-estrus in ewes with up to 4-6 pulses per day. Prostaglandin F(2α) is synthesized from arachidonic acid, which is released from phospholipids by phospholipase A2. Endocannabinoids are also derived from phospholipids and are associated with infertility. Endocannabinoid-induced infertility has been postulated to occur primarily via negative effects on implantation. Cannabinoid (CB) type 1 (CB1) or type 2 (CB2) receptor agonists and an inhibitor of the enzyme fatty acid amide hydrolase, which catabolizes endocannabinoids, decreased luteal progesterone, prostaglandin E (PGE), and prostaglandin F(2α) (PGF(2α)) secretion by the bovine corpus luteum in vitro by 30 percent. The objective of the experiment described herein was to determine whether CB1 or CB2 receptor agonists given in vivo affect circulating progesterone, luteal weights, luteal mRNA for LH receptors, and luteal occupied and unoccupied LH receptors during the estrous cycle of ewes. Treatments were: Vehicle, Methanandamide (CB1 agonist; METH), or 1-(4-chlorobenzoyl)-5-methoxy-1H-indole-3-acetic acid morpholineamide (CB2 agonist; IMMA). Ewes received randomized treatments on day 10 post-estrus. A single treatment (500 μg; N=5/treatment group) in a volume of 1 ml was given into the interstitial tissue of the ovarian vascular pedicle adjacent to the luteal-containing ovary. Jugular venous blood was collected at 0 h and every 6-48 h for the analysis of progesterone by radioimmunoassay (RIA). Corpora lutea were collected at 48 h, weighed, bisected, and frozen in liquid nitrogen until analysis of unoccupied and occupied LH receptors and mRNA for LH receptors. Profiles of jugular venous progesterone, luteal weights, luteal mRNA for LH receptors, and luteal occupied and unoccupied LH receptors were decreased (P≤0.05) by CB1 or CB2 receptor agonists when compared to Vehicle controls. Progesterone in 80 percent of CB1 or CB2 receptor agonist-treated ewes was decreased (P≤0.05) below 1 ng/ml by 48 h post-treatment. It is concluded that the stimulation of either CB1 or CB2 receptors in vivo affected negatively luteal progesterone secretion by decreasing luteal mRNA for LH receptors and also decreasing occupied and unoccupied receptors for LH on luteal membranes. The corpus luteum may be an important site for endocannabinoids to decrease fertility as well as negatively affect implantation, since progesterone is required for implantation.     

Diurnal variation in LH and temporal relationships between oscillations in LH and progesterone during the luteal phase in heifers

Diurnal variation in progesterone and LH during the luteal phase and the temporal relationships between oscillations of the two hormones were studied in 10 heifers by collection of blood samples at 0100, 0700, 1300, and 1900 h each day, beginning on Day 1 (Day 0 = ovulation). Concentration of LH on Days 5-9, but not on Days 10-14, was lower (P < 0.05) at 0700 h (0.25 ± 0.02 ng/mL) than at each of the other three hours (combined, 0.32 ± 0.02 ng/mL). An oscillation was defined as an uninterrupted increase and decrease in concentrations. The number of LH oscillations/heifer with the peak at 1900 h (6.1 ± 0.7) throughout the luteal phase was greater (P < 0.01) than for each of the other hours (combined, 4.0 ± 0.2). Diurnal variation in progesterone was not detected. Only statistically defined LH oscillations were used to determine the temporal association between the peak of an LH oscillation and various components of a progesterone oscillation. On Days 5-14, the frequency of the peak of an LH oscillation occurring at the same hour as the peak of a progesterone oscillation (26/48, 54%) was greater (P < 0.0001) than at the progesterone nadir (3/48, 6%). The frequency of the LH peak occurring during increasing (11/34, 32%) and decreasing (8/25, 32%) progesterone concentrations was intermediate (P < 0.05). Results indicated the following: 1) diurnal variation occurred in LH as determined by concentration and by the hour of the peak of an oscillation; and 2) LH oscillations were temporally and positively related to progesterone oscillations.     

Precision-cut luteal slices: A promising approach for studying luteal function in pigs

The study was aimed to validate the precision-cut luteal slices to investigate porcine luteal function. Corpora lutea (CLs) were cut into 180-μm thick slices using Krumdick Tissue Slicer. The viability, tissue structure and steroidogenic acute regulatory protein (STAR) expression in the luteal slices did not differ between the beginning and the end of the 24-h incubation period. The luteal progesterone secretion showed a time- and dose-dependent response to porcine luteinizing hormone. The effects of prostaglandin F_2α and 17β-estradiol on progesterone secretion by porcine luteal slices were comparable to the previously reported in vivo results of the CL microdialysis system in the pig.     

Differential patterns in luteal prolactin and LH receptors during pregnancy in sows and ewes

In the sow, a dramatic increase of LH specific binding was observed during the second half of pregnancy. This was due to an increase in receptor number (41 fmol and 95 fmol/mg protein at Days 50 and 105 respectively). The apparent association constant was unchanged. The pattern of prolactin receptor content showed two peaks at Day 60 and Day 105. Prolactin receptors increased earlier during pregnancy than did LH receptors, suggesting a possible role of prolactin in the induction of LH receptors. In the ewe, the receptor content of LH and prolactin did not change very much during pregnancy. The corpus luteum showed normal luteal function until parturition although it was not necessary for maintenance of pregnancy in the ewes.     

Oxytocin administration prolongs luteal function in cyclic mares

Recent evidence indicates that, in mares, as in the domestic ruminants, oxytocin and its endometrial receptor play important roles in stimulating the pulsatile releases of prostaglandin F2 alpha from the endometrium that effect luteolysis. In the present experiment, continuous administration of oxytocin by subcutaneous minipump to five mares during days 8-20 after ovulation abolished luteolysis in four of them, while all four of the control mares infused similarly with saline underwent luteolysis at the expected time. When oxytocin administration began on day 10, instead of on day 8, after ovulation luteolysis occurred rapidly in two of the five treated mares, indicating that the development of oxytocin responsiveness begins on or about day 10 of dioestrus in cyclic mares.     

Secretory patterns of LH and FSH and follicular growth following administration of PGF(2)alpha during the early luteal phase in cattle

Two studies were conducted to determine the changes in gonadotropin secretion associated with growth and development of the largest follicle and the ability of the largest ovarian follicle present on Day 5 following estrus to ovulate if luteal regression is induced. In both studies, cows received either saline (i.m.) or prostaglandin F(2)alpha (PGF(2)alpha; 25 mg i.m.) on the fifth day post estrus. Frequency of LH pulses declined (P<0.01) with increasing day of cycle, while pulse amplitude and duration increased (P<0.05) in saline-treated cows. In PGF(2)alpha-treated cows, LH remained as high frequency-low amplitude pulses. Secretory patterns of FSH were similar between the two groups. In Experiment 2, the largest ovarian follicle present was marked around its periphery with sub-epithelial injections of charcoal. In saline-treated cows, the size of the charcoal marked follicles generally decreased, indicating atresia. A corpus luteum was present within the area of a previously marked follicle in three PGF(2)alpha-treated cows. The size of the marked follicles either decreased or increased in the remaining PGF(2)alpha-treated cows, with ovulation occurring at a different site. In summary, PGF(2)alpha-induced luteal regression on the fifth day of estrus subsequently alters the frequency, amplitude and duration of LH pulses, but not FSH pulses, and the largest follicle present on Day 5 either increases or decreases in size or ovulates when PGF(2)alpha is given on Day 5 following estrus.     

2-bromopalmitate inhibition of stimulatory effect of LH in isolated luteal cells

The effect of 2-bromopalmitate, an inhibitor of fatty acid oxidation, on progesterone synthesis in isolated luteal cells was studied. Incubation of the cells with increasing concentrations (0 – 2 mM) of the inhibitor resulted in an initial enhancement of progesterone synthesis, both in the presence and absence of LH (1 μg/m1). In the LH-treated cells, this stimulation in steroid synthesis becomes markedly impaired at 2 mM 2-bromopalmitate. In the control cells, however, progesterone synthesis was sustained at the elevated level. At high concentrations of 2-bromopalmitate, the stimulatory effect of LH (relative to the controls) on steroidogenesis was progressively diminished, until it was completely abolished at an inhibitor concentration of 2 mM. The oxidation of labelled palmitic acid by luteal cells was also effectively inhibited by 2-bromopalmitate (1 mM). The results indicate that the steroidogenic effect of LH is mediated, in part, by fatty acid oxidation, and were explained in terms of the interaction between carbohydrate and fatty acid oxidation in supporting ovarian steroidogenesis.