Relaxin and Progesterone Secretion as Affected by Luteinizing Hormone and Prolactin after Hysterectomy in the Pig

Plasma levels of relaxin and progesterone in hysterectomized and pregnant gilts were determined from days 100-120 to evaluate the effects of purified porcine (p) LH and pPRL on the secretory activity of the aging corpora lutea. Gilts were bred on the second observed estrus or were hysterectomized between 6-8 days after estrus (estrus = day 0) and were assigned randomly to one of three treatment groups; saline-treated control, im injections of pLH, and iv injections of pPRL from days 110–120. In control, pLH-treated, and pPRL-treated animals, average gestation lengths were 114 ± 0,8, 116 ± 1.9, and 115 ± 0.5 days (±SE), respectively. The relaxin level in mated gilts on day 100 was less than 2 ng/ml; it began to increase after day 110 and peaked in control animals on day 113 (66 ng/ml), whereas in pLH- and pPRL-treated animals, prepartum peak values were greater (P < 0.01) and occurred on days 113 (104 ng/ml) and 114 (117 ng/ml), respectively. Relaxin dropped to basal levels (<1 ng/ml) by day 115 in control...