Relaxin Secretion and Gene Expression in Porcine Granulosa and Theca Cells Are Stimulated during In Vitro Luteinization1

Abstract

During formation of the corpus luteum, the primary source of relaxin switches from theca cells (TC) to granulosa-derived, large luteal cells. What controls this shift in relaxin production is poorly understood. The objective of this study was to observe the effect of luteinization on relaxin gene expression and secretion by porcine granulosa (GC) and TC using an in vitro model. TC and GC from medium-sized porcine follicles (4-6 mm) were treated for up to 8 days with LH (250 ng/ml) and/or insulin-like growth factor-I (IGF-I; 10 ng/ml). Media were assayed for relaxin and progesterone by RIA, changes in cell morphology were recorded, and total RNA was subjected to reverse transciption-polymerase chain reaction to monitor relaxin gene expression. In vitro luteinization, induced with LH + IGF-I treatment, was confirmed in both GC and TC by a change in morphology and a sustained, significant rise in progesterone secretion. In luteinizing GC, relaxin secretion was first detected after 5 treatment days, and steadily rose until it became significantly higher (p < 0.001) by treatment Days 7-8. In contrast, relaxin release from luteinizing TC was significant after only 2 days of treatment (p < 0.05) and increased consistently over the 8-day culture period (p < 0.001). In GC, relaxin mRNA was not detected until treatment Day 4 and became significantly higher (p < 0.001) by Day 8, the final treatment day. Relaxin transcript in luteinizing TC was low on treatment Days 2-4 and significantly higher (p < 0.01) by treatment Days 6 and 8. In summary, the present study demonstrates that hormones important in the control of luteinization are essential for regulating relaxin gene expression and secretion by GC and TC in the porcine follicle.

Effects of LPS on the accumulation of lipid droplets, proliferation, and steroidogenesis in goat luteinized granulosa cells

“…Luteinization was a complex process, including slightly morphologic switch from fibroblastic to epitheloid phenotype . With long term in vitro culture, the GCs characterized from spherical to star‐shaped with multiple prolongations .…”

Regulation of the reproductive cycle and early pregnancy by relaxin family peptides

“…Why this is important is that relaxin expression can also be detected in theca interna cells of antral follicles in both humans and pigs before the LH surge (Blankenship et al, 1994;Ohleth and Bagnell, 1999), as well as in both cell types after culture with luteinizing levels of the gonadotropin (Ohleth and Bagnell, 1999). Whilst this relaxin probably does not contribute to the circulation it likely is the major contributor to the relaxin detected in follicular fluid (Wathes et al, 1986).…”