Steroidogenesis in bovine granulosa cells: the effect of short-term changes in dietary intake.
The nutritional status of a cow is a key factor in the regulation of both follicle growth and oocyte quality. In this study, the effect of diets designed to increase circulating insulin and insulin-like growth factor I (IGF-I) concentrations on steroid production by granulosa cells in vitro was examined to analyse the mechanisms through which these changes occur. Hereford x Friesian heifers (n = 24) were offered maintenance or twice maintenance diets during the experimental period (17 days). Circulating concentrations of FSH did not differ between the two dietary groups, whereas insulin and IGF-I concentrations showed significant diet x day of oestrous cycle interactions. Ovaries were collected on day 3 of the first follicle wave after synchronization of oestrus. Granulosa cells were isolated from small (1-4 mm) and medium-sized (4-8 mm) follicles and cultured in the presence of long R3-IGF-I or bFSH or both. After 4 days in culture, granulosa cells isolated from small follicles, but not medium-sized follicles, collected from cattle offered the twice maintenance diet secreted significantly higher (P < 0.05) amounts of oestradiol compared with granulosa cells collected from cattle offered the maintenance diet. The effect was apparent in either the presence or absence of FSH and long R3-IGF-I. This nutritional effect on aromatase activity in granulosa cells was not apparent after day 6 of culture. There was no effect of diet on progesterone production by granulosa cells after 4 or 6 days of culture. These results support the hypothesis that dietary-induced changes in circulating insulin and IGF-I concentrations have a direct effect on the steroidogenic potential of bovine granulosa cells from small follicles. The dietary-induced increases in aromatase activity in small follicles combined with the increased concentration of metabolic hormones are possible mechanisms through which short-term changes in nutrition may affect follicle dynamics.
Armstrong
D G
DG
Division of Integrative Biology, Roslin Institute (Edinburgh), Roslin, Midlothian EH25 9PS, UK. david.armstrong@bbsrc.ac.uk
Gong
J G
JG
Gardner
J O
JO
Baxter
G
G
Hogg
C O
CO
Webb
R
R
D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle / Q000378:metabolism*; D002478:Cells, Cultured; D004958:Estradiol / Q000096:biosynthesis*; D004971:Estrus / Q000502:physiology*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood / Q000494:pharmacology; D006107:Granulosa Cells / Q000378:metabolism*; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D011374:Progesterone / Q000096:biosynthesis; D013997:Time Factors
D007328:Insulin; C085700:long R(3)-insulin-like growth factor-I; D011374:Progesterone; D004958:Estradiol; D007334:Insulin-Like Growth Factor I; D005640:Follicle Stimulating Hormone