The Effects of Elevation and Depletion of Intracellular Free Calcium on Progesterone and Prostaglandin Production by the Primate Corpus Luteum1

Abstract

The role of the phosphatidylinositol second messenger system in luteal regulation has not been extensively studied, particularly in the primate. The objectives of this study were (1) to further characterize the response of the primate CL to the calcium ionophore A23187, in terms of intracellular free calcium concentrations ([Ca2+]i) and progesterone (P) production; and (2) to assess the effects of depleting, as well as elevating, available calcium on luteal P and prostaglandin (PG) production. The response to A23187, in terms of [Ca2+]i, was measured by fura-2 fluorescence microscopy of single small and large luteal cells. A23187 significantly increased [Ca2+]i in both cell types (p less than 0.01). P production (basal and hCG-stimulated) by dispersed primate luteal cells incubated for various times (1-8 h) with and without A23187 was measured. Treatment with A23187 rapidly (within 1-2 h) attenuated (p less than 0.05) the time-dependent increase in basal and hCG-stimulated P production. Luteal P and PG production following treatment with the calcium ionophore, ionomycin, alone or in combination with additional CaCl2, was also monitored. Treatment with ionomycin (p less than 0.01) and CaCl2 (p less than 0.01) inhibited luteal P production. In contrast, treatment with ionomycin stimulated (p less than 0.01) luteal PG production. To determine the effects of Ca2+ depletion on luteal function, P and PG production by cells incubated for 2 and 8 h in the absence and presence of the Ca(2+)-chelator EGTA was measured. Luteal production of both P and PG was inhibited by 8-h treatment with EGTA.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of Intracellular Calcium Homeostasis in Developing and Mature Bovine Corpora Lutea1

“…The importance of intracellular calcium in luteal steroidogenesis has been documented in several species, including the primate [27], mouse [30], sheep [21], and cow [17]. Additional studies are needed to fully comprehend the nature of the calcium regulatory mechanism in the bovine CL.…”

“…Additionally, increasing [Ca 2þ ] i by pharmacological means in developing bovine luteal cells reduced the stimulatory effect of LH on progesterone secretion, an effect that cannot be induced by PGF2a at this developmental stage [25]. Several authors have stressed the importance of this increase in [Ca 2þ ] i in inhibiting progesterone production by bovine LLCs, [26], mature ovine LLCs, [21] and mature primate CL [23,27].…”