REPORT ON THE USES FOR VARIOUS EMPIRE WOODS BOTH HOME-GROWN AND OVERSEAS, AS DISPLAYED AT THE FORUM CLUB EXHIBITION, LONDON February 1933 Get access JOHN R. COSGROVE, D.S.O.M.C. JOHN R. COSGROVE, D.S.O.M.C. MAJOR Search for other works by this author on: Oxford Academic Google Scholar Forestry: An International Journal of Forest Research, Volume 7, Issue 1, 1933, Pages 50–54, https://doi.org/10.1093/oxfordjournals.forestry.a063321 Published: 01 January 1933
This study determined effects of treatment with the endogenous opioid peptide (EOP) antagonist naloxone on LH and prolactin (PRL) secretion in late gestation, as well as possible relationships between LH and progesterone secretion. Ten sows of mixed parity were sampled via indwelling jugular vein catheters for two periods of 12 h (0600–1800 h) on Days 107 and 108 of gestation. In a repeat measures design, all sows received naloxone on either the first or the second day of sampling at an initial dose of 2.0 mg/kg BW 6 h after sampling began, followed by two further injections of 1.0 mg/kg at hourly intervals, and acted as controls on the alternate day of sampling. Plasma LH, PRL, and progesterone concentrations were determined by RIA. For statistical analysis, each 12-h sampling block was split into 6-h pre- and posttreatment periods, designated as Periods 1 and 2 on control days and Periods 3 and 4 on naloxone days. There was a significant period x day interaction for LH (p < 0.03) and PRL (p < 0.015). Naloxone elevated LH concentrations whether compared across days (Period 4 vs. 2; p = 0.003) or within days (Period 4 vs. 3; p = 0.007) and decreased PRL concentration in the within-day comparison (Period 4 vs. 3; p = 0.0067). The EOP therefore modulate LH and PRL secretion during late gestation in the sow. A daily rhythm of PRL secretion was also detected. The data were also consistent with the existence of a luteotropic complex that supports progesterone secretion at this stage of gestation.
The objectives of the present study were 1) to study potential effects of previous nutritional treatment on developmental competence of early fertilized oocytes in vitro; 2) to study responses to insulin treatment during the period of feed restriction in the late luteal phase which has deleterious effects on subsequent fertility; and 3) to establish the metabolic and endocrine status of gilts during treatment and the subsequent periestrous period. Nineteen trios of littermate gilts were subjected to feed restriction during the first (RH) or second (HR) week of the estrous cycle. A second group of HR gilts received injections of long-acting insulin during their period of feed restriction (HR+I). Intensive sampling was performed in a subgroup of 23 animals on d 15 and 16 of the cycle for analyses of endocrine (gonadotropins and steroid hormones) and metabolic (insulin, IGF-I, leptin, total triiodothyronine [T3], and free T3) variables. Gilts were checked for estrus every 6 h, and time of ovulation was monitored by transcutaneous ultrasonography. Surgeries were performed 12 to 20 h after ovulation, and the early-fertilized oocytes recovered were cultured in vitro under standardized conditions. There was no treatment effect on the developmental competence of fertilized oocytes in vitro; however, ovulation rate was increased in HR+I gilts. No effect of treatment was observed on plasma leptin and IGF-I concentrations on d 15 and 16. However, HR+I gilts had higher (P < 0.05) postprandial insulin and lower (P < 0.05) postprandial total and free T3 on d 15. Plasma concentrations of LH, FSH, and progesterone on d 15 and 16 and plasma estradiol concentrations on d 16 were not affected by previous nutritional or insulin treatment. In the periestrous period, plasma concentrations of LH, FSH, and estradiol were higher (P < 0.05) in RH and HR+I, and the rise in plasma progesterone after the LH surge was lower (P < 0.05), than in HR gilts. No effect of treatment was observed on plasma concentrations of metabolic hormones, except on plasma leptin concentrations, which were higher (P < 0.05) at the time of the LH surge in RH gilts. These results suggest that feed restriction during the late luteal phase may have deleterious effects on ovarian function in the periestrous period, which may be counteracted by insulin.
The effect of the timing of nutritional changes during the immediate period after mating on early embryonal survival and of progesterone as a potential mediator of such changes was studied. A total of 82 gilts were initially fed 2.5 kg·gilt−1·d−1 for one estrous cycle before they were inseminated at 16 and 24 h after the onset of estrus (d 0) using fresh, pooled semen. After AI, gilts were randomly allocated to one of the three feeding regimens, normal NRC allowance of 1.5 × maintenance per day from d 1 (Group N1) or d 3 (Group N3) or an allowance of 2 × maintenance from d 1 (Group H1). All gilts were fed on an individual basis. Single blood samples were collected 72 h after first detection of standing estrus. From d 15 onward, all gilts were fed 1.8 kg/d until they were slaughtered on d 28 ± 3. Total and viable embryonal survival were affected by dietary treatment (P = .044 and .027, respectively), and viable embryonal survival in group N1 was greater than in group H1 (84.7 ± 4.5 vs 64.5 ± 7.6%; P < .05). Plasma progesterone was greater in group N1 than in groups N3 and H1 (10.5 ± 1.0 vs 3.7 ± .8 and 4.5 ± .7 ng/mL, respectively; P < .05). The timing of the change in feed allowance after mating is therefore crucial for demonstrating effects of nutrition on embryonal survival in gilts, and progesterone may mediate these effects.
Summary. Prepubertal gilts, having undergone a 7-day period of feed restriction to a maintenance ration, were allocated to one of 4 treatments; restricted feeding at 09:00 and 17:00 h for an 8th day both with (Group RN) and without (Group R) administration of the opioid antagonist naloxone hydrochloride (1 mg·kg−1 at 09:30 h followed by 0·5 mg·kg−1 at hourly intervals for 7 h), or feed to appetite with (Group ALN) and without (Group AL) naloxone administration. Gilts were bled at 10-min intervals on Day 8 from morning to evening feed and plasma LH, FSH and prolactin concentrations were measured by radioimmunoassay. Compared with Group R gilts, Group AL gilts exhibited significantly (P ⩽ 0·05) higher mean and maximum LH concentrations and pulsatility, lower prolactin concentrations (P < 0·05) but no significant difference in FSH secretion. Naloxone significantly depressed the increase in LH after re-feeding (Group ALN) (P < 0·05). Once again there were no significant effects on FSH secretion. Naloxone also significantly depressed prolactin secretion in feed-restricted gilts (P < 0·05). These results confirm that re-feeding of feed-restricted prepubertal gilts stimulates an immediate increase in LH secretion and that this elevation is not mediated via a suppression of inhibitory endogenous opioidergic tone. Rather, naloxone treatment appeared to expose a latent inhibition of LH secretion. The control of LH secretion is distinct from that of FSH in this model. Keywords: prepubertal gilt; realimentation; gonadotrophin; naloxone
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