Concentrations of circulating hormones during the interval between pulses of a PGF2α metabolite in mares and heifers

The temporal relationship of several hormones to a metabolite of prostaglandin F2α (PGFM) was studied in mares and heifers from the beginning of the first PGFM pulse during luteolysis to the end of the second pulse. Mares (n=7) were selected with a 9-h interval between the peaks of the two pulses. In mares, estradiol-17β (estradiol) increased (P<0.05) within each PGFM pulse and plateaued for a mean of 6h between the pulses, resulting in a stepwise estradiol increase. Progesterone decreased linearly (P<0.0001) throughout the intra-pulse and inter-pulse intervals of PGFM. In heifers (n=6), inter-pulse intervals were variable, and therefore Hours 1-4 of the first pulse (Hour 0=PGFM peak) and Hours -4 to -1 of the second pulse were used to represent the mean 8-h interval between peaks of the two pulses. Estradiol increased (P<0.05) during the ascending portion of each PGFM pulse and then decreased (P<0.05) beginning at Hour -1 of the first PGFM pulse and Hour 0 of the second pulse. The 1-h delay during the second pulse was accompanied by an apparent increase in PRL. A transient decrease in estradiol occurred in individuals between PGFM pulses at a mean of 5h after the first PGFM peak, concomitant with a transient LH increase (P<0.05). Results indicated that estradiol plateaued in mares and fluctuated in heifers during the interval between PGFM pulses. Heifers also showed temporal relationships between estradiol and LH and apparently between estradiol and PRL.     

Direct effect of PGF2α pulses on PRL pulses, based on inhibition of PRL or PGF2α secretion in heifers

The relationships between PRL and PGF_2α and their effect on luteolysis were studied. Heifers were treated with a dopamine-receptor agonist (bromocriptine; Bc) and a Cox-1 and -2 inhibitor (flunixin meglumine [FM]) to inhibit PRL and PGF_2α, respectively. The Bc was given (Hour 0) when ongoing luteolysis was indicated by a 12.5% reduction in CL area (cm²) from the area on Day 14 postovulation, and FM was given at Hours 0, 4, and 8. Blood samples were collected every 8-h beginning on Day 14 until Hour 48 and hourly for Hours 0 to 12. Three groups of heifers in ongoing luteolysis were used: control (n = 7), Bc (n = 7), and FM (n = 4). Treatment with Bc decreased (P < 0.003) the PRL concentrations averaged over Hours 1 to 12. During the greatest decrease in PRL (Hours 2-6), LH concentrations were increased. Progesterone concentrations averaged over hours were greater (P < 0.05) in the Bc group than in the controls. In the FM group, no PGFM pulses were detected, and PRL concentrations were reduced. Concentrations of PGFM were not reduced in the Bc group, despite the reduction in PRL. Results supported the hypothesis that a decrease (12.5%) in CL area (cm²) is more efficient in targeting ongoing luteolysis (63%) than using any day from Days 14 to ≥19 (efficiency/day, 10-24%). The hypothesis that PRL has a role in luteolysis was supported but was confounded by the known positive effect of LH on progesterone. The hypothesis was supported that the synchrony of PGFM and PRL pulses represents a positive effect of PGF_2α on PRL, rather than an effect of PRL on PGF_2α.     

Stimulatory effect of PGF2α on PRL based on experimental inhibition of each hormone in mares

During the luteolytic period in mares, the peak of 65% of pulses of a PGF2α metabolite (PGFM) and the peak of a pulse of PRL have been reported to occur at the same hour. It is unknown whether the synchrony reflects an effect of PGF2α on PRL or vice versa. Controls, a flunixin meglumine (FM)-treated group (to inhibit PGF2α), and a bromocriptine-treated group (to inhibit PRL), were used at 14 days postovulation in June and in September (n = 6 mares/group/mo). Blood samples were collected hourly from just before treatment (Hour 0) to Hour 10. Concentrations of PGFM in the FM group were lower (P < 0.05) at Hours 4 to 6 than in the controls in each month, but bromocriptine had no detected effects on PGFM. Concentrations of PGFM averaged over all groups and within each group did not differ between June and September. Compared to the controls, concentrations of PRL in June were lower (P < 0.05) in the FM group at Hours 4 to 8 and in the bromocriptine group at Hours 4 to 10. Concentration of PRL averaged over groups was lower (P < 0.0001) in September (0.9 ± 0.05 ng/mL, mean ± SEM) than in June (3.0 ± 0.3 ng/mL). Results supported the hypothesis that the positive association between PGFM and PRL concentrations in mares represents an effect of PGF2α on PRL rather than an effect of PRL on PGF2α.     

Combination of the ram effect with PGF2α estrous synchronization treatments in ewes during the breeding season

The role of the ram effect on the reproductive performance of ewes that have initiated estrous cycles following lambing in combination with synchronization of estrus using PGF(2α) was examined. A total of 1264 Corriedale × Merino ewes in the breeding season (March-April) were allocated to one of three treatments. The control group (PG2) of ewes (n=415) were in permanent direct contact with vasectomized rams throughout the experiment from 60 d prior to the administration of the first luteolytic dose of PGF(2α) which was followed by a second dose 13 d later (Day 0 of the experiment). Ewes assigned to the other two treatments remained isolated from rams until Day 0. In the second treatment, ewes (PG2RE; n=445) were administered PGF(2α) in the same manner and were joined with vasectomized rams at Day 0. Ewes allocated to the third treatment (PGRE; n=404) did not receive the second dose of PGF(2α) but were introduced to vasectomized rams on Day 0. Sexual receptivity, as indicated by tail-head marking, was recorded until d 11. More PG2RE ewes (407/445; 92%) were observed in estrus by Day 11 than occurred for PG2 ewes (353/415; 85%; P=0.003). The accumulated frequency of PG2RE ewes in estrus was greater than for PG2 ewes for each period from Day 3 (P<0.001) to Day 11 (P<0.01). The onset of estrus was earlier in PG2RE ewes (2.98±0.07 d) than for PG2 ewes (3.31±0.07 d; P<0.0001). In contrast, the total frequency of PGRE ewes observed in estrus by Day 11 (356/404; 88%) was similar to that observed for PG2 ewes. However, the trajectory of the accumulated frequency of the incidence of estrus was less for the PGRE ewes initially, particularly during the period of Days 3-6 of observation (P<0.0001). Consequently, onset of estrus was earlier in PG2 ewes (3.31±0.07 d) than for PGRE ewes (5.30±0.11 d; P<0.0001). It was concluded that the introduction of vasectomized rams simultaneously with the second administration of PGF(2α) advanced the onset of estrus and increased the number of ewes that responded. The introduction of rams 13 d after a single dose of PGF(2α) did not substitute for the second administration of PGF(2α).     

Temporal relationships of a pulse of prolactin (PRL) to a pulse of a metabolite of PGF2α in mares

Hourly blood samples were collected from 10 mares during 24 h of each of the preluteolytic, luteolytic, and postluteolytic periods. The autocorrelation function of the R program was used to detect pulse rhythmicity, and the intra-assay CV was used to locate and characterize pulses of prolactin (PRL) and a metabolite of prostaglandin F2α (PGFM). Rhythmicity of PRL and PGFM concentrations was detected in 67% and 89% of mares, respectively. Combined for the three periods (no difference among periods), the PRL pulses were 5.2 ± 0.4 h (mean ± SEM) at the base, 7.5 ± 1.5 h between nadirs of adjacent pulses, and 12.3 ± 1.5 h from peak to peak. The peaks of PRL pulses were greater (P < 0.05) during the luteolytic period (46 ± 14 ng/mL) and postluteolytic period (52 ± 15 ng/mL) than during the preluteolytic period (17 ± 3 ng/mL). Concentrations of PRL during hours of a PGFM pulse were different (P < 0.003) within the luteolytic period and postluteolytic period and were greatest at the PGFM peak; PRL concentrations during a PGFM pulse were not different during the preluteolytic period. The frequency of the peak of PRL and PGFM pulses occurring at the same hour (synchrony) was greater for the luteolytic period (65%, P < 0.01) and postluteolytic period (50%, P < 0.001) than for the preluteolytic period (17%). This is the first report in mares on characterization and rhythmicity of PRL pulses, synchrony between PRL and PGFM pulses, and greater PRL activity during the luteolytic and postluteolytic periods than during the preluteolytic period.     

Advances in modeling of the bovine estrous cycle: Synchronization with PGF2α

Our model of the bovine estrous cycle is a set of ordinary differential equations which generates hormone profiles of successive estrous cycles with several follicular waves per cycle. It describes the growth and decay of the follicles and the corpus luteum, as well as the change of the key reproductive hormones, enzymes and processes over time. In this work we describe recent developments of this model towards the administration of prostaglandin F2α. We validate our model by showing that the simulations agree with observations from synchronization studies and with measured progesterone data after single dose administrations of synthetic prostaglandin F2α.     

Mechanical stimulation suppresses phosphorylation of eIF2α and PERK-mediated responses to stress to the endoplasmic reticulum

Cellular perturbations such as stress to the endoplasmic reticulum induce an integrated stress response, which activates phosphorylation of eIF2α and leads to alleviation of cellular injury or apoptosis. This study investigated the role of mechanical stimulation in the regulation of eIF2α and cell death. Mechanical stimulation was applied to mouse ulnae, MC3T3 cells, and mesenchymal stem cells. The results demonstrate that mechanical stimulation reduces phosphorylation of eIF2α through inactivation of Perk. Furthermore, flow pre-treatment reduces thapsigargin-induced cell mortality through suppression of phosphorylation of Perk. However, H₂O₂-driven cell mortality, which is not mediated by Perk, is not suppressed by mechanical stimulation. Taken together, our observations suggest a pro-survival role of mechanical stimulation in Perk-mediated stress responses.     

Role of PGF2α in luteolysis based on inhibition of PGF2α synthesis in the mare

The effects of inhibition of PGF2α synthesis on luteolysis in mares and on the incidence of prolonged luteal activity were studied in controls and in a group treated with flunixin meglumine (FM), a PGF2α inhibitor (n = 6/group). The FM was given every 8 hours (1.0 mg/kg) on each of Days 14.0 to 16.7. Concentration (pg/mL) of PGF2α metabolite averaged over 8 hours of hourly blood sampling at the beginning of each day, was lower in the FM group than in the controls on Day 14 after ovulation (6.7 ± 1.3 vs. 13.8 ± 2.9, P < 0.05), Day 15 (15.0 ± 3.9 vs. 35.2 ± 10.4, P < 0.10), and Day 16 (21.9 ± 5.7 vs. 54.7 ± 11.4, P < 0.03). Concentration (ng/mL) of progesterone (P4) was greater in the FM group than in the controls on Day 14 (10.1 ± 0.9 vs. 7.7 ± 0.9, P < 0.08), Day 15 (9.2 ± 1.0 vs. 4.3 ± 1.0, P < 0.008), and Day 16 (5.6 ± 1.6 vs. 1.2 ± 0.4, P < 0.02). The interval from ovulation to the beginning of a decrease in P4 and to the end of luteolysis (P4 < 1 ng/mL) was each delayed (P < 0.03) by ∼1 day in the FM group. Intervals involving the luteal phase were long (statistical outliers, P < 0.05) in two mares in the FM group, indicating prolonged luteal activity. Results supported the hypotheses that (1) inhibition of PGF2α synthesis interferes with luteolysis in mares and (2) inhibition of PGF2α at the expected time of luteolysis may lead to prolonged luteal activity.     

Detection of estrous behavior in buffalo heifers by radiotelemetry following PGF2α administration during the early or late luteal phase

This study examined the usefulness of radiotelemetry for estrous detection in buffalo heifers and the impact of prostaglandin F_2α (PGF_2α) administration during the early or late luteal phase on estrous behavior and ovulatory follicle variables. Induction of estrus with PGF_2α at a random stage of the estrous cycle was followed by the arbitrary division of heifers into groups receiving a second dose of PGF_2α during either the early (n = 33) or late (n = 17) luteal phase (6–9 or 11–14 days after estrus, respectively) for the induction of synchronized estrus. The electronic detection of synchronized estrus by radiotelemetry was confirmed using ultrasonography every 6 h until ovulation. Radiotelemetry was 90% efficient and 100% accurate for estrous detection. Intervals between the PGF_2α dose and the beginning of synchronized estrus (40.7 ± 10.9 vs. 56.7 ± 12.8 h) or ovulation (70.0 ± 11.3 vs. 85.6 ± 12.5 h) were shorter (P < 0.05) for heifers receiving PGF_2α during the early luteal phase. PGF_2α administration during the early or late luteal phase produced similar (P > 0.05) results for the duration of estrus, the intervals from the beginning or end of estrus to ovulation, the number and duration of mounts per estrus, the duration of mounts, the diameter of the ovulatory follicle and the luteal profile on day 5 after estrus. In conclusion, radiotelemetry was a suitable tool for the efficient and accurate detection of estrus in buffalo heifers. Treatment with PGF_2α during the early luteal phase had a shorter interval to synchronized estrus and ovulation; however, estrous behavior, ovulatory follicle dynamics and subsequent luteal activity were similar following PGF_2α administration during the early or late luteal phase.     

Metabolites of PGF2α in Blood Plasma and Urine as Parameters of PGF2α Release in Cattle

The metabolism of PGF2α in cattle results initially in the formation of 15-keto-13,14-dihydro-PGF2α (15-ketodihydro-PGF2α) and later the 11-ketotetranor PGF metabolites. Both types of metabolites appear in the peripheral circulation and finally the 11-ketotetranor PGF metabolites are found in large quantities in the urine in a species-related pattern. Several approaches can be made to the quantitative analysis of PGF2α release during reproductive studies. First, assay of the 15-ketodihydro-PGF2α metabolite in the peripheral circulation; second, analysis of the longer-lived 11-ketotetranor PGF metabolites in the peripheral circulation; and finally analysis of the latter metabolites in the urine. The antibodies used in radioimmunoassays of both types of metabolites of PGF2α were found to be specific and the results agree well with those obtained earlier by mass spectrometric analysis. The assay of 11-ketotetranor PGF metabolites was used to study the excretion of urinary metabolites in the cow after i.v. infusion of PGF2α and also during the normal estrous cycle and early pregnancy. These studies suggest that 11-ketotetranor PGF metabolites in cow urine serve as a good parameter of PGF2α release, especially for long–term studies, but when a precise pattern of PGF2α release is required, measurement of 15-ketodihydro-PGF2α levels in frequently collected plasma samples is preferable.     

Regulation of Akt expression and phosphorylation by 17β-estradiol in the rat uterus during estrous cycle

Background

Ablation of the low-affinity receptor subunit for leukemia inhibitory factor (LIFR) causes multi-systemic defects in the late gestation fetus. Because corticosterone is known to have a broad range of effects and LIF function has been associated with the hypothalamo-pituitary-adrenal axis, this study was designed to determine the role for LIFR in the fetus when exposed to the elevated maternal glucocorticoid levels of late gestation. Uncovering a requirement for LIFR in appropriate glucocorticoid response will further understanding of control of glucocorticoid function.

Methods

Maternal adrenalectomy or RU486 administration were used to determine the impact of the maternal glucocorticoid surge on fetal development in the absence of LIFR. The mice were analyzed by a variety of histological techniques including immunolabeling and staining techniques (hematoxylin and eosin, Alizarin red S and alcian blue). Plasma corticosterone was assayed using radioimmunoassay.

Results

Maternal adrenalectomy does not improve the prognosis for LIFR null pups and exacerbates the effects of LIFR loss. RU486 noticeably improves many of the tissues affected by LIFR loss: bone density, skeletal muscle integrity and glial cell formation. LIFR null pups exposed during late gestation to RU486 in utero survive natural delivery, unlike LIFR null pups from untreated litters. But RU486 treated LIFR null pups succumb within the first day after birth, presumably due to neural deficit resulting in an inability to suckle.

Conclusion

LIFR plays an integral role in modulating the fetal response to elevated maternal glucocorticoids during late gestation. This role is likely to be mediated through the glucocorticoid receptor and has implications for adult homeostasis as a direct tie between immune, neural and hormone function.     

Does corpus luteum function autonomously during estrous cycle in the rat? A possible involvement of LH and prolactin

This study examined the of LH and prolactin in the control of corpus luteum function during 4-day cycles in the rat. Bromocriptine (BRC) treatment was performed on proestrus or/and estrus morning that means before or after the preovulatory release of LH. This caused complete blood prolactin depression from the time of injection until diestrus 1 afternoon. This decrease in blood prolactin concentration was associated with a rise in the tonic level of LH secretion in those females which received BRC as soon as on proestrus. We first observed that injection on the morning of proestrus of doses of BRC capable of blunting prolactin secretion on proestrus afternoon did not significantly impair the preovulatory release of LH and did not prevent ovulation occurring during the following night. The life span of the corpora lutea edified from ovarian follicles rupturing before or under BRC administration did not exceed that of those formed under physiological circumstances since 4-day cycles culminating in ovulation constantly took place in all the treated animals whatever the time of BRC injection. To determine the pattern of luteal activity in the absence of prolactin secretion, we measured blood progesterone concentration from estrus until late diestrus in female rats injected with BRC on proestrus and/or estrus at 1100 h. The initiation of the function of corpus luteum on estrus and the achievement of its full activity on diestrus 1 did not appear to be affected by BRC. By contrast the level of blood progesterone declined more rapidly on the morning of diestrus 2 in BRC-treated than in control females. The capacity for autonomous progesterone secretion by corpus luteum of the cycle was discussed in the light of previous and present observations.     

Effect of uterine luminal perfusion of PGF2α and PGE2 on uterine vasomotor response and PGF2α output in cyclic cattle

Six cyclic Holstein dairy cows were anesthetized on days 12–14 post-oestrus. Reproductive tract was exposed by midventral incision, and the ovarian (utero-ovarian) vein and facial artery cannulated. Oviduct was ligated, and a catheter (affluent) introduced into the tip of the uterine horn. The uterine horn was ligated above the uterine body, a second catheter (effluent) introduced into the uterine lumen, and an electromagnetic blood flow transducer placed around the uterine artery. On the day following surgery, the uterine horn was infused constantly for 9 h with PGF_2α dissolved in PBS (0.7 ml/min, 177 ng/ml). During periods 1 and 3 (first 3 h and last 3 h, respectively) only PGF_2α was perfused; during period 2 (between 3 h and 6 h) 101tgμg/ml of PGE₂ were added to the perfusate together with PGF_2α. Uterine venous and peripheral blood samples were collected simultaneously every 15 min, and uterine blood flow recorded continuously. Least-square means for PGF measured in uterine venous drainage for periods 1, 2 and 3 were 315 ± 26, 557 ± 24 and 511 ± 26 pg/ml, respectively (P < 0.05). Uterine blood flow values were 52 ± 5, 67 ± 4 and 61 ± 4 ml/min for periods 1, 2 and 3 (P < 0.08), respectively.Results do not support the hypothesis that the antiluteolytic effect of PGE₂ is associated with a suppression of uterine PGF_2α release into the circulation. Greater release of PGF to the circulation in period 2 (addition of PGE₂) is probably the result of the vasodilatory effect of PGE₂ on uterine endometrial vasculature.     

p600 stabilizes microtubules to prevent the aggregation of CaMKIIα during photoconductive stimulation

The large microtubule-associated/Ca²⁺-signalling protein p600 (also known as UBR4) is required for hippocampal neuronal survival upon Ca²⁺ dyshomeostasis induced by glutamate treatment. During this process, p600 prevents aggregation of the Ca²⁺/calmodulin-dependent kinase IIα (CaMKIIα), a proxy of neuronal death, via direct binding to calmodulin in a microtubuleindependent manner. Using photoconductive stimulation coupled with live imaging of single neurons, we identified a distinct mechanism of prevention of CaMKIIα aggregation by p600. Upon direct depolarization, CaMKIIα translocates to microtubules. In the absence of p600, this translocation is interrupted in favour of a sustained self-aggregation that is prevented by the microtubule-stabilizing drug paclitaxel. Thus, during photoconductive stimulation, p600 prevents the aggregation of CaMKIIα by stabilizing microtubules. The effectiveness of this stabilization for preventing CaMKIIα aggregation during direct depolarization but not during glutamate treatment suggests a model wherein p600 has two modes of action depending on the source of cytosolic Ca²⁺.     

Translocation of dna polymerase-α during the mitotic cycle of Physarum polycephalum

The location of DNA polymerase-α within nuclei of a macroplasmodium of Physarum polycephalum was identified at successive stages of the highly synchronous mitotic cycle by indirect immunofluorescence. The distribution of α-tubulin, the nucleolar protein fibrillarin and DNA were also identified.In G2-phase the polymerase-α was found mainly in the region of the nucleolus. In prophase the polymerase became dispersed into the nucleus with the breakdown of the nucleolus. In metaphase, the polymerase-α was located in two zones separated by the metaphase plate. In S-phase, which follows immediately after mitosis, the distribution of the polymerase was initially punctate but later segments were noted during nucleolar reconstruction. We infer that DNA polymerase-α is stored mainly in the region of the nucleolus (or the reconstructing nucleolus) when it is not needed for DNA replication.     

The effect of basic fibroblast growth factor 2 on the bovine corpus luteum depends on the stage of the estrous cycle and modulates prostaglandin F2α action

The roles of fibroblast growth factor 2 (FGF2) in the corpus luteum (CL) function and its modulatory effect on prostaglandin (PG) F_2α during the bovine estrous cycle were studied using the following design of in vivo and in vitro experiments: (1) effects of FGF2 and FGF receptor 1 inhibitor (PD173074) on bovine CL function in the early (PGF_2α-resistant) and mid (PGF_2α-responsive) luteal stage in vivo, (2) the modulatory effect of FGF2 on PGF_2α action during the luteal phase in vivo and (3) effects of FGF2 and PD173074 on bovine CL secretory function in vitro. Cows were treated by injection into the CL with: (1) saline (control), (2) FGF2, (3) PD173074, (4) FGF2 followed by intramuscular (i.m.) PGF_2α, (5) PD173074 followed by i.m. PGF_2α and (6) i.m. PGF_2α as a positive control. For in vitro experiments, CL explants were treated with the aforementioned factors. Progesterone (P₄) concentrations of blood samples or culture media were determined by radioimmunoassay. Relative mRNA expressions of the genes involved in angiogenesis and steroidogenesis were determined by quantitative real-time PCR. Although FGF2 treatment on day 4 of the estrous cycle did not change the cycle length, FGF2 with PGF_2α decreased the P₄ concentrations observed during the estrous cycle compared to the control group (P < 0.001). Moreover, FGF2 treatment on day 10 prolonged CL function as indicated by a significantly greater concentration of P₄ on day 21 compared to the control group. In the in vitro study, FGF2 decreased cytochrome P450 family 11 subfamily A member 1 (CYP11A1) and hydroxy-delta-5-steroid dehydrogenase (HSD3B1) mRNA expression (P < 0.01) and decreased P₄ production in the early-stage CL (P < 0.001). However, FGF2 + PGF_2α or PGF_2α alone resulted in an elevation of steroidogenic acute regulatory protein and CYP11A1 mRNA expression and P₄ secretion in the early-stage CL (P < 0.01). In the mid-luteal phase, FGF2 upregulated CYP11A1 and HSD3B1 mRNA expression (P < 0.01), while FGF2 + PGF_2α increased only HSD3B1 mRNA expression (P < 0.001). In conclusion, FGF2 seems to play a modulatory role in CL development or luteolysis, differentially regulating steroidogenesis and angiogenic factors as well as PGF_2α actions.     

Pulses of prolactin before, during, and after luteolysis and synchrony with pulses of a metabolite of prostaglandin F2α in heifers

Pulses of prolactin (PRL) and a metabolite of prostaglandin F2α (PGFM) were determined from hourly blood samples collected before, during, and after luteolysis (n=7 heifers). Progesterone concentrations were used to partition the results into six 12-h sets from 12h before to 36h after luteolysis. Pulses of PRL with a nadir-to-nadir interval of 4.4±0.2h were detected in each 12-h set. Pulses were rhythmic (P<0.05) in six heifers, beginning 12h before the end of luteolysis. The peak of a PRL pulse was greater (P<0.05) for the 12h after the end of luteolysis than for other 12-h sets, except for the last set of luteolysis. Area under the curve of a pulse was greater (P<0.05) for the 24h that encompassed the end of luteolysis than for two previous 12-h sets. Synchrony between the peaks of PRL and PGFM pulses was greater (P<0.03) during and after luteolysis (same hour for 29/39 pairs) than before luteolysis (0/12). Concentration of PRL centralized to the peak (Hour 0) of PGFM pulses was greater (P<0.05) at Hours 0 and 1 than at Hours -2, -1, and 3. Results supported the hypothesis that PRL is secreted in pulses in heifers. The pulses were most prominent and rhythmic during the last 12h of luteolysis and thereafter. The pulse peaks of PRL and PGFM were synchronized for most PRL pulses during and after luteolysis.     

Increased squalene concentrations in the clitoral gland during the estrous cycle in rats: an estrus-indicating scent mark?

Squalene in the rat clitoral gland is reported to be semi-volatile and may serve as a chemo-signal. The objective was to determine squalene concentrations in the clitoral gland throughout the reproductive cycle. Clitoral glands were extracted with dichloromethane; 23 compounds were identified with Gas Chromatography linked Mass Spectrometry (GC-MS). Since squalene concentrations were significantly higher during proestrus and estrus, and remarkably reduced during metestrus and diestrus, we inferred that it could be an ovulation-indicating chemosignal in the female rat, acting as a scent mark for the male. This hypothesis was tested by investigating its efficacy to attract males, including studying the role of the olfactory-vomeronasal system of the male in perceiving squalene. For detection of squalene, males used their conventional olfactory system when at a distance from the female, whereas the vomeronasal organ was used when they were in close proximity to the female. We concluded that squalene was a female-specific chemosignal that attracted males, and furthermore, that the olfactory-vomeronasal system had an important role in the perception of squalene.