Incomplete Uptake Research Articles

Effects of dietary fat on metabolic disorders and reproductive performance of dairy cattle

Improved reproductive performance and reduced incidence of metabolic disorders have been postulated to be benefits of feeding supplemental fat to dairy cows. Increased plasma nonesterified fatty acid concentrations during fat supplementation may result from incomplete tissue uptake of fatty acids after lipoprotein lipase hydrolysis of very-low-density lipoprotein triglyceride; however, evidence suggests that net adipose tissue triglyceride hydrolysis may be increased during fat supplementation. Plasma 3-OH-butyrate concentrations remain relatively constant during fat supplementation but may have a tendency to be reduced if fat is supplemented to cows having relatively high basal plasma 3-OH-butyrate concentrations. Because plasma ketone levels usually increase when nonesterified fatty acid concentrations are elevated, it is hypothesized that potential antiketogenic effects of added fat are due to a glucose sparing effect. Supplemental fat does not seem to reduce hepatic lipid infiltration near the time of calving. Potential mechanisms by which supplemental fat may improve reproductive performance include stimulation of prostaglandin F2 a synthesis and secretion and enhanced utilization of blood cholesterol for progesterone synthesis. Days postpartum until first ovulation and luteal function of dairy cattle have been related to energy balance during the first 3 wk postpartum. Energy balance data for early lactation cows fed supplemental fat are not plentiful; however, slight but statistically nonsignificant increases have been observed when feeding fat. Cows fed supplemental fat that experience improved energy balance may begin to cycle sooner because of enhanced follicular growth and development. Applied studies examining the effects of supplemental fat on reproductive performance have provided inconsistent results.

Pharmacokinetics of pafenolol in the rat: A suitable model for studying absorption mechanisms of a drug exhibiting unusual absorption properties in man

The pharmacokinetics of pafenolol, a highly selective beta 1-adrenoceptor antagonist, have been studied in starved and unstarved rats. Separate groups received intravenous doses (0.3 and 3.0 mumol kg-1) and oral doses (1 and 25 mumol kg-1). The systemic clearance of pafenolol was constant in the dose range investigated where the absolute oral bioavailability increased from 15 to 27 per cent in the starved and from 9.1 to 21 per cent in the unstarved rats, when the oral dose was raised from 1 to 25 mumol kg-1. The blood concentration profile after an oral solution of pafenolol exhibited two peaks in the majority of the rats. The major part of the absorption was associated with the second peak which appeared about 4 h after dosing in both starved and unstarved rats. Food lowered the degree of bioavailability and shifted the tmax1 to about 1 hour compared to half an hour in starved rats. The low bioavailability was primarily due to incomplete uptake from the gastrointestinal tract. Our study shows that pafenolol is absorbed in a similar way to that in man. The mechanisms behind the dose-dependent bioavailability and the two peaks in the absorption profile after an oral solution will be further explained in the rat.

Absence of postnatal death among motoneurones supplying the inferior gluteal nerve of the rat

Motoneurones innervating the caudal part of the gluteus maximus muscle of 0–2 day, 10–12 day and 2–3-month-old rats were labelled by a half-hour application of a solution of 30% horseradish peroxidase (HRP) and 2% lysophatidylcholine delivered by suction electrode to the cut inferior gluteal nerves. The numbers of motoneurones labelled 24–48 h later were not significantly different in the 3 age groups (mean = 58.75, 54.0, 57.5, respectively). When a simple 30% HRP solution was used in adult rats, the number of motoneurones labelled was significantly less (mean = 48.75). In contrast, application of 0.5 μl of HRP in a pledget of gelfoam to either the cut or uncut inferior gluteal nerve of neonates labelled large numbers of motoneurones, presumably by diffusion into nearby muscles. It is concluded that no death of motoneurones innervating the gluteus maximus muscle occurs postnatally, and that spread of HRP to neighbouring muscles can give rise to spuriously high motoneurone counts in neonates, and that incomplete uptake or transport of HRP in adults can lead to incorrectly low counts.

Particle-Size-Conversion Efficiency and Contaminant Concentrations in Lake Ontario Biota

The particle-size-conversion efficiency (log food consumption/production divided by log predator prey size ratio) is shown to be directly related to the relationship between the concentration of persistent contaminants accumulated primarily through the food chain and body size for organisms in pelagic ecosystems. The difference between particle-size-conversion efficiency for biomass and that for the contaminant gives the slope of the relationship between log contaminant concentration and log body size. This provides a useful theoretical framework for analyzing contaminant concentrations in aquatic biota without the need for specifying trophic level but still incorporating the idea of food chain accumulation. Concentrations of PCB, DDT, and mercury were examined in aquatic organisms from Lake Ontario, ranging in size from zooplankton to large salmonids (a 108 -fold range in dry weight). The slope of the double log plot of concentration versus weight varied from 0.20 to 0.22 for PCB and DDT and was approximately equal to 0.13 for mercury. This indicates that mercury is accumulated less efficiently through the food chain than PCB or DDT. After correcting for incomplete uptake and retention of the contaminant, an estimate of particle-size-conversion efficiency for biomass of about 0.26 was obtained, which agrees reasonably well with previous estimates obtained from growth efficiency experiments and analysis of particle-size spectra. These calculations indicate that potential fish production in Lake Ontario is ~ 120-fold lower than zooplankton production (for fish averaging 108-fold larger in body size as compared to zooplankton).Key words: particle-size-conversion efficiency, PCB, DDT, mercury, zooplankton production, fish production

Mechanism(s) of altered mitochondrial calcium transport in acutely ischemic canine hearts.

Studies were undertaken to determine the mechanisms leading to altered mitochondrial function in ischemic myocardium. A new procedure has been developed to routinely isolate 60-70% of the total mitochondrial protein from heart tissue. After 1 hour of ischemia, mitochondria exhibit decreases of more than 50% in phosphorylating respiration for both NADH- and succinate-linked substrates compared to controls. However, no significant decreases in the efficiency of mitochondrial ATP synthesis (ADP:0) or ATPase activity are observed. Rates of substrate-driven Ca2+ uptake exhibit decreases greater than that seen with phosphorylating respiration with incomplete uptake and premature release of Ca2+. Spectrophotometric measurements in ischemic heart reveal rapid oxidation or loss of mitochondrial NADH with marked "swelling" of the inner membrane compartment; both changes parallel the loss of Ca2+. Significant losses in intramitochondrial adenine nucleotides also are found. Mitochondrial retention of accumulated Ca2+ can be restored by addition of small amounts of exogenous adenine nucleotides (ATP or ADP) with concomitant attenuation of both NADH oxidation and "swelling." The data indicate that, following 1 hour of ischemia, the efficiency of mitochondrial ATP production is still relatively intact whereas both electron transport chain activity and calcium transport are severely compromised. These decreases appear to be related to selective membrane damage in the mitochondrial inner membrane.

Absorption, Distribution, and Form of Ca in Relation to Ca Deficiency (Tip Burn) of Sugarbeets1

Sugarbeet plants (Beta vulgaris L.) were grown in the greenhouse in nutrient solutions containing 0.33 and 5.0 meq Ca/liter. Carrier‐free 45Ca was added at transplanting to nutrient solutions of a set of sugarbeet pots and the rest were left untreated. Two weeks later, the 45Catreated pots were harvested and another set was treated with 45Ca. This process was repeated for three more harvests with addition of 45Ca at 2, 4, and 6 weeks and harvesting, respectively, at 4, 6, and 8 weeks after transplanting. All in all, there were four 45Ca additions and four harvests. At each harvest, the various parts of the plant were assayed for 45Ca that was associated with Ca soluble hi 80% alcohol, as chloride and nitrate, in water as salts of organic acids, in 1 N NaCI as pectate, in 2% CH3COOH as di‐ and triphosphate, in 0.6 N HCI as oxalate and insoluble residue.Symptoms of Ca deficiency were associated with an incomplete uptake of Ca from the nutrient solution, a high rate of Ca consumption by the storage roots, and a failure to translocate sufficient Ca to the tops to support rapid young leaf growth, but were not associated with the formation of an insoluble Ca compound(s). Since 45Ca was detected in various forms in all parts of Cadeficient sugarbeets, the pathway for Ca remained functional even as the symptoms increased in severity.Calcium phosphate, rather than Ca oxalate, was at a high concentration hi all parts of the Ca‐deficient and Ca‐sufficient plant, except Ca oxalate exceeded Ca phosphate in the mature and old blades of the Ca‐sufficient plant. If Ca immobility inhibits the transport of Ca from older to younger parts, then the formation of Ca phosphate could be a limiting factor under deficiency and not under sufficiency conditions.

The uptake curve in tracer kinetics

The uptake function for a stationary, open, compartmental system is shown to be equal to the steady-state value less the washout function for the same system: g in( t)= G− g out( t). This relation between an uptake experiment and a washout experiment and the established convexity of the washout curve directly proves that uptake curves must be concave. The usual semilogarithmic plot of the tracer uptake function is shown to be equivalent to graphing the normalized washout function, whose logarithmic convexity has been shown previously for a large class of systems including passive systems. Underestimation of G in such a system may cause this curve to be log concave. It is shown, however, that the complete uptake curve and thus the correct G in all systems can be constructed from an incomplete uptake curve and the elution curve starting from the end point of the uptake experiment.