Relationships among Prolactin Binding, Prolactin Concentrations in Plasma and Metabolic Activity of the Porcine Mammary Gland

Abstract

The current studies were designed to investigate relationships among prolactin (PRL) binding, PRL concentrations in plasma and metabolic activity of porcine mammary glands. Preliminary studies revealed specific high-affinity binding of oPRL to porcine mammary gland. Conditions for optimal specific binding were similar to those observed for other species. To address the main objectives of the study, four mammary biopsies and blood samples were obtained from each of four gilts during lactogenesis and lactation (d-11, 4, 21 and 42 of lactation) to measure in vitro rates of metabolic activity, PRL binding to mammary membranes and PRL concentrations in plasma. Metabolic activity, as measured by oxidation of glucose or acetate to CO2 and incorporation into lipid, was low during pregnancy, increased two- to five-fold on d 4, and then paralleled the lactation curve for sows. There were highly significant positive correlations between PRL binding and all measures of mammary metabolism when data from pregnancy and lactation were utilized. Coefficients were positive but generally not statistically significant when lactation data only were utilized. During lactation, significant negative correlations were observed between concentrations of PRL in plasma and PRL binding and between PRL in plasma and mammary metabolic rate. These data provide evidence that binding of PRL to its receptor is an important effector of milk production in sows. Furthermore, oPRL is a suitable ligand to quantify PRL binding to porcine mammary tissue.

Tissue-specific regulation of porcine prolactin receptor expression by estrogen, progesterone, and prolactin

“…The increase in pPRLR levels occurs prior to the peak of PRL in serum at parturition (DeHoff et al 1986, Plaut et al 1989, Farmer et al 2000, and likely prepares the mammary gland for lactogenesis. Within the porcine endometrium, an increase in pPRLR-LF mRNA levels during gestation mirrors the increase in pPRLR-LF mRNA expression in the ovine endometrium (Stewart et al 2000).…”

“…Conversely, administering porcine pPRL to lactating sows does not increase nursing pig growth or mammary gland development, probably because PRL receptors (PRLR) in the mammary gland are ligand-saturated (Farmer et al 1999). These results suggest that PRLR abundance (as a determinant of receptor site availability) may be a major limiting factor for responsiveness of the mammary gland to PRL during lactation in pigs (Plaut et al 1989).…”

“…The LF is the only PRLR isoform that has been identified in pigs to date. As in other species, the pPRLR is expressed in various tissues including the mammary gland from nulliparous (Trott et al 2007), pregnant (Plaut et al 1989, Young et al 1990, and lactating females (Sakai et al 1985, Berthon et al 1987, liver, kidney (Trott et al 2007), ovary (Bramley & Menzies 1987, Slomczynska et al 2001, uterus (Young & Bazer 1989), adrenal cortex (Klemcke et al 1989), and brain (Muccioli et al 1988). However, the factors that regulate pPRLR expression have not been assessed.…”

Endocrinology and mammary development of lactating Genex-Meishan and Large White sows

“…It was immediately frozen in liquid nitrogen and stored at -80°C until used for measurements of number and affinity of PRL receptors. The methodology used for membrane preparation was as described by Plaut et al (1989), with a few modifications (Farmer et al 1999). Prolactin binding studies were also done essentially as described by Plaut et al (1989), but we used 200 ng of unlabelled ovine PRL per tube to calculate nonspecific binding.…”

“…The methodology used for membrane preparation was as described by Plaut et al (1989), with a few modifications (Farmer et al 1999). Prolactin binding studies were also done essentially as described by Plaut et al (1989), but we used 200 ng of unlabelled ovine PRL per tube to calculate nonspecific binding. In order to calculate receptor affinity, we used unlabelled ovine PRL at concentrations varying from 0.008 to 0.5 ng per tube.…”