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.
The relationship of excitatory amino acid (EAA) activity to LH secretion was investigated in ovariectomized crossbred prepuberal gilts (93 +/- 1 kg BW) and Yorkshire barrows (94 +/- 2 kg BW) in two experiments. In Exp. 1, eight gilts received, i.m., saline (S) or 20 mg of Ketamine (K)/kg BW, a noncompetitive EAA receptor antagonist. Within these groups, four then received 10 mg of N-methyl-DL-aspartate (NMA)/kg BW, an EAA agonist, or S i.v. Mean serum LH concentrations were similar among groups before treatment, did not change after S+S, but decreased (P < .05) by 1 h after S+NMA, 3 h after K+S, and 2 h after K+NMA. Serum cortisol concentrations did not change after S+S, but were increased (P < .05) from 30 to 90 min after S+NMA, at 120 min after K+S, and from 30 to 120 min after K+NMA. In Exp. 2, barrows received 2.5 mg of NMA/kg BW i.v. immediately after i.m. injection of S (n = 7) or 19.9 mg of K/kg BW (n = 8). Mean serum LH concentrations for the 2 h before treatment were similar among barrows, but decreased (P < .05) by 2 h after K+NMA and was not altered after S+NMA. Serum cortisol concentrations were increased at 30 min after S+NMA and from 60 to 90 min after K+NMA. We suggest that EAA both inhibit and stimulate LH secretion, with the inhibitory effects lying within the basal hypothalamus and the stimulatory effects lying within higher brain centers.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.