Stimulation of collagen secretion by relaxin and effect of oestrogen on relaxin binding in uterine cervical cells of pigs.

The role of relaxin and oestrogen in the remodelling of connective tissue was investigated by testing collagenase-dispersed cells (3 x 10(5) cells per well) from the uterine cervix of gilts for relaxin binding and collagen secretion. Relaxin-binding sites on these cells were quantified by specific binding of a saturating dose of 125I-labelled monotyrosyl relaxin at optimal conditions. Oestrogen at doses from 0.4 to 50 ng ml-1 increased relaxin binding in a time- and dose-dependent manner. Scatchard plot analysis exhibited curvilinearity, which suggested two classes of relaxin-binding sites. The addition of relaxin (0, 100, 500 ng ml-1) alone (P < 0.05) or in combination with oestrogen (oestradiol benzoate: 0, 50, 250 ng ml-1) increased protein secretion into the culture medium. Hydroxyproline concentration (as an index of collagen) in the medium was increased (P < 0.05) only in the presence of both relaxin and oestrogen. Actinomycin D (500 ng ml-1) and cycloheximide (500 ng ml-1) inhibited hydroxyproline secretion induced by combined relaxin and oestrogen treatment. Dibutyryl cyclic adenosine 3',5'-monophosphate (dibutyryl cAMP: 0, 0.1, 1.0, 5.0 mmol l-1) was a potent stimulator of hydroxyproline secretion. These results indicate that relaxin, probably via a cAMP pathway, stimulates hydroxyproline secretion in the presence of oestrogen through a protein- and RNA-synthesis dependent process. Oestrogen plays a role in augmenting the sensitivity of uterine cervical cells to relaxin in the pig.