Biomedical subjects
Publications and source records attributed to J France.
A theoretical exposition of methods for estimating the quantity of digesta in the rumen using digesta-flow markers and intraruminal sampling is given, with emphasis on the kinetic assumptions underlying each method. Single- and dual-marker approaches to estimating volume in steady and non-steady-state are presented.
Migraine occurring at menstruation is frequently difficult to treat. A 38-year-old woman with exceptionally severe menstrual migraine was treated by temporary ovarian suppression using Zoladex, a long acting luteinizing hormone-releasing hormone agonist. There was prompt relief of headache, and after several months of treatment the patient elected to undergo surgical oophorectomy with subsequent resolution of her migraine. A trial of reversible hypogonadism using an LHRH agonist may thus be helpful in predicting the result of surgical castration in this situation.
An indirect approach to quantification of the fibrolytic anaerobic fungi in the rumen is described. A mathematical model of the life cycle of anaerobic fungi, based upon observations of the life histories and growth kinetics of these organisms in vitro and in vivo, is constructed and solved in the steady-state to determine the population of particle-attached (substrate-associated) fungal thalli from the concentration of free-swimming zoospores in rumen liquid. The values obtained are broadly consistent with ruminal observations and with observations on faecal populations, which assume that a significant proportion of fungi leaving the rumen (as cysts or spores) can ultimately be accounted for in the faeces.
An analysis of the compartmental scheme used to determine the rate and extent of ruminal degradation of feeds is presented. Attention is given to the kinetic representation of the degradation of the potentially degradable fraction. Changing the kinetic order of the rate, and introducing indigestible substrate inhibition and microbial activity into its representation, are investigated. This leads to response functions such as the Gompertz and logistic for describing the cumulative disappearance of potentially degradable substrate during in-sacco and in-vitro incubation.
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A mathematical and numerical appraisal of the double-exponential model is presented, with particular reference to its ability to reproduce preset values of biological measures such as rumen and whole-tract mean retention times and faecal production rate. A complete, formal mathematical derivation is provided, with consideration given to a solution to the model when the two smallest rate constants are equal. It is concluded that any error introduced by using an approximation in deriving the double-exponential form is negligible in practice, and that the double exponential in logarithmic form is able to determine the relevant biological measures quite satisfactorily and speedily.
A mathematical integration of whole-body protein synthesis and degradation based on protein metabolism in 10 individual tissues in growing lambs is described. The tissues represented are adipose, central nervous system (CNS), gastrointestinal tract (GIT), heart, kidney, liver, muscle, pancreatic and salivary glands (PSG), reticuloendothelial system (RES) and skin, together with a blood pool of amino acids. The fluxes represented in the equations are generally assumed to follow simple or modified mass-action kinetics. The fractional rates for protein synthesis in each tissue were calculated from published values for lambs, where these were available, or alternatively derived using assumptions based on data obtained with rats. The initial protein content of each tissue and the fractional degradation rate were assigned values calculated using data from a slaughter experiment. The model was used to examine whole-body protein synthesis at different rates of growth and to compare the relative contributions of each tissue. The GIT (25-26%) and skin (23-26%) had the highest contributions to total protein synthesis, followed by muscle (21-26%), liver (13-14%), RES (6-7%) and PSG (3-6%), while adipose, CNS, heart and kidney together contributed less than 5%. These values agree reasonably well with experimental values, and thus the model can be used to examine the effect of different growth rates on protein metabolism and its associated energy costs.
A mathematical representation of the energy-requiring processes of protein turnover and Na+,K+-transport in the tissues of growing lambs is described. This model was then used to examine the relative contributions of these processes to ATP expenditure at two different growth rates (90-230 g/d). Protein turnover accounted for 19% of whole-body ATP expenditure at both growth rates examined, with the gastrointestinal tract (GIT), accounting for 25-27%, muscle for 21-26%, skin for 23-26% and liver for 13% of total protein turnover energy costs. The contribution of Na+,K+-transport increased from 18 to 23% of whole-body heat production as growth rate increased, with the GIT accounting for 39 and 50%, muscle for 17 and 10% and liver for 18 and 23% of total Na+,K+-transport costs at low and high nutrient inputs, respectively. Thus, protein turnover accounted for 19% of the increment in ATP expenditure due to the increased nutrient input at the higher rate of growth, while Na+,K+-transport accounted for 39%, and fat turnover and accretion accounted for 25%, leaving 17% of the ATP increment unaccounted for.
A double blind crossover study of transdermal oestradiol (50 micrograms/day) and ethinyl oestradiol (20 micrograms/day) was conducted with 25 postmenopausal women. Transdermal oestradiol increased circulating levels of oestradiol and oestrone. Both preparations favourably improved patients' symptoms and vaginal cytology, lowered gonadotrophin levels and urinary calcium loss and gave a satisfactory menstrual pattern. Transdermal oestradiol had no effect on measures of hepatic function whereas oral ethinyl oestradiol significantly altered levels of sex hormone binding globulin, plasma renin substrate and lipoproteins. Transdermal oestradiol has a comparable beneficial effect on postmenopausal symptoms to ethinyl oestradiol without the adverse effects on hepatic proteins.
The use of faecal marker concentration curves, in conjunction with compartmental analysis, is examined as a method for predicting faecal output in ruminants. Formulae for faecal production are derived for the various multicompartment models currently used to interpret marker concentration data. A comparison of observed and model-derived estimates of faecal dry matter production using three different markers is given for sheep consuming hay or a mixed diet.
A mathematical framework is presented for unifying and extending the various compartmental models and formulae used to calculate fractional protein synthesis and degradation rates in animals from data obtained by infusing labelled amino acids. It is shown how the various schemes can be derived as special cases of the product-precursor model or some three-pool variant. Three-compartment representations, which circumvent the need to measure the specific radioactivity of the precursor pool, are proposed. The mathematical solutions are generally presented in a form that is amenable to parameter estimation by non-linear least squares. The problems of measuring the true precursor pool for protein synthesis are addressed, and theoretical consideration is given to assaying aminoacyl-tRNA.
A mechanistic model of dairy cow metabolism is described. The model was constructed as part of a programme directed toward quantitative and dynamic analysis of concepts and data regarding factors which influence the partition of nutrients in lactating dairy cows. Sensitivity and behavioural analyses undertaken using the model indicate that concepts and data arising from tissue level experiments conducted in vitro can be used to structure and parameterize whole-animal models since the quantitative and dynamic behaviour of such a model is acceptable. These analyses indicate further that such models can be used to evaluate factors which influence patterns of nutrient utilization. By way of illustrating the model's utility regarding evaluation of concepts relating to the interpretation of energy balance experiments, results of a simulated energy balance experiment are presented. Apparent costs of milk synthesis are partitioned among biosynthetic costs, physiological costs, ion transport costs and the reductions in energy expenditures in synthesis of body components which accompany increasingly negative energy balances due to feed restriction.
Two models of lactating dairy cows were constructed by combining mechanistic models of digestion and metabolism reported previously and by adding elements to allow simulation of changes in tissue metabolic capacities over time. One model (day version) had an integration interval of 0.005 d and was suitable for simulation of within-day dynamics of nutrient supply and partition. The other (lactation version) had an integration interval of 1 d and was suitable for simulation of full lactation cycles. A number of simulation analyses were conducted to characterize and evaluate the models, to examine quantitative and dynamic properties of mechanisms which influence partition of nutrients, to identify aspects requiring further study, and to illustrate the potential usefulness of mechanistic, as compared to empirical, models in analyses of energy balance in lactating dairy cows.
A new suction catheter, designed to deliver alternately oxygen or suction, prevented episodes of hypoxia and hyperoxia in a group of infants during endotracheal suctioning. Twenty infants received both conventional endotracheal suctioning and suctioning by the new catheter. The infants had a maximal change from a presuctioning transcutaneous oxygen (PtcO2) of 12 +/- 8 torr and required 3.1 +/- 2 min to regain their presuctioning oxygenation level compared to a maximal change of 21 +/- 10 torr (p less than .05) and a stabilization time of 5.3 +/- 2.6 min (p less than .05) in the conventionally treated group. Three study infants experienced an abnormal PtcO2 (either less than 40 or greater than 90 torr), while 13 control infants suffered these abnormalities (p less than .01). The use of this new suction device effectively reduced the exposure of this group of infants to episodes of aberrant oxygen states and allowed for a shorter recovery time.
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1. Pure swards of perennial ryegrass (Lolium perenne L. cv. Melle) or white clover (Trifolium repens L. cv. Blanca) were harvested daily as either primary growth (May-June) or mid- (July) and late- (August-September) season 4-week regrowths and offered to Friesian steers at two levels of feed allowance (18 and 24 g dry matter (DM)/kg live weight), to examine the effect of forage species and stage of harvest on nutrient digestion and supply. 2. The early- and mid-season grasses had low nitrogen (23 g/kg DM) and high water-soluble carbohydrate (169 g/kg) contents whilst the late-season grass had a higher N content (28 g/kg). All clover diets had high N (average 45 g/kg) and low water-soluble carbohydrate (89 g/kg) contents, and DM digestibility on all diets ranged from 0.77 to 0.83 (mean of two feeding levels). 3. Mean total rumen volatile fatty acid concentrations were significantly (P less than 0.001) higher on the clover diets, whilst on the grass diets molar proportions of propionate showed a slight but not significant decline with advancing season and tended to be higher than those on the clover diets. Mean rumen ammonia concentrations were significantly (P less than 0.001) lower on the early- and mid-season grasses (59 mg NH3-N/l) than the late-season grass (242 mg/l) and early-season clover (283 mg/l) which were all significantly (P less than 0.01) lower than the mid- and late-season clovers (372 and 590 mg/l) respectively. 4. Rates of organic matter (OM) and N digestion in the rumen were estimated using established nylon-bag techniques and found to be high on all diets, but significant effects due to forage species (clover greater than grass; P less than 0.001) were detected, whilst overall potential degradability in the rumen exceeded 0.89 for both OM and N on all diets. 5. Significantly (P less than 0.001) more OM entered the small intestine of calves fed on white clover (10.2 g/kg live weight) than those fed on ryegrass (8.33 g/kg) and similar effects due to level of feeding (g/kg; low 7.9, high 10.6; P less than 0.05) and stage of harvest (g/kg; early 8.3 v. mid 10.0, late 9.50; P less than 0.05) were also detected.(ABSTRACT TRUNCATED AT 400 WORDS)
A unifying mathematical analysis of the use of compartmental models with and without time lags is given, with particular reference to the use of such models for digesta movement along the gastro-intestinal tract of the ruminant. First the generalized compartmental model without time lags is developed, and then it is shown how discrete time lags may be incorporated into this formalism. The important relationship between distributed lags, especially the gamma-distributed time lags, and the equivalent compartmental scheme, is emphasized. It is shown how distributed time lags can be included in a general compartmental model. The treatment covers, as special cases, some widely used models, and shows their relationship to each other and to other possible models. Finally a compartmental interpretation is outlined for a recently proposed double-exponential model.
A multicompartmental model, which assumes first-order kinetics, is proposed to describe digesta flow along the gastrointestinal tract of ruminants. Solution of the model yields a multiplicative equation, containing a single-exponential term and a double-exponential term, for describing faecal outflow rate. The logarithmic transformation of the equation was fitted to eighty-two excretion curves obtained after the administration of marker into the rumen of cattle and sheep, and compared with other published models. It was found to be superior to the other models in that it fitted all the data sets successfully.