Intrinsic and extrinsic factors influencing steroid production in vitro by bovine follicles.
Nonatretic bovine follicles were cultured on grids in a conventional static system, in roller tubes or in a continuous flux system. Culture medium from the static and roller tube system was replaced after 24 h of culture, while in the continuous flux system, only a small sample was taken aseptically at that time. Steroid concentrations in these samples were estimated by radioimmunoassay (RIA) and related to intrinsic factors like follicle size, day of cycle and micromorphological appearance at the end of culture and to extrinsic factors like the culture system, O(2)-concentration applied in the gasphase and time of culture. Bovine nonatretic follicles from 2 to 8 mm showed the same amount of estradiol-17beta (E2) production as pmol mg protein(-1) 24 h. Follicles over 8 mm had a significantly higher E2 production. Follicles from the follicular phase of the cycle produced more E2 than follicles from the luteal phase, independent of follicular size and culture system. Degeneration of follicles during culture resulted, independent of the culture system, in a decline of E2-production, and in an increase of P4-production; whereas the T-production initially (primary atresia) rose but subsequently (secondary and tertiary atresia) declined. The difference between the culture systems were reflected by quantitative differences in the production of the steroids measured. The most striking difference between the continuous flux system on one hand and the static and rolling tube system on the other is the predominant E2 production in the former by every follicle. It is thought that this difference might be caused by a better 02 supply in the continuous flux system. This hypothesis is tested in the static culture system. The more 02 the more E2 production. The increase in culture time resulted in an increase of E2 and P4, whereas the testosterone production was not significantly decreased.
Kruip
T A
TA
Clinic for Herd Health and Reproduction Veterinary Faculty, State University Utrecht, Yalelaan 7, 3508 TD Utrecht, The Netherlands.
Dieleman
S J
SJ