Follicular Growth and Atresia during the Last Half of the Luteal Phase of the Guinea Pig Estrous Cycle: Relation to Serum Progesterone and Estradiol Levels and Utero-Ovarian Blood Flow*

Abstract

The relationships among follicular growth, changes in serum progesterone (P) and estradiol (E) levels, and utero-ovarian blood flow (OBF) through the guinea pig ovary were examined during days 7-16 of the luteal phase (day 0 = estrus) of the estrous cycle and during the subsequent ovulatory (proestrous-estrous) period. Follicles were classified as either viable or atretic based on strict criteria and grouped according to diameter. No changes in follicular growth were observed between days 7-9 of the cycle when serum P levels were elevated and OBF was at low rates. Between days 13-15 when serum P levels were low and both OBF and serum E levels were rising, there was a dramatic increase in the number of viable follicles present in all follicle classes. As the percentage of viable follicles increased, the number of atretic follicles in each size population decreased. Peaks in the number of large follicles (300-450 microns), OBF, and serum E levels were observed during the subsequent ovulatory period. These data suggest that as luteal activity declines during the last half of the estrous cycle, follicular recruitment and growth are stimulated. The concomitant elevations in OBF suggest a supportive role for this parameter in follicular development. In turn, the subsequent elevation in serum E levels serves as an index of follicular maturation. These data suggest that the elevated P levels during the luteal phase of the estrous cycle may either directly or indirectly, through the regulation of gonadotropin secretion, regulate follicular growth in the guinea pig.

The effect of deslorelin acetate on the oestrous cycle of female guinea pigs

“…Opening of the membrane precedes oestrus, but its timing is too variable to be used in accurately establishing the onset of oestrus (Sisk 1976). The monophasic cyclic fluctuations of P 4 , coincident with the ovarian luteal phase (dioestrus, lack of sexual behaviour) found in the current study are in accordance with the data of others (Challis et al 1971;Garris et al 1984), whereas the E 2 levels in the current study did not show cyclic fluctuation which is in agreement with the non-cyclic fluctuation reported by Croix and Franchimont (1975). These data run counter to previous findings of Hutz et al (1990) who describe a biphasic follicular growth associated with biphasic E 2 production.…”

“…P 4 concentrations decreased from day fifteen in all treated females and remained low throughout the study. Instead of an expected decrease of E 2 concentrations after an initial "flare-up" effect, as described in dogs and cats (Garris et al 1984), E 2 concentrations remained very high in treated guinea pigs during the twelve months of the study. The exact reason for the high E 2 concentrations remains unclear.…”

“…Previously, it has been shown that there is a significant elevation of plasma progesterone (P 4 ) coincident with the luteal phase (dioestrus) in guinea pigs (Feder et al 1968;Challis et al 1971;Blatchley et al 1976;Garis and Foreman 1984), whereas fluctuations of plasma oestradiol (E 2 ) levels occur throughout the oestrous cycle (Chalis et al 1971;Croix and Franchimont 1975;Garris and Foreman 1984;Westfahl and Vekasy 1988;Hutz et al 1990).…”

Ovarian Localization of Immunoglobulin G and Inhibin .ALPHA.-Subunit in Guinea Pigs after Passive Immunization against the Inhibin .ALPHA.-Subunit.

“…These sections were analyzed for the number and size (mean of two largest diameters measured at right angles) of follicles large than 200 µm in diameter (this excludes small preantral follicles); follicle measurements were made without regard to the healthy or atretic status [2] but the follicles that contained a visible oocyte nucleus and some granulosa cells were included in the counts. A follicle large than 500 µm in size denotes a large antral follicle [17][18][19].…”

Induction of follicular luteinization by equine chorionic gonadotropin in cyclic guinea pigs

“…The follicular size was determined as the mean of two diameters, which were recorded at right-angles by measuring the largest follicular diameter through a section containing the largest cut surface of oocyte as described previously (Bland, 1980;Hutz et al, 1990). Follicles were classified as small (<300 μm), medium (300-600 μm), or large (>600 μm) (Curry et al, 1984a;1984b;Garris and Foreman, 1984). The number of corpora lutea, weights of single ovary and uterus, number of luteinized cells in CL, and proportion of apoptotic luteinized cells in luteinized follicles were also determined (Li et al, 2014).…”