Inositol phosphates accumulation in ovarian granulosa after stimulation by luteinizing hormone.

Abstract

Accumulation of inositol phosphates by granulosa cells from medium follicles of porcine ovaries was studied to determine if hydrolysis of phosphoinositides is stimulated by luteinizing hormone (LH). Although follicle-stimulating hormone (FSH), D-alanine-gonadotropin-releasing hormone (D-ala-GnRH), and dibutyryl cyclic adenosine 3',5'-monophosphate (dbcAMP) had no effect, LH increased accumulation of inositol phosphate (IP), -bisphosphate (IP2), and trisphosphate (IP3) by severalfold. Furthermore, 0.01 microgram LH/ml increased IP3 accumulation threefold, while 0.1 microgram/ml stimulated accumulation of all inositol phosphates. Compared to untreated cells, LH-treated granulosa cells produced approximately twice as much progesterone in 30 min. Preincubation of cells with lithium chloride (LiCl) was necessary to measure IP accumulation, but not IP2 and IP3 accumulations. However, IP2 and IP3 accumulations were higher in LH-treated granulosa after pretreatment with LiCl. Maximal increases in IP3 and IP2 accumulations occurred approximately 15 min and 30 min, respectively, after LH stimulation, whereas the effect of LH on IP accumulation continued for at least 60 min. Granulosa, made permeable to IP3 with saponin treatment, did not hydrolyze [3H]IP3 to [3H]IP2 or [3H]IP. Thus, it is hypothesized that LH stimulates phosphoinositide hydrolysis in granulosa cells, thereby generating putative second messengers.