Effect of unilateral ovariectomy on compensatory ovarian hypertrophy, peripheral concentrations of follicle-stimulating hormone and luteinizing hormone, and ovarian venous concentrations of estradiol-17 beta in prepuberal gilts

A study was designed to characterize the compensatory ovarian response to unilateral ovariectomy (ULO) in prepuberal gilts and to investigate further the mechanisms involved in compensatory ovarian hypertrophy (COH). Forty-eight crossbred gilts were sham ovariectomized (Sham) or unilaterally ovariectomized at 130 days of age (Day 0). Remaining ovaries in ULO gilts were removed and Sham gilts were bilaterally ovariectomized 2, 4 or 8 days later. A peripheral blood sample was taken before surgery and ovarian venous blood samples were taken before removal of each ovary. Serum estradiol-17 beta (E2) concentrations were determined. Mean wet and dry ovarian weights per ovary on Day 2 for ULO and Sham gilts were 3.4 versus 2.8 and 0.26 versus 0.24 g, respectively. Those weights on Days 4 and 8 were greater (P less than 0.01) for ULO than Sham gilts. Follicular fluid weight per ovary was greater (P less than 0.05) for ULO than Sham gilts on Days 2, 4 and 8. Ovarian venous E2 concentrations were greater (P less than 0.01) for ULO than for Sham gilts on Days 2 and 4 but were similar on Day 8. In a second experiment, 42 prepuberal gilts 130 days of-age were subjected to Sham (n = 18), ULO (n = 18) or bilateral ovariectomy (BLO; n = 6) to evaluate follicle-stimulating hormone (FSH) and luteinizing hormone (LH) secretion immediately after surgical treatment. Release of FSH within the first 24 h was greater for BLO than ULO and for ULO than Sham gilts.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influences of age and ovarian follicular reserve on estrous cycle patterns, ovulation, and hormone secretion in the Long-Evans rat

This study examined the influences of aging and reduced ovarian follicular reserve on estrous cyclicity, estradiol (E(2)) production, and gonadotropin secretion. Young virgin and middle-aged (MA) retired breeder female rats were unilaterally ovariectomized (ULO) or sham operated (control). Unilateral ovariectomy of young rats reduced the ovarian follicular reserve by one-half, to a level similar to that found in MA controls. Unilateral ovariectomy of MA females reduced the follicular pool further, to one half of MA controls. The incidence of regular cyclicity was significantly lower in MA ULO females than in young controls, with intermediate cycle frequency in young ULO and MA controls. Among cyclic rats, the magnitude of the proestrous LH surge was highest in young controls, intermediate in young ULO rats and MA controls, and lowest in MA ULO females. Similarly, ovulation rates were highest in young controls, intermediate in young ULO rats and MA controls, and lowest in MA ULO females. While young ULO rats exhibited augmented secondary FSH surges on estrous morning, middle-aged ULO females displayed secondary FSH levels comparable to young controls. The effects of age and reduced follicle number on estrous cyclicity and gonadotropin secretion were not due to altered E(2) secretion, as preovulatory E(2) levels were similar among all groups. Thus, experimental reduction in the follicular reserve exerts acute effects on the preovulatory LH surge, ovulation rate, and estrous cyclicity in both young and MA rats. However, decreased follicle number increases FSH levels only in young rats, indicating aging-related alterations in the feedback regulation of FSH.     

Follicle stimulating hormone secretion and compensatory ovarian hypertrophy in prepubertal ewes

A study was conducted to determine the effect of unilateral ovariectomy (ULO) on follicle stimulating hormone (FSH) secretion and compensatory ovarian hypertrophy in prepubertal ewes. Thirty-three ewe lambs were allotted according to age and weight to a control (C) or ULO group. In the C group, a sham ovariectomy was performed on day 0 and both ovaries were removed on day 7. In the ULO group, one ovary was removed on day 0 and the remaining ovary was removed on day 7. Blood samples were collected from the jugular vein via venipuncture at 0, 6, 12 and 24 hours after the time of sham surgery or ULO (day 0). Subsequent samples were collected daily until day 7, and all samples were assayed for FSH and LH. Unilateral ovariectomy increased (P<0.01) ovarian weight and follicular fluid weight; however, lyophilized ovarian weight was similar for both groups. Within the ULO group, removal of the ovary having the largest follicle(s) did not prevent an increase in ovarian weight or follicular fluid weight of the remaining ovary. Unilateral ovariectomy had no effect on the total number of follicles (1 to 6 mm) per ovary; however, the number of large (5 to 6 mm) follicles per ovary was increased (P<0.05) following ULO. By 12 hours after ULO there was a transient increase (P<0.05) in the circulating concentrations of FSH. Circulating concentrations of luteinizing hormone (LH) were either low or undetectable in these prepubertal ewes and no LH response was observed following ULO. These results indicate that compensatory ovarian hypertrophy in ULO prepubertal ewes is accompanied by a transient rise in circulating FSH concentrations.     

Effect of follicular fluid treatment on follicle-stimulating hormone, luteinizing hormone and compensatory ovarian hypertrophy in prepuberal gilts

Prepuberal 130-day-old gilts were treated with 10 ml of charcoal-stripped porcine serum (PS), whole porcine follicular fluid (WpFF) or charcoal-stripped pFF (CpFF) twice daily beginning the day before and continuing 8 days after unilateral ovariectomy (ULO). Follicle-stimulating hormone (FSH) declined for the first 14 h after ULO in WpFF and CpFF gilts and then by 24 h returned to values observed at or before ULO, whereas FSH was increased nearly twofold at 14 h in PS gilts. At 8 days after ULO the remaining ovaries from PS-treated gilts were heavier than ovaries from follicular fluid-treated gilts. In a second experiment, ovariectomized 130-day-old gilts were assigned to either a group infused with PS, a group infused with 5 ml CpFF, or a group infused with 10 ml Cpff at 18 and 2 h before a gonadotropin-releasing hormone (GnRH) challenge. Porcine follicular fluid had no effect on luteinizing hormone (LH) response to GnRH, depressed the FSH response to a 10-micrograms challenge of GnRH, but had no effect on FSH response to a 50-micrograms challenge of GnRH. In a third study, gilts were subjected to sham ovariectomy (Sham) or ULO at 130 days of age. GnRH (10 micrograms) was given on Days 1, 2 or 8 after surgery. The response to GnRH in ULO versus Sham gilts did not differ for FSH or LH on any day.(ABSTRACT TRUNCATED AT 250 WORDS)     

Short- and long-term effects of unilateral ovariectomy in sheep: causative mechanisms

The mechanisms of ovulatory compensation following unilateral ovariectomy (ULO) are still not understood. In the present study, we investigated the short- and long-term effects of ULO in sheep using transrectal ovarian ultrasonography and hormone estimations made during the estrous cycle in which surgery was done, the estrous cycle 2 mo after surgery, and the 17-day period during the subsequent anestrus. The ULOs were done when a follicle in the first follicular wave of the cycle reached a diameter > or =5 mm, leaving at least one corpus luteum and one ovulatory-sized follicle in the remaining ovary. Ovulation rate per ewe was 50% higher in the ULO ewes compared with the control ewes at the end of the cycle during which surgery was performed, but it did not differ between groups at the end of the cycle, 2 mo later. This compensation of ovulation rate in ULO ewes was due to ovulation of follicles from the penultimate follicular wave in addition to those from the final wave of the cycle. Ovulation from multiple follicular waves appeared to be due to a prolongation of the static phase of the largest follicle of the penultimate wave of the cycle. Interestingly, the length of the static phase of waves was prolonged in ULO ewes compared with control ewes in every instance where the length of the static phase could be determined. Changes in follicular dynamics due to ULO were not associated with alterations in FSH and LH secretion. In conclusion, ovulatory compensation in ULO sheep involves ovulation from multiple follicular waves due to the lengthened static phase of ovulatory-sized follicles. These altered antral follicular dynamics do not appear to be FSH or LH dependent. Further studies are required to examine the potential role of the nervous system in the enhancement of the life span of the ovulatory-sized follicles leading to ovulatory compensation by the unpaired ovary in ULO sheep.     

Compensatory responses after unilateral ovariectomy in rabbits

Compensatory ovarian and gonadotropic responses to unilateral ovariectomy (ULO) were examined in the rabbit doe, an induced ovulator. On Days 2, 4, 5, 6, 8, 10, 15 and 20 after ULO, ovaries from 3 hemiovariectomized does and 1 sham-hemiovariectomized doe were examined macro- and microscopically for number, size and signs of atresia of follicles. The number of surface follicles increased initially to 7 or 8 follicles 2 days after ULO, followed by an increase to 10 or more follicles by Day 15 (control ovaries had 5.7 +/- 0.4 follicles). Total numbers of antral follicles and the proportion of follicles which were atretic did not vary relative to day after ULO. However, distributions of antral follicles in classes of 0.2-mm increments were significantly different between sham-ovariectomized and hemiovariectomized does after Day 2 due to shifts of follicles into larger size classes. Peripheral serum concentrations of follicle-stimulating hormone (FSH), but not luteinizing hormone (LH), increased temporarily during the 48 h after ULO. Follicular compensation after ULO in the doe entailed nonlinear increases in numbers of preovulatory follicles, due to increased growth within the antral population of follicles, probably the result of an acute surge of FSH. A period of more than 10 days was necessary to restore the number of preovulatory follicles after ULO. Exogenous human chorionic gonadotropin (hCG) induced ovulation of recruited follicles.     

Evidence that the anterior hypothalamus contributes to the control of tonic secretion of follicle-stimulating hormone in the female rat

A horizontal knife cut was placed between the dorsal anterior hypothalamic area (DAHA) and the medial basal hypothalamus to examine the role of the DAHA in the selective secretion of follicle-stimulating hormone (FSH) following unilateral ovariectomy (ULO) and bilateral ovariectomy of the rat. Complete cuts markedly attenuated the increase in FSH observed 8 h after ULO, whereas incomplete or sham cuts did not. Concentration of luteinizing hormone (LH) did not increase in any group. These cuts also blocked the prolongation of estrous FSH secretion observed in long-term hemicastrated rats, since FSH levels on estrus were significantly lower in rats with complete cuts than in those rats given sham or incomplete cuts. In contrast, neural surgery had no effect on proestrous FSH concentrations. Finally, when FSH levels were monitored 2 days after bilateral ovariectomy, the postcastration rise in FSH was not altered by any neurosurgical procedures. These results support the hypothesis that a neural system originating in, or passing through, the DAHA is necessary for the selective increase in FSH following ULO.     

Gonadotropin-independent mechanisms participate in ovarian responses to realimentation in feed-restricted prepubertal gilts.

Short-term feed restriction in prepubertal gilts suppresses episodic LH secretion in the absence of changes in body weight or composition. To assess non-gonadotropin-mediated effects of realimentation at the ovarian level, 52 gilts were assigned to six treatments after 7 days (Days 1-7) of maintenance feeding (approximately 30% ad libitum). Groups R12 and R9 were maintenance-fed Days 8-12 or Days 8-9, respectively; A12 and A9 were fed to appetite Days 8-12 or Days 8-9, respectively. Groups R9P and A9P were fed as groups R9 and A9 were but received 750 IU eCG at 1500 h on Day 8. Groups R12 and A12 were ovariectomized at 1500 h on Day 12, and all other groups were ovariectomized at 1500 h on Day 9. All gilts received oral progestogen (15 mg allyl trenbolone) from Day 1 to ovariectomy, to antagonize the usual increases in endogenous gonadotropins that follow realimentation. Blood samples were obtained at 10-min intervals during selected windows during the experiment. Ovarian follicles were analyzed for development and steroidogenesis, and plasma samples were analyzed by RIA to determine concentrations of LH, FSH, insulin, and insulin-like growth factor-1 (IGF-1). Allyl trenbolone abolished pulsatile LH secretion, and realimentation did not stimulate LH or FSH secretion, with the exception of FSH secretion on Day 8 in A9 gilts. Postprandial insulin concentrations on Day 9 were greater after feeding to appetite (A9, A9P, and A12) than after feed restriction (R9, R9P, and R12). Pre- and postprandial IGF-1 concentrations were higher in re-fed gilts on Day 9 (A9 and A12) and Day 12 (A12) than in feed-restricted gilts. Follicular diameter, fluid volume, and basal granulosa cell estradiol synthesis per follicle were greater in A12 gilts than in R12 gilts, although there was no difference between A9 and R9 gilts. There was no effect of realimentation on follicular fluid concentrations of estradiol or testosterone, or on androgen-driven granulosa cell estradiol synthesis. Treatment with eCG increased follicular diameter, fluid volume, basal and androgen-driven estradiol synthesis, and fluid estradiol concentrations without interaction with feeding level. In conclusion, in the absence of LH elevations, realimentation over 5 days exerts effects at the ovary, increasing follicular growth and estradiol synthesis. These effects may be mediated by insulin, IGF-1, or unmeasured growth factors and would be expected to synergize with increases in endogenous gonadotropin that follow realimentation.     

Effect of reduced ovarian tissue on cyclicity, basal hormonal levels and follicular development in old rats

Reduction of the number of growing follicles was proposed to contribute to the decline in reproductive performance with aging (Butcher and Page, 1981). To investigate the effects of a reduced number of follicles, rats which maintained regular estrous cycles at greater than 1 yr of age had either unilateral ovariectomy (ULO) or control surgery. Irregular estrous cycles and periods of constant estrus were more frequent during a period of 90 days after ULO than in controls. Follicle-stimulating hormone (FSH) concentration in plasma collected at 0900-1100 h of the metestrus nearest to 20, 50, and 90 days after surgery was increased by ULO; in both treatment groups, FSH increased between 20 and 90 days. Compensation in ovarian weight and number of corpora lutea had occurred by 90 days after ULO. Estradiol, estrone and luteinizing hormone (LH) concentrations did not change with time or treatment. Numbers of small, medium and large antral follicles per ovary at metestrus were increased by ULO, while the number of follicles per rat was decreased. It was concluded that the reduction in ovarian tissue (which decreased the number of growing follicles) resulted in an elevation of basal FSH followed by irregularity in estrous cycles.     

Passive immunization of the pig against gonadotropin releasing hormone during the follicular phase of the estrous cycle

Three experiments were conducted to determine the effects of passively immunizing pigs against gonadotropin releasing hormone (GnRH) during the follicular phase of the estrous cycle. In Experiment 1, sows were given GnRH antibodies at weaning and they lacked estrogen secretion during the five days immediately after weaning and had delayed returns to estrus. In Experiment 2, gilts passively immunized against GnRH on Day 16 or 17 of the estrous cycle (Day 0 = first day of estrus) had lower (P<0.03) concentrations of estradiol-17beta than control gilts, and they did not exhibited estrus at the expected time (Days 18 to 22). When observed three weeks after passive immunization, control gilts had corpora lutea present on their ovaries, whereas GnRH-immunized gilts had follicles and no corpora lutea. The amount of GnRH antiserum given did not alter (P<0.05) serum concentrations of LH or pulsatile release of LH in sows and gilts. In Experiment 3, prepuberal gilts were given 1,000 IU PMSG at 0 h and GnRH antiserum at 72 and 120 h. This treatment lowered the preovulatory surge of LH and FSH, but it did not alter serum estradiol-17beta concentrations, the proportion of pigs exhibiting estrus, or the ovulation rate. These results indicate that passive immunization of pigs against GnRH before initiation of or during the early part of the follicular phase of the estrous cycle retards follicular development, whereas administration of GnRH antibodies during the latter stages of follicular development does not have an affect. Since the concentration of antibodies was not high enough to alter basal or pulsatile LH secretion, the mechanism of action of the GnRH antiserum may involve a direct ovarian action.     

Time-dependent changes in gonadotropin synthesis following gonadectomy in the frog, Rana pipiens

Anterior pituitary glands from frogs gonadectomized (gonadx) for various periods (0-90 days) were labeled in vitro with 35S-methionine. Shortly (7-10 days) after gonadx, plasma levels and the in vitro basal pituitary secretion of LH and FSH are elevated compared to values in sham-operated frogs. However, LH and FSH become dissociated in long-term (over 40 days) gonadx frogs; FSH remains elevated while LH returns to sham levels. Gth (gonadotropin: LH and FSH) synthesis shows a similar pattern. Gth synthesis becomes elevated after gonadx, but returns to sham levels after 80 days. In short-term (15 days) gonadx females, LH and FSH each comprise approximately the same percentage of counts immunoprecipitated. In contrast, in long-term (90 days) gonadx females, nearly 100% of Gth synthesis can be accounted for solely by FSH; LH synthesis is barely or not detectable. Although the elevated in vitro secretion rate of LH and FSH following gonadx diminishes within 24 h in culture, Gth synthesis remains elevated. This study demonstrates that although the pattern of Gth secretion and synthesis generally parallel each other following gonadx, these two cellular processes can be dissociated from one another. Furthermore, it appears that in frogs, not only the secretion, but also the synthesis, of LH and FSH may be under independent regulation.     

Inhibin-like activity in ovarian venous serum after unilateral ovariectomy in prepubertal gilts

To examine a role for inhibin in compensatory ovarian hypertrophy after unilateral ovariectomy (ULO) of prepubertal gilts, changes in inhibin activity in ovarian venous blood were estimated by bioassay. Three groups of 130-day-old gilts were unilaterally ovariectomized after collecting blood from an ipsilateral ovarian vein (Day O); blood samples were obtained from the remaining ovary on Day 2, 4, or 8. Coetaneous gilts underwent sham ovariectomy on Day 0, and venous blood was collected from both ovaries on Day 2, 4, or 8. An assay for inhibin activity, which measured inhibition of secretion of follicle-stimulating hormone (rFSH) by rat pituitary cells in culture, was validated for serum samples. Presumptive inhibin activity was always greater in ovarian venous serum than in peripheral serum samples. In the ULO groups, inhibin activity (in terms of a house reference preparation) in ovarian venous serum was 55 +/- 13 micrograms/ml (means +/- SE, n = 13) on Day 0, 251 +/- 79 (n = 5) on Day 2, 275 +/- 111 (n = 4) on Day 4, and 68 +/- 14 micrograms/ml (n = 4) on Day 8. The five-fold increases on Days 2 and 4 were significant (p less than 0.05). In contrast, no significant differences in inhibin activity were detected between ovarian venous serum (within gilts) or between Days 2, 4, and 8: 82 +/- 29, 73 +/- 30, and 99 +/- 48 micrograms/ml (n=4/day) in control groups. These results demonstrate that, in prepubertal gilts, the remaining ovary's response to ULO includes a major increase in release of inhibin-like activity.     

Time of ovarian follicle selection during the porcine estrous cycle

Two experiments were conducted to: 1) determine the time during the procine estrous cycle when compensation in ovulation rate after unilateral ovariectomy (ULO) ceases to be complete, 2) compare the follicle selection process in gilts selected for high ovulation rate with unselected control gilts and 3) determine the number of follicles on the right ovary at various stages of the estrous cycle. Experiment I included 25 crossbred gilts, while Experiment II included 17 gilts selected for high ovulation rate and 16 unselected control gilts. The right ovary was removed via a mid-ventral laparotomy on either day 13, 15, 17 or 19 of the cycle. In Experiment I, compensation in ovulation rate ceased between days 13 and 15; whereas, in Experiment II, cessation occurred between days 15 and 17. Selected and control gilts responded alike to ULO, indicating similarity in the follicle selection process. Follicle numbers in the right ovary showed a general decline, especially between days 17 and 19, indicating that atresia was occurring during the follicular phase. The results indicate that the selection of ovarian follicles for ovulation at the ensuing estrus occurs before day 17 of the porcine estrous cyle.     

The temporal relationship between patterns of LH and FSH secretion, and development of ovulatory-sized follicles during the mid- to late-luteal phase of sheep

The aim of the present study was to investigate the temporal relationship between the secretory pattern of serum LH and FSH concentrations and waves of ovarian antral follicles during the luteal phase of the estrous cycle in sheep. The growth pattern of ovarian antral follicles and CL were monitored by transrectal ultrasonography and gonadotropin concentrations were measured in blood samples collected every 12 min for 6 h/d from 7 to 14 d after ovulation. There were two follicular waves (penultimate and final waves of the cycle) emerging and growing during the period of intensive blood sampling. Mean and basal LH concentrations and LH pulse frequency increased (P < 0.001) with decreasing progesterone concentration at the end of the cycle. Mean and basal FSH concentrations reached a peak (P < 0.01) on the day of follicular wave emergence before declining to a nadir by 2 d after emergence. None of the parameters of pulsatile LH secretion varied significantly with either the emergence of the final follicular wave or with the end of the growth phase of the largest follicle of the penultimate wave of the cycle. However, mean and basal LH concentrations did increase (P < 0.05) after the end of the growth phase of the largest follicle of the final follicular wave of the cycle. Furthermore, the end of the growth phase of the largest follicle of the final wave coincided with functional luteolysis. In summary, there was no abrupt or short-term change in pulsatile LH secretion in association with the emergence or growth of the largest follicle of a wave. We concluded that the emergence and growth of ovarian antral follicles in follicular waves do not require changes in LH secretion, but may involve changes in sensitivity of ovarian follicles to serum LH concentrations.     

Elevated inhibin concentration in the follicular fluid of dairy cows with chronic cystic ovarian disease

This study compared serum and follicular fluid inhibin and gonadotropin profiles between chronic cystic ovarian diseased (CCOD) and normal cyclic dairy cows. Blood samples and follicular fluid were collected from CCOD cows (n=15) and cyclic cows in the follicular phase of the estrous cycle (control, n=6) and analyzed for inhibin, follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations. There was a significant increase in inhibin and a decrease in FSH and LH concentrations in the follicular fluid of CCOD cows compared with those of cyclic cows (P < 0.05). Mean serum inhibin, FSH and LH concentrations between CCOD and cyclic cows were not differnt (P > 0.05), however, there was a tendency for serum inhibin to be higher and FSH to be lower in CCOD cows compared to cyclic animals (P < 0.1). The FSH pulse frequency also was lower in CCOD cows than in cyclic cows (P < 0.05). These data suggest that increased production of inhibin from cystic follicles of CCOD cows alters pituitary FSH secretion and subsequently reduces the concentration of FSH in follicular fluid. As a result, decreased FSH stimulation at the ovarian level could ultimately lead to the reduction in follicular LH and FSH receptor concentrations, resulting in abnormal follicular steroidogenesis in CCOD dairy cows.     

Unilateral ovariectomy increases egg size and reduces follicular atresia in the semelparous coho salmon, Oncorhynchus kisutch

Unilateral ovariectomy (ULO, removal of one ovary) is a powerful technique for studying aspects of reproductive physiology, including follicular recruitment and growth. To examine effects of ULO for the first time in a semelparous species, coho salmon (Oncorhynchus kisutch) were unilaterally ovariectomized during mid-vitellogenesis approximately 3 months before spawning. At termination of the study (79 days post-surgery), single ovaries of ULO fish were gravimetrically equivalent to paired ovaries of sham surgery, control fish. There was no evidence of recruitment of new vitellogenic follicles. Instead, the dramatic increase in ovary mass was attributable to hypertrophy of existing vitellogenic follicles (33% increase in volume) and increased fecundity achieved through a greater than two-fold reduction in follicular atresia. The composition of whole ovaries on a dry weight basis from ULO fish was greater in protein, but lower in lipid than that of control fish. Expressing the data on a per follicle basis, however, showed that follicles of ULO fish contained more protein, ash, water, and lipid. The results indicate that ULO of coho salmon induces compensatory hypertrophy of existing vitellogenic follicles, while maximizing fecundity through reduction of atresia. Thus, 3 months before spawning, coho salmon exhibit the ability to adjust final egg size and number when faced with significant depletion of ovarian follicles. This in vivo system provides a platform for further study of physiological mechanisms regulating follicular growth and atresia, and the trade-off between egg size and egg number. J. Exp. Zool. 309A:468-476, 2008. (c) 2008 Wiley-Liss, Inc.     

Effect of alterations in pulsatile luteinizing hormone release on ovarian follicular atresia and steroid secretion on diestrus 1 in the rat estrous cycle

This study examined the importance of pulsatile luteinizing hormone (LH) release on diestrus 1 (D1; metestrus) in the rat estrous cycle to ovarian follicular development and estradiol (E2) secretion. Single injections of a luteinizing hormone-releasing hormone (LHRH) antagonist given at -7.5 h prior to the onset of a 3-h blood sampling period on D1 reduced mean blood LH levels by decreasing LH pulse amplitude, while frequency was not altered. Sequential injections at -7.5 and -3.5 h completely eliminated pulsatile LH secretion. Neither treatment altered the total number of follicles/ovary greater than 150 mu in diameter, the number of follicles in any size group between 150 and 551 mu, or plasma E2, progesterone, or follicle-stimulating hormone (FSH) levels. However, both treatments with LHRH antagonist significantly increased the percentage of atretic follicles in the ovary. These data indicate that: 1) pulsatile LH release is an important factor in determining the rate at which follicles undergo atresia on D1; 2) reductions in LH pulse amplitude alone are sufficient to increase the rate of follicular atresia on D1; 3) an absence of pulsatile LH release for a period of up to 10 h on D1 is not sufficient to produce a decline in ovarian E2 secretion, most likely because the atretic process was in its early stages and had not yet affected a sufficient number of E2-secreting granulosa cells to reduce the follicle's capacity to secrete E2; and 4) suppression or elimination of pulsatile LH release on D1 is not associated with diminished FSH secretion.     

Effects of exogenous FSH on follicular recruitment in a viviparous lizard Niveoscincus metallicus (Scincidae)

In the viviparous skink Niveoscincus metallicus clutch size appears to be determined before vitellogenesis, and is not altered later by follicular atresia or embryonic loss. This suggests that the number of follicles recruited is determined by the endocrine environment early in the vitellogenic period. Through a series of experiments in which we manipulated gonadotropin concentrations by administering exogenous FSH, we aimed to investigate this hypothesis. Pre-vitellogenic females showed no response to exogenous ovine FSH. In early vitellogenic females, FSH induced follicular recruitment: follicles were enlarged and clutch size increased by recruitment of a second cohort of follicles; some females also ovulated. Females treated with FSH in mid-vitellogenesis had elevated mean plasma estradiol concentrations compared to controls; no follicular recruitment was observed, but most of these animals ovulated. Females treated with a range of doses of FSH in late vitellogenesis ovulated at least one month before natural ovulation, again without recruitment of extra follicles. It appears therefore that in Niveoscincus metallicus exogenous FSH can induce recruitment of additional follicles only if administered during early vitellogenesis. We conclude that in this species clutch size is determined by proximate environmental factors influencing gonadotropin levels early in follicular recruitment, and cannot be increased even if conditions become more favourable once vitellogenesis is established.     

Ovarian follicular dynamics in the llama

Ovarian follicular dynamics were determined in adult llamas by ultrasonography and palpation per rectum and hormone analysis (estradiol-17 beta and estrogen conjugates) of plasma and urine. The relationship of gonadotropin secretion to follicular development was determined by the analysis of plasma FSH and LH concentrations. Progesterone analysis of plasma was used to verify or deny the presence of CL. Final follicular development (from 3 mm) averaged 4.8 days, while the duration of the mature follicle (8-12 mm) averaged 5.0 days; regression of the follicle occurred over about 4 days. The development of a subsequent dominant follicle usually began within 2-3 days after onset of regression of the dominant follicle. While several follicles were present at the time of the demise of the dominant follicle, only one follicle continued to develop. The interval between ovarian follicle waves averaged 11.1 days. Dominant follicle activity alternated between ovaries in 81% of the cycles. The occurrence of dominant follicles was evenly distributed between ovaries. While plasma estradiol and estrogen conjugate concentrations were positively associated (p less than 0.05) with follicular activity, urinary estrogen conjugate concentrations best reflected ovarian follicular dynamics (p less than 0.001). Daily FSH concentrations in plasma were not correlated with follicular activity. LH concentrations in plasma were low in all animals throughout the study, indicating estrogen from developing ovarian follicles does not induce the release of LH. Progesterone values were low during the study, indicating that the llama does not spontaneously ovulate, at least under the conditions of this study. In summary, llamas have overlapping ovarian follicle waves that occur at about 11-day intervals.(ABSTRACT TRUNCATED AT 250 WORDS)     

An ultrasound-aided study of temporal relationships between the patterns of LH/FSH secretion, development of ovulatory-sized antral follicles and formation of corpora lutea in ewes

To characterize the pulsatile secretion of LH and FSH and their relationships with various stages of follicular wave development (follicles growing from 3 to > or =5 mm) and formation of corpora lutea (CL), 6 Western white-faced ewes underwent ovarian ultrasonography and intensive blood sampling (every 12 min for 6 h) each day, for 10 and 8 consecutive days, commencing 1 and 2 d after estrus, respectively. Basal serum concentrations of LH and LH pulse frequency declined, whereas LH pulse duration and FSH pulse frequency increased by Day 7 after ovulation (P<0.05). LH pulse amplitude increased (P<0.05) at the end of the growth phase of the largest ovarian follicles in the first follicular wave of the cycle. The amplitude and duration of LH pulses rose (P<0.05) 1 d after CL detection. Mean and basal serum FSH concentrations increased (P<0.05) on the day of emergence of the second follicular wave, and also at the beginning of the static phase of the largest ovarian follicles in the first follicular wave of the cycle. FSH pulse frequency increased (P<0.05) during the growth phase of emergent follicles in the second follicle wave. The detection of CL was associated with a transient decrease in mean and basal serum concentrations of FSH (P<0.05), and it was followed by a transient decline in FSH pulse frequency (P<0.05). These results indicate that LH secretion during the luteal phase of the sheep estrous cycle reflects primarily the stage of development of the CL, and only a rise in LH pulse amplitude may be linked to the end of the growth phase of the largest follicles of waves. Increases in mean and basal serum concentrations of FSH are tightly coupled with the days of follicular wave emergence, and they also coincide with the end of the growth phase of the largest follicles in a previous wave, but FSH pulse frequency increases during the follicle growth phase, especially at mid-cycle.