Alternative approaches for identifying acute systemic toxicity: Moving from research to regulatory testing

Acute systemic toxicity testing provides the basis for hazard labeling and risk management of chemicals. A number of international efforts have been directed at identifying non-animal alternatives for in vivo acute systemic toxicity tests. A September 2015 workshop, Alternative Approaches for Identifying Acute Systemic Toxicity: Moving from Research to Regulatory Testing, reviewed the state-of-the-science of non-animal alternatives for this testing and explored ways to facilitate implementation of alternatives. Workshop attendees included representatives from international regulatory agencies, academia, nongovernmental organizations, and industry. Resources identified as necessary for meaningful progress in implementing alternatives included compiling and making available high-quality reference data, training on use and interpretation of in vitro and in silico approaches, and global harmonization of testing requirements. Attendees particularly noted the need to characterize variability in reference data to evaluate new approaches. They also noted the importance of understanding the mechanisms of acute toxicity, which could be facilitated by the development of adverse outcome pathways. Workshop breakout groups explored different approaches to reducing or replacing animal use for acute toxicity testing, with each group crafting a roadmap and strategy to accomplish near-term progress. The workshop steering committee has organized efforts to implement the recommendations of the workshop participants.

Perceived time is spatial frequency dependent

We investigated whether changes in low-level image characteristics, in this case spatial frequency, were capable of generating a well-known expansion in the perceived duration of an infrequent “oddball” stimulus relative to a repeatedly-presented “standard” stimulus. Our standard and oddball stimuli were Gabor patches that differed from each other in spatial frequency by two octaves. All stimuli were equated for visibility. Rather than the expected “subjective time expansion” found in previous studies, we obtained an equal and opposite expansion or contraction of perceived time dependent upon the spatial frequency relationship of the standard and oddball stimulus. Subsequent experiments using equi-visible stimuli reveal that mid-range spatial frequencies (ca. 2 c/deg) are consistently perceived as having longer durations than low (0.5 c/deg) or high (8 c/deg) spatial frequencies, despite having the same physical duration. Rather than forming a fixed proportion of baseline duration, this bias is constant in additive terms and implicates systematic variations in visual persistence across spatial frequency. Our results have implications for the widely cited finding that auditory stimuli are judged to be longer in duration than visual stimuli.

Development of a risk-ranking framework to evaluate potential high-threat microorganisms, toxins, and chemicals in food

Through a cooperative agreement with the U.S. Food and Drug Administration, the Institute of Food Technologists developed a risk-ranking framework prototype to enable comparison of microbiological and chemical hazards in foods and to assist policy makers, risk managers, risk analysts, and others in determining the relative public health impact of specific hazard-food combinations. The prototype is a bottom-up system based on assumptions that incorporate expert opinion/insight with a number of exposure and hazard-related risk criteria variables, which are propagated forward with food intake data to produce risk-ranking determinations. The prototype produces a semi-quantitative comparative assessment of food safety hazards and the impacts of hazard control measures. For a specific hazard-food combination the prototype can produce a single metric: a final risk value expressed as annual pseudo-disability adjusted life years (pDALY). The pDALY is a harmonization of the very different dose-response relationships observed for chemicals and microbes. The prototype was developed on 2 platforms, a web-based user interface and an Analytica(R) model (Lumina Decision Systems, Los Gatos, Calif., U.S.A.). Comprising visual basic language, the web-based platform facilitates data input and allows use concurrently from multiple locations. The Analytica model facilitates visualization of the logic flow, interrelationship of input and output variables, and calculations/algorithms comprising the prototype. A variety of sortable risk-ranking reports and summary information can be generated for hazard-food pairs, showing hazard and dose-response assumptions and data, per capita consumption by population group, and annual p-DALY.

Tobacco smoke control of mucin production in lung cells requires oxygen radicals AP-1 and JNK

In smokers' lungs, excessive mucus clogs small airways, impairing respiration and promoting recurrent infection. A breakthrough in understanding this pathology was the realization that smoke could directly stimulate mucin synthesis in lung epithelial cells and that this phenomenon was dependent on the cell surface receptor for epidermal growth factor, EGFR. Distal steps in the smoke-triggered pathway have not yet been determined. We report here that the predominant airway mucin (MUC5AC) undergoes transcriptional up-regulation in response to tobacco smoke; this is mediated by an AP-1-containing response element, which binds JunD and Fra-2. These transcription factors require phosphorylation by upstream kinases JNK and ERK, respectively. Whereas ERK activation results from the upstream activation of EGFR, JNK activation is chiefly EGFR-independent. Our experiments demonstrated that smoke activates JNK via a Src-dependent, EGFR-independent signaling cascade initiated by smoke-induced reactive oxygen species. Taken together with our earlier results, these data indicate that the induction of mucin by smoke is the combined effect of mutually independent, reactive oxygen species activation of both EGFR and JNK.

Effects of concentrated ambient particles on normal and hypersecretory airways in rats

Epidemiological studies have reported that elevated levels of particulate air pollution in urban communities are associated with increases in attacks of asthma based on evidence from hospital admissions and emergency department visits. Principal pathologic features of chronic airway diseases, like asthma, are airway inflammation and mucous hypersecretion with excessive amounts of luminal mucus and increased numbers of mucus-secreting cells in regions of the respiratory tract that normally have few or no mucous cells (ie, mucous cell metaplasia). The overall goal of the present project was to understand the adverse effects of urban air fine particulate matter (PM2.5; < or = 2.5 pm in aerodynamic diameter)* on normal airways and airways compromised with airway inflammation and excess mucus. Our project was specifically designed to (1) examine the chemical and physical characteristics of PM2.5 and other airborne pollutants in the outdoor air of a local Detroit community with a high incidence of childhood asthma; (2) determine the effects of this community-based PM2.5 on the airway epithelium in normal rats and rats compromised with preexisting hypersecretory airway diseases (ie, animal models of human allergic airway disease--asthma and chronic bronchitis); and (3) identify the chemical or physical components of PM2.5 that are responsible for PM2.5 -induced airway inflammation and epithelial alterations in these animal models. Two animal models of airway disease were used to examine the effects of PM2.5 exposure on preexisting hypersecretory airways: neutrophilic airway inflammation induced by endotoxin challenge in F344 rats and eosinophilic airway inflammation induced by ovalbumin (OVA) challenge in BN rats. A mobile air monitoring and exposure laboratory equipped with inhalation exposure chambers for animal toxicology studies, air pollution monitors, and particulate collection devices was used in this investigation. The mobile laboratory was parked in a community in southwestern Detroit during the summer months when particulate air pollution is usually high (July and September 2000). We monitored the outdoor air pollution in this community daily, and exposed normal and compromised rats to concentrated PM2.5 from this local urban atmosphere. Rats in the inhalation studies were exposed for 1 day or for 4 or 5 consecutive days (10 hours/day) to either filtered air (controls) or concentrated ambient particles (CAPs) delivered by a Harvard ambient fine particle concentrator. Rats were killed 24 hours after the end of the exposure. Biochemical, morphometric, and molecular techniques were used to identify airway epithelial and inflammatory responses to CAPs. Lung lobes were also either intratracheally lavaged with saline to determine cellular composition and protein in bronchoalveolar lavage fluid (BALF) or removed for analysis by inductively coupled plasma-mass spectrometry (ICPMS) to detect retention of ambient PM2.5--derived trace elements. The Harvard concentrator effectively concentrated the fine ambient particles from this urban atmosphere (10-30 times) without significantly changing the major physicochemical features of the atmospheric particles. Daily CAPs mass concentrations during the 10-hour exposure period (0800-1800) in July ranged from 16 to 895 microg/m3 and in September ranged from 81 to 755 microg/m3. In general, chemical characteristics of ambient particles were conserved through the concentrator into the exposure chamber. Single or repeated exposures to CAPs did not cause adverse effects in the nasal or pulmonary airways of healthy F344 or BN rats. In addition, CAPs-related toxicity was not observed in F344 rats pretreated with bacterial endotoxin. Variable airway responses to CAPs exposure were observed in BN rats with preexisting allergic airway disease induced by OVA sensitization and challenge. Only OVA-challenged BN rats exposed to CAPs for 5 consecutive days in September 2000 had significant increases in airway mucosubstances and pulmonary inflammation compared to saline-challenged/air-exposed control rats. OVA-challenged BN rats that were repeatedly exposed to CAPs in July 2000 had only minor CAPs-related effects. In only the September 5-day exposure protocol, PM2.5 trace elements of anthropogenic origin (La, V, and S) were recovered from the lung tissues of CAPs-exposed rats. Recovery of these specific trace elements was greatest in rats with OVA-induced allergic airway disease. Additional laboratory experiments using intratracheal instillations of ambient PM2.5 samples were performed to identify bioactive agents in the CAPs to which rats had been exposed in the inhalation exposure component. Because the most pronounced effects of CAPs inhalation were found in BN rats with OVA-induced allergic airways exposed in September, we used ambient PM2.5 samples that were collected on 2 days during the September CAPs inhalation exposures to use for instillation. Ambient PM2.5 samples were collected, fractionated into soluble and insoluble species, and then compared with each other and with total PM2.5 for their effects in healthy BN rats and those with OVA-induced allergic airway disease. Intratracheal instillation of the insoluble fraction of PM2.5 caused mild neutrophilic inflammation in the lungs of healthy rats. However, total PM2.5 or the soluble or insoluble fractions instilled in rats with OVA-induced airway inflammation did not enhance the inflammation or the airway epithelial remodeling that was evident in some of the BN rats exposed to CAPs by inhalation. Therefore, the results from this instillation component did not suggest what fractions of the CAPs may have been responsible for enhancing OVA-induced airway mucosubstances and pulmonary inflammation observed in the inhalation exposure component. In summary, inhaled CAPs-related pulmonary alterations in the affected OVA-challenged rats appeared to be related to the chemical composition, rather than the mass concentration, to which the animals were exposed. Results of the trace element analysis in the lungs of CAPs-exposed BN rats exposed in September suggested that air particles derived from identified local combustion sources were preferentially retained in allergic airways. These results demonstrate that short-term exposures to CAPs from this southwestern Detroit community caused variable responses in laboratory rats and suggest that adverse biological responses to ambient PM2.5 may be associated more closely with local sources of particles and weather patterns than with particle mass.

Effects of respiratory impedance on the performance of bi-level pressure ventilators

BACKGROUND

Noninvasive positive pressure ventilation (NPPV) has been studied in several settings and shown to reduce patient morbidity associated with endotracheal intubation. Intolerance to NPPV has been estimated at 25-33%, a substantial proportion of attempts to ventilate noninvasively. Bi-level pressure ventilators (BPVs) have been designed for NPPV, yet their response to changes in respiratory impedance has not been extensively evaluated. To determine responses of BPVs to changing impedance conditions, we tested 4 BPVs to evaluate the potential for intolerance. We also developed a mathematical model for BPV performance that accounted for impedance conditions, leak, pressure settings, and inspiratory flow cutoff level.

METHODS

Four BPV models at the same settings were challenged to ventilate a triggered test lung under a range of impedance conditions while measuring tidal volume (VT) and intrinsic positive end-expiratory pressure (auto-PEEP). The model was used to predict VT and auto-PEEP under normal, restrictive, and obstructive conditions.

RESULTS

The BPV models tested delivered VT in a similar manner. VT decreased with decreased compliance and increased resistance. Auto-PEEP developed with increased resistance and compliance. The model predicted a VT delivery dependent on inspiratory flow cutoff level. For the obstructive condition, the model predicts an optimal VT delivery within a specific inspiratory flow cutoff range that becomes narrower with increasing resistance.

CONCLUSIONS

VT delivery and auto-PEEP generated by BPVs are highly dependent on the prevailing impedance condition. Though there are differences between BPV models, generally, performance was similar between the models tested. This report suggests that knowledge of both respiratory system impedance and the performance of the BPV in use are required to attend to inadequate VT delivery and auto-PEEP generation. Furthermore, the model predicts a relatively narrow range for inspiratory flow cutoff that provides adequate ventilatory support without causing hyperinflation in patients with obstructive conditions.

Toxin production by Clostridium botulinum in pasteurized milk treated with carbon dioxide

The addition of carbon dioxide to milk at levels of <20 mM inhibits the growth of selected spoilage organisms and extends refrigerated shelf life. Our objective was to determine if the addition of CO2 influenced the risk of botulism from milk. Carbon dioxide was added to pasteurized 2% fat milk at approximately 0, 9.1, or 18.2 mM using a commercial gas-injection system. The milk was inoculated with a 10-strain mixture of proteolytic and nonproteolytic Clostridium botulinum spore strains to yield 10(1) to 10(2) spores/ml. Milk was stored at 6.1 or 21 degrees C for 60 or 6 days, respectively, in sealed glass jars or high-density polyethylene plastic bottles. Milk stored at 21 degrees C curdled and exhibited a yogurt-like odor at 2 days and was putrid at 4 days. Botulinal toxin was detected in 9.1 mM CO2 milk at 4 days and in all treatments after 6 days of storage at 21 degrees C. All toxic samples were grossly spoiled based on sensory evaluation at the time toxin was detected. Although botulinal toxin appeared earlier in milk treated with 9.1 mM CO2 compared to both the 18.2 mM and untreated milk, gross spoilage would act as a deterrent to consumption of toxic milk. No botulinal toxin was detected in any treatment stored at 6.1 degrees C for 60 days. At 6.1 degrees C, the standard plate counts (SPCs) were generally lower in the CO2-treated samples than in controls, with 18.2 mM CO2 milk having the lowest SPC. These data indicate that the low-level addition of CO2 retards spoilage of pasteurized milk at refrigeration temperatures and does not increase the risk of botulism from treated milk stored at refrigeration or abuse temperatures.

On the mechanism of the positive feedback action of estradiol on luteinizing hormone secretion in the rhesus monkey

In women and rhesus monkeys, both the negative and positive feedback actions of estradiol (E2) on gonadotropin secretion (inhibition followed by a surge) can be exerted directly at the level of the pituitary gland. We have tested the hypothesis that the positive feedback action of E2 represents but an "escape" from its negative feedback inhibition of gonadotropin secretion consequent to a desensitization of the gonadotropes occasioned by sustained exposure to elevated concentrations of the steroid. We have attempted to replicate such a desensitization by blocking the negative feedback action of E2 by the administration of a potent estrogen receptor antagonist devoid of any agonistic properties (ZM 182,780) to rhesus monkeys in the midfollicular phase of the menstrual cycle (n = 14). The estrogen antagonist, administered at a dose that in separate experiments completely blocked both the negative and the positive feedback effect of exogenous E2 on pituitary LH secretion, failed to produce a surge-like increase in serum LH concentrations. The present results do not support the hypothesis that the LH surge is the consequence of the removal of the negative feedback action of E2. Evidence is presented that ZM 182,780, in contrast to its inhibition of E2-induced LH surges, cannot block the inhibition of hypothalamic GnRH pulse generator activity by E2.

On the mechanism of lactational anovulation in the rhesus monkey

The relative roles of infant suckling and of maternal prolactin (PRL) secretion in lactational anovulation were studied in ovary-intact and ovariectomized rhesus monkeys nursing young that had been removed from their natural mothers. Hypothalamic gonadotropin-releasing hormone (GnRH) pulse generator activity was monitored electrophysiologically in freely behaving animals by radiotelemetry. Serum luteinizing hormone, PRL, estradiol, and progesterone were also measured. Suckling inhibited GnRH pulse generator activity and ovarian cyclicity in all ovary-intact females but had no such effect on the pulse generator in long-term ovariectomized animals. When PRL secretion was suppressed by daily bromocriptine administration, GnRH pulse generator activity remained significantly inhibited and ovulation was prevented in four monkeys (6 trials), whereas in two females (6 trials) a rapid increase in pulse generator frequency and the resumption of ovarian cyclicity were observed although suckling activity was maintained. One monkey displayed both response types. Although these results indicate that suckling per se is able to restrain GnRH pulse generator activity in the absence of PRL, they also suggest that the relative importance of these determinants is variable depending on factors that remain to be determined. The present study also confirms the permissive role of the ovary in the lactational suppression of GnRH pulse generator activity.

Concurrent increases in the storage and release of mucin-like molecules by rat airway epithelial cells in response to bacterial endotoxin

Mucus hypersecretion is a prominent response of the airways to bacterial infections. Recent findings showed that bacterial endotoxin, a lipopolysaccharide complex released from the bacterial cell wall, was able to induce at least one component of the hypersecretory response, i.e., an increase in the amount of stored epithelial mucosubstances (1, 2). The goal of the present study was to determine whether endotoxin also was capable of increasing mucosubstance release from cells. Based on evidence that human mucin antibodies A10G5 and B6E8 cross-reacted with rat mucin-like molecules, we used the antibodies in enzyme-linked immunosorbent assays (ELISA) to compare mucin concentrations in bronchoalveolar lavage (BAL) fluid from endotoxin-treated and control rats. Results showed that endotoxin treatment increased the amount of released mucin over that in controls 1.5-fold at 96 h and 2.5-fold at 168 h after instillation. Thus, these studies have defined the previously detected mucosubstances as mucin-like molecules and showed that endotoxin increases their release from, as well as their storage in, rat airway epithelium. Concurrent increases in storage and release suggest that endotoxin also stimulates mucin synthesis and/or stability.

Ambient light modifies gonadotropin-releasing hormone pulse generator frequency in the rhesus monkey

In the course of previous studies using continuous monitoring of the electrophysiological correlates of GnRH pulse generator activity, characterized by episodic increases in hypothalamic multiunit electrical activity (MUA volley), it was noticed that the nocturnal slowing of pulse generator frequency was an acute phenomenon observable in the first MUA volleys after the lights were turned off, as was the increase in frequency when the lights were turned on in the morning. This suggested that the reduction in pulse generator frequency at night may not be the consequence of an intrinsic diurnal rhythm, but an effect of light per se. Indeed, as reported herein, such an effect was observed when the lights were turned on or off at times other than the normal illumination period (normal light schedule, lights on from 0700-1900 h). That this was not simply a response to arousal was shown by awakening the animals with loud recorded noises in total darkness at the same unaccustomed times without a resulting change in frequency. This suggests that the effect of light is specific, perhaps mediated by the retino-hypothalamic tract. This direct action of light, however, is superimposed upon a diurnal rhythm, as shown by a reduction in pulse generator frequency during the subjective night when the monkeys were kept in constant light or constant darkness.

Tuberculosis and poverty

OBJECTIVE

To examine whether the historical link between tuberculosis and poverty still exists.

DESIGN

Retrospective study examining the notifications of all forms of tuberculosis by council ward over a six year period and correlating this with four indices of poverty; council housing, free school meals, the Townsend overall deprivation index, and the Jarman index.

SETTING

The 33 electoral wards of the city of Liverpool.

SUBJECTS

344 residents of Liverpool with tuberculosis.

RESULTS

The rate of tuberculosis was correlated with all measures of poverty, the strongest correlation being with the Jarman index (r = 0.73, p < 0.0001). This link was independent of the high rates of tuberculosis seen in ethnic minorities.

CONCLUSION

Tuberculosis remains strongly associated with poverty.

Ovarian control of gonadotropin hormone-releasing hormone pulse generator activity in the rhesus monkey: duration of the associated hypothalamic signal

The activity of the GnRH pulse generator in the rhesus monkey is associated with abrupt increases in multiunit electrical activity (MUA) volleys recorded from the mediobasal hypothalamus that precede each pulse of LH in the peripheral circulation. In long-term ovariectomized animals the duration of these MUA volleys is 10-25 min and consists of a brief initial 'overshoot' followed by a plateau phase that ends in a rapid decline to baseline activity. In intact monkeys, however, the MUA volley lasts only 1-3 min, a duration equivalent to the overshoot in ovariectomized animals. In addition, the maximal frequency of neuronal activity during each MUA volley is reduced in normal animals when compared to castrates. As shown in earlier studies, estradiol given to ovariectomized monkeys causes a reduction in the duration of MUA volleys to that characteristic of intact animals within 3-5 h. In contrast to this acute effect of estradiol, the increase in MUA volley duration following ovariectomy is a gradual phenomenon, 4-6 weeks being required to achieve the MUA volley duration observed in long-term ovariectomized monkeys. A similar slow time course was observed for the increase in maximal neuronal frequency during each MUA volley. This protracted effect of ovariectomy on MUA volley duration and firing rate may be the consequence of hypothalamic remodelling but this consideration must be tempered by the observation that estradiol reverses these phenomena within hours.

Effects of naloxone on estrogen-induced changes in hypothalamic gonadotropin-releasing hormone pulse generator activity in the rhesus monkey

In the ovariectomized rhesus monkey, estradiol (E2) markedly reduces the frequency of the GnRH pulse generator as monitored by LH pulse frequency and the concurrent changes in hypothalamic electrical activity, an action mimicked by morphine. In addition, the duration of the increments in multiunit electrical activity (MUA volleys) that precede each LH pulse is decreased by estrogen administration, an action also shared by morphine. The role of endogenous opioids in these actions of E2 was investigated in 8 ovariectomized animals restrained in primate chairs. They were fitted with indwelling cardiac catheters and with bilateral arrays of recording electrodes chronically implanted in the mediobasal hypothalamus. Physiological serum E2 levels achieved by subcutaneous implantation of E2-containing Silastic capsules increased MUA volley interval from 50.8 +/- (SEM) 1.6 min in the control period to 81.1 +/- 6.2 min following E2. Mean MUA volley duration decreased from 21.9 +/- 1.0 to 13.0 +/- 0.7 min. The placement of empty Silastic capsules had no effect on MUA volley duration or interval. Naloxone administration (2.5 mg bolus followed by a 1 mg/h infusion lasting 4-8 h) completely (n = 4) or partially (n = 2) blocked the effects of E2 on MUA volley interval in 6 of the 8 monkeys, and was without effect in the remainder. In contrast, however, naloxone had little or no effect on the action of E2 on MUA volley duration, (13.0 +/- 0.7 vs. 14.0 +/- 0.9 min). These findings suggest that the inhibitory action of E2 on GnRH pulse generator frequency, like that of all other gonadal steroids studied to date, may be mediated by endogenous opioids.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypoglycemic 'stress' and gonadotropin-releasing hormone pulse generator activity in the rhesus monkey: role of the ovary

Observations of long standing have suggested that the 'stress' of chair restraint inhibits the GnRH pulse generator in normal female monkeys while this phenomenon is rarely observed in ovariectomized animals. The role of the ovary in the response of the GnRH pulse generator to the stress of insulin hypoglycemia was investigated in both intact and ovariectomized rhesus monkeys. Following an overnight fast the animals, previously habituated to restraint, were placed in primate chairs and GnRH pulse generator activity monitored electrophysiologically. Insulin-induced reductions in mean blood glucose concentrations of 10-40% of control values interrupted pulse generator activity in intact monkeys but were without effect in ovariectomized animals. With larger reductions in blood glucose, pulse generator activity was interrupted in both groups but the inhibition was twice as long in intact than in ovariectomized animals. The reduced responsiveness of ovariectomized animals to insulin hypoglycemia was significantly reversed by estradiol replacement. Naloxone administration did not prevent the hypoglycemia-induced inhibition of pulse generator activity in either intact or ovariectomized rhesus monkeys. It is concluded that hypoglycemic 'stress' inhibits the GnRH pulse generator by a nonopioidergic mechanism and that ovarian products, most probably estradiol, exacerbate this effect.

Radiotelemetric monitoring of hypothalamic gonadotropin-releasing hormone pulse generator activity throughout the menstrual cycle of the rhesus monkey

Continuous monitoring of the electrophysiological manifestations of GnRH pulse generator activity was achieved by radiotelemetry throughout the menstrual cycles of unrestrained rhesus monkeys. The characteristic increases in hypothalamic multiunit activity (MUA volleys) associated with each LH pulse measured in the peripheral circulation were of lower frequency during the luteal phase than in the follicular phase of the cycle. Multiunit activity volley frequency increased as functional luteolysis progressed and achieved maxima of approximately one volley per hour within the first few days of the follicular phase. Unexpectedly, a dramatic decline in pulse generator frequency was observed coincidentally with the initiation of the preovulatory LH surge. Evidence is presented to support the conclusion that this deceleration of pulse generator activity is the consequence of the preovulatory rise in plasma estrogen concentration. As reported in women, a significant reduction in GnRH pulse generator frequency was observed at night during the follicular phase, but not during the luteal phase, of the menstrual cycle.

Duration of phasic electrical activity of the hypothalamic gonadotropin-releasing hormone pulse generator and dynamics of luteinizing hormone pulses in the rhesus monkey

The secretion of luteinizing hormone (LH) by the pituitary gland is a pulsatile phenomenon. In the rhesus monkey, each pulse of LH in the peripheral circulation is associated with a characteristic increase in multiunit electrical activity (MUA) recorded from the medial basal hypothalamus. These "volleys" of electrical activity initiate the release of gonadotropin-releasing hormone (GnRH) into the pituitary portal circulation from the terminals of neurosecretory cells. Their duration varies from 1-3 min in normal, adult intact females to 10-25 min in long-term ovariectomized monkeys. A variety of pharmacological interventions also modify volley duration. The purpose of this investigation was to determine the physiological significance of alterations in volley duration. The dynamics of LH pulses in ovariectomized animals were observed in a number of experimental circumstances in which MUA volley duration was reduced from a maximum of 23 min to a minimum of 4 min without significantly altering their frequency. The magnitude of each LH pulse was assessed by calculating the area under the curve delineated by the time course of LH above baseline. In eight experiments, a linear regression of these values on volley duration failed to reveal a significant correlation between MUA volley duration and the magnitude of LH pulses. These results suggest that all of the GnRH secreted per pulse is released at the onset of each MUA volley, the remainder of the increase in electrical activity having no further action on GnRH secretion, although effects on other systems cannot be excluded.

Duration and frequency of multiunit electrical activity associated with the hypothalamic gonadotropin releasing hormone pulse generator in the rhesus monkey: differential effects of morphine

The effects of morphine on the frequency and duration of the characteristic bursts or 'volleys' of multiunit electrical activity (MUA) associated with pulsatile pituitary luteinizing hormone (LH) secretion were studied in unanesthetized ovariectomized rhesus monkeys bearing bilateral arrays of electrodes implanted in the mediobasal hypothalamus. Morphine administration resulted in a dose-dependent decrease in MUA volley duration and frequency. When morphine was infused at 10 micrograms/kg/h, the inhibiting effect on volley duration was observed without a change in volley frequency. It is concluded that the frequency and duration of hypothalamic MUA volleys associated with pulsatile LH secretion may be independently regulated.

Corticotropin-releasing factor and gonadotropin-releasing hormone pulse generator activity in the rhesus monkey. Electrophysiological studies

The effect of corticotropin-releasing factor (CRF) on the hypothalamic gonadotropin-releasing hormone (GnRH) pulse generator, the central neuronal system governing pulsatile pituitary luteinizing hormone (LH) secretion, was studied electro-physiologically in 6 ovariectomized rhesus monkeys bearing bilateral arrays of recording electrodes implanted in the mediobasal hypothalamus. 'Volleys' of increased multiunit activity (MUA) were recorded for 6-10 h in animals placed in primate chairs. The circulating concentrations of LH and cortisol were determined by radioimmunoassay in blood samples taken every 10 min for 3-4 h prior to the administration of CRF (200 micrograms, i.v.) and for 3-6 h thereafter. CRF resulted in a significant decrease in the frequency of pulse generator activity in 4 of 6 animals, a significant decrease in the duration of MUA volleys and a rise in circulating cortisol levels in all 6 monkeys. Treatment with metyrapone (30 mg/kg, i.m.), an inhibitor of adrenal steroidogenesis that prevented the CRF-induced rise in serum cortisol levels, did not reverse the inhibitory effects of CRF on the frequency or duration of MUA volleys. The opiate antagonist naloxone (0.8 mg/kg, i.v., 10 min prior to CRF followed by 0.8 mg/kg/h infusion) blocked the effects of CRF on MUA volley frequency in 2 of 3 animals, but failed to block the effect of CRF on MUA volley duration, suggesting that endogenous opioids may mediate the action of CRF on pulse generator frequency but not on duration.

Unexpected responses of the hypothalamic gonadotropin-releasing hormone "pulse generator" to physiological estradiol inputs in the absence of the ovary

In the rhesus monkey (Macaca mulatta), the frequency of pulsatile gonadotropic hormone release is relatively constant in the face of widely varying levels of estradiol (E2) in the peripheral circulation--e.g., in the course of the follicular phase of the menstrual cycle and after ovariectomy. This suggests that modulation of the hypothalamic gonadotropin-releasing hormone (GnRH) "pulse generator" by this steroid is not of major physiological importance. Herein is described the unexpected inhibition or total blockade of the electrical activity of this pulse generator in ovariectomized monkeys by physiological levels of exogenous E2. This inhibition began 2-4.5 hr after the initiation of E2 infusion and was noted 1 to 3 weeks after subcutaneous implantation of E2-containing capsules. Pulse generator activity was also arrested during the initiation and subsequent development of estrogen-induced surges of luteinizing hormone. We propose that this inhibition of hypothalamic GnRH pulse generator activity by E2 in ovariectomized monkeys reflects the absence of an ovarian factor that normally protects this neuronal system from the inhibitory action of estrogen during the menstrual cycle.

Gas Chromatographic-Thermal Energy Analysis Method for iV-Nitrosodibutylamine in Latex Infant Pacifiers: Collaborative Study

Each of 5 collaborating laboratories determined volatile N-nitrosamines in 3 blind quadruplicate sets of latex rubber infant pacifier samples, using a gas chromatographic-thermal energy analysis (GCTEA) method. Volatile N-nitrosamines are extracted from cut-up pacifier nipples with CH2C12. The extract is concentrated and subjected to high temperature purge and trap, and the nitrosamines are eluted from the trap and determined by GC-TEA. N-Nitrosodibutylamine (NDBA) was the only nitrosamine found in sufficient concentration to allow analysis. NDBA concentrations of the 3 sets of samples were 82.6,21.0, and 7.12 ng/g rubber. The repeatability relative standard deviations ranged from 7.46 to 24.0% and the reproducibility relative standard deviations from 7.46 to 29.2%. The minimum detectable level of NDBA by this method is 3.6 ng/g rubber. The method has been adopted official first action.

Changes in sex hormone-binding globulin binding capacity and percent free estradiol during development in the female rhesus monkey (Macaca mulatta): relation to the metabolic clearance rate of estradiol

Circulating sex hormone-binding globulin (SHBG) binding capacity and percent free estradiol (% free E2) were measured in separate groups of female rhesus monkeys from 2 months of age through adulthood (greater than 4.5 yr old). The SHBG concentration alone was also measured in 11 adult and 6 sexually immature animals on the same day as the blood MCR of E2. Serum SHBG levels were the highest (range, 12-25 micrograms T/dl) and the % free E2 the lowest (0.88%) in animals 6 months old or less. After the age, serum SHBG binding capacity declined generally at an average rate of 0.11 SHBG U (microgram T/dl)/month toward a nadir in adulthood. There was no difference in the SHBG levels in the follicular or luteal phase of the menstrual cycle. The relative blood MCR E2 and circulating SHBG binding capacity were significantly greater (P less than 0.001) in the sexually immature animals [MCR E2, 48.4 +/- 5.2 (SEM) liters/day . kg body wt; SHBG, 9.8 +/- 1.0 microgram T/dl, n = 6] than in adult animals (MCR E2, 27.7 +/- 1.7 liters/day kg body wt; SHBG, 4.6 +/- 0.3 microgram T/dl, n = 11). There was no relation between the MCR E2 and circulating SHBG levels within each group of adult or immature animals. The mean % free E2 doubled (to 1.6%) between 1 and 54 months of age; there was no relation between total circulating E2 and % free E2. Although a high SHBG binding capacity and a low % free E2 in the circulation of the immature animal does not inhibit the metabolic clearance of E2; it remains possible that these factors (and others) may hinder the access of E2 to reproductive target tissues and thereby contribute to the slow acquisition of reproductive competence in this species.

The metabolic clearance rate and the production rate of estradiol in sexually immature and adult female rhesus monkeys

The blood MCR of estradiol (MCRE2) was measured in 34 experiments with 10 adult (4.7-8.2 kg) and 13 prepubertal (1.8-3.0 kg; 13-23 months old) female rhesus monkeys using the constant infusion technique. Twenty-six of the studies were performed using an adult and an immature animal simultaneously. Twenty-four of the studies were performed in pentobarbital-anesthetized animals, while the remainder used conscious animals restrained in primate chairs. The blood MCRE2 in the adult female was 167.5 +/- 9.5 liters/day (mean +/- SE; n = 14) or 27.5 +/- 1.4 liters/day x kg BW, and was not altered by anesthesia, stage of the menstrual cycle, amenorrhea of more than 60 days duration, or the site of origin of the blood used to calculate the MCR (radial artery, femoral artery, femoral vein, or saphenous vein). While the absolute MCRE2 in the immature animal (either anesthetized or conscious) was less than that in the adult, when corrected for body weight, the relative MCRE2 (in liters per day/kg BW) of the conscious immature animal was double that seen in the adult [48.4 +/- 5.2 (n = 6) vs. 27.5 +/- 1.4 (n = 1.4)]. Anesthesia caused a profound depression of the MCRE2 in the immature animal, which could be prevented if the body temperature of the animal was maintained at 37 C during the prolonged period of anesthesia. The production rate of estradiol (PRE2) was calculated as the product of the serum estradiol concentration (in micrograms per liter; measured by RIA techniques) and the plasma MCRE2 (blood MCRE2 x 1 - hematocrit). In the adult animals, the PRE2 ranged from 1.9 - 35.5 micrograms/day, and was lowest in the amenorrheic animals and highest during the late follicular phase. The PRE2 in the immature animals ranged from unmeasurable to 1.7 micrograms/day, averaging 0.7 +/- 0.2 micrograms/day (n = 12) in those animals where it could be measured. These data support the hypothesis that the low circulating estradiol levels in the immature animal are the consequence of a low PRE2 coupled with a high MCRE2.

Relation between levels of circulating ovarian steroids and pituitary gonadotropin content during the menstrual cycle of the rhesus monkey

Anterior pituitary glands were removed from 27 intact cycling rhesus monkeys sacrificed in the early (Day 2), mid (Days 6--9) and late (Days 11--12) follicular phase, and in the early and late luteal phase (3--5 and 10--15 days after the midcycle luteinizing hormone (LH) surge). Assignment of cycle stage was confirmed by the pattern of circulating steroid and gonadotropin levels seen in the blood samples taken daily throughout the cycle. The anterior pituitary glands were weighed, stored at -30 degrees C and assayed for LH and follicle-stimulating hormone (FSH) content by specific radioimmunoassays. Serum estradiol levels and pituitary LH and FSH contents rose simultaneously during the follicular phase. After the preovulatory gonadotropin surge, pituitary LH content was low and invariant. Pituitary FSH content reached a nadir in the early luteal phase and tended to rise in the late luteal phase. Multiple correlation analyses revealed that there is a positive correlation between rising levels of estradiol in the circulation and pituitary LH (p = 0.003) and FSH (p = 0.017) content, and that there is a significant negative correlation between circulating progesterone levels and pituitary FSH content (p = 0.002). Pituitary LH content is less strongly related to circulating progesterone levels. There was no significant difference in the wet weights of the anterior pituitary glands during the five phases of the menstrual cycle studied.

Monkey pituitary oestrogen receptors and the biphasic action of oestradiol on gonadotropin secretion

Evidence has been advanced in favour of the hypothesis that, in the rhesus monkey, the negative feedback as well as the stimulatory or so-called "positive feedback" action of oestrogen on gonadotropin secretion is at the level of the pituitary gland. The cellular basis for this biphasic action of oestrogen on the gonadotroph is not understood. In oestrogen target tissues the elicitation of physiological responses is generally associated with the binding of oestrogen to cytoplasmic receptor proteins which are subsequently translocated to the nucleus. Such receptors have been characterized in the anterior pituitary of the rat. In the ovariectomized rhesus monkey refused with 3H-oestradiol, autoradiography and parallel cell fractionation have demonstrated the accumulation of 3H-oestradiol by the nuclei of a significant number of pituitary cells. We describe here some of the properties of these putative oestrogen receptors in the anterior pituitary of the monkey and observe that their distribution between cytoplasmic and nuclear compartments is constant in response to sustained elevations in serum oestrogen concentration which produce a biphasic pattern of circulating gonadotropins.

Periparturitional serum concentrations of prolactin, the gonadotropins, and the gonadal hormones in the rhesus monkey

The time courses of serum concentrations of prolactin, estradiol, estrone, progesterone, LH, and FSH were studied in seven pregnant rhesus monkeys from 1 month prior to delivery until 1 month after parturition. All animals nursed their young. Circulating levels of estradiol and estrone increased during the last few days of pregnancy, reaching peak values of 700 pg/ml and 350 pg/ml, respectively, on the day prior to delivery, fell precipitously to about 25 pg/ml within 1 day after parturition, and remained at this level for at least 30 days. Serum prolactin concentrations also increased during the week preceding parturition, rose abruptly at delivery, and then declined gradually. Serum progesterone levels ranged between 2 and 3 ng/ml during the last month of pregnancy, rose slightly a few days prior to parturition, decreased sharply at delivery to 50% of prepartum levels and declined gradually thereafter. Serum LH and FSH levels were not detectable during the entire sampling period. The administration of estradiol benzoate to two pregnant monkeys at midgestation, in a manner which replicated the normal prepartum increase in serum estradiol concentrations, failed to elicit an elevation in circulating prolactin levels or to induce premature delivery of the fetus.

Functional luteolysis in the rhesus monkey: ovarian estrogen and progesterone during the luteal phase of the menstrual cycle

In a continuing effort to elucidate the processes underlying in primates, the concentrations of estradiol, estrone and progesterone were measured in ovarian tissues and in ovarian vein plasma through the luteal phase of the menstrual cycle of the rhesus monkey. The concentration of progesterone in corpora lutea collected 4-6 days after the preovulatory LH peak (early luteal phase) was more than twice that found in those collected 8-13 days after the LH surge (late luteal phase) while estradiol and estrone concentrations in the latter had increased 4-fold. These changes in luteal steroid concentrations were paralleled by a striking increase in the concentration of estrone in the ipsilateral ovarian vein. Estrone predominated in the venous effluent of the ovary beaing the corpus luteum while estradiol concentrations were similar in both ovarian veins suggesting that estrone is the principal estrogen released by the corpus luteum. The results of this study are consonant with the hypothesis that estrogen produced by the corpus luteum is the physiologic luteolsin in the rhesus monkey.

Surgical disconnection of the medial basal hypothalamus and pituitary function in the rhesus monkey. II. GH and cortisol secretion

Eighteen female rhesus monkeys subjected to complete or anterior disconnection of the medial basal hypothalamus (MBH) were studied to assess the effects of these deafferentation procedures on GH and cortisol secretion. Basal serum levels of GH were not disturbed or were slightly elevated following complete or anterior MBH disconnection. GH secretion in response to vasopressin administration or insulin hypoglycemia, however, was abolished by complete isolation of the MBH. In contrast, the elevations in serum cortisol concentrations observed in response to these noxious stimuli were not noticeably affected. The normal diurnal rhythm in cortisol secretion remained fully evident following anterior deafferentation, but was severely attenuated or abolished when all neuronal inputs to the MBH were transected. Such observations suggest that the central components of the neuroendocrine systems which regulate basal GH secretion and which subserve stress-induced elevations in cortisol secretion are resident within the MBH-hypophysial unit. In addition, these data indicate that the mechanisms underlying the diurnal rhythm in cortisol secretion, as well as those mediating the discharges of GH in response to vasopressin administration and insulin hypoglycemia, are dependent on the integrity of neuronal connections between the MBH and other hypothalamic and/or extrahypothalamic areas.