Steroidhormongehalt in Blut und Ovarfollikeln des Rindes während des Zyklus*

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.

Steroid hormone concentrations in the fluid of bovine follicles relative to size, quality and stage of the oestrus cycle

Eight hundred and seven bovine antral follicles from 2 mm to 20 mm in diameter were dissected free of stromal tissue, measured, qualified and divided into 36 groups according to size, quality and stage of cycle. The follicular fluid was collected and assayed by RIA for oestradiol-17beta, testosterone and progesterone. The steroid hormone concentrations vary with follicular size, degree of atresia and stage of the cylce. Non-atretic follicles of less than 8 mm are generally androgen-dominated and non-atretic follicles of more than 11 mm are oestrogen-dominated. Follicles betwen 8 mm and 11 mm are intermediate in this respect. Degeneration leads to a gradual decrease of oestradiol-17beta and testosterone concentration and increase of progesterone. It is suggested that the ratio of oestradiol-17beta/testosterone and oestradiol- 17beta/progesterone and oestradiol-17beta/testosterone + progesterone cannot generally be used to discriminate between non-atretic and atretic follicles. Large follicles present during the early luteal stage contain as much oestradiol-17beta in the follicular fluid as large follicles during the follicular stage, whereas large follicles of the luteal stage contain only 15% of the maximal amount of the latter's. This and other presented data support the statement that follicles present during the early luteal, late luteal and follicular stages of the cycle belong to different groups of growing follicles. It has been concluded that groups of macroscopically qualified follicles can be distinguished from each other by the steroid hormone concentration in the follicular fluid. It is therefore possible to predict the hormonal environment of the oocyte in any individual follicle of a defined size and quality.

Oestrogens in milk

The steroid oestrogens oestradiol-17 beta, oestrone and oestradiol-17 alpha have all been adequately identified in various body fluids and tissues of cattle. There is also good evidence for the presence of oestrone sulphate. Oestriol (or similar triols) may also be present. The oestrogens found in the systemic plasma of cattle are present in milk in similar concentrations; whether their passage into milk involves metabolism by the mammary gland is uncertain. Oestrone sulphate, at least at relatively high levels of secretion, is believed to be found only in pregnant cattle and measurement of its concentration in milk is in use as a practical test for pregnancy. A close correlation has been found between the concentrations of oestradiol-17 beta in systemic plasma and milk of non-pregnant cows and levels of this oestrogen in milk may, together with those of progesterone, now be used in studies of post-partum ovarian function.