title: Discordant secretion of relaxin by individual porcine large luteal cells: quantitative analysis by a reverse haemolytic plaque assay.
abstract: Individual large luteal cells (LLC) derived from pregnant swine differ conspicuously in their ability to secrete the peptide hormone relaxin under basal and stimulated conditions--the phenomenon of functional heterogeneity. The purpose of this study was to quantitate knowledge of this phenomenon through use of a reverse haemolytic plaque assay, a technique that utilizes antibody-directed, complement-mediated erythrocyte lysis to detect hormone secretion by single LLCs in culture. Measurement of individual plaque areas (an index of the amount of relaxin secreted) demonstrated an approximate 100-fold range in the amount of relaxin secreted by a single cell under basal conditions. This range was doubled by exposure to the phorbol ester, 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA; 50 nmol/l). Under basal conditions, 50 and 80% of the total amount of relaxin was secreted by approximately 10 and 30% of all LLCs respectively. The size of these fractions was not influenced by the time of incubation (1-8 h), or by the presence of either of two non-specific stimulatory relaxin secretagogues, PMA (50 nmol/l) or arachidonic acid (1 mumol/l). The unimodal frequency distribution of plaque areas (under basal or stimulated conditions) suggests that relaxin-secreting LLCs comprise a discrete functional population of secretory cells, at least under these experimental conditions. We conclude that a remarkably small fraction of LLCs secretes the majority of relaxin, and that the size of this fraction was not influenced by time or secretagogues.
authors.affiliation: Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine, Iowa State University, Ames 50011.
authors.forename: M J
authors.initials: MJ
authors.lastname: Taylor
authors.forename: C L
authors.initials: CL
authors.lastname: Clark
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D015941:Complement Hemolytic Activity Assay / Q000379:methods; D003338:Corpus Luteum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D011247:Pregnancy; D012065:Relaxin / Q000032:analysis / Q000096:biosynthesis*; D013268:Stimulation, Chemical; D013552:Swine / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013997:Time Factors
chemical_list: D012065:Relaxin; D013755:Tetradecanoylphorbol Acetate