Effect of negative energy balance on the insulin-like growth factor system in pre-recruitment ovarian follicles of post partum dairy cows.
Post partum negative energy balance (NEB) in dairy cattle is associated with a delayed return to ovarian cyclicity and reduced fertility. This study compared the IGF system of pre-recruitment ovarian follicles between cows in mild (n = 6) or severe (n = 6) NEB during early lactation. Ovaries were collected in the second week post partum, when circulating concentrations of IGF-I and glucose were lower (P < 0.01) in severe NEB cows. mRNA expression for IGF-II, type 1 IGF receptor (IGF-1R) and IGF-binding proteins (IGFBP)-1 to IGFBP-6 was determined by in situ hybridisation in individual follicles using radiolabelled oligonucleotide probes. Follicles were classified as very small (1-2.5 mm) or small (2.5-5 mm) and healthy or atretic. Relative mRNA concentrations were measured as optical density (OD) units using image analysis. Thecal IGF-II mRNA expression was highest in very small, healthy follicles (P < 0.05). Granulosa cell IGFBP-2 was the only component to change with EB status, with higher mRNA expression in mild compared with severe NEB cows (P < 0.05). IGFBP-1 and IGFBP-3 mRNA expression were undetectable. IGF-1R, IGFBP-4 and IGFBP-5 mRNA expression were not significantly altered by follicle size or health, but IGFBP-5 tended to increase in atretic follicles. The pattern of IGFBP-6 mRNA expression in theca paralleled that of IGF-II mRNA, with higher (P < 0.05) levels in healthy, very small follicles. In conclusion, the reduced expression of IGFBP-2 mRNA in severe NEB cows may alter the bioavailability of circulating IGF-I and locally produced IGF-II to modulate the pre-recruitment stages of follicles required to maintain normal post partum ovarian cyclicity.
Llewellyn
S
S
Reproduction, Genes and Development Group, Royal Veterinary College, Hawshead Lane, North Mymms, Hatfield, Herts AL9 7TA, UK. sllewellyn@rvc.ac.uk
Fitzpatrick
R
R
Kenny
D A
DA
Murphy
J J
JJ
Scaramuzzi
R J
RJ
Wathes
D C
DC
D000818:Animals; D002417:Cattle / Q000378:metabolism*; D005260:Female; D005498:Follicular Phase / Q000378:metabolism; D015870:Gene Expression; D006107:Granulosa Cells / Q000378:metabolism; D017403:In Situ Hybridization; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000235:genetics; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000235:genetics; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000235:genetics; D018974:Insulin-Like Growth Factor Binding Protein 4 / Q000235:genetics; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000235:genetics; D018976:Insulin-Like Growth Factor Binding Protein 6 / Q000235:genetics; D007334:Insulin-Like Growth Factor I / Q000235:genetics; D007335:Insulin-Like Growth Factor II / Q000235:genetics; D006080:Ovarian Follicle / Q000378:metabolism*; D049590:Postpartum Period / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D017526:Receptor, IGF Type 1 / Q000235:genetics; D013002:Somatomedins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D013799:Theca Cells / Q000378:metabolism
D018970:Insulin-Like Growth Factor Binding Protein 1; D018971:Insulin-Like Growth Factor Binding Protein 2; D018972:Insulin-Like Growth Factor Binding Protein 3; D018974:Insulin-Like Growth Factor Binding Protein 4; D018975:Insulin-Like Growth Factor Binding Protein 5; D018976:Insulin-Like Growth Factor Binding Protein 6; D012333:RNA, Messenger; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D017526:Receptor, IGF Type 1