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  • Author: G. B. Rampacek x
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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.