Development of glomerular filtration rate and electrolyte and osmolal clearance in the late-embryonic and newly hatched chicken

Summary Techniques have been developed for collection of urine in embryonic and newly hatched chickens for the purpose of studying the development of renal function.The reliability of EDTA-⁵¹Cr as a substitute for inulin-¹⁴C in the determination of GFR was studied. Since inulin and EDTA-⁵¹Cr clearances in the hatched chicken averaged 1.61±0.23 (S.E.) ml/min per kg body weight and 1.58±0.27 ml/min per kg body weight, respectively, EDTA-⁵¹Cr clearance was considered a suitable measure of GFR.GFR increased significantly in the first few days after hatching. Filtration rate was 0.068±0.008 (S.E.) ml/min per g kidney weight in the embryo and increased to 0.148±0.008 ml/min per g shortly after hatching. By nine days after hatching GFR had risen to 0.290±0.015 ml/min per g, a value comparable to that reported for the adult.Clearances of sodium, potassium, chloride and total osmolyte also increased with age. When these clearances were corrected for changing glomerular filtration rates the embryonic chicks were found to excrete a greater percentage of the filtered load. These results show that adult levels of glomerulo-tubular balance are not attained until after hatching.A preliminary report of this work has already been published [3].     

Force enhancement by PEG during ramp stretches of skeletal muscle

We have investigated the effects of a stronger actomyosin bond on force (Ps) during rapid stretch of active permeabilized rabbit psoas muscle fibers as a function of temperature from 5 to 30 degrees C. The strength of the actomyosin bond is enhanced by addition of polyethylene glycol (PEG), especially in pre-powerstroke states [Chinn et al. (2000) Biophys J 49: 437-451]. We have hypothesized that such states produce much of the force when activated muscles are stretched [Getz et al. (1998) Biophys J 75: 2971-2983]. Addition of PEG to activated fibers produced a small increase in isometric tension, Po (50-90 kN/m2), which was approximately independent of temperature. In contrast PEG produced a dramatic increase in Ps at low temperatures (200-300 kN/m2), but a modest increase at higher temperatures (70-90 kN/m2). We also measured Ps and Po in solutions containing the phosphate analog aluminum fluoride (AlF4) with and without PEG. In the absence of PEG, AlF4 reduced Po much more than Ps. Addition of PEG did not enhance Po, but enhanced Ps significantly. The contrasting effects of PEG on Ps and Po, and the effect of temperature can be explained by a model in which stretch force is produced by pre-powerstroke cross-bridges whose maximum distension is increased by PEG, and isometric force is produced by strongly bound cross-bridges whose bond strength is also enhanced by PEG, but to a lesser extent.     

Rabbit anti-EL4 serum. A reagent which discriminates between murine cytotoxic and suppressor cells.

Antisera against the C57B1 (H-2b) mouse lymphoma, EL4, were prepared in rabbits. After absorption with mouse liver, red cells and thymocytes, the antisera appeared to be cytotoxic for a subpopulation of peripheral T cells. The absorbed antisera blocked the immunosuppressive function observed when spleen cells from mice undergoing a graft versus host reaction were added to cells responding in vitro to sheep erythrocytes. This antiserum was unreactive against the cytotoxic cells also induced in this system. These results substantiate our previous finding that these antisera are specific for T-suppressor as opposed to T-helper or cytotoxic lymphocyte subpopulations.     

Vibration-induced changes in movement-related EMG activity in humans

The effect of muscle tendon vibration during voluntary arm movement was studied in normal humans. Subjects made alternating step flexion and extension movements about the elbow. A small vibrator was mounted over either the biceps or the triceps muscle and vibration was applied during flexion or extension movements. The vibrator was turned off between movements. After a period of practice, subjects learned the required movements and were able to make them with their eyes closed. Application of vibration to the muscle antagonist to the movement being performed produced an undershoot of the required end-movement position. The undershoot was 20-30% of the total movement amplitude. In contrast, vibration of the muscle agonist to the movement resulted in no change in movement end position. The vibration-induced undershoot was associated with an increase in the EMG activity of the vibrated (antagonist) muscle and a resultant increase in the ratio of the antagonist to agonist EMG activity. The increase in antagonist EMG produced by the vibration occurred with a latency of approximately 60 ms from vibration onset. The observed results are consistent with vibration-induced activation of muscle spindle receptors in the lengthening muscle during movement. It is suggested that, during movement, the sensitivity of the spindle receptors in the shortening muscle is decreased and the information concerning limb position during movement comes primarily from the lengthening muscle.     

An analysis of the outcome of microsurgical and laparoscopic adhesiolysis for infertility

We evaluated 81 women with adnexal adhesions and no male factorwho underwent microsurgical (n = 59) and laparoscopic (n = 22)adhesiolysis for infertility. The cumulative conception ratesfor all 81 patients at 12 and 24 months were 41 and 44% respectively.The impact of the following variables on cumulative conceptionrates for all patients was examined: age, duration of infertility,type of infertility, ovulatory status, presence and stage ofendometriosis, adhesion grade, adnexal status (bilateral orunilateral disease, unilateral tubal absence), history of previoussurgery, history of pelvic inflammatory disease and treatmentmodality (microsurgical versus laparoscopic). The results ofindependent comparisons of subgroups within each of these variablesmay be biased because of the interrelationships between thevariables. To overcome this problem, a stepwise Cox's proportionalhazards regression analysis was employed. Our analysis showedthat the single most significant variable influencing the cumulativeconception rates was the duration of infertility (P < 0.005).For every additional year of infertility, the probability ofpregnancy after adhesiolysis (microsurgical or laparoscopic)was reduced by 20%. Cumulative conception rates at 12 and 24months after microsurgical adhesiolysis were 36 and 40% respectively,while after laparoscopic adhesiolysis they were 57% at 12 and24 months. When imbalances were adjusted between the two treatmentgroups, there was no statistically significant difference betweenthe cumulative conception rates for microsurgical and laparoscopicadhesiolysis.     

Screening methods for thyroid hormone disruptors

The U.S. Congress has passed legislation requiring the EPA to implement screening tests for identifying endocrine-disrupting chemicals. A series of workshops was sponsored by the EPA, the Chemical Manufacturers Association, and the World Wildlife Fund; one workshop focused on screens for chemicals that alter thyroid hormone function and homeostasis. Participants at this meeting identified and examined methods to detect alterations in thyroid hormone synthesis, transport, and catabolism. In addition, some methods to detect chemicals that bind to the thyroid hormone receptors acting as either agonists or antagonists were also identified. Screening methods used in mammals as well as other vertebrate classes were examined. There was a general consensus that all known chemicals which interfere with thyroid hormone function and homeostasis act by either inhibiting synthesis, altering serum transport proteins, or by increasing catabolism of thyroid hormones. There are no direct data to support the assertion that certain environmental chemicals bind and activate the thyroid hormone receptors; further research is indicated. In light of this, screening methods should reflect known mechanisms of action. Most methods examined, albeit useful for mechanistic studies, were thought to be too specific and therefore would not be applicable for broad-based screening. Determination of serum thyroid hormone concentrations following chemical exposure in rodents was thought to be a reasonable initial screen. Concurrent histologic evaluation of the thyroid would strengthen this screen. Similar methods in teleosts may be useful as screens, but would require indicators of tissue production of thyroid hormones. The use of tadpole metamorphosis as a screen may also be useful; however, this method requires validation and standardization prior to use as a broad-based screen.     

The dissemination of a smoking cessation program to 23 antenatal clinics: the predictors of initial program adoption by managers

Objective: To investigate whether the method of dissemination, antenatal clinic practice norms for smoking intervention and subjective evaluation of the attributes of a new smoking cessation program are associated with a nurse unit manager's initial decision to adopt the new program.
Method: Twenty-three hospital clinics were randomly allocated to two groups which received the program either by simple or intensive dissemination methods. Simple dissemination involved a mailout of the 'Fresh Start' program and intensive dissemination involved a mailout which was enhanced by personal contact with midwifery facilitators who provided support and training for the program. It was hypothesised that intensive dissemination would improve program adoption compared to simple dissemination. It was also hypothesised that managers' perceptions of the program and clinic smoking intervention practice norms would predict program adoption. A hierarchical regression analysis was used to examine the association between these variables and the adoption of program components.
Results: The results indicated that the method of dissemination and the managers' perceptions of the program are significant predictors of program adoption.
Conclusions: Although clinic practice norm for smoking cessation education is not a significant predictor of program adoption, it appears to mediate managers' perceptions of the program.