Comparative biochemistry and physiology. Part C, Pharmacology, toxicology & endocrinology最新文献

Danger from snake bites, especially those of Elapidae, pose a public health problem in a large number of tropical and sub-tropical countries. Since the advent of serotherapy, the morality rate has decreased, but suitable sera are not always available, explaining the usefulness of developing symptomatic treatments. The present study is a test of the preventative and curative efficacy of anticholinesterases in the treatment of Naja haje haje venom envenomation. It is clearly shown that the early use of these products leads to a considerable increase in the LD50 in mice having undergone experimental envenomation.

Dopamine administered continuously through osmotic pumps altered the PHA wattle response and in vitro leukocyte capillary tube migration in UNH 105 chickens. The PHA wattle response was suppressed significantly by 48 hr exposure to dopamine at a dose of 1 microgram/hr. Administration of 10 micrograms/hr dopamine for 48 hr enhanced significantly in vitro leukocyte migration.

Glucagon, dibutyryl cAMP (Bt2cAMP) and 8-(4-chlorophenylthio) cAMP (CptcAMP), singly or when combined, stimulated tyrosine aminotransferase (TAT) activity in 17-day-old chick embryos in ovo. Maximal induction was produced within 4 hr of injection of the inducers. The effects of glucagon and the cAMP analogues were not additive. Glucagon administration was accompanied by a rapid increase in hepatic cAMP concentration which remained elevated for at least 4 hr. The stimulated increase in TAT activity elicited by the hormone or cyclic nucleotide was prevented by injection of cycloheximide or cordycepin. These results are discussed vis-à-vis the possible regulation of TAT in ovo by physiological concentrations of glucagon and the likely role of cAMP as a second messenger in this process during chick embryogenesis.

A major component of the cellular stress response entails the induced synthesis of a suite of stress proteins under environmentally adverse conditions that functions to protect organisms from environmentally induced damage. Here, we examined induction of the stress response in the embryos of the sea urchin Strongylocentrus purpuratus under a combination of environmentally realistic conditions. First, we examined the response elicited over a range of free cupric ion activities, (Cu2+), using a metal buffer system to control trace metal speciation. We observed no pronounced differences in translational patterns in embryos exposed to free cupric ion activities, (Cu2+), of 10(-13)-10(-9) M by metabolic labeling, 1-dimensional electrophoresis and autoradiography. Further separation by 2-dimensional electrophoresis, however, revealed electrophoretically discernable variants of several groups of proteins at the higher Cu concentrations and the synthesis of a 60 kDa protein at (Cu2+) of 10(-9) M. In addition, there were differences in the stress response induced by heat-shock treatment in embryos cultured in seawater with different Cu concentrations; radiolabel was incorporated into a greater number of cellular proteins in embryos at lower (Cu2+) and the induced synthesis of stress proteins was greater. These data suggest that elevations in (Cu2+) impair the ability of the embryos to mount the stress response upon exposure to elevated temperatures and that Cu may alter critical developmental pathways by inhibiting the synthesis of regulatory proteins. Such effects on gene expression can result in manifestations that have been widely attributed to Cu toxicity, including developmental abnormalities and increased sensitivity to environmental extremes. We suggest that the particular sensitivity of embryonic systems upon exposure to multiple stressors may be a consequence of these mechanisms.

[3H]Choline was taken up by tissue slices of the cestode Hymenolepis diminuta by sodium-dependent and sodium-independent mechanisms. The sodium-dependent uptake was saturable, against an apparent concentration gradient, and by analysis of the kinetics of uptake could be delineated into a high-affinity choline uptake (HAChU) mechanism (Kt of approximately 2.0 microM; Vmax of approximately 0.15 pmol/mg wet weight tissue/min), and a low-affinity choline uptake (LAChU) mechanism (Kt of approximately 20.0 microM and a Vmax of approximately 2.0 pmol/mg wet weight tissue/min). Unlike the HAChU system, the LAChU system was unaffected by potassium. Furthermore, the responses of the LAChU and the HAChU transporters to pharmacological agents were distinctive, indicating that these transporters are two separate entities. Moreover, the entry or exit of choline via the LACh transporter was dependent upon the direction of the sodium gradient. Furthermore, the majority of released radiolabel from preloaded [3H]choline was associated with choline and was via a proteinaceous transporter. The present study is the first to provide direct evidence for a partial chemosmotic coupling of a LAChU system to the sodium electrochemical gradient.

The effect of rat atrial natriuretic peptide (rANP) on hormonal stimulated osmotic water permeability (Jw, hydrosmotic effect) and net ion transport (short-circuit current, SCC, natriferic effect) was studied on toad skin, a tissue with functional similarities to the mammalian distal nephron, in order to assess actions on transport mechanisms. Rat atrial natriuretic peptide, rANP-99-126 (rANP) inhibited stimulated SCC and Jw to submaximal concentrations of arginine vasotocin (AVT) at a site before cyclic AMP generation. The angiotensin-converting enzyme inhibitor (ACEI) MK-422 did not modify the inhibitory effect of ANP in the stimulated Jw.

The importance of thyroid hormones (TH) in the normal development of muscles has been repeatedly postulated. The effects of physiological TH doses on ornithine decarboxylase (ODC) and protein synthesis in muscle cells have been studied using cell cultures prepared from 11-day-old chick embryos. Triiodothyronine nuclear receptors in primary muscle cell culture were characterized on the basis of the specific binding analysis as a single receptor class with the equilibrium dissociation constant Kd = 1.2 +/- 0.4 x 10(-10) mol/l and binding capacity Bmax = 0.21 +/- 0.09 fmol/micrograms DNA. While the physiological amounts of both triiodothyronine (T3) and thyroxine (T4) stimulated ODC activity after 2 hr of treatment, only T3 had the same stimulatory effect after 4 hr of treatment. Twenty-four hour exposure of muscle cell culture to TH did not change ODC activity. The incorporation of [3H]leucine into proteins was elevated only after 120 hr incubation in the presence of T4. Application of T4 caused also an increase in the protein content after 24 hr.