Effects of an ACTH/MSH(4-9) analog (HOE 427) on the sleep EEG and nocturnal hormonal secretion in humans.

The synthetic ACTH/MSH(4-9) analog HOE 427 ("ebiratide"), which is behaviorally the most potent ACTH-derived peptide but which is devoid of endocrine activity, was administered intravenously in a pulsatile mode 4 times (120 micrograms each) at 2200, 2300, 2400 and 0100 to study its effect on the sleep EEG and on concomitant hormonal secretion of cortisol and growth hormone. In comparison to placebo, the peptide produced signs of general activation associated with specific deteriorating effects on the quality of sleep. Sleep onset latency and intermittent wakefulness were increased, slow wave sleep was reduced, but only during the first 3 hours of the sleep period. The nocturnal secretory patterns of cortisol and growth hormone were unaffected by HOE 427. These effects are different from those reported in similar studies in which corticotropin-releasing hormone (CRH) was applied in humans, and they suggest that peripherally administered neuropeptides have specific nonendocrine behavioral effects.     

Modulation of the Na–;H antiport by insulin: Interplay between protein kinase C,tyrosine kinase,and protein phosphatases

The insulin modulation of Na-H antiport in rat hepatocytes was studied using the fluorescent, pH-sensitive intracellular probe, 2′,7′ bis (carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Our data show that insulin stimulates the Na? H antiport. The dose-response of insulin effect shows a behavior typical of other insulin responses: a maximum in the physiological range (1 nM) and smaller effects at higher and lower hormone concentrations. The time-course of activation is very fast at high hormone concentrations and slow, but reaching a higher value, for the physiological concentrations (0.26± 0.05 and 0.18 ± 0.022 pH units for 1 nM and 1 μM insulin respectively). The use of phorbol, 12-myristate, 13-acetate (PMA), a potent activator of protein kinase C and its inhibitor staurosporine, and the inhibitor of tyrosine kinase erbstatin analog, suggests that both protein kinase C and tyrosine kinase could be involved in the mechanism leading to Na? H antiport activation by insulin. We suggest that the activation of the antiport involves the two pathways depending on the hormone concentration. In particular, protein kinase C would mediate the effects of high hormone concentrations, acting as a growth factor, since staurosporine fully inhibited insulin 1 μM, but only partially 1 nM effects, and tyrosine kinase would mediate the effect of insulin 1 nM and only partially 1 μM. Okadaic acid 1 μM, a potent inhibitor of protein phosphatases, mimicked the hormone effects on the antiport and abolished the different time-course due to hormone concentration, suggesting a role of kinases and phosphatases in the signal transduction. The effect of all activators was abolished by amiloride analog, 5-(N-ethyl-N-isopropyl) amiloride (EIPA), confirming the specificity of these effects. © 1994 wiley-Liss, Inc.     

Thyrotropin-Releasing Hormone and Its Analog MK-771 Increase the Cerebroventricular Perfusate Content of Dihydroxyphenylacetic Acid

The effects of thyrotropin-releasing hormone (TRH) and its synthetic analog, pyro-2-aminoadipyl-histidyl-thiazolidine-4-carboxamide (MK-771), were determined on the efflux of dihydroxyphenylacetic acid (DOPAC) collected from push-pull cannulae chronically implanted into the lateral cerebral ventricles of rats. Intracerebroventricular and intraperitoneal injections of both peptides increased the efflux of DOPAC. These results suggest that TRH and MK-771 increase the activity of dopaminergic neurons that terminate in periventricular regions.     

The effects of a hypothalamic peptide factor,MIF and its cyclic analog on tolerance to haloperidol in the rat

The effects of the hypothalamic peptide, ProLeuGlyNH₂ (MIF) and its analog, cyclo (LeuGly) (CLG) on the development of tolerance to haloperidol were investigated in male Sprague-Dawley rats. Chronic oral administration of haloperidol (1.5 mg/kg/day) for 21 days resulted in the development of tolerance to its pharmacological effects. A dose of haloperidol (3 mg/kg ip) exhibited an absence of cataleptic as well as hypothermic response in chronically haloperidol treated rats. Subcutaneous administration of MIF or CLG (2 mg/kg each) daily one hour prior to haloperidol injection blocked the haloperidol-induced tolerance as evidenced by the appearance of both the cataleptic and hypothermic responses. It is concluded that the hypothalamic peptide hormone, MIF may be important in regulating chronic effects of neuroleptic drugs.     

The coupling of beta1-24-corticotropin to the adenylate-cylase system in rat adipocytes. Evidence for hormone-nucleotides interaction (author's transl)]

The general aim was to define some of the most important parameters involved in the coupling step between the synthetic analog of adrenocoricotropin hormone (beta1-24-corticotropin tetracosa peptide) and the catalytic unit of the adenylate-cyclase system of fat cells. These studies were performed with a purified plasma membrane fraction from rat adipose tissue. In this regard, some effects of ions, pH, and nucleotides (ATP nad GTP) on this hormone sensitive system were studied A simple model based on a random association process of reactants yeilded a statisfactory approximation of the kinetic data. In contract to results obtained by two other groups, which were analyzed by De Haen, no evidence was found for a regulation of the adenylate-cyclase activity by the adenosine triphosphate which was not complexed to magnesium...     

Degradation of a radiolabeled juvenile hormone analog using two insect species

A synthetic insect juvenile hormone analog (a juvenoid), ethylN-[2-[4-[[2,2-(ethylenedioxy)cyclohexyl]methyl]phenox]ethyl]carbamate, which has displayed high biological activity against different insect species and high stability under field conditions, was selected as a biologically active model compound for a study of a juvenile hormone analog degradation. The biologically active compound itself and its three diversely radiolabeled derivatives were applied to the flesh fly (Sarcophaga bullata) or the tsetse fly (Glossina palpalis), respectively. Monitoring of a fate of the applied juvenile hormone analog was carried out using a detection method of the radioactivity microdistribution within the whole insect body in combination with a radio high performance liquid chromatography (radio-HPLC), both of whole-body extracts made in different, but in advance scheduled, time intervals, and of extracts of insect excreta accumulated over an eight-day experiment.     

Fluorescence study of conformational properties of melanotropins labeled with aminobenzoic acid.

The native hormone alpha-melanocyte-stimulating hormone (alpha-MSH) and its more potent analog [Nle(4),D-Phe(7)]alpha-MSH (NDP-alpha MSH), labeled at the amino terminal with the fluorescent aminobenzoic acid (Abz) isomers, were examined by fluorescence methods. We observed energy transfer between the tryptophan(9) residue acting as donor and Abz as acceptor, the transfer being more pronounced to the ortho-form of the acceptor. Within the hypothesis that different peptide conformations coexist in equilibrium during the fluorescence decay, we supposed that the intensity decay was modulated by an acceptor-donor distance distribution function f(r). From the time-resolved fluorescence experimental data, we recovered the distance distribution between Abz and Trp(9), using the CONTIN program, within the framework of the F?rster resonance energy transfer model. The methodology proved to be useful to provide quantitative information about conformational dynamics of melanotropins and its dependency on the solvent. In aqueous medium, alpha-MSH has a broad Abz-Trp(9) distance distribution, reflecting the structural flexibility of the peptide. Three different distance populations could be identified in the labeled analog NDP-alpha MSH in water, indicating distinct conformational states for the synthetic peptide, compared with the native hormone. Measurements in trifluoroethanol resulted in the recovery of two Abz-Trp(9) distance populations, both for the native and the analog hormones, reflecting the decrease, induced by the solvent, of the conformational states available to the peptides.     

Inhibition of Farnesoic Acid Methyl transferase by Sinefungin

Sinefungin inhibited the S-adenosylmethionine-dependent farnesoic acid methyltransferase in a cell-free system containing a homogenate of corpora allata from female locusts, Locusta migratoria. The enzyme catalyzed the penultimate step of juvenile hormone biosynthesis in the insects. Culturing corpora allata in the presence of sinefungin greatly suppressed juvenile hormone production. The following in vivo effects were visible after injection of the inhibitor: increase in mortality and reduction of total haemolymph protein titer and ovary fresh weight, as well as length of terminal oocytes. Attempts to reverse these effects by topical application of the juvenile hormone analog ZR-515 (methoprene) were only partly successful. Therefore, the in vivo effects may be due to a general inhibition of methyltransferase enzymes in the insect. Sinefungin appeared to be of potential interest as the first representative of a new class of insect growth regulators.     

Stimulation and inhibition of Leydig cell steroidogenesis by the phorbol ester 12-O-tetradecanoylphorbol 13-acetate: similarity to the effects of gonadotropin-releasing hormone

To explore the mechanism of gonadotropin-releasing hormone (GnRH) action on Leydig cell steroidogenesis the effects of a GnRH analog (GnRHa) were compared to those of 12-O-tetradecanoylphorbol 13-acetate (TPA). Both compounds acutely stimulated androgen production 2-4 fold with EC50's of 9 nM (TPA) and 0.2 nM (GnRHa). The effects of TPA and GnRHa were not additive and neither compound acutely altered the luteinizing hormone (LH) concentration-response relationship. After 24 h of exposure to TPA or GnRHa the ability of LH to stimulate androgen production was impaired. The parallel effects of TPA and GnRHa on Leydig cell steroidogenesis suggest that they are acting via similar mechanisms; presumably the activation protein kinase C.     

Growth hormone responses to growth hormone-releasing hormone (1-29)-NH2 and a D-Ala2 analog in normal men

Synthetic analogs of growth hormone-releasing hormone, GHRH(1-29)-NH2 and D-Ala2 GHRH(1-29)-NH2 were administered as a bolus intravenous injection to five normal men in a dose range of 0.015 to 0.5 micrograms/kg body weight. Vehicle only was administered in a control study. Peak responses to GHRH analogs occurred at 15 or 30 min. An increase in the integrated plasma growth hormone (GH) response was observed at each dose. The dose-response curve of GHRH(1-29)-NH2 indicated that it has a similar molar potency to GHRH(1-40) and GHRH(1-44). The potency of D-Ala2 GHRH(1-29)-NH2 was approximately twice that of GHRH(1-29)-NH2. Neither analog affected blood levels of PRL, TSH, LH, FSH, ACTH, insulin, glucagon, glucose, cortisol, free thyroxine, and free triiodothyronine. No side effects were noted other than transient flushing with the highest dose administered. The findings demonstrate GHRH(1-29)-NH2 and its D-Ala2 analog are potent stimulators of GH release and have potential application in clinical medicine.     

8-P-Chlorophenylthio-cyclic AMP: a potent partial simulator of antidiuretic hormone action.

In the toad urinary bladder 8-p-chlorophenylthio-cyclic AMP mimics the stimulatory effects of antidiuretic hormone on osmotic water permeability, 3H2O diffusion, and transepithelial sodium transport; but unlike the hormone does not cause an increase in urea permeability. Trheshold activation for the hydroosmotic response is observed at 1 micrometer and full activation at 100 micrometer. These results suggest that cyclic AMP may not mediate all the physiological effects of antidiuretic hormone and that this highly potent cyclic AMP analog may be useful in elucidating the precise role of cyclic AMP in other biomediate hormone action.     

Evaluation of synthetic antidiuretic hormone as a corrective substance following a head-down tilt

The effects of the administration of desmopressin, a synthesized analog of antidiuretic hormone, together with a water-salt supplement on the renal function and orthostatic stability were investigated. Six healthy men spent 12 h in the head-down tilt (HDT) position. It was demonstrated that administration of desmopressin led to normalization of salt and water homeostasis; moreover, the tolerance of the standard 20 min passive standing test was improved significantly. These observations indicate that intake of the synthetic vasopressin analog combined with water-salt supplement counteracts hypohydration of the body during HDT and improved orthostatic tolerance.     

Direct inhibitory effect of gonadotropin releasing hormone in the uterus of rat

Estradiol induced increase in ornithine decarboxylase (ODC) and glucosamine-6-phosphate synthase activities of rat uterus were inhibited by simultaneous treatment with gonadotropin releasing hormone (GnRH) or its agonists. The direct inhibitory effect of GnRH analogs was found to be dose dependent. It was observed that a higher dose of GnRH analog was needed to cause inhibition of glucosamine-6-phosphate synthase when compared to ODC activity. The inhibitory effect of GnRH was not observed if its injection was delayed following estradiol treatment. These results show that the extra-pituitary inhibitory effects of GnRH involves enzymes associated with cell proliferation.     

Response variability of juvenile hormone and juvenile hormone analogs in workers of the Formosan subterranean termite (Coptotermes formosanus Shiraki)

Juvenile hormone (JH) or juvenile hormone analog (JHA) can induce soldier formation in termites. However, different studies have yielded inconsistent results on the effects of JHA on soldier production in Coptotermes formosanus Shiraki. Using filter paper as the testing substrate, the effects of JH III, pyriproxyfen and methoprene on the intact filter paper left, worker mortality and presoldier formation were tested on six colonies. Our results showed that pyriproxyfen and methoprene were more repellent than JH III. No significant difference in toxicity was observed among methoprene, pyriproxyfen and JH III. JH III and pyriproxyfen did not cause workers to differentiate into presoldiers, but methoprene can induce formation of presoldiers. Colony response variability to methoprene was observed. The confirmation of the effects of JH/JHA on C. formosanus establishes the foundation for molecular studies of soldier differentiation in this species.     

Improvement of chilling resistance in rice by application of an abscisic acid analog in combination with the growth retardant tetcyclacis

The protective effect of a synthetic terpenoid Analog of the plant hormone abscisic acid (ABA) coded LAB 173711 applied alone or in combination with the growth retardant tetcyclacis on chilling injury of rice was studied under growth chamber, greenhouse, and field conditions. The compounds were applied as a foliar spray before and after the onset of chilling treatment, as a substrate via the root system, and as a medium for seed soaking. The ABA analog increased chilling resistance in a manner similar to ABA. Combination of the analog with tetcyclacis revealed additive effects. Increased chilling resistance involved several processes: stomatal closure which reduced water loss during chilling, stabilization of the membranes, stabilization of the chlorophyll level, and stabilization of the root system. Possibilities for practical use of the compounds in rice production are discussed.     

Regulation of infant and developing rat testicular gonadotropin and prolactin receptors and steroidogenesis by treatments with human chorionic gonadotropin, gonadotropin-releasing hormone analogs, bromocriptine, prolactin, and estrogen

Infant (5-day-old) male rats were treated with hormonal regimens to alter their exposure to gonadotropins, prolactin (Prl), and estrogen, and the response of testicular endocrine functions was measured. Human chorionic gonadotropin (hCG) or a potent gonadotropin-releasing hormone agonist analog (GnRH-A) resulted in a short-lived decrease of testicular receptors (R) for luteinizing hormone (LH), but no deleterious effects were found on testicular capacity to produce testosterone (T), which is a typical response of the adult testis. Only GnRH-A, through probable direct testicular action, induced a relative blockade of C21 steroid side-chain cleavage that was observed in vitro upon hCG stimulation. Human chorionic gonadotropin treatment, but not GnRH-A treatment, increased testicular Prl-R. GnRH antagonist analog (GnRH-Ant) treatment did not affect testicular LH-R, but decreased Prl-R and testicular T production. Decrease of serum Prl by bromocriptine had no effect on testicular LH-R or Prl-R, but slightly decreased T production in vitro. Ovine Prl increased binding sites for LH/hCG. The postnatal rats were insensitive to negative effects of diethylstilbestrol when monitored by testis weight, T, and LH-R. In conclusion, the responses to changes in the hormonal environment differed greatly between infant and adult testes. Mainly positive effects of elevated gonadotropin and Prl levels were seen on infant rat Leydig cell functions. Likewise, decreased tropic hormone levels, and exposure to estrogen, were ineffective in bringing about the inhibitory actions seen in the adult.     

A synthetic analog of prostaglandin E2 is able to induce in vivo theta antigen on spleen cells of adult thymectomized mice

The effect of prostaglandins on the in vivo induction of theta antigen in splenic spontaneous rosette-forming cells derived from adult thymectomized mice was studied. A long-acting synthetic analog of prostaglandin E₂, di-M-PGE₂, mimicked the effects of thymic hormone and was active when mice were treated with as little as 0.1 μg ip. In addition, indomethacin, a potent inhibitor of prostaglandin biosynthesis, was able to reverse the inductive effects of exogenous thymic hormone and inhibit the expression of theta antigen in normal mice, presumably by interfering with the effect of endogenous thymic factors. Finally, indomethacin also partially suppressed the stimulatory effects of exogenously administered di-M-PGE₂, suggesting that this agent is effective, at least in part, because it stimulates endogenous prostaglandin biosynthesis. Possible mechanisms of action for the effects of prostaglandins are presented.     

On the mechanism of action of thyroxin, an amino acid analog of tyrosine

The concept of a hormone inevitably carries with it a set of specific connotations and prejudices which in the case of thyroxin may obscure rather than elucidate its mechanism of action. Viewed as a hormone, the very number and broad range of thyroxin effects defy resolution. Viewed as an amino acid analog, the behavior of this molecule becomes coherent, in that it resembles the behavior of amino acids in general and tyrosine in particular, with distinguishing characteristics appropriate to its own structure and its analog status.Thyroxin is only one of a number of amino acids appearing in the course of phylogeny, derived from modifications of aminoacyl residues in protein. Comparative physiologic studies suggest that the biogenesis of iodine-modified tyrosines long preceded their useful biological function. Eventually their presence in threatened aquatic forms may have provided survival advantage with regard to terrestrial adaptation.Both structure and function of the vertebrate thyroid gland reflect its foregut ancestry. Iodoproteins within the lumen of the thyroid follicle are subject to a process similar to gastric digestion of ordinary dietary proteins. Free iodoamino acids together with other amino acid constituents of the digest are then absorbed into the blood stream. As expected of an amino acid, thyroxin leaving the extracellular space enters into and influences the function of almost all cells and subcellular organelles, including the nucleus. Its analog properties are reflected in the fact that only small fractions of the available thyroxin pools participate at any one time in biological reactions.The diverse actions of thyroxin are compatible with the model set by the parent amino acid tyrosine, which is notably active at a number of branch points in its own metabolism. Thyroxin effects on growth and development conform with the known alterations in genetic response which occur in the presence of false protein amino acids and are also consistent with the rapid turnover and remodelling of protein systems which follow the incorporation of false amino acid residues into protein. Its effects on overall metabolic processes are consistent with the known propensity of tyrosine-like compounds to become converted to false transmitters in the adrenergic nervous system, which in the case of thyroxin, would result in the development of iodothyronine-derived adrenergic transmitter substances. Altered pigment metabolism in patients with thyroid disease and localization of iodoamino acids in pigment-bearing cells of many vertebrate species suggest that thyroxin may be an alternate substrate in the melanin biosynthetic pathway.Since thyroxin is required for normal body function, it may be classified as an indispensable amino acid along with the other biologically more ancient members of its class.     

Semisynthetic D-His1,N epsilon-acetimidoglucagon: structure-function relationships

The histidine residue at the amino terminus of lysine-12 protected glucagon was replaced by its D-isomer by an established semisynthetic strategy to extend a stepwise series of replacements at this position. The product was examined for its secondary structure and its function. Circular dichroism spectra obtained at concentrations from 0.25 to 1.09 mg/ml at pH 10.2 in 0.2 M phosphate buffer were similar to those obtained with native hormone. Competitive binding assays and adenylate cyclase activation assays with partially purified rat liver plasma membranes show this D-His1 analog of glucagon to be a full agonist, causing the same maximum activation of adenylate cyclase as native hormone; but both binding and activation assays show the binding affinity to be diminished about 10-fold. The data suggest that the adjustment of the bonding of the imidazole group to the receptor to bring about transduction results in constraints on the conformation along the peptide sequence which interfere with the peptide adopting the same binding conformation achieved by the native hormone.     

The effects of structure-conformation modifications of melanotropin analogs on learning and memory: D-amino acid substituted linear and cyclic analogs

Alpha-MSH has a wide variety of putative biological activities in addition to its classical melanocyte dispersing activity. Since each of these activities appears to be mediated by a discrete receptor, this peptide is an excellent candidate for exploring conformational restrictions which determine the chemical-physical basis for hormone action on specific activities. Experiments One and Two evaluated several cyclic and linear analogs of alpha-MSH on retrieval of memory during the reactivation of memory for a passive avoidance response following hypothermia-induced amnesia. Three of the cyclic analogs appear to have enhanced the peptide's ability to serve as a reactivation agent. One of the linear Nle4,D-Phe7 analogs antagonized whereas three others enhanced reactivation. The D-Phe7 substitution in cyclic analogs did not affect reactivation. Another group of animals were trained on a step-through passive avoidance task and tested 25 days later. The cyclic analog enhanced memory whereas the D-Phe7 analog and alpha-MSH had no effect. Finally, two analogs were tested on a black-white discrimination. Although the cyclic analog had no effect on either acquisition or reversal of this learning, the Nle4,D-Phe7 analog significantly impaired reversal learning. The results from these preliminary studies suggest that structural modifications of alpha-MSH do alter its potency and pattern of actions in learning and memory situations.