Acute shifts in relaxin, progesterone, prolactin, and growth hormone secretion in Chinese Meishan gilts during late pregnancy and after hysterectomy.

Abstract

Pregnant and hysterectomized Chinese Meishan gilts were used to investigate mechanisms regulating the production and secretion of relaxin, progesterone, prolactin (PRL), and growth hormone (GH) during different reproductive states. Gilts were bred to Meishan boars on the 1st d of the second observed estrus, and unmated gilts were hysterectomized on d 8 (estrus = d 0). Blood samples (10 mL) were collected twice daily (0800 and 2000) from d 9 to 120 and every 20 min within a 3-h period on d 112 to 116. Relaxin plasma concentrations were consistently greater in hysterectomized than in pregnant (6 vs 2 ng/mL, P < .05) gilts on d 99 to 109. The surge relaxin release on d 114 was greater in pregnant (66 ng/mL) than in hysterectomized gilts (34 ng/mL, P < .05). Thereafter, relaxin remained consistently increased (12 ng/mL) in hysterectomized gilts, whereas it was basal (< .5 ng/mL) during lactation. Progesterone concentrations decreased by half from d 109 to 115 and remained at 16 ng/mL through d 120 in hysterectomized pigs, whereas in pregnant pigs progesterone became basal after parturition. Prolactin in hysterectomized gilts remained at 4 ng/mL throughout the study period, whereas in pregnant gilts PRL increased steadily from 16 ng/mL on d 99 to 39 ng/mL at parturition and remained increased during lactation. Growth hormone concentrations were similar in hysterectomized and pregnant gilts from d 99 to 114; however, GH concentrations were consistently greater (P < .05) in lactating than in hysterectomized gilts (2.6 vs 1.0 ng/mL, respectively). These results indicate that PRL and GH secretions differ in pregnant and hysterectomized pigs because of the physiological changes necessitated by the onset of lactation.

Hormonal, behavioural and performance characteristics of Meishan sows during pregnancy and lactation

“…Concentrations of prolactin in peripheral plasma of Meishan gilts increased steadily from 16 ± 0.8 ng mL -1 on day 99 of gestation to 39 ± 10 ng mL -1 at parturition (day 114) and there were occasional episodes of pulsatile release. Relaxin and prolactin followed similar secretory patterns, yet the relaxin prepartum surge occurred before the surge in prolactin release (Dlamini et al 1995). This is consistent with the finding that the periparturient relaxin surge in swine may cause the prolactin surge before delivery (Li et al 1993).…”

“…This is consistent with the finding that the periparturient relaxin surge in swine may cause the prolactin surge before delivery (Li et al 1993). From day 112 until parturition there were episodic releases of growth hormone but no consistent profiles were detected, mean values oscillated around 0.5 ng mL -1 and went up to 1.2 ng mL -1 (Dlamini et al 1995). Meunier-Salaün et al (1991) found that peripartal concentrations of cortisol and prolactin were not affected by breed, while progesterone values were significantly greater in Meishan than Large White sows from 12 h before to 48 h after parturition.…”

“…Furthermore, profiles of progesterone concentrations during late pregnancy were similar in both breeds. It was therefore suggested that a common mechanism controls the initiation of processes that lead to parturition in these two breeds with different reproductive potential (Dlamini et al 1995). Profiles of relaxin from day 112 of gestation onward in Meishan gilts showed no evidence of consistent episodic release and, once again, patterns were similar to those reported in gilts from European breeds (Felder et al 1986).…”

“…There was a gradual increase in relaxin beginning on day 111 of pregnancy leading to a sharp increase on days 112 to 114, with a peak value of 66 ± 10.9 ng mL -1 occurring on day 114. It was stipulated that, as seen in gilts from European breeds, ovarian secretion of progesterone and relaxin in pregnant Meishan gilts is controlled by aging corpora lutea (Dlamini et al 1995). Concentrations of prolactin in peripheral plasma of Meishan gilts increased steadily from 16 ± 0.8 ng mL -1 on day 99 of gestation to 39 ± 10 ng mL -1 at parturition (day 114) and there were occasional episodes of pulsatile release.…”

“…Dlamini et al (1995) investigated mechanisms regulating the production and secretion of relaxin, progesterone, prolactin and growth hormone, as of day 90 of gestation. As seen in gilts from European breeds (Felder et al 1986), there was a marked decrease in progesterone a few days before parturition.…”