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Biomedical subjects

S J Gray

Publications and source records attributed to S J Gray.

At least 37 records · Page 2Linked to original sources

Ecology of weaning among nomadic Turkana pastoralists of Kenya: maternal thinking, maternal behavior, and human adaptive strategies.

Weaning of human children is a complex process involving the introduction of non-breast-milk foods, reduction in suckling activity, and eventual termination of breast feeding. Because the choice of strategies for each component of the weaning process depends on the operating environmental constraints, reproductive demands on women, and prevailing levels of infant and weanling mortality, it is appropriate to examine weaning practices as human adaptive strategies. Here, I examine the structure of weaning and maternal attitudes toward weaning among nomadic Turkana pastoralists from the perspective of human adaptation. Using retrospective and prospective data on breast feeding, the use of non-breast-milk foods, and the cessation of breast feeding. I identify ideal strategies as those defined by Turkana women. Real behavior in relation to weaning, however, deviates considerably from the ideal, and this deviation reflects adaptive responses to nutritional and disease risks to infants. Particular attention is given to problematic aspects of weaning practices in Turkana, such as premature introduction of non-breast-milk foods and abrupt termination of breast feeding, which have been shown to contribute to high infant and weanling mortality in populations in developing countries. These practices have evolved from the dual caretaking and childbearing role of women and the necessity of reconciling the needs of the breast-feeding child with the demands of the next pregnancy. As such, they represent rational strategies for enhancing reproductive success in this and other similarly stressful environments.

Adaptation, Psychological↗

Correlates of breastfeeding frequency among nomadic pastoralists of Turkana, Kenya: a retrospective study.

Recent research has shown that significant variation in breast-feeding behavior exists among natural fertility populations, all of whom have been characterized as practicing "on-demand" breastfeeding. A number of recent prospective studies have contributed to a better understanding of breastfeeding structure and of its consequences for population differences in fertility. Currently, there is a growing interest in quantifying the complex environmental and biocultural interactions which influence that structure; in other words, in establishing an ecology of breastfeeding. In this paper, a carefully structured retrospective study of breastfeeding behavior among nomadic Turkana is used to identify environmental, biobehavioral, and socioeconomic factors associated with variation in breastfeeding frequency among Turkana women. In agreement with the results of a prospective study conducted as part of the same research, the age (growth) and physical development of nurslings show significant correlations with breastfeeding frequency. Maternal physical status, the depth of the maternal social network, and, to a lesser degree, rainfall patterns are also significant. All of these factors appear to influence breastfeeding through their effects on maternal participation in herding activities and related absences from camp. Finally, the study also presents new strategies for collecting and utilizing retrospective data, which are notoriously unreliable and difficult to classify according to operational definitions recently developed for prospective studies. Results of the present study suggest methods by which the quality and reliability of recall data may be enhanced.

Adult↗

Comparison of effects of breast-feeding practices on birth-spacing in three societies: nomadic Turkana, Gainj, and Quechua.

Variation in the duration and pattern of breast-feeding contributes significantly to inter-population differences in fertility. In this paper, measures of suckling frequency and intensity are used to compare the effects of breast-feeding practices on the duration of lactational amenorrhoea, and on the length of the birth interval in three prospective studies undertaken during the 1980s, among Quechua Indians of Peru, Turkana nomads of Kenya, and Gainj of Papua New Guinea. In all three societies, lactation is prolonged well into the second year postpartum, and frequent, on-demand breast-feeding is the norm. However, the duration of lactational amenorrhoea and the length of birth intervals vary considerably. Breast-feeding patterns among Gainj and Turkana are similar, but Turkana women resume menses some 3 months earlier than do the Gainj. The average birth interval among the Gainj exceeds that of nomadic Turkana by over 15 months. Suckling activity decreases significantly with increasing age of nurslings among both Gainj and Quechua, but not among Turkana. Earlier resumption of menses among Turkana women may be linked to the unpredictable demands of the pastoral system, which increase day-to-day variation in the number of periods of on-demand breast-feeding, although not in suckling patterns. This effect is independent of the age of infants. The short birth intervals of Turkana women, relative to those of the Gainj, may be related to early supplementation of Turkana nurslings with butterfat and animals' milk, which reduces energetic demands on lactating women at risk of negative energy balance.

Adult↗

Inhaled nitric oxide in patients with normal and increased pulmonary vascular resistance after cardiac surgery.

We studied the haemodynamic effects of inhaled nitric oxide 40 p.p.m. in two groups of patients after cardiac surgery (mitral valve surgery or coronary artery bypass grafting). Nitric oxide caused a significant reduction in pulmonary vascular resistance after mitral valve surgery in patients who had pre-existing pulmonary hypertension, but no change in haemodynamic state in the coronary artery bypass group of patients, who had normal pulmonary arterial pressures.

Administration, Inhalation↗

Growth of nomadic and settled Turkana infants of northwest Kenya.

Turkana tribespeople reside in a semi-arid savanna ecosystem in northwest Kenya. For over a decade, Ngisonyoka Turkana nomads have been studied within a multidisciplinary framework that embraces ecology, anthropology, and human population biology. Original research objectives of the South Turkana Ecosystem Project were to study nomads longitudinally and within the context of the dry savanna ecosystem. These objectives have been expanded to incorporate settled Turkana who were nomads in the recent past, but who, for a variety of reasons, have taken up a life of sedentary cultivation. The research described here focused on comparisons of growth patterns of nomadic and settled infants from birth to 24 months of age. Infants were measured (recumbent length, weight, head circumference, arm and calf circumference, and selected skinfolds) in 1989 and 1990. Settled infants were slightly longer, but nomadic infants were heavier and fatter. Head circumferences were the same. Some variation was observed by season and year of measurement (from comparative surveys). Both groups showed pronounced weight faltering after 6 months of age when compared with U.S. NCHS reference values. Head circumference faltering was moderate and recumbent length faltering was only slight after 12 months of age. Comparisons of Turkana infant growth in the two populations can contribute indirectly to a better understanding of infant nutritional status, probable morbidity, and other factors, some of which may be linked to female reproduction.

Anthropometry↗

The pharmacokinetics, tolerability and pharmacodynamics of tucaresol (589C80; 4[2-formyl-3-hydroxyphenoxymethyl] benzoic acid), a potential anti-sickling agent, following oral administration to healthy subjects.

1. Tucaresol (589C80; 4[2-formyl-3-hydroxyphenoxymethyl] benzoic acid) interacts stoichiometrically with haemoglobin to increase oxygen affinity. By decreasing the proportion of insoluble deoxy sickle haemoglobin at capillary oxygen concentrations, tucaresol may be of therapeutic benefit in sickle cell anaemia. 2. In this study, which involved the first administration to man, the pharmacokinetics and pharmacodynamics of tucaresol were studied in healthy male volunteers following oral doses of 200-3600 mg. 3. Peak drug concentrations in plasma and erythrocytes were linearly related to dose; mean (s.d.) values were 95.8 (26.1) and 1035 (67) micrograms ml-1, respectively, at the highest dose. Median tmax in plasma was 6.5 h and in erythrocytes 24.5 h, when approximately 60% of the administered dose was in the target tissue. Plasma drug concentrations fell biexponentially with commencement of the apparent terminal elimination phase at approximately 24 h. The terminal elimination half-life from plasma increased with dose (r = 0.77; P < 0.0001) from 133-190 h at 400 mg to a mean (s.d.) of 289 (30) h at 3600 mg. Erythrocyte drug concentrations declined mono-exponentially with a half-life that was always shorter than the apparent terminal half-life in plasma: overall mean (95% CI) of t1/2 erythrocyte/t1/2 plasma ratio was 0.57 (0.53, 0.61). The erythrocyte AUC/plasma AUC ratio increased with dose (r = 0.67; P < 0.001). 4. The proportion of haemoglobin modified to a form with high oxygen affinity (%MOD) increased in a dose-related manner above doses of 800 mg reaching 19-26% after the 3600 mg dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗

The effect of a prostaglandin DP-receptor partial agonist (192C86) on platelet aggregation and the cardiovascular system in healthy volunteers.

1. PGD2 (DP)-receptors mediate inhibition of platelet aggregation and vasodilatation. If receptor reserve were greater on platelets it might be possible to separate these effects. To determine whether such a difference in receptor reserve exists, we have examined the effects of a highly selective DP-receptor partial agonist 192C86 on platelet aggregation and the cardiovascular system in healthy volunteers. 2. Using an open, dose-escalating study design, four male volunteers received constant rate intravenous infusions of 192C86 for up to 60 min. Ex vivo platelet aggregation to ADP and collagen in platelet-rich plasma (PRP) and whole blood (WB) was studied at baseline, after 15, 30 and 60 min of each infusion and at 180 min post-infusion. Heart rate (HR), systolic and diastolic (DBP) blood pressure were measured at frequent intervals. Adverse experiences were monitored by checklist. Facial flushing was assessed by the volunteer using a visual analogue scale, by an observer using a numerical scale and by full-face colour photographs. Blood was taken for assay of plasma 192C86 concentrations by radio-immunoassay (r.i.a.). 3. 192C86 (0.007-0.058 micrograms kg-1 min-1) inhibited platelet aggregation to ADP and collagen both in PRP and WB in a dose-dependent manner. However, this was always accompanied by a decrease in DBP, increase in HR and facial flushing. Plasma concentrations of 192C86 were at or below the limits of sensitivity of the r.i.a. (0.5 ng ml-1). 4. The highest infusion rate was stopped after 20 min due to symptomatic hypotension on standing.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

Interactions between prostaglandin E2 and inhibitors of platelet aggregation which act through cyclic AMP.

Prostaglandin (PG) E2 potentiates platelet aggregation at low concentrations (10(-8)-10(-6) M). It also inhibits aggregation at a higher concentration (10(-5) M), probably by acting through cyclic adenosine 3',5'-monophosphate (cyclic AMP). The mechanism of this biphasic effect of PGE2 and its implications for thrombosis are not clearly understood. Using a sensitive cyclic AMP assay, in conjunction with platelet aggregation studies, we have examined the interactions between PGE2 and other inhibitors of platelet aggregation which act through cyclic AMP. Low concentrations of PGE2 reversed the inhibition of platelet aggregation and increase in cyclic AMP levels induced by PGI2, PGD2 and adenosine (which stimulate adenylate cyclase (AC) through separate and specific platelet receptors). In contrast, low concentrations of PGE2 added to the inhibition of platelet aggregation and increase in cyclic AMP levels induced by forskolin (which stimulates AC directly) and AH-P 719 and DN-9693 (which inhibit cyclic AMP phosphodiesterase (PDE]. These results suggest that the biphasic effect of PGE2 may be mediated by interaction with two separate platelet receptors. Low concentrations appear to potentiate aggregation by acting at a receptor which is directly coupled to an inhibitory guanine nucleotide-binding protein (Gi), possibly the putative PG endoperoxide receptor. High concentrations of PGE2 appear to inhibit aggregation by acting at an additional receptor, probably the PGI2 receptor. The ease with which PGE2 reverses the effects of PGI2, PGD2 and adenosine, but adds to the effects of AH-P 719 and DN-9693, suggests that PDE inhibitors might offer greater potential than these AC stimulators as an anti-thrombotic strategy.(ABSTRACT TRUNCATED AT 250 WORDS)

3',5'-Cyclic-AMP Phosphodiesterases↗

An epidemiologically valuable typing method for Neisseria meningitidis by analysis of restriction fragment length polymorphisms.

A restriction fragment length polymorphism (RFLP) typing method was developed for Neisseria meningitidis. A cloned EcoRI fragment from a Neisseria meningitidis Group B serotype 15P1.16 sulphonamide-resistant strain was used to probe Southern blots of total chromosomal DNA restriction fragments (enzyme AvaI). A group of 75 apparently unrelated organisms gave rise to 26 different restriction fragment length patterns and two different groups of epidemiologically related strains had RFLP patterns that were distinct for each group. The technique was highly reproducible and discriminatory. The RFLP data were compared with the results of serotyping and subtyping and isoenzyme electrophoretotyping. The RFLP data were consistent with those from the alternative typing methods; clones defined by isoenzyme analysis were subdivided by this technique. The use of RFLP typing by cloned probes should be of considerable epidemiological value.

Blotting, Southern↗

The effect of 443C81, a mu opioid receptor agonist, on the response to inhaled capsaicin in healthy volunteers.

Activation of mu opioid receptors on sensory nerves in the lung represents an attractive mechanism for reducing cough and reflex bronchoconstriction. We have examined the effect of the peptide 443C81, a peripherally acting mu opioid agonist, on the cough and reflex increase in respiratory resistance (Rrs) produced by capsaicin in nine healthy male volunteers. Using a randomised, double-blind crossover design, each subject inhaled either saline, 1 mg ml-1 443C81 or 4 mg ml-1 443C81 for 10 min from an ultrasonic nebuliser. The cough response to a range of doses of inhaled capsaicin and the increase in Rrs caused by inhalation of a single subtussive dose of capsaicin were measured before and after each treatment. There was no evidence of an effect of either 1 or 4 mg ml-1 443C81 on cough or increase in Rrs produced by capsaicin when compared with the saline placebo. It is concluded that inhalation of this mu opioid receptor agonist had no effect on capsaicin-induced cough or reflex bronchoconstriction in healthy volunteers.

Administration, Inhalation↗

Can innuendos in headlines affect perceptions?

The effect of innuendos in headlines on the memory and attitudes of 67 male and 81 female college student who read simulated news articles were studied. Analysis indicated no main or interactive effect of headlines containing innuendo on memory, rated responsibility of the accused or victim, or on sentencing. Memory and attitudes were affected by identification and stereotyping.

Adult↗

The innervation of tracheal smooth muscle in the ferret.

The innervation of tracheal smooth muscle in the ferret has been studied by monitoring pressure changes in a fluid-filled segment of trachea in pentobarbitone anaesthetized animals. Stimulation of the peripheral cut end of the vago-sympathetic trunk elicited increases in trachea segment pressure only when activity was evoked in non-myelinated efferent axons, myelinated axons were without effect. Such excitatory responses were blocked by atropine. After atropine and elevation of trachealis muscle tone with 5-hydroxytryptamine, stimulation of the vago-sympathetic trunk produced a fall in tracheal segment pressure. These inhibitory responses were completely blocked by bretylium tosylate in six animals and markedly reduced in a seventh. It is concluded that contraction of tracheal smooth muscle in the ferret is cholinergically mediated and solely dependent on activity in non-myelinated vagal efferent axons and that inhibition is mediated by noradrenaline released from sympathetic nerve endings. A non-adrenergic inhibitory system would not appear to be present in the ferret.

Animals↗

The incidence of virulence factors in mesophilic Aeromonas species isolated from farm animals and their environment.

Sixty-one isolates of Aeromonas spp. from the faeces of pigs, cows and a variety of associated environmental sources were examined for the characteristics that are reputed to have roles in pathogenicity. Most isolates of Aeromonas hydrophila were cytotoxic (96.4%) and were capable of producing cell elongation factor (75%) and haemagglutinins (67.9%). In contrast few of the Aeromonas caviae isolates produced these three markers (13.6%, 27.3% and 36.4% respectively). In general, Aeromonas sobria occupied an intermediate position (36.4%, 27.3% and 54.5%), but they did produce the highest mean invasion index for HEp-2 cells. Statistical analysis revealed significant associations between the carriage of these factors and it was clear that many isolates of aeromonads from water and animals possessed the full battery of putative virulence factors.

Aeromonas↗

Some observations on the faecal carriage of mesophilic Aeromonas species in cows and pigs.

Replicate faecal samples from healthy individual pigs and cows were examined for the presence of Aeromonas sp. over a 12-month period. Aeromonads were found to be minor components of the faecal flora, only 8.8% of 520 samples from pigs and 4.6% of 481 samples from cows proving positive. Isolation rates in both groups of animals were seasonal. A hydrophila (62% of the isolates) was the predominant species in cows, followed by A. caviae (32%) and A. sobria (15%). This pattern was also recorded in the natural waters that the animals drank from during the period when the faecal carriage rate was at its highest. In pigs, A. caviae (59%) was more common than A. hydrophila (41%). A. sobria was not found in any of the pig-associated samples. It seems that cattle acquire their faecal aeromonads from drinking water. The source of the organisms in pigs is less clear.

Aeromonas↗

The effects of PGE2 and CL 115,347, an antihypertensive PGE2 analogue, on human blood platelet behaviour and vascular contractility.

The effects of prostaglandin E2 (PGE2) and an antihypertensive PGE2 analogue, CL 115,347 (d,l-15-deoxy-16-hydroxy-16 (alpha/beta)-vinyl prostaglandin E2 methyl ester), were examined on human blood platelet behaviour in platelet-rich plasma (PRP) and in whole blood (WB). The effects on baseline tone of isolated human carotid arterial strips were also examined. PGE2 had a biphasic effect on platelet behaviour, potentiating ADP- and collagen-induced aggregation at low concentrations (10(-8)-10(-6) M) and inhibiting aggregation at higher concentrations (10(-5) M). In contrast, low concentrations of CL 115,347 (10(-9)-10(-5) M) had no effect on platelet aggregation and higher concentrations (10(-4) M) potentiated ADP- and collagen-induced aggregation. The effects of PGE2 and CL 115,347 on adrenaline-induced aggregation were different to those of the other aggregating agents since only inhibition of platelet aggregation was observed. In the presence of PGI2 (10(-9)-10(-8) M) however, PGE2 (10(-8)-10(-6) M) was able to potentiate both ADP- and adrenaline-induced aggregation. Results obtained in WB were similar to those obtained in PRP. Both PGE2 and CL 115,347 contracted isolated human carotid arterial strips in a dose-dependent manner, with PGE2 being approximately 20 times more potent than its synthetic analogue. These results indicate that CL 115,347 is less potent than PGE2 in its effects on human blood platelet behaviour and vascular contractility in vitro.

Adenylyl Cyclase Inhibitors↗