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  • Author: R. R. Kraeling x
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R. R. KRAELING and B. J. DAVIS

Summary.

Pregnant crossbred gilts were hypophysectomized or subjected to sham hypophysectomy at 70, 80 or 90 days of gestation. Eleven of twelve gilts subjected to the sham operation maintained pregnancy to term and farrowed live pigs. One gilt subjected to the sham operation at 80 days aborted approximately 48 hr after surgery. All hypophysectomized gilts aborted approximately 60 hr after surgery. These data indicate that the placenta of the pig failed to secrete progestagens or a luteotrophic substance which would maintain pregnancy and that the pig requires the presence of the pituitary through to at least Day 90 of gestation for the maintenance of pregnancy.

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J. D. Armstrong, R. R. Kraeling and J. H. Britt

Summary. Sows (N = 16) were infused intravenously for 8 h with saline or naloxone (200 mg/h) or their litters were transiently weaned for 8 h. Before infusion, 200 mg naloxone were administered to elevate quickly concentrations of naloxone. Blood samples were collected from sows at 15 min intervals for 24 h, beginning 8 h before and continuing until 8 h after imposition of treatments during the middle 8-h segment. Frequency of episodic release of LH and concentrations of prolactin were similar before, during and after infusion of saline. Average concentration of LH was greater during the last than during the middle 8-h segment when sows were given saline. Frequency of episodic release of LH increased and concentrations of prolactin decreased during infusion of naloxone or transient weaning; however, average concentration of LH increased during transient weaning, but not during infusion of naloxone. After transient weaning or infusion of naloxone, frequency of release of LH decreased, returning to pretreatment values in sows infused with naloxone but remaining above pretreatment values in sows subjected to transient weaning. At the resumption of suckling by litters in sows subjected to transient weaning, prolactin increased to levels not different from those observed during the 8-h pretreatment segment. Prolactin did not increase until 4–5 h after cessation of naloxone infusion. We conclude that continuous infusion of naloxone altered secretory patterns of LH and prolactin. Collectively these results provide evidence that the immediate effects of weaning on LH and prolactin in sows are mediated in part through a mechanism involving endogenous opioid peptides.

Keywords: LH; endogenous opioid peptides; naloxone; lactation; prolactin

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K. H. Young, R. R. Kraeling and F. W. Bazer

Summary. Hypoprolactinaemia was induced by bromocriptine (CB154; 100 mg/day) which decreased circulating prolactin by 40% (P < 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 < 0·02) and total recoverable Ca2+ Na +, K+ and Cl (P < 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/12h) increased (P < 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 > 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 < 0·05) for oestradiol-treated gilts, but effects of prolactin were not significant. Total recoverable glucose (P < 0·01), PGF-2α (P < 0·02), uteroferrin (P < 0·01) and specific activity of uteroferrin (P < 0·001) were increased by prolactin and oestradiol, but not oestradiol alone. Calcium (P < 0·05), chloride (P < 0·05) and potassium (P < 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.

Keywords: prolactin; endometrium; secretion; pig; pregnancy

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C. A. Pinkert, G. B. Rampacek and R. R. Kraeling

Summary. 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 < 0·01) was detected for serum prolactin concentrations. A preovulatory oestrogen surge occurred in all gilts but was of lesser magnitude (P < 0·01) and duration (P < 0·05) in the prepubertal gilts without prolactin and LH surges compared to mature gilts and of lesser magnitude (P < 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 < 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. The temporal relationships amongst serum oestrogen, prolactin and LH concentrations during the perioestrous period were dramatically different in prepubertal gilts induced to ovulate and mature gilts. Such differences may contribute to early pregnancy failure in the prepubertal gilt.

Keywords: prolactin; oestrogen; LH; prepubertal; pigs

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C. R. Barb, J. B. Barrett, J. T. Wright, R. R. Kraeling and G. B. Rampacek

Summary. The effects of naloxone and β-endorphin on LH secretion by pig pituitary cells were studied in primary cultures. On Day 4 of culture, cells (105 seeded/well) were challenged with 10−9, 10−8 or 10−7 m gonadotrophin-releasing hormone (GnRH), 10−10, 10−9, 10−8 or 10−7 m-β-endorphin or 10−6 m-naloxone individually or in combinations. Secreted LH was measured at 4 h and 24 h after treatment and cellular content of LH was measured after 24 h. Basal LH secretion (control) was 23·5 ± 7·6 and 36·9 ± 10·3 ng/well at 4 h and 24 h, respectively. Relative to control at 4 h, 10−9, 10−8 or 10−7 m-GnRH stimulated (P < 0·05) LH secretion 140%, 210% and 250%, respectively. At 24 h, LH secretion was increased (P < 0·05) by GnRH compared to control, but the does–response to GnRH was absent. Naloxone increased (P < 0·01) LH secretion 166 ± 13% at 4 h and 141 ± 13% (P < 0·06) at 24 h. Secretion of LH after simultaneous addition of 10−8 m-GnRH plus naloxone was greater (P < 0·01) than after GnRH alone at 4 h but not at 24 h. β-Endorphin at 10−10, 10−9, 10−8 or 10−7 m failed to alter basal LH secretion at 4 h but decreased secretion at 24 h, while cellular LH content was similar to control at 24 h. LH secretion after simultaneous addition of 10−7 m-GnRH and 10−7 m-β-endorphin was less (P < 0·01) than after GnRH at 4 h but not at 24 h, while 10−10 m-β-endorphin plus 10−9 m-GnRH failed to suppress LH secretion, compared to GnRH alone. These results indicate that endogenous opioids may directly modulate LH secretion at the level of the pituitary.

Keywords: opioid; LH; pituitary; pig

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C. R. Barb, R. R. Kraeling, G. B. Rampacek, E. S. Fonda and T. E. Kiser

Summary. Treatment with ACTH (100 i.u.) or hydrocortisone acetate (250 mg) twice daily for 12 days to increase cortisol concentrations blocked ovulation in all gilts. The preovulatory surge of LH was also blocked in the treated gilts. Oestrous cycle length and number of days in oestrus were similar for all treatments except that in one of the 2 experiments ACTH suppressed oestrus in 4 of the 5 gilts treated.

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C Richard Barb, Robert R Kraeling, George B Rampacek and Gary J Hausman

Two experiments (EXP) were conducted in ovariectomized prepubertal gilts to test the hypothesis that neuropeptide Y (NPY) stimulates appetite and modulates LH and GH secretion, and that leptin modifies such acute effects of NPY on feeding behavior and LH and GH secretion. In EXP I, gilts received intracerebroventricular (ICV) injections of 0.9% saline (saline; n=6), or 10 μg (n=7), 50 μg (n=5) or 100 μg (n=7) NPY in saline and blood samples were collected. In EXP II, gilts received ICV injections of S (n=4), or 50 μg leptin (n=4), or 100 μg NPY (n=4) or 100 μg NPY +50 μg leptin (n=4) in saline, and feed intake was measured at 4, 20 and 44 h after feed presentation and blood samples collected. In EXP I, NPY suppressed LH secretion and the 100 μg dose stimulated GH secretion. In EXP II, NPY reversed the inhibitory effect of leptin on feed intake and suppressed LH secretion, but serum GH concentrations were unaffected. These results support the hypothesis that NPY modulates feed intake, and LH and GH secretion and may serve as a neural link between metabolic state and the reproductive and growth axis in the pig.

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L. S. Leshin, S. M. P. Raj, C. K. Smith, S. C. M. Kwok, R. R. Kraeling and W. I. Li

Pig seminal proteins PSP-I and PSP-II are major protein components of boars' ejaculate and are present as heterodimers (PSP-dimer) in seminal plasma. These proteins were examined for their ability to modulate pig lymphocyte activity in vitro in mitogen-induced lymphocyte proliferation assays and in one-way mixed lymphocyte reactions. Pig lymphocytes were cultured with phytohaemagglutinin, concanavalin A, or pokeweed mitogen (PWM) in the presence or absence of pig seminal proteins and the amount of cellular [3H]thymidine was used as an indication of proliferation. In the absence of mitogens, none of the three pig seminal proteins affected lymphocyte proliferation suggesting that these proteins are not antigenic or mitogenic. PSP-dimer enhanced lymphocyte proliferation induced by PWM (156–227%, P < 0.05) in a concentration-dependent manner, but had no effect on phytohaemagglutinin- or concanavalin A-induced proliferation. PSP-I enhanced (127–185%, P < 0.05) phytohaemagglutinin-induced proliferation. PSP-II augmented (130–240%, P < 0.05) lymphocyte proliferation induced by concanavalin A and PWM. Lymphocytes from gilts were significantly more responsive to concanavalin A- and PWM-induced lymphocyte proliferation in the presence of PSP-I compared with boars (concanavalin A: gilts 131%, boars 91%; PWM: gilts 188%, boars 134%; P < 0.05). In the mixed lymphocyte reaction, pretreating stimulating cells with increasing concentrations of PSP-I or PSP-II elicited a 400% concentration-dependent increase (P <0.01) in lymphocyte proliferation. The abundance of pig seminal proteins in boar seminal plasma, their ability to enhance lymphocyte proliferation, and their previously reported ability to bind to lymphocytes suggest that these proteins are immunostimulatory and supports the hypothesis that they modulate uterine immune activity to ensure reproductive success.