Some aspects of thecal and granulosa cell function during follicular development in the bovine ovary

128

Follicle classification is an important aid to the understanding of follicular development and atresia. Some bovine primordial follicles have the classical primordial shape, but ellipsoidal shaped follicles with some cuboidal granulosa cells at the poles are far more common. Preantral follicles have one of two basal lamina phenotypes, either a single aligned layer or one with additional layers. In antral follicles !5 mm diameter, half of the healthy follicles have columnar shaped basal granulosa cells and additional layers of basal lamina, which appear as loops in cross section ('loopy'). The remainder have aligned single-layered follicular basal laminas with rounded basal cells, and contain better quality oocytes than the loopy/columnar follicles. In sizes O5 mm, only aligned/rounded phenotypes are present. Dominant and subordinate follicles can be identified by ultrasound and/or histological examination of pairs of ovaries. Atretic follicles !5 mm are either basal atretic or antral atretic, named on the basis of the location in the membrana granulosa where cells die first. Basal atretic follicles have considerable biological differences to antral atretic follicles. In follicles O5 mm, only antral atresia is observed. The concentrations of follicular fluid steroid hormones can be used to classify atresia and distinguish some of the different types of atresia; however, this method is unlikely to identify follicles early in atresia, and hence misclassify them as healthy. Other biochemical and histological methods can be used, but since cell death is a part of normal homoeostatis, deciding when a follicle has entered atresia remains somewhat subjective.

Section: Atresia Of Antral Follicles !5 MM In Diametermentioning

confidence: 56%

Section: Healthy Antral Folliclesmentioning

confidence: 99%

Morphological classification of bovine ovarian follicles

Rodgers¹,

Irving-Rodgers²

2010

128

“…As atresia progresses, peribasal cells differentiate into luteal-like cells that express StAR and P450 side-chain cleavage and most likely are able to secrete progesterone. Supporting this concept, it has been shown that as bovine follicles undergo atresia, the progesterone content of the follicular fluid increases significantly (McNatty et al 1984b, Jolly et al 1994. However, the lack of apoptosis in peribasal granulosa cells is not clear.…”

Section: Discussionmentioning

confidence: 99%

Gene expression for LH receptor, 17α-hydroxylase and StAR in the theca interna of preantral and early antral follicles in the bovine ovary

Braw–Tal

Roth²

2005

The onset of gene expression for three proteins that play pivotal roles in theca interna function, namely the LH receptor (LH-R), cytochrome P450 17a-hydroxylase (17aOH) and the steroidogenic acute regulatory protein (StAR), was determined. Ovaries were obtained on day 9 of the oestrus cycle from mature synchronized dairy cows (n 5 5) and gene expression in preantral and antral follicles up to 4 mm in diameter was evaluated by in situ hybridization. LH-R and 17aOH mRNAs were observed first, in the theca interna of large preantral follicles (type 4), concurrent with its morphological differentiation. StAR mRNA appeared later during follicular growth, in follicles >1 mm in diameter (type 6). LH-R and 17aOH mRNAs were found exclusively in the thecal cells, whereas StAR mRNA appeared in thecal cells, granulosa cells of late atretic follicles and oocytes. In early atresia, thecal cells expressed all three mRNAs, and their expression decreased gradually as atresia progressed. Atresia in granulosa cells was characterized by massive apoptosis of periantral, but not peribasal cells, that differentiated into luteallike cells expressing StAR. In summary, our study suggests that in spite of the presence of 17aOH, a key enzyme in steroidogenesis, the ability to produce steroids by bovine follicles smaller than 1 mm in diameter must be very limited due to the absence of StAR protein.During the early stages of atresia, thecal cells remain morphologically and functionally healthy, and continue to express all three studied mRNAs.

“…In the cow, peripheral blood concentrations of androstenedione and oestradiol were reported to be similar during the follicular phase (McNatty et al, 1984). Since bovine follicles >2 mm in diameter secrete androstenedione in the follicular fluid (McNatty et al, 1984) it is likely that the androstenedione concentration is the result of the accumulated secretion by several follicles. Androstenedione is the main substrate for the aromatase and thus the primary precursor for oestradiol synthesis by bovine granulosa cells (Dieleman & Blankenstein, 1984).…”

Section: Discussionmentioning

confidence: 99%

Changes in pulsatile secretion patterns of LH, FSH, progesterone, androstenedione and oestradiol in cows after superovulation with PMSG

Bevers

Dieleman²,

Tol³

et al. 1989

Summary. Six heifers were injected i.m. with 2500 i.u. PMSG followed by 15 mg prostaglandin 48 h later. Serial blood samples were collected through a catheter in the caudal vena cava every 10 min for 8 h on Day 10 (7 h after PMSG administration), during luteal regression (7 h after prostaglandin administration) and on the day thereafter. Four normally cyclic heifers served as a control group. Concentrations of progesterone, androstenedione, oestradiol, LH, FSH, and PMSG in the vena cava samples were measured and the frequency and amplitudes of episodic pulses of all hormones were estimated except for PMSG. Ovaries were collected by ovariectomy at 50 h after onset of luteal regression to determine the number of preovulatory follicles (non-atretic follicles \ m=ge\ 10 mm).Stimulation of follicular growth by administration of PMSG resulted in the following effects on the secretion of steroids and endogenous gonadotrophins.(1) There were no alterations in progesterone concentration and the amplitude and frequency of episodic pulses. Mean ( \m=+-\s.e.m.) concentrations were 54\m=.\1\ m=+-\5\ m=. \ 8, 19\m=.\1\ m=+-\3\m=.\1and 3\m=.\4\ m=+-\0\m=.\9nmol/l on Day 10 (L), during luteal regression (LR) and on the day thereafter (F) respectively. (2) There were no alterations in the episodic secretion patterns of androstenedione. Mean concentrations were 0\m=.\20\ m=+-\0\m=.\02, 0\m=.\15\ m=+-\0\m=.\02and 0\m=.\11\ m=+-\ 0\m=.\02nmol/l for the L, LR and F periods respectively. (3) There was an increase in oestradiol concentration from 17\m=.\1\m=+-\3\m=.\0 pmol/l during the L period to 233\m=.\7\ m=+-\ 86\m=.\4pmol/l during the F period. Pulse amplitude was enhanced compared to corresponding periods in control animals whereas pulse frequency remained the same. The oestradiol concentration was significantly correlated with the number of preovulatory follicles (r = 0\m=.\82, P < 0\m=.\05).(4) There was a suppression of the frequency of episodic LH pulses (/8 h) during the LR (3\m=.\2\ m=+-\ 0\m=.\7) and F (4\m=.\3\ m=+-\ 0\ m=. \ 4) periods compared to corresponding periods in control heifers (9\m=.\5 \m=+-\0\m=.\9and 7\m=.\0\m=+-\1\ m=. \ 5 respectively). The preovulatory LH peak occurred earlier in 4 of 6 treated heifers. (5) There was a suppression of FSH concentrations, pulse amplitude and frequency during the LR and F (17\m=.\4\ m=+-\0\m=.\9 mg/l, 4\m=.\7\ m=+-\ 0\m=.\8 \ g = m \ g / l and 7\m=.\5\ m=+-\0\m=.\4 pulses/8 h) periods compared to the corresponding F-period values (35\m=.\6 \m=+-\ 6\m=.\2 mg/l, 9\ m=. \ 8 \m=+-\ 1\m=.\6 \ g=m\ g/ l and 9\m=.\3\ m=+-\0\m=.\3 pulses/8 h) in control heifers.It is concluded that the increased number of preovulatory follicles after PMSG administration severely suppresses endogenous FSH secretion by means of enhanced concentrations of oestradiol and probably also of inhibin.