F. Gaytan et al., FOLLICULAR-GROWTH PATTERN IN CYCLIC RATS FROM LATE PRO-ESTRUS TO EARLY ESTRUS, Journal of Reproduction and Fertility, 110(1), 1997, pp. 153-159
Adult cyclic rats were studied from 16:00 h on pro-oestrus to 07:00 h
on oestrus to relate the cyclic hormonal changes to the proliferative
activity and growth pattern of growing follicles. The proliferative ac
tivity was studied by 5-bromodeoxyuridine (BrdU) labelling and by the
presence of mitoses. Small growing follicles (less than 275 mu m in di
ameter) were divided into five classes: multilaminar classes a (Ma, up
to 75 mu m in diameter), b (Mb, 76-150 mu m), c (Mc, 151-200 mu m) an
d d (Md, 201-274 mu m) and follicles measuring greater than or equal t
o 275 mu m in diameter were considered as greater than or equal to cla
ss I, following previous classifications. LH concentrations were maxim
al at 18:30 h on pro-oestrus, and this was coincident with an increase
in FSH, prolactin and progesterone concentrations, whereas oestradiol
and testosterone concentrations were decreased. From 02:00 h on oestr
us the concentrations of all hormones, except those of FSH, were decre
ased. The number of Ma, Mb and Mc follicles did not change during pro-
oestrus-oestrus, whereas an increase in the number of follicles greate
r than or equal to class I was found at 07:00 h on oestrus. This appea
rs to be a consequence of the increased proliferative activity of Md f
ollicles, evidenced by the increase in the BrdU labelling and mitotic
index of this follicle class, found from 02:00 to 07:00 h on oestrus,
together with a decrease in the percentage of early atretic follicles
greater than or equal to class I at 07:00 h on oestrus. This study pro
vides an improved classification of small growing follicles into discr
ete classes and delineates a size class of follicles (Md follicles) th
at is responsive to the cyclic hormonal changes on early oestrus.