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

Abstract

SUMMARY1. 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+]. to 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+]., to 100 mm had no effect.The response to LH was also unaffected by the absence of C1-. 6. Ouabain (10-4 M) inhibited 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+]0 and lanthanide ions, however, are probably due to inhibition of hormonestimulated adenyl cyclase.

Mechanisms by which Calcium Ions Regulate the Steroidogenic Actions of Luteinizing Hormone in Isolated Ovarian Cells in Vitro*

“…Thus, incubation of swine granulosa cells in the absence of added extracellular calcium ions [final approximate concentration of calcium ions is 5 / XM (7)] significantly impaired progesterone production in both cells and medium. Higuchi et al (14) described a similar dependence of LH/hCG action on extracellular calcium ions in perifused ovine luteal slices, in contrast to an earlier report of the independence of LH-stimulated steroidogenesis on extracellular concentrations of calcium in rabbit ovarian slices (15). The present studies with dispersed granulosa cells indicate that available extracellular calcium is required for both submaximal and maximal effects of LH on progesterone production and that the concentration of extracellular calcium influences the magnitude of cellular responsivity.…”