Luteotropic regulation of dispersed rat luteal cells in early pregnancy.

Viable and functional luteal cells were prepared, using a combination of hyaluronidase, collagenase, and a low concentration of trypsin in a Dulbecco's modified Eagle medium containing 0.5% bovine serum albumin and 3.3 mM Ca++, from corpora lutea taken from 2-day pregnant rats. The viability and functional capacity of the dispersed cells were evaluated by electronmicroscopy and by measuring steroidogenic capicity during perifusion. Dispersed luteal cells previously exposed in vivo to biphasic prolactin (PRL) surges were found to respond during perifusion to as little as 0.5 ng/ml LH by increased steroid secretion. The net progesterone synthesis and secretion remained elevated over a time course of 2 1/2 hours perifusion, and the magnitude of the luteotropic stimulation was dose dependent on LH. However, luteotropic stimulation of LH could not be maintained beyond 2 1/2 h without renewed (in vitro) PRL exposure. PRL by itself maintained the low initial secretion rate of progesterone but demonstrated no stimulatory effect. Different steroidogenic responses were noted during the in vitro administration of LH alone and the administration of LH plus PRL. In the former case, the decreasing rate of progesterone secretion was accompanied by an increasing 20 alpha-dihydroprogesterone secretion, suggesting that luteal 20 alpha-hydroxysteroid dehydrogenase activity was not suppressed. In the latter case, progesterone secretion was maintained and 20 alpha-dihydroprogesterone secretion fell suggesting an inhibitory action by PRL against 20 alpha-hydroxysteroid dehydrogenase activity. Dispersed luteal cells, preincubated at 36 C in medium containing only PRL, retained viability and functional capacity in response to LH-PRL stimulation for periods of time up to 48 h. Preincubation with LH alone did not prolong cell viability.