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Biology of Reproduction, Vol 53, 1359-1364, Copyright © 1995 by Society for the Study of Reproduction

ARTICLES

Influence of stage of the estrous cycle on insulin-like growth factor-I modulation of luteinizing hormone secretion in the gilt

NC Whitley, CR Barb, RV Utley, JM Popwell, RR Kraeling and GB Rampacek
Animal and Dairy Science Department, University of Georgia, Athens 30602, USA.

Follicular phase (FOL; Days 17-19; n = 8), luteal phase (LUT; Days 7-9; n = 6), and ovariectomized (OVX; n = 5) crossbred gilts were used (Day 0 = onset of estrus). Blood samples were collected via jugular vein cannula every 15 min for 2 h the day before pituitary collection. Serum was assayed for insulin-like growth factor (IGF)-I, IGF-I binding proteins (IGFBP), LH, estradiol (E2), and progesterone (P4). Anterior pituitary cells were dispersed, cultured, and challenged on Day 4 of culture (Day 0 = day of seeding) with 10(-7) M GnRH or IGF-I (10(-11), 10(-10), 10(-9), 10(-8), or 3 x 10(-8) M) individually or in combination. Serum E2 and P4 concentrations indicated that the animals were in the appropriate stage of the estrous cycle. Mean serum LH concentrations were greater (p < 0.0004) for OVX animals compared to FOL and LUT animals. Mean serum IGF-I concentrations were lower (p < 0.05) for OVX compared to FOL and LUT animals, while serum IGFBP were not different among animals. Basal LH secretion (control) was greater (p < 0.04) in OVX than in FOL or LUT cultures. Relative to control, 10(- 11) M IGF-I increased (p < 0.02) LH secretion in FOL, LUT, and OVX cultures, and this response was greater (p < 0.05) in FOL and OVX than in LUT cultures. Only the 10(-11) M IGF-I enhanced basal LH secretion in LUT cultures. In addition, 10(-10) M IGF-I increased (p < 0.05) LH secretion in OVX cultures, and 10(-10) and 10(-9) M IGF-I stimulated (p < 0.05) LH secretion in FOL cultures, whereas basal LH secretion in all groups was unaffected (p > 0.05) by 10(-8) or 3 x 10(-8) M IGF-I. The GnRH-induced LH secretion was unaltered by IGF-I treatment. Results indicate that in vitro IGF-I treatment increased basal LH secretion, with reproductive status modulating LH response to IGF-I.




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Copyright © 1995 by the Society for the Study of Reproduction.