Regulation of fetal growth: consequences and impact of being born small

The first trimester of pregnancy is the time during which organogenesis takes place and tissue patterns and organ systems are established. In the second trimester the fetus undergoes major cellular adaptation and an increase in body size, and in the third trimester organ systems mature ready for extrauterine life. In addition, during that very last period of intrauterine life there is a significant increase in body weight. In contrast to the postnatal endocrine control of growth, where the principal hormones directly influencing growth are growth hormone (GH) and the insulin-like growth factors (IGFs) via the GH-IGF axis, fetal growth throughout gestation is constrained by maternal factors and placental function and is coordinated by growth factors. In general, growth disorders only become apparent postnatally, but they may well be related to fetal life. Thus, fetal growth always needs to be considered in the overall picture of human growth as well as in its metabolic development.

Experimental arthritis: effect on growth parameters and total skeletal calcium

Aim of the study was to investigate the possible mechanisms leading to stunted growth and osteoporosis in experimental arthritis. Fourty-two female rats of 7-8 weeks of age were randomly assigned to three groups of 14 animals each: (a) controls; (b) adjuvant-inoculated (AA); and (c) adjuvant-inoculated rats receiving 10 mg cyclosporin A (CsA) orally for 30 days. Biological parameters studied were: hindpaw swelling; vertebral length progression expressed as Delta increments between days 1 and 30 as a parameter of skeletal growth, and estimation of total skeletal mineral content by dual energy X-ray absorptiometry (n=10 each group) on day 30. Endocrine parameters measured were pulsatile release of growth hormone (rGH) on day 30 following jugular cannulation and measurement of insulin-like growth factor (IGF-1) in pooled plasma from rGH profiles. Results can be summarized as follows: Untreated AA rats exhibited local signs of inflammation in comparison with controls (hindpaw diameter 8.1-8.9 mm vs. 5.3-5.6 mm in controls). Treatment with CsA normalized this parameter (4.9-5.6 mm). Vertebral growth was significantly retarded in AA rats in comparison with controls (214+/-32 vs. 473+/-33 microm; p<0.001). Administration of CsA normalized vertebral size increment with a clear tendency to overgrowth (523+/-43 microm, n.s.). There was also a marked reduction in total skeletal mineral content in diseased (AA) rats as compared to controls (5.8+/-0.1 vs. 7.5+/-0.1g [OH-apatite]; p<0.001), and a moderate but significant increment above controls in the group receiving CsA (8.0+/-0.1 vs. 7.5+/-0.1g [OH-appatite]; p<0.04). Integrated rGH profiles exhibited a significant fall in arthritic rats and were completely restored to normal under CsA treatment. A trend toward higher rGH values was observed in the latter group (2908+/-554 in AA vs. 8317+/-1492 ng/ml/240 min in controls; p<0.001, and 10940+/-222 ng/ml/240 min, n.s. in the CsA group). There was a good correlation between skeletal growth and rGH pulsatility (r=0.81; p<0.001). IGF-1 followed a similar pattern (630+/-44 in AA vs. 752+/-30 ng/ml in controls; p<0.04, and 769+/-59 ng/ml in the CsA group, n.s. vs. controls). Thus, a clear tendency to skeletal overgrowth following treatment was observed in agreement with the hormonal data. It can therefore be concluded that, in experimental arthritis, attenuated GH-spiking and reduced circulating IGF-1 appear to be causally related to growth retardation, probably mimicking signs and symptoms observed in juvenile arthritis. Therapy with CsA is followed by normalization of hormonal and biological parameters accompanied by a catch up phenomenon in skeletal growth which is also observed clinically in juvenile arthritis. Generalized osteopenia is a prominent feature seemingly connected with the growth abnormalities as they parallel each other during the evolution of the disease and respond equally to therapy.

Associations with multiple pituitary hormone deficiency in patients with an ectopic posterior pituitary gland

INTRODUCTION: The presence of an ectopic posterior pituitary gland (EPP) on magnetic resonance imaging (MRI) is associated with hypopituitarism with one or more hormone deficiencies. We aimed to identify risk factors for having multiple pituitary hormone deficiency (MPHD) compared to isolated growth hormone deficiency (IGHD) in patients with an EPP. METHODS: In 67 patients (45 male) with an EPP on MRI, the site (hypothalamic vs. stalk) and surface area (SA) [ x (maximum diameter/2) x (maximum height/2), mm(2)] of the EPP were recorded and compared in patients with IGHD and MPHD in relation to clinical characteristics. RESULTS: In MPHD (n = 32) compared to IGHD (n = 35) patients: age of presentation was younger (1.4 [0.1-10.7]vs. 4.0 [0.1-11.3] years, P = 0.005), major incidents during pregnancy were increased (47%vs. 20%, P = 0.02) as were admissions to a neonatal intensive care unit (NICU) (60%vs. 26%, P = 0.04), whilst EPP SA was lower (12.3 [2.4-34.6]vs. 25.7 [6.9-48.2] mm(2), P < 0.001). In patients with a hypothalamic (n = 56) compared to a stalk sited EPP (n = 11): prevalence of MPHD was greater (55%vs. 9%,P = 0.05) and EPP surface area was smaller (17.3 [2.4-48.2]vs. 25.3 [11.8-38.5] mm(2), P < 0.001). In regression analysis, after adjusting for age, presence of MPHD was associated with: major incidents during pregnancy (RR 6.8 [95%CI 1.2-37.7]), hypothalamic EPP site (RR 10.9 [1.0-123.9]) and small EPP SA (RR 2.5 [1.0-5.0] for tertiles of SA). CONCLUSION: In patients with an EPP, adverse antenatal events, size (small) and position (hypothalamic) of the posterior pituitary gland on MRI were associated with MPHD. These findings suggest that adverse factors during pregnancy may be important for the development of an EPP.

Growth after Hypophyseal Stalk Transection and Hypophysectomy in Beef Calves

Growth hormone (GH) is a metabolic hormone that plays an important role in long-bone growth and muscle accretion in mammals. The anterior pituitary gland at the base of the brain is the primary site of GH production and release into the general circulation. Neurons in the arcuate nucleus of the hypothalamus in the lower part of the brain secrete GH-releasing hormone ([GHRH] or factor [GRF]) and GH-release-inhibiting hormone ([GHRIH] or somatostatin [SRIH]) that acutely modulate GH secretion by the pituitary gland. The pituitary gland is connected to the median eminence of the hypothalamus by a stalk (hypophyseal stalk). Complete surgical removal of the pituitary gland (hypophysectomy) arrests growth and greatly impairs metabolism in laboratory and farm animal species. Daily subcutaneous injection of bovine GH (bGH) in immature hypophysectomized rats significantly increased body growth and epiphyseal plate width of the long-bone (tibia) compared with diluent-treated hypophysectomized controls. Growth rate was less, however, in the bGH-treated animals compared with intact controls. In beef calves, hypophysectomy completely arrested body weight gain and long-bone growth. GH is secreted in an episodic pattern in young growing intact calves. Episodic GH secretion was abolished immediately following hypophyseal stalk transection, and basal GH blood concentration was less than in shamoperated controls. Regardless, growth continued in these stalk-transected calves during a 1,008-day period, but at a lower growth rate than seen in the sham-operated controls. At autopsy, pituitary gland weight was greatly decreased in hypophyseal stalktransected compared with sham-operated calves. Thus, in spite of obliterated episodic GH release and decreased basal secretion of GH, the isolated pituitary gland of hypophyseal stalk transected calves continues to secrete sufficient amounts of GH for significant growth and development throughout a long period.

Brain Regulation of Growth in Beef Calves

Small peptide hormones produced in the lower part of the brain (hypothalamus) regulate episodic and basal secretion of hormones from the anterior pituitary gland that affect metabolism and growth in cattle. This study focused on long-term growth in young calves subjected to hypophysectomy (HYPOX), hypophyseal stalk transection (HST), and sham operation control (SOC). Crossbred (Hereford x Aberdeen Angus) and Hereford, and Aberdeen Angus calves were HYPOX (n = 5), HST (n = 5), or SOC (n = 8) at 146 days of age, whereas another group was HST (n = 5) or SOC (n = 7) at 273 days of age. Body weight was determined every 21 days from birth to 1008 days of age. From day 146-1008, growth was arrested (P < 0.001) in HYPOX (0.06 kg/day) compared with SOC (0.50 kg/day) calves. Growth continued but at a significantly lower rate (P < 0.05) in calves HST at 146 days (0.32 kg/day) and 273 days (0.32 kg/day) compared with SOC (0.50 kg/day). Although episodic growth hormone (GH) secretion was abolished and peripheral blood serum GH concentration remained consistently lower in HST calves (2.4 ng/ml) than in the SOC (5.5 ng/ml; P < 0.01), the calves continued to grow throughout 1008 days. Peripheral serum thyroid stimulating hormone (TSH) concentration was less (P < 0.05) in HST compared with SOC calves. There was an abrupt decrease (P < 0.001) in serum thyroxine (T4) (4-fold) and triiodothyronine (T3) (3-fold) concentration after surgery that remained to 360 days in HST compared with SOC calves. At sacrifice, pituitary gland weight was markedly reduced (P < 0.001) in HST (0.18 g/100 kg body weight) compared with SOC (0.55 g/100 kg body weight) calves. Histological examination of pituitary glands from HST calves indicated the persistence of secretory GH and TSH cells in the same areas of the anterior pituitary gland as SOC calves. Coronal sections of the gland revealed GH and TSH secreting cells in HST calves that were similar to the controls. These results indicate that long-term growth continues, but at a slower rate, after hypophyseal stalk transection of immature calves in spite of complete abolition of episodic GH secretion and consistently decreased basal secretion of GH, TSH, T4, and T3 compared with sham-operated animals. Growth was abolished after hypophysectomy of immature calves in which circulating GH and TSH was undetectable.

Congenital proprotein convertase 1/3 deficiency causes malabsorptive diarrhea and other endocrinopathies in a pediatric cohort

BACKGROUND & AIMS Proprotein convertase 1/3 (PC1/3) deficiency, an autosomal-recessive disorder caused by rare mutations in the proprotein convertase subtilisin/kexin type 1 (PCSK1) gene, has been associated with obesity, severe malabsorptive diarrhea, and certain endocrine abnormalities. Common variants in PCSK1 also have been associated with obesity in heterozygotes in several population-based studies. PC1/3 is an endoprotease that processes many prohormones expressed in endocrine and neuronal cells. We investigated clinical and molecular features of PC1/3 deficiency. METHODS We studied the clinical features of 13 children with PC1/3 deficiency and performed sequence analysis of PCSK1. We measured enzymatic activity of recombinant PC1/3 proteins. RESULTS We identified a pattern of endocrinopathies that develop in an age-dependent manner. Eight of the mutations had severe biochemical consequences in vitro. Neonates had severe malabsorptive diarrhea and failure to thrive, required prolonged parenteral nutrition support, and had high mortality. Additional endocrine abnormalities developed as the disease progressed, including diabetes insipidus, growth hormone deficiency, primary hypogonadism, adrenal insufficiency, and hypothyroidism. We identified growth hormone deficiency, central diabetes insipidus, and male hypogonadism as new features of PCSK1 insufficiency. Interestingly, despite early growth abnormalities, moderate obesity, associated with severe polyphagia, generally appears. CONCLUSIONS In a study of 13 children with PC1/3 deficiency caused by disruption of PCSK1, failure of enteroendocrine cells to produce functional hormones resulted in generalized malabsorption. These findings indicate that PC1/3 is involved in the processing of one or more enteric hormones that are required for nutrient absorption.

The effect of idursulfase on growth in patients with Hunter syndrome: data from the Hunter Outcome Survey (HOS)

Hunter syndrome (mucopolysaccharidosis type II) is a rare and life-limiting multisystemic disorder with an X-linked recessive pattern of inheritance. Short stature is a prominent feature of this condition. This analysis aimed to investigate the effects of enzyme replacement therapy with idursulfase on growth in patients enrolled in HOS - the Hunter Outcome Survey which is a multinational observational database. As of Jan 2012, height data before treatment were available for 567 of 740 males followed prospectively after HOS entry. Cross-sectional analysis showed that short stature became apparent after approximately 8 years of age; before this, height remained within the normal range. Age-corrected standardized height scores (z-scores) before and after treatment were assessed using piecewise regression model analysis in 133 patients (8-15 years of age at treatment start; data available on ≥ 1 occasion within +/-24 months of treatment start; growth hormone-treated patients excluded). Results showed that the slope after treatment (slope=-0.005) was significantly improved compared with before treatment (slope=-0.043) (difference=0.038, p=0.004). Analysis of covariates (age at treatment start, cognitive involvement, presence of puberty at the start of ERT, mutation type, functional classification), showed a significant influence on growth of mutation type (height deficit in terms of z-scores most pronounced in patients with deletions/large rearrangements/nonsense mutations, p<0.0001) and age (most pronounced in the 12-15-year group, p<0.0001). Cognitive involvement, pubertal status at the start of ERT and functional classification were not related to the growth deficit or response to treatment. In conclusion, the data showed an improvement in growth rate in patients with Hunter syndrome following idursulfase treatment.

Radiometrical, hormonal and biological correlates of skeletal growth in the female rat from birth to senescence

OBJECTIVE We investigated the skeletal growth profile of female rats from birth to senescence (100weeks) on the basis of sequential radiometrical, hormonal and biochemical parameters. DESIGN Weaning rats entered the study which was divided into two sections: a) sequential measurements of vertebral and tibial growths and bone mineral density (BMD), estimation of mineral content of the entire skeleton (BMC) and chemical analysis of vertebral Ca; and b) determination of basal and pulsatile growth hormone (rGH), insulin-like growth hormone (IGF-I), estradiol (E2), parathyroid hormone (PTH), osteocalcin (OC) and urinary d-pyridinoline (dp) throughout the experimental period. RESULTS Vertebral and tibial growths ceased at week 25 whereas BMD and BMC as well as total vertebral Ca exhibited a peak bone mass at week 40. rGH pulsatile profiles were significantly higher in younger animals coinciding with the period of active growth and IGF-I peaked at 7weeks, slowly declining thereafter and stabilizing after week 60. OC and dp closely paralleled IGF-I coinciding with the period of enhanced skeletal growth, remaining thereafter in the low range indicative of reduced bone turnover. E2 increased during reproductive life but the lower values subsequently recorded were still in the physiological range, strongly suggesting a protective role of this steroid on bone remodeling. PTH followed a similar profile to E2, but the significance of this after completion of growth remains unclear. CONCLUSIONS Mechanisms governing skeletal growth in the female rat appear similar to those in humans. Bone progression and attainment of peak bone mass are under simultaneous control of rGH, IGF-I and calciotropic hormones and are modulated by E2. This steroid seems to protect the skeleton from resorption before senescence whereas the role of PTH in this context remains uncertain.

Invited review: Growth-promoting effects of colostrum in calves based on interaction with intestinal cell surface receptors and receptor-like transporters

The postnatal development and maturation of the gastrointestinal (GI) tract of neonatal calves is crucial for their survival. Major morphological and functional changes in the calf's GI tract initiated by colostrum bioactive substances promote the establishment of intestinal digestion and absorption of food. It is generally accepted that colostrum intake provokes the maturation of organs and systems in young calves, illustrating the significance of the cow-to-calf connection at birth. These postnatal adaptive changes of the GI tissues in neonatal calves are especially induced by the action of bioactive substances such as insulin-like growth factors, hormones, or cholesterol carriers abundantly present in colostrum. These substances interact with specific cell-surface receptors or receptor-like transporters expressed in the GI wall of neonatal calves to elicit their biological effects. Therefore, the abundance and activity of cell surface receptors and receptor-like transporters binding colostral bioactive substances are a key aspect determining the effects of the cow-to-calf connection at birth. The present review compiles the information describing the effects of colostrum feeding on selected serum metabolic and endocrine traits in neonatal calves. In this context, the current paper discusses specifically the consequences of colostrum feeding on the GI expression and activity of cell-receptors and receptor-like transporters binding growth hormone, insulin-like growth factors, insulin, or cholesterol acceptors in neonatal calves.

EXPRESSION OF THE HUMAN PLACENTAL LACTOGEN GENES

The placenta is the site of synthesis of various peptide and steroid hormones related to pregnancy. Human placental lactogen (hPL) is the predominant peptide hormone secreted by term placenta and its synthesis is tissue-specific and coupled to placenta development. The objective of this work was to study the structure and expression of the hPL.^ Poly(A('+))RNA from human term placenta was translated in a mouse-derived cell-free system. A major band corresponding to pre-hPL and a minor band comigrating with mature hPL, represent (TURN)15% of the total radioactively labeled proteins. Analysis of the poly(A('+))RNA showed a prominent band at approximately 860 nucleotides. A corresponding band was observed in Northern blots of total RNA, hybridized with {('32)P}-labeled recombinant plasmid containing a portion of hPL cDNA. Similar analyses of nuclear RNA showed at least four additional bands at 990, 1200, 1460 and 1760 nucleotides, respectively, which are likely precursors of hPL mRNA. Poly(A('+))RNA was used to construct a cDNA library, of which approximately 5% of the clones were found to hybridize to hPL DNA sequences. Heteroduplexes constructed between a clone containing a 815 bp hPL cDNA insert and a hPL genomic DNA clone revealed four small intervening sequences which can account for the lengths observed in hnRNA molecules.^ Recombinant plasmid HCS-pBR322 containing a 550 bp insert of a cDNA transcript of human placental lactogen (hPL) mRNA was ('3)H-labeled an hybridized in situ to human chromosome preparations. These experiments allowed assignment of the hPL and growth hormone (hGH) genes, which have over 90% nucleotide homology in their coding sequences, to band q22-24 of chromosome 17. A gene copy number experiment showed that both genes are present in (TURN)3 copies per haploid genome.^ Experiments were designed to determine if all members of the hPL gene cluster, consisting of four non-allelic genes, are transcribed in term placenta. Advantage was taken of differences in restriction endonuclease sites in the coding portions of the different hPL genes, to distinguish the putative cDNAs of the transcriptionally active genes. Two genes were found to be represented in the cDNA library and their cDNA transcripts were isolated and characterized. Three independent methods showed that their corresponding mRNAs are about equally represented in the hPL mRNA population. The two cDNAs code for prehPL proteins which differ at a single amino acid position. However the secreted hPLs have identical amino acid sequences. A tetramer insertion duplication was found in a palindrome area of the 3' untranslated region of one of the hPL mRNAs. ^

An interferon-inducible protein, p202, in cancer gene therapy

Interferons (IFNs) have been shown to exert antiviral, cell growth regulatory, and immunomodulatory effects on target cells. Both type I (α and β) and type II (γ) IFNs regulate cellular activities by specifically inducing the expression or activation of endogenous proteins that perform distinct biological functions. p202 is a 52 kDa nuclear phosphoprotein known to be induced by IFNs. p202 interacts with a variety of cellular transcription and growth regulatory factors and affects their functions. ^ In this report, we showed that the expression of p202 was associated with an anti-proliferative effect on human prostate cancer cells. Cells that expressed p202 showed reduced ability to grow in soft-agar, indicating a loss of transformation phenotype. More importantly, p202 expression reduced the tumorigenicity of human prostate cancer cells. p202-expressing cells exhibit an elevated level of hypophosphorylated form of pRb, and reduced level of cyclin B1 and p55CDC. ^ Our data suggest that p202 is a growth inhibitor gene in prostate cancer cells and its expression may also suppress transformation phenotype and tumorigenicity of prostate cancer cells. ^ In addition to inhibiting in vitro cell growth, suppressing the tumorigenicity of breast cancer cells in vivo, p202 expression could sensitize breast cancer cells to apoptosis induced by TNF-α treatment. One possible mechanism contributing to this sensitization is the inactivation of NF-κB by its interaction with p202. These results provide a scientific basis for a novel therapeutic strategy that combines p202 and TNF-α treatment against breast cancer. ^ It has been reported that NF-κB is constitutively active in human pancreatic cancer cells. Since p202 interacts with NF-κB and inhibits its activity, we examined a potential p202-mediated anti-tumor activity in pancreatic cancer. We used both ectopic and orthotopic xenograft models and demonstrated that p202 expression is associated with multiple anti-tumor activities that include inhibition of tumor growth, reduced tumorigenicity, prolonged survival, and remarkably, suppression of metastasis and angiogenesis. In vitro invasion assay also showed that p202-expressing pancreatic cancer cells are less invasive than those without p202 expression. That observation was supported by the findings that p202-expressing tumors showed reduced expression of angiogenic factors such as IL-8, and VEGF by inhibiting their transcription, and p202-expressing pancreatic cancer cells have reduced level of MAP-2 activity, a secreted protease activity important for metastasis. Together, our results strongly suggest that p202 expression mediates multiple anti-tumor activities against pancreatic cancer, and that may provide a scientific basis for developing a p202-based gene therapy in pancreatic cancer treatment. ^ Importantly, we demonstrated a treatment efficacy by using p202/SN2 liposome complex in a nude mice orthotopic breast cancer, and an ectopic pancreatic cancer xenograft model, through systemic and intra-tumor injection respectively. These results suggest a feasibility of using p202/SN2 liposome in future pre-clinical gene therapy experiments. ^

Insulin-like growth factor binding protein 2 is a growth inhibitory protein conserved in zebrafish

Fish serum contains several specific binding proteins for insulin-like growth factors (IGFBPs). The structure and physiological function of these fish IGFBPs are unknown. Here we report the complete primary sequence of a zebrafish IGFBP deduced from cDNA clones isolated by library screening and rapid amplification of cDNA ends. The full-length 1,757-bp cDNA encodes a protein of 276 aa, which contains a putative 22-residue signal peptide and a 254-residue mature protein. The mature zebrafish IGFBP has a predicted molecular size of 28,440 Da and shows high sequence identity with human IGFBP-2 (52%). The sequence identities with other human IGFBPs are <37%. Chinese hamster ovary cells stably transfected with the zebrafish IGFBP-2 cDNA secreted a 31-kDa protein, which bound to IGF-I and IGF-II with high affinity, but did not bind to Des(1–3)IGF-I or insulin. Northern blot analyses revealed that the zebrafish IGFBP-2 transcript is a 1.8-kb band expressed in many embryonic and adult tissues. In adult zebrafish, IGFBP-2 mRNA levels were greatly reduced by growth hormone treatment but increased by prolonged fasting. When overexpressed or added to cultured zebrafish and mammalian cells, the zebrafish IGFBP-2 significantly inhibited IGF-I-stimulated cell proliferation and DNA synthesis. These results indicate that zebrafish IGFBP-2 is a negative growth regulator acting downstream in the growth hormone-IGF-I axis.

Human trophoblast and choriocarcinoma expression of the growth factor pleiotrophin attributable to germ-line insertion of an endogenous retrovirus

Retroviral elements are found in abundance throughout the human genome but only rarely have alterations of endogenous genes by retroviral insertions been described. Herein we report that a human endogenous retrovirus (HERV) type C is inserted in the human growth factor gene pleiotrophin (PTN) between the 5′ untranslated and the coding region. This insert in the human genome expands the region relative to the murine gene. Studies with promoter-reporter constructs show that the HERV insert in the human PTN gene generates an additional promoter with trophoblast-specific activity. Due to this promoter function, fusion transcripts between HERV and the open reading frame of PTN (HERV-PTN) were detected in all normal human trophoblast cell cultures as early as 9 weeks after gestation (n = 7) and in all term placenta tissues (n = 5) but not in other normal adult tissues. Furthermore, only trophoblast-derived choriocarcinoma cell lines expressed HERV-PTN mRNA whereas tumor cell lines derived from the embryoblast (teratocarcinoma) or from other lineages failed to do so. We investigated the significance of HERV-PTN mRNA in a choriocarcinoma model by targeting this transcript with ribozymes and found that the depletion of HERV-PTN mRNA prevents human choriocarcinoma growth, invasion, and angiogenesis in mice. This suggests that the tissue-specific expression of PTN due to the HERV insertion in the human genome supports the highly aggressive growth of human choriocarcinoma and possibly of the human trophoblast.

Two gonadotropin-releasing hormone receptor subtypes with distinct ligand selectivity and differential distribution in brain and pituitary in the goldfish (Carassius auratus)

In the goldfish (Carassius auratus) the two endogenous forms of gonadotropin-releasing hormone (GnRH), namely chicken GnRH II ([His5,Trp7,Tyr8]GnRH) and salmon GnRH ([Trp7,Leu8]GnRH), stimulate the release of both gonadotropins and growth hormone from the pituitary. This control is thought to occur by means of the stimulation of distinct GnRH receptors. These receptors can be distinguished on the basis of differential gonadotropin and growth hormone releasing activities of naturally occurring GnRHs and GnRHs with variant amino acids in position 8. We have cloned the cDNAs of two GnRH receptors, GfA and GfB, from goldfish brain and pituitary. Although the receptors share 71% identity, there are marked differences in their ligand selectivity. Both receptors are expressed in the pituitary but are differentially expressed in the brain, ovary, and liver. Thus we have found and cloned two full-length cDNAs that appear to correspond to different forms of GnRH receptor, with distinct pharmacological characteristics and tissue distribution, in a single species.