Control of human luteal steroidogenesis: role of growth hormone-releasing hormone, vasoactive intestinal peptide, and pituitary adenylate cyclase-activating peptide

Female reproductive functions of the neuropeptide PACAP

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide originally isolated as a hypothalamic peptide. It has a widespread distribution in the body and has a diverse spectrum of actions. Among other processes, PACAP has been shown to be involved in reproduction. In this review we summarize findings related to the entire spectrum of female reproduction. PACAP is a regulatory factor in gonadal hormone production, influences follicular development and plays a role in fertilization and embryonic/placental development. Furthermore, PACAP is involved in hormonal changes during and after birth and affects maternal behavior. Although most data come from cell cultures and animal experiments, increasing number of evidence suggests that similar effects of PACAP can be found in humans. Among other instances, PACAP levels show changes in the serum during pregnancy and birth. PACAP is also present in the human follicular and amniotic fluids and in the milk. Levels of PACAP in follicular fluid correlate with the number of retrieved oocytes in hyperstimulated women. Human milk contains very high levels of PACAP compared to plasma levels, with colostrum showing the highest concentration, remaining steady thereafter for the first 7 months of lactation. All these data imply that PACAP has important functions in reproduction both under physiological and pathological conditions.

Cellular localization of PACAP and its receptors in the ovary of the spotted ray Torpedo marmorata Risso 1880 (Elasmobranchii: Torpediniformes)

The pituitary adenylate cyclase-activating polypeptide (PACAP) is a member of the glucagon-related family and occurs in two amidated forms, PACAP38 and PACAP27, with 38 and 27 amino acids, respectively. PACAP acts by binding to three different receptors, that are classified by their binding affinity for PACAP and VIP (vasoactive intestinal polypeptide): PAC(1)R (PACAP-specific receptor) exclusively binds PACAP, while VPAC(1)R (VIP/PACAP receptor, subtype 1) and VPAC(2)R (VIP/PACAP receptor, subtype 2) bind both PACAP and VIP. PACAP, first discovered in the brain, was then localized in several peripheral tissues of mammals, including the ovary. Besides mammals, PACAP and its receptors have been reported in fish too; however, less is known about the presence of PACAP in the fish ovary and the studies are limited to teleosts. The aim of our work was to study the distribution of the PACAP/PACAP-Rs system in the ovary of the cartilaginous fish Torpedo marmorata. Using in situ hybridization (ISH) and immunohistochemistry techniques, we demonstrated that PACAP and its receptors are widely represented in the Torpedo ovary in a stage-dependent manner. Moreover, our findings suggest an involvement of this peptide in the whole follicologenesis, probably influencing steroidogenesis, follicle development, and oocyte growth.

Role of PACAP in Female Fertility and Reproduction at Gonadal Level - Recent Advances

Pituitary adenylate cyclase activating polypeptide (PACAP) is a pleiotropic neuropeptide, first isolated from hypothalamic extracts, but later shown in peripheral organs, such as endocrine glands, gastrointestinal system, cardiovascular system, and reproductive organs. PACAP plays a role in fertility and reproduction. Numerous studies report on the gonadal regulatory effects of PACAP at hypothalamo-hypophyseal levels. However, the local effects of PACAP at gonadal levels are also important. The present review summarizes the effects of PACAP in the ovary. PACAP and its receptors are present in the ovary, and PACAP plays a role in germ cell migration, meiotic division, follicular development, and atresia. The autocrine-paracrine hormonal effects seem to play a regulatory role in ovulation, luteinization, and follicular atrophy. Altogether, PACAP belongs to the ovarian regulatory peptides.

Investigation of pituitary adenylate cyclase activating polypeptide in human gynecological and other biological fluids by using MALDI TOF mass spectrometry

Pituitary adenylate cyclase activating polypeptide (PACAP) is a multifunctional and pleiotropic neuropeptide. PACAP has diverse effects in the endocrine system, among others, it plays important roles in oogenesis, implantation and development of the nervous system. However, it is not known whether PACAP is present in the fluids of the human reproductive organs. The aim of the present study was to determine, by means of mass spectrometry and radioimmunoassay, whether PACAP is present in human amniotic fluid, ovarian follicular fluid and cervico-vaginal fluid. Samples were obtained from healthy adult volunteers. Our MALDI TOF and MALDI TOF/TOF spectrometry results show that PACAP38 is present in all of the follicular fluid samples, and PACAP-like immunoreactivity was also measured by radioimmunoassay. However, we did not find the characteristic peak representing the unmodified 38 amino acid form of the peptide in normal cervico-vaginal smear and amniotic fluid samples. Furthermore, we analyzed other body fluids for comparison, such as human nasal fluid, saliva and aqueous humor. PACAP was not found in these latter samples. In summary, the present study provides evidence for the presence of PACAP in human follicular fluid, suggesting a role in oocyte function, but determination of the exact physiological significance awaits further investigation.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is important for embryo implantation in mice

Mice lacking pituitary adenylate cyclase-activating polypeptide (PACAP) show high mortality during the postnatal period, as well as impaired reproduction in females. This study characterizes the reproductive phenotype in female mice lacking PACAP due to targeted disruption (knockout) of the single copy pacap gene (Adcyap1) to determine the site(s) of action of PACAP in the cascade of reproductive events. PACAP null females showed normal puberty onset, estrous cycles, and seminal plugs when paired with a male of proven fertility. However, significantly fewer PACAP null females (21%) than wild-type females (100%) gave birth following mating. Although a defect was not detected in ovulation, ovarian histology or fertilization of released eggs in PACAP null females, only 13% had implanted embryos 6.5 days after mating. Associated with the decrease in implantation, prolactin and progesterone levels were significantly lower in females lacking PACAP than in wild types on day 6.5 after mating. Our evidence suggests that impaired implantation is the defect responsible for decreased fertility in PACAP null female mice.

Cloning and characterization of a PAC1 receptor hop-1 splice variant in goldfish (Carassius auratus)

In several vertebrates, it has been demonstrated that alternative splicing of PAC1 receptor (PAC1-R) transcripts can generate a number of functional receptor variants which utilize different signal transduction pathways to mediate their activities. As PACAP is a physiological growth hormone-releasing factor in fish, and PACAP and the PAC1-R are highly conserved in vertebrate evolution, it would be of interest to investigate the structure and cellular distribution, particularly in the pituitary, of PAC1-R splice variants in a fish model. Our laboratory has previously cloned a receptor cDNA corresponding to the goldfish PAC1-R-s (goldfish PAC1-R-short). In the present study, a goldfish PAC1-R-hop1 variant was characterized. Functional expression of goldfish PAC1-R-s and PAC1-R-hop1 in Chinese Hamster Ovary cells revealed that, upon stimulation by ovine PACAP38, these receptor variants exhibited similar EC50 values (8.7+/-1.5 and 8.8+/-1.9 nM, respectively) and maximal responses in activating intracellular cAMP production. The presence and expression levels of these transcripts were measured by quantitative real-time PCR in the brain, heart, pituitary and male gonad, and goldfish PAC1-R-s were found to be the predominant form. In situ hybridization of goldfish PAC1-R in the pituitary revealed its prevalent presence in the pars distalis. In summary, the present study provides information to confirm the role of PACAP in the pituitary and to elucidate the pleiotropic effects of PACAP in fish.

Decrease of Pituitary Adenylate Cyclase Activating Polypeptide and Its Type I Receptor mRNAs in Rat Testes by Ethanol Exposure

The present study was designed to evaluate the effect of ethanol on pituitary adenylate cyclase activating polypeptide (PACAP) and its typ I (PAC1) receptor expression in adult rat testes. Ethanol (3 g/kg i.p., 15% v/v in saline) was administrated to adult male rats for 10 days. Using northern blot analysis, the present study showed the reduction of PACAP mRNA levels in rat testes by ethanol administration. Also, ethanol decreased the expression level of PAC1 receptor in testes. In particular, in situ hybridization clearly showed the decrease of PAC1 receptor mRNA expression in Leydig cells, which produce testosterone. Furthermore, the serum level of testosterone was significantly decreased in the ethanol-treated group. In conclusion, our findings suggest that the decrease of PACAP and PAC1 receptor expression in rat testes by ethanol exposure may partly contribute to the suppression of male reproductive activity.

Endogenous Ligands of PACAP/VIP Receptors in the Autocrine–Paracrine Regulation of the Adrenal Gland

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are the main endogenous ligands of a class of G protein-coupled receptors (Rs). Three subtypes of PACAP/VIP Rs have been identified and named PAC(1)-Rs, VPAC(1)-Rs, and VPAC(2)-Rs. The PAC(1)-R almost exclusively binds PACAP, while the other two subtypes bind with about equal efficiency VIP and PACAP. VIP, PACAP, and their receptors are widely distributed in the body tissues, including the adrenal gland. VIP and PACAP are synthesized in adrenomedullary chromaffin cells, and are released in the adrenal cortex and medulla by VIPergic and PACAPergic nerve fibers. PAC(1)-Rs are almost exclusively present in the adrenal medulla, while VPAC(1)-Rs and VPAC(2)-Rs are expressed in both the adrenal cortex and medulla. Evidence indicates that VIP and PACAP, acting via VPAC(1)-Rs and VPAC(2)-Rs coupled to adenylate cyclase (AC)- and phospholipase C (PLC)-dependent cascades, stimulate aldosterone secretion from zona glomerulosa (ZG) cells. There is also proof that they can also enhance aldosterone secretion indirectly, by eliciting the release from medullary chromaffin cells of catecholamines and adrenocorticotropic hormone (ACTH), which in turn may act on the cortical cells in a paracrine manner. The involvement of VIP and PACAP in the regulation of glucocorticoid secretion from inner adrenocortical cells is doubtful and surely of minor relevance. VIP and PACAP stimulate the synthesis and release of adrenomedullary catecholamines, and all three subtypes of PACAP/VIP Rs mediate this effect, PAC(1)-Rs being coupled to AC, VPAC(1)-Rs to both AC and PLC, and VPAC(2)-Rs only to PLC. A privotal role in the catecholamine secretagogue action of VIP and PACAP is played by Ca(2+). VIP and PACAP may also modulate the growth of the adrenal cortex and medulla. The concentrations attained by VIP and PACAP in the blood rule out the possibility that they act as true circulating hormones. Conversely, their adrenal content is consistent with a local autocrine-paracrine mechanism of action.

Role of pituitary adenylate cyclase-activating peptide (PACAP) in the cyclic recruitment of immature follicles in the rat ovary

Following the midcyclic gonadotropin surge, PACAP is transiently expressed for approximately 12 h in the cyclic adult rat ovary. PACAP is observed in granulosa/lutein cells of the large mature follicles destined to ovulate and is believed to be a regulator of acute progesterone production and luteinization in these follicles. PACAP is also observed in solitary theca cells of immature follicles and in interstitial glandular cells intimately surrounding immature follicles. To examine if PACAP could be involved in the process of cyclic recruitment of such immature follicles, we primed immature granulosa cells from prepubertal ovaries with PACAP (1 nM and 100 nM) for 12 h. The treatment significantly stimulated the subsequent 24 h FSH-induced estradiol production (2.2 and 2.4 fold, respectively). The response seemed to be caused by a stimulation of aromatase activity. Estradiol production induced by testosterone was increased 2.4 and 2.6 fold, respectively, whereas functional FSH-receptors (cAMP production following FSH stimulation) or spontaneous apoptosis (immunohistochemical detection of DNA fragments) was unaffected. We conclude that PACAP priming of immature rat granulosa cells for 12 h increases subsequent FSH induced estradiol production and that PACAP could be involved in the cyclic recruitment of immature follicles in the adult rat ovary.

Neuropeptides of the pituitary adenylate cyclase-activating polypeptide/vasoactive intestinal polypeptide/growth hormone-releasing hormone/secretin family in testis

Mammalian testicular development and the maintenance of spermatogenesis are hormone-dependent processes that are controlled by the pituitary gonadotropins and testosterone. Recent studies have demonstrated the presence of many neuropeptides and their receptors in the testis, suggesting that these peptides operate as local regulators of testicular germ cell development and function. Among these testicular neuropeptides, the peptides that belong to the pituitary adenylate cyclase-activating polypeptide (PACAP) family, particularly growth hormone-releasing hormone and secretin, appear to show some unique common features in terms of intratesticular localization and the time of expression during the spermatogenic cycle. However, their precise physiologic roles and mechanisms of action remain unknown. This review analyzes the available information on the functional interactions among the testicular cells that appear to be mediated by locally produced neuropeptides, with a special emphasis on the peptides of the PACAP family.

Neuropeptides of the pituitary adenylate cyclase-activating polypeptide/vasoactive intestinal polypeptide/growth hormone-releasing hormone/secretin family in testis

Mammalian testicular development and the maintenance of spermatogenesis are hormone-dependent processes that are controlled by the pituitary gonadotropins and testosterone. Recent studies have demonstrated the presence of many neuropeptides and their receptors in the testis, suggesting that these peptides operate as local regulators of testicular germ cell development and function. Among these testicular neuropeptides, the peptides that belong to the pituitary adenylate cyclase-activating polypeptide (PACAP) family, particularly growth hormone-releasing hormone and secretin, appear to show some unique common features in terms of intratesticular localization and the time of expression during the spermatogenic cycle. However, their precise physiologic roles and mechanisms of action remain unknown. This review analyzes the available information on the functional interactions among the testicular cells that appear to be mediated by locally produced neuropeptides, with a special emphasis on the peptides of the PACAP family.

Growth hormone-releasing hormone and pituitary adenylate cyclase-activating polypeptide in the reproductive system

Growth hormone-releasing hormone (GHRH) and pituitary adenylate cyclase-activating polypeptide (PACAP) are both members of the glucagon superfamily that, with gonadotropins, act at central and peripheral levels as paracrine and autocrine coregulators of reproductive function. GHRH and PACAP are ancient peptides. Their original forms (both 27 amino acids long) were encoded by a single ancestral gene, several duplications of which led to the genes that encode the neuropeptides of the glucagon superfamily. In the male and female reproductive tracts, GHRH and PACAP interact with a subset of G protein-coupled receptors that are structurally similar to the PACAP receptor and variants of the vasoactive intestinal peptide receptor, and share several biological actions. These are related mainly to the modulation of cAMP-dependent and other signal transduction pathways in several cells of the pituitary-gonadal axis. The recent discovery that antagonists of GHRH and PACAP suppress the growth of human cancer cell lines that are derived from reproductive tissues indicates the potential importance of these peptides as local regulators of cell division, cell cycle arrest, differentiation and cell death.

Pituitary adenylate cyclase-activating polypeptide and its receptors in amphibians

Pituitary adenylate cyclase-activating polypeptide (PACAP), a novel peptide of the secretin/glucagon/vasoactive intestinal polypeptide superfamily, has been initially characterized in mammals in 1989 and, only 2 years later, its counterpart has been isolated in amphibians. A number of studies conducted in the frog Rana ridibunda have demonstrated that PACAP is widely distributed in the central nervous system (particularly in the hypothalamus and the median eminence) and in peripheral organs including the adrenal gland. The cDNAs encoding the PACAP precursor and 3 types of PACAP receptors have been cloned in amphibians and their distribution has been determined by in situ hybridization histochemistry. Ontogenetic studies have revealed that PACAP is expressed early in the brain of tadpoles, soon after hatching. In the frog Rana ridibunda, PACAP exerts a large array of biological effects in the brain, pituitary, adrenal gland, and ovary, suggesting that, in amphibians as in mammals, PACAP may act as neurotrophic factor, a neurotransmitter and a neurohormone.

Pituitary adenylate cyclase-activating polypeptide precursor is processed solely by prohormone convertase 4 in the gonads

Pituitary adenylate cyclase-activating polypeptide (PACAP) is abundant not only in the brain, but also in the testis. Immunohistochemical studies have shown that PACAP-LI in rat testis is expressed stage specifically in spermatids. This suggests that testicular PACAP participates in the regulatory mechanism of spermatogenesis. Additionally, the ovary contains a relatively small amount of PACAP, conceivably involved in the regulation of folliculogenesis. PACAP is synthesized as a preprohormone and is processed by prohormone convertases, such as PC1, PC2, and PC4. PC4 is expressed only in the testis and ovary, where neither PC1 nor PC2 is expressed. However, whether PC4 is the sole endoprotease for the PACAP precursor in the gonads remains unknown. Recent studies using PC4-transgenic mice revealed that male PC4-null mice exhibited severely impaired fertility, although spermatogenesis appeared to be normal. The female PC4-null mice exhibited delayed folliculogenesis in the ovaries. To examine whether PC4 is the sole processing enzyme for the PACAP precursor in the gonads, we analyzed testicular and ovarian extracts from the PC4-null and wild-type mice for PACAP (PACAP38 and PACAP27) and its messenger RNA using reverse phase HPLC combined with specific RIAs and ribonuclease protection assay, respectively. For RIAs, three different polyclonal antisera with different recognition sites were used to identify PACAP38, PACAP27, and its precursor. Neither the testis nor the ovary from the PC4-null mice expressed PACAP38 or PACAP27, but the levels of PACAP transcripts in the testis and ovary of homozygous PC4-deficient mice were considerably elevated compared with those of the wild-type and heterozygous animals. The findings indicate that PC4 is the sole processing enzyme for the precursor of PACAP in the testis and ovary of mice. The possibility that the absence of bioactive PACAP in the testis and ovary of PC4-null mice caused severely impaired fertility in the males and delayed folliculogenesis in females warrants investigation.

Pituitary adenylate cyclase-activating peptide stimulates acute progesterone production in rat granulosa/Lutein cells via two receptor subtypes

Pituitary adenylate cyclase-activating peptide (PACAP) is transiently expressed in ovarian granulosa/lutein cells from eCG/hCG-treated rats, and in vitro immunoneutralization of endogenously released PACAP inhibits acute progesterone secretion and subsequent luteinization in such cells. This suggests that PACAP mediates locally some of the effects of the LH surge, but the putative PACAP receptor(s) involved in such an auto or paracrine activity is presently unknown. Reverse-transcription polymerase chain reaction with specific primers to the three cloned PACAP-binding receptors called PAC(1), VPAC(1), and VPAC(2) demonstrated both PAC(1) and VPAC(2) mRNA in extracts from preovulatory follicular cells. Radioligand-binding assays revealed the presence of high-affinity binding sites with characteristics of these two receptors on the intact cells, and autoradiography demonstrated that the binding was restricted to a minor proportion of the follicular cells as well as the oocytes. Pituitary adenylate cyclase-activating peptide and vasoactive intestinal peptide (VIP) dose-dependently stimulated cAMP accumulation and acute progesterone accumulation. Forskolin and db-cAMP also stimulated acute progesterone accumulation, and the protein kinase A inhibitor H89 dose-dependently inhibited peptide induced acute progesterone accumulation, suggesting involvement of cAMP and the protein kinase A pathway in the process. In conclusion, two of the three PACAP binding receptors are present on preovulatory follicular cells and are involved in the effects of PACAP on acute progesterone production. The data provide further evidence to establish PACAP as an auto- or paracrine regulator of LH-induced acute progesterone production in rat preovulatory follicles.

Expression of pituitary adenylate cyclase activating polypeptide (PACAP) and PACAP type I A receptor mRNAs in granulosa cells of preovulatory follicles of the rat ovary

Pituitary adenylate cyclase activating polypeptide (PACAP) was isolated from ovine hypothalamus and known to stimulate the production of cAMP in anterior pituitary cells. In the recent report, the expression of PACAP was detected in preovulatory follicles, and treatment with PACAP stimulated the production of progesterone and prostaglandin E(2) through the action of AC and PLC pathways in the ovary. PACAP binds to three type receptors. Type I A receptor is coupled to adenylate cyclase (AC) and phospholipase C (PLC) pathways, while type I B and type II receptors are only coupled to AC. Thus, the present study aimed to evaluate the temporal expression of PACAP and its type I A receptor mRNAs in the rat ovary after treatment with pregnant mare's serum gonadotropin and human chorionic gonadotropin (hCG). Northern blot analysis showed that PACAP transcripts were transiently expressed from 3-9 hr after hCG treatment, reaching a maximum at 6 hr. During these time points, PACAP mRNAs were specifically and strongly expressed in granulosa cells and cumulus cells of large preovulatory follicles and interstitial glandular cells. Type I A receptor mRNAs were also transiently expressed in granulosa cells of large preovulatory follicles from 3-9 hr after hCG treatment. PACAP and its type I A receptor mRNAs were expressed in the same preovulatory follicles. These results demonstrate that PACAP acts as an autoregulator or pararegulator through type I A receptor in granulosa cells and cumulus cells of large preovulatory follicles. Thus, we suggest that PACAP may have a critical role in granulosa cells of preovulatory follicles for the preparation of ovulation.

Pituitary adenylate cyclase-activating polypeptide gene expression regulated by a testis-specific promoter in germ cells during spermatogenesis

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a member of the glucagon-related family of hormones that is widely expressed in various tissues. The PACAP messenger RNA (mRNA) and protein is expressed at high levels in the germ cells of the testis, where it locally activates cAMP-coupled receptors located in the somatic Sertoli cells. The PACAP mRNA expressed specifically in the testis is shorter than the mRNA expressed in hypothalamus and includes 127 nucleotides of novel sequence at the 5'-end, suggesting a different start site of transcription in the testes and the utilization of a tissue-specific promoter. Here we present evidence that a single PACAP gene uses a testis-specific promoter to express a mRNA containing a unique exon located 13.5 kb upstream from the first coding exon. As determined by RT-PCR analysis of testis mRNA, the expression of the first testis-specific exon is relatively specific for the testis, as no PACAP mRNA containing the testis-specific first exon was detected in hypothalamic mRNAs. The promoter for the testis-specific PACAP gene was cloned, and a start site for transcription was mapped by primer extension. The testis-specific promoter sequence directs germ cell-specific expression upon transfection of promoter-transcriptional reporter plasmids to populations of testicular cells in vitro and upon expression of a promoter-reporter transgene in mice. Analyses of PACAP gene expression during the spermatogenic cycle, accomplished by RT-PCR of segments of isolated seminiferous tubules, identified intense expression in the postmeiotic round spermatids during developmental stages I-VIII. These observations establish the existence of a specialized PACAP gene promoter whose activity is highly regulated during the spermatogenic cycle.

Effects of exogenous somatotropin (ST) on gonadal function in ruminants and swine

During the past 15 years, many investigators have examined the effects of somatotropin (ST) on growth and lactation in farm animals. Throughout this period, concerns about potential effects of ST on reproduction have been expressed. The objective of the present review will be to focus on the effects of exogenous ST on the hypothalamic-pituitary-gonadal axis. Plasma progesterone is increased when recombinant bovine (rb)ST is given to cattle, early in lactation, and also to sheep. Also, the release of progesterone from cultured swine and human luteal cells is increased by ST. Treatment with rbSt increases the numbers of small follicles, but does not increase the ovulatory rate of ruminants. Doses of ST similar to those used to increase milk production do not affect the secretion of testosterone or spermatogenesis in rams or bulls. Stimulatory and inhibitory effects of exogenous ST on reproductive function of gilts have been reported. Daily injections of porcine ST (pST) delayed puberty and expression of estrus after puberty. Daily administration of pST increased the number of small follicles, but not of medium follicles, whereas administration of pST by using a sustained release implant increased the number of medium follicles. Size and weight of reproductive organs and concentration of testosterone are not affected when pST is administered for at least 42 d. However, pST enhanced testicular development and spermatogenesis when given to neonatal boars. In summary, administration of exogenous ST at doses known to alter milk production and carcass composition may have subtle positive and/or negative effects on the reproductive systems of cattle and swine; however, these effects appear to be transient.

Pituitary adenylate cyclase-activating polypeptide is an auto/paracrine stimulator of acute progesterone accumulation and subsequent luteinization in cultured periovulatory granulosa/lutein cells

Recently, we have demonstrated that pituitary adenylate cyclase-activating polypeptide (PACAP) is transiently expressed in steroidogenic ovarian cells during the periovulatory period. This prompted us to establish an in vitro system in which the potential local regulatory role of PACAP during periovulatory progesterone production could be examined. Granulosa/lutein cells from PMSG- and human CG (hCG)-stimulated immature rats were used. The cells were isolated from preovulatory follicles 4-6 h after the hCG injection, at which time the transient ovarian PACAP expression begins in vivo. By immunocytochemistry on intact cells and RIA on cell extracts and culture medium, granulosa/lutein cells were found to accumulate and secrete PACAP during incubation. Furthermore, the cells responded to exogenous PACAP 38 with a rapid (10(-7) M induced a peak value 20-fold higher than controls at 2 h) and dose-dependent accumulation of progesterone. PACAP 38 (5 x 10(-9) M), in combination with an approximately half-maximal dose of hCG (1 ng/ml), showed an additive effect on progesterone accumulation. Immunoneutralization of endogenously released PACAP was performed using the IgG fraction from a specific PACAP antiserum that dose-dependently inhibits the progesterone accumulating effect of exogenous PACAP 38. The acute effects of endogenously released PACAP were studied during 8 h of incubation of granulosa/lutein cells with anti-PACAP IgG (100 microg/ml). A significant reduction in progesterone accumulation was observed after 4, 6, and 8 h [38.7% (P < 0.05), 41.2% (P < 0.02), and 50% (P < 0.002), respectively], compared with nonimmune IgG (100 microg/ml) treated cultures. The long-term effects on luteinization induced by endogenously released PACAP were studied after incubation of the cells with anti-PACAP IgG or nonimmune IgG for 24 h, followed by incubation for 9 days in serum-containing medium. Under these conditions, nonimmune IgG-treated cells assumed a luteal phenotype, accumulating large and stable amounts of progesterone and acquiring hypertrophic cell bodies with numerous lipid droplets and distinct nucleoli in the large nuclei. Anti-PACAP IgG-treated cells displayed morphological and functional signs of impaired luteinization being smaller and more irregular and with progesterone accumulation being significantly lower throughout the incubation period [56.4% (P < 0.02), 69.2% (P < 0.05), 43.8% (P < 0.02), and 52.2% (P < 0.02) at 1, 4, 7, and 10 days, respectively]. Together, these findings support an auto- or paracrine role for PACAP during gonadotropin-induced acute periovulatory progesterone production and subsequent luteinization in granulosa/lutein cells.