Efficacy of the topical skin protectant in advanced development.

A topical skin protectant (TSP) (ICD 2289) is being developed to protect service members from exposure to chemical warfare agents (CWA). The TSP is designed for use on the skin at the overgarment closures and other vulnerable areas to enhance protection. The TSP, which is in phase II clinical studies, is a cream containing two chemically inert substances: perfluoroalkylpolyether and polytetrafluoroethylene. Animal data showed that the TSP was effective against percutaneous penetration of a blister agent, sulfur mustard (HD), by reducing the size of skin lesions and against T-2 mycotoxin by preventing the development of erythema and edema. The insect repellent N,N-diethyl-m-toluamide (DEET) reduced the TSP protection against HD regardless of the order of application on rabbit skin prior to dosing of HD. The protection was sustained when DEET was removed with a dry gauze prior to TSP application. The TSP was also effective against percutaneous exposure of nerve agents-thickened (with 5% methyl methacrylamide) soman (TGD) and VX (O-ethyl-S-[2-(diisopropylamino)ethyl]methylphosphonothioate )-by reducing the mortality rate and protecting the red blood cell acetylcholinesterase activity. The TSP was effective against VX when DEET was applied prior to TSP application. Because human efficacy studies using CWA cannot be conducted, the efficacy will be demonstrated by the level of protection against poison ivy (urushiol) contact dermatitis in humans.

Protection by the heavy metal chelator N,N,N',N'-tetrakis (2-pyridylmethyl)ethylenediamine (TPEN) against the lethal action of botulinum neurotoxin A and B.

The ability of N,N,N',N'-tetrakis (2-pyridylmethyl)-ethyenediamine (TPEN) to protect against botulinum neurotoxin (BoNT) A and B was examined in vivo in mice. To determine the protective efficacy of TPEN, mice were injected i.p. with TPEN as a single bolus or as multiple injections 30 min before and 0, 2, 4 and 6 hr following i.v. challenges with BoNT-A or -B. TPEN treatment did not alter the 24 hr lethality of BoNT but did produce a significant delay in the time to death. For a moderate dose of serotype A (20 LD50), five divided doses of TPEN prolonged the time to death from 7.8 +/- 0.4 hr to 9.9 +/- 0.5 hr. For serotype B, examined under comparable conditions, the prolongation of the time to death was from 6.1 +/- 0.2 hr to 9.4 +/- 0.6 hr. The range of TPEN doses that could be examined in vivo was limited by its acute toxicity. Although low doses of TPEN (< or = 10 mg/kg) were well tolerated, higher doses (> or = 30 mg/kg) led to ataxia, loss of coordination, convulsions and death in 20.3 min or less. In clonal NG108-15 cells, TPEN was found to produce cytotoxicity as revealed by increases in the secretion of the marker enzyme lactate dehydrogenase (LDH), and enhanced reactivity with the vital dye trypan blue. From LDH concentration-response data determined 24 hr after addition of TPEN, the threshold concentration for observing cytotoxicity was 10 microM and the IC50 was 19.8 microM. At the highest TPEN concentration tested (100 microM), cytotoxicity was detected 8 hr after TPEN addition and increased in severity over a 3 day period. The cytotoxicity in NG108-15 cells appears to be distinct from the rapid-onset toxicity observed in whole animals. These results suggest that TPEN may be of potential benefit in delaying the lethal actions of BoNT-A and -B, but its use is limited by its initial and delayed toxicity. Since the therapeutic and toxic actions of TPEN are both related to zinc chelation, the use of TPEN would need to be restricted to low doses as part of a combination therapy.

A high-performance liquid chromatographic method for determining [3H]T-2 and its metabolites in biological fluids of the cynomolgus monkey.

High-performance liquid chromatography (HPLC) was used to separate, identify, and quantitate the trichothecin mycotoxin, T-2 (4 beta,15-diacetoxy-3 aopha-hydroxy-8 alpha [3-methyl-butyryloxy]-12,13-epoxy delta 9-trichothecin), and its metabolites in plasma and urine samples from cynomolgus monkeys treated with the toxin. A 15-min gradient elution system was developed to separate and measure radiolabeled T-2 mycotoxin and its metabolites. The HPLC technique for separating T-2 and its metabolites was compared with thin-layer chromatography. Samples from the in vitro metabolism of T-2 by plasma and urine were included as controls and as a measure of the toxin's stability in biological samples. Within 5 min, 22% of the plasma radiolabeled T-2 toxin was detected as metabolites after an intravenous administration of [3H] T-2 toxin to cynomolgus monkeys. By 24 h post-exposure, there was no parent T-2 toxin detected in plasma or urine. T-2 tetraol was the major metabolite detected in the plasma and urine of monkeys. Other metabolites observed in urine up to 5 days after exposure were 3'OH-T-2 and 3'OH-HT-2. We conclude that T-2 toxin was rapidly metabolized to more polar metabolites, which were eliminated in urine.

[3H]-saxitoxinol metabolism and elimination in the rat.

Tritiated saxitoxinol was used to obtain preliminary information on saxitoxin metabolism in the rat. Sublethal doses of tritiated saxitoxinol (18.9-microCi/kg; 3.8 micrograms/kg) were injected i.v. into each of six rats. Urine and fecal samples were collected up to 144 hr post-injection. Within 4 hr, 60% of injected radioactivity was excreted in urine. No radioactivity was found in feces. High performance liquid chromatography analyses of urine showed that saxitoxinol was not metabolized by the rats.

In vivo effects of T-2 mycotoxin on synthesis of proteins and DNA in rat tissues.

Rats were given an ip injection of T-2 mycotoxin (T-2), the T-2 metabolite, T-2 tetraol (tetraol), or cycloheximide. Serum, liver, heart, kidney, spleen, muscle, and intestine were collected at 3, 6, and 9 hr postinjection after a 2-hr pulse at each time with [14C]leucine and [3H]thymidine. Protein and DNA synthesis levels in rats were determined by dual-label counting of the acid-precipitable fraction of tissue homogenates. Rats given a lethal dose of T-2, tetraol, or cycloheximide died between 14 and 20 hr. Maximum inhibition of protein synthesis at the earliest time period was observed in additional rats given the same lethal dose of the three treatments and continued for the duration of the study (9 hr). With sublethal doses of T-2 or tetraol, the same early decrease in protein synthesis was observed but, in most of the tissues, recovery was seen with time. In the T-2-treated rats. DNA synthesis in the six tissues studied was also suppressed, although to a lesser degree. With sublethal doses, complete recovery of DNA synthesis took place in four of the six tissues by 9 hr after toxin exposure. The appearance of newly translated serum proteins did not occur in the animals treated with T-2 mycotoxin or cycloheximide, as evidenced by total and PCA-soluble serum levels of labeled leucine. An increase in tissue-pool levels of free leucine and thymidine in response to T-2 mycotoxin was also noted. T-2 mycotoxin, its metabolite, T-2 tetraol, and cycloheximide cause a rapid inhibition of protein and DNA synthesis in all tissue types studied. These results are compared with the responses seen in in vitro studies.

Acute inhalation toxicity of T-2 mycotoxin in the rat and guinea pig.

In this study, concentration-response parameters were determined for rats and guinea pigs systematically exposed to an aerosol of T-2 toxin. The LC50 for a 10-min exposure to T-2 toxin aerosol was 0.02 mg T-2/liter air for rats and 0.21 mg T-2/liter air for guinea pigs. Data from total T-2 deposition in rats and guinea pigs exposed to their respective LC50 aerosol concentration gave an LD50 of 0.05 mg T-2/kg body weight for the rat and 0.4 mg T-2/kg body weight for the guinea pig. These data show that inhaled T-2 toxin is approximately 20 times more toxic to the rat (0.05 mg T-2/kg body wt inhaled vs 1.0 mg T-2/kg body wt ip) and at least twice as toxic to the guinea pig (0.4 mg T-2/kg body wt inhaled vs 1-2 mg T-2/kg body wt ip) than ip administered T-2 toxin. Histopathologic examination of major organs in both the rat and guinea pig after respiratory exposure to T-2 toxin indicated that lesions were similar to those described after systemic administration of the toxin. Gross and microscopic alterations of respiratory tract tissue after T-2 aerosol exposure were minimal and could not account for the increase in toxicity.

Cutaneous absorption and decontamination of [3H]T-2 toxin in the rat model.

Cutaneous absorption and decontamination of [3H]T-2 mycotoxin using various treatment modalities incorporating water, detergent, sprays, and scrubbing of application sites were examined in the rat model at 5, 30, 60, and 1440 min (24 h) postexposure. Rats were killed immediately after treatment and radiolabeled T-2 remaining in full-thickness skin samples were determined. Absorption and decontamination were followed over time, and decontaminating treatment modalities were evaluated for efficacy. Less than 1% of the applied dose was absorbed in 5 min, and 50% was absorbed in 24 h. At 5 min, 99.5 +/- 0.05% of nonabsorbed (residual) [3H]T-2 was removed, and 58 +/- 5.2% of residual toxin was removed at 24 h with a 2.5% detergent/water spray. When treatment modalities were evaluated at 60 min, a 2.5% detergent/water scrub followed by a detergent/water spray produced optimal decontamination by removing 81 +/- 2.2% of residual toxin. All treatment modalities using detergent and/or water removed significant amounts of toxin (p less than or equal to .0001); a dry scrub was not efficacious. Treatment should be initiated as soon as possible after exposure for best results. However, the stratum corneum acts as a reservoir for the toxin, and decontamination should be carried out even if delayed several hours or days after exposure. Dermal absorption pharmacokinetics found in these studies are similar to those described for other low-molecular-weight compounds, and the decontamination results from T-2 toxin should be applicable to other, similar toxic substances.

Essential fatty acid deficiency and neutrophil function: studies of lipid-free total parenteral nutrition in monkeys.

Linoleic acid (18:2 omega 6), the obligate precursor of arachidonic acid (20:4 omega 6), is an essential nutrient for humans and other mammals. Because arachidonic acid release and metabolism are components of neutrophil activation by certain stimuli, we questioned whether neutrophils depleted of arachidonate as a result of essential fatty acid deficiency might be functionally impaired. We examined this possibility by producing essential fatty acid deficiency in monkeys with lipid-free total parenteral nutrition (TPN). Rhesus and African green monkeys were given calorically equal TPN for up to 23 days with and without a vegetable fat emulsion rich in linoleic acid. Fatty acids were analyzed in total lipid extracts of serum and isolated blood neutrophils by gas-liquid chromatography. Although fatty acids in the serum and neutrophils of monkeys given TPN with lipid did not change, linoleic acid levels decreased by at least 60% in serum and 50% in neutrophils from animals given TPN with no lipid. Moreover, arachidonate levels in neutrophil lipids decreased by at least 50% within 12 days of lipid-free TPN, and the abnormal fatty acid 20:3 omega 9 (characteristic of essential fatty acid deficiency) appeared and steadily increased with time. These biochemical signs of omega 6 fatty acid deficiency were associated with impaired neutrophil function in vitro. Both migration responses and superoxide generation stimulated by N-formyl-methionyl-leucyl-phenylalanine were significantly decreased by 12 days of lipid-free TPN, as was the capacity of activated cells to synthesize leukotriene B4. In contrast, functional responses of fatty acid-deficient neutrophils to leukotriene B4 and phorbol myristate acetate, which have little or no effect on arachidonate release or metabolism, were not significantly altered. These findings indicate that endogenous supplies of arachidonic acid and other essential omega 6 fatty acids influence the functional responsiveness of neutrophils. These studies also indicate that altered neutrophil function is a feature of essential fatty acid deficiency and that it may contribute to the increased risk of infection and decreased inflammatory responses observed in this condition.

Acute inhalation toxicity of T-2 mycotoxin in mice.

Experiments were conducted to study the acute inhalation toxicity of T-2 mycotoxin in both young adult and mature mice. For a 10-min aerosol exposure, the 24-hr LC50 of T-2 mycotoxin in young adult mice was 0.08 +/- 0.04 mg T-2/liter air and that for mature mice was 0.325 +/- 0.1 mg T-2/liter air. Deaths among mice exposed to the higher aerosol concentrations used in this study (i.e., 1.5 to 2.4 mg T-2/liter air) occurred in less than 5 hr. General clinical symptoms in these animals immediately postexposure were tremors, lethargy, stilted gait, and, in some animals, prostration. In experiments separate from the concentration-response studies, total deposition of T-2 aerosol and selective retention of T-2 in the respiratory tract and nasal turbinates were determined analytically from 3H-labeled T-2. When total deposition of T-2 was quantitated, there was excellent agreement between that amount of T-2 deposited and that amount of T-2 predicted from calculations based on aerosol size and animal minute volume. Based on the aerosol deposition data, the LD50 values of T-2 mycotoxins was 0.24 mg/kg for young adult mice and 0.94 mg/kg for mature mice. For mice, inhalation of T-2 mycotoxin is at least 10 times more toxic than systemic administration (LD50 approximately 4.5 mg/kg) and at least 20 times more toxic than dermal administration (LD50 greater than 10 mg/kg).

The hemostatic derangement produced by T-2 toxin in cynomolgus monkeys.

T-2 toxin, a mycotoxin produced by several strains of the genus Fusarium, has been implicated as a cause of serious illness in both animals and man. Hemorrhage is a feature of the syndromes which have been described. An LD20 dose of T-2 was administered im to adult cynomolgus monkeys. This resulted in prolongation of prothrombin and activated partial thromboplastin times and a decrease in multiple coagulation factors. These changes were detected within hours of toxin administration, were maximal at 24 hr, and returned to normal over the next 3 days. Fibrin-fibrinogen degradation products were not detected at any time point. Repeated phlebotomy produced a significantly greater increase in platelet count in control monkeys, which could be taken as evidence for an effect of toxin on platelet kinetics. In treated animals, the hematocrit level declined by about 10%, but a similar decrease occurred in control animals. The white blood cell count increased 4 to 5 times over pretreatment values. Despite the changes in multiple laboratory parameters, treated monkeys did not exhibit clinical evidence of hemorrhage. In three animals which died as a result of toxicosis, necropsy revealed mild petechial hemorrhage involving the colon and heart, as well as necrosis of lymphoid tissues.

Structure-function relationships of 12,13-epoxytrichothecene mycotoxins in cell culture: comparison to whole animal lethality.

Nineteen 12,13-epoxytrichothecene mycotoxins were tested for their relative capabilities to inhibit protein synthesis in Vero cells and rat spleen lymphocytes. Although the lymphocytes were generally more sensitive to the mycotoxins, good correlation existed between the relative potencies of the various trichothecenes in the two cell systems. The most potent mycotoxins (T-2, verrucarin A and roridin A) have acetyl side groups on, or a hydrocarbon chain between, carbons 4 and 15 of the basic ring structure. Loss of side groups from either of these positions or an isovaleryl group at carbon 8 resulted in reduced protein synthesis inhibition (T-2 to HT-2, neosolaniol or diacetoxyscirpenol). Any combination of loss from all three positions (T-2 triol, T-2 tetraol, 15-monoacetyl DAS, scirpentriol, fusarenon X and deoxynivalenol) further weakens their effect. Reduction of the hydroxyl groups to hydroxides, forming verrucarol and deoxyverrucarol, reduced their effectiveness by over a thousand-fold compared to the most potent mycotoxins. Addition of side groups resulted in reduced effectiveness only when an acetyl group was added to the carbon 3 position of T-2 (acetyl T-2) and deoxynivalenol (3-acetyl deoxynivalenol) or on substitution of an epoxide across the 9,10 carbons of diacetoxyscirpenol (beta-epoxide DAS). Effects of combining these and other mycotoxins were additive and showed no synergism or competition for binding to the active site. When in vitro effects of the mycotoxins were compared with results from whole animal lethality tests, several of the trichothecenes were weak inhibitors of protein synthesis in vitro but had in vivo toxicities similar to that of T-2 toxin. Thus, the in vitro cell response of a given trichothecene is not always an accurate predictor of toxicity in whole animals.

Fate and distribution of 3H-labeled T-2 mycotoxin in guinea pigs.

T-2 toxin is a potent cytotoxic metabolite produced by the Fusarium species. The fate and distribution of 3H-labeled T-2 toxin were examined in male guinea pigs. Radioactivity was detected in all body tissues within 30 min after an im injection of an LD50 dose (1.04 mg/kg) of T-2 toxin. The plasma concentration of trichothecene molar equivalents versus time was multiphasic, with an initial absorption half-life equal to or less than 30 min. Bile contained a large amount of radioactivity which was identified as HT-2, 4-deacetylneosolaniol, 3'-hydroxy HT-2, 3'-hydroxy T-2 triol, and several more-polar unknowns. These T-2 metabolites are excreted from liver via bile into the intestine. Within 5 days, 75% of the total radioactivity was excreted in urine and feces at a ratio of 4 to 1. The appearance of radioactivity in the excreta was biphasic. Metabolic derivatives of T-2 excreted in urine were T-2 tetraol, 4-deacetylneosolaniol, 3'-hydroxy HT-2, and several unknowns. These studies showed a rapid appearance in and subsequent loss of radioactivity from tissues and body fluids. Only 0.01% of the total administered radioactivity was still detectable in tissues at 28 days. The distribution patterns and excretion rates suggest that liver and kidney are the principal organs of detoxication and excretion of T-2 toxin and its metabolites.

Detection and quantitation of T-2 mycotoxin with a simplified protein synthesis inhibition assay.

We describe a simple, rapid, and sensitive bioassay for the detection and quantitation of T-2 mycotoxin by using a protein synthesis assay in cultured cells. Increased sensitivity of the cells to the mycotoxin occurred with time up to ca. 60-min. Time and dose response curves show that an average of 10 to 20 ng of T-2 per ml was sufficient to cause 50% inhibition of protein synthesis in tissue culture cells. A wide range of tissue culture cells with varied type, tissue, and species sources and growth characteristics were tested by this system. All showed approximately the same sensitivity to the mycotoxin. A slight modification of the procedure was used for suspended cultures of mitogen-stimulated lymphocytes, which also showed an equal degree of sensitivity to the mycotoxin. By simply changing the labeled precursor, the inhibition of RNA, DNA, and protein synthesis by T-2 mycotoxin can be compared. Although T-2 mycotoxin had little effect on RNA synthesis, DNA and protein synthesis were equally inhibited. Because of its sensitivity and its capacity to quickly assay a large number of samples, this technique has been a valuable tool in screening samples for the presence of active toxin and has been used to help establish laboratory safety standards for the inactivation of T-2 mycotoxin by chemical agents. It is presently being used in studies of mycotoxin mechanism of action and approaches toward in vivo neutralization of the toxic effects of mycotoxins.

The hemostatic derangement produced by T-2 toxin in guinea pigs.

T-2 toxin produced significant coagulation abnormalities when administered parenterally to Hartley strain guinea pigs. The animals developed depressed activity of all coagulation factors except fibrinogen. Platelet aggregation in whole blood was depressed in response to ADP and collagen. The animals also exhibited an initial rise followed by a fall in hematocrit level, leukocytosis, and a decrease in platelet count. These changes were detectable within hours of toxin administration, reached a maximum at 24 hr, and returned to normal over the next 2 days. Pretreatment of animals with vitamin K1 had no effect on the activity of coagulation factors. The activated partial thromboplastin time of dilutions of plasma from animals given T-2 toxin with plasma from control animals revealed a pattern which pointed to a deficiency of coagulation factors as the principal cause of prolonged clotting times in treated animals. The presence of a weak circulating anticoagulant could not be ruled out. The addition of T-2 to plasma and blood of normal animals in a concentration of 1 microgram/ml had no effect on clotting times or platelet aggregation.

Metabolic effects of carbohydrate in low-calorie diets.

Fasting plasma glucose turnover, urinary 3-methylhistidine excretion, and fasting plasma protein profiles were compared in a 4-week randomized clinical trial of two very low-calorie weight-reduction diets. Diet A (360 kcal) provided 1.5 g egg protein per kg ideal body weight (IBW) but no carbohydrate. Diet B (340 kcal) provided 0.8 g egg protein per kg IBW plus 0.7 g carbohydrate per kg IBW. Eleven moderately obese healthy young women were studied. After 3 weeks of dieting, fasting plasma glucose appearance and oxidation decreased by equal amounts (20% and 30%, respectively) for both diets. 3-methylhistidine excretion remained at control rates for the first week on the diets, then fell by equal amounts (25% to 30%) with both diets. Similar declines were observed for both diets in serum prealbumin and retinol-binding protein concentrations. Mean serum transferrin declined with both diets, but the changes were not statistically significant. Serum albumin was unchanged by either diet. Thus, there were no significant differences between the two diets with regard to any of the measured parameters.

A surgical procedure and tethering system for chronic blood sampling, infusion, and temperature monitoring in caged nonhuman primates.

A jacket and tethering system was used to maintain chronic catheters in monkeys, which provided catheter access and manipulability without further restraint. Surgical placement of catheters and a temperature probe allowed for a common cutaneous exit and interface with the jacket and tether. Monkeys were fitted in a sterile leather or denim jacket which was attached to a sterilized flexible stainless steel cable. Through this conduit, an indwelling temperature probe, as well as catheters from the internal jugular and femoral veins, were attached to a swivel unit located on the upper portion of the cage. The internal jugular catheter was used for the continuous infusion of support solution. The catheter from the femoral vein was maintained with a heparin lock and used for serial blood sampling. Using this system, it was possible to obtain frequent blood samples and body temperature readings, and to administer a continuous intravenous infusion without chemical or excessive physical restraint. To date, 367 monkeys, 322 cynomolgus (Macaca fasicularis), 16 rhesus (Macaca mulatta), and 21 African green (Cercopithecus aethiops) have been studied using this procedure.

Trichothecenes, 1: The synthesis of 4-deoxyverrucarol from verrucarol and diacetoxyscirpenol.

4-Deoxyverrucarol (4) has been synthesized for use in studies for the preparation and development of monoclonal antibodies for trichothecenes. Both verrucarol (1) and anguidine (2) have been converted to deoxyverrucarol (DOVE) (4) by deoxygenation at C3 and at C3 and C4, respectively.

Leukocyte endogenous mediator alters protein dynamics in rats.

Leukocyte endogenous mediator (LEM), a low-molecular-weight peptide synthesized by monocytic cells during phagocytosis, has been implicated as the host's initiator of the protein metabolic response to infection and inflammation. To determine whether administration of LEM would alter protein kinetics, appearance and oxidation of plasma tyrosine as well as the rates of protein synthesis in liver and skeletal muscle were determined in fasted rats that received a 30-hour continuous infusion of either physiologic saline, LEM, or heat-inactivated LEM. The LEM was obtained from rabbit peritoneal exudate and the treatment solutions supplied 2.8 X 10(8) cell equivalents/100 g of body weight (BW) per day. Endogenous tyrosine oxidation increased from 4.0 +/- 0.4 mumol/100 g BW/h to 5.4 +/- 0.7 mumol/100 g BW/h in animals infused with heat-inactivated LEM and to 7.5 +/- 1.5 mumol/100 g BW/h in rats receiving LEM (P less than 0.01). Nonsecretory protein synthesis in the liver was greatest in rats administered LEM (2239 +/- 325 mg/d) when compared with control groups receiving physiologic saline (1122 +/- 195 mg/d) or heat-inactivated LEM (1374 +/- 62 mg/d; P less than 0.01), whereas skeletal protein synthetic rates were unchanged. Rates of muscle and collagen protein breakdown were estimated from the urinary excretion rate of Nt-methylhistidine and hydroxyproline, respectively, and their excretion rose by 30% (P less than 0.05) and 42% (P less than 0.05) with LEM administration. These results suggest that administration of LEM stimulates a mobilization of amino acids from peripheral tissues to support increased visceral protein anabolism while whole body amino acid oxidation is also enhanced. Since similar effects follow fever and infection, these results suggest that LEM may play an underlying role in the protein metabolic response to infection and inflammation.

Acute clinical malaria (Plasmodium inui) in a cynomolgus monkey (Macaca fascicularis).

Acute clinical malaria caused by Plasmodium inui was diagnosed in an adult female cynomolgus monkey (Macaca fascicularis) 4 years after importation into the United States. Stress and immunosuppression associated with experimentation completed 2 weeks earlier may have contributed to the development of severe clinical disease. Clinical findings included severe regenerative anemia, hepatosplenomegaly, weakness, lethargy, weight loss, and anorexia. The infection was treated and successfully eliminated with chloroquine hydrochloride administered intramuscularly at a dose of 5 mg/kg base given at 0, 6, 24, 48, and 72 hours. Treatment also included a blood transfusion and intensive supportive care.

Lack of enhanced nocturnal growth hormone release in tethered cynomolgus monkeys.

To determine spontaneous 24-h patterns of growth hormone (GH) plasma levels in unsedated and unrestrained nonhuman primates, a jacket and tethering system were used to study six cynomolgus monkeys. Hourly blood samples were collected, and body temperatures were recorded over 24-h periods. Measurements of GH were made on all samples. In one 24-h study cortisol levels were also measured as well to document a normal circadian rhythm. GH was released at mean intervals of 4.5 +/- 0.47 h (mean +/- SE) over the 24-h studies. There were no day-to-night differences in either the mean interval of GH release (day, 4.6 +/- 0.66 h; night, 4.4 +/- 0.51) or the mean GH values (day, 9.8 +/- 1.7 mU/l; night, 7.9 +/- 0.8). An apparent midday peak in GH in the 24-h studies followed feeding. As expected, body temperature was higher during the day than night, documenting a normal circadian rhythm. Plasma cortisol also showed a normal circadian variation with a low point midday and a progressive rise during the night in the one 24-h cycle in which it was measured. GH in unsedated, unrestrained cynomolgus monkeys was released in 4- to 5-h cycles both day and night without increased nighttime release. This contrasts sharply with the known nocturnal sleep release of GH seen in humans.