Temporal changes in steroids, prolactin and growth hormone in pregnant and pseudopregnant gilts during mammogenesis and lactogenesis

Abstract

Estrogen, progesterone and prolactin are involved in control of mammary growth in all species studied to date. The primary hormonal change temporally related to mammary development in swine is the estrogen rise which begins on day 60 of pregnancy. However, hormonal regulation of mammary development in swine is poorly understood. Plasma was obtained at 15-day intervals (days 15–112) throughout pregnancy, day of parturition and day 4 of lactation to determine relationships between hormonal profiles and mammary development in swine. Fetal plasma was also obtained from day 60 until parturition. Additional gilts were made pseudopregnant and sampled on days 60, 90 and 112. Plasma samples were assayed for estrogens, progesterone, prolactin and growth hormone. Maternal profiles of estrone- and estradiol-sulfate, increased to 2.6 and 0.6 ng/ml, repectively on day 30 of pregnancy, with return to basal concentrations by day 45. Periparturient concentrations of estrone and estradiol did reach 13 and 2.6 ng/ml, respectively. Free estrogen concentrations (estrone and estradiol) did not change significantly at day 30, but were elevated to 6 and 0.7 pg/ml at parturition. Progesterone concentration fluctuated only slightly from a mean concentration of 25 ng/ml until the preparturient decline, resulting in concentrations of <5 ng/ml through day 4 of lactation. Prolactin and growth hormone concentrations remained at basal values (13 and 12 ng/ml, respectively) until the periparturient rise to 68 and 28 ng/ml. Total fetal estrogen concentrations rose steadily throughout the sampling period; progesterone declined through day 105, but rose significantly by day 112 of gestation. Fetal prolactin concentration rose slowly throughout the sampling period to reach 12 ng/ml by day 105 of gestation. The profile for fetal growth hormone differed from that of other fetal hormones, in that concentrations were above maternal values for the entire sampling period, and the profile was best fitted by a second order curve with the peak at day 90 (> 150 ng/ml). With the exception of estrone, hormonal concentrations in estrogen-treated pseudopregnant gilts did not differ from pregnant counterparts, demonstrating that pseudopregnant gilts are an excellent in vivo model to study estrogen effects on mammary development in swine.