Ovarian follicular development in Holstein cows following synchronisation of oestrus with oestradiol benzoate and an intravaginal progesterone releasing insert for 5-9 days and duration of the oestrous cycle and concentrations of progesterone following ovulation

The aim of this study was to determine if the duration of treatment with an intravaginal progesterone releasing insert (IVP(4)) after treatment with oestradiol benzoate (ODB) at the time of insertion and 24 h after removal would affect selected variables including: size of ovarian follicles at the time of removal of inserts, diameter of ovulatory follicles, plasma concentrations of progesterone following ovulation, and duration of the following oestrous cycle. Characteristics of oestrus at a synchronised and spontaneous oestrus were also monitored. Non-lactating Holstein cows were synchronised with an IVP(4) for 5 (n = 10), 7 (n = 10), 8 (n = 9) or 9 (n = 9) days together with injections of ODB at device insertion (2 mg) and 24 h after removal (1 mg). Ultrasonography showed no significant effect of treatment on the day of emergence of preovulatory follicles relative to the day of removal of inserts (overall mean = -4.22 +/- 0.58; P = 0.15) for cows that ovulated within 120 h insert removal (n = 36). Treatment with ODB and an IVP(4) for 5 days reduced the diameter of preovulatory follicles at the time of removal of inserts and for the following 2 days compared to cows treated for 7-9 days (mean difference 2.56 +/- 1.15 mm; P = 0.033) but did not reduce the diameter of the ovulatory follicle (P = 0.21). Day of emergence relative to removal of inserts was associated with the diameter of the ovulatory follicle (R2 = 0.69; P < 0.001). Concentrations of progesterone and the diameter of the corpus luteum following ovulation were not affected by treatment (P > 0.20), but were affected by the diameter of the ovulatory follicle (P < 0.01). Diameter of the ovulatory follicle did not affect interoestrous and interovulatory intervals (P > 0.40). We conclude that treatment with an IVP(4) for 5 compared to 7-9 days with ODB administered at device insertion, and 24 h after removal reduced the diameter of preovulatory follicles at the time of removal of the insert but did not reduce the diameter of the ovulatory follicle or concentrations of progesterone in plasma. Emergence of preovulatory follicles closer to the time of removal of inserts reduced the diameter of the ovulatory follicle when oestrus was induced with ODB. Ovulation of smaller follicles reduced concentrations of progesterone in plasma following ovulation but did not affect oestrous cycle duration.     

Gene expression of matrix metalloproteinases and LH receptors in mare follicular development

The period from the emergence of a dominant follicle until its formation requires tissue remodeling. Enzymes promoting collagen lysis, such as matrix metalloproteinases (MMPs), are fundamental for the process of extracellular matrix remodeling, which allows changes in ovarian tissue architecture during follicular growth. It has been suggested that the production of these enzymes may be affected by the rise in circulating concentrations of LH, which acts on the ovarian surface epithelium (OSE). The aim of this study was to determine the expression of MMP-1, MMP-2, and LH receptor (LHR) in the ovulation fossa and in the central portion of the equine ovary during follicular deviation and dominance. Ovaries of 12 cyclic mares were selected and subsequently divided into two groups: development (DEV) group and dominant (DOM) group. The DEV group consisted of ovaries from six animals whose follicles were less than 28 mm in diameter (follicular deviation), and the DOM group consisted of ovaries from six animals whose follicles measured 28 mm or more in diameter (dominant follicles). The latter group was divided into two subgroups: the group of ovaries with a dominant follicle (DOM-D) and the group of contralateral ovaries (DOM-C). Our results showed that mRNA for MMP-1, MMP-2, and LHR was present in the equine ovary during follicle development, in the ovulation fossa, and in the central portion of the ovary. MMP-1 and LHR gene expression was greater (P < 0.05) for the DOM-D group compared with the DOM-C group. In the DOM-D group, MMP-1, MMP-2, and LHR gene expression was greater (P < 0.05) in the ovarian stroma compared with the ovulation fossa. Using immunohistochemistry, OSE from the DOM group showed increased expression compared with the DEV group (P < 0.05). In conclusion, we demonstrated that MMP-1 and MMP-2 might be fundamental for events related to tissue remodeling, which occurs during follicular development until the formation of the dominant follicle. We also demonstrated the relationship between the gene expression of MMPs and the gene and protein expression of LHR, suggesting that LHR in the OSE might be an important factor to initiate the signaling cascade that culminates with the production of MMPs.     

Relationships among concentrations of steroids, inhibin, insulin-like growth factor-1 (IGF-1), and IGF-binding proteins during follicular development in weaned sows.

The experimental objective was to determine how insulin-like growth factor binding proteins (IGFBP), as examined by Western ligand blot procedures, related to porcine follicular steroidogenesis. Weaned sows were ovariectomized at various times after litter removal in three experiments. In experiments 1 and 2, sows were ovariectomized at 48-120 h after weaning. In experiment 1, pools of all small (1-3 mm), medium (greater than 3-6 mm), or large (greater than 6-9 mm) follicles were made for each sow; in experiment 2, fluid was collected individually from the 10 largest follicles per ovary. A third experiment was conducted to examine changes after an ovulatory dose of hCG, but prior to ovulation. In this experiment, sows were treated with eCG at weaning, given hCG 72 h later, and ovariectomized 0-36 h after the ovulatory dose of hCG. Follicular fluid was collected from the 10 largest follicles per sow. In experiments 1 and 2, IGFBP-3 in follicular fluid remained constant over follicle diameters and stage sof development, and IGFBP-2 decreased with advancing follicular development as concentrations of estradiol, androstenedione, and progesterone increased. In experiment 1, after the presumed LH surge when the concentration of all steroids was low, there was a sharp increase in band intensity for IGFBP-2. Similarly, estradiol and androstenedione were low in preovulatory sows in experiment 2, though progesterone increased and IGFBP-2 decreased with follicle diameter. In experiment 3, progesterone remained elevated from 0 to 36 h after hCG, even though IGFBP-2 did not increase until after 24 h post-hCG.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ovarian follicular populations and preovulatory enlargement in Booroola and control Merino ewes

To investigate the factors contributing to the different ovulation rates observed in two strains of sheep (Booroola 5.2, Merino 1.2), in-vivo monitoring of follicular kinetics followed by histological examination of both ovaries was performed during the late luteal and follicular phases. Ewes of both strains were either ovariectomized at Day 13, or had the 3 largest follicles of each ovary ink-labelled at Day 13 and were ovariectomized at Day 15, or had the 3 largest follicles of each ovary ink-labelled at Days 13 and 15 and were ovariectomized 16 h after the beginning of oestrus (N = 6 per time per strain). In another experiment, the age effects on the follicular populations of these two strains were also studied. There were 2-4 times more primordial follicles and 1.5-2 times more preantral follicles in the ovaries of Booroola than in control Merino ewes, although the number of antral follicles was the same. The percentage of normal follicles in this population was higher in Merino than Booroola ovaries. In Booroola ewes, there was no correlation between the number of antral follicles per ovary and the ovulation rate at the previous cycle (r = 0.22). This suggests that follicle numbers do not play a key role in the high ovulation rate of the Booroola strain. The number of follicles initiating growth from the primordial pool, the number of growing follicles disappearing at the preantral stage, the pattern of antrum development, granulosa cell multiplication and appearance of atresia differed between strains. The reasons for the high ovulation rate of the Booroola strain became clear when preovulatory enlargement was followed by ink labelling. An extended period of time during which recruitment of ovulatory follicles takes place, together with a low incidence of selection and the ability of the follicles to wait for ovulation are the features involved in this high ovulation rate.     

Elevated peripheral concentrations of LH block ovulation and increase thecal and serum progesterone in the hamster

Insertion of osmotic minipumps containing 1 mg ovine LH on Day 1 (oestrus) elevated circulating serum concentrations of LH, progesterone and androstenedione when compared with values at pro-oestrus. Ovulation was blocked for at least 2 days at which time there were twice the normal numbers of preovulatory follicles. Follicular and thecal progesterone production in vitro was elevated when compared with that in pro-oestrous controls. Follicular and thecal androstenedione production in vitro was lower than in controls even though serum concentrations of androstenedione were elevated; the higher androstenedione values may be due to the increase in number of preovulatory follicles when compared with pro-oestrous controls. Follicles from LH-treated hamsters aromatized androstenedione to oestradiol and follicular production of oestradiol was similar to that in pro-oestrous follicles despite low follicular androstenedione production in the LH-treated group. Treatment with 20 i.u. hCG on Days 4 or 6 after insertion of an LH osmotic minipump on Day 1 induced ovulation of approximately 30 ova, indicating that the blockade of ovulation was not due to atresia of the preovulatory follicles. Serum progesterone concentrations on Days 2, 4 and 6 in LH-treated hamsters were greater than 17 nmol/l, suggesting that the blockade of ovulation might have been due to prevention of the LH surge by high serum progesterone concentrations.     

Ultrasonic evaluation of the preovulatory follicle in the mare

Ultrasonically visible characteristics of preovulatory follicles in mares which single ovulated were studied daily for 79 preovulatory periods in 40 mares. The preovulatory follicle became the largest follicle in the ovary from which ovulation later occurred six or more days before ovulation in 65 of 79 (82%) preovulatory periods; the mean was day -7 (range, day -14 to day -4). The increase in mean diameter of the preovulatory follicle was linear (R(2)=99.5%) over day -7 (29.4 +/- 0.8 mm) to day -1 (45.2 +/- 0.5 mm; growth rate, 2.7 mm/day). Follicles which double-ovulated were smaller (P<0.05) on day -1 (36 +/- 1.6 mm; n=12 follicles). Preovulatory follicles exhibited a pronounced change in shape from a spherical to a conical or pear-shaped structure in 84% of the preovulatory periods. Remaining follicles retained a spherical shape. Scores representing thickness of the follicular wall increased (P<0.05) as the interval to ovulation decreased. There was no significant difference among days in mean gray-scale value of the follicular wall or in echogenicity of the follicular fluid. Although diameter and shape of the follicle and thickness of the follicular wall changed during the preovulatory period, no reliable ultrasonically visible predictor of impending ovulation was found.     

Expression of basigin, an inducer of matrix metalloproteinases, in the rat ovary

The extensive tissue remodeling that occurs during follicular development, ovulatory rupture, and the formation and regression of the corpus luteum (CL) requires local degradation of the extracellular environment by matrix metalloproteinases (MMPs). This report characterizes the expression pattern of basigin (Bsg), a putative regulator of MMP induction, in the rat ovary. An induced superovulation model (eCG/hCG) was used in immature rats to evaluate Bsg expression profiles in ovaries collected during the follicular phase, the preovulatory period, and the luteal lifespan. Levels of Bsg mRNA were unchanged through follicular growth (0-48 h post-eCG) and increased during postovulatory luteinization (24 and 48 h post-hCG; P < 0.01). Bsg expression persisted into pseudopregnancy (4-8 days post-hCG) and after functional luteal regression (12 days post-hCG). The profile of Bsg expression during regression of the CL was examined using a model of induced luteolysis. Both functional and structural regression was associated with a decline in Bsg expression levels. Bsg mRNA and protein localized to the theca of preovulatory follicles (12 h post-hCG) and formative and functional CL (24 h-8 days post-hCG). Bsg expression profiles in the induced ovulation and CL regression models were similar to observations made in naturally cycling mature rats. In the cycling ovary, Bsg signaling localized to newly forming CL, the theca of preovulatory follicles, and appeared to be lower in CL from previous estrous cycles. A putative regulatory mechanism of Bsg expression was identified using an in vitro model; treatment of cultured granulosa cells with hCG significantly augmented Bsg mRNA expression levels. The processes of ovulation and luteogenesis may be facilitated by Bsg expression and its induction or regulation of the MMPs.     

Effects of bromocriptine administration during the follicular phase of the oestrous cycle on prolactin and gonadotrophin secretion and follicular dynamics in merino monovular ewes

Two experiments using Spanish Merino ewes were conducted to investigate whether the secretion of prolactin during the follicular phase of the sheep oestrous cycle was involved in the patterns of growth and regression of follicle populations. In both experiments, oestrus was synchronized with two cloprostenol injections which were administered 10 days apart. Concurrent with the second injection (time 0), ewes (n = 6 per group) received one of the following treatments every 12 h from time 0 to 72 h: group 1: vehicle injection (control); group 2: 0.6 mg bromocriptine (0.03 mg per kg per day); and group 3: 1.2 mg bromocriptine (0.06 mg per kg per day). In Expt 1, blood samples were collected every 3 h from 0 to 72 h, and also every 20 min from 38 to 54 h to measure prolactin, LH and FSH concentrations. In Expt 2, transrectal ultrasonography was carried out every 12 h from time 0 until oestrus, and blood samples were collected every 4 h to measure prolactin, LH and FSH concentrations. Ovulation rates were determined by laparoscopy on day 4 after oestrus. Bromocriptine markedly decreased prolactin secretion, but did not affect FSH concentrations, the mean time of the LH preovulatory surge or LH concentrations in the preovulatory surge. Both doses of bromocriptine caused a similar decrease in LH pulse frequency before the preovulatory surge. The highest bromocriptine dose led to a reduction (P < 0.01) in the number of 2-3 mm follicles detected in the ovaries at each time point. However, bromocriptine did not modify the total number or the number of newly detected 4-5 mm follicles at each time point, the number of follicles > 5 mm or the ovulation rate. In conclusion, the effects of bromocriptine on gonadotrophin and prolactin secretion and on the follicular dynamics during the follicular phase of the sheep oestrous cycle indicate that prolactin may influence the viability of gonadotrophin-responsive follicles shortly after luteolysis.     

Complex interrelationships among CL,preovulatory follicle,number of follicular waves,and right or left ovaries in heifers

The diameter of the dominant follicle (DF) of wave 1 was studied on Days 9 to 17 (Day 0 = ovulation) in a survey of the ipsilateral and contralateral relationships between the location of the DF and CL, and number of follicular waves per interovulatory interval (IOI). For contralateral relationships, regardless of number of waves the diameter of the DF of wave 1 decreased (P < 0.03) between Days 11 and 13 when referenced to the follicle–CL relationship of wave 1 and decreased (P < 0.008) between Days 9 and 11 when referenced to the preovulatory follicle (PF)–CL relationship. For wave 2 in two-wave IOIs, the CL ovary of ipsilateral relationships had more (P < 0.05) follicles that reached at least 6 mm than the non-CL ovary. In three-wave IOIs, frequency of IOIs with the DF in the CL ovary was greater (P < 0.02) for wave 2 than for wave 3. In wave 3, the preovulatory and the largest subordinate follicles were located more frequently (P < 0.005) in the contralateral ovary. Ovulation in two-wave IOIs occurred more frequently (P < 0.0009) from the right ovary. In three-wave IOIs with a contralateral relationship ovulation occurred more frequently (P < 0.003) from the left ovary; a negative intraovarian effect of the CL on location of the PF may account for more ovulations from the left ovary and a reported greater frequency of the contralateral relationship. The hypothesis was supported that the ipsilateral versus contralateral relationship between the PF and CL is affected by the DF–CL relationship during the previous follicular waves and by the number and identity of waves per IOI.     

A model for follicular selection and ovulation: lessons from superovulation

A model for selection of the preovulatory follicle during the normal ovarian cycle is proposed. During menstruation the concentration of FSH rises to a level high enough to "activate" a single small antral follicle (2-4 mm dia.) so that it can produce large amounts of oestradiol. As the follicle develops, the concentration of FSH is suppressed below this threshold level by the secretion of oestradiol and inhibin. The dominant follicle becomes increasingly sensitive to FSH so that it continues to develop in an environment which inhibits development of other follicles. Multiple ovulation can be achieved by extending the period during which the level of FSH remains above this threshold level (e.g. during treatment with clomiphene or gonadotrophins). Although multiple ovulation occurs when the gate is widened in this way, the follicles are never completely synchronous as they continue to grow at approximately the same rate. Current evidence suggests that ovulation occurs at random between the two ovaries in successive cycles and that the corpus luteum exerts an inhibitory effect on folliculogenesis by suppressing the secretion of FSH and LH. These observations are compatible with the hypothesis that while small antral follicles are recruited continuously, at all stages of reproductive life, selection of the dominant follicle requires the unique gonadotrophic environment which is only present in the early follicular phase. The follicle of the month is, therefore, selected by chance because it is at the right place at the right time.     

Peripheral plasma concentrations of oestradiol, progesterone, cortisol, LH and prolactin during the oestrous cycle in the cow, with emphasis on the peri-oestrous period

Interrelationships of circulating hormone levels and their implications for follicular development were studied throughout the oestrous cycle with emphasis on the perioestrous period in heifers and cows. The oestradiol level showed a major peak (45 pmol/1) before and coinciding with oestrus, and a second peak (27 pmol/1) around day 5–6 (day 0: day of first standing oestrus); it was low during the luteal phase of the cycle when progesterone was higher than 14 nmol/1 from day −12 to day −2. Large antral follicles, which had developed during the luteal phase, did not secrete significant amounts of oestradiol, degenerated after luteolysis, and were replaced by a newly developing follicle which became preovulatory. Parallel with this development the oestradiol level increased from the onset of luteolysis to reach a plateau about 26 h before the onset of oestrus. The interval between the onset of luteolysis and the onset of oestrus was 58 h; luteolysis proceeded at a slower rate in heifers than in cows. At 4.6 h after the onset of oestrus the maximum of the LH surge was recorded; the LH surge appeared to be postponed in the period October–December in comparison to the period August–September. The maximum of the LH surge was higher in heifers (45 μg/l) than in cows (30 μg/l), but its duration was similar (8.0 h). The oestradiol level decreased significantly from 6 h after the maximum of the LH surge, and standing oestrus (duration 18 h) was terminated almost at the same time as the return to basal values of oestradiol. Cortisol and prolactin levels did not show a peak during the peri-oestrus period. Cortisol fluctuated irrespective of the stage of the oestrus cycle and prolactin was significantly higher during the luteal phase.

The results of this study indicate that development of the preovulatory follicle starts in the cow at the onset of luteolysis, about 2.5 days before the preovulatory LH surge, and that oestradiol secretion by this follicle is possibly inhibited by the LH surge.     

Effects of an LHRH antagonist on gonadotrophin and oestradiol secretion, follicular development, oestrus and ovulation in Holstein heifers

Mature cyclic Holstein heifers were given a luteolytic dose of cloprostenol followed by two i.v. injections, 12 h apart, of various doses of [Ac-D-Nal1, D-p-Cl-Phe2, D-Trp3, D-Arg6, D-Ala10]-LHRH, beginning either at the time of first observation of behavioural oestrus, or 48 h after the cloprostenol injection. When treatment began at the first observation of oestrus, the time of ovulation, as determined by ultrasonic echography, was significantly delayed by total doses of 0.8 mg or more of the antagonist. When given at 48 and 60 h after cloprostenol injection, a total dose of 1.5 mg of the antagonist significantly delayed the growth of the ovulating follicle, the onset of oestrus, the preovulatory surges of oestradiol, LH and FSH, and ovulation. It is concluded that the LHRH antagonist can effectively suppress endogenous LH secretion and may therefore be useful in the study of follicular development, ovulation, and other events in the oestrous cycle of the cow.     

Ovarian activity in Booroola X Romney ewes which have a major gene influencing their ovulation rate

A marked difference in both the function and composition of individual ovarian follicles was noted in Booroola X Romney ewes (6-7 years of age) which had previously been segregated on at least one ovulation rate record of 3-4 (F + ewes, N = 21) or less than 3 (++ ewes, N = 21). Follicles in F + ewes produced oestradiol and reached maturity at a smaller diameter than in ++ ewes. In F+ ewes (N = 3), the presumptive preovulatory follicles were 4.4 +/- 0.5 (s.e.m.) mm in diameter and contained 2.1 +/- 0.3 X 10(6) (s.e.m.) granulosa cells, whereas in ++ ewes (N = 3), such follicles were 7.3 +/- 0.3 mm in diameter and contained 6.5 +/- 0.8 X 10(6) cells. During a prostaglandin (PG)-induced follicular phase, the secretion rate of oestradiol from ovaries containing 3 presumptive preovulatory follicles in F + ewes was similar to that from ovaries with only one such follicle in ++ ewes. We suggest that the putative 'gene effect' in F + ewes is manifested during early follicular development and that it may be mediated via an enhanced sensitivity of granulosa cells to pituitary hormones. As a consequence, the development of 3 preovulatory follicles in F + ewes may be necessary to provide a cell mass capable of producing the same quantity of oestradiol as that from one preovulatory follicle in ++ ewes.     

Concentrations of inhibin,progesterone and oestradiol in fluid from dominant and subordinate follicles from mares during spring transition and the breeding season

Dominant and subordinate follicles were collected from mares on the day after the dominant follicle reached 30 mm in diameter, to investigate regulation of folliculogenesis during spring transition and the breeding season. Concentrations of oestradiol-17beta, progesterone and inhibin A, but not inhibin isoforms with pro- and alpha C-immunoreactivity, were significantly higher in preovulatory follicles than in dominant anovulatory transitional follicles. Steroidogenic activity was regained gradually in the dominant follicles of successive anovulatory waves through spring transition. The dominant follicles, during both spring transition and cyclicity, contained higher concentrations of oestradiol, progesterone and inhibin A, but not inhibin pro- and alpha C-isoforms, than subordinate follicles. The results indicate that high follicular levels of oestradiol, progesterone and inhibin A are associated with continued follicle growth and ovulation. The low concentrations of oestradiol and progesterone in transitional follicles indicate that the deficiency in steroidogenesis exists early in the steroidogenic pathway. The similarity in patterns of follicular hormones in spring transition and during cyclicity strongly suggests that the mechanism of dominance is the same in both types of follicle.     

Time of ovarian follicular recruitment in cyclic pony mares

An experiment was carried out on pony mares to establish the time of the oestrous cycle at which ovarian follicles are recruited for ovulation. In one group (n=7), the cycle was interrupted at the preovulatory stage by removing the preovulatory follicle; in another group (n=13) the cycle was interrupted at day 6 of the luteal phase by inducing luteolysis with a prostaglandin injection (PG). In a subgroup (n=7) of those given PG, the ovary not bearing the corpus luteum was removed at the time of injection. A further group (n=6) served as surgical controls. The interval to the next ovulation and blood concentrations of FSH were observed. Anaesthesia alone induced in preovulatory mares was followed by normal ovulation 2.5+/-1 days later. Removal of the preovulatory follicle delayed the next ovulation (14.6+/-2.1 days; P < 0.01). Following PG injection, the interval to ovulation was similar regardless of whether an ovary was removed (12.8+/-4.3 days) or not (10+/-4.1 days). This similarity occurred despite a large and prolonged rise in plasma FSH levels that occurred only in the hemiovariectomized group. In addition, the intervals found after PG injection did not differ from those found after ablation of the preovulatory follicle. These observations indicate that 1) in the presence of the early active corpus luteum or dominant follicle, follicles grow to a similar stage of development; 2) recruitment of the follicle due to ovulation occurs 12 to 14 days before ovulation; 3) limiting new follicular growth to one ovary does not affect the time course to ovulation; and 4) prolonged high FSH levels do not alter the time course or ovulation rate.     

Changes in follicle-stimulating hormone and follicle populations during the ovarian cycle of the common marmoset

The common marmoset (Callithrix jacchus) belongs to the family Callitrichidae, the only anthropoid primates with a high and variable number of ovulations (one to four). An understanding of folliculogenesis in this species may provide some insight into factors regulating multiple follicular growth in primates. The aims of this study were to characterize in detail changes in the antral follicle population at different stages of the ovarian cycle, to characterize the marmoset FSH profile, and to relate cyclic changes in FSH to changes in follicle sizes and circulating estradiol concentrations. Fifty-five pairs of ovaries were collected (32 of which were at five distinct stages of the cycle) from adult marmosets, and antral follicles were manually excised and separated into four size groups. Daily urinary FSH and plasma estradiol and progesterone concentrations from Day 0 of the follicular phase to 2 days postovulation were measured in 22 marmosets using enzyme immunoassays. The FSH profile revealed two distinct peaks, on Days 2 and 6, during the 10-day follicular phase, with a marginal periovulatory increase on Days 9 and 10. Estradiol levels rose significantly (P: < 0.05) above baseline (Days 1-4) on Day 5 and continuously increased to a peak on the day preceding ovulation (Days 8 and 9). Follicle dissection revealed a high (mean = 68) and variable (range, 14-158) total number of antral follicles >0.6 mm. The number of antral follicles significantly declined (P: < 0.001) with age. The number of preovulatory follicles (>2 mm) was positively correlated with the number of antral follicles (P: < 0. 001) and tended to be negatively related to age (P: = 0.06). The number of antral follicles did not vary significantly with stage of the ovarian cycle, although the follicle size distribution was cycle-stage dependent (P: < 0.05). Follicles >1.0 mm appeared only in the follicular phase, and preovulatory follicles (>2.0 mm) appeared only at the end of the follicular phase (Days 7-9). The Day 2 FSH peak corresponded to emergence of a population of medium-size antral follicles, and the Day 6 peak was consistent with rising estradiol levels and appearance of the preovulatory follicles. These results suggest that some aspects of marmoset folliculogenesis are comparable to those in Old World primates, including the absence of multiple follicular waves and the appearance of an identifiable dominant follicle in the midfollicular phase. However, the midphase FSH peak, multiple dominant follicles, and abundance of nonovulatory antral follicles differ strongly from the pattern in Old World primates and humans. The findings are discussed in relation to the regulation of growth of multiple ovulatory follicles and provide the basis for further studies on factors influencing the dynamics of follicular growth and development in this species.     

Granulosa cell steroidogenesis and follicular fluid steroid concentrations after the onset of oestrus in cows

Granulosa cell responsiveness at an early (1-2 h) or late (14-16 h) stage of differentiation following the onset of oestrus [and presumably the LH surge] was studied in 16 cows. Follicular fluid collected at the early stage (8 preovulatory follicles) had a higher concentration of testosterone (P less than 0.05), oestradiol (P less than 0.01) and oestrone (P less than 0.01) than did follicular fluid collected at the late stage of oestrus (8 preovulatory follicles). No difference in follicular fluid progesterone was noted between follicles collected at the early and late stages of oestrus. Granulosa cells collected at the early stage of oestrus had a higher in-vitro response (progesterone production) to LH (P less than 0.05), forskolin (P less than 0.08) and diacylglycerol (P less than 0.05) than did granulosa cells collected at the late stage of oestrus. However, later stage granulosa cells produced more (P less than 0.01) progesterone after culture with prostaglandin E-2 than did earlier stage granulosa cells. These results show that follicular fluid oestrogen decreases, which suggests a loss of aromatase activity as oestrus progresses, and that granulosa cells become refractory (low progesterone production) to in-vitro LH, forskolin, and diacylglycerol challenge, yet acquire responsiveness to prostaglandin E-2 as oestrus progresses.     

Behavioral, follicular and gonadotropin changes during the estrous cycle in donkeys

Sexual behavior, follicular development and ovulation, and concentrations of circulating gonadotropins during the estrous cycle were studied during the summer in 7 jennies. Mean behavioral estrous length was 6.4 +/- 0.6 days (mean +/- SEM, n=19; 5.6 +/- 0.5 days preovulatory and 0.8 +/- 0.2 days post-ovulatory). Mean diestrous length was 19.3 +/- 0.6 days (n=14). Females in estrus typically showed posturing, mouth clapping, clitoral winking, urinating and tail raising. Mouth clapping began approximately one day sooner and lasted approximately one day longer than winking and tail raising, so that the total duration of clapping was significantly greater than for the other two signs. Follicular changes and concentrations of gonadotropins were determined for 14 estrous cycles (2 per jenny). The follicular end points [diameter of the largest follicle and number of large (>25 mm), medium (20-24 mm), and small follicles (<20 mm)] showed a significant day effect. The diameter of the largest follicle and the number of large follicles began to increase significantly 7 days prior to ovulation with a maximum value the day before ovulation. Medium follicles reached a maximum number 4 days prior to ovulation, and small follicles decreased significantly prior to ovulation. After ovulation, all follicular end points, except the number of small follicles, remained low for the next 12 days. Mean values of FSH were low during estrus and high during diestrus with 2 significant peaks, one 3 days and one 9 days after ovulation. In contrast, mean levels of LH were low during diestrus and high during estrus with a maximum value the day after ovulation. The LH profile showed a more prolonged gradual increase prior to ovulation, than that which has been reported for ponies and horses.