Wednesday, August 4, 2004
10:30 AM–12:30 PM
(658) THE EFFECT OF DIETARY RESTRICTION AND EXOGENOUS STEROID TREATMENT ON INTRAFOLLICULAR IGF-I, IGFBP, AND EXPRESSION OF THE TYPE-I IGF RECEPTOR IN BOVINE GRANULOSA CELLS.
Canty, Mary1, 2, Austin, Edward1, Boland, Maurice2, 3, Crowe, Mark1, 3, 1 University College Dublin, Dublin, Ireland2 University College Dublin, Dublin, Ireland3 University College Dublin, Dublin, Ireland
ABSTRACT- Insulin-like growth factor-I synergises with FSH in stimulating granulosa cell proliferation and steroidogenesis. To determine whether intrafollicular concentrations of insulin-like growth factor-I (IGF-I), insulin-like growth factor binding proteins (IGFBP) and granulosa cell IGF type I receptor mRNA are affected by short-term fasting or short-term exposure to exogenous steroids 24 heifers were blocked by body weight and within block randomly allocated to one of three treatments: (i) no treatment, slaughtered Day 5 (Controls; n=8); (ii) progesterone-releasing intravaginal device (PRID) without estradiol (E2) capsule inserted on D3 (72 hours post estrous detection) and slaughtered on Day 5 (PRID; n=8); or (iii) fasted 48 hours before slaughter on D5 (FAST, n=8). Water was available ad libitum. Intrafollicular IGFBP-2 concentrations were lower (P<0.05) in the largest follicles (F1) from fasted heifers compared with F1 follicles from PRID-treated heifers, but were not different from controls. Intrafollicular IGFBP-2 and -5 concentrations were lower (P<0.05) in the F1 compared with the second largest follicle (F2) in PRID-treated and fasted heifers and was associated with increased (P<0.05) intrafollicular IGF-I in F1 compared with F2 follicles from fasted heifers. Expression of the IGF type-I receptor was unaffected by treatment and there was no difference in level of expression between F1 and F2 follicles. The results indicate that short-term fasting or exposure to exogenous progesterone had no effect on IGF type I receptor mRNA expression, but was associated with decreased intrafollicular IGFBP-2 and -5 concentrations in F1 follicles.
KEY WORDS: IGF type-I receptor, IGFBP, dietary restriction