Second Form Of Gonadotropin-Releasing Hormone Research Articles

PSV-A-7 Quality Assessments of Sperm from Gnrh-II Receptor Knockdown (KD) Boars

Abstract Pigs are the only livestock species encoding functional proteins for both the second form of gonadotropin-releasing hormone (GnRH-II) and its receptor (GnRHR-II). Previously, we determined that GnRHR-II localizes to the connecting piece of ejaculated sperm, whereas GnRH-II is present within seminal plasma, suggesting an autocrine/paracrine interaction influencing porcine sperm function. To examine the GnRH-II/GnRHR-II system further, we produced a swine line with reduced endogenous expression of GnRHR-II (GnRHR-II KD). Therefore, our objective was to assess sperm quality of ejaculates collected from GnRHR-II KD (n = 3) and littermate control (n = 3) boars. Semen was extended (37.5 x 106 sperm/mL) in Androstar Plus and subjected to flow cytometry (Kuster Research and Consulting, Inc.; Atkinson, IL). Assays measured DNA compaction, membrane fluidity and viability, acrosome integrity, mitochondrial depolarization, and morphology. Data were analyzed using the MIXED procedure of SAS; the model included ejaculate as the experimental unit and line as a fixed effect. DNA compaction, membrane fluidity, acrosome integrity, mitochondrial depolarization, and morphology were not statistically different between lines (P > 0.05). However, the percentage of sperm with a viable (intact) plasma membrane was reduced in GnRHR-II KD boars (87.4 ± 0.8%) compared with controls (89.6 ± 0.8%; P < 0.05). Although differences did not reach significance, DNA compaction (a measure of sperm chromatin integrity when undergoing acid stress) was doubled and mitochondrial depolarization (reflective of mitochondrial function) was 11% greater in sperm from transgenic males relative to littermate controls, indicating that GnRHR-II KD sperm are more susceptible to environmental stressors and have altered energy production. Thus, these initial data suggest disruptions in the function and fertilizing capacity of GnRHR-II KD sperm, implying that GnRHR-II may represent a potential biomarker for boar fertility. Supported by USDA/NIFA AFRI (2017-67015-26508) and Hatch Multistate (NEB-26-244) funds. USDA is an equal opportunity provider and employer.

PSX-A-3 Late-Breaking: Analysis of serum chemistry for metabolic function in GnRH-II receptor knockdown and littermate control boars

Abstract Pigs are the only livestock species encoding functional proteins for both the second form of gonadotropin-releasing hormone (GnRH-II) and its receptor (GnRHR-II), which are uniquely expressed in reproductive and non-reproductive tissues. To examine the physiological role of the GnRH-II/GnRHR-II system, we produced a swine line with reduced endogenous levels of GnRHR-II (GnRHR-II KD); males exhibit 70% diminished testicular GnRHR-II mRNA levels and 82% reduced circulating testosterone concentrations. Given that testosterone impacts metabolism, blood was collected from GnRHR-II KD (n = 5) and littermate control (n = 5) boars via indwelling jugular catheters, with serum isolated and subjected to veterinary diagnostic panels for metabolic analyte examination (PhysLab, Lincoln, NE). Statistical analyses utilized the MIXED procedure of SAS; the model included line as fixed and litter as random effects. Creatine kinase and blood urea nitrogen (BUN):creatinine ratios were elevated, creatinine was reduced (P < 0.01), and thyroxine tended to be decreased (P < 0.10) in GnRHR-II KD compared with control boars. Glucose, BUN, amylase, and lipase levels were not different. Liver products differed in transgenic versus control boars; levels of lactic dehydrogenase, aspartate and alanine aminotransferases (AST; ALT), and gamma-glutamyl transpeptidase were higher, whereas AST:ALT ratios, total protein, albumin, and globulin levels were lower (P < 0.05) in GnRHR-II KD boars. Albumin:globulin ratios and bilirubin (total and direct) did not differ. Additionally, serum cholesterol was decreased (P < 0.05), non-high density lipoproteins (HDLs) and low density lipoproteins (LDLs) tended to be decreased (P < 0.10), and triglycerides, HDLs, and cholesterol:HDL ratios did not differ between GnRHR-II KD and control males. These data suggest metabolic disruption in GnRHR-II KD boars, which may be due to suppressed gonadal steroidogenesis or ubiquitous knockdown of GnRHR-II expression. Supported by USDA/NIFA AFRI (2017-67015-26508) and Hatch Multistate (NEB-26–244) funds. USDA is an equal opportunity provider and employer.

Differential role of gonadotropin-releasing hormone on human ovarian epithelial cancer cell invasion

Ovarian cancer is the most lethal of all gynecological cancers. Most deaths from ovarian cancer are due to widespread intraperitoneal metastases and malignant ascites. However, mechanisms of invasion in ovarian cancer remain poorly understood. In this study, we examined the effects of gonadotropin-releasing hormone (GnRH)-I (the classical mammalian GnRH), GnRH-II (a second form of GnRH), and GnRH receptor on invasion using two human ovarian carcinoma cell lines, OVCAR-3 and SKOV-3. Here we demonstrated that in OVCAR-3, GnRH-I and GnRH-II promoted cell invasion, whereas in SKOV-3, GnRH-I and GnRH-II inhibited cell invasion. Transfection of small interfering RNA to abrogate the gene expression of GnRH receptor reversed GnRH-I and GnRH-II-mediated invasion activities, suggesting that the same receptor, type I GnRH receptor, is essential for the effects of GnRH-I and GnRH-II in both OVCAR-3 and SKOV-3. Treatment of SKOV-3 cells with GnRH-I or GnRH-II resulted in a decrease in matrix metalloproteinase 2 but an increase in tissue inhibitor of metalloproteinase 2 secretions. In addition, we found that GnRH-I and GnRH-II interfered with activation of the phosphatidylinositol-3-kinase/AKT pathway that is well documented to stimulate proteolysis and invasion of ovarian cancer cells. Taken together, these observations suggest that GnRH-I and GnRH-II play key regulatory roles in ovarian tumor cell invasion and extracellular matrix degradation.

Differential regulation of two forms of gonadotropin-releasing hormone messenger ribonucleic acid by gonadotropins in human immortalized ovarian surface epithelium and ovarian cancer cells

Although gonadotropin-releasing hormone (GnRH) has been shown to play a role as an autocrine/ paracrine regulator of cell growth in ovarian surface epithelium and ovarian cancer, the factors which regulate the expression of GnRH and its receptor in these cells are not well characterized. In the present study, we employed real-time PCR to determine the potential regulatory effect of gonadotropins on the expression levels of GnRH I (the mammalian GnRH), GnRH II (a second form of GnRH) and their common receptor (GnRHR) in immortalized ovarian surface epithelial (IOSE-80 and IOSE-80PC) cells and ovarian cancer cell lines (A2780, BG-1, CaOV-3, OVCAR-3 and SKOV-3). The cells were treated with increasing concentrations (100 and 1000 ng/ml) of recombinant follicle-stimulating hormone (FSH) or luteinizing hormone (LH) for 24 h. Treatment with FSH or LH reduced GnRH II mRNA levels in both IOSE cell lines and in three out of five ovarian cancer cell lines (A2780, BG-1 and OVCAR-3). A significant decrease in GnRHR mRNA levels was observed in IOSE and ovarian cancer cells, except CaOV-3 cells, following treatment with FSH or LH. In contrast, treatment with either FSH or LH had no effect on GnRH I mRNA levels in these cells, suggesting that gonadotropins regulate the two forms of GnRH and its receptor differentially. In separate experiments, the effect of gonadotropins on the anti-proliferative action of GnRH I and GnRH II agonists in IOSE-80, OVCAR-3 and SKOV-3 cells was investigated. The cells were pretreated with FSH or LH (100 ng/ml) for 24 h after which they were treated with either GnRH I or GnRH II (100 ng/ml) for 2 days, and cell growth was assessed by the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide] assay. Pretreatment of the cells with FSH or LH significantly reversed the growth inhibitory effect of GnRH I and GnRH II agonists in these cell types. These results provide the first demonstration of a potential interaction between gonadotropins and the GnRH system in the growth regulation of normal ovarian surface epithelium and its neoplastic counterparts.

Gonadotropin-Releasing Hormone (GnRH) Receptors in Tumors: a New Rationale for the Therapeutical Application of GnRH Analogs in Cancer Patients?

Gonadotropin-Releasing Hormone (GnRH) is the hypothalamic decapeptide which plays a key role in the control of reproductive functions. By binding to specific receptors present on the pituitary gonadotropes, GnRH regulates gonadotropin release and, consequently, steroid hormone secretion from the gonads. When given continuously and at high doses, GnRH agonists suppress the pituitary gonadal axis through the down-regulation and desensitization of its own receptors. Based on this rationale, pituitary GnRH receptors represent the target for the successful utilization of GnRH agonists (that are more stable than the native peptide) for the treatment of hormone-dependent tumors (e.g., prostate, breast, endometrial, ovarian cancers). The observation that GnRH receptors are expressed in steroid-dependent tumors, and that their activation reduces cell proliferation and metastatic behavior of cancer cell lines, both in vitro and in vivo (when inoculated into nude mice), indicates a possible additional and more direct antitumor activity for these compounds. Interestingly, GnRH receptors have been shown to be expressed also in androgen-independent prostate carcinoma, as well as in tumors that are not classically considered hormone-related (e.g., melanoma), suggesting a clinical utility of the administration of GnRH analogs also in these tumors. More recently, GnRH agonists have been proposed as useful carriers to target cytotoxic drugs or toxins to cancer cells displaying the specific GnRH receptors. A second form of GnRH (designated GnRH-II) has been discovered in most vertebrates, including humans. GnRH-II has been suggested to act through a 'putative' cognate type II GnRH receptor, which is distributed in different tissues, both normal and tumoral. In humans, a full-length functional type II GnRH receptor has not been found. Therefore, its functions as well as its possible utility as a molecular target for a GnRH-II based therapy in oncology still has to be clarified. This review will focus on the role of GnRH receptors in the control of tumor growth, progression and dissemination. It will also be discussed whether the presence of these receptors might represent an additional rationale for the clinical utility of GnRH analogs as anticancer drugs.

Human Leiomyoma Express a Second Form of Gonadotropin-Releasing Hormone (GnRH 2) and Receptor (GnRHR 2)

To determine the presence or absence of a second form of gonadotropin-releasing hormone (GnRH 2) and corresponding receptor (GnRHR 2) in human uterine myometrium and leiomyomata. High throughput genotyping of human leiomyoma and patient-matched myometrium, followed by confirmatory studies for both mRNA and protein expression of GnRH 2 and GnRHR 2. Differential expression was evaluated by paired Student’s t tests. Confidence intervals were calculated. Leiomyoma and adjacent myometrium was obtained following a hysterectomy for a symptomatic fibroid uterus from eight women enrolled into an IRB approved protocol. Microarray analysis was performed to screen for the genes of interest. Confirmation was performed by Reverse-Transcriptase Polymerase Chain Reaction (RT-PCR). Real-Time RT-PCR quantified the relative gene expression of these genes in leiomyoma compared with patient matched myometrium. Confirmation of protein expression was performed by immunohistochemistry of GnRH 2 in both leiomyoma and myometrium. Microarray analysis demonstrated expression, which was confirmed by Reverse-Transcriptase Polymerase Chain Reaction (RT-PCR). Real-Time RT-PCR demonstrated mean GnRH 2 fold difference in myometrium compared to fibroid was 0.99 (95% C.I. 0.47, 1.51), while the GnRHR 2 fold difference was 1.28 (95% C.I. 0.90, 1.66), see Table 1. Tabled 1 Immunohistochemistry confirmed the protein expression of GnRH 2 in both leiomyoma and myometrium. Figure 1 demonstrates the H&E stain of myometrium (A) and fibroid (C), immunohistochemistry staining with GnRH 2 of myometrium (B) and fibroid (D). A second form of GnRH, GnRH 2, and its corresponding receptor, GnRHR 2, exists in fibroid and myometrium. Our results support a hypothesis by which GnRH agonists could directly influence uterine fibroid regression separate from a mechanism involving estrogen and progesterone.

Differential regulation of gonadotropin-releasing hormone (GnRH)I and GnRHII messenger ribonucleic acid by gonadal steroids in human granulosa luteal cells.

In humans, reproduction was generally believed to be controlled by only one form of GnRH (called mammalian GnRH or GnRHI). However, recently, a second form of GnRH, analogous to chicken GnRHII, was discovered in several tissues, including the human ovary. The regulation and function of GnRHI in the hypothalamus has been well studied. However, the function and regulation of GnRHI, and particularly GnRHII in the ovary, is less well understood. Because gonadal sex steroids are one of the main regulators of reproduction, we investigated, in the present study, the regulation of GnRHI and GnRHII mRNA expression by 17beta-estradiol (E2) and RU486 (a progesterone antagonist) in human granulosa luteal cells (hGLCs). The levels of the mRNA transcripts encoding the two GnRH forms were examined using semiquantitative RT-PCR followed by Southern blot analysis. With time in culture, GnRHI and GnRHII mRNA levels significantly increased, by 120% and 210%, at d 8 and d 1, respectively. The levels remained elevated until the termination of these experiments at d 10. A 24-h treatment of hGLCs with E2 (10(-9) to 10(-7) M) resulted in a dose-dependent decrease and increase in mRNA expression of GnRHI and GnRHII, respectively. E2 (10(-9) M) significantly decreased GnRHI mRNA levels (by 55%) and increased GnRHII mRNA levels (by 294%). Time-course studies demonstrated that E2 (10(-9) M) significantly decreased GnRHI mRNA levels in a time-dependent manner, with maximal inhibition of 77% at 48 h. In contrast, GnRHII mRNA levels significantly increased in a time-dependent fashion, reaching a maximum level of 280% at 24 h. Cotreatment of hGLCs with E2 and tamoxifen (an E2 antagonist) reversed the inhibitory and stimulatory effects of E2 on the mRNA expression of GnRHI and GnRHII, respectively. Time- and dose-dependent treatment with RU486 did not affect GnRHI mRNA levels in hGLCs. In contrast, RU486 treatment significantly increased GnRHII mRNA levels in hGLCs in a time- and dose-dependent fashion, with a maximum increase being observed at 24 h (with 10(-5)M RU486). In summary, the present study demonstrated that the expression of GnRHI and GnRHII at the transcriptional level is differently regulated by E2 and P4 in hGLCs.

Expression and antiproliferative effect of a second form of gonadotropin-releasing hormone in normal and neoplastic ovarian surface epithelial cells.

Epithelial ovarian carcinomas are the most common cause of death from gynecological malignancies and appear to arise from ovarian surface epithelium (OSE), but the exact mechanism of ovarian tumorigenesis has not been elucidated. Recent cloning of a second form of gonadotropin-releasing hormone (GnRH-II) has been reported in various human tissues including the ovary. However, the expression and role of GnRH-II in human OSE and ovarian carcinomas is not known. In the present study, we demonstrated that in addition to the GnRH receptor (GnRH-R), GnRH-II mRNA is expressed in normal OSE, immortalized OSE (IOSE) cells, primary cultures of ovarian tumors and ovarian cancer cell lines. Treatments with increasing doses (10(-9)-10(-7) M) of GnRH-I and -II resulted in a growth-inhibition in both non-tumorigenic IOSE-29 and tumorigenic IOSE-29EC cells. These results indicate for the first time the expression and potential anti-proliferative effect of GnRH-II, suggesting that GnRH-II, similar to GnRH-I, may have a growth-regulatory effect in normal and neoplastic OSE cells.

Expression and Antiproliferative Effect of a Second Form of Gonadotropin-Releasing Hormone in Normal and Neoplastic Ovarian Surface Epithelial Cells

Epithelial ovarian carcinomas are the most common cause of death from gynecological malignancies and appear to arise from ovarian surface epithelium (OSE), but the exact mechanism of ovarian tumorigenesis has not been elucidated. Recent cloning of a second form of gonadotropin-releasing hormone (GnRH-II) has been reported in various human tissues including the ovary. However, the expression and role of GnRH-II in human OSE and ovarian carcinomas is not known. In the present study, we demonstrated that in addition to the GnRH receptor (GnRH-R), GnRH-II mRNA is expressed in normal OSE, immortalized OSE (IOSE) cells, primary cultures of ovarian tumors and ovarian cancer cell lines. Treatments with increasing doses (10−9–10−7 M) of GnRH-I and -II resulted in a growth-inhibition in both non-tumorigenic IOSE-29 and tumorigenic IOSE-29EC cells. These results indicate for the first time the expression and potential anti-proliferative effect of GnRH-II, suggesting that GnRH-II, similar to GnRH-I, may have a growth-regulatory effect in normal and neoplastic OSE cells.

A second form of gonadotropin-releasing hormone (GnRH II) activates the MMPs/TIMP-1 cascade in human decidual cells in vitro.

Objective: Implantation in the human is dependent upon the invasion of embryonic trophoblasts into the decidua of the maternal endometrium. The regulated expression of matrix metalloproteinases (MMPs) and their tissue specific inhibitors (TIMPS) have been shown to play a key role in human implantation by modulating the invasive capacity of the trophoblasts and/or mediating the cellular remodelling processes that occur in the endometrium in preparation for the implanting embryo. To date, the factors capable of regulating the expression of MMPs and TIMPs remain poorly characterised. In the present study, we have examined the ability of a novel form of Gonadotropin-Releasing Hormone (GnRH II), that is expressed in the human placenta, to regulate MMP/TIMP mRNA levels in primary cultures of human decidual cells.

A Developmental Increase in the Expression of Messenger Ribonucleic Acid Encoding a Second Form of Gonadotropin-Releasing Hormone in the Rhesus Macaque Hypothalamus

A Developmental Increase in the Expression of Messenger Ribonucleic Acid Encoding a Second Form of Gonadotropin-Releasing Hormone in the Rhesus Macaque Hypothalamus

The expression, regulation and signal transduction pathways of the mammalian gonadotropin-releasing hormone receptor

Normal mammalian sexual maturation and reproductive functions require the integration and precise coordination of hormones at the hypothalamic, pituitary, and gonadal levels. Hypothalamic gonadotropin-releasing hormone (GnRH) is a key regulator in this system; after binding to its receptor (GnRHR), it stimulates de novo synthesis and release of gonadotropins in anterior pituitary gonadotropes. Since the isolation of the GnRHR cDNA, the expression of GnRHR mRNA has been detected not only in the pituitary, but also in extrapituitary tissues, including the ovary and placenta. It has been shown that change in GnRHR mRNA is one of the mechanisms for regulating the expression of the GnRHR. To help understand the molecular mechanism(s) involved in transcriptional regulation of the GnRHR gene, the 5' flanking region of the GnRHR gene has recently been isolated. Initial characterization studies have identified several DNA regions in the GnRHR 5' flanking region which are responsible for both basal expression and GnRH-mediated homologous regulation of this gene in pituitary cells. The mammalian GnRHR lacks a C-terminus and possesses a relatively short third intracellular loop; both features are important in desensitization of many others G-protein coupled receptors (GPCRs), Homologous desensitization of GnRHR has been shown to be regulated by various serine-threonine protein kinases including protein kinase A (PKA) and protein kinase C (PKC), as well as by G-protein coupled receptor kinases (GRKs). Furthermore, GnRHR was demonstrated to couple with multiple G proteins (Gq/11, Gs, and Gi), and to activate cascades that involved the PKC, PKA, and mitogen-activator protein kinases. These results suggest the diversity of GnRHR-G protein coupling and signal transduction systems. The identification of second form of GnRH (GnRH-II) in mammals adds to the complexity of the GnRH-GnRHR system. This review summaries our recent progress in understanding the regulation of GnRHR gene expression and the GnRHR signal transduction pathways.Key words: gonadotropin-releasing hormone receptor, transcriptional regulation, desensitization, signal transduction.

The expression, regulation and signal transduction pathways of the mammalian gonadotropin-releasing hormone receptor

Normal mammalian sexual maturation and reproductive functions require the integration and precise coordination of hormones at the hypothalamic, pituitary, and gonadal levels. Hypothalamic gonadotropin-releasing hormone (GnRH) is a key regulator in this system; after binding to its receptor (GnRHR), it stimulates de novo synthesis and release of gonadotropins in anterior pituitary gonadotropes. Since the isolation of the GnRHR cDNA, the expression of GnRHR mRNA has been detected not only in the pituitary, but also in extrapituitary tissues, including the ovary and placenta. It has been shown that change in GnRHR mRNA is one of the mechanisms for regulating the expression of the GnRHR. To help understand the molecular mechanism(s) involved in transcriptional regulation of the GnRHR gene, the 5' flanking region of the GnRHR gene has recently been isolated. Initial characterization studies have identified several DNA regions in the GnRHR 5' flanking region which are responsible for both basal expression and GnRH-mediated homologous regulation of this gene in pituitary cells. The mammalian GnRHR lacks a C-terminus and possesses a relatively short third intracellular loop; both features are important in desensitization of many others G-protein coupled receptors (GPCRs), Homologous desensitization of GnRHR has been shown to be regulated by various serine-threonine protein kinases including protein kinase A (PKA) and protein kinase C (PKC), as well as by G-protein coupled receptor kinases (GRKs). Furthermore, GnRHR was demonstrated to couple with multiple G proteins (Gq/11, Gs, and Gi), and to activate cascades that involved the PKC, PKA, and mitogen-activator protein kinases. These results suggest the diversity of GnRHR-G protein coupling and signal transduction systems. The identification of second form of GnRH (GnRH-II) in mammals adds to the complexity of the GnRH-GnRHR system. This review summaries our recent progress in understanding the regulation of GnRHR gene expression and the GnRHR signal transduction pathways.

Regional expression of mRNA encoding a second form of gonadotropin-releasing hormone in the macaque brain.

In mammals, reproduction is thought to be controlled by a single neuropeptide, gonadotropin-releasing hormone (GnRH-I), which regulates the synthesis and secretion of gonadotropins from the pituitary gland. However, another form of this decapeptide (GnRH-II), of unknown function, also exists in the brain of many vertebrate species, including humans; it is encoded by a different gene and its amino acid sequence is 70% identical to that of GnRH-I. Here we report the cloning of a GnRH-II cDNA from the rhesus macaque (Macaca mulatta), and show for the first time by in situ hybridization that GnRH-II mRNA is expressed in the primate midbrain, hippocampus and discrete nuclei of the hypothalamus, including the supraoptic, paraventricular, suprachiasmatic and arcuate. Because the regional distribution pattern of cells containing GnRH-II mRNA is largely dissimilar to that of cells containing GnRH-I mRNA, it is likely that these two cell populations receive distinct neuroendocrine inputs and thus regulate GnRH synthesis and release differently.

Regional Expression of mRNA Encoding a Second Form of Gonadotropin-Releasing Hormone in the Macaque Brain

Regional Expression of mRNA Encoding a Second Form of Gonadotropin-Releasing Hormone in the Macaque Brain

A Second Form of Gonadotropin-Releasing Hormone (GnRH) with Characteristics of Chicken GnRH-II Is Present in the Primate Brain

A Second Form of Gonadotropin-Releasing Hormone (GnRH) with Characteristics of Chicken GnRH-II Is Present in the Primate Brain

A second form of gonadotropin-releasing hormone (GnRH) with characteristics of chicken GnRH-II is present in the primate brain.

The primate brain was thought to contain only the GnRH known as mammalian GnRH (mGnRH). This study investigates whether a second form of GnRH exists within the primate brain. We found that brain extracts from adult stumptail and rhesus monkeys contained two forms of GnRH that were similar to mGnRH and chicken GnRH-II (cGnRH-II) based on the elution position of the peptides from HPLC and on cross-reactivity with antisera that are specific to mammalian or chicken GnRH-II in RIAs. The fetal brain of rhesus monkeys also contained mGnRH and a cGnRH-II-like peptide by the same criteria. Immunocytochemistry with a cGnRH-II-specific antiserum in adult and fetal rhesus monkeys showed immunopositive neurons generally scattered in the periaqueductal region of the midbrain, with a few positive cells in the posterior basal hypothalamus. Neurons immunopositive for cGnRH-II were fewer in number and smaller in size, with less defined nuclei and thinner neurites compared with those for mGnRH. Administration of synthetic cGnRH-II to adult rhesus monkeys resulted in a significant increase in the plasma LH concentration during the luteal phase of the menstrual cycle, but not during the midfollicular phase. We conclude that the primate brain contains mGnRH and a cGnRH-II-like molecule, although the function of the latter is unknown.

Primary structure of gonadotropin-releasing hormone from lamprey brain.

The primary structure of gonadotropin-releasing hormone (GnRH) isolated from whole brains of lamprey is pGlu-His-Tyr-Ser-Leu-Glu-Trp-Lys-Pro-Gly-NH2. This unique decapeptide was isolated and purified from brain extracts by reverse-phase high performance liquid chromatography. The structure of the peptide was established from chymotryptic fragments that were identified by protein sequence analysis and fast atom bombardment mass spectrometry. The peptide reacts with an antiserum raised against mammalian GnRH and is structurally identified as a member of the GnRH family by the amino and carboxyl termini of pGlu1-His2 and Pro9-Gly10NH2, the conservation of Ser4 in the internal segment of the molecule and its length of 10 amino acids. For the first time, amino acid substitutions are found in positions 3 and 6, critical for biological potency and conformation, respectively. Additionally, a second form of GnRH (lamprey II GnRH), representing about 10% of the total GnRH immunoreactive material in the brain, was isolated; its amino acid composition differs by 3 residues from lamprey I GnRH. Synthetic lamprey I GnRH elevates plasma estradiol in adult female lampreys.