Steroid secretion by perifused rabbit follicles: effect of repeated gonadotropin challenges

• Published in: Biology of reproduction Vol. 25; no. 4; pp. 843 - 850
• Main Authors: D'Amato, C, Calvo, F O, Stockert, B, Bahr, J M
• Format: Journal Article
• Language: English
• Published: United States Society for the Study of Reproduction 01-11-1981
• Subjects: Animals; Dose-Response Relationship, Drug; Estradiol - metabolism; Female; Follicle Stimulating Hormone - pharmacology; Gonadal Steroid Hormones - metabolism; In Vitro Techniques; Kinetics; Luteinizing Hormone - pharmacology; Ovarian Follicle - drug effects; Ovarian Follicle - metabolism; Progesterone - metabolism; Rabbits; Testosterone - metabolism
• ISSN: 0006-3363; 1529-7268
• DOI: 10.1095/biolreprod25.4.843

The capacity of a follicle to respond to a second challenge of LH is lost after exposure to a high
dose of LH as indicated by a loss of hormone-stimulable adenylyl cyclase activity. To determine if
a similar depression of steroidogenesis occurs, large follicles (1.5-2.0 mm) were isolated from
estrous rabbits, placed in a perifusion system, and challenged at 6 h intervals for a 24-36 h period
with LH:FSH at one of the following doses: 10 ng:2.5 µg; 40 ng:2.5 µg; 1 µg:2.5 µg; or
phosphate-buffered saline (PBS). Progesterone (P), testosterone (T), and estradiol-17β (E) were
measured in the perifusate. At the completion of the perifusion, follicles were fixed in Bouin’s
solution, embedded, sectioned, and stained with hematoxylin and eosin for histological studies.
Basal steroid secretion decreased gradually during the first 12 h and was then maintained at a
constant low level for the remaining 24 h. Follicles stimulated with 1 µg:2.5 µg of LH:FSH at 12,
18, 24, and 30 h produced a significant (P<0.05) increase in T and E after only the first challenge
of LH:FSH, whereas P increased significantly (P<0.05) after each challenge. The repeated challenge
of follicles with 1 µg:2.5 µg of LH:FSH at 0, 6, 12, 18, 24, and 30 h resulted in a significant
(P<0.05) increase in P production after each gonadotropin stimulation while T and E secretion
was elevated significantly (P<0.01) after only the first challenge. Follicles stimulated with 10 ng:
2.5 µg of LH-FSH at 0, 6, 12, 18, 24, and 18 h produced a significant (P<0.05) increase P after only
the fourth challenge and in T after the second, third, and fourth challenge. There was no increase
in E. Repeated stimulation with 40 ng:2.5 µg of LH:FSH at 0. 6, 12, and 18 h resulted in a significant (P<0.05) increase in
T after the second challenge and in P after the third and fourth challenges.
Luteal cells were present only in follicles challenged with the 1 µg:2.5 µg dose of LH:FSH, regardless of whether the follicles
were challenged 4 or 6 times.
These results indicate, first, that the steroid secretion profile depends upon the dose of the
gonadotropin. While low (10 ng) and medium (40 ng) doses of LH with a constant high dose of
FSH (2.5 µg) elevated significantly the secretion of P and T, only a high dose of LH (1.0 µg) with
FSH (2.5 µg) increased E secretion. Second, P secretion, unlike T and E secretion, is not depressed
following a challenge with a maximum dose of LH:FSH. Third, luteinization of perifused follicles
apparently depends upon exposure to a high dose of gonadotropin.