Follicular fluid concentrations of free insulin-like growth factor (IGF)-I during follicular development in mares.
The objective of the present study was to evaluate changes in concentrations of free insulin-like growth factor (IGF)-I in follicular fluid (FFL) during follicle development in the mare. Mares (n = 14) were classified as either in the follicular phase (n = 8) or luteal phase (n = 6). Follicles (n = 92) were categorized as small (6-15 mm; n = 54), medium (16-25 mm; n = 23) or large (>25 mm; n = 15) and FFL was collected. Free IGF-I levels in FFL in large follicles of follicular phase mares were greater (P < 0.05) than in large follicles of luteal phase mares and small or medium follicles of luteal and follicular phase mares. Free IGF-I concentrations were greater (P < 0.05) in large follicles of luteal phase mares than small but not medium follicles of luteal phase mares. FFL ratio of estradiol:progesterone paralleled changes in free IGF-I. Free IGF-I concentrations were negatively correlated (P < 0.05) with insulin-like growth factor binding protein (IGFBP)-2, -4 and -5 but not IGFBP-3 levels. In addition, free IGF-I concentrations in FFL were positively correlated (P < 0.01) with FFL estradiol, progesterone, androstenedione, estradiol:progesterone ratio, total IGF-I and total IGF-II. We conclude that increases in intrafollicular levels of bioavailable (free) IGF-I are associated with increased steroidogenesis in developing mare follicles.
Spicer
L J
LJ
Department of Animal Science, Oklahoma State University, Stillwater, OK 74078, USA. igf1Leo@okstate.edu
Santiago
C A
CA
Davidson
T R
TR
Bridges
T S
TS
Chamberlain
C S
CS
D000735:Androstenedione / Q000378:metabolism; D000818:Animals; D004958:Estradiol / Q000378:metabolism; D005260:Female; D015571:Follicular Fluid / Q000378:metabolism; D005498:Follicular Phase / Q000378:metabolism; D006736:Horses / Q000378:metabolism*; D018969:Insulin-Like Growth Factor Binding Proteins / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008183:Luteal Phase / Q000378:metabolism; D006080:Ovarian Follicle / Q000254:growth & development* / Q000378:metabolism*; D011374:Progesterone / Q000378:metabolism
D018969:Insulin-Like Growth Factor Binding Proteins; D000735:Androstenedione; D011374:Progesterone; D004958:Estradiol; D007334:Insulin-Like Growth Factor I