Gonadotropin-Independent Mechanisms Participate in Ovarian Responses to Realimentation in Feed-Restricted Prepubertal Guts1

Abstract

Short-term feed restriction in prepubertal gilts suppresses episodic LH secretion in the absence of changes in body weight or composition. To assess non-gonadotropin-mediated effects of realimentation at the ovarian level, 52 gilts were assigned to six treatments after 7 days (Days 1-7) of maintenance feeding (approximately 30% ad libitum). Groups R12 and R9 were maintenance-fed Days 8-12 or Days 8-9, respectively; A12 and A9 were fed to appetite Days 8-12 or Days 8-9, respectively. Groups R9P and A9P were fed as groups R9 and A9 were but received 750 IU eCG at 1500 h on Day 8. Groups R12 and A12 were ovariectomized at 1500 h on Day 12, and all other groups were ovariectomized at 1500 h on Day 9. All gilts received oral progestogen (15 mg allyl trenbolone) from Day 1 to ovariectomy, to antagonize the usual increases in endogenous gonadotropins that follow realimentation. Blood samples were obtained at 10-min intervals during selected windows during the experiment. Ovarian follicles were analyzed for development and steroidogenesis, and plasma samples were analyzed by RIA to determine concentrations of LH, FSH, insulin, and insulin-like growth factor-1 (IGF-1). Allyl trenbolone abolished pulsatile LH secretion, and realimentation did not stimulate LH or FSH secretion, with the exception of FSH secretion on Day 8 in A9 gilts. Postprandial insulin concentrations on Day 9 were greater after feeding to appetite (A9, A9P, and A12) than after feed restriction (R9, R9P, and R12). Pre- and postprandial IGF-1 concentrations were higher in re-fed gilts on Day 9 (A9 and A12) and Day 12 (A12) than in feed-restricted gilts. Follicular diameter, fluid volume, and basal granulosa cell estradiol synthesis per follicle were greater in A12 gilts than in R12 gilts, although there was no difference between A9 and R9 gilts. There was no effect of realimentation on follicular fluid concentrations of estradiol or testosterone, or on androgen-driven granulosa cell estradiol synthesis. Treatment with eCG increased follicular diameter, fluid volume, basal and androgen-driven estradiol synthesis, and fluid estradiol concentrations without interaction with feeding level. In conclusion, in the absence of LH elevations, realimentation over 5 days exerts effects at the ovary, increasing follicular growth and estradiol synthesis. These effects may be mediated by insulin, IGF-1, or unmeasured growth factors and would be expected to synergize with increases in endogenous gonadotropin that follow realimentation.

Effect of castration on serum concentrations of gonadal hormones, insulin-like growth factor-I and its binding proteins in male pigs

“…This is also probably due to the fact that our pigs were underfed from birth. Such a hypothesis agrees well with earlier reports showing that feed restriction is susceptible to a decrease in circulating IGF-I in pigs (Buonomo and Baile, 1991;Cosgrove et al, 1992;Charlton et al, 1993). Similarly, underfeeding significantly reduces plasma IGF-I concentrations in heifers (Spicer et al, 1992).…”

Regulation of IGF-I and porcine oviductal secretory protein (pOSP) secretion into the pig oviduct in the peri-ovulatory period, and effects of previous nutrition

“…IGF-I concentration in peripheral and oviductal plasma was determined using the homologous double antibody radioimmunoassay described previously [13]. The anti-human IGF-I antiserum (product name AFP4892898, obtained from Dr. AF Parlow through the NIDDK's National Hormone and Pituitary Program), was used at a 1/654000 final dilution, resulting in 38% specific binding.…”

“…Total RNA was extracted, quantified, and RNA integrity was assessed according to the protocols outlined elsewhere [21]. The RNA was prepared for Northern blotting as previously described [13]. Blots were then hybridized overnight in fresh prehybridization solution using a 0.8 kb cDNA for pOSP, to assess steady state mRNA levels.…”

“…Nutrition affects follicular development, particularly steroidogenesis and subsequent luteal function, through metabolic hormones and metabolites acting centrally on hypothalamic regulation of LH [6], and through direct local effects on the ovary [13]. As part of the collaborative study which provided the tissues analyzed in Experiment 3, we have already established that the RH and HR+I gilts had higher follicular phase E 2 concentrations, a greater preovulatory LH surge, and a faster rise in P 4 after ovulation than the HR gilts, which were considered to be indicative of greater follicular maturity and an accelerated process of luteinization [3,21].…”

Feeding lactating primiparous sows to establish three divergent metabolic states: I. Associated endocrine changes and postweaning reproductive performance.

“…Average sensitivity, estimated as 85% of total binding, was .01 ng/tube. Plasma insulin and IGF-I concentrations were determined in duplicate using the double antibody RIA previously described by Cosgrove et al (1992). For insulin, 100 mL of plasma was assayed; the intra-and interassay CV were 6.0 and 6.1%, respectively.…”