PROLACTIN IN FOLLICULAR-FLUID AND INTRACELLULAR STORE CALCIUM IN FOLLICULAR CELLS ARE RELATED TO MORPHOLOGICAL SIGNS OF OVARIAN FOLLICLE ATRESIA IN COWS - WORK-IN-PROGRESS

It is known that prolactin (PRL) is the third pituitary hormone servin g gonadotropic function in mammals. However, its role in the regulatio n of ovarian folliculogenesis and, in particular, its relationship to follicular atresia as well as the mechanism of its influence on follic ular cells are poorly understood. We investigated PRL levels in follic ular fluids (FFs) and intracellular store calcium ([Ca2+](is)) in cell walls of bovine ovarian follicles with diameters of 10 to 20 mm and t heir relationship to follicular atresia. Ovarian follicles were catego rized on the basis of macroscopic criteria and of microscopic examinat ion of granulosa cell (GC) smears. Prolactin concentrations in FFs wer e measured by RIA and levels of [Ca2+](is) in follicular cells were de termined by using the fluorophore chlortetracycline. Compared to atret ic follicles, morphologically normal follicles were characterized by h igher concentrations of PRL in FFs (P<0.001) and lower contents of [Ca 2+](is) in follicular cells (P<0.01). Furthermore, follicles containin g no more than 20% of pycnotic GCs had higher levels of PRL in their f luids than those containing over 40% of pycnotic GCs (P<0.05). Finally , the direct effect of PRL on [Ca2+](is) content in follicular cells w as studied in vitro. Compared to control, PRL decreased (P<0.001) the levels of [Ca2+](is) in the cells after 24 h culture of follicular wal ls from morphologically normal follicles in TCM 199 supplemented by 10 % fetal calf serum. Our findings suggest that the decline of PRL conce ntrations in FFs and the rise of [Ca2+](is) contents in follicular cel ls are related to atresia of large bovine follicles and that there app ears to be a relationship between the two biochemical parameters. (C) 1998 by Elsevier Science Inc.