Prolactin-mediated cellular interactions in the thymus

Diurnal changes in plasma prolactin during the last one third of pregnancy in the baboon

Previous studies in our laboratory revealed that daily plasma prolactin (Prl) levels were higher in the evening than in the morning in the pregnant baboon suggesting a diurnal variation. The goal of this study was to examine in more detail the diurnal alterations in plasma Prl levels. A tethered pregnant baboon model was utilized for these studies. Hourly venous blood samples were taken from 0700 to 2400 hr (n=10) or until 0700 hr the following day (n=5). The studies were performed at various days of pregnancy from day 135 until delivery. Plasma samples were analyzed for Prl by radioimmunoassay. A surge in plasma Prl was detected, starting around 1500 to 1600 hr and lasting for 3 to 5 hr. The surge occurred before the lights went off in the colony (1800 hr). Baseline Prl levels were higher in animals < 15 days before delivery compared to those > 15 days before delivery (P < 0.05). In contrast, no differences were found in the average peak Prl values between these two groups of animals. In summary, in the pregnant baboon during the last one-third of pregnancy plasma Prl surges, beginning around 1500 to 1600 hr and lasting for 3 to 5 hr. Less than 15 days before delivery the mean baseline Prl levels are higher compared to animals greater than 15 days before delivery.

Interdependence of the endocrine and immune systems

The cross-talk involving the endocrine and immune systems is now largely established. These systems actually use similar ligands and receptors to establish a physiological intra- and inter-system communication circuitry, which apparently plays a relevant role in homeostasis (reviewed in Blalock, 1992). Accordingly, classical hormones such as prolactin (PRL), growth hormone (GH) and even glucocorticoids (GC) can be produced by cells of the immune system, whereas a variety of cytokines, originally described as being produced by cells of the immune system, are synthesized and released by a variety of endocrine glands and nervous tissue. Moreover, specific receptors for such distinct molecular families can be detected in both the immune and endocrine systems.