Abstract
BackgroundRemoval of the follicular content by ultrasound-guided transvaginal follicle aspiration (TVFA) may fail to induce immediate atresia and loss of function, resulting in the occurrence of residual follicles (RF). The aims of this study were to characterize the blood flow in RF and to determine the effects of the treatment with estradiol benzoate on RF fate. Lactating, cyclic Holstein-Gir crossbred cows were used. In Experiment 1, follicular wave emergence (D0) was synchronized in cows (n = 10) and follicular growth was then monitored by transrectal ultrasonography from D0 to D8, followed by TVFA of the largest follicle present on the ovaries 24 h later. Color Doppler ultrasound imaging was used to examine blood flow on the follicular wall, which was recorded immediately before and every 12 h after TVFA, up to 72 h. In experiment 2, cows (n = 22) were randomly allocated to receive either 2 mL of saline i.m. (Control group, n = 11) or 2 mL estradiol benzoate i.m. (EB group, n = 11) immediately after TVFA. Ovaries were scanned every 12 h to confirm the presence and to measure the diameter of RF. The contents of the RF, if present, were collected 72 h after the first TVFA, using the same aspiration procedures. Follicular fluid from original follicles and RF were stored at -20 °C until hormonal assays.ResultsIn Experiment 1, there was no reduction (P > 0.05) of blood flow in the remaining follicle walls after TVFA and maximum blood flow values were observed at 49.5 ± 19.7 h post-TVFA. In Experiment 2, formation of RF after TVFA was proportionally similar between Controls (5/9) and EB (5/10) cows. Also, RF diameter did not differ between groups (P > 0.05). Nonetheless, the content of RF from cows in the EB group had lower (P = 0.0004) estradiol (E2) concentration and lower (P = 0.0005) E2:P4 ratio compared with Controls.ConclusionsIn conclusion, 1) the persistence of vascularization in the remaining follicle wall may contribute to the formation of RF after follicle aspiration, and 2) the treatment with estradiol benzoate does not prevent formation of RF, but does reduce their estradiol production.
Highlights
Removal of the follicular content by ultrasound-guided transvaginal follicle aspiration (TVFA) may fail to induce immediate atresia and loss of function, resulting in the occurrence of residual follicles (RF)
To standardize the size and developmental status of the follicles at aspiration, follicular wave emergence was synchronized using a protocol designed for timed artificial insemination, except that ovulation was not induced at the end of the protocol: on d 0 (D0) cows were treated with sodium cloprostenol (500 μg im, Sincrocio, Ourofino Agronegocio, Sao Paulo, SP, Brazil), estradiol benzoate (EB, 2 mg im, Sincrodiol, Ourofino) and received an intravaginal progesterone implant (1 g, Sincrogest, Ourofino), which was removed 8 d later (D8)
The maximum values of blood flow and blood flow percent change relative to h 0 were observed at 49.5 ± 7.0 h after TVFA; due to the high individual variation (84.7 %) in the maximum values of blood flow, there was no effect (P > 0.05) of hour on RF blood flow (Fig. 1)
Summary
Removal of the follicular content by ultrasound-guided transvaginal follicle aspiration (TVFA) may fail to induce immediate atresia and loss of function, resulting in the occurrence of residual follicles (RF). Follicle ablation by TVFA is extensively used as a method to synchronize the emergence of ovarian follicular waves [6,7,8] and to reduce the detrimental effects of follicular dominance during superovulation [9,10,11] These strategies are based on the assumption that aspirated follicles will undergo atresia after removal of the fluidic content and collapse. Previous studies from our and other groups reported that the follicle wall may remain functional after being aspirated, forming a fluid-filled antrum which eventually persist as a steroidogenically-active structure [12, 13] These were referred to as residual follicles (RF) and their occurrence is more frequent after aspiration of large follicles, i.e., follicles likely to have greater intrafollicular estradiol (E2) concentrations [13]. The presence of RF may disturb the expected results of any procedures performed after follicle ablation by TVFA, such as follicular wave synchronization and/or superovulation
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