Transforming growth factor-beta is a potent inhibitor of basal and stimulated relaxin release by porcine luteal cells maintained in monolayer culture.

The effect of transforming growth factor-beta (TGF-beta) on relaxin release by porcine large luteal cells (LLC) was examined by use of a reverse haemolytic plaque assay. In this assay, mixed luteal cells were co-cultured in monolayers with protein A-coupled sheep erythrocytes. In the presence of complement and porcine relaxin antiserum, a zone of haemolysis (a plaque) developed around relaxin-releasing LLCs. The rate of plaque development in time-course experiments and the average size of plaque areas were used to monitor the rate of relaxin release and cumulative amounts of hormone respectively. Monolayers were bathed in medium containing TGF-beta alone, or in the co-presence of a stimulatory secretagogue (prostaglandin E2; PGE2). Exposure of luteal cell-containing monolayers to TGF-beta (1 ng/1-100 micrograms/1) elicited a dose-related inhibition in the rate of basal relaxin release. Minimal and maximal concentrations were approximately 10 ng/1 and 10 micrograms/1 respectively. Treatment with 1 microgram TGF-beta/1 reduced the cumulative amount of relaxin released to 63 +/- 6% of control values (mean +/- S.D., P < 0.05, n = 6; averaged over the whole course of the experimental incubation). Exposure of monolayers treated with TGF-beta to the relaxin-stimulatory secretagogue PGE2 (0.1 mumol) resulted in a significant (P < 0.05) increase in the amount of relaxin released by TGF-beta-suppressed LLCs, and restored rates of hormone release to control levels. This is evidence that TGF-beta and PGE2 interact antagonistically in the modulation of relaxin. The effect of TGF-beta was strictly time-dependent.(ABSTRACT TRUNCATED AT 250 WORDS)