Ionic dependence of luteinizing-hormone-induced steroidogenesis in the rabbit ovary.

1. Investigations were made into the influence of the ionic environment on the steroidogenic response of the rabbit ovary to luteinizing hormone (LH). 2. Removal of Ca2+ from the medium was without effect on the response to LH. A similar result was obtained in Ca2+-free medium containing EGTA. 3. A tenfold increase in [Ca2+]o to 25.6 mM, or the addition of La3+ or Eu3+ (0.25 mM) to medium containing the normal concentration of Ca2+, caused a marked inhibition of the response to LH. 4. Removal of Na+ from the medium, and replacement by choline, had no effect on the response to LH. Replacement of Na+ by Li+ inhibited the response to the hormone strongly, but the addition of 4 mM-Li+ to normal medium was without effect. 5. Removal of K+ from the medium inhibited LH-induced steroidogenesis, whereas a twentyfold increase in [K+]o to 100 mM had no effect. The response to LH was also unaffected by the absence of Cl-. 6. Ouabain (10(-4) M) inhbited the response to LH, but nupercaine (10(-4) M) was without effect. 7. The inhibitory effect of ouabain was reversed by the addition of 2 mM-NADP+ to the medium. In contrast, the inhibitory effect of Eu3+ persisted in the NADP+-rich medium. 8. It is suggested that the intracellular ratio of Na+ or Li+) to K+ is important for the expression of the steroidogenic response of the ovary to LH. Altered concentrations of these ions might affect the formation or availability of NADP+. The inhibitory effects of high [Ca2+]o and lanthanide ions, however, are probably due to inhibition of hormone-stimulated adenyl cyclase.