Role of lipoproteins and prolactin in luteal function in the ferret.

This study investigatedlutealfunction in vitroduring earlypregnancy and pseudopregnancy in the ferret.Corpora lutes taken from animals on Day 13 following the ovulatory stimulus (mating or gonadotropin treatment) were dissociatedwith collagenaseand incubated with ovine prolactin (PrI), ovine luteinizing hormone (LH), total lipoprotein fraction from canine serum, canine highdensity lipoproteins (HDL), canine low-density lipoproteins (LDL) or combinations of PrI, LH, HDL and LDL. Total lipoproteins produced statistically definable increases in progesterone accumulation in incubation media at 5 p1 (approx. 50 j.�g protein) through 25 p1 (250 pg protein) of the total lipoprotein solution. LDL in doses of I or more pg protein stimulated progesterone accumulation in 2-h incubations and a similar stimulation was observed in the presence of 60 or more pg HDL. PrI, LH or the combination of PrI and LH had no apparent stimulatory influence on progesterone accumulation in vitro. PrI in combination with LDL further stimulated progesterone output by luteal cells in short-term incubation relative to LDL alone. PrI and LH together with LDL produced an increase in stimulation over LDL alone, but, for the most part, this augmentation did not exceed that recorded in the presence of the combination of PrI and LDL. No interactions between HDL and luteotropic hormones were present. The results indicate that lipoproteins increase progesterone output from ferret luteal cells, presumably by providing substrate for steroid hormone synthesis. No direct role for LU in ferret luteal function emerged from these experiments. The interaction between Prl and LDL suggests that PrI may exert its luteotropic effects in this species by increasing uptake or liberation of lipoprotein-borne cholesterol to allow it to enter hormone synthetic pathways.