Effects of Exposure to Single or Multiple Combinations of the Predominant Toxic Gases and Low Oxygen Atmospheres Produced in Fires

Effects of Exposure to Single or Multiple Combinations of thePredominant Toxic Gases and Low Oxygen Atmospheres Producedin Fires. LEVIN, B. C., PAABO, M., GURMAN, J. L., AND HARRIS,S. E. (1987). Fundam. Appl. Toxicol. 9, 236–250. The toxicityof single and multiple fire gases is studied to determine whetherthe toxic effects of the combustion products from materialscan be explained by the toxicological interactions (as indicatedby lethality) of the primary fire gases or if minor, more obscuregases need to be considered. LC50 values for Fischer-344 ratshave been calculated for the individual gases, carbon monoxide(CO), hydrogen cyanide (HCN), or decreased oxygen (O₂), for30-min exposures plus relevant postexposure periods using theNBS Toxicity Test Method. Combination experiments with CO andHCN indicate that they act in an additive manner. Synergisticeffects have been found when the animals are exposed to certaincombinations of CO and carbon dioxide (CO₂). Five percent CO₂raised the threshold for deaths due to hypoxia and decreasedthe LC50 of HCN. Decreasing the O₂ concentration in the presenceof various mixtures of the other major fire gases increasedthe toxicity even further. A comparison of the concentrationsof the major combustion products generated from a number ofpolymeric materials at their LC50 (30-min exposure plus 14-daypostexposure) values with the combined pure gas results indicatesthat, in most cases, the observed toxicity may be explainedby the toxicological interactions of the examined primary toxicfire gases. These results provide necessary information forthe computer model currently being developed at the Center forFire Research to predict the toxic hazard that people will experienceunder various fire scenanos.     

Patterns and stability of cardiovascular responses to variations of the cold pressor test

Test-retest reliabilities and patterns of heart rate and blood pressure responses were examined using variations in the cold pressor test in 113 normotensive white college men. Comparisons were made of stimulus site (forehead vs. foot) and bodily posture (seated vs. supine) across four separate groups of men. The stability of cardiovascular responses was examined over a 2-week test-retest interval. Different cardiovascular response patterns emerged as a function of stimulation site and posture. Systolic and diastolic blood pressure increases were accompanied by bradycardia in the forehead cold pressor task but by tachycardia in the foot cold pressor task. Systolic blood pressure increases were larger for foot than for forehead stimulation. Heart rate increases were larger for supine than for seated men. Effects on response were independent of postural differences at baseline, and there were no stimulation site by posture interactions. The cardiovascular responses to stimulation did not attenuate across sessions in any experimental condition but were more reliable for foot than for forehead stimulation and for supine than for seated posture. Short-term stability for changes to the task approached that for baseline and task and was higher than has been reported elsewhere.     

FERTILITY AFTER CHILDBIRTH: PREGNANCY ASSOCIATED WITH BREAST FEEDING

During studies on the resumption of fertility postpartum in 12 breast feeding mothers who were using no contraception, eight pregnancies occurred. In seven cases these pregnancies occurred while the mothers continued to breast feed while in one it occurred within 2 weeks of weaning. In two cases pregnancy occurred prior to first postpartum menstruation but followed an abrupt decline in suckling frequency and duration resulting in resumption of follicular development and ovulation. In the remaining six cases, pregnancy was preceded by between 1 and 7 menstrual cycles, the majority of which (13/19) had deficient luteal phases or were anovular (4/19). In all mothers a significant decrease in the suckling frequency and duration observed during lactational amenorrhoea had occurred prior to the resumption of ovulation and conception. No mother conceived with a suckling frequency of greater than three times per day although some mothers ovulated without conceiving when suckling four times per day. The results suggests that if a breast feeding mother wishes to rely upon the infertility associated with lactational amenorrhoea, she must suckle at least five times per day with a total suckling duration of more than 65 min per day (more than 10 min per feed). Any reduction below either of these limits may result in a return of fertility.     

CIRCULATING LEVELS OF PROLACTIN DURING THE MENSTRUAL CYCLE

In detailed studies on seventeen volunteers, it has been shown that changes in prolactin levels during the menstrual cycle are irregular and inconsistent. Some, but not all, subjects have elevated levels at mid-cycle, and higher levels in the luteal phase than in the follicular phase. At all stages of the cycle, prolactin levels may show short-term random fluctuations of as much as 110%. There was no apparent relation between levels of prolactin and those of LH, FSH, oestradiol-17β or progesterone. It is suggested that if prolactin has any role in the control of the menstrual cycle, then the normal circulating levels are considerably in excess of the threshold requirements for its action.     

THE TSH, FSH AND PROLACTIN RESPONSES TO CONTINUOUS INFUSIONS OF TRH AND THE EFFECTS OF OESTROGEN ADMINISTRATION IN NORMAL MALES

Four normal males received a constant infusion of 0.9% NaCl for 1 hr followed immediately by 500 μg of TRH infused over the same period. A rise in serum TSH was observed in all subjects while in three there was also a significant FSH response. The prolactin response, unlike that of TSH, was markedly pulsatile indicating that different mechanisms exist for the release of these two hormones from the pituitary after TRH. Circulating levels of LH were unaffected. Ethinyl oestradiol, 30 μg daily for 3 days, was administered to two of the subjects and the infusions were repeated. Both basal FSH and LH levels were depressed, as was the FSH response to the infusion of TRH. By contrast, however, the TSH response to thyrotrophin releasing hormone was enhanced after oestrogen. In one subject the basal prolactin levels were significantly higher while in both there was an augmented prolactin response to TRH, the pulsatile pattern of release being maintained.