Differential blood flow changes between the future dominant and subordinate follicles precede diameter changes during follicle selection in mares

Diameter deviation during a follicular wave is characterized by the continued growth of the developing dominant follicle and reduced growth and regression of the subordinate follicles. This study considered the hypothesis that reduced blood flow in the future largest subordinate follicle precedes the beginning of diameter deviation. The hypothesis was tested by quantifying the daily changes in blood-flow velocities and blood-flow area within the wall of follicles before and during diameter deviation in mares (n = 7). The blood-flow end points were quantified daily by transrectal color Doppler ultrasonography. Follicles were identified retrospectively by rank as F1 (largest) and F2 according to the maximum attained diameter. Follicles were grouped into nine F1 diameter ranges of 3.0 mm each (equivalent to 1 day's growth) centered on 6.5, 9.5, 12.5, 15.5, 18.5, 21.5, 24.5, 27.5, and 30.5 mm. Diameter deviation began in the 24.5-mm group, as indicated by a smaller (P < 0.05) difference between F1 and F2 in the 24.5-mm group than in the 27.5-mm group. Based on a similar approach, peak systolic velocity and time-averaged maximum velocity of blood flow began to deviate between F1 and F2 in the 18.5-mm group (P < 0.04) and blood flow area began to deviate in the 21.5-mm group (P < 0.009). Thus, differential blood flow area between F1 and F2 began an average of 3.0 mm (equivalent to 1 day) and differential blood-flow velocities began an average of 6.0 mm before the beginning of diameter deviation. The results demonstrated that deviation between F1 and F2 in the blood flow of the follicle walls occurred 1 or 2 days before deviation in follicle diameter during follicle selection in mares.     

Luteal blood flow during the estrous cycle in mares

Transrectal color Doppler ultrasound was used for the noninvasive investigation of luteal blood flow during the estrous cycle in six mares. Color was displayed in Power-Mode, in which the number of color pixels on the ultrasound image is related to the number of moving blood cells. Three pictures with a maximum number of color pixels of the corpus luteum (CL) during an examination period of about 20 min were selected and digitized on a laptop equipped with an external frame grabber card. The intra-class correlation coefficient for the number of color pixels was 0.90. In all estrous cycles similar patterns of changes in (C), in the cross-sectional area of sectional planes of the CL (A), and in plasma progesterone levels (P) occurred. Variance component estimates for the effect of the mare on (C), (A) and (P) were 14, 23 and 4%, for the influence of day of estrous cycle they were 41, 5 and 58% and for the effect of estrous cycle they were 7, 5 and 5%, respectively. There were high positive correlations between cyclic changes in (C) and (P) (r = 0.58; P < 0.0001). The increase in (C) between Days 0 and 5 (Day 0: ovulation) remained at high levels until Day 7 and then decreased until Day 15. There were relationships between (C) and (A) (r = 0.37; P < 0.0001) and between (A) and (P) (r = 0.24; P < 0.05), but correlation coefficients were not as high as between (C) and (P). Differences in (C), (A) and (P) between estrous cycles within mares and between mares were not related to each other (P > 0.05). The results show that transrectal color Doppler sonography is a useful, noninvasive method for examining luteal blood flow in mares, and that there are cyclic changes and individual differences in the vascularization of the CL. The possible influence of luteal perfusion on fertility in mares needs to be investigated in further studies.     

Uterine and ovarian blood flow during the estrous cycle in mares

Uterine and ovarian blood flow was investigated in four mares during two consecutive estrous cycles using transrectal color Doppler sonography. The uterine and ovarian arteries of both sides were scanned to obtain waves of blood flow velocity. The pulsatility index (PI) reflected blood flow. There were significant time trends in PI values of all uterine and ovarian blood vessels during the estrous cycle (P < 0.05). PI values did not differ between the uterine arteries ipsi- and contralateral to the corpus luteum or the ovulatory follicle. PI values of the uterine arteries showed a wave shaped profile throughout the estrous cycle. The highest PI values occurred on Days 0 and 1 (Day 0 = ovulation) and around Day 11, and the lowest PI values were measured around Days 5 and -2 of the estrous cycle. During diestrus (Days 0-15) PI values of the ovarian artery ipsilateral to the corpus luteum were significantly lower than PI values of the contralateral ovarian artery (P < 0.0001). No differences (P > 0.05) in resistance to ovarian blood flow occurred between sides during estrus (Days -6 to -1). In this cycle stage PI values decreased in both ovarian vessels (P < 0.05). During diestrus, high PI values of the ovarian artery ipsilateral to the corpus luteum were measured between Days 0 and 2, followed by a decline until Day 6 (P < 0.05). From this time on, the resistance to blood flow increased continuously until Day 15 (P < 0.05). The cyclic blood flow pattern in the contralateral ovarian artery was similar to that in the uterine arteries (r = 0.68; P < 0.0001). No correlations occurred between the diameter of the corpus luteum and the PI values of the ipsilateral ovarian artery (P > 0.05) during diestrus. During estrus, there was a negative relationship between growth of the diameter of the ovulatory follicle and changes in PI values of the dominant ovarian artery (r = -0.41; P < 0.05). PI values of the uterine arteries and of the ovarian artery ipsilateral to the ovulatory follicle were negatively related to estrogen (E) levels in plasma during estrus (uterine arteries: r = -0.21; P < 0.05; dominant ovarian artery: r = -0.35; P < 0.05). In diestrus, PI values of the dominant ovarian artery were negatively related to plasma progesterone levels (r = -0.38; P < 0.0001), but not the PI values of the uterine arteries (P > 0.05). The findings of this study show that there are characteristic changes in blood supply of the uterus and the ovaries throughout the equine estrous cycle. There are negative correlations between resistance to blood flow in the uterine and ovarian arteries and the plasma estrogen levels during estrus. In diestrus, there is a negative relationship between the resistance to ovarian blood flow and the progesterone levels.     

Follicular and FSH responses to parturition during the anovulatory season in mares

The ovaries of periparturient pony mares (n=9 to 16 parturitions per month for January to April) were scanned ultrasonically on the day of parturition, while those of postpartum and control mares (n=12) were examined at least twice weekly. Four mares had apparent lactational anovulation (incidence, 7%) that corrected spontaneously (1 mare) or within 14 d after the weaning of foals on August 10 (3 mares). All but 2 of the postpartum ovulations occurred after April 29; that is, parturition did not effectively stimulate ovulation in ponies foaling during the anovulatory season. Mean diameter of the largest follicle per month increased (P<0.001) progressively in the controls (means: 11.4, 14.4, 19.0 and 24.5 mm for January to April, respectively). In the parturient mares, the diameter of the largest follicle on day of parturition did not increase over months (range of means: 13.6 to 16.9 mm), indicating that a suppressive effect of pregnancy counteracted the stimulatory effect of season. Within each month of parturition, diameter of the largest follicle increased (P<0.05) between Day 0 (day of parturition) and Day 3 or 7. Blood samples for FSH assay were taken daily for 14 d from 6 mares with parturition in the middle of each month and from 6 controls on the corresponding calendar days. In periparturient mares, a significant increase in mean FSH concentrations occurred for all months of parturition between Day-2 and Day 0, followed by a significant decrease between Day 3 and Day 7. Maximum means for the periparturient FSH profile were temporally related to the beginning of follicular growth. In the controls, FSH concentrations were not affected by month or day, or by their interaction. Within each month, mean FSH concentrations were lower (P<0.05) in the periparturient mares than in the controls (averaged over all months: 3.9 +/- 0.1 versus 7.9+/-0.3 ng/ml) even though follicular growth was greater following parturition than during the corresponding calendar days in controls.     

Administration of sulpiride to anovulatory mares in winter: effects on prolactin and gonadotropin concentrations, ovarian activity, ovulation and hair shedding

Sixteen seasonally anovulatory mares were randomly allotted to two groups and injected daily with either sulpiride (1 mg/kg body weight) or vehicle from 14 January to 14 February. Sulpiride administration increased daily plasma prolactin concentrations (P < 0.05), although the prolactin response during the 6 h following sulpiride injections decreased markedly from the 1st to the 6th day of treatment (treatment by day, P < 0.0001). Plasma concentrations of LH and FSH were not affected by treatment (P > 0.1). Injection of GnRH and TRH on 15 February showed that the response of plasma prolactin to secretagogue was increased in sulpiride-treated mares (P < 0.005), while there was no effect (P > 0.1) of sulpiride treatment on the response of LH or FSH. Both treatment groups had similar changes in numbers of follicles 10-19 and > or = 20 mm during the experiment (P > 0.1). Similarly, the mean change in maximal follicular size was not affected by treatment (P > 0.9). No mare ovulated during the study, and plasma progesterone concentrations were similar in both groups (P > 0.1), always at levels < 1 ng/ml. Hairshedding increased with time in all mares (P < 0.001) and was increased by sulpiride injections (P = 0.09). It was concluded that sulpiride administration to seasonally anovulatory mares under the conditions of our experiment increased daily plasma prolactin levels but did not stimulate gonadotropin secretion or ovarian activity.     

Alterations in follicular estradiol and gonadotropin receptors during development of bovine antral follicles

It was hypothesized that growth divergence of dominant and subordinate follicles during Wave 1 and growth termination of the dominant follicle would be associated with changes in the number of gonadotropin receptors on granulosa cells and estradiol in follicular fluid. To test this hypothesis, follicular development of 16 Holstein heifers was monitored by ultrasound, and follicles were collected on Days 2,4,6 and 10 (Day 0 = ovulation). Dominant follicles were compared across days, whereas dominant and largest subordinate follicles were compared on Days 2 and 4 only. The numbers of LH and FSH receptors on the granulosa cells of dominant follicles did not differ significantly over Days 2, 4, 6 and 10. In contrast, concentrations of estradiol in follicular fluid decreased (P < 0.05) from Days 2 to 10 (373 +/- 150 to 42 +/- 12 ng/ml) and concentrations of progesterone in follicular fluid increased (P < 0.05) from Days 2 to 10 (12.2 +/- 2.3 to 24.4 +/- 4.8 ng/ml). Correspondingly, the ratio of estradiol:progesterone in the dominant follicles decreased (P < 0.05) from Days 2 to 10. Comparisons between dominant and subordinate follicles indicated greater (P < 0.05) estradiol concentrations in the dominant follicle on Day 2, but the number of gonadotropin receptors was not different until Day 4. Thus, differences in concentrations of follicular fluid estradiol, but not numbers of granulosa cell gonadotropin receptors, were associated with the early growth divergence of dominant and subordinate follicles (Day 2) and the eventual growth termination of the dominant follicle (Day 10). Late divergence (Day 4) was associated with higher gonadotropin receptor numbers and follicular estradiol concentrations in the dominant than in the subordinate follicles. These results indicate that an increase in estradiol productivity of the selected dominant follicle occurred before an increase in the number of gonadotropin receptors.     

Effect of GnRH treatment during the anovulatory season on multiple ovulation rate and on follicular development during the ensuing pregnancy in mares

Seasonally anovulatory mares were injected, i.m., twice daily with a GnRH analogue (GnRH-A), and hCG was given when the largest follicle reached 35 mm in diameter. In Exp. 1, treatment was initiated on 23 December when the largest follicle per mare was less than or equal to 17 mm. An ovulatory response (ovulation within 21 days) occurred in 17 of 30 (57%) GnRH-A-treated mares on a mean of 15.8 days. The shortest interval to ovulation in control mares (N = 10) was 57 days. The diameter of the largest follicle first increased significantly 6 days after start of treatment. In Exp. 2, treatment was begun on 15 January and mares were categorized according to the largest follicle at start of treatment. The proportion of mares ovulating within 21 days increased significantly according to initial diameter of largest follicle (less than or equal to 15 mm, 9/25 mares ovulated; 15-19 mm, 13/21; 20-24 mm, 20/24; greater than 25 mm, 3/3). The multiple ovulation rate was greater (P less than 0.01) for treated mares (27/86 mares had multiple ovulations) than for control mares (2/35). Treated mares in which the largest follicle at start of treatment was greater than or equal to 25 mm had a higher (P less than 0.01) multiple ovulation rate (9/14) than did mares in which the largest follicle was less than 25 mm (18/72). The pregnancy rate for single ovulators was not different between control mares (26/30 pregnant mares) and treated mares (43/54).(ABSTRACT TRUNCATED AT 250 WORDS)     

Ovarian follicles, ovulations and progesterone concentrations in aged versus young mares

The objectives of this study were: 1) to document age-related ovulation failure in mares and 2) to contrast the number of ovarian follicles, occurrence of ovulations, and postovulatory concentrations of progesterone in aged versus young mares. In Experiment 1, 4 of 10 aged (25- to 33-years-old) mares were anovulatory between July 1 and September 1, 1989. In Experiment 2, two of 25 aged (20- to 30-years-old) and none of 21 young (3- to 12-years-old) mares were anovulatory between February 1 and June 30, 1990. The average (+/- SEM) day of the first ovulation was later (P<0.05) for aged versus young mares (May 9 +/- 7.1 vs April 25 +/- 7.4 days, respectively). There tended (P<0.10) to be fewer 11- to 20-mm ovarian follicles in aged versus young mares (2.8 +/- 0.2 vs 5.3 +/- 0.1, respectively), but there was no difference (P>0.10) in the total number of ovarian follicles in aged versus young mares (21.0 +/- 0.3 vs 26.1 +/- 0.2, respectively) during the pooled periovulatory period of the first and second (single) ovulations. The number of ovulatory cycles during the study period was less (P=0.01) for aged versus young mares (2.2 +/- 0.3 vs 3.2 +/- 0.3). Plasma progesterone concentrations on Days 10 and 15 of the first ovulatory cycle were higher (P<0.05) in aged versus young mares.     

Steroid concentrations in follicular fluid aspirated repeatedly from transitional and cyclic mares

The objectives of the present study were to determine follicular progesterone (P4) and estradiol-17beta (E2) in transitional mares and to compare follicular steroid concentrations between transitional and cyclic mares. Follicles > 8 mm were aspirated under transvaginal ultrasound-guidance 4 times at 3 to 4 day intervals (T1-T4) in Norwegian pony mares during vernal transition. During the breeding season, follicular aspirations were conducted in each mare on Day 6, Day 14 and Day 18 after ovulation of 3 separate estrous cycles (Day of ovulation = Day 0). Plasma and follicular fluids were analyzed for P4 and E2 with ELISA and RIA, respectively. Plasma P4 concentrations remained below 1 ng/mL throughout T1-T4, while the follicular P4 concentrations increased significantly to cyclic levels after the first transitional aspiration. Plasma E2 concentrations similarly remained at low levels during the course of the transitional aspirations, while the follicular E2 concentrations increased gradually over the 4 aspirations to cyclic concentrations. The mares ovulated on average 9.8 +/- 1.6 (mean +/- SEM) days after the last transitional aspiration, and 16.6 +/- 0.2, 11.3 +/- 1.5 and 23.2 +/- 4.4 days after aspirations conducted on Day 6, 14 and 18, respectively. The present study demonstrates that in the transitional mare newly developing follicles exhibit biosynthesis of P4 and E2. Furthermore, an increase in follicular steroid concentrations is not necessarily reflected in the peripheral steroid concentrations.     

Folliculogenesis during the transitional period and early ovulatory season in mares

Individual follicles were monitored by ultrasonography in 15 mares during the transitional period preceding the first ovulation of the year and in 9 mares during the first interovulatory interval. During the transitional period, 7 mares developed 1-3 anovulatory follicular waves characterized by a dominant follicle (maximum diameter greater than or equal to 38 mm) that had growing, static, and regressing phases. The emergence of a subsequent wave (anovulatory or ovulatory) did not occur until the dominant follicle of the previous wave was in the static phase. After the emergence of the subsequent wave, the previous dominant follicle regressed. The mean (+/- s.d.) length of the interval between successive waves was 10.8 +/- 2.2 days. Before the emergence of waves (identified by a dominant follicle), follicular activity seemed erratic and follicles did not reach greater than 35 mm. During the interovulatory interval, 6 mares developed 2 waves (an anovulatory wave and a subsequent ovulatory wave) and 3 mares developed only 1 detected wave (the ovulatory wave). The ovulatory follicle at the end of the transitional period reached 20 mm earlier (Day - 15), grew slower (2.6 +/- 0.1 mm/day; mean +/- s.e.m.) but reached a larger diameter on Day - 1 (50.5 +/- 1.1 mm) than for the ovulatory follicle at the end of the interovulatory interval (Day - 10, 3.6 +/- 0.2 mm/day, 44.4 +/- 1.0 mm, respectively; P less than 0.05 for each end point). The interval from cessation of growth of the largest subordinate follicle to the occurrence of ovulation was longer (P less than 0.05) for end of the transitional period (9.5 +/- 0.7 days) than for the end of the interovulatory interval (6.8 +/- 0.6 days). Results demonstrated the occurrence of rhythmic follicular waves during some transitional periods and the occurrence of 2 waves during some of the first oestrous cycles of the year.     

Transrectal Doppler sonography of uterine and umbilical blood flow during pregnancy in mares

Transrectal color Doppler sonography was used to investigate uterine and umbilical blood flow during pregnancy (duration, 46-48 weeks) in four mares. The resistance index (RI) and blood flow volume (VOL) of the uterine arteries ipsilateral and contralateral to the conceptus, and the presence of an early diastolic notch in the Doppler wave, were evaluated every 4 week throughout pregnancy. Fetal blood flow was calculated semiquantitatively every 2 week (from 20 to 40 weeks), using the RI of the umbilical arteries. During the entire period of investigation, there were no significant individual variations in uterine RI and VOL nor differences between the two uterine arteries. Mean RI decreased by more than half during pregnancy from 0.89 +/- 0.01 to 0.39 +/- 0.03, and mean VOL increased almost 400-fold from 69 +/- 37 to 27,467 +/- 8851 ml/min. There were relationships (P<0.0001) between week of pregnancy (x) and RI as well as VOL. These were described by the equations RI=0.938-0.150 ln(x) and VOL (ml/min)=7.621x(2.157). Log transformed total estrogen (TE) were related to RI (r=-0.879; P<0.05) as well as to VOL (r=0.888; P<0.05). The notch in the Doppler wave of the uterine artery disappeared between 18 and 26 weeks. There was a correlation (P<0.0001) between week of gestation (x) and RI values of the umbilical arteries; this was described by the equation RI=1.763-0.071x+0.001x2. Further studies are needed to determine whether transrectal color Doppler sonography could be used to identify mares at risk of abortion.     

Transrectal Doppler sonography of uterine blood flow during early pregnancy in mares

Transrectal color Doppler sonography was used for the noninvasive investigation of uterine blood flow in five mares. Both the left and right uterine arteries were scanned to obtain blood flow velocity waveforms during two consecutive estrous cycles and two early pregnancies in each mare. Blood flow was expressed as the time-averaged maximum velocity (TAMV) and the resistance index (RI). In all pregnancies the embryonic vesicle could be detected for the first time on Day 11 (day of ovulation: Day 0). No differences in mean TAMV and RI values of both uterine arteries were observed in comparison to the corresponding days of the estrous cycle until Day 11 of pregnancy (P>0.05). From Day 11 onwards, mean TAMV values were higher and mean RI values lower in pregnant mares than in cyclic mares (P<0.05). During the estrous cycle TAMV and RI values did not differ between the right and left uterine arteries (P>0.05). From Days 15 to 29 of pregnancy, TAMV values were consistently higher and RI values lower in the uterine artery ipsilateral to the conceptus and they had a more distinct rise and decline, respectively, compared to the contralateral uterine artery (P<0.05). The variance component estimates for the effect of mare on TAMV and RI values during pregnancy were 60 and 53%, respectively, and for the effect of day of pregnancy, they were 29 and 34%, respectively (P<0.0001). Within mares there were no significant differences between the two pregnancies with regard to blood flow (P>0.05). The results show that uterine blood supply increases in mares during the second week of pregnancy compared to cyclic mares. Furthermore there are individual variations in blood flow between mares.     

Luteal blood flow and progesterone production in mares

The temporal relationships between blood flow in the corpus luteum (CL) and circulating progesterone concentrations were studied in 20 mares. Retrospective inspection of plasma progesterone concentrations indicated that a precipitous decrease occurred during Days 15-17 (Day 0 = ovulation) and was defined as the luteolytic period. Mean percentage of CL with color-Doppler signals for blood flow was maximum on Day 10 (77.3%), and Days 10-14 (49.8%) were defined as the preluteolytic period. The cross-sectional area of the CL decreased progressively from Day 4 (9.0 cm2) to Day 19 (1.5 cm2). Progesterone reached maximum concentration on Day 8 (12.8 ng/ml) and thereafter CL area and plasma progesterone decreased in parallel until the onset of luteolysis. During the luteolytic period, the decrease in plasma progesterone was about sixfold greater than during the preluteolytic period, whereas the decrease in CL area and in percentage of CL with blood-flow area were about twofold greater. There was no indication that an acute increase or decrease in luteal blood flow occurred prior to the precipitous decrease in plasma progesterone.     

Elevated plasma testosterone concentrations during stallion-like sexual behavior in mares (Equus caballus)

Mounting interactions in mares isolated from stallions and the relationship to stage of the estrous cycle and level of circulating hormones were studied for 3 years in a herd averaging 105 mares. Mares were assigned to mounting, standing, and control groups. A control mare was selected by being within 1 day of the number of days after ovulation in a mounting mare. A total of 15 mounting interactions were detected by chance observation during the 3 years. A blood sample was collected immediately after the mounting interaction from each mare in the three groups, and a transrectal ultrasonographic examination of the reproductive tract was done. Two mounting interactions occurred during the early luteal phase and 13 during the follicular phase. The interactions that occurred during the follicular phase were used for comparisons among groups. The interval between mounting and the next ovulation, diameter of the two largest follicles, and the number of follicles larger and smaller than 20 mm were not different significantly among the mounting, standing, and control groups. Testosterone concentrations were higher (P<0.01) in the mounting group (17.7+/-2.3 pg/ml) than in standing group (10.9+/-0.5 pg/ml), and the difference between the mounting group and the control group (12.8+/-0.6 pg/ml) approached significance (P<0.08). Concentrations of androstenedione, estradiol, estrone, and progesterone did not differ significantly among groups. Results indicated that mounting behavior between mares is rare, usually occurs during the follicular phase, and is related to high circulating concentrations of testosterone.     

The effect of GnRH on induction of follicular development and ovulation in anovulatory and ovulatory mares

The effects of estradiol cypionate (ECP) and GnRH injections were tested on mares during January and February. Sixteen mares were blocked on their ovarian status and equally allotted to two groups. Group one received daily injections of 500 μg ECP (im) for 14 days followed by a 21 day period of twice daily injections of 200 μg GnRH (im). Group two received the carrier vehicle.Mean length of diestrus of ovulatory mares was 14.3 ± 1.6 days and 17.8 ± 3.5 days for treated and control groups respectively. Corresponding estrus lengths were 8.0 ± 1.4 days and 6.3 ± 2.1 days. Plasma LH levels, number of follicles < 20 mm, number of follicles > 20 mm and diameter of the largest follicle in ovulatory mares were not significantly affected by treatment with ECP or GnRH.Anovulatory mares treated with ECP and GnRH exhibited estrus more frequently (54% and 70% of the time) than sham injected controls (17% and 15% of the time). Plasma LH levels were significantly elevated (P<.05) in anovulatory mares treated with GnRH. Also more follicles < 20 mm (P<.09) were detected on the ovaries of GnRH treated mares than on those of control mares. Effects of the treatment were transient since LH levels and ovarian activity were similar in both mare groups after cessation of treatment.     

Structure-function relationships during preovulatory development of porcine follicles following equine chorionic gonadotropin stimulation.

Porcine follicular maturation begins by recruitment from a continually proliferating pool of small antral follicles; those receiving the appropriate stimulus differentiate rapidly through a series of structural and functional changes. Such ovarian activity can be induced in prepubertal gilts with a single injection of equine chorionic gonadotropin (eCG). Average follicular diameter in eCG treated females increased from approximately 2 mm before stimulation to 3.5 mm by 24 hr after injection, with subsequent growth to ovulatory size (8 or 9 mm) by 96 hr. Both theca and granulosa layers increased in thickness and complexity, and a prominent capillary bed evolved immediately outside the basement membrane separating the two layers. Cytoplasmic organelles associated with increased metabolic activity and steroidogenesis proliferated within the first 24 hr. Progressive changes included increasing amounts of lipid and rough and smooth endoplasmic reticulum, with the latter occurring in vesicular or lamellar forms and as lipid-associated whorls. Bizarre mitochondrial forms also appeared, often associated with lipids. The amount and proportion of rough and smooth endoplasmic reticulum shifted dramatically as follicles matured. By 24 hr, rough endoplasmic reticulum in thecal cells increased from 4.2 to 7% of cell volume, while the amount in granulosa cells increased from less than 3.5% to more than 10%; the quantity remained relatively constant in the theca but declined to prestimulation values in the granulosa layer. Rough endoplasmic reticulum predominated over smooth in the first 24 hr following stimulation but the proportions were then reversed, so that more than 10% of both layers was composed of smooth endoplasmic reticulum by the time ovulation was imminent. Some follicles had or were in the process of ovulating by 96 hr. Their walls were collapsed into prominent folds with the two cell types beginning to mix. Slight undulations and some regions of discontinuity were observed in basement membranes of large unovulated follicles at this time. In specimens collected at 96 hr poststimulation and processed for retention of lipid, lipid-like material was noticeable in the extracellular matrix surrounding cells that contained organelle configurations suggestive of steroidogenesis.     

Renal blood flow, early distal sodium, and plasma renin concentrations during osmotic diuresis

Inconsistencies in previous reports regarding changes in early distal NaCl concentration (ED(NaCl)) and renin secretion during osmotic diuresis motivated our reinvestigation. After intravenous infusion of 10% mannitol, ED(NaCl) fell from 42.6 to 34.2 mM. Proximal tubular pressure increased by 12.6 mmHg. Urine flow increased 10-fold, and sodium excretion increased by 177%. Plasma renin concentration (PRC) increased by 58%. Renal blood flow and glomerular filtration rate decreased, however end-proximal flow remained unchanged. After a similar volume of hypotonic glucose (152 mM), ED(NaCl) increased by 3.6 mM, (P < 0.01) without changes in renal hemodynamics, urine flow, sodium excretion rate, or PRC. Infusion of 300 micromol NaCl in a smaller volume caused ED(NaCl) to increase by 6.4 mM without significant changes in PRC. Urine flow and sodium excretion increased significantly. There was a significant inverse relationship between superficial nephron ED(NaCl) and PRC. We conclude that ED(Na) decreases during osmotic diuresis, suggesting that the increase in PRC was mediated by the macula densa. The results suggest that the natriuresis during osmotic diuresis is a result of impaired sodium reabsorption in distal tubules and collecting ducts.     

Blood flow to follicles and CL during development of the periovulatory follicular wave in heifers

The hemodynamics of the developing CL and the future dominant follicle (DF) was studied in 22 heifers during wave 1 on Days 0 to 5 (Day 0 = ovulation). Color-Doppler ultrasonography was used to determine the resistance index (RI) at the most prominent Doppler signal in an ovarian arterial branch before entry into the ovary; a decrease in RI indicates a downstream increase in vascular perfusion. The RI for each of four intraovarian patterns averaged over days was different (P < 0.05) from each of the other patterns as follows: DF–CL (DF and CL in the same ovary), 0.52 ± 0.02; CL alone, 0.60 ± 0.01; DF alone, 0.67 ± 0.01; neither DF nor CL, 0.78 ± 0.01. The differences in RI among intraovarian patterns began on Day 0 or 1, indicating that the extent of vascular perfusion on Days 0 to 5 for the various patterns may have been influenced by events that occurred before ovulation. The percentage of the DF wall with color-flow signals was greater (P < 0.05) in the DF–CL pattern than in the DF pattern on each of Days 2 to 5 and was greater (P < 0.0001) in the DF–CL pattern when the DF was adjacent to the CL (40.2 ± 2.0%) than when separated (24.5 ± 1.9%). Dimensions of DF (P < 0.01) and CL (P < 0.02) were greater when adjacent to each other. The results supported the hypotheses for wave 1 that (1) vascular perfusion is greater for the DF–CL intraovarian pattern than for the DF or CL pattern and (2) the extent of blood-flow Doppler signals in the wall of the developing DF is greater for the DF–CL pattern than for the DF pattern. Our preferred interpretation is that a change in vascular perfusion of the CL is accompanied by a similar change in perfusion of the DF when the two structures are in the same ovary especially adjacent.     

Changes in plasma gonadotropin concentrations and urethral closure pressure in the bitch during the 12 months following ovariectomy

Urinary incontinence due to acquired urethral sphincter incompetence is a common side effect of spaying, for which the underlying cause remains unknown. Spaying not only results in a significant reduction in the urethral closure pressure within 1 year but also in an increase in the plasma gonadotropin concentrations. To investigate the possible link between the post-ovariectomy changes in plasma gonadotropins and in urethral closure pressure, gonadotropin and urodynamic measurements were performed in 10 Beagle bitches before and for a period of 1 year after spaying. Plasma gonadotropin concentrations rose quickly after ovariectomy and peak levels were seen within 3-5 weeks, followed by a sharp drop until week 10. A steady increase was observed subsequently until week 42, when a plateau was reached. One year after spaying, the mean FSH concentration was 75.3 +/- 32.1 ng/ml, a 17-fold increase, and the LH was 8.3 +/- 3.8 ng/ml, an eightfold increase over the pre-spaying values. Ten months after spaying, the mean urethral closure pressure (9.7 cm H2O) was significantly reduced when compared to the mean pre-operative value of 15.4 cm H2O. However, there was no clear relationship between the gonadotropin concentrations and the urethral closure pressure. From these results it seems unlikely that chronically elevated gonadotropins are the underlying cause for reduced urethral closure pressure after spaying resulting in urinary incontinence.     

Age-related dynamics of follicles and hormones during an induced ovulatory follicular wave in mares

An ovulatory follicular wave was induced by ablation of follicles ≥6 mm and treatment with prostaglandin F2α (PGF) on Day 10 (ovulation = Day 0). Follicle and hormone dynamics of the induced waves were compared among three age groups: young (5-6 y, n = 14 waves), intermediate (10-14 y, n = 16), and old (≥18 y, n = 15). During the common-growth phase of the induced wave (Days 12-17), diameter of the future ovulatory follicle was not different among ages, but the young group had more (P < 0.05) follicles that reached ≥10 mm. The number was correlated (r = +0.7; P < 0.0001) within mares between consecutive interovulatory intervals, indicating repeatability. Concentrations of LH increased in all age groups during Days 12-17, but were greatest (P < 0.002) in the young group and continued to be greater (P < 0.0001) throughout the ovulatory LH surge. During several days before Day −1, there were no age-related effects on systemic estradiol concentrations, diameter of the preovulatory follicle, or B-mode echo texture or color-Doppler signals of blood flow in the follicle wall. Interpretations were: (1) greater number of follicles in the young group reflected a greater follicle reserve, (2) greater LH concentrations throughout the ovulatory surge in the young group reflected a more positive response to an extraovarian/environmental influence after removal of the negative effect of progesterone, and (3) lower LH concentrations in the older groups were adequate for the preovulatory changes in the follicle.