Further evidence for the usefulness of the salivary testosterone radioimmunoassay in the assessment of androgenicity in man in basal and stimulated conditions

Since correct assessment of testicular function and androgenic status in humans requires multiple sampling, a sensitive and accurate radioimmunoassay (RIA) of testosterone (T) was established for male and female saliva samples. This easily collected biological fluid, which contains nonprotein-bound T, may represent an attractive alternative or a complement to total plasma T assays. In saliva samples from 5 normal males, a clear circadian rhythm was observed, and morning concentrations (135 +/- 31 pg/ml) were significantly higher (p less than 0.02) than evening samples (85 +/- 23 pg/ml). In 11 normal females, morning saliva levels were 12.8 +/- 1.8 pg/ml. The levels of T in male saliva, in response to both exogenous T administration (100 mg i.m.) and HCG stimulation (2 X 2,000 IU i.m.), accurately reflected the changes observed in plasma T, and the magnitude of increase in T levels was clearly greater in saliva than in plasma samples during the intramuscular administration of the long-acting T preparation. In males, significant correlations were observed between salivary and plasma T concentrations in morning samples (r = 0.61, p less than 0.01), following HCG stimulation (r = 0.89, p less than 0.05) and during T administration (r = 0.87, p less than 0.05). In women, the correlation at 8 a.m. was also significant (r = 0.82, p less than 0.05).     

Genetic and environmental influences on IL-6 and TNF-alpha plasma levels in apparently healthy general population

Dysregulation of cytokines synthesis is thought to play a role in the development of a number of age-related conditions, such as rheumatoid arthritis, osteoporosis, atherosclerosis, and others, but observational studies have led to contradictory results. We investigated potential familial influences on the plasma levels of IL-6 and TNF-alpha in 91 nuclear and more complex pedigrees of Caucasian ethnic origin (N=401 individuals). The maximum likelihood based variance decomposition analysis showed significant positive correlation between circulating IL-6 and age in both genders. The magnitude of these correlations in our sample ranged from 0.22 in females to 0.28 in males (P<0.001). Significant association between TNF-alpha and IL-6 (r=0.28, r=0.43; P<0.001; respectively for men and women) was also observed. Likelihood ratio test clearly revealed that additive genetic effect for TNF-alpha was highly significant (P<0.001), and accounted over 80% of its variation, adjusted for IL-6 levels and age. In contrast, heritability estimate for IL-6 adjusted for age and TNF-alpha, revealed small contribution of genetic factors (24.1 +/- 10.2%). The bivariate variance component analysis demonstrated that significant relationship between IL-6 and TNF-alpha was due to shared environment only (r(E)=0.760 +/- 0.140). As evinced from our complex segregation analysis the nature of the genetic determinant of each of these two cytokines is quite complex and it is probably oligogenic.     

Responses of plasma adrenocorticotropin and cortisol to intravenous injection of synthetic ovine corticotropin releasing factor in the morning and early evening in normal human subjects

This study was designed to compare the responsiveness of adrenocorticotropin (ACTH) and cortisol secretion to corticotropin-releasing factor (CRF) in the morning and early evening in normal human subjects. Synthetic ovine CRF (1.0 micrograms/kg) or normal saline, was administered as an i.v. bolus injection to six normal males at 900 h and 1700 h. Blood samples were obtained before and 15, 30, 60, 90 and 120 min after CRF or saline injection. Significant increases in plasma ACTH and cortisol levels were observed in all subjects at the both time of testing after CRF injection. The net increments in the areas under the concentration curve (areas in the CRF experiment minus those in the saline control experiment) were not statistically different for both ACTH (mean +/- SEM: 41.0 +/- 10.6 pg/ml h in the morning: 51.1 +/- 8.9 pg/ml h in the evening) and cortisol (mean +/- SEM: 28.5 +/- 5.0 micrograms/dl h in the morning; 36.2 +/- 4.0 micrograms/dl h in the evening). Also no significant difference was observed in net increment, peak level and the ratio of peak level to the basal level of ACTH and cortisol after CRF injection. There were no appreciable changes in plasma concentrations of growth hormone, thyroid-stimulating hormone or prolactin, although slight but statistically significant rises in plasma levels of luteinizing hormone and follicle-stimulating hormone were observed. These results suggest that there is no significant difference in responsiveness of the pituitary-adrenal axis to CRF in the morning (900 h) and early evening (1700 h), and thus the time of day will not necessarily have to be considered when CRF is used between these times in a clinical test to evaluate pituitary ACTH reserve.     

Acute changes in knee-extensors torque, fiber pennation, and tendon characteristics

The aim of the current study was to examine the relationships between quadriceps torque, vastus lateralis pennation angle (theta), and patella tendon stiffness (K) at 07:45 and 17:45 h. Using short-duration static contractions, simultaneous recordings were made of vastus lateralis (VL) electromyograph (EMG), theta and patella tendon K. Peak isometric extension torque (Peak torque Ext(corr)) increased by 29.4+/-6.5% at a knee angle of 70 degrees (p=0.03) in the evening compared to the morning. In the contracted muscle, a 35.0+/-11.0% (p=0.02) time-of-day (TOD)-related change in theta (to a greater evening compared to morning theta) was observed. Morning and evening measures of theta were also made, both at rest and at a standardized force level (250 N), to separate architecture change effects from increased torque capacity effects. Significant increments in theta in both the resting muscle (13.0+/-5.1%, p=0.046) and during the standardized exertions (8.0+/-3.1%, p=0.04) were observed in the evening versus the morning. Increases in theta with TOD were significantly correlated with the 40% (p=0.018) decrease in K both during the standardized contractions (r=0.788, p<0.001) and at rest (r=0.77, p=0.026). These data show that TOD affects K and theta and that these two important factors involved in in-vivo muscle torque generation capacity are associated. The data also show that despite the potentially deleterious effects of the direction of the changes in both K and theta with TOD, peak torque Ext(corr) still shows a significant upward shift in the evening relative to the morning.     

Gender-related differences in basal DNA damage in lymphocytes of a healthy Indian population using the alkaline Comet assay

The Comet assay, a sensitive, rapid and non-invasive technique, measures DNA damage in individual cells and has found wide acceptance in epidemiological and biomonitoring studies to determine the DNA damage resulting from lifestyle, occupational and environmental exposure. The present study was undertaken to measure the basal level of DNA damage in a normal, healthy Indian male and female population. Out of the 230 volunteers included in this study, 124 were male and 106 were female. All the individuals belonged to a comparable socio-economic background and aged between 20 and 30 years. They were also matched for their smoking and dietary habits. The period of sample collection was also matched. The results revealed a statistically significant higher level of DNA damage in males when compared to females as evident by an increase in the Olive tail moment [3.76+/-1.21 (arbitrary units) for males as compared to 3.37+/-1.47 for females (P<0.05)], tail DNA (%) [10.2+/-2.96 for males as compared to 9.40+/-2.83 for females (P<0.05)] and tail length (microm) [59.65+/-9.23 for males and 49.57+/-14.68 for females (P<0.001)]. To our knowledge, this report has, for the first time demonstrated significant differences in the basal level of DNA damage between males and females in a normal healthy Indian population.     

Differential control of morning and evening components in the activity rhythm of Drosophila melanogaster--sex-specific differences suggest a different quality of activity

The rhythms of locomotor activity of male and virgin or mated female flies were compared in the Drosophila melanogaster wild-type strains CantonS, Berlin, and OregonR. Under light-dark conditions, most flies showed a bimodal activity pattern with a morning peak around lights-on and an evening peak before lights-off. For all strains, a distinct sexual dimorphism was observed in the phase of the morning peak. Males had a significantly earlier morning peak than females and consequently a larger phase angle between morning and evening peak (psi(m, e)). Under constant dark conditions, the morning component merged with the evening component to a unimodal activity band in about half of the flies. In those flies who maintained bimodality, the sex-specific difference in psi(m, e) disappeared. Other sex-specific differences were now apparent: Males showed a shorter free-running period than females, and in two of the three strains, females were more active than males. Morning and evening components seem to contribute to the free-running period. Spontaneous or externally provoked change in psi(m, e) were correlated with period changes. In some flies, the morning and the evening components showed splitting, indicating that they are the output of two different oscillators. The sexual dimorphism in the phase of the morning peak under LD-conditions suggests that the function of activity during morning and evening peak might be different, for example, during the morning peak, males are active to find females. Overall, the results underline the multioscillatory nature of Drosophila's circadian system.     

Diurnal variation of insulin clearance and sensitivity in normal man

Sixteen normal healthy volunteers were randomized into two groups, receiving either low doses insulin infusion clamp study (8mU/M2/min) or high dose (40mU/M2/min) to determine the diurnal insulin clearance and sensitivity. Each subject received the assigned dose of insulin clamp twice; one in the morning (0800-1000) and the other in the evening (1800-2000), each with a precedent 9 hours of fasting, respectively. The results showed that there were diurnal variation of serum insulin clearance in the high dose study (AM:791 +/- 54ml/min/M2, PM:947 +/- 53ml/min/M2, p less than 0.01), and the small dose study (AM:411 +/- 32ml/min/M2, PM:716 +/- 87ml/min/M2, p less than 0.001). Diurnal variation of insulin sensitivity as judged by dividing glucose infusion rate by the ambient serum free insulin level (M/FI ration), was only noted in the low dose insulin infusion clamp study (AM:14.6 +/- 2.4, PM:10.5 +/- 1.1, p less than 0.05). In summary, at low physiological levels of insulin the insulin sensitivity is better in the morning, whereas at both high and low insulin levels the insulin clearance of normal subject is greater in the evening. The mechanism of this diurnal variation of insulin clearance and sensitivity awaits further studies.     

An increase in in vivo release of LHRH and precocious puberty by posterior hypothalamic lesions in female rhesus monkeys (Macaca mulatta)

We have previously shown that a decrease in gamma-aminobutyric acid (GABA) tone and a subsequent increase in glutamatergic tone occur in association with the pubertal increase in luteinizing hormone releasing hormone (LHRH) release in primates. To further determine the causal relationship between developmental changes in GABA and glutamate levels and the pubertal increase in LHRH release, we examined monkeys with precocious puberty induced by lesions in the posterior hypothalamus (PH). Six prepubertal female rhesus monkeys (17.4 +/- 0.1 mo of age) received lesions in the PH, three prepubertal females (17.5 +/- 0.1 mo) received sham lesions, and two females received no treatments. LHRH, GABA, and glutamate levels in the stalk-median eminence before and after lesions were assessed over two 6-h periods (0600-1200 and 1800-2400) using push-pull perfusion. Monkeys with PH lesions exhibited external signs of precocious puberty, including significantly earlier menarche in PH lesion animals (18.8 +/- 0.2 mo) than in sham/controls (25.5 +/- 0.9 mo, P<0.001). Moreover, PH lesion animals had elevated LHRH levels and higher evening glutamate levels after lesions, whereas LHRH changes did not occur in sham/controls until later. Changes in GABA release were not discernible, since evening GABA levels already deceased at 18-20 mo of age in both groups and morning levels remained at the prepubertal levels. The age of first ovulation in both groups did not differ. Collectively, PH lesions may not be a good tool to investigate the mechanism of puberty, and, taking into account the recent findings on the role of kisspeptins, the mechanism of the puberty onset in primates is more complex than we initially anticipated.     

Diurnal Variation in Insulin-stimulated Systemic Glucose and Amino Acid Utilization in Pigs Fed with Identical Meals at 12-Hour Intervals.

The diurnal variation in insulin-stimulated systemic glucose and amino acid utilization was investigated in eleven pigs of approximately 40 kg. Pigs were fed isoenergetic/isoproteinic diets (366 kJ/kg BW (0.75) per meal) in two daily rations (06:00 and 18:00 h). After a 3-week habituation period, hyperinsulinemic euglycemic euaminoacidemic clamp studies (by intra-portal insulin, glucose and amino acids infusion and arterial blood sampling) were performed starting at 06:00 or 18:00 h (while skipping the meal), using a cross-over within-animal design. Basal (preclamp) plasma concentrations of insulin, glucose, lactate, individual amino acids and urea were similar in the morning compared to the evening. Insulin-stimulated ( approximately 4-fold increase over basal) systemic glucose utilization was similar (17.6+/-1.4 and 18.9+/-1.8 mg.kg (-1).min (-1)) but amino acid utilization was 19% greater in the morning VS. the evening (2.37+/-0.21 VS. 1.99+/-0.15 mg.kg (-1).min (-1), p<0.05), respectively. Insulin-stimulated plasma lactate concentrations remained constant in the morning (0.77+/-0.06 to 0.71+/-0.04 mmol.l (-1)) but declined in the evening (0.89+/-0.09 to 0.65+/-0.06 mmol.l (-1), p<0.05). By contrast, insulin-stimulated plasma urea concentrations declined in the morning (2.48+/-0.11 to 2.03+/-0.10 mmol.l (-1), p<0.005) but remained constant in the evening (2.18+/-0.14 to 2.12+/-0.12 mmol.l (-1)). In conclusion, pigs fed identical meals at 12-hour intervals follow a clear diurnal biorhythm in protein anabolism, with greater insulin-stimulated systemic amino acid utilization and lower plasma urea response in the morning compared to the evening.     

Excretion of corticosteroid metabolites in urine and faeces of rats.

Stress enhances the production of corticosteroids by the adrenal cortex, resulting in the increased excretion of their metabolites in urine and faeces. An intraperitoneal injection of radioactive corticosterone was applied to adult, male Sprague-Dawley rats to monitor the route and delay of excreted metabolites in urine and faeces. Peak concentrations appeared in urine after 3.2 +/- 1.9 h and in faeces after 16.7 +/- 4.3 h. Altogether about 20% of the recovered metabolites were found in urine and about 80% in faeces. Using high-performance liquid chromatography (HPLC), several peaks of radioactive metabolites were found. Some metabolites were detected by enzyme immunoassay (EIA) using two different antibodies (corticosterone, 11beta-OH-aetiocholanolone). There was a marked diurnal variation with low levels of faecal corticosterone metabolites in the evening and higher values in the morning. This diurnal variation was influenced neither by the intraperitoneal injection of isotonic saline nor by ACTH. However, the administration of dexamethasone eliminated the morning peak for 2 days.     

Thermal comfort conditions in the morning and in the evening

Eight females and eight males participated each in 4 comfort experiments on 4 different days. Two experiments took place in the morning and two in the evening. In each experiment (21/2 hours) the preferred ambient temperature was determined for each subject by adjusting the ambient temperature according to his wishes. The subjects were sedentary. Skin temperatures, rectal temperature and evaporative weight loss were measured. Although the rectal temperature and the mean skin temperature were slightly higher in the evening than in the morning the subjects did not prefer an ambient temperature which was different from that in the morning. This indicates that the same thermal comfort conditions can be used from morning to evening.     

Effects of glucocorticoids on generation of reactive oxygen species in platelets

Since prednisolone and dexamethasone are known as potent anti-inflammatory agents, the effects of prednisolone and dexamethasone on production of intracellular reactive oxygen species (ROS) were investigated in human platelets. Platelet ROS were measured using the intracellular fluorescent dye dichlorofluorescein diacetate after activation of protein kinase C by phorbol-12-myristate-13-acetate (PMA) or 1-oleoyl-2-acetyl-sn-glycerol (OAG). NAD(P)H oxidase activity was measured photometrically. PMA and OAG significantly increased ROS in platelets (P<0.001). Prednisolone or dexamethasone concentration-dependently reduced the PMA-induced ROS production. The PMA-induced ROS increase was significantly reduced in the presence of 10 micromol/l prednisolone to 9+/-1% (n=31; P<0.001) or in the presence of 10 micromol/l dexamethasone to 9+/-1% (n=24; P<0.001). The inhibitory effect of prednisolone or dexamethasone could also be observed in the presence of the glucocorticoid receptor inhibitor, mifepristone (RU486). Administration of testosterone or aldosterone did not significantly reduce PMA-induced ROS increase. Prednisolone had no effect on platelet NAD(P)H oxidase activity. The inhibition of oxidative phosphorylation by sodium azide reduced platelets ROS to 8+/-1% (n=35). It is concluded that glucocorticoids, prednisolone and dexamethasone, directly inhibit production of intracellular ROS. This effect may contribute to the anti-inflammatory actions of these agents.     

Circadian variation and age dependence of human atrial natriuretic peptide levels in hospitalized patients

Circadian variation of plasma levels of human atrial natriuretic peptide (hANP) was studied in 8 patients less than or equal to 65 a of age (mean +/- SD = 43.8 +/- 13 a; 5 females, 3 males) and in 15 patients greater than 65 years of age (mean +/- SD = 81.4 +/- 5.7 a; 9 females, 6 males). Intraindividual variation was up to 40% relative to the day's mean level in both groups. A significant elevation of hormone levels in the evening was observed in patients greater than 65 years of age (P less than 0.002), no circadian rhythm could be detected in patients less than or equal to 65 years of age. All patients except the two eldest had average plasma levels of hANP within our normal range of 3-75 ng/l (N = 106; mean +/- SD = 29.9 +/- 15.3), found in healthy persons up to 65 years of age. We propose, that in the elderly hANP levels rise during the day by edema because of latent renal and/or cardial insufficiency. At rest, in the evening and during the night edema is eliminated by the well known nycturia, which might well be facilitated or at least partially caused by elevated levels of hANP.     

Morning-to-evening differences in oxygen uptake kinetics in short-duration cycling exercise

This study analyzed diurnal variations in oxygen (O(2)) uptake kinetics and efficiency during a moderate cycle ergometer exercise. Fourteen physically active diurnally active male subjects (age 23+/-5 yrs) not specifically trained at cycling first completed a test to determine their ventilatory threshold (T(vent)) and maximal oxygen consumption (VO(2max)); one week later, they completed four bouts of testing in the morning and evening in a random order, each separated by at least 24 h. For each period of the day (07:00-08:30 h and 19:00-20:30 h), subjects performed two bouts. Each bout was composed of a 5 min cycling exercise at 45 W, followed after 5 min rest by a 10 min cycling exercise at 80% of the power output associated with T(vent). Gas exchanges were analyzed breath-by-breath and fitted using a mono-exponential function. During moderate exercise, the time constant and amplitude of VO(2) kinetics were significantly higher in the morning compared to the evening. The net efficiency increased from the morning to evening (17.3+/-4 vs. 20.5+/-2%; p<0.05), and the variability of cycling cadence was greater during the morning than evening (+34%; p<0.05). These findings suggest that VO(2) responses are affected by the time of day and could be related to variability in muscle activity pattern.     

Influence of chronotype, season, and sex of subject on sleep behavior of young adults

The aim of this study was to investigate whether sex, season, and/or chronotype influence the sleep behavior of university students. Detailed data were collected on activity/rest patterns by wrist actigraphy combined with diaries. Thirty-four medical students (19 female and 15 male) were monitored by Actiwatch actometers for 15 consecutive days in May and again in November. The data of a modified Horne and Ostberg chronotype questionnaire, which were collected from 1573 female and 1124 male medical school students surveyed in the spring and autumn over an eight-year period, were evaluated. Actiwatch sleep analysis software was used to process the activity data with statistical analyses performed with ANOVA. We found no significant sex-specific differences in sleep efficiency, sleep onset latency, or actual sleep-time duration. However, we did find a difference in sleep efficiency between morning and evening types, with morning types having a higher sleep efficiency (87.9%, SD=1.3) than evening types (84.3%, SD=0.87%; p=0.007). Seasonal differences were also detected: the actual sleep-time duration in autumn was significantly longer (mean 6.9 h, SD=0.13 h) than in spring (6.6 h, SD=0.1 h; p=0.013). Evaluation of the chronotype questionnaire data showed that individuals with no special preference for morningness or eveningness (i.e., so-called intermediates) were most common. The distribution of chronotypes was related to the sex of subject. Men displayed eveningness significantly more often than women (28.9% males vs. 20.8% females; p<0.001), while females exhibited greater morningness (20.3% females vs.15.6% males; p<0.001). Sex influences chronotype distribution, but not actual sleep time-duration, sleep onset latency, or sleep efficiency. The latter, however, differed among chronotypes, while actual sleep-time duration was affected by season.     

Sexual dimorphism in the renin-angiotensin system in aging spontaneously hypertensive rats

In young adult spontaneously hypertensive rats (SHR), mean arterial pressure (MAP) is higher in males than in females and inhibition of the renin-angiotensin system (RAS) eliminates this sex difference. After cessation of estrous cycling in female SHR, MAP is similar to that in male SHR. The purpose of this study was to determine the role of the RAS in maintenance of hypertension in aging male and female SHR. At 16 mo of age, MAP was similar in male and female SHR (183+/-5 vs. 193+/-8 mmHg), and chronic losartan (40 mg.kg-1.day-1 po for 3 wk) reduced MAP by 52% (to 90+/-8 mmHg, P<0.05 vs. control) in males and 37% (to 123+/-11 mmHg, P<0.05 vs. control) in females (P<0.05, females vs. males). The effect of losartan on angiotensin type 1 (AT1) receptor blockade was similar: MAP responses to acute doses of ANG II (62.5-250 ng/kg) were blocked to a similar extent in losartan-treated males and females. F2-isoprostane excretion was reduced with losartan more in males than in females. There were no sex differences in plasma renin activity, plasma angiotensinogen or ANG II, or renal expression of AT1 receptors, angiotensin-converting enzyme, or renin. However, renal angiotensinogen mRNA and protein expression was higher in old males than females, whereas renal ANG II was higher in old females than males. The data show that, in aging SHR, when blood pressures are similar, there remains a sexual dimorphism in the response to AT1 receptor antagonism, and the differences may involve sex differences in mechanisms responsible for oxidative stress with aging.     

Prenatal androgens and the timing of seasonal reproductive transitions in sheep.

Both the onset of puberty in the lamb and the annual resumption of reproductive activity in adult male and female sheep are characterized by increased secretion of LH due to reduced responsiveness to steroid inhibition. However, the timing of puberty is sexually differentiated, for males undergo a reduction in sensitivity to steroid feedback at 10 wk of age, whereas females remain highly responsive to steroid inhibition until 30 wk. This sex difference is determined by androgens in utero. The present study was conducted to determine whether a sex difference exists in the timing of seasonal transitions in adult males and females. We compared serum LH in gonadectomized, estradiol-treated males (n = 7), females (n = 6), and androgenized females (n = 5) from blood samples collected twice weekly for one year. As determined by changes in the pattern of LH secretion, the onset and termination of the autumn breeding season were not different between males, females, and androgenized females (termination: 1 February +/- 4 days, mean +/- SE all groups; onset: males, 22 August +/- 4 days; females, 5 September +/- 18 days; androgenized females, 16 September +/- 10.5 days). However, there was a transient increase in LH (20 May to 23 June) in males, but not in females or androgenized females. Although no effects of prenatal testosterone were evident in the control of LH secretion in adult androgenized females, LH secretion in androgenized males was elevated throughout the nonbreeding season in 3 of 5 animals, indicating that exogenous testosterone may reduce seasonal increases in responsiveness to steroid inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)     

Morning versus evening power output and repeated-sprint ability

We investigated the effect of time-of-day on both maximal sprint power and repeated-sprint ability (RSA). Nine volunteers (22+/-4 yrs) performed a RSA test both in the morning (07:00 to 09:00 h) and evening (17:00 to 19:00 h) on different days in a random order. The RSA cycle test consisted of five, 6 sec maximal sprints interspersed by 24 sec of passive recovery. Both blood lactate concentration and heart rate were higher in the evening than morning RSA (lactate values post exercise: 13+/-3 versus 11+/-3 mmol/L(-1), p<0.05). The peak power developed during the first sprint was higher in the evening than morning (958+/-112 vs. 915+/-133 W, p<0.05), but this difference was not apparent in subsequent sprints, leading to a higher power decrement across the 5x6 sec test in the evening (11+/-2 vs. 7+/-3%, p<0.05). Both the total work during the RSA cycle test and the power developed during bouts 2 to 5 failed to be influenced by time-of-day. This suggests that the beneficial effect of time-of-day may be limited to a single expression of muscular power and fails to advantage performance during repeated sprints.     

Gastrointestinal and renal responses to water intake in the green-backed firecrown (Sephanoides sephanoides), a South American hummingbird

To maintain water balance, nectar-feeding vertebrates oscillate between meeting the challenges of avoiding overhydration and preventing dehydration. To understand how green-backed firecrowns (Sephanoides sephanoides) accomplish this, we examined the response of water-handling processes in the gastrointestinal tract (GIT) and kidney to different rates of water intake during the evening, night, and morning. Fractional water absorption in the GIT was independent of water intake rate (evening: 0.91 +/- 0.08; morning: 0.88 +/- 0.04). Consistent with this nonregulated water absorption, we found linear increases in water flux, fractional turnover of body water, and the rate of renal water loading as water intake rate increased during both the evening and morning. Despite these relationships, glomerular filtration rate (GFR) was insensitive to water loading (evening: 2.08 +/- 0.56 ml/h; morning: 1.84 +/- 0.68 ml/h) and less than the allometric expectation (2.92 ml/h). During the evening, fractional renal water reabsorption decreased linearly as the rate of water intake increased. At night, a period of natural fasting for hummingbirds, mean GFR was not different from zero (0.00 +/- 0.05 ml/h). These findings indicate that green-backed firecrowns eliminate excess ingested water by decreasing water reabsorption in the kidney; to conserve water, it appears that hummingbirds arrest whole kidney GFR, effectively preventing urinary water losses. After discounting evaporative water losses, our results show that hummingbirds rely principally on their renal system to resolve the osmoregulatory quandary posed by nectarivory.     

Non-invasive assessment of endocrine differences in day-old chicks (Gallus domesticus) by analysis of the immunoreactive oestrogen excreted in the egg

Oestrone, oestradiol and an uncharacterized polar fraction of oestrogenic substances were monitored by radioimmunoassay in Day-0 domesticated chickens (Gallus domesticus) after routine 21.5-day artificial incubation. Paired adrenals and gonads, blood serum and in-ovo excrement (allantoic urates plus cloacal expressions) were collected from 9 female and 10 male chicks. All samples were homogenized, hydrolysed and extracted with ether. Component oestrogens were isolated by celite:ethylene glycol column co-chromatography before assay. All egg excretory oestrogen measurements were higher (P less than 0.001) in females than in males. Oestradiol was the major excretory oestrogen in both sexes; oestradiol:oestrone ratios (mean +/- s.e.m.) in females and males were 18.45 +/- 2.42 and 3.03 +/- 0.37, respectively. Females had higher (P less than 0.01) total oestrogens for gonadal and adrenal homogenates and for blood serum samples than did the males; oestradiol was generally the major component.