ACTH receptors and the effect of ACTH on adrenal organelles

Erectile Dysfunction: Treatments, Advances and New Therapeutic Strategies

Erectile dysfunction (ED) is the inability to get and maintain an adequate penile erection for satisfactory sexual intercourse. Due to its negative impacts on men's life quality and increase during aging (40% of men between 40 and 70 years), ED has always attracted researchers of different disciplines, from urology, andrology and neuropharmacology to regenerative medicine, and vascular and prosthesis implant surgery. Locally and/or centrally acting drugs are used to treat ED, e.g., phosphodiesterase 5 inhibitors (first in the list) given orally, and phentolamine, prostaglandin E1 and papaverine injected intracavernously. Preclinical data also show that dopamine D4 receptor agonists, oxytocin and α-MSH analogues may have a role in ED treatment. However, since pro-erectile drugs are given on demand and are not always efficacious, new strategies are being tested for long lasting cures of ED. These include regenerative therapies, e.g., stem cells, plasma-enriched platelets and extracorporeal shock wave treatments to cure damaged erectile tissues. Although fascinating, these therapies are laborious, expensive and not easily reproducible. This leaves old vacuum erection devices and penile prostheses as the only way to get an artificial erection and sexual intercourse with intractable ED, with penile prosthesis used only by accurately selected patients.

Local oxytocin tempers anxiety by activating GABAA receptors in the hypothalamic paraventricular nucleus

Oxytocin (Oxt) is released in various hypothalamic and extrahypothalamic brain areas in response to anxiogenic stimuli to regulate aspects of emotionality and stress coping. We examined the anxiolytic action of Oxt in the hypothalamic paraventricular nucleus (PVN) while appraising if Oxt recruits GABA neurons to inhibit the behavioral, hormonal, and neuronal response to stress in female prairie voles (Microtus ochrogaster). Voles received an injection of Oxt in the PVN either before or after an elevated platform stress to determine a time-course for the effects of Oxt on the hormonal stress response. Subsequently, we evaluated if ante-stress injections of Oxt affected anxiety-like behaviors as well as neuronal activity in the PVN, using real-time in-vivo retrodialysis and immunohistochemistry with c-Fos expression as a biomarker of neural activity. In addition, we exposed voles to Oxt and a GABAA receptor antagonist, concurrently, to evaluate the impact of pharmacological blockade of GABAA receptors on the anxiolytic effects of Oxt. Elevated platform stress amplified anxiety-like behaviors and hypothalamic-pituitary-adrenal (HPA) axis activity-catalyzing corticotrophin-releasing hormone (CRH) neuronal activity and augmenting corticosterone release in circulation. Ante-stress Oxt injections in the PVN blocked these stress effects while promoting PVN GABA activity and release. Post-stress Oxt treatments were ineffective. The anxiolytic effects of Oxt were hindered by concurrent pharmacological blockade of GABAA receptors. Together, our data demonstrate ante-stress treatments of Oxt in the PVN inhibit stress activation of the HPA axis through recruitment of GABAergic neurons, providing insights to the local circuitry and potential therapeutically-relevant mechanisms.

Neuropeptidergic regulation of pair-bonding and stress buffering: Lessons from voles

This article is part of a Special Issue "SBN 2014". Interpersonal attachment is a critical component of the human experience. Pair-bonding ameliorates the severity of several mental and physical diseases. Thus, a better understanding of how the central nervous system responds to and encodes social-buffering during stress is a valuable research enterprise. The prairie vole (Microtus ochrogaster), as a laboratory animal model, provides the gold standard for the investigation of the neurobiology underlying attachment. Furthermore, emerging research in voles, additional laboratory rodents, transgenic mice, primates, and humans has provided novel insight into the neurochemical mechanisms underlying the therapeutic effects of social bonds reducing anxiety, depression, and drug abuse liability. In the present review, we highlight the work from this burgeoning field and focus on the role(s) of the neuropeptides oxytocin (OT), vasopressin (AVP), and corticotrophin releasing hormone (CRH) mediating stress buffering. Together, the data suggest that OT underlies social bonding to reduce stress-induced psychological illness while AVP and CRH facilitate arousal to enhance autonomic reactivity, increasing susceptibility to adverse mental and physical health.

Neuropeptides and central control of sexual behaviour from the past to the present: a review

Of the numerous neuropeptides identified in the central nervous system, only a few are involved in the control of sexual behaviour. Among these, the most studied are oxytocin, adrenocorticotropin, α-melanocyte stimulating hormone and opioid peptides. While opioid peptides inhibit sexual performance, the others facilitate sexual behaviour in most of the species studied so far (rats, mice, monkeys and humans). However, evidence for a sexual role of gonadotropin-releasing hormone, corticotropin releasing factor, neuropeptide Y, galanin and galanin-like peptide, cholecystokinin, substance P, vasoactive intestinal peptide, vasopressin, angiotensin II, hypocretins/orexins and VGF-derived peptides are also available. Corticotropin releasing factor, neuropeptide Y, cholecystokinin, vasopressin and angiotensin II inhibit, while substance P, vasoactive intestinal peptide, hypocretins/orexins and some VGF-derived peptide facilitate sexual behaviour. Neuropeptides influence sexual behaviour by acting mainly in the hypothalamic nuclei (i.e., lateral hypothalamus, paraventricular nucleus, ventromedial nucleus, arcuate nucleus), in the medial preoptic area and in the spinal cord. However, it is often unclear whether neuropeptides influence the anticipatory phase (sexual arousal and/or motivation) or the consummatory phase (performance) of sexual behaviour, except in a few cases (e.g., opioid peptides and oxytocin). Unfortunately, scarce information has been added in the last 15 years on the neural mechanisms by which neuropeptides influence sexual behaviour, most studied neuropeptides apart. This may be due to a decreased interest of researchers on neuropeptides and sexual behaviour or on sexual behaviour in general. Such a decrease may be related to the discovery of orally effective, locally acting type V phosphodiesterase inhibitors for the therapy of erectile dysfunction.

ACTH- and alpha-MSH-induced grooming, stretching, yawning and penile erection in male rats: site of action in the brain and role of melanocortin receptors

The effect of adrenocorticotropin (ACTH)(1-24) and alpha-melanocyte stimulating hormone (alpha-MSH) on grooming, stretching, yawning and penile erection was studied after injection into different brain areas. Both peptides induce the above responses when injected into the hypothalamic periventricular region of the third ventricle. This region includes the paraventricular nucleus, the dorsomedial nucleus, the ventromedial nucleus and the anterior hypothalamic area. The minimal effective dose of both peptides was 0.5 microg and the maximal effect was seen with 2 microg, the highest dose tested. Irrespective of the injection site, grooming started 5-7 min after injection of either peptide, while stretching, yawning and penile erection started only after 15-35 min and lasted for 90-120 min. In contrast both peptides were ineffective when injected into the preoptic area, the caudate nucleus or the CA1 field of the hippocampus. Grooming, stretching and yawning, but not penile erection, were prevented by cyclic[AcCys(11), D-Nal(14), Cys(18), AspNH(2)(22)]-beta-MSH (11-22) (HS014), a selective melanocortin 4 receptor antagonist, injected into the same periventricular area 10 min before of ACTH(1-24) or alpha-MSH. The results show that ACTH(1-24) and alpha-MSH act in the hypothalamic periventricular region to induce the above responses and that grooming, stretching and yawning, but not penile erection, are mediated by melanocortin 4 receptors.

Neuropeptides and sexual behaviour

Many neuropeptides are involved in the control of sexual behaviour at the central level. Among these, the most studied are adrenocorticotropin, alpha-melanocyte stimulating hormone, oxytocin and opioid peptides. This attempt to review old and new neuropharmacological, biochemical and psychobiological studies in this field, shows that all these neuropeptides apparently facilitate sexual behaviour, except for opioid peptides, which inhibit sexual performance, in most of the species studied so far (rats, mice, monkeys and humans). However, gonadotropin-releasing hormone, corticotropin releasing factor, neuropeptide Y, galanin, cholecystokinin, substance P and vasoactive intestinal peptide may be also involved in the control of sexual behaviour. Apparently, corticotropin releasing factor, neuropeptide Y and cholecystokinin inhibit, while substance P and vasoactive intestinal peptide facilitate, sexual behaviour. In contrast, gonadotropin-releasing hormone has been reported to exert a facilitative, inhibitory or no effect at all on sexual behaviour. Galanin was also shown either to facilitate or inhibit sexual behaviour. The above-mentioned putative role of the neuropeptides in sexual behaviour derives mainly from studies done in rats. In these studies, neuropeptides, their antisera or drugs that act as agonists or antagonists of neuropeptide receptors, were tested for their effect on sexual behaviour after systemic, intracerebroventricular, or intracerebral administration. The latter were infused into brain areas relevant for sexual behaviour, such as the medial preoptic area, and the ventromedial and paraventricular nuclei of the hypothalamus. The above studies show that little information is available on the mechanisms by which neuropeptides influence sexual behaviour. Also unclear is whether the above neuropeptides influence the anticipatory phase (sexual arousal and/or motivation) or the consummatory phase (performance) of sexual behaviour, except for opioid peptides. New information about the role of neuropeptides may come from the application of molecular biology and genetic manipulation techniques to the study of sexual behaviour. Of these, FOS protein determination, antisense oligonucleotides aimed at the neutralisation of neuropeptide and/or neuropeptide receptor mRNAs in specific brain areas, and gene ablation seem the most promising. Although still in the early stages, it is likely that these methodologies will provide new insights into the role of neuropeptides in the control of sexual behaviour.

The neuropharmacology of yawning

Yawning is a phylogenetically old, stereotyped event that occurs alone or associated with stretching and/or penile erection in humans and in animals from reptiles to birds and mammals under different conditions. Although its physiological function is still unknown, yawning is under the control of several neurotransmitters and neuropeptides at the central level as this short overview of the literature on the neurochemistry of yawning shows. Among these substances, the best known are dopamine, excitatory amino acids, acetylcholine, serotonin, nitric oxide, adrenocorticotropic hormone-related peptides and oxytocin, that facilitate yawning and opioid peptides that inhibit this behavioral response. Some of the above compounds interact in the paraventricular nucleus of the hypothalamus to control yawning. This hypothalamic nucleus contains the cell bodies of oxytocinergic neurons projecting to extra-hypothalamic brain areas that play a key role in the expression of this behavioral event. When activated by dopamine, excitatory amino acids and oxytocin itself, these neurons facilitate yawning by releasing oxytocin at sites distant form the paraventricular nucleus, i.e. the hippocampus, the pons and/or the medulla oblongata. Conversely, activation of these neurons by dopamine, oxytocin or excitatory amino acids, is antagonized by opioid peptides, that, in turn, prevent the yawning response. The activation and inhibition, respectively of these oxytocinergic neurons is related to a concomitant increase and decrease, respectively, of paraventricular nitric oxide synthase activity. However, other neuronal systems in addition to the central paraventricular oxytocinergic neurons are involved in the control of yawning, since they do not seem to be involved in the expression of yawning induced by the stimulation of acetylcholine or serotoninergic receptors, nor by adrenocorticotropic hormone (ACTH) and related peptides. Nitric oxide is also involved in the induction of yawning by the latter compounds and neuronal links, for instance between dopamine and acetylcholine and dopamine and serotonin, seem to be involved in the yawning response. Finally, other neurotransmitters, i.e. gamma-aminobutyric acid (GABA) and noradrenaline, and neuropeptides, i.e. neurotensin and luteinizing hormone-releasing hormone (LH-RH), influence this behavioral response. In conclusion, in spite of some recent progress, little is known of, and more has to be done to identify, the neurochemical mechanisms underlying yawning at the central level.

Adrenocortical ACTH receptors in pigs of differing in vivo response to adrenocorticotropin

1. Adrenocortical membrane protein was isolated from the adrenal glands of 12 Large White x Landrace male pigs, six with high adrenocortical response to adrenocorticotropic hormone (ACTH) and six with low response. 2. The peptide (Phe2, Nle4) ACTH was iodinated by the chloramine-T method and served as the radioligand in receptor binding studies. 3. Only one class of ACTH receptor was detected, with Kd = 2.57 +/- 0.35 x 10(9) M and Bmax = 1.59 +/- 0.06 pmol/mg protein in high responders and Kd = 1.68 +/- 0.18 x 10(-9) M and Bmax = 1.17 +/- 0.11 pmol/mg protein in low responders. 4. The difference in the Bmax between high and low responders was significant (P < 0.05), the difference in Kd was not statistically significant.

NH2-terminal specificity and axonal localization of adrenocorticotropin binding sites in rat median eminence

Adrenocorticotropin binding sites in the rat median eminence have been localized in vivo. These binding sites occur in the basalar zone, which is rich in axonal endings. Using competitive binding and quantitative light-microscope radioautography, we found that the median-eminence binding site, in contradistinction to the adrenal receptor, binds specifically the residue 4-10 region of the adrenocorticotropin molecule. Using quantitative electron-microscope radioautography and median-eminence deafferentation, we localized the binding sites to axon terminals in this region. In time-delayed uptake studies using light-microscope radioautography, we failed to observe concentration of radiolabel in neurons of the medial basal hypothalamus after the direct injection of radioiodinated adrenocorticotropin(1-24) into the median eminence.

Role of cAMP for regulation of impulse-evoked noradrenaline release from the rabbit pulmonary artery and its possible relationship to presynaptic ACTH receptors

Strips of the rabbit pulmonary artery preincubated with 3H-noradrenaline were superfused with physiological salt solution containing cocaine, corticosterone and propranolol. Basal tritium efflux and electrically evoked tritium overflow were determined. The basal efflux of tritium was not affected by forskolin 0.01-10 mumol/l, 8-Br-cAMP and dibutyryl-cAMP 10-330 mumol/l, or the phosphodiesterase inhibitors rolipram 1-10 mumol/l and AH 21-132 l mumol/l; it was increased by AH 21-132 10-100 mumol/l. Forskolin concentration-dependently increased the evoked 3H overflow, and this effect was not attenuated by omission of cocaine. The facilitatory effect of forskolin was more pronounced at 0.66 Hz than at 2 Hz. Rolipram, AH 21-132, 8-Br-cAMP or dibutyryl-cAMP also produced a concentration-dependent increase in evoked 3H overflow (8-Br-cAMP was more effective than dibutyryl-cAMP in this respect). Except for the highest concentration investigated, AH 21-132 was more effective in facilitating evoked overflow than in increasing basal efflux. Forskolin, AH 21-132 or 8-Br-cAMP did not alter the percentages of 3H-noradrenaline and 3H-metabolites contained in basal tritium efflux or in stimulation-evoked tritium overflow. When a combination of AH 21-132 plus 8-Br-cAMP or AH 21-132 plus forskolin was administered, the facilitatory effect on evoked tritium overflow was more pronounced than with the single compounds alone. ACTH1-24 also facilitated the evoked tritium overflow. Combined exposure to ACTH1-24 plus forskolin, ACTH1-24 plus AH 21-132 or ACTH1-24 plus forskolin plus AH 21-132 resulted in a clearly more pronounced increase in evoked tritium overflow than exposure to the single compounds alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Corticotropin peptides and melanotropins elevate the level of adenosine 3':5'-cyclic monophosphate in cultured murine brain cells

Cell cultures derived from mouse and rat brain and consisting mainly of astroblasts are known to respond to several hormones by increasing or decreasing their intracellular concentration of cyclic AMP. In the present study these cultures were analyzed for their susceptibility to various additional hormonal and other neuroactive compounds. Only the peptides of the corticotropin (ACTH)/melanotropin (MSH) family were found active. Their potency for elevating the intracellular level of cyclic AMP decreases in the sequence (values for the half-maximally stimulating concentrations, EC50, in parentheses) ACTH-(1-24) (10 m) greater than alpha-,beta-MSH (30 nm) greater than ACTH (greater than or equal to 100 nm) gamma-MSH, ACTH-(1-10), -(4-10), -(4-11) (greater than or equal to 0.5 microM). The lack of additivity of the maximal effects of the peptides suggests that they all act at the same receptor. The stimulation exerted by these peptides is partially suppressed by hormones known to inhibit cyclic AMP formation in that culture, i.e., noradrenaline (acting via an alpha-adrenergic receptor), adenosine (acting via an A1 receptor), and somatostatin. It is concluded that the receptors for the ACTH/MSH peptides and the inhibitory hormones are located on the same cells, presumably the astroblasts. The maximal response to ACTH and alpha- and beta-MSH depends strongly on the age of culture. The results are discussed in view of the facts that (1) peptides of the ACTH/MSH family affect behavior and learning in animals, and (2) ACTH and alpha-MSH occur in brain.

Circumventricular organs: receptors and mediators of direct peptide hormone action on brain

The concept of the brain as an endocrine target organ is not new, nor is it novel to consider the circumventricular organs as receptive regions of the brain for circulating substances. However, in this review we have emphasized the relatively novel concept that CVOs mediate exclusively the direct feedback actions of circulating peptide hormones on brain function. In addition we have presented speculations concerning the neural mechanisms by which signals arising from peptide hormone-receptor interaction might be relayed into the CNS, and indicated the possible involvement of CVO receptors in endocrine disorders. We hope that this analysis provides a conceptual framework for evaluating the functional relationship of circulating peptides to brain and inspires interest in this fascinating area of neuroendocrinology.

Electrophysiological and contractile responses of canine atrial tissue to adrenocorticotropin

The direct extra-adrenal actions of adrenocorticotropin 1-39 (ACTH) on electrical (E) and mechanical (M) characteristics of canine atrial tissues (AT) were investigated in in vitro experiments. One hundred twenty-five mU/ml of ACTH 1-39 significantly augmented the catecholamine induced positive inotropism as seen by shortening the time to peak tension (10.6%, p = 0.01) and increasing peak isometric tension (3.5 times, p = 0.001). Effects on the M responses were inhibited by propranolol (10(-6) M) (P). ACTH did not significantly modify action potential E or M parameters during cholinergic receptor antagonism or alpha-adrenergic receptor antagonism. Existence of a specific ACTH receptor was demonstrated using 125I radioiodinated ACTH 1-24. Significant binding of 125I-ACTH to AT was observed. Intracellular C-AMP levels were also measured in AT using radioimmunoassay. Tissues were exposed to 125mU/ml ACTH 1-39 plus combinations of norepinephrine (10(-6) M) (NE) and P. ACTH alone did not elevate intracellular C-AMP levels. NE increased C-AMP levels were not further increased by ACTH. Exposure to antagonist returned elevated C-AMP levels to control values. In conclusion (1) ACTH augments the NE induced M positive inotropism of the beta adrenergic receptor system. (2) ACTH specifically binds to AT and (3) ACTH does not utilize the C-AMP second messenger system.

Inhibition of dibutyryl cyclic AMP induced steroidogenesis in rat adrenocortical cells by the putative calcium antagonist TMB-8

A significant proportion of the steroidogenic response of isolated rat adrenocortical cells to dibutyryl cyclic AMP does not require extracellular calcium, and this component is profoundly depressed by low concentrations of the putative calcium antagonist, TMB-8. The inhibition is reversed by either the readdition of calcium or the calcium ionophore A23187. The steroidogenic response to pregnenolone, whose mode of action does not require calcium, was not depressed by TMB-8. Corticotropin (ACTH)-induced steroidogenesis, which requires extracellular calcium, was markedly depressed by TMB-8, although enhanced cyclic AMP formation is only slightly depressed by this drug. Adrenal cortical microsomes possess an ATP-dependent 45calcium (45Ca2+) uptake system which responded to EGTA with a rapid efflux of 45Ca2+; EGTA-induced calcium efflux from this microsomal fraction was markedly reduced by a concentration of TMB-8 that blocked dibutyryl cyclic AMP-evoked steroidogenesis. TMB-8 produced a smaller but significant reduction of EGTA-facilitated 45Ca2+ efflux from a mitochondrial-enriched fraction. We interpret these results to mean that TMB-8 blocks the steroidogenic effect of dibutyryl cyclic AMP by interfering with the mobilization of a cellular pool of calcium that is probably localized to the endoplasmic reticulum. The physiological implications of these findings in relation to the complex interactions between calcium and cyclic AMP in adrenal steroidogenesis are discussed.

Characterization of corticotropin receptors on adrenocortical cells

The binding of corticotropin (ACTH) to receptors on isolated rat adrenocortical cells was investigated with the aid of [[125I]ITyr23, Phe2, Nle4]ACTH-(1-38) (125I-ACTH analog) which retained full biological potency and had a specific radioactivity of 1800 +/- 75 Ci/mmol. Binding was highly specific to adrenocortical cells, and the radioactive peptide was displaced by low concentrations of ACTH but not by other basic peptides. Binding was rapid, reversible, and linearly related to the number of cells. 125I-ACTH analog was not significantly degraded by incubation with the cells at 23 degrees C for 1 hr. Scatchard analysis of the binding was compatible with a single class of binding sites with Kd = 1.41 +/- 0.21 nM, and the number of sites was estimated to be 3840 +/- 1045 per cell. The binding curve was superimposable on the concentration-response curve for cyclic AMP. Small, but significant amounts of 125I-ACTH analog were bound at concentrations sufficient for maximal stimulation of steroidogenesis. For a series of ACTH analogs, the concentrations of the peptides required for half-maximal stimulation of cyclic AMP production were in excellent agreement with the concentration required for half-maximal inhibition of binding. These results suggest that the adrenocortical cells contain only one class of ACTH receptors and that stimulation of a small fraction of these receptors (less than 3%) is sufficient for maximal steroidogenesis.