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The objective of the present study was to investigate the effect of reproductive hormones (GnRH, hCG, LH and progesterone) on the regulation of corpus luteum (CL) and ovarian blood flow. Diestrous mares received a single treatment of saline, 100 μg gonadorelin (GnRH), or 1500 IU hCG 10 days after ovulation. Plasma LH and progesterone concentrations, resistance index (RI) for ovarian artery blood-flow, and percentage of corpus luteum (CL) with color-Doppler signals of blood flow were determined immediately before treatment (hour 0) and at hours 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, and 6. In the GnRH group, LH increased (P < 0.0001) between hours 0 and 0.25 and then progressively decreased; concentration of LH was not affected in the saline and hCG groups. Progesterone concentration was not different among groups. In the GnRH group, RI tended (P < 0.07) to decrease between hours 0 and 1.5 and increased (P < 0.01) between hours 1.5 and 4. In the hCG group, two transient RI decreases (P < 0.05) occurred before hour 2. The percentage change from hour 0 in the percentage of CL with blood-flow signals was greater at hour 0.5 in the GnRH group than in the saline group and was intermediate in the hCG group. The similarity among groups in progesterone concentration indicated that changes in progesterone were not involved in the GnRH and hCG stimulation of ovarian vascular perfusion. Effects of treatment might have been mediated through LH; however, since hCG biological activity is primarily LH-like, the differences in timing and degree of ovarian and luteal blood flow changes after GnRH or hCG administration in the present study suggest that GnRH might have a direct effect on ovarian blood vessels and vascular control. [ABSTRACT FROM AUTHOR]

In experiment 1, daily blood samples were available from Days 0 to 20 (Day 0 = ovulation) in mares with an interovulatory interval (IOI, n = 5) and in mares that developed idiopathic persistent corpus luteum (PCL, n = 5). The PCL was confirmed by maintenance of progesterone (P4) concentration until end of the experiment (Day 20). Significant interactions of group and day revealed the novel findings that luteinizing hormone (LH) was lower ( P < 0.05) in the PCL group than that in the IOI group on Days 0 to 4, and prolactin was lower ( P < 0.05) on Days 1, 4, 6, and 7. In experiment 2, treatment with a gonadotropin-releasing hormone antagonist (n = 6) significantly reduced LH on Days 1 to 6 compared with the controls (n = 6) but did not support the hypothesis that low LH during the postovulatory period increases the frequency of PCL. In experiment 3, P4, PGFM (a PGF2α metabolite), and prolactin concentrations on Days 12 to 20 from 2 reported experiments were combined to increase the number of mares with an IOI (n = 11) or a PCL (n = 11). An abrupt and complete decrease in P4 (luteolysis) began on Day 13 in the IOI group compared with a gradual and partial P4 decline after Day 12 in the PCL group. Concentrations of PGFM and prolactin were lower ( P < 0.05) in the PCL group than those in the IOI group on the day at the end of the most pronounced decrease in P4. The PCL mares were subgrouped into those with an abrupt but incomplete P4 decrease (partial luteolysis; n = 5) at the expected time and those without partial luteolysis (n = 6). There were no significant differences between the 2 subgroups in concentrations of PGFM and prolactin, but on a tentative basis ( P < 0.10), the concentration of PGFM seemed more focused on the day of the most pronounced decrease in P4 in the subgroup with partial luteolysis. Results for PCL compared with IOI indicated (1) postovulatory LH and prolactin were lower, (2) treatment to reduce postovulatory LH did not increase the incidence, and (3) both PGFM and prolactin were lower on the day of the most pronounced decrease in P4. [ABSTRACT FROM AUTHOR]

During the last wave of the interovulatory interval (IOI), the permutations of the relationship between the ovulatory follicle and the CL (ipsilateral vs. contralateral) and the number of follicular waves (two vs. three) per IOI differ in frequency of occurrence as follows: ipsilateral relationship and two waves (34%), contralateral relationship and two waves (34%), ipsilateral relationship and three waves (8%), and contralateral relationship and three waves (24%). Deviation or the continuation in growth rate of the future ovulatory follicle and a decrease in growth rate of the future subordinate follicles begin well before luteolysis in two-wave IOIs and during luteolysis in three-wave IOIs. The largest follicle decreases in diameter and loses its dominant status before completion of deviation when it is ipsilateral and adjacent to the regressing CL during wave 3. Dominant status switches from the largest follicle in the ipsilateral ovary to the next-largest follicle which may be in either ovary. Switching accounts for the greater frequency of a contralateral follicle–CL relationship than for ipsilateral follicle–CL relationship during the ovulatory wave in three-wave IOIs. It is proposed that the phenomenon results from commonality in angioarchitecture so that the decrease in blood flow to the regressing CL is associated with a decrease in blood flow to adjacent follicles. [ABSTRACT FROM AUTHOR]

The effect of the future dominant follicle (DF), corpus luteum (CL), and side (left ovary [LO] and right ovary [RO]) on FSH-induced recovery (increase in diameter) of regressing subordinate follicles was studied in heifers. The DF of wave 2 and the largest subordinate follicle remained intact (controls, n = 14 heifers) or were ablated (n = 14 heifers) on a mean of 13 d postovulation when the DF was ∼10 mm (hour 0). Concentration of FSH ( P < 0.0004) and diameter of subordinate follicles ( P < 0.0002) decreased between hours −48 to 0 combined for the control and ablation groups. Thereafter, follicle diameter continued to decrease in the controls. Concentration of FSH increased ( P < 0.05) and diameter of subordinates began to increase at hour 12 in the ablation group. Follicle-stimulating hormone increased to hour 24 and then returned to the hour 0 concentration by hour 72, completing the induced FSH surge. Concentration of LH began to increase at hour 0 in each group and at a similar rate between groups. Follicle recovery in the ablation group was compared among 8 subgroups as defined by the 2 sides and 4 intraovarian patterns (DF–CL pattern, both structures in same ovary; DF pattern, DF alone; CL pattern, CL alone; and devoid pattern, both structures absent). Follicle diameter increased ( P < 0.05) between hours 24 and 48, and diameter at hours 24, 48, 72, and 96 involved a 3-way interaction ( P < 0.0001) of pattern, side, and hour. The interaction was similar when diameter of the DF that originated from a recovered subordinate was either included or excluded in the analysis. Diameter of subordinate follicles in the ablation group at hour 96 was greater ( P < 0.05) in the DF–CL/RO and DF/RO subgroups than that in the devoid/LO, devoid/RO, and CL/LO subgroups. The DF–CL/LO and CL/RO subgroups were intermediate. For follicles that decreased in diameter before hour 0, a greater ( P < 0.05) percentage increased after hour 0 when the ovary contained a DF and was in the RO (DF–CL/RO and DF/RO subgroups) than for the remaining subgroups even after excluding the DF that originated from a subordinate. Results supported the hypotheses that (1) an induced FSH surge can stimulate the recovery of regressing subordinate follicles and (2) recovery of regressing subordinate follicles by FSH involves an intraovarian mechanism. Our interpretation is that the intraovarian mechanism that enhances the stimulatory effect of FSH on recovery of subordinate follicles was effective only in RO and only when it contained a DF. [ABSTRACT FROM AUTHOR]

In single ovulating cattle, ipsilateral versus contralateral interovarian relationships refer to a dominant follicle (DF) and CL in the same versus opposite ovaries. The ipsilateral relationship consists of the DF−CL and the devoid (no DF or CL) intraovarian pattern, and the contralateral relationship consists of the DF pattern and the CL pattern. The DF–CL pattern involves positive effects on both the DF and CL when adjacent (≤3-mm apart) versus separated as follows: greater diameter of DF (e.g., 10.5 ± 0.4 vs. 9.0 ± 0.4 mm), greater percentage of the DF wall with color Doppler signals of blood flow (40.2% ± 2.0% vs. 24.5% ± 1.9%), greater cross-sectional area of the CL (2.2 ± 0.1 vs. 1.8 ± 0.2 cm 2 ), and greater percentage of the entire CL with blood flow signals (51.8% ± 1.2% vs. 42.5% ± 3.1%). Additional examples of positive coupling are (1) future DF on Day 0 (day of ovulation) is closer to the CL than the future largest subordinate and (2) diameter of growing follicles on Day 0 and the growth rate on Days 0 to 2 are greater for follicles that are adjacent than separated from the CL. An example of a negative intraovarian effect is decreasing diameter and loss of future DF status of a largest follicle when adjacent to a regressing CL. The impact of the continuity of ovarian angioarchitecture during the periovulatory follicular wave was exemplified in 17 of 18 waves by conversion of an ovary with only the preovulatory follicle to the postovulatory DF−CL pattern. Functional angiocoupling from commonality in angioarchitecture of the DF and adjacent CL would account for both the positive two-way coupling between DF and CL during the luteal phase and the negative effect of a regressing CL on an adjacent follicle during luteolysis. [ABSTRACT FROM AUTHOR]

Five mares that developed idiopathic persistent corpus luteum (PCL) were compared with 5 mares with apparently normal interovulatory intervals (IOIs). Progesterone (P4) and a metabolite of prostaglandin F2α (PGFM) were assayed daily beginning on the day of ovulation (Day 0). Transition between the end of an initial progressive P4 increase and the beginning of a gradual decrease in P4 occurred on mean Day 6. The gradual decrease in P4 between Days 6 and 12 was less (approached significance, P < 0.06) in the PCL group than in the IOI group. The P4 concentration on Day 12 (before luteolysis in IOI group) was greater ( P < 0.05) in the PCL group than in the IOI group. In a post hoc comparison, an interaction ( P < 0.04) of group by day for Days 4 to 7 indicated that the end of the progressive increase in P4 was temporally associated with a transient increase in concentration of PGFM in IOI mares but not in PCL mares. Complete luteolysis (P4 < 1 ng/mL) occurred in the IOI mares on Days 13 to 15. Partial luteolysis (mean P4 decrease, 62%) occurred in 3 of the 5 PCL mares. Normalization to the day at the end of the most pronounced P4 decrease in the IOI mares and in the 3 PCL mares with partial luteolysis resulted in a day-by-group interaction ( P < 0.05) for PGFM concentration. The interaction was partly from lower PGFM concentration on the day at the end of the pronounced P4 decrease in the 3 PCL mares than in the IOI mares. The peak of a transient PGFM increase and the day at the end of the most pronounced decrease in P4 were synchronized in each IOI mare but not in any of the 3 PCL mares. In the other 2 PCL mares, partial luteolysis did not occur, and a transient increase in PGFM was not apparent. Results tentatively indicated that the relationship between P4 and PGFM may be altered as early as Day 6 in PCL mares and supported the hypothesis that prostaglandin F2α secretion is defective in mares with idiopathic PCL. [ABSTRACT FROM AUTHOR]

Each subordinate of the second follicular wave (wave 2) was monitored, and the outcome was classified as fully regressed (decreased in diameter to 2 mm) or recovered (decreased initially and then increased to become a growing follicle of the subsequent wave 1). The changing diameter of each follicle after emergence at 2 mm and plasma concentration of follicle-stimulating hormone were determined every 12 h from the day of ovulation (Day 0) to 4 d after the subsequent ovulation in heifers with 2 follicular waves per interovulatory interval (n = 10). The number and percentage of wave-2 subordinates that initially regressed and then recovered (7.2 ± 1.0 follicles; 33.2 ± 5.1%) were less ( P < 0.0008) than the number and percentage that completely regressed (15.0 ± 1.7; 66.8 ± 5.1%). Follicles that later recovered initially reached maximal diameter on a later day ( P < 0.0001) after emergence at 2 mm (4.3 ± 0.2 d) and at a larger ( P < 0.0001) diameter (5.8 ± 0.2 mm) than follicles that completely regressed (3.2 ± 0.1 d; 4.7 ± 0.1 mm). The follicle-stimulating hormone surge that stimulated wave 2 began earlier and was more sustained in a subgroup with a high percentage of recovered follicles (61%) than in a subgroup with a low percentage (24%). Recovery began on Day −1.0 ± 0.1 when the follicles had regressed to 3.7 ± 0.1 mm. Diameter of subordinate follicles on Day −6 or before the expected days of luteolysis was greater ( P < 0.05) when in the corpus luteum (CL) ovary than when in the non-CL ovary. During expected luteolysis, more follicles ( P < 0.008) per ovary continued to regress when ipsilateral to the CL (9.2 ± 1.1 follicles) than when contralateral (5.8 ± 1.1), and more follicles ( P < 0.02) recovered from regression when contralateral to the CL (5.0 ± 0.8) than when ipsilateral (2.2 ± 0.6). The hypothesis that the CL has a local effect on the development, regression, and recovery of the subordinate follicles of wave 2 was supported. [ABSTRACT FROM AUTHOR]

The factors involved in the switching of a future dominant follicle (DF) to subordinate status were studied (n = 42) by induction of luteolysis with PGF2α (hour 0) when the largest follicle (F1) in follicular wave 2 was 7.0 or 8.5 mm. Combined for 7.0- and 8.5-mm groups, the frequency of switching was greater (P < 0.01) when F1 and CL were ipsilateral (10 of 28, 36%) than when contralateral (0 of 14). The frequency of switching in the ipsilateral relationship was greater (P < 0.002) when F1 and CL were adjacent (<3 mm apart; 10 of 17) than when separated (0 of 11). The difference in diameter between F1 and F2 was less (P < 0.005) when switching occurred (0.4 ± 0.1 mm) than when switching did not occur (ipsilateral, 1.3 ± 0.2 mm; contralateral, 1.1 ± 0.2 mm). Treatment at hour 0 when F1 was 7.0 mm and ipsilateral to the CL resulted in smaller diameter (P < 0.001) of F1 at hour 12 (7.6 ± 0.2 mm) than when treatment was not given (8.3 ± 0.1 mm). The hypotheses were supported that (1) switching from a future DF to a future subordinate is functionally related to luteolysis, and (2) factors involved in switching include an ipsilateral relationship between the largest follicle and CL and close intraovarian proximity of the follicle to the regressing CL. It is proposed that switching of the future DF to subordinate status during spontaneous luteolysis accounts for the reported greater frequency of the contralateral than ipsilateral relationships between the preovulatory follicle and CL in three-wave interovulatory intervals. [ABSTRACT FROM AUTHOR]

The conversion of preovulatory intraovarian patterns based on location of the preovulatory follicle (PF) and the associated corpus luteum (cl) to postovulatory patterns based on location of the future and established dominant follicle (DF) and corpus luteum (CL) was studied daily in 26 heifers from Days −5 to 6 (Day 0 = ovulation). The two ipsilateral preovulatory patterns were PF–cl and devoid (neither PF nor cl), and the two contralateral patterns were PF and cl. The postovulatory patterns were DF–CL, devoid, DF, and CL. For the contralateral preovulatory relationships, a conversion from PF to DF–CL and the accompanying conversion from cl to devoid occurred most frequently (17 of 18 conversions, 94%). For the ipsilateral preovulatory relationships, a conversion from PF–cl to CL and from devoid to DF occurred most frequently (6 of 8, 75%). Number of 2-mm follicles during preovulation was greatest (P < 0.05) for the devoid and PF patterns, and number of 6-mm follicles during postovulation was greatest (P < 0.05) for the DF–CL and DF patterns. Blood flow resistance at a color Doppler signal in the ovarian pedicle indicated increasing ovarian perfusion over days in the PF to DF–CL and devoid to DF conversions and decreasing perfusion in the PF–cl to CL and cl to devoid conversions. In addition to formation of the CL from the PF, it was interpreted that the conversion of patterns involved number of newly emerging 2-mm follicles per ovary before ovulation and a continuation of the preovulatory angioarchitecture into postovulation. Results supported the novel hypothesis that the four preovulatory intraovarian patterns determine the frequency of the four postovulatory patterns. [ABSTRACT FROM AUTHOR]

An intraovarian positive physiologic coupling between the extant CL and the ipsilateral preovulatory follicle (PF) or the future or established postovulatory dominant follicle (DF) was studied in 26 heifers. Ovaries were scanned by ultrasonic imaging from Day 16 (Day 0 = ovulation) of the preovulatory period until Day 6 of the postovulatory period. Hemodynamics of the follicles and CL were assessed by color-Doppler ultrasonography. When the PF and CL were ipsilateral compared with contralateral, blood-flow resistance in wall of the PF was lower (P < 0.04) on Days –2 and –1, and percentage blood-flow signals in the CL approached being greater (P < 0.08) on Days –4 to –1. During the postovulatory period, percentage of DF wall with blood-flow signals (44.1 ± 1.2% vs. 31.4 ± 2.8%) and percentage of CL with blood-flow signals (51.8 ± 1.2% vs. 42.5 ± 3.1%) were each greater (P < 0.05) when the two ipsilateral structures were adjacent (distance between antrum and CL wall, ≤ 3 mm) than when separated. On Day 0, the distance between follicle and ipsilateral CL was less (P < 0.02) for the future DF than for the future largest subordinate. Growth rate between Days 0 and 2 averaged over all growing follicles was greater (P < 0.01) when the follicles were ≤3 mm from the CL (1.1 ± 0.1 mm/day) than when farther from the CL (0.9 ± 0.1 mm/day). Results supported the hypotheses that (1) a positive intraovarian coupling occurs between the PF or postovulatory DF and the extant CL and (2) the coupling is enhanced when the ipsilateral DF and CL are in close proximity. [ABSTRACT FROM AUTHOR]

A study was performed on the effect of a single dose per mare of 0 (n = 9), 100 (n = 8), or 300 (n = 9) of GnRH on Day 10 (Day 0 = ovulation) on concentrations of LH, FSH, and progesterone (P4) and blood flow to the CL ovary. Hormone concentration and blood flow measurements were performed at hours 0 (hour of treatment), 0.25, 0.5, 1, 2, 3, 4, and 6. Blood flow was assessed by spectral Doppler ultrasonography for resistance to blood flow in an ovarian artery before entry into the CL ovary. The percentage of the CL with color Doppler signals of blood flow was estimated from videotapes of real-time color Doppler imaging by an operator who was unaware of mare identity, hour, or treatment dose. Concentrations of LH and FSH increased (P < 0.05) at hour 0.25 and decreased (P < 0.05) over hours 1 to 6; P4 concentration was not altered by treatment. Blood flow resistance decreased between hours 0 and 1, but the decrease was greater (P < 0.05) for the 100-μg dose than for the 300-μg dose. The percentage of CL with blood flow signals increased (P < 0.05) between hours 0 and 1 with no significant difference between the 100- and 300-μg doses. The results supported the hypothesis that GnRH increases LH concentration, vascular perfusion of the CL ovary, and CL blood flow during the luteal phase; however, P4 concentration was not affected. [ABSTRACT FROM AUTHOR]