Corticotropic peptides in the human fetal pituitary

The vasotocinergic system and its role in the regulation of stress in birds

The regulation of stress in birds includes a complex interaction of neural systems affecting the hypothalamic-pituitary-adrenal (HPA) axis. In addition to the hypothalamic paraventricular nucleus, a structure called the nucleus of the hippocampal commissure likewise affects the output of pituitary stress hormones and appears to be unique to avian species. Within the anterior pituitary, the avian V1a and V1b receptors were found in corticotropes. Based on our studies with central administration of hormones in the chicken, corticotropic releasing hormone (CRH) is a more potent ACTH secretagogue than arginine vasotocin (AVT). In contrast, when applied peripherally, AVT is more efficacious. Co-administration of AVT and CRH peripherally, resulted in a synergistic stimulation of corticosterone release. Data suggest receptor oligomerization as one possible mechanism. In birds, vasotocin receptors associated with stress responses include the V1a and V1b receptors. Three-dimensional, homology-based structural models of the avian V1aR were built to test agonists and antagonists for each receptor that were screened by molecular docking to map their binding sites on each receptor. Additionally, binding affinity values for each available peptide antagonist to the V1aR and V1bR were determined. An anterior pituitary primary culture system was developed to determine how effective each antagonist blocked the function of each receptor in culture when stimulated by a combination of AVT/CRH administration. Use of an antagonist in subsequent in vivo studies identified the V1aR in regulating food intake in birds. The V1aR was likewise found in circumventricular organs of the brain, suggesting a possible function in stress.

Fetal and Neonatal HPA Axis

Stress is an integral part of life. Activation of the hypothalamus-pituitary-adrenal (HPA) axis in the adult can be viewed as mostly adaptive to restore homeostasis in the short term. When stress occurs during development, and specifically during periods of vulnerability in maturing systems, it can significantly reprogram function, leading to pathologies in the adult. Thus, it is critical to understand how the HPA axis is regulated during developmental periods and what are the factors contributing to shape its activity and reactivity to environmental stressors. The HPA axis is not a passive system. It can actively participate in critical physiological regulation, inducing parturition in the sheep for instance or being a center stage actor in the preparation of the fetus to aerobic life (lung maturation). It is also a major player in orchestrating mental function, metabolic, and cardiovascular function often reprogrammed by stressors even prior to conception through epigenetic modifications of gametes. In this review, we review the ontogeny of the HPA axis with an emphasis on two species that have been widely studied-sheep and rodents-because they each share many similar regulatory mechanism applicable to our understanding of the human HPA axis. The studies discussed in this review should ultimately inform us about windows of susceptibility in the developing brain and the crucial importance of early preconception, prenatal, and postnatal interventions designed to improve parental competence and offspring outcome. Only through informed studies will our public health system be able to curb the expansion of many stress-related or stress-induced pathologies and forge a better future for upcoming generations.

Developmental changes in molecular forms of immunoreactive adrenocorticotropin in the anterior pituitary gland of humans

In extracts of anterior pituitary tissue obtained at autopsy of fetal, infant, and adult humans, five molecular forms of immunoreactive ACTH (ACTHi) were detected that had apparent molecular weights of approximately 4044, 30-34, 24-28, 16-18, and 4.5 kilodaltons (K). The relative proportion of each molecular form of ACTHi was similar in tissues that were extracted at the time of autopsy and in tissues that were stored frozen (-20 degrees C) for up to 2 years prior to extraction. We found that 40-44K ACTHi comprised a significantly greater proportion of total ACTHi in fetuses (12.3+/-3.5%) than in adults (3.8+/-0.8%); intermediate amounts of this form of ACTHi (8.0+/-4.1%) were found in tissues obtained from infants. On the other hand, the proportion of 4.5 K ACTHi in fetal pituitaries (67 %) was less than that in those of adults (84 %). The ratio of 40-44/30-34K ACTHi was significantly greater (P<0.001) in fetuses (1.46+/-0.12) and infants (1.31+/-0.07) than in adults (0.52+/-0.07). The ontogenetic differences in molecular forms of pituitary ACTHi are thought to reflect alterations in the processing of proopiomelanocortin as a function of human development.

A critical review of the origin and control of adrenal androgens

The reticularis and fasciculata zones of the adrenal cortex are the predominant sources of dehydroepiandrosterone (DHEA) and DHEA-sulphate and contribute directly or indirectly 60-75% of androstenedione and testosterone in women. The specific control of adrenal androgens remains unclear. While ACTH stimulates adrenal androgen secretion, the dissociation of cortisol and androgens occurring during adrenarche and under pathological conditions suggests other factors are involved. Recent studies using human adrenal cells in vitro have demonstrated that the ratio of androgen to cortisol produced is substantially independent of the age and gender of the adrenal, indicating that extra-adrenal factors are of greater importance. beta-Endorphin and joining peptide have been shown to stimulate androgen production in human adrenal cells and to influence ACTH-stimulated steroidogenesis in a manner that promotes adrenal androgen production. The activity of these pro-opiomelanocortin-derived peptides may explain the physiological and pathological dissociations of androgens and cortisol.

A trace-enrichment technique for the loading of gel-permeation high-performance liquid chromatography columns

Gel-permeation high-performance liquid chromatography (GP-HPLC) columns provide rapid high-resolution separations but are frequently limited to analytical tasks because the injection volumes must be small. The reduction of volume required for the loading of solutes can often be impractical and lead to poor recoveries. We have developed a trace-enrichment technique to circumvent this problem. By placing a Waters Guard Pak within the loop of a Valco injector and connecting a pump to the injection port it is possible to concentrate proteins and peptides onto the guard column from relatively large volumes. Enrichment onto a reversed-phase guard column insert is achieved by loading solutes in an aqueous solution or one of low organic solvent concentration. Provided that the GP-HPLC is mean-while equilibrated with a solvent system of sufficiently high organic solvent concentration (i.e., 40% acetonitrile containing 0.1% trifluoroacetic acid) it is possible to elute material that has been loaded in this manner by simply placing the injection loop in line with the column. The solvent strength abruptly increases and the peptide or protein sample is loaded onto the column in a very small volume. We have applied this loading principle to both analytical and semipreparative problems. The amino-terminal fragment of pro-opiomelanocortin (POMC) has been extracted from a single human fetal pituitary (18 weeks gestation) and characterized in terms of its molecular weight. This study indicated that no proteolytic processing of the amino-terminal fragment of POMC takes place at this stage in development. In a larger scale application the amino-terminal fragment of POMC was purified from bovine anterior pituitaries.(ABSTRACT TRUNCATED AT 250 WORDS)

Des-acetyl-alpha-MSH and not alpha-MSH is the major form of alpha-MSH in amniotic fluid

Immunoreactive alpha-melanocyte stimulating hormone (IR-alpha-MSH)-like activity was measured by radioimmunoassay (RIA) in at term pregnancy amniotic fluid prior and after adsorption on a Sep-pak C18 cartridge. alpha-MSH activity was 3-4 times lower after Sep-pak purification but, unlike the levels of IR-alpha-MSH in the fluid analyzed in toto, increased linearly with the volume of fluid analyzed. Furthermore, fractionation by high pressure liquid chromatography (HPLC) revealed that IR-alpha-MSH recovered from the Sep-pak was due to several peptides rather than to a single peptide. The most abundant of them (50% of total activity) behaved like authentic des-acetyl-alpha-MSH. Since des-acetyl-alpha-MSH is also the most abundant alpha-MSH-like peptide in the fetal pituitary gland, the present results suggest that the fetal pituitary is a main source of des-acetyl-alpha-MSH in the amniotic fluid.

Presence of immunoreactive alpha-bag cell peptide[1-8] in bag cell neurons of Aplysia suggests novel carboxypeptidase processing of neuropeptides

alpha-bag cell peptide (alpha BCP) is a putative neurotransmitter released from bag cell neurons of the marine mollusc Aplysia. alpha BCP is present in bag cell extracts and releasate from bag cells in two neuroactive forms: alpha BCP[1-9] and alpha BCP[1-8]. alpha BCP[1-8] is 30 times as potent as [1-9] in inhibiting target neurons, suggesting that both forms of the peptide serve as neurotransmitters. However, biochemical and molecular genetic data suggest that only alpha BCP[1-9] is originally cleaved directly from a larger precursor protein and that generation of alpha BCP[1-8] would require an unusual C-terminal leucine cleavage of alpha BCP[1-9]. To further ascertain which forms of alpha BCP are normally present in bag cells, we generated highly specific antisera to each peptide. We found intense immunostaining for both peptides in bag cell somata and nerve terminals. Moreover, both forms were stable in bag cell extract for at least 1 hr, which suggests that proteolysis in the extracts had been effectively inhibited. These results suggest that both alpha BCP[1-8] and [1-9] are normally present in bag cell somata and terminals and that a small amount of alpha BCP[1-9] is processed to alpha BCP[1-8] in vesicles before release. The results support the interpretation that the activity of an intravesicular carboxypeptidase generates alpha BCP[1-8] and thereby regulates the amount of inhibitory activity released during a bag cell discharge.

Ontogeny of pituitary beta-endorphin and related peptides in the human embryo and fetus

In this study we evaluated the presence of proopiomelanocortin-related peptides (beta-lipotropin, beta-endorphin, and gamma-endorphin) in five embryos (5 to 10 weeks of pregnancy) and 11 fetal pituitaries (15 to 25 weeks) by means of high-performance liquid chromatography coupled with specific radioimmunoassays. Tissues were collected at laparotomy for ectopic pregnancy (five embryos) or after spontaneous (seven) or prostaglandin-induced (four) abortion. beta-Endorphin and beta-lipotropin were present starting at the seventh week of pregnancy while gamma-endorphin appeared only in the second trimester. During embryonic life opioid activity was limited to the cephalic portion. The three peptides, but little, if any, acetylated 1-31 beta-endorphin, were recognized in the fetal pituitary throughout the second trimester, at which time beta-lipotropin and beta-endorphin showed constant values in spite of increasing gamma-endorphin concentrations. beta-Lipotropin was the predominant peptide in both embryonic and fetal life. In conclusion, the three peptides related to proopiomelanocortin were expressed from the precursor at different times throughout development. By the beginning of the second trimester the pituitary processing of proopiomelanocortin is similar to that of adult life and the functional activity of the anterior lobe seems to prevail over that of the "fetus-related" neurointermediate lobe around the twenty-fifth week of pregnancy.

Existence of different forms of adrenocorticotropin in rat hypothalamus

Adrenocorticotropin (ACTH)-like immunoreactivity and bioactivity were extracted from rat hypothalamus and fractionated by high pressure liquid chromatography. Analysis of the fractions either by radioimmunoassay or bioassay (corticosteroid production from rat adrenal cells) revealed several peaks of immunoreactivity and bioactivity. Only 20-25% of total ACTH-like immunoreactivity and bioactivity eluted with the same retention time as authentic ACTH 1-39. The results suggest that different forms of ACTH exist in rat hypothalamus.

Circulating forms of alpha MSH in the carp and trout blood: an HPLC and RIA study

The three forms of MSH(desacetyl-, monoacetyl-, and diacetyl) circulate in the carp and trout blood. Their proportions there are as follows: in the carp, the desacetylated form is 2.5% of total MSH and the monoacetylated form 72% of the acetylated forms of alpha MSH. In the trout, similar proportions were found: desacetyl alpha MSH was 5% of total alpha MSH and monoacetyl-, 70% of the acetylated MSHs.

Non-ACTH components of adult human pituitary extracts which stimulate adrenal steroidogenesis

Human pituitary extracts were fractionated by chromatography on Sephadex G-50 and G-25, and low molecular weight components were further separated by HPLC. Eluates were tested for their activity in stimulating steroidogenesis in suspensions of rat adrenal capsule (largely zona glomerulosa) and inner zone (fasciculata/reticularis) cells. Several biologically active components were reproducibly isolated. Three stimulated glomerulosa cells specifically, and one of these was tentatively identified by HPLC and RIA criteria as desacetyl-alpha-MSH. Alpha-MSH was not detected. One component stimulated both cell types but two others stimulated inner zone cells, and were without effect on glomerulosa cells: this type of activity has not previously been described, and is not associated with any peptide derived from pro-opiomelanocortin which has so far been tested. The data suggest that, in addition to corticotrophin, further pituitary peptides may be involved in the control of adrenocortical function.

Plasma immunoreactive beta-endorphin and cortisol in the newborn infant after elective caesarean section and after spontaneous labour

The effect of the mode of delivery on the plasma concentration of immunoreactive beta-endorphin (irbeta-E) and cortisol was studied in 27 newborn infants, 10 delivered by caesarean section and 17 by spontaneous vaginal labour. After elective caesarean section, the mean plasma concentration of cortisol rose from 227 +/- 27 nmol/l (S.E.) at birth to 705 +/- 90 nmol/l at the age of 2 h, indicating a significant increase in cortisol secretion, and the mean irbeta-E remained high, being 111 +/- 24 ng/l at birth and 117 +/- 21 ng/l at the age of 2 h. After spontaneous labour, the plasma cortisol level was already high at birth, 735 +/- 78 nmol/l, and remained so to the age of 2 h, 659 +/- 43 nmol/l, whereas the plasma irbeta-E decreased from 181 +/- 29 at birth to 64 +/- 7 ng/l at the age of 2 h. All newborns were in a good condition except one in whom transitory tachypnea developed during the follow-up. In this newborn the plasma level of irbeta-E increased greatly: from 210 ng/l to 705 ng/l. These results show that, irrespective of the route, the delivery is stressfull to the newborn infant. In newborns delivered by caesarean section the stress response comes after birth. Additional stress such as respiratory difficulties seems to increase the secretion of beta-endorphin.

Separation and partial characterization by high-performance liquid chromatography and radioimmunoassay of different forms of melanocyte-stimulating hormone from fish (Cyprinidae) neurointermediate lobes

From neurointermediate lobe (NIL) extracts of two species of Cyprinidae, Carassius auratus and Cyprinus carpio, several peptides were separated by high-performance liquid chromatography (HPLC) on a C18 muBondapak column eluted with a methanol/acetic acid/triethylamine mixture. Monitoring all fractions by radioimmunoassay (RIA) with an antibody against melanocyte-stimulating hormone (MSH) C terminal gave positive reactions for fractions 7, 11-12, 15-16, 23-24, and 25-27. For further characterization, the elution positions of these peaks were compared to those of known synthetic reference substances. Peak 7 elutes in the same position as oxidized alpha MSH, whereas peak 15-16 matches the elution position of des-acetyl alpha MSH and 23-24 that of alpha MSH. The product from peak 26-27 has several characteristics of the diacetylated form of alpha MSH: its immunoreactivity in RIA, its sensitivity to weak bases and to HCl and its mass spectrum which is identical with that of mammalian diacetyl alpha MSH. In both species, the diacetylated form is predominant in the intracellular pool. This study establishes the coexistence of three different forms of alpha MSH, a des-acetylated, monoacetylated, and diacetylated in the cyprinid NIL extracts.

Novel variants of adrenocorticotrophic hormone in porcine anterior pituitary

Extracts of porcine anterior pituitary contain several corticotrophic variants of ACTH 1-39. They were isolated by adsorption chromatography, ion-exchange chromatography and reverse-phase high-performance liquid chromatography. Four variants were then identified as starting and ending at positions corresponding to ACTH 1-38, 1-37, 7-39 and 7-38. Several of these fragments were recovered in chromatographically multiple forms. Although all fragments isolated had corticotrophic activity (measured on isolated rat adrenal cells) those with a shortened N-terminal region had a lower potency than those with an intact N-terminal region. Corticotrophic activity of porcine ACTH 7-38 was detected in a preparation with a beta-aspartyl shift at position 25. However, in agreement with previous studies, synthetic human ACTH 7-38, in which an intact Asn-Gly bond was structurally proven, possessed no such activity. The results indicate that position 25 as well as positions 1-6 are important for corticotrophic activity, and that a deamidative beta-aspartyl shift at position 25 can influence the activity.

Biosynthesis and processing of pro-opiomelanocortin-derived peptides during fetal pituitary development

We have investigated the molecular weight forms of pro-opiomelanocortin (POMC)-derived peptides present in rat pituitaries during fetal and early postnatal development (embryonic Day 14 to 3 day neonate). At all early ages examined, the major immunoreactive form of corticotropin (ACTH) was POMC. Only during late fetal and early postnatal stages did progressively larger amounts of 4.5K ACTH, a major POMC processing end product, appear. This form was found almost exclusively in isolated anterior lobes. In contrast, 3.5K size endorphin(s), another POMC derivative, were present in whole glands even at early stages (Day 14), and were the major POMC derivative(s) found in isolated intermediate-posterior lobes of older fetuses. Despite the early appearance of 3.5K endorphin(s), alpha-MSH did not appear until Day 19 and was detected only in isolated intermediate-posterior lobes. We have also cultured dispersed fetal pituitary cells in the presence of radioactive amino acids. After immunoprecipitation using affinity-purified antisera, followed by fractionation of the radiolabeled products, we found that POMC biosynthesis does occur in cultures of Day 14 embryonic pituitary cells, and that the major POMC-derived end product produced is 3.5K size endorphin(s). These findings demonstrate that POMC is synthesized at least by Day 14 of rat pituitary development and that lobe-specific processing characteristic of the corresponding adult lobe is apparent at the earliest stages that the lobes can be separated. The presence of 3.5K-sized endorphins at early ages is consistent with the possibility that POMC synthesis first occurs in the intermediate lobe. The noncoordinate appearance of alpha-MSH, 1-39 ACTH, and endorphins implies that the activities of certain cleavage enzymes and acetylation enzymes responsible for lobe-specific post-translational POMC processing may be expressed at different times during development.

Lack of correlation between amniotic fluid and maternal plasma contents of beta-endorphin, beta-lipotropin, and adrenocorticotropic hormone in normal and pathologic pregnancies

Reported are the concentrations of beta-endorphin, beta-lipotropin, and adrenocorticotropic hormone (ACTH) in the amniotic fluid and plasma of 40 healthy pregnant women at different stages of gestation. Moreover, the amniotic fluid levels of the three peptides were evaluated in 20 other pregnant women affected by different pathologic conditions (Cooley's disease, gestosis, diabetes, placental insufficiency, etc.). A silicic acid extraction procedure was performed on the samples. Each extract was subjected to Sephadex G-75 column chromatography, and the two fractions corresponding to beta-lipotropin and beta-endorphin were collected, freeze-dried, and assayed by two specific radioimmunoassays. Levels of ACTH were measured by radioimmunoassay directly on the extracts. Levels of beta-endorphin in amniotic fluid showed the highest values in the first trimester (173 +/- 30 fmol/ml, mean +/- SEM) but were significantly decreased in the second (75.2 +/- 14) and third trimesters (14.3 +/- 1.8). An inverse trend characterized plasma levels of beta-endorphin, which showed a progressive increase from the first trimester to term (10.4 +/- 11.1). Amniotic fluid levels of beta-lipotropin remained stable during the first (48.6 +/- 6.3) and second (54.6 +/- 11.1) trimesters, but decreased significantly in the third trimester (17.9 +/- 2.3). The plasma concentrations of beta-lipotropin showed the highest levels in the first trimester (10.9 +/- 0.9), and decreased significantly at term (8.9 +/- 1.3). Last, amniotic fluid levels of ACTH decreased from 55.3 +/- 4.75 fmol/ml in the first trimester to 12.5 +/- 1.16 in the second trimester, and rose again in the third trimester to 34.4 +/- 6.6 fmol/ml. Plasma levels of ACTH were characterized in the first two trimesters by values twice those recorded for nonpregnant women, and decreased at term to 8.9 +/- 1.4 fmol/ml. In the pregnant patients with fetuses affected by Cooley's disease (second trimester) and in those with edema-proteinuria-hypertension (EPH) gestosis (third trimester), amniotic fluid levels of beta-endorphin, beta-lipotropin, and ACTH were in the same range as those in healthy pregnant women.

Control of adrenal androgen production

The major adrenal androgens are dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulphate (DHEAS) and androstenedione (delta 4). Studies by Cutler et al in 1978 demonstrated that these androgens are detectable in blood of all domestic and laboratory animals studied, but that only 4 species show increase in one or more with sexual maturation: rabbit, dog, chimpanzee and man. Studies by Grover and Odell in 1975 show these androgens do not bind to the androgen receptor obtained from rat prostate and thus probably are androgens only by conversion to an active androgen in vivo. Thomas and Oake in 1974 showed human skin converted DHEA to testosterone. The control of adrenal androgen secretion is in part modulated by ACTH. However, other factors or hormones must exist also, for a variety of clinical observations show dissociation in adrenal androgen versus cortisol secretion. Other substances that have been said to be controllers of adrenal androgen secretion include estrogens, prolactin, growth hormone, gonadotropins and lipotropin. None of these appear to be the usual physiological modulator, although under some circumstances each may increase androgen production. Studies from our laboratory using in vivo experiments in the castrate dog and published in 1979 indicated that crude extracts of bovine pituitary contained a substance that either modified ACTH stimulation of adrenal androgen secretion, or stimulated secretion itself - Cortisol Androgen Stimulating Hormone. Parker et al in 1983 showed a 60,000 MW glycoprotein was extractable from human pituitaries, which stimulated DHA secretion by dispersed canine adrenal cells in vitro, but did not stimulate cortisol secretion. This material contained no ACTH by radioimmunoassay. In 1982 Brubaker et al reported a substance was also present in human fetal pituitaries, which stimulated DHA secretion, but did not effect cortisol.

Adrenocorticotropin: ACTH1-38 is a major product of biotransformation by brain synaptic membranes

Since adrenocorticotropic hormone is found in the brain, and several of its fragments affect adaptive behavior, the formation of fragments of ACTH1-39 by a rat brain synaptic membrane fraction was investigated. Following the incubations at physiological pH conditions, the digests were fractionated by HPLC to quantitate the amounts of ACTH1-39 remaining and products formed. Time- and enzyme-dependent disappearance of ACTH1-39 was accompanied by the accumulation of a major peptide metabolite (product B). Amino acid analysis and NH2-terminal end-group determination revealed that product B was identical to ACTH1-38. These results indicate the predominance of carboxypeptidase activity in the degradation of ACTH1-39 by brain synaptic membranes.

Co-occurrence of immunoreactive corticotropin-like and alpha-melanotropin-like material in pituitary cells: differences between young and adult rats

We examined to which extent adrenocorticotropin (ACTH)-like substances are cleavable into alpha-melanotropin (MSH)-like material by application of exogenous enzymes on pituitary sections prior to immunocytochemical stainings. In pro-opiomelanocortin (POMC) cells of the anterior lobe from developing rats (1 to 21 postnatal days) at least one of two cells contained alpha-MSH-like immunoreactivity besides ACTH-like immunostaining. Pretreatment of these tissue sections with tryptic enzymes enhanced remarkably alpha-MSH-like immunostaining. In contrast, alpha-MSH-like immunoreactivity was almost not detectable in anterior lobes from adult rats, also after treatment with enzymes. After adrenalectomy (ax) POMC cells in anterior lobes behaved similarly: a few days after the operation almost all ACTH cells contained also alpha-MSH immunostaining, whereas after more than two weeks alpha-MSH immunostaining was nearly absent, also after application of enzymes. In contrast to rats, in young and adult guinea pig pituitaries all ACTH-like immunoreactivity was prevented by treatment with tryptic enzymes. These observations are consistent with the assumption that occurrence of ACTH- and alpha-MSH-like substances in rat pituitaries is regulated by a protection mechanism against proteolytic cleavage in the ACTH sequence which appears with delay in differentiating and maturing cells.