Daily Patterns of Pituitary Prolactin Secretion and their Role in Regulating Maternal Serum Progesterone Concentrations Across Pregnancy in the Djungarian Hamster (Phodopus Campbelli)1

Abstract

Profiles of serum prolactin (PRL) and progesterone (P4) were determined in repeatedly (every 2 h) sampled female Djungarian hamsters (Phodopus campbelli) over a 24-h period on Days 3, 6, 9, 12, and 15 of the 18-day pregnancy. The first half of pregnancy was characterized by significant surges of PRL within a 2-h period around dawn (0500 h) and dusk (1900 h), with some females also showing a weak midday surge at 1300 h. By Day 9, dusk and midday surges were absent, but the dawn surge remained at its initial amplitude. On Day 12, no PRL surges were seen. Resumption of both the dusk and dawn PRL surges occurred on Day 15 of gestation. Considerable interindividual variability in the amplitude of PRL surges, the timing of PRL surges, and the number of surges per day was detected and would complicate any assessment of PRL levels based on single samples per female. Serum P4 concentrations were 8-10 ng.ml-1 before doubling on Day 15. A 3-day treatment of 50 and 300 micrograms bromocryptine (CB 154; on Days 13-15) effectively suppressed PRL during late pregnancy (Day 15) but did not alter serum P4 concentrations or interfere with parturition. Therefore, surges of PRL are not an essential luteotropic stimulus during late gestation. Compared to oil-injected controls, CB 154-treated females had a higher incidence of infanticide postpartum. Growth rates of the pups, mammary gland development, and successful delivery of milk to pups, however, did not differ between groups. Further studies will be required to determine the function of late-gestation PRL surges.

Opioidergic Control of Luteinizing Hormone and Prolactin Secretion in Late Gestation in the Sow1

“…morning to reach a nadir by approximately mid-day, and OURS then rise again in the late afternoon[66].In the present study, LH and PRL were found to be and naloxjectione days formg/kg, 1 mg/kg, 1 positively correlated during the entire control day and the dicate values that were below the control period of the treated day, but after naloxone adc shape of profiles on control days. ministration this relationship was abolished.…”

Reproductive performance in female common hamsters

“…Postnatal mortality could occur due to infanticide or insufficient maternal care. Infanticide has been observed in several other hamster species in captivity (Da Silva et al 1989;Edwards et al 1995), but in the field no evidence was found. Females were very aggressive during lactation (Franceschini personal observation) and stayed close to the breeding burrow when feeding above ground (Franceschini personal observation).…”

Monthly Patterns of Testosterone and Behavior in Prospective Fathers

“…Peaks were chosen rather than troughs as the focus of this study was on testosterone increases in response to sexual activity, as well as on the reverse direction of these interactions (Stoléru et al, 1993). A "peak" was defined as an androgen level greater than or equal to the individual mean plus standard deviation (Edwards, Reburn, and Wynne-Edwards, 1995;Fig. 1) and as sexual activities of intensities greater than 35 (data above the third quartile).…”