Author:
Shores Ellen M.,Hunter Morag G.
Abstract
The steroidogenic enzymes, P450 aromatase
(P450 arom ) and P450 17a-hydroxylase (P450
17a ), were precisely located
within the healthy porcine follicle by immunohistochemistry. Enzyme
distribution was examined throughout follicular development during natural
oestrous cycles (n = 14 gilts) and was compared
with steroid production by healthy whole and theca-only follicles. All
follicles 2 mm or more in diameter were either fixed for immunohistochemistry
(n = 380 of which 197 were assessed as healthy)
or incubated as whole (n = 110) or theca-only
(n = 110) follicles to measure steroidogenesis.
P450 17a was confined to the theca
layer. The number of positive cells and staining intensity increased with
follicle size. P450 arom was consistently detected in
the granulosa layer of follicles measuring 6 mm or more in diameter and those
cells furthest from the antrum were most strongly stained.
P450arom was also detected in the theca layer of these
large follicles. Whole and theca-only follicles produced oestradiol and
androstenedione, and the levels of both hormones increased with follicle size
(P<0.001). Whole follicles produced more oestradiol
(P<0.001), but less androstenedione
(P = 0.01) than theca-only follicles of the same
size. Although granulosa cells contained P450 arom and
synthesized oestradiol, only theca cells contained P450
17a. Theca cells therefore
provided granulosa cells with androgen substrate. In addition, theca cells
possessed P450 arom , making them capable of independent
oestradiol production, which may be required to trigger the LH surge. This
study confirms the vital role of theca cells in follicular steroidogenesis in
the pig.
Subject
Developmental Biology,Endocrinology,Genetics,Molecular Biology,Animal Science and Zoology,Reproductive Medicine,Biotechnology
Cited by
17 articles.
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