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Biomedical subjects

N P Nekvasil

Publications and source records attributed to N P Nekvasil.

5 recordsLinked to original sources

Using round table labs to complement didactic lectures and experimental labs.

In an effort to teach the volume of material needed by physiology students as well as to enhance the student's understanding of physiological mechanisms, a combination of teaching methods is being used at the undergraduate level. Didactic lectures are used to convey the mass of information needed, experimental labs are used to aid the student in visualizing concepts, and situational labs [called round table labs (RTLs) here] are used to provide an opportunity for the student to learn, in a risk-free setting, how to answer application questions. The RTLs utilize discussion, writing, verbal communication, and analytic thinking. The major emphasis of the RTLs is on the integrative nature of physiology. Use of the RTLs bridges, the gap among the facts learned in the didactic lecture, the hands-on learning of the experimental lab, and the need to be able to apply what is being learned. Using this combination facilitates student learning such that the student reaches a level of proficiency with the subject beyond that which can be attained with the more traditional lecture-exam format.

Clinical Laboratory Techniques↗

The influence of dietary restriction, germ-free status, and aging on adrenal catecholamines in Lobund-Wistar rats.

Adrenal catecholamines (CA) were measured in 6-, 18-, and 30-mo Lobund-Wistar rats (LWR) maintained under germ-free or conventional conditions and fed either ad libitum or a restricted (70% of adult ad libitum) diet. Levels of dopamine (DA), norepinephrine (NE), epinephrine (E), and dihydroxymandelic acid (DHMA) were determined by HPLC-EC. Compared with values from 6- and 18-mo rats, mean adrenal weight, DA and NE content and concentration, and E content were increased in the 30-mo rats; E concentration was not. The ratio of E:NE declined in the 30-mo group. Germ-free status and dietary restriction had little effect in modulating these age-related changes. Reanalysis of adrenal weights of 30-mo rats revealed two clear subgroups, hyperplastic and non-hyperplastic; the data from hyperplastic adrenals revealed an exaggerated form of the "aged" CA profile, whereas data from the nonhyperplastic adrenals more closely resembled that of younger rats. Thus, aging in LWR is associated with adrenal hyperplasia and a tendency toward elevated adrenomedullary stores of DA and NE, while E stores are maintained near levels found in young rats.

Adrenal Glands↗

Plasma clearance, metabolism, and tissue accumulation of 3H-labeled catecholamines in trout.

Plasma clearance, metabolism, and tissue accumulation of [3H]norepinephrine (NE) and [3H]epinephrine (E) were measured after injection into the dorsal aorta of chronically catheterized trout, Salmo gairdneri. Sucrose, an inert volume marker, was injected with the catecholamines (CAs). Ion-exchange chromatography was used to separate unmetabolized CAs from deaminated and O-methylated metabolites in plasma. Both CAs are cleared from plasma at an exponential two-component rate. By 10 min postinjection, CA-specific extraction lowered plasma [3H]NE by 65% and [3H]E by 50%. Over 80% of the 3H remaining in plasma 10 min after injection was metabolized to O-methylated and deaminated products. Thus trout are able to quickly and efficiently lower circulating CA levels through tissue accumulation and metabolism. Kidney, liver, spleen, and atrium accumulate more CA than other tissues, although most tissues bind CA to some extent. Gills preferentially accumulate CAs over sucrose. Skeletal muscle has a low affinity for CAs but by virtue of its large mass may be an important organ in CA metabolism. NE is removed from the circulation faster, and more NE is bound to tissues than E. A blood-brain barrier for E but not NE was observed.

Animals↗

Extraction and metabolism of circulating catecholamines by the trout gill.

Extraction and metabolism of [3H]-norepinephrine (NE) and [3H]epinephrine (E) by the respiratory (efferent branchial) and filamental (venous) vasculature of the trout gill were examined using an isolated perfused arch technique in which outflow from the two circulations was separated. Deaminated and O-methylated metabolites in the effluent were identified by ion-exchange chromatography. Metabolism by tissue homogenates was also measured. Gill homogenates deaminate catecholamines (CAs) faster than homogenates of liver, kidney, and skeletal muscle; branchial O-methylation was comparable to that of liver and kidney. The perfused gill extracted 60% of a NE pulse and 47% of an E pulse. During continuous CA perfusion the gill removed greater than 30% of the NE from the circulation through extraction and metabolism; only 7% of the E was removed. The gill venous system extracts and metabolizes more CAs than the efferent. NE is the preferred substrate for extraction and metabolism. A mechanism is proposed whereby high circulating CA levels, common during stress, are maintained through CA-induced reduction in venous blood flow. After the stress is alleviated, CA levels begin to fall, flow to the venous pathway increases, and the rate of inactivation of circulating CAs increases.

Animals↗