Effect of Estrogen Administration on Endogenous and Luteinizing Hormone-Releasing-Hormone-Induced Luteinizing Hormone Secretion and Follicular Development in the Lactating Sow

BIOLOGY OF 44, REPRODUCTION 975-982 (1991) Effect of Estrogen Administration Hormone-Releasing-Hormone-Induced and Follicular Development F. DE RENSIS,3 AFRC MORAG Group Faculty G. HUNTER, on Hormones of Agricultural SHONA on Endogenous and Luteinizing Luteinizing Hormone Secretion in the Lactating Sow’ A. GRANT, and Farm Animal and Food Sciences, LE12 5RD United and R T. LANCASTER, G. R FOXCROFT2 Reproduction, University of Nottingham Sutton Bonington, Loughborough Kingdom The objectives endogenous of LH, 18 sows the follicular ovary. (5 on sows) (FFD) received 800 of LHRH UI and estradiol-l7( frequency inhibition treatment, #{247} E2 groups compared lactation to between in the secretion caused sow, by acute the chronic C and groups, inhibition elevation chronic any in plasma effects at the for periods pituitary levels LH [1-41. seems quarters are increase low in This inhibitory proportional suckled by the during lactation episodic W effect to the this concept, increase in early Suckling tuitary the piglets and LH response in LH secretion and late lactation. changes axis the to estradiol Accepted January Received September 15, the neural intensity assumed during decline. to the that such lactation as Consistent administration following sensitivity of the and a of from a NATO 2Correspondence: Fellowship G.R and Forestry, 310C T6G 2P5, Canada. tCurrent address: di Medicina does differences PRL not increase an acute and in FSH the LHRI-I and that during 2) inhibits secretion, of absence LHRH demonstrate and PRL late UI of the sensitivity hypothalamic-pi- both an F. De Veterinaria, from the Development Foxcroft, the Consiglio Department Agriculture/Forestry Rensis, Instituto via Celoria AFRC (UK), Corporation; inhibitory Nazionale della of Animal Building, di Fisiologia 10, 20123, the Rensis was Ricerche, Science, University e Biochimica Milano, (Canada), NSERC F. De the supof Ag- of Alberta, LH response [3] time led to the has been described in vitro [16-19]. positive feedback in sows treated with on Day 5 of lactation. to the effects of es- estradiol A better of weaning. Ed- lamic-hypophysial tive-feedback Veterinaria, Italy. 975 effects sow. in- benzoate response and W or fourth [20], also of the neuroendocrine patheffects of estrogens. lactation have been described and pituitary level [review, 15; 21]. between gonadotropin and proreproductive activity in the weaned proposal after weaning and therefore possessing ovarian may be insufficient ing-associated rise Italy. Faculty effect on LH release in vivo [9-15] and at both the hypothalamic A study of the relationship lactin (PRL) secretion and 1990. ported Facolta’ 3) no concentration In the in the suggests a gradual recovery ways mediating the stimulatory Actions of estradiol during secretion opment by grants monton, and greater data FSH UI however, to estradiol injection in terms of estrous behavior secretion when sows were treated during the third week of lactation, compared to the second week of administration feedback, was supported and the Alberta Pork Producers’ riculture modify subcutaneous a combination E2 groups; were These crease in LH levels on Day 35 but not of 1991. 25, work by levels, The sow ‘This not does There groups. received each LHRH trogen treatment also changes during lactation in the Elsaesser and Parvizi [10] found a small but significant on LH semammary LHRH increases with time after parturition [6]; however, Stevenson et a!. [7] and Rojanasthien et al. [8] reported similar LHRH FFE). and Group administered application. was from 2) considerable. + implant FFD 1) LHRH and a stimulatory in various species in the sow release after of suckling number of the suckling stimulus [5]. It is generally inhibitory effects of suckling decrease suckling frequency and milk production with and repeatedly dissected sows) the by measuring treatment; were PHI was and estradiol within E2 (4 sows) 3) and to gonadotropins. concentrations a consistent weaning cretion FSH, L1{RH development hypothalamic and INTRODUCTION with UI, follicles no of patterns taken assessed was largest Group Follicular both ten the of LHRH; in samples received + E2 (5 after of sampling estradiol 3) LHRH in the secretion. determined of the 1) injections development sows) period; Group immediately 0.05 < (FFE) for plasma group were folilcular C (4 sampling 4) modifies to exogenous PRL and treatment of UI (p between the LH1.H latter E2 groups nor a chronic and in the and 1) Group variability after FSH, lactation during pituitary concentration of sampling; <0.05) observed LH, treatments: 2 h throughout start treatment of the recovered, then estradiol-1713 of four h after (p estradiol sensitivity Plasma Between-animal implants. increased estradiol concentrations every 24 was fluid to one of LHRH of LH secretion LHR}I ovary ng the were Ovaries follicular and whether 2) to gonadotropin. allocated estradiol-l7 pulse investigate release; of lactation. randomly containing implants and were to (PRL) follicles 24-27 diameter Sows prolactin ovarian Days were study and of the responsiveness from this FSH, that the characteristics of LH may depend on follicular develthe extent of estradiol feedback at The authors suggested that in sows follicles in a less advanced state there plasma estradiol to augment the weanin LH or, conversely, that the hypothaaxis of some of estrogen sows “escaped” the earlier than others. nega- ABSTRACT 976 DE Therefore, two the hypotheses in late and lactation 3) of this research determine was whether to examine estradiol these treatment may 1) modify 2) aim RENSIS the release, modify pattern the of endogenous sensitivity injections of LHRI-1, act ovarian at the of the level gonadotropins growth. and LH, FSH, pituitary to increase to and exogenous sensitivity therefore, promote PRL El AL. LHRH + sured in all sows LH was vals) FSH and at 30-mm LHRH, E2, and of cava average and the weaned killed 18 primiparous herd (Landrace Ovarian METHODS weight average at the sows from x Large-White) 2 days before the the University of were used Sows start of sampling. The of the sows at surgery was 130 ± 4.2 kg, litter size was 9.8 ± 0.7 piglets. Sows were end of sampling (Day 27 of lactation) and 1 h. Blood samples were taken every h, beginning at Day 24 of lactation. at 3 000 rpm, and plasma was stored 15 mm (2.5 ml) for 72 Blood was centrifuged at 20#{176}C until analysis. - Treatments sows Sows were 1) Controls randomly (4 sows, 2) LHRH-trea (...truncated)