Identification and quantitation of tetrapeptide deamidation products by mass spectrometry

A method to quantify asparagine (Asn), aspartate (Asp) and isoaspartate (isoAsp) residues in small peptides by fast atom bombardment mass spectrometry (FAB-MS) was developed. Discrimination of isoAsp from Asp residues was accomplished by selective derivatization of isoAsp residues in acetic anhydride, D2O and pyridine. Deuteration occurred at any carbon adjacent to a free alpha-carboxyl group, through a transient oxazalone intermediate, allowing the isoAsp side chain and the C-terminus to incorporate deuterium. Thus, isoAsp-containing peptides incorporate one more deuterium than peptides with Asp and two more than Asn peptides. FAB CID-MS spectra of the Asn tetrapeptide, Thr-Asn-Ser-Tyr, were used to confirm the position of deuteration to the C-terminal residue. FAB and FAB CID-MS spectra demonstrated that the 1 amu shift in mass was not caused by derivatization induced deamidation of the Asn residue. FAB-MS spectra of deuterated peptide standards and mixtures containing deamidation products were obtained over the molecular ion region and deconvoluted using non-deuterated control spectra. Deuterium incorporation values for the Asn, Asp and iosAsp containing peptide standards were 80% mono-deuterated peptide, 95% mono-deuterated peptide and 63% di-deuterated peptide, respectively. IsoAsp to Asp ratios in an unknown mixture were obtained by a least-squares minimization of the difference between the unknown deuterated mixture and the isotopic envelopes from the deuterated standards. The mixture was found to contain 85% isoAsp peptide by FAB-MS, which agreed well with 81% isoAsp peptide when assayed by reversed-phase LC.

Haemodynamic and neurohumoral response in heart failure produced by rapid ventricular pacing

OBJECTIVE

The aim was to determine the exact sequence of hormone changes during the progression of fluid retention in a canine model of "congestive cardiac failure" induced by rapid right ventricular pacing, and during recovery when pacing is stopped.

METHODS

Rapid ventricular pacing at a rate of 250 pulses.min-1 was used in six mongrel dogs with implanted right ventricular pacemakers. Right heart haemodynamics were measured by means of Swan Ganz catheterisation, allowing flow measurement by thermodilution and pressure measurement by external manometry. Plasma renin activity, arginine vasopressin, and atrial natriuretic factor were assayed on venous blood samples by radioimmunoassay. Noradrenaline was assayed by high pressure liquid chromatography.

RESULTS

The onset of rapid pacing was accompanied by a fall in cardiac output and a rise in pulmonary arterial, pulmonary capillary wedge, and right atrial pressures. Noradrenaline and atrial natriuretic factor rose. Plasma renin activity showed an initial fall followed by a rise, and arginine vasopressin was unchanged in the first 8 h. When rapid pacing was continued for a further 35 d, clinical signs of fluid retention appeared by day 28, by which time cardiac output had fallen, and central pressures risen further. Atrial natriuretic factor peaked at around 14 d whereas plasma renin activity, arginine vasopressin, and noradrenaline tended to reach a plateau at about d 20 and then to show further increases as clinical signs of fluid retention appeared; this was most marked with plasma renin activity. Cessation of pacing at d 35 caused a rapid reversal (increase) of cardiac output but a more gradual reversal (decrease) of right heart pressures over 5 d; only wedge pressure returned to base line. Arginine vasopressin and plasma renin activity fell rapidly to around 40% of the final pacing levels and reached basal values after 8 h and 48 h respectively. Noradrenaline fell after 8 h and reached basal levels in 5 d. Atrial natriuretic factor fell quickly by 60% after 8 h but remained above basal levels for 5 d. At the end of pacing, body weight fell rapidly in conjunction with a large diuresis.

CONCLUSIONS

These findings are compatible with a major role of one or more of renin, vasopressin, and noradrenaline in the pathophysiology of the fluid retention of heart failure; the manifestations are not counteracted by the rise in atrial natriuretic factor.

Position of the fovea centralis with respect to the optic nerve head

Examination of the ocular fundus via indirect ophthalmoscopy gives the clinician an impression of foveal position relative to the nerve head. In some patients, the fovea appears to be in an unusual position (i.e., ectopic): it may appear to be higher or lower than expected, or closer to or farther from the nerve head. There is little published quantitative information on this subject. The purpose of this study was to examine foveal position in a group of normal adult eyes, so that clinicians and other researchers will be able to determine on a more objective basis whether or not a given patient shows foveal ectopia. Using ocular fundus photographs for 446 normal adult eyes, we found the foveal center to be, on average, 6.11 degrees +/- 3.32 degrees below a horizontal line bisecting the nerve head. For a smaller sample of 66 eyes, we found the average distance between the nerve head and foveal centers to be 4.93 +/- 0.33 mm (right eye) and 4.88 +/- 0.36 mm (left eye). Correlations of these data for right and left eyes are also examined. Nerve head data for the group of 66 right eyes were also analyzed to yield dimensions of a best-fitting ellipse: the mean minor axis was 1.75 +/- 0.2 mm; the mean major axis 1.95 +/- 0.2 mm. Ectopia (heterotopia) of the fovea has been found in association with chorioretinitis, fibrous traction bands, and/or colobomas of the choroid and optic nerve (including anomalous insertion of the optic nerve), microcephalus, and microphthalmia. A number of separate cases with anomalous nerve heads and/or foveal positions are discussed in this paper.(ABSTRACT TRUNCATED AT 250 WORDS)

Retention of central visual field in retinitis pigmentosa

According to Kanski, roughly one in four patients with retinitis pigmentosa retains visual acuity adequate for reading, although the electroretinogram may be extinguished and the visual field constricted to 2 to 3 degrees (whether diameter or radius is not stated). Under the age of 20 years, an acuity as poor as 6/60 is relatively uncommon, whereas over the age of 50 years such an acuity becomes common. Heckenlively comments that by the end of the 4th decade of life, most males with X-linked retinitis pigmentosa have vision reduced to hand motion or light perception. Women tend to be less severely affected than men: in a study by Bird, only 3 of 48 female heterozygotes had an acuity of less than 6/9, whereas only 8 of 28 hemizygous males had an acuity of 6/9 or better. I thought it would be instructive to analyze the visual field data for a female patient who, although she had suffered considerable loss of peripheral vision, is continuing to function visually quite well.

Reproductive endocrinology of macaroni (Eudyptes chrysolophus) and gentoo (Pygoscelis papua) penguins. I. Seasonal changes in plasma levels of gonadal steroids and LH in breeding adults

Changes in plasma luteinizing hormone (LH), testosterone, oestradiol, and progesterone were measured throughout the breeding and molt cycle in free-living male and female macaroni (Eudyptes chrysolophus) and gentoo (Pygoscelis papua) penguins, at Bird Island, South Georgia (54 degrees S, 38 degrees W). These two species are sympatric but have a markedly different breeding cycle. In macaroni penguins plasma levels of all hormones, except LH in males, were significantly elevated at the time of arrival at the breeding colony. In both species and sexes plasma LH, testosterone (males), and estradiol (females) levels were highest during nest-building and postcopulation, coincident with the period of frequent agonistic interactions in males and egg-formation in females. Elevated testosterone levels occurred in females of both species during the postcopulation period and may be associated behaviourally with both sexes being involved in nest defence. Male birds also had elevated estradiol levels. Following copulation, plasma levels of LH, testosterone, and estradiol decreased to basal levels in both sexes and species and, except for a transient increase in testosterone in male macaroni penguins, remained low through to the end of molt. There was no associated rise in LH or testosterone during premolt and early molt despite a further period of agonistic and social interaction, suggesting that birds were in a photorefractory state at this time. Plasma progesterone showed a pattern of variation different from that of the other hormones. In both species and sexes, plasma levels were elevated between arrival and early chick-rearing and then decreased slowly to low levels during molt.

Reproductive endocrinology of macaroni (Eudyptes chrysolophus) and gentoo (Pygoscelis papua) penguins. II. Plasma levels of gonadal steroids and LH in immature birds in relation to deferred sexual maturity

Plasma levels of LH, testosterone, estradiol, and progesterone were measured, during the breeding season, in adult and immature macaroni (Eudyptes chrysolophus) and gentoo (Pygoscelis papua) penguins, at Bird Island, South Georgia (54 degrees S, 38 degrees W), in relation to deferred sexual maturity. Macaroni penguins do not breed until 6-8 years of age whereas gentoo penguins first breed at 2 years of age. Plasma LH was elevated in 3- to 5-year-old macaroni penguins, but not in 1- to 2-year-old birds nor 1-year-old gentoos. However, 1 year olds of both species responded to an injection of exogenous LH-RH by increasing LH secretion. Some individual 3-, 4-, and 5-year-old macaroni penguins had circulating testosterone levels within the range of peak values in adults, suggesting that in males, gonads were physiologically mature several years in advance of the age of first breeding. One year old macaroni penguins had elevated progesterone levels and basal estradiol levels, but in 2-4 year olds plasma levels of both progesterone and estradiol were low. This does not support the hypothesis that high progesterone levels "block" ovarian maturation in immature penguins. Immature gentoo penguins showed a different pattern of hormone secretion. Plasma testosterone was low in all breeding periods, but estradiol levels increased to a peak during the incubation period, 4 weeks later than peak values occurred in adults. In both species, therefore, deferred sexual maturity was associated with delayed and/or reduced secretion of LH and gonadal steroids.

Full recovery following massive overdose with insulin and thyroxine

Specific treatment is available for only a few substances taken in overdose. We report here a patient who attempted suicide with a massive overdose of insulin and thyroxine, a combination not previously reported, and discuss the specific treatments given to mitigate the harmful effects of this combination.

Investigations of gas-phase lithium-peptide adducts: Tandem. mass spectrometry and semiempirical studies

Tandem mass spectrometry using a hybrid mass spectrometer of BEqQ geometry was used to investigate the gas-phase formation of the [An (+) Li - H)(+) ion from lithium-peptide adducts. High resolution mass measurements as well as precursor and product ion scans of five peptides indicate that one source of [An (+) Li - H) arises from [An (+) Li](+). Semiempirical calculations (MNOO) and metastable ion decomposition studies of the peptide Gly-Gly-Gly show that the lithium ion prefers to coordinate to the three internal carbonyls of the neutral molecule to give a species that is energetically more stable than the lithiated zwitterion by 305 kJ/mol. Theoretical and experimental evidence suggest that the monolithiated precursor ion population may be a distribution of structural isomers. (J Am Soc Mass Spectrom 1990, 1, 473-480).

Altered cardiovascular and neurohumoral responses to head-up tilt after heart-lung transplantation

Heart-lung transplantation results in afferent and efferent denervation of the transplanted organs including interruption of the central connections from the low-pressure receptors in the atria and pulmonary veins. We investigated whether the cardiovascular and neurohumoral responses to the postural stimulus of head-up tilt were affected after transplantation. Responses in eight heart-lung transplant recipients were studied and compared with those in eight normal subjects matched for age and sex during passive head-up tilt at 45 degrees for 1 hour. The transplant group had a higher initial heart rate (99 +/- 2 versus 68 +/- 2 beats/min, p less than 0.001) and diastolic blood pressure (88 +/- 5 versus 76 +/- 2 mm Hg, p less than 0.05) than did the control group. The increases in heart rate and diastolic blood pressure during head-up tilt were similar in the two groups. Systolic blood pressure remained unchanged. The decrease in cardiac output (30% versus 18%, p less than 0.05) and the increase in systemic vascular resistance (52% versus 28%, p less than 0.05) were greater in the transplant group. Baseline levels of norepinephrine, epinephrine, vasopressin, and plasma renin activity were similar in the two groups. Atrial natriuretic peptide concentrations were higher in the transplant group (26 +/- 3.8 versus 9.7 +/- 1.6 pmol/l, p less than 0.001). During head-up tilt, plasma norepinephrine levels increased to a greater extent in the transplant group than in the control group (83% versus 53%, p less than 0.01), indicating an increased sympathetic response. In contrast, plasma renin activity increased significantly in the control group but not in the transplant group.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of impaired excretion of a fluid load after cardiac denervation in dogs

The influence of cardiac innervation on the renal response to volume expansion was investigated. Systemic hemodynamic, plasma hormone, and renal clearance measurements were made before, during, and after intravenous administration of 1,000 ml 0.9% saline over 10 min to six control and six cardiac-denervated, chloralose-anesthetized mongrel dogs. Volume expansion resulted in a two- to threefold rise in plasma atrial natriuretic peptide (ANP) concentrations and a 50% rise in glomerular filtration rate (GFR) in both groups. Plasma renin activity (PRA) and plasma arginine vasopressin remained higher throughout in cardiac-denervated compared with control dogs. The marked increases in urine flow rate and sodium and free water clearances seen in the controls were attenuated or abolished after cardiac denervation. These differences were due to the influence of higher PRA and vasopressin in these animals compared with the controls, rather than differences in hemodynamic responses operating via GFR or in direct humoral responses via ANP secretion.

Visual fields, acuity, and intraocular pressure in a pseudophakic patient

A 55-year-old white male underwent an uneventful cataract extraction with implantation of a posterior chamber intraocular lens (IOL) in his left eye. Two years after the cataract surgery, his visual acuity decreased due to opacification of the posterior lens capsule. This report addresses the effect of laser capsulotomy on the patient's visual acuity, intraocular pressure (IOP), and visual field. Although the first two have improved nicely, the size of the last remains considerably below the norm for his phakic contemporaries.

Vasopressin secretion in diabetic subjects with and without autonomic neuropathy: responses to osmotic and postural stimulation

1. The release of arginine vasopressin (AVP) after an osmotic stimulus and head-up tilt was assessed in diabetic subjects with and without autonomic neuropathy. 2. Six diabetic subjects with (DAN +ve) and five without (DAN -ve) evidence of autonomic neuropathy and five normal subjects were infused with 5% (w/v) NaCl at a rate of 0.05 ml min-1 kg-1 body weight for 120 min. Blood pressure, heart rate and plasma AVP were measured over this period. 3. Seven DAN +ve, six DAN -ve and six normal subjects were tilted head-up to 45 degrees for 120 min. Blood pressure, heart rate and plasma AVP were measured during the study. 4. Infusion of 5% (w/v) NaCl produced appropriate rises in plasma osmolality and plasma AVP levels which did not differ between the three groups, confirming the normal osmotic release of AVP in the diabetic subjects. 5. During head-up tilt, there were no differences in AVP responses between the three groups, despite a major hypotensive stimulus in the DAN +ve group. 6. We conclude that osmotic release of AVP is normal in diabetes, but that cardiovascular release of AVP is impaired in diabetic subjects with cardiovascular reflex evidence of autonomic neuropathy, reflecting an afferent defect.

Dependent effect of drinking volume on vasopressin but not atrial peptide in humans

The act of drinking causes a fall in plasma arginine vasopressin (AVP) concentration that precedes changes in plasma osmolality. To investigate the specificity of this drinking stimulus on hormone secretion, six volunteers (5 male, 1 female, aged 22-39 yr) were water deprived for 36 h and then drank 15 ml/kg water at 10-12 degrees C using 15-20 swallowing actions/min over 3.5 +/- 0.5 min (mean +/- SE). This caused a fall in plasma AVP from 4.5 +/- 0.7 to 3.2 +/- 0.5 pmol/l (P less than 0.05) and in thirst (by 5.7 +/- 0.6 on a 10-cm linear analog scale) (P less than 0.05) 5 min after drinking. No significant changes occurred in mean arterial pressure, heart rate, or plasma atrial natriuretic peptide (ANP) concentration. A second study was undertaken to determine whether the reflex inhibition of AVP secretion is activated simply by the act of swallowing regardless of the volume of liquid consumed. The six volunteers were water deprived for 36 h and then sipped and swallowed 1 ml/kg water at 10-12 degrees C using 15-20 swallowing actions/min over 3.0 +/- 0.1 min. There was no change in plasma AVP concentration, although thirst was reduced by 2.3 +/- 0.6 (P less than 0.05) at 5 min. Plasma AVP 10 min after sipping and swallowing (4.2 +/- 0.8 pmol/l) was significantly greater than at 10 min after drinking 15 ml/kg (2.8 +/- 0.5 pmol/l) (P less than 0.05) despite the fact that plasma osmolality at this stage was similar in both studies. We conclude that the drinking-mediated reflex inhibition of AVP secretion in humans is dependent on swallowing an adequate volume and is not accompanied by changes in hemodynamics or in plasma ANP concentration.

Atrial natriuretic peptide response to rapid atrial pacing in cardiac-denervated dogs

The effects of rapid atrial pacing on central hemodynamics, plasma hormones, and renal function were investigated in eight control and nine cardiac-denervated dogs under chloralose anesthesia. Pacing at approximately 250 ppm for 60 min caused similar increases in pulmonary wedge and right atrial pressures, systemic vascular resistance, and plasma atrial natriuretic peptide (ANP) in both groups. In control dogs, pacing produced a fall in both plasma vasopressin (AVP) and plasma renin activity (PRA) and a rise in urine flow rate associated with an increase in free water but not sodium clearance. In contrast, in cardiac-denervated dogs, both plasma AVP and PRA increased during pacing; urine flow rate did not change, and marked sodium retention occurred. This study supports the concept that the increase in urine flow during rapid atrial pacing is mediated by inhibition of renin and AVP secretion through intact cardiac nerves. The secretion of ANP is unaffected by cardiac denervation. The natriuretic and vasodilator actions of high plasma ANP concentrations during rapid atrial pacing can be inhibited either by neurally mediated cardiorenal effects in normal animals or by stimulation of the renin-angiotensin system after cardiac denervation.

Selective defect in gonadotrophin secretion in patients with autonomic failure

We studied the neuroendocrine effects of a condition associated with abnormal hypothalamic amines. Hypothalamo-anterior pituitary function was assessed in five male subjects with autonomic failure (AF) and in five age and sex-matched controls. All subjects showed normal gonadotrophin and TSH responses to GnRH and TRH, respectively. In control subjects, intravenous infusion of naloxone caused a significant rise in overall LH concentrations as well as increased frequency and amplitude of LH pulses. In contrast, in AF subjects naloxone did not alter LH concentrations or increase LH pulse frequency. Naloxone also caused an increase in neurosecretory GH pulses not only in AF subjects but also in the controls. These results suggest that in man, ascending catecholamine pathways are important in the control of gonadotrophin secretion. The markedly different response of GH to an opioid antagonist in elderly subjects should be further investigated.