Cyclic Gilts Research Articles

Effect of dose and route of administration of thyroid releasing hormone (TRH) on the concentration of prolactin (PRL) and thyroxine (T 4) in cyclic gilts

Our objective was to examine the ability of thyroid releasing hormone (TRH) to stimulate not only the release of the thyroid hormones, but also prolactin (PRL) in the female pig. An experiment was conducted to determine the effect of dose and route of administration of TRH on the concentration of PRL and thyroxine (T 4) in cyclic gilts. Six gilts were injected with 0, 5, 25, 125, and 625 μg TRH and fed 0, .5, 2.5, 12.5 and 62.5 mg TRH. Gilts received TRH once daily. During the 10-day treatment period, route of TRH administration alternated between i.v. injection and feeding. The dose of TRH progressed from the lowest to the highest. Blood samples were taken prior to TRH injection and thereafter at 15-min intervals for 3 hr. Sampling continued for an additional 3 hr at 30-min intervals when TRH was fed. Concentrations of PRL and T 4 were determined by radioimmunoassay. Intravenous injection of gilts with 125 and 625 μg TRH resulted in an increase in PRL from 0 to 15 min (P<.05). All doses of TRH given i.v. elevated T 4 over a 2-hr period (P<.01). TRH failed to increase PRL when TRH was fed (P>.5). The feeding of 62.5 mg TRH elevated T 4 from 0 to 6 hr (P <.01). Thus, TRH injection increased PRL rapidly and T 4 gradually. When TRH was fed, only a gradual elevation in T 4 was observed. We conclude that TRH can elicit the release of both PRL and T 4 in the cyclic gilt, but magitude and duration of the PRL and T 4 response depends on the dose and route of TRH administration.

Differences in follicular morphology, steroidogenesis and oocyte maturation in naturally cyclic and PMSG/hCG-treated prepubertal gilts

Ovaries were obtained from naturally cyclic pigs on Days 16-17, 18, 19, 20 and 21 of the oestrous cycle and on the basis of observed follicular characteristics were assigned as representative of the early (Group 1), mid- (Groups 2 and 3) or late (after LH; Group 4) follicular phase. Follicular development in cyclic gilts was compared with that in ovaries obtained from late prepubertal gilts 36 (Group 5) or 72 (Group 6) h after treatment with 750 i.u. PMSG alone, or with a combination of 500 i.u. hCG 72 h after PMSG and slaughter 30-40 h later (Group 7). After dissection of all follicles greater than 2 mm diameter, follicular diameter, follicular fluid volume, follicular fluid concentrations of progesterone, oestradiol and testosterone, and the stage of oocyte maturation were determined. Combined PMSG/hCG treatment of immature gilts resulted in a pattern of follicular development different from that in naturally cyclic gilts during the follicular phase. Overall exogenous gonadotrophin treatment also increased (P less than 0.001) the variability in follicular diameter and fluid volume. Comparisons between appropriate groups also established differences in the variability of both morphological (diameter and volume, Group 1 vs Group 5; P less than 0.05) and biochemical development (follicular fluid oestradiol, Group 3 vs Group 6 and Group 4 vs Group 7; both P less than 0.05). Such differences in both morphological and biochemical characteristics between cyclic and PMSG/hCG-treated gilts were particularly evident in the population of larger (greater than 6 mm) follicles. These results indicate that the pattern of follicular development in naturally cyclic and in PMSG/hCG-treated gilts is dissimilar and suggests that the ovaries of gonadotrophin-treated prepubertal gilts are functionally different from the ovaries of mature females.

Evidence for steroid control of a putative angiogenic factor in the porcine uterus

The formation of new capillaries, both in extraembryonic membranes and in the maternal endometrium, is an essential prerequisite for appropriate feto-maternal relationships throughout pregnancy. At present there is no indication of the nature of the uterine angiogenic stimulus. In-vitro, degradation products of hyaluronic acid, following its catalysis by hyaluronidase, have been shown to have angiogenic properties. In the current study, levels of hyaluronic acid in endometrial tissues and of hyaluronidase and hyaluronic acid in uterine flushings were measured during the oestrous cycle and early pregnancy. The concentration of both hyaluronic acid and hyaluronidase in uterine flushings followed the growth and regression of the corpus luteum, in that basal levels detected on days 0 and 6 increased to peak concentrations on days 12 and 15. By day 18, levels of both hyaluronidase and hyaluronic acid had decreased in cyclic gilts, but remained increased in pregnant pigs. Tissue concentrations of hyaluronic acid were not affected by pregnancy or by the day of the oestrous cycle. In a subsequent experiment, four groups of gilts were ovariectomized on day 4 and thereafter received daily injections of corn oil, progesterone, oestrogen or a combination of oestrogen and progesterone. Hyaluronidase was undetectable in uterine flushings collected on day 15 from corn oil- and oestrogen-treated gilts, but present in similar amounts in uterine flushings from gilts treated with progesterone and progesterone plus oestrogen. Similarly, uterine fluid concentrations of hyaluronic acid were increased in progesterone- and progesterone plus oestrogen-treated gilts, but not in corn oil- or oestrogen-treated pigs. Tissue concentrations of hyaluronic acid were unaffected by steroid treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of altrenogest on litter size in primiparous sows

Aitrenogest (17 α -allyl-17-hydroxyestra-4,9,11-trien-3-one; Regumate Porcine; Hoechst Animal Health) is a synthetic progestagen which has been used to control and synchronise the ovarian cycle particularly in cyclic gilts. However progestagens have also been used in various species to induce and synchronise the first ovulation post partum. The present study was undertaken to determine the effect of altrenogest treatment on the reproductive performance of primiparous sows.

Corpus luteum function in the pig: progesterone profiles of cyclic and pregnant gilts.

Progesterone profiles of 7 cycling gilts and those of 6 gilts inseminated on day 1 (1 day after the onset of oestrus) were studied. The results showed that plasma progesterone concentration in the inseminated group was higher (P

Onset of secretion of proteins with antiviral activity by pig conceptuses

In Exp. 1, antiviral activity was detected in Day-15 pregnant uterine flushings (6222 +/- 2167 units/ml) and in conceptus culture medium collected at 0, 1, 2, 4, 8, 16, 24, 32, 40, and 48 h (95, 375, 650, 1216, 1600, 2100, 2017, 2083, 3500 and 5000 units/ml, respectively; R2 = 0.81, P less than 0.01; y = 190.0 + 252.7x - 11.2x2 + 0.2x3. In Exp. 2, antiviral activity of Day-15 conceptus culture medium was reduced 99% after boiling for 20 min (P less than 0.01) and, after 18 h dialysis (6000-8000 Mr cut-off), 100% of the activity was in the retentate. In Exp. 3, antiviral activity was not detected in cultures of conceptuses from Days 10 and 11 and activity was maximal for Day 14 and Day 15 conceptuses (2100 and 2083 units/ml, respectively). Effects of day were best described by a quadratic regression equation (y = 17,652 - 3263x + 150x2; R2 = 0.55, P less than 0.01). In Exp. 4, changes in antiviral activity detected in uterine flushings from pregnant gilts on Days 8, 10, 11, 12, 14 and 15 (1.3, 0, 6.7, 63.3, 580 and 1663 units/ml, respectively) were described by the equation y = -20,743 + 6189x - 606x2 + 20x3 (R2 = 0.85, P less than 0.01). In Exp. 5, low antiviral activities (5-30 units/ml) were detected in all plasma samples collected from the uterine artery and uterine vein of pregnant and cyclic gilts, but values were not significantly influenced by pregnancy status, day or site of collection.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of conceptus and conceptus secretory products on uterine development in the pig

Pregnant gilts (n = 6) were subjected to surgery on Day 3 of pregnancy and uterine horns, within gilts, were assigned to either (1) ligation 15 cm below the uterotubal junction (REST) or (2) ligation proximal to the uterine body (NONREST). On Day 15 of pregnancy gilts were hysterectomized and length and weight of both uterine horns were recorded. NONREST uterine horns were longer (P less than .05) than those of REST, but weights were similar. Conceptuses from the REST uterine horns were retarded in development. Morphometric analysis of surface (SE) and glandular (GE) epithelial cells detected no effect of treatment on height, width, area, nuclear area or percentage of nucleus. Porcine conceptus secretory proteins (pCSP) were obtained from medium in which pig conceptuses, collected on Day 15 of pregnancy, were cultured for 30 h. Culture medium was pooled, dialysed and concentrated by Amicon ultrafiltration for intrauterine infusion. Serum proteins (SP) were obtained from blood collected from a Day 15 pregnant gilt and diluted for intrauterine infusion. Catheters were placed into both uterine horns or cyclic gilts (n = 8) on Day 10 of the oestrous cycle and uterine horns were ligated proximal to the uterine body. Gilts received either oestradiol valerate (E2) (5 mg) or corn oil (CO) on Days 11 and 12. On Days 12-14 each gilt received twice daily infusions of Day 15 pCSP in one uterine horn and SP in the other uterine horn.(ABSTRACT TRUNCATED AT 250 WORDS)

Active immunization of pigs against growth hormone-releasing factor: effect on concentrations of growth hormone and insulin-like growth factor 1.

Cyclic gilts (96 +/- 1 kg) were used to determine the effect of active immunization against growth hormone-releasing factor GRF(1-29)-NH2 on concentrations of growth hormone (GH) and insulin-like growth factor 1 (IGF-1). Gilts were immunized against GRF conjugated to human serum albumin (GRF-HSA, n = 5) or HSA alone at 180 d of age (wk 0). Booster doses were administered at wk 9 and 13. Seven days after the second booster (wk 14), blood samples were collected at 15-min intervals for 6 h before feeding and 30, 60, 120, 180 and 240 min after feeding. Eight days after the second booster, all gilts were administered a GRF analog, [desNH2Tyr1,Ala15]-GRF(1-29)-NH2, followed by an opioid agonist, FK33-824. Blood samples were collected at 15-min intervals from -30 to 240 min after injection. Immunization against GRF-HSA resulted in antibody titers, expressed as dilution required to bind 50% of [125I]GRF, ranging from 1:11,000 to 1:60,000 (wk 11 and 14); binding was not detectable or was less than 50% at 1:100 in HSA gilts (P less than .05). Episodic release of GH was abolished by immunization against GRF-HSA (P less than .05). Mean GH was decreased (P less than .07), but basal GH concentrations were not altered (P greater than .15) by immunization against GRF-HSA. Serum concentrations of IGF-1 were similar at wk 0, but concentrations were lower in GRF-HSA than in HSA gilts (P less than .05) at wk 14.(ABSTRACT TRUNCATED AT 250 WORDS)

Spontaneous electromyographic activity throughout the cycle in the sow and its change by intrauterine oestrogen infusion during oestrus.

Two experiments were carried out to monitor influences on the uterine electromyographic activity (EMG) in cyclic gilts with chronic uterine EMG electrodes. In Exp. 1 the EMG was recorded continuously from Day -1 for 24 days and was evaluated for frequency, duration and amplitude. Progesterone and oestradiol in peripheral plasma were measured daily. As high amounts of oestrogens are characteristic for boar semen, in Exp. 2 the influence of seminal oestrogens on uterine contractions at Day 0 (first day of standing reflex) was investigated in gilts with chronic intrauterine catheters. They were infused with 10 ml saline (N = 4) or saline with physiological amounts of oestrogens (5 micrograms oestradiol + 2 micrograms oestrone + 4.5 micrograms oestrone sulphate; N = 4). Sham-treated gilts (infusion catheters, no infusion; N = 5) served as controls. The EMG was recorded for 2 h before and 9 h after infusion. In Exp. 1 the maximal amplitude (2040 +/- 98 microV) and duration (32 +/- 1.7 sec) but the lowest frequency (15.8 +/- 2.1 contractions/h) were found on Day 0. With decreasing oestrogen and increasing progesterone concentrations the frequency increased continuously until Day 5 (63.5 +/- 1.0 contractions/h) while the amplitude (183 +/- 13 microV) and duration (3.3 +/- 0.7 sec) decreased. During Days 6-13 the EMG activity was not detectable. The reverse pattern was found from the onset of luteolysis until the following Day 0. On Day 0 a significant correlation between oestradiol and the duration (r = 0.81; P less than 0.01; n = 10) but not the frequency was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in plasma gonadotropins, ovarian steroids and inhibin concentrations in gilts following progesterone treatment with implantable osmotic pumps

Endocrine changes in cyclic gilts (10 months old, n=5) were examined during and following the measured administration of progesterone with implantable osmotic pumps, commencing during the late luteal phase of a cycle. Exogenous progesterone delivered from the pumps (115 mg/day) maintained high plasma progesterone levels (> 10 ng/ml) that effectively suppressed follicular growth and prevented the gilts from returning into estrus. Thus, 7 days progesterone implantation resulted in an extension of the estrous cycle by about a week. Progesterone withdrawal initiated the increase of plasma inhibin as well as of estradiol and the decrease of plasma FSH. In four out of five treated gilts, the exception being one gilt that developed follicular cysts, the LH surge was observed 6.3±0.3 (s.e.m.) days after the removal of progesterone implants. The overall plasma inhibin profiles were inversely correlated with those of FSH: during follicular development, inhibin levels were high while plasma FSH remained low, then, after the LH surge, a decline of plasma inhibin preceded the secondary surge of FSH around the time of ovulation. The method herein described appears to be a useful tool for synchronizing the preovulatory endocrine events in gilts.

EFFECT OF THE STRESS OF INJECTIONS ON THE SERUM CONCENTRATION OF CORTISOL, PROLACTIN, AND GROWTH HORMONE IN GILTS AND LACTATING SOWS

Three experiments were conducted to determine the effect of subcutaneous injections of saline on serum concentrations of cortisol, prolactin and growth hormone in cycling gilts and lactating sows. In exp. 1, five crossbred cycling gilts were given one subcutaneous injection and blood was sampled during the preceding and following four hours. In exp. 2, blood samples were taken from six purebred lactating sows on a control day and on a day when they were injected with saline in a latin square design. Serum concentrations of cortisol, prolactin and growth hormone were monitored in exps. 1 and 2. In exp. 3, 11 purebred primiparous sows received subcutaneous injections twice daily from 5 to 25 d postpartum. Blood samples were collected for cortisol assay on days 5, 15 and 25. Serum cortisol concentrations increased significantly after saline injection in the three experiments, confirming that injections cause a stimulation of the hypothalamic-hypophyseal-adrenal axis in cycling gilts and lactating sows. When additional stressors such as handling and physical restraint were imposed prior to the injection, a release of prolactin and growth hormone was also observed in cycling gilts. The serum cortisol profiles of lactating sows repeatedly injected showed that their cortisol response to subcutaneous injections attenuated over days. Furthermore, these data indicate that the animals became readily acclimated to blood collection from a catheter within the first day of sampling. Key words: Cortisol, prolactin, growth hormone, stress, gilts, lactating sows

Effect of intraluteal estradiol-17β implants on weight and progesterone secretion of porcine corpora lutea

Estradiol-17β (E 2) decreases the effectiveness of prostaglandin F 2α (PGF 2α) to induce luteolysis in hysterectomized gilts, and E 2 locally increases corpus luteum (CL) weight in pigs, suggesting a direct luteotropic effect. This study examined the effect of intraluteal E 2 implants on utero-ovarian vein (UOV) progesterone (P 4), E 2, PGF 2α and CL weight in cyclic gilts. Eight gilts were laparotomized on day 11 (day 0 =first day of estrus), catheters were placed in both UOV, and gilts were then divided into two equal groups (E 2-treated and controls). Each CL on one ovary of E 2-treated gilts was injected with a quick-curing silastic implant containing E 2, and each CL on the contralateral ovary received a vehicle implant. Control gilts received bilateral vehicle implants. Blood was collected at 10-min intervals for 1 h beginning at 06.00 and 18.00 h from days 11 to 18. Gilts were subsequently ovariectomized on day 19. Corpora lutea were weighed, homogenized and assayed for P 4. UOV plasma was assayed for P 4, E 2 and PGF 2α by validated RIA. No side differences were observed in CL weight or UOV P 4 within groups. CL were maintained in E 2-treated, but not control gilts, as evidenced by CL weight (333±20 vs 154±12 mg), CL P 4 content (21.8±2.1 vs 0.3±0.1 μg) and CL P 4 concentration (65.7±5.5 vs 2.3±0.6 ng/mg), respectively. UOV P 4 values were similar between groups up to 18.00 h on day 15, declining from 346±122 ng/ml at 18.00 h on days 11 to 147±20 ng/ml on day 12, then remaining constant to 18.00 h on day 15. Thereafter, UOV P 4 in E 2-treated gilts returned progressively to day 11 values by 18.00 h on day 18 (364±97 ng/ml) while values of control gilts declined to low levels (5.4±0.6 ng/ml). In E 2-treated gilts, UOV plasma E 2 was elevated 13-fold ipsilateral, and 4-fold contralateral, to the E 2-treated ovary when compared with levels in control gilts. Further, uterine PGF 2α release was suppressed in E 2-treated when compared with control gilts. Although E 2 did not prevent the initial decline in UOV P 4 observed between days 11 and 15 in all gilts, reduced uterine PGF 2α release may have facilitated the progressive return in CL function observed in E 2-treated gilts.

Effect of porcine conceptus secretory proteins on interestrous interval and uterine secretion of prostaglandins.

Porcine conceptus secretory proteins (pCSP) were obtained from medium in which pig conceptuses, collected on Day 15 of pregnancy, were cultured for 30 h. Culture medium was pooled, dialyzed, and concentrated by Amicon ultrafiltration for intrauterine infusion. Serum proteins (SP) were obtained from blood collected from a Day 15 pregnant gilt and diluted for intrauterine infusion. Catheters were placed into both uterine horns and the inferior vena cava of cyclic (Day 8) gilts. Single blood samples were collected at 0800 h on Days 9, 10, and 11. On Day 11, all gilts received 1 mg estradiol-17 beta (E2) i.m. at 0800 h. Protein infusions commenced on Day 12 and continued through Day 15, twice daily at 0800 h and 2000 h. Protein infusions per uterine horn were (1) 4.0 mg pCSP + 4.0 mg SP (pCSP, 4 gilts) and (2) 8.0 mg SP (SP, 4 gilts). Blood samples were collected every 15 min on Days 12 through 17 between 0805 h and 1100 h. Single blood samples were collected at 0800 h after Day 17 until gilts exhibited estrus. Concentrations of prostaglandin (PG) E, 13,14-dihydro-15-keto-PGF2 alpha (PGFM), and progesterone (P4) were measured by specific radioimmunoassays. Interestrous intervals for pCSP-treated (18.2 days) and SP-treated (18.0 days) gilts were not different (SEM = 0.8 days) and temporal changes in concentrations of P4 in plasma did not differ between pCSP-treated (29.2 ng/ml) and SP-treated (31.2 ng/ml) gilts.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of prolactin on conceptus survival and uterine secretory activity in pigs

Hypoprolactinaemia was induced by bromocriptine (CB154; 100 mg/day) which decreased circulating prolactin by 40% (P less than 0.06), but did not affect conceptus survival at Day 25 when administered on Days 10-16 when compared to saline:ethanol-treated control gilts. Bromocriptine or vehicle was administered to cyclic gilts on Days 10-11, oestradiol valerate was injected on Day 11 and uterine flushings were collected on Day 12. Total recoverable protein and uteroferrin in uterine flushings were not affected by treatment. However, leucine aminopeptidase activity (P less than 0.02) and total recoverable Ca2+, Na+, K+ and Cl- (P less than 0.05) were decreased in uterine flushings of gilts that received bromocriptine, suggesting that hypoprolactinaemia decreased general secretory activity of the endometrial epithelium and modulated ionic changes, respectively, in the uterine environment of pigs. Subcutaneous administration of pig prolactin (1 mg/12 h) increased (P less than 0.001) serum prolactin 4.5-fold. The interaction between hyperprolactinaemia and progesterone, without oestrogen, on components of uterine flushings were determined using gilts that received progesterone (200 mg/day) and prolactin or saline on Days 4-14 after ovariectomy on Day 4. On Day 15, there were no differences (P greater than 0.05) in any of the uterine secretory components measured. Hyperprolactinaemia (1 mg pig prolactin on Days 6-11) enhanced overall uterine secretory response on Day 12 to oestradiol (5 mg) administered on Day 11 compared to gilts that received 1 ml saline on Days 6-11 of the oestrous cycle. Total recoverable protein and leucine aminopeptidase activity were greater (P less than 0.05) for oestradiol-treated gilts, but effects of prolactin were not significant. Total recoverable glucose (P less than 0.01), PGF-2 alpha (P less than 0.02), uteroferrin (P less than 0.01) and specific activity of uteroferrin (P less than 0.001) were increased by prolactin and oestradiol, but not oestradiol alone. Calcium (P less than 0.05), chloride (P less than 0.05) and potassium (P less than 0.01) were increased in response to oestradiol. These results indicate an interaction between oestradiol and prolactin, but not progesterone and prolactin, which enhances secretion of some products of the pig uterine endometrium.

Effect of in-vitro heat stress on prostaglandin and protein secretion by endometrium from pregnant and cyclic gilts at day 14 after oestrus.

Endometrium from cyclic (N = 4) and pregnant (N = 4) gilts at Day 14 after oestrus was placed into three bilateral perifusion devices which allow separate perifusion of luminal and myometrial sides. Perifused endometrium was subjected to 39 or 42 degrees C. Incorporation of [3H]leucine into secreted and tissue proteins by endometrial explants following incubation at 39 or 42 degrees C was examined using trichloroacetic acid (TCA) precipitation and one-dimensional SDS polyacrylamide gel electrophoresis. Secretion of PGF was greater from the myometrial side for cyclic gilts (endocrine orientation), but greater from the luminal side for pregnant gilts (exocrine orientation). Regardless of reproductive status or endometrial side, heat stress induced a rapid increase (P less than 0.01) in PGF secretion rates. However, PGF secretion in response to heat stress was greater (P less than 0.01) from the myometrial side and greater (P less than 0.01) for pregnant gilts. PGF secretion rates increased by 63% and 42% from the luminal side, and 40% and 156% from the myometrial side in response to heat stress for cyclic and pregnant gilts, respectively (status x treatment x side interaction; P less than 0.01). Heat stress did not alter incorporation of [3H]leucine into secreted proteins regardless of reproductive status, while incorporation into tissue proteins was decreased (P less than 0.05) by heat stress for pregnant gilts, but not altered for cyclic gilts. Heat stress, in vitro, redirects PGF secretion for endometria of pregnant gilts from an exocrine to an endocrine orientation where it would be available to effect luteolysis and compromise the establishment of pregnancy.

Autofluorescence of the porcine endometrium during early pregnancy.

Uteri recovered from cyclic gilts (n = 5) on Days 15-19 and pregnant animals (n = 34) on Days 13-40 were opened and examined under UV light. A line of greenish fluorescence was present in the mesometrial region in contact with embryonic membranes at Day 13. Small patches of reddish fluorescence subsequently appeared on the uterine mucosa near the embryonic disc, and these increased in intensity and size until they encompassed the entire area of contact between each conceptus and the endometrium, for lengths of about 20 cm, by Day 29. Fluorescence then diminished gradually and was almost totally absent by Day 40. Three additional gilts were unilaterally hysterectomized on Day 15 and treated with Evans blue dye 10 min before removal of the second uterine horn. Both horns were opened and compared under UV light, but no difference in the pattern of fluorescence could be detected. All fluorescence was associated with uterine rather than conceptus tissues. The occurrence of autofluorescence in uteri of pregnant pigs precludes use of Evans blue dye as an indicator of vascular permeability.

THE INFLUENCE OF EXOGENOUS GROWTH HORMONE ON OVULATION RATE IN GILTS

A total of 32 prepubertal gilts of Yorkshire and Landrace breeding were selected at 138 d and fed ad libitum a 16.2% crude protein diet formulated to provide 13.1 MJ DE kg−1. From selection until the end of second estrus, the gilts were exposed to a boar for 30 min d−1 to facilitate the detection of pubertal and second estrous periods. From 14 d after puberty, the gilts received daily injections of either porcine growth hormone at 90 μg kg−1 body weight (GH; n = 20) or vehicle (CT; n = 12) until 24 h after the onset of second estrus and were then killed 9 d later to determine ovulation rate. Gilts not displaying a second estrus by 24 day after puberty were considered anestrus and the injection regime was halted. Anestrous gilts were killed 30–32 d after puberty and their ovaries examined for the presence of corpora albicantia and the absence of corpora lutea. Blood samples were obtained from all gilts at 14, 17, and 20 d after puberty. There was no treatment effect on the duration of the estrous cycle (20.8 vs. 21.3 d for GH and CT, respectively), but while all CT gilts cycled normally, only 55% of the GH gilts had a second estrus (P &lt; 0.01). In those gilts having a second estrus, the daily injection of growth hormone increased ovulation rate (14.3 vs. 12.4 for GH and CT respectively; P &lt; 0.03). Serum type 1 insulin-like growth factor (IGF-1) concentrations were higher (P &lt; 0.001) in GH than in CT gilts, but there was no difference between cycling and anestrous GH gilts. We suggest that the effect of growth hormone on ovulation rate was mediated by increased secretion of IGF-1. The etiology of the high incidence of anestrus is, however, not known. Key words: Gilts, growth hormone, ovulation rate

Serum concentrations of prolactin, oestrogen and LH during the perioestrous period in prepubertal gilts induced to ovulate and mature gilts.

The temporal relationships of serum prolactin, oestrogen and LH concentrations during the perioestrous period were compared in prepubertal gilts induced to ovulate by PMSG and hCG and in mature gilts. In Exp. 1, 2 sustained prolactin surges, beginning 4 days and 1 day before the preovulatory LH surge, occurred in all mature gilts. A single preovulatory prolactin surge occurred in 3 prepubertal gilts, starting just before the preovulatory LH surge, but 4 prepubertal gilts had neither a prolactin nor an LH surge. A status (prepubertal or mature) versus time interaction (P less than 0.01) was detected for serum prolactin concentrations. A preovulatory oestrogen surge occurred in all gilts but was of lesser magnitude (P less than 0.01) and duration (P less than 0.05) in the prepubertal gilts without prolactin and LH surges compared to mature gilts and of lesser magnitude (P less than 0.01) compared to prepubertal gilts with prolactin and LH surges. The relative timing of the oestrogen surge in prepubertal gilts corresponded with that of mature gilts when adjusted to the LH surge (if present) but was delayed (P less than 0.01) in all prepubertal gilts if standardized to the hCG injection. In Exp. 2, mature gilts were examined to determine whether 2 perioestrous prolactin surges were characteristic of all cycling gilts. Of 9 gilts, 8 exhibited an initial prolactin surge 4-5 days before oestrus and 5/9 gilts exhibited a periovulatory prolactin surge. The presence of 2 perioestrous serum prolactin surges was not a requirement for subsequent pregnancy maintenance.(ABSTRACT TRUNCATED AT 250 WORDS)

Prostaglandin secretion by perifused porcine endometrium: Further evidence for an endocrine versus exocrine secretion of prostaglandins

Bilateral perifusion devices were utilized for measurement of prostaglandin secretion by luminal and myometrial surfaces of porcine endometrium. Tissues were collected from Days 10, 12 and 14 pregnant, Day 14 cyclic and Day 14 estrogen-induced pseudopregnant gilts. Each tissue was placed into duplicate perifusion devices and perifused with Krebs-Ringer Bicarbonate solution at 3 ml/10 min for 2 h, fractions collected every 10 min and oxytocin (1 IU/ml) perifused during fractions 6–10 to the luminal side of one chamber and to the myometrial side of the other chamber. Secretion rates of PGF were higher (P< 0.05) than PGE 2 for each status. Secretion rates of PGF and PGE 2 were higher (P< 0.01) from the luminal side for Day 12 pregnant, Day 14 pregnant and Day 14 pseudo-pregnant gilts, whereas secretion was higher from the myometrial side for Day 10 pregnant and Day 14 cyclic gilts. Oxytocin increased (P< 0.01) prostaglandin secretion from the luminal side regardless of reproductive status. Pregnancy at Day 12 and Day 14, as well as estrogen treatment, were associated with prostaglandin secretion in a luminal (exocrine) orientation versus a myometrial (endocrine) orientation for Day 14 cyclic and Day 10 pregnant gilts. These data indicate an estrogen associated switch between Days 10 and 12 of pregnancy from an endocrine to an exocrine secretion of prostaglandins.

Characterization of gonadotropic and ovarian steroid hormones during the periovulatory period in high ovulating select and control line gilts.

Cyclic gilts from Control (C, randomly selected, n = 11) and Relax Select (RS, nine generations of selection for increased ovulation rate followed by seven generations of relaxed or random selection, n = 9) lines of the University of Nebraska Gene Pool population (derived from 14 different breeds) were utilized to characterize differences in gonadotropic and ovarian steroid hormones during preovulatory and postovulatory phases of the estrous cycle. Blood samples were collected during four periods (0500, 1100, 1700 and 2300) daily beginning 2 d prior to anticipated estrus (d -2, d 18 of a 20-d estrous cycle), and continuing through d 4 postestrus (d 0 = 1st of standing estrus). Sampling within a period consisted of five blood samples at 15-min intervals. All plasma samples were analyzed for concentrations of follicle stimulating hormone (FSH) and luteinizing hormone (LH). Neither mean LH nor peak concentration of LH during the preovulatory surge differed between genetic lines (P greater than .10). Concentrations of FSH increased faster (line X period, P less than .05) and tended (P less than .1) to peak at a higher concentration in RS (.88 ng/ml) than in C (.54 ng/ml) gilts (P less than .05) during the 12 h preceding the FSH and LH preovulatory peaks. The second FSH surge began approximately 24 h after the preovulatory FSH peak. Peak FSH concentrations were observed at 42 h in both lines (1.46 vs 1.74 ng/ml for C and RS gilts, respectively). The higher FSH concentration in RS gilts established during the preovulatory surge was maintained through the second FSH surge (P less than .01). No line differences were detected in plasma concentrations of estradiol-17 beta and progesterone.