Basic fibroblast growth factor inhibits basal and stimulated relaxin secretion by cultured porcine luteal cells: analysis by reverse hemolytic plaque assay.
The role of the basic fibroblast growth factor (basic FGF) in the control of secretion of the ovarian protein hormone relaxin (RLX) by porcine large luteal cells (LLCs) was examined by use of a reverse hemolytic plaque assay. In this assay, luteal cells were cocultured in monolayers with protein-A-coupled sheep erythrocytes. In the presence of complement and porcine relaxin antiserum, a zone of hemolysis (a plaque) developed around a RLX-releasing LLC. The rate of plaque development in time-course experiments was used as an index of the rate of RLX secretion. Monolayers were bathed in medium containing graded concentrations of basic FGF in the presence or absence of a stimulatory secretagogue [0.01 microM prostaglandin E2 (PGE2)]. Exposure of luteal cell-containing monolayers to basic FGF resulted in a significant reduction (P less than 0.05) in the rate of RLX-induced plaque formation, evidence of an inhibitory effect of basic FGF on the rate of basal RLX secretion. This suppressive effect was variable in onset (1-3 h of incubation) and dose related. Minimally and maximally effective doses were about 10 and 30 ng/ml basic FGF, respectively. Higher doses of basic FGF (20 and 30 ng/ml) entirely suppressed RLX from a substantial subset of LLCs (10-20% of all LLCs), an indication of a differentially sensitive subpopulation. Addition of basic FGF (30 ng/ml) to monolayes also treated with PGE2 resulted in a significant (P less than 0.05) attenuation of the stimulatory effect of PGE2 on RLX secretion, evidence that these agents functionally interact in the modulation of RLX. We conclude that these results taken in association with the prior demonstration of the presence of basic FGF in luteal tissue suggest that basic FGF serves as a local inhibitory mechanism that regulates RLX secretion. Furthermore, the ability of basic FGF to counteract the effect of PGE2 implies that intraluteal stimulatory/inhibitory agents may act in concert to achieve fine control of RLX secretion. The observation of a preferentially responsive subpopulation is consistent with the possibility that basic FGF is implicated in heterogenous RLX secretion. Nevertheless, the physiological role(s) of basic FGF in the control of RLX secretion and the interrelationships of basic FGF with other local and systemic secretagogues remain to be clearly defined.
Taylor
M J
MJ
Department of Veterinary Physiology and Pharmacology, Iowa State University, Ames 50010.
Clark
C L
CL
D000818:Animals; D002478:Cells, Cultured; D003338:Corpus Luteum / Q000187:drug effects / Q000378:metabolism*; D015232:Dinoprostone / Q000494:pharmacology; D005260:Female; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology*; D006462:Hemolytic Plaque Technique; D011247:Pregnancy; D012065:Relaxin / Q000378:metabolism*; D013268:Stimulation, Chemical; D013552:Swine
D016222:Fibroblast Growth Factor 2; D012065:Relaxin; D015232:Dinoprostone