The evolutionary origins of hormones, neurotransmitters, and other extracellular chemical messengers: implications for mammalian biology

Diarrhoea and malabsorption in acquired immune deficiency syndrome: a study of four cases with special emphasis on opportunistic protozoan infestations

Chronic diarrhoea is frequent in acquired immune deficiency syndrome (AIDS) but has been poorly investigated so far. We report four patients with AIDS in whom diarrhoea and malabsorption were outstanding features, and who underwent extensive digestive investigations. Diarrhoea was a presenting symptom in all subjects and was of secretory type in three of them. D-xylose and vitamin B12 were malabsorbed in all cases; steatorrhea was found in the two patients who could ingest significant amounts of fat. Faecal alpha 1-antitrypsin clearance was increased in all subjects. Search for digestive pathogens showed unusual protozoans in all patients: in case 1, optical and electron microscopy revealed the presence in the cytoplasm of villous enterocytes of Microsporidia protozoans still unreported in AIDS. Stool and jejunal fluid examination showed Isospora belli in case 2 and Cryptosporidium in cases 3 and 4. On histological and ultrastructural study the former was localised in the cytoplasm of a few enterocytes and the latter was scattered throughout the villus and crypt brush border. Otherwise small intestinal histology only showed minor non-specific changes and the enterocytes were ultrastructurally normal. In patient 3 the slow marker intestinal perfusion technique showed a profuse fluid secretion in the duodenum and proximal jejunum. All patients needed prolonged total parenteral nutrition. Cryptosporidium and Microsporidia could not be eradicated despite multiple drug trials. Isospora belli was transiently cured by pyrimethamine-sulphadiazine. Only patient 2 is presently at home, and patients 1, 3, and 4 died after two, six, and nine months of total parenteral nutrition, respectively.

Neurohumoral mechanisms involved in congestive heart failure

Congestive heart failure (CHF) promotes an array of biologic changes that are largely designed to compensate for reduced flow. These include activation of the sympathetic nervous system and the renin-angiotensin system, as well as the release of arginine vasopressin. The ultimate expression of these compensatory mechanisms is heightened vascular tone, increased sodium and water retention and antidiuresis. The peripheral circulation is normally under the fine control of circulating and neuronally released moieties, which can directly or indirectly alter vascular tone. Angiotensin II appears to be a key element in this regard because of its multiple biologic activities. Direct arteriolar vasoconstriction, facilitation of norepinephrine release and stimulation of aldosterone are some of the activities that are likely to be of major importance in the syndrome of CHF. Therefore, it is not surprising that converting enzyme inhibitors have a growing role as treatment. Other pharmacologic agents that can reduce sympathetic tone by acting on presynaptic receptors are being developed. Selective dilation of certain vascular beds may be possible with agents designed to interact with vascular dopaminergic receptors. The mechanisms whereby circulating epinephrine and norepinephrine modulate norepinephrine release and vascular tone are beginning to be understood and likely involve presynaptic, postsynaptic and nonsynaptic vascular receptors. A better appreciation of the mechanisms involved in the fine control of the peripheral circulation should allow for more selective and more imaginative pharmacologic therapy for CHF.

Thymic peptide hormones: basic properties and clinical applications in cancer

The manuscript will provide an in-depth and critical review of the nomenclature, biochemistry, biological properties, and a summary of published and on-going clinical trials with all reported thymic preparations, including both partially purified thymic factors (e.g., thymosin fraction 5, thymostimulin) as well as purified and synthesized thymic peptides (e.g., thymosin alpha 1, thymulin). Particular emphasis will be placed on which thymic peptides should be categorized as true hormones. In addition, the comparative biochemistry and biological activity in animals will be summarized and contrasted for all the currently available thymic factors. The effects, in vitro of thymic factors, on peripheral blood lymphocytes isolated from normal donors and patients with primary immunodeficiency disorders, autoimmune disorders, and neoplastic disorders will also be reviewed. Finally, a detailed critical summary of the clinical trials performed with each of the thymic preparations will be presented with an emphasis on treatment of patients with cancer.

"Kassinin" in mammals: the newest tachykinins

Until recently, substance P was widely believed to be the only mammalian representative of the tachykinin peptide family. In 1983, however, four independent groups using three different approaches reported that mammalian tissues also contain two novel tachykinins which resemble the amphibian tachykinin kassinin in both C-terminal sequence and pharmacology. Thus, the discovery of an active peptide in anuran skin has once again preceded the discovery of its mammalian analogs. While the discovery of the new peptides, substance K and neuromedin K, has clarified some issues in substance P research, it has raised some questions about others. With hindsight, it is clear that some of the activities once thought to be mediated by substance P may in fact be mediated by another mammalian tachykinin. Current knowledge of tachykinins and their receptors in mammals represents only a lower limit on the complexity of the system. This review summarizes recent progress in a rapidly developing field.

Differentiation in Acanthamoeba castellanii is induced by specific monoclonal antibodies

Monoclonal antibodies that bind a large molecular weight plasma membrane protein of Acanthamoeba castellanii cause the cells to differentiate. A different monoclonal antibody that binds specifically to the major plasma membrane protein has no effect upon cell division or differentiation. The induction of differentiation by the monoclonal antibodies requires a bivalent attachment, more than a single binding cycle of the antibody to the plasma membrane protein, does not require cell-cell contact, and appears to be mediated by an inhibition of pinocytosis. These results suggest one of two alternatives: either this free living amoeba possesses a cell surface receptor that serves to initiate the differentiation process when stimulated, or the specific plasma membrane antigen for the differentiation-inducing monoclonal antibodies is an essential component of the pinocytotic mechanism. While it seems more likely on the basis of available evidence that we are observing the biological effects of a cell surface receptor, either of the two alternative circumstances open up investigative areas of large significance.

Fetal growth control: the role of insulin and related peptides

Both insulin and the related peptides, the insulin-like growth factors/somatomedins, may function as anabolic factors in the regulation of fetal body size. Infants born to women suffering from diabetes mellitus may show increased deposition of subcutaneous fat and enhanced lean body mass, findings reproduced in experimental animal fetuses with induced hyperinsulinaemia. Fetal adiposity may be associated with a life-time tendency to obesity and its associated diseases. Insulin-like growth factors I (IGFI) and II are present in the circulation of the newborn infant and animal fetus and correlate positively with birth size. The fetal tissues are biologically responsive to IGFs in vitro and are rich in specific cell membrane receptors, those predominantly recognizing IGFI being structurally and functionally similar to the insulin receptor. Insulin could theoretically influence fetal tissues by an interaction with either the insulin or IGF receptor. IGF release is a property of multiple fetal tissues in vitro, but, in contrast to postnatal life, is not dependent on growth hormone. Fetal IGF production may be influenced by placental lactogen, especially IGFII which rapidly declines in the circulation following parturition in the rat and sheep. A positive association also exists between circulating levels of insulin and IGFs when the former is experimentally manipulated in the animal fetus. Similarly the infant born with transient diabetes mellitus has low cord blood levels of insulin and IGFI. Insulin has a dual role in prenatal life. In the last trimester insulin functions as a glucoregulatory hormone, but from much earlier in gestation creates an anabolic environment in the fetus supplied with optimal nutrients. This latter mechanism of action is unclear and probably heterogeneous, but in overview is permissive rather than obligatory. In contrast the growth-promoting role of the IGFs is direct but their interaction with fetal tissues, and thus the overall emphasis of fetal growth, may be paracrine.

Small cell carcinoma of the lung: macrophage-specific antigens suggest hemopoietic stem cell origin

Four surface antigens previously recognized only in macrophages are present on human small cell lung carcinoma cells and tumors. Cancerous cells may arise from macrophage precursors in bone marrow, and these precursors migrate to lung to participate in the repair of damaged tissue produced by continuous heavy smoking. The characteristic presence of neuropeptides such as bombesin in small cell carcinoma, when considered along with these findings, presents new possibilities for the role of such peptides in nervous, endocrine, and immune system function.

Identification of 17 beta-estradiol as the estrogenic substance in Saccharomyces cerevisiae

Saccharomyces cerevisiae possesses a high-affinity estrogen binding protein and an endogenous ligand that displaces [3H]estradiol from both the yeast binding protein and mammalian estrogen receptors. Semipurified preparations of this ligand have been shown to exhibit estrogenic activity in mammalian systems. We now describe the purification procedure and ultimate identification of the estrogenic substance in extracts of S. cerevisiae as 17 beta-estradiol. Organic solvent extracts of commercially obtained dried yeast were sequentially chromatographed on silica gel columns and then subjected to a series of reversed phase HPLC fractionations. Active ligand was monitored by [3H]estradiol displacement in a rat uterine cytosol assay. After seven chromatography steps, the purified and highly active ligand exhibited a single peak with retention times identical to those of 17 beta-estradiol on both HPLC and GC. The yeast material was identified as 17 beta-estradiol by its UV absorbance and mass spectrometric fragmentation pattern. In addition, radioimmunoassay confirmed the presence of approximately the same mass of 17 beta-estradiol (approximately equal to 800 ng/1.5 kg of yeast) as estimated both by a competitive binding assay with estrogen receptor and by mass spectrometry. Extraneous contamination by estradiol was excluded by repeat experiments with different batches of starting material and demonstration of estradiol by RIA in conditioned medium and cell pellets of laboratory-grown S. cerevisiae whereas non-conditioned medium did not possess the steroid. We conclude that 17 beta-estradiol is a yeast product.

Muscarinic cholinergic receptors on skin fibroblasts in familial affective disorder

Cultured human skin fibroblasts possess muscarinic receptors with the properties of specific binding, saturability, pharmacologic specificity, inhibition of norepinephrine-stimulated adenylate cyclase, and increased binding after incubation with an antagonist. The number of binding sites appears to be a stable characteristic of each cell line. We studied fibroblasts from 18 patients with a major affective disorder and found that they had a higher density of binding sites than cells from 12 normal controls. Fibroblasts from 18 relatives who had histories of major or minor affective disorder also had a higher density, and those from five normal relatives were similar to controls. These results, although still preliminary, suggest that increased cholinergic-receptor density may be associated with vulnerability to affective disorders in some familial cases.

Carcinoid tumour secreting dopa

A middle aged woman referred for an abdominal mass was found to have large amounts of dopa (3-4-dihydroxyphenylalanine) metabolites in her urine. At operation a tumour affecting almost the entire left lobe of the liver was removed. Histologically the tumour was a metastatic carcinoid. After operation the excretion of dopa metabolites fell substantially, confirming that the tumour was the source. Apparently, owing to an enzyme defect the tumour had been unable to decarboxylate dopa. These findings are further evidence of a neural origin for the endocrine system of the gut.

Immunoreactive thymosin alpha 1 is associated with murine T-cell lymphomas

Growth of murine spontaneous and transplanted AKR T-cell lymphomas results in marked elevations of serum immunoreactive thymosin alpha 1. Thymosin alpha 1 is one of the peptide hormones believed to be secreted primarily by the thymic epithelium. This elevation, however, is not mediated by the thymus but rather, seems to be directly associated with the tumor cells. Growth of a B-cell lymphoma does not generate elevated immunoreactive thymosin alpha 1 in the serum, thus, a thymosin alpha 1-like peptide is selectively associated with these T-cell lymphomas. The possible relationship between expression of T-leukemia viruses and alpha 1 expression is discussed.

Serological evidences for a membrane structure related to human beta 2-microglobulin expressed by certain earthworm leukocytes

Indirect immunofluorescence performed with 2 polyclonal and 4 monoclonal antibodies directed against human beta 2-microglobulin (beta 2m) revealed the presence of a beta 2m-like determinant on the membrane of a subpopulation of earthworm leukocytes classified as weakly adherent acidophils. Two out of the 4 monoclonal antibodies were found to bind to 15% of the earthworm leukocytes. Similar results were obtained with antibodies specific for beta 2m and isolated by affinity chromatography from either polyclonal antiserum or anti-beta 2m hybridoma supernatant. Additional binding inhibition and competition experiments strengthened the results and suggested that the homology between the structure present on earthworm leukocytes and human beta 2m may be restricted to only one major determinant. The existence of a beta 2m-like molecule in earthworms may provide important clues for understanding protein evolution and basic immune mechanisms.

High concentrations of p-Glu-His-Pro-NH2 (thyrotropin-releasing hormone) occur in rat prostate

Thyrotropin-releasing hormone (TRH) immunoreactivity occurs in high concentration within the rat prostate. Previous studies have shown that the immunoreactive species consists of more than one TRH-like tripeptide which cross-reacts in the TRH radioimmunoassay. The component which was highly retained during cation exchange chromatography was subjected to a preparative scale isolation, purification and structural analysis. The methods used included methanol extraction, water-ethyl ether partitioning, cation exchange chromatography, affinity chromatography, high pressure liquid chromatography, TRH radioimmunoassay, in vitro pituitary bioassay, TRH receptor assay, and amino acid analysis. The mean concentration of the predominant amino acids (Glu, His, Pro), 344 pmoles/ml, and the TRH concentration measured by TRH radioimmunoassay prior to acid hydrolysis, 372 pmoles/ml, were nearly identical. Because the material analyzed cochromatographed with synthetic TRH in several chromatographic systems, had a radioreceptor potency which was indistinguishable from that for synthetic TRH, and released TSH and prolactin but not growth hormone from rat pituitaries in vitro, it is concluded that pGlu-His-Pro-NH2 is one of the TRH-like peptides in the rat vental prostate.

Angiotensin synthesis in the brain and increased turnover in hypertensive rats

The missing link in the evidence for an active endogenous renin angiotensin system in the brain has been the demonstration of local angiotensin synthesis in the central nervous system in vivo. In this report the extraction and characterization of angiotensin I and angiotensin II from the brain of rats is described. The accumulation of angiotensin I was enhanced in hypertensive rats when the conversion to angiotensin II was blocked in vivo by the converting enzyme inhibitor captopril.

Entamoeba histolytica causes intestinal secretion: role of serotonin

Lysates of the protozoan parasite Entamoeba histolytica altered active electrolyte transport when present on the serosal surface of rabbit ileum and rat colon. The lysate-induced effects on electrolyte transport were similar to those caused by serotonin, and were blocked by bufotenine, an analog known to inhibit the action of serotonin. The transport effects were partially inhibited by antibody to serotonin. The amebic lysates were shown to contain serotonin by radioimmunoassay, high-performance liquid chromatography, and thin-layer chromatography. These results suggest that the serotonin present in Entamoeba histolytica may be important in the diarrhea seen in amebiasis.

An ultrastructural study of intranuclear rodlets in a malignant extracranial neuroepithelial neoplasm

This report describes for the first time the presence of intranuclear rodlets in a malignant extracranial neuroepithelial neoplasm. This malignant neoplasm appeared poorly differentiated by light microscopy and presented initially as a diagnostic problem. Electron microscopy revealed neoplastic cells joined by macula adherens-type junctions and containing numerous interdigitating cell processes diagnostic of a neuroepithelial neoplasm. A quantitative analysis of 500 cells revealed the presence of intranuclear rodlets in 5% of the neoplastic cells. The rodlets were composed of individual filaments that measured 7-9 nm in width. An extensive review of the literature revealed the high frequency of reported rodlets in normal neurons, normal paraneurons, neoplasms of the nervous system, and paraneuromas. The significance of this interesting structure to the physiology of the cell is discussed.

Chromogranin: widespread immunoreactivity in polypeptide hormone producing tissues and in serum

Chromogranin A is the major soluble protein, co-stored and co-released with catecholamines from storage vesicles of adrenal medulla and sympathetic nerve, and has been used as an index of exocytotic sympathoadrenal neurosecretion. Since some neuropeptides have a rather wide distribution in nerve, gut, and endocrine glands, we used a sensitive chromogranin A radioimmunoassay to probe the occurrence of chromogranin in several polypeptide hormone producing tissues. Immunoreactive chromogranin was ubiquitous in such tissues, in rank order of concentration (microgram/g wet weight): adrenal medulla greater than pituitary gland (anterior greater than intermediate greater than posterior) greater than pancreas greater than small intestine greater than thyroid greater than hypothalamus. In each case, the tissue homogenate displaced 125I-labelled chromogranin A from antibody in parallel with displacement generated by pure unlabeled chromogranin A, and the immunoreactivity was not abolished by boiling or by several protease inhibitors. Quantitatively, the endocrine tissues other than adrenal medulla possessed 0.1-2.8% of the immunoreactivity found in the adrenal medulla. Immunoreactive chromogranin was also present in serum and sympathetic nerve, but contamination of the endocrine tissues by chromogranin from serum or sympathetic innervation could not account for the observed immunoreactivity. Immunoreactive chromogranin was undetectable in platelets. Tissues with predominant exocrine function (salivary glands) had very little chromogranin (0.004-0.005% of that found in the adrenal medulla). Within the cell, differential centrifugation localized the immunoreactive chromogranin to a hormone storage granule fraction in the anterior pituitary gland (60 +/- 6% of total, with 2.0 +/- 0.3-fold enrichment in the granule) and the adrenal medulla (74 +/- 13% of total, with 1.7 +/- 0.2-fold enrichment in granules). Gel filtration suggested a lower effective molecular radius for pituitary and pancreatic immunoreactive chromogranin than for purified 125I-labelled chromogranin A. Thus, chromogranin in the other endocrine glands differed from adrenal medullary chromogranin both quantitatively (less microgram/g tissue) and qualitatively (lower molecular weight). The results suggest a widespread, though as yet undefined, role for chromogranin in the neurosecretory process, and raise the possibility that chromogranin may be co-stored and secreted with a variety of polypeptide hormones.

Insulin-like peptides in the lobster Homarus americanus. I. Insulin immunoreactivity

Experiments were conducted to determine if insulin-like peptides are present in the lobster Homarus americanus. Peptides were found that bind specifically to bovine insulin antibodies in a modified vertebrate radioimmunoassay. Extracts of whole hepatopancreas, gut, and hemolymph contained insulin immunoreactivity (IRI) concentrations of 67.5, 14.0, and 11.0 ng, respectively, per 700-g lobster. No insulin immunoreactivity was detected in neurosecretory cells of the eyestalk. The highest immunoreactivity was measured in the hepatopancreas, in the same fractions of eluate which contained the highest immunoreactivity when a bovine insulin standard was passed through the same chromatographic column.

Melanin: the organizing molecule

The hypothesis is advanced that (neuro)melanin (in conjunction with other pigment molecules such as the isopentenoids) functions as the major organizational molecule in living systems. Melanin is depicted as an organizational "trigger" capable of using established properties such as photon-(electron)-phonon conversions, free radical-redox mechanisms, ion exchange mechanisms, and semiconductive switching capabilities to direct energy to strategic molecular systems and sensitive hierarchies of protein enzyme cascades. Melanin is held capable of regulating a wide range of molecular interactions and metabolic processes primarily through its effective control of diverse covalent modifications. To support the hypothesis, established and proposed properties of melanin are reviewed (including the possibility that (neuro)melanin is capable of self-synthesis). Two "melanocentric systems"--key molecular systems in which melanin plays a central if not controlling role--are examined: 1) the melanin-purine-pteridine (covalent modification) system and 2) the APUD (or diffuse neuroendocrine) system. Melanin's role in embryological organization and tissue repair/regeneration via sustained or direct current is considered in addition to its possible control of the major homeostatic regulatory systems--autonomic, neuroendocrine, and immunological.

Biologically active chorionic gonadotropin: synthesis by the human fetus

The kidney, and to a slight extent the liver, of human fetuses were found to synthesize and secrete the alpha subunit common to glycoprotein hormones. Fetal lung and muscle did not synthesize this protein. Since fetal kidney and liver were previously found to synthesize beta chorionic gonadotropin, their ability to synthesize bioactive chorionic gonadotropin was also determined. The newly synthesized hormone bound to mouse Leydig cells and elicited a biological response: namely, the synthesis of testosterone. These results suggest that the human fetus may participate in metabolic homeostasis during its development.

The James Ewing lecture. The relationship between tumor mass and resistance to chemotherapy. Implications for surgical adjuvant treatment of cancer

Tumor mass negatively influences the outcome of surgery and radiotherapy by its influence on invasiveness and the propensity to metastasize before local treatment is applied. Tumor mass negatively affects the outcome of cancer chemotherapy in a manner quite different from the way in which it does surgery or radiotherapy. Cancer chemotherapy fails because cells develop resistance to anticancer drugs. Conceptually, there are two types of resistance both of which are mass related: temporary resistance (due to pharmacologic sanctuaries or altered cell kinetics) or permanent resistance (mutant lines developing specific and permanent resistance to one or more cancer drugs). Based on somatic mutation theory, it now appears that resistant mutants arise spontaneously early in the natural history of cancers, and the likelihood of a resistant line developing appears closely related to cell number, such that one or more resistant lines are likely present before most human malignancies become clinically evident. The development of permanent resistance more precisely accounts for the invariable inverse relationship between cell number and curability by drugs and the greater effectiveness of combination chemotherapy over single agents. New information on common pathways of drug resistance appear exploitable using tools available today or on the horizon. Treatment of bacterial infections, particularly tuberculosis, now truly appears to be a paradigm for cancer chemotherapy.

Human chorionic gonadotropin immunoreactivity in serum of patients with malignant neoplasms

The beta-human chorionic gonadotropin (HCG) radioimmunoassay was used to determine the presence of HCG immunoreactivity in serum of patients (n = 71) with diagnosis of cancer. Of patients with active neoplasia, 60.5% showed HCG immunoactivity above controls (greater than 5 mIU/ml). An apparent degree of correlation was observed with tumor activity in that a case with widespread metastases due to a colonic carcinoma exhibited the highest HCG levels while, in one patient, the level of HCG decreased progressively according to therapeutic response. A high frequency of immunoactive HCG was found in patients with carcinomas of the cervix, breast, gonad, and digestive system and in patients with melanoma. Trophoblastic cells were not evident in the tumors biopsied. Immunologic similarity of HCG secreted by tumors and that contained in serum of pregnant women, of patients with hydatidiform mole, and of males injected with exogenous HCG was shown by parallel inhibition curves in the radioimmunoassay. The positivity of HCG was predominant in cases of cervix carcinoma.

Demonstration of a saturable binding site for thyrotropin in Yersinia enterocolitica

Several lines of evidence suggest that there might be immunologic cross-reactivity between the thyroid plasma membrane in humans and antigenic determinants in the enteric pathogen Yersinia enterocolitica. Studies were therefore performed to determine whether Y. enterocolitica, like the thyroid membrane, contains a thyrotropin binding site. A saturable binding site for bovine thyrotropin was indeed demonstrable, particularly in preparations of the organism that have been treated with ethylenediaminetetraacetate and lysozyme. Hormonal specificity of the binding site, as judged from the inhibition of binding of 125I-labeled bovine thyrotropin, was similar to that of the thyrotropin receptor in human thyroid tissue.

Corticotropin-releasing factor (CRF)-like immunoreactivity in the vertebrate endocrine pancreas

The light microscopic immunocytochemical localization of corticotropin-releasing factor (CRF) is described in the endocrine pancreas of several species representing the major classes of vertebrates: fishes (channel catfish, Ictalurus punctatus), amphibians (African clawed toad, Xenopus laevis), reptiles (chameleon, Anolis carolinensis), birds (chicken, Gallus domesticus), and several mammals (rat, mouse, cat, rhesus monkey, and man). The CRF-containing cells are scattered over the entire islet tissue in primates and cat, whereas in rat and mouse they are located at the periphery of the islets. In the chicken and catfish, the CRF-containing cells are found in a central location within islets and form larger clusters or cords. Single cells with CRF-like immunoreactivity are interspersed between acinar cells of the exocrine pancreas in all species studied. The CRF cells show a substantial topographical overlap with glucagon cells, but their precise identity and function remain to be determined.

Some aspects of sodium efflux from single barnacle muscle fibres

This mini-review attempts to summarize information about the efflux of 22Na from single barnacle muscle fibres, based on the use of the microinjection technique. The view is put forward that the Na efflux consists of three components: an ouabain-sensitive component, an ouabain-insensitive component (representing secondary active transport), and an Na-Na exchange diffusion component. Evidence is brought forward which supports the view that the ouabain-insensitive Na efflux is divisible operationally into 3 phases: (i) the cyclic nucleotide-sensitive phase, (ii) the Cai-sensitive phase, and (iii) the pHe-sensitive phase. It is shown how the barnacle muscle fibre preparation has yielded information about the validity of the cAMP-protein kinase hypothesis and how it can be used to shed some light on the post-translational mechanism of aldosterone action.

Yeast mating pheromone activates mammalian gonadotrophs: evolutionary conservation of a reproductive hormone?

alpha-Factor, a tridecapeptide mating pheromone of yeast (Saccharomyces cerevisiae), has extensive sequence homology with the hypothalamic decapeptide gonadotropin-releasing hormone (GnRH). Both synthetic and natural preparations of alpha-mating factor were found to bind specifically to rat pituitary GnRH receptors and to stimulate the release of luteinizing hormone from cultured gonadotrophs. The ability of the yeast pheromone to reproduce the biological actions of GnRH in the mammalian pituitary gland indicates that the structural and functional properties of GnRH-related peptides may have been highly conserved during evolution.

An estrogen-binding protein and endogenous ligand in Saccharomyces cerevisiae: possible hormone receptor system

A protein macromolecule in the cytosol of the unicellular eukaryotic yeast Saccharomyces cerevisiae selectively binds the vertebrate estrogen hormone 17 beta-estradiol with high affinity. Lipid extracts of the yeast cells or the conditioned growth medium yield a substance that can bind competitively to the tritiated estradiol-binding sites in the yeast and to mammalian estrogen receptors. These findings suggest that the binding protein may be a primitive hormone receptor and that the lipid-extractable substance represents the endogenous ligand.