Human chorionic gonadotropin activates the inositol 1,4,5‐trisphosphate‐Ca2+ intracellular signalling system in bovine luteal cells

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Abstract
Human chorionic gonadotropin, hCG, a hormone which increases intracellular cAMP, provoked rapid (30 s) and sustained (up to 30 min) increases in the levels of inositol mono‐, bis‐ and trisphosphates (IP, IP2 and IP3, respectively) in bovine luteal cells. LiCl (10 mM) enhanced inositol phosphate accumulation in response to hCG. Concentration‐dependent increases in inositol phosphates, cAMP and progesterone accumulation were observed in hCG‐treated luteal cells. hCG also induced rapid and concentration‐dependent increases in cytosolic free Ca2+ as measured by quin 2 fluorescence. These findings demonstrate that hCG stimulates the phospholipase C‐IP3 and diacylglycerol ‘second messenger’ system in the bovine corpus luteum.