Critical role of insulin-like growth factor system in follicle selection and dominance in mares.
The role of the insulin-like growth factor (IGF) system in the deviation in growth rates among follicles (follicle selection) was studied in mares using an IGF binding protein (BP) to reduce the follicular-fluid concentrations of IGFs. The future dominant follicle (F1) was treated by intrafollicular injection at the expected beginning of deviation (F1 > or = 20 mm; Day 0). The experimental groups were control (no injection, n = 8), vehicle (injection of vehicle; n = 6), and BP (injection of 250 microg of recombinant human IGFBP-3; n = 6). A sample of follicular fluid was taken from F1 on Day 1 in all groups. Compared with the control group, IGFBP-3 reduced (P < 0.05) the follicular-fluid concentration of free IGF-1 by 90%; lowered (P < 0.05) the concentrations of estradiol, activin-A, inhibin-A, and vascular endothelial growth factor; and increased (P < 0.05) the concentration of androstenedione. The diameter of F1 decreased and the diameter of F2 increased after Day 0 in the BP group, compared with the control and vehicle groups. A greater (P < 0.05) increase in circulating concentrations of FSH between Days 0 and 1 occurred in the BP group than in the other groups and accounted for the increased growth of F2. Dominance and ovulation from F1 occurred from fewer (P < 0.03) mares in the BP group (1 of 6) than from the control and vehicle groups combined (11 of 14); the remaining mares in the BP group ovulated from F2. Results indicated that the IGF system has a critical intrafollicular role in the differential changes in concentrations of follicular-fluid factors between the future dominant and subordinate follicles, leading to the development of follicle dominance (selection) and ovulation in mares.
Ginther
O J
OJ
Eutheria Foundation, Cross Plains, Wisconsin 53528, USA. ginther@svm.vetmed.wisc.edu
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D000818:Animals; D005260:Female; D015571:Follicular Fluid / Q000378:metabolism; D006727:Hormone Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D006728:Hormones / Q000378:metabolism; D006736:Horses / Q000378:metabolism / Q000502:physiology*; D007267:Injections; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000008:administration & dosage / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000037:antagonists & inhibitors / Q000378:metabolism; D006080:Ovarian Follicle / Q000000981:diagnostic imaging / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D013002:Somatomedins / Q000502:physiology*; D014463:Ultrasonography; D042461:Vascular Endothelial Growth Factor A / Q000037:antagonists & inhibitors
D006727:Hormone Antagonists; D006728:Hormones; D018972:Insulin-Like Growth Factor Binding Protein 3; D013002:Somatomedins; D042461:Vascular Endothelial Growth Factor A; D007334:Insulin-Like Growth Factor I