Compartmentalization of human chorionic gonadotrophin sensitivity and luteinizing hormone receptor mRNA in different subtypes of the human corpus luteum

Abstract

The relationship was investigated between different ultrasonographically defined subtypes of the human corpus luteum and progesterone production. Twenty-one women in the mid-luteal phase who underwent laparotomy for benign uterine conditions volunteered for this study. The corpus luteum was identified by preoperative ultrasound and classified into four types according to earlier established criteria, where types a and c were centrally hypoechoic, types b and d were centrally echogenic, types a and b had thin surrounding 'walls' (< 3 mm) and types c and d had thick walls (< 3 mm). After luteectomy, the theca externa capsule was removed and tissue from directly beneath the surface ('peripheral region') and the layer immediately beneath ('inner region') minced into 4-6 mg pieces. Following preincubation, pieces were incubated for 3 h at 37°C in HEPES-minimal essential medium buffer with or without human chorionic gonadotrophin (HCG; 10 IU/ml), and subsequently progesterone accumulation in the medium was determined by radioimmunoassay. The highest progesterone production was consistently seen in the peripheral region. Type a had a significantly (P > 0.01) lower progesterone production (3.2 ± 1.5 nmol/g tissue wet weight, mean ± SEM, n = 4) than that of types b, c and d (17.7 ± 3.5 nmol/g tissue wet weight, n = 9). All types responded to HCG with an almost two-fold increase in progesterone production. However, the maximal progesterone produced following stimulation by HCG in the type a corpus luteum was < 50% of the basal (unstimulated) progesterone synthesis of any other type of corpus luteum. Using in-situ hybridization, with a primate RNA probe complementary to the region coding the extracellular part of the luteinizing hormone (LH) receptor, a highly localized expression of LH receptor mRNA to the peripheral region was found. Negligible or low levels of expression were found in the theca externa capsule and the inner region. No obvious correlations between the different subtypes of corpora lutea and LH receptor mRNA expression were seen. Thus, the ultrasonographic detection of a thin-walled and centrally hypoechoic corpus luteum correlates well with reduced progesterone secretion. The underlying cellular mechanism does not appear to involve a diminished sensitivity to the gonadotrophic stimulation by LH or HCG.