No abstract

The widely used plasticizer di(2-ethylhexyl) phthalate (DEHP) is a male reproductive toxicant. Its toxicity has been shown to be due primarily to the action of its metabolite mono(2-ethylhexyl) phthalate (MEHP) on Sertoli cells. We have previously shown that at least one of the sites of action of MEHP on the Sertoli cell is the cAMP second messenger system. MEHP inhibits the ability of FSH but not isoproterenol, forskolin, or cholera toxin to stimulate cAMP accumulation in cultured Sertoli cells in a dose- and time-dependent manner. To further characterize this effect of MHP, we prepared a light membrane fraction from control and MEHP-treated Sertoli cells cultured from 18-day-old Fischer 344 rats and measured FSH binding in a radioligand receptor assay using 125I-labeled human FSH (125I-hFSH). MEHP inhibited FSH binding when preincubated with Sertoli cells in culture but not when added simultaneously with 125I-hFSH to the purified membrane preparation. Attenuation of FSH binding was evident after a 3-h preincubation with 100 microM MEHP (18%) and was maximal after 15-24 h of preincubation (70-90%). Preincubation of Sertoli cells for 24 h with 100 microM DEHP had no effect on FSH binding. Half-maximal inhibition occurred at approximately 0.1 microM MEHP. Scatchard analysis indicated a four-fold decrease in FSH affinity with no change in receptor concentration. Exposure of Sertoli cells to MEHP amplified the attenuating effect of guanosine triphosphate (GTP) on FSH binding, suggesting that the action of MEHP may be at the level of the GTP-binding protein that couples the FSH receptor to the adenylate cyclase catalytic subunit.(ABSTRACT TRUNCATED AT 250 WORDS)

Pituitary adenylate cyclase-activating peptide (PACAP) is a novel peptide that was isolated from ovine hypothalamic tissue on the basis of its ability to stimulate cAMP accumulation in cultured rat pituitary cells. Recently we demonstrated that PACAP can stimulate cAMP accumulation and secretory function in cultured rat Sertoli cells. Since ovarian granulosa cells share many properties with Sertoli cells, we have examined the effect of PACAP (consisting of 38 or 27 amino acid residues) on cultured granulosa cell function. Granulosa cells were obtained from the ovaries of 25-day-old rats implanted with a silastic capsule containing diethylstilbestrol 5 days prior to culture. PACAP 38 (0.1 microM-0.01 pM), both alone and in the presence of the phosphodiesterase inhibitor, methylisobutylxanthine, stimulated cAMP accumulation 4-8-fold with an ED50 of approximately 100 pM. Maximal PACAP 38 or PACAP 27 stimulation of granulosa cell cAMP was significantly greater than that produced by a maximally effective concentration of FSH. Because PACAP 38 and 27 have 68% sequence homology with vasoactive intestinal peptide (VIP), and since VIP stimulates granulosa cell cAMP accumulation and estradiol and progesterone secretion, we examined the possibility that PACAP could be acting via the VIP receptor. VIP stimulated cAMP only at concentrations of 10 nM or greater, whereas the PACAP stimulation was evident at 10 pM. Moreover, only one of three potent VIP antagonists inhibited VIP stimulation of cAMP accumulation, and only at 1 microM or greater. This VIP antagonist did not inhibit PACAP 38 action at 2000-fold excess concentration. Interestingly PACAP 38 was more effective than PACAP 27 with regard to steroid secretion and the ability to induce LH responsiveness. PACAP and VIP stimulation of granulosa cell cAMP accumulation or estradiol or progesterone secretion was not additive. Thus, these data support the hypothesis that granulosa cells have specific PACAP 38 receptors and that VIP acts via these receptors. In addition, PACAPs 38 and 27 are more potent stimulators of cAMP accumulation in luteinized granulosa cells than LH. These results both pre- and postovulation, along with previous data indicating that the PACAPs are found in the ovaries, suggest a role for PACAP in the regulation of ovarian function.

Pituitary adenylate cyclase-activating peptide (PACAP), a novel hypothalamic peptide that has been shown to exist in several tissues including the testis, was examined for its effects on cultured rat Sertoli cells. PACAP stimulates cAMP accumulation in Sertoli cells cultured from 15-day-old rats in the presence or absence of methylisobutylxanthine, a phosphodiesterase inhibitor, and in the presence of pertussis toxin, a blocker of the adenylate cyclase inhibitory pathway. Maximal stimulation, which is 20-40% of that attainable with FSH, occurs at PACAP concentrations of 10 nM: the ED50 is approximately 100 pM. The ability of PACAP to stimulate Sertoli cell cAMP declines with increasing age of donor animals (15-60 days of age) in a fashion similar to the FSH effect. PACAP stimulation of Sertoli cell cAMP accumulation is additive with submaximal, but not maximal, concentrations of FSH or forskolin. PACAP also stimulates the secretion of lactate, estradiol, and inhibin in a concentration-dependent manner. The stimulation of Sertoli cell cAMP accumulation by PACAP is not altered by a vasoactive intestinal peptide antagonist, and vasoactive intestinal peptide alone does not stimulate cAMP accumulation, indicating that PACAP is not acting via vasoactive intestinal peptide receptors. Further experiments are needed to determine whether PACAP is synthesized within the testis and if so, in which cell types; however, the present data clearly demonstrate that PACAP can modulate Sertoli cell function in vitro.