Comparative Biochemistry and Physiology Part A: Physiology最新文献

Maintenance of a hydrated integument is essential to the normal function of amphibian skin, and amphibians have developed mechanisms to minimize cutaneous dessication. The present work was conducted on skins of amphibians exhibiting a clear preference for either of two such mechanisms to study the influence of such mechanisms on the characteristics of epithelial transport. The response to norepinephrine (NE) was studied in isolated skins of a semiaquatic frog (Leptodactylus chaquensis), known to maintain indispensable skin moisture by secreting a superficial film of mucus via sympathetic stimulation of skin glands, and a terrestrial toad (Bufoarenarum), which replenishes a superficial film of fluid by drawing soil water upward by capillarity. In L. chaquensis skin, NE 5.0 × 10⁻⁷ M, induced slow onset, sustained increases in short-circuit current (SCC) and transepithelial conductance, which were abolished by amiloride, a specific sodium transport inhibitor. At 1.2 × 10⁻⁵ M, the response to NE exhibited a faster onset and a shorter time course. The SCC response also became insensitive to amiloride and could thus be induced by exposing the skin to NE in the presence of the inhibitor. The response was also greatly reduced in the absence of chloride, strongly suggesting a greater dependence on the glandular secretory response. In B. arenarum skin, the response to NE was far more sensitive to amiloride, regardless of the concentration of NE used. Induction of a response in the amiloride-blocked skin required a 10-fold higher concentration of NE, and the resulting effect was still considerably smaller than that observed in the skin of L. chaquensis after the same treatment. The number of mucous glands per unit area in B. arenarum skin was found to be around one-fifth of that observed in L. chaquensis, thus in part explaining the difference in the magnitude of the responses. The response of the skin of L. chaquensis to NE in the presence of sulfate was found to be consistent with the postulated involvement of frog skin glands in sulfate excretion. In contrast, this function was not evident in the skin of B. arenarum. The pattern of response of B. arenarum skin to all concentrations of NE tested closely resembles that seen after exposure to agents known to activate a cyclic AMP-dependent, high-permeability Cl⁻ pathway previously described by us in the skin of the toad. Our observations underscore the physiological differences existing in skins from different species, particularly regarding the relative importance of the glandular component of transport.

Pelage growth cycles are regulated by circulating prolactin in many mammals, but the intercellular mediators of this signaling are unknown. Binding sites for insulin-like growth factors (IGFs) were examined in sheep skin to show changes in distribution and abundance of IGF receptors associated with a prolactin stimulus and the subsequent hair follicle growth cycle. Follicle cycles were induced in New Zealand Wiltshire ewes by a surge in plasma prolactin following a 4-month period of prolactin suppression with bromocriptine. Eight treated and three control sheep were slaughtered at intervals over 43 days during the follicle growth cycle. At 12–20 days after the elevation of prolactin, wool follicles passed through brief catagen and telogen phases, followed by a return to anagen. IGF binding sites were localized in skin sections by incubation with ¹²⁵I-IGF-I or ¹²⁵I-IGF-II. Displacement with competitive binding inhibitors (unlabeled IGF-I, IGF-II, des(1–3)IGF-I, des(1–6)IGF-II, or insulin) and affinity cross-linking showed that these binding sites were predominantly IGF type 1 and type 2 (mannose-6-phosphate) receptors. The radiologands bound especially to follicle germinal cells and prekeratinocytes. Increases in specific binding of both radioligands were observed after the rise in prolactin, but prior to anatomical changes in follicles associated with cessation of growth. For IGF-I, highest binding density was observed during catagen in the germinal matrix and dermal papilla cells. For IGF-II, peak density occurred during late anagen/early catagen in the germinal matrix and during telogen in the dermal papilla. These cycle associated changes in receptor availability suggest that IGF receptors are involved in control of the wool growth.

The hematological properties and the oxygen-transport system of the antarctic fish Pleuragramma antarcticum were investigated. Most blood parameters are at the lower end of the range of values known for red-blooded antarctic fish, suggesting a link with the sluggish mode of life of this species. P. antarcticum is the only species of the family Nototheniidae and of the suborder Notothenioidei having three major hemoglobins, which were isolated and fully characterized. The complete amino acid sequence of the α- and β-globin chains was determined. The three hemoglobins showed strong Bohr and Root effects, and their oxygen-binding properties were differently regulated by temperature. None of the three hemoglobins of P. antarcticum can be considered as evolutionary (or larval) remnants. Therefore, this oxygen-transport system is one of the most specialized ever found in fish. The data suggest a strong relationship between hematological/biochemical adaptation and life style.

Over the last 20 years, dietary nitrate has been implicated in the formation of methemoglobin and carcinogenic nitrosamines in humans. This has led to restrictions of nitrate and nitrite levels in food and drinking water. However, there is no epidemiological evidence for an increased risk of gastric and intestinal cancer in population groups with high dietary vegetable or nitrate intake. A reevaluation of our currently very negative perception of dietary nitrates comes from recent research into the metabolism and enterosalivary circulation of nitrate in mammals. These studies showed that nitrate is converted to nitrite in the oral cavity that then “fuels” an important mammalian resistance mechanism against infectious diseases. Moreover, there is now evidence that the conversion of nitrate into oxides of nitrogen prevents the formation carcinogenic nitrosamines.

The effect of the hypertrehalosemic hormones, HTH-I and HTH-II, on free fatty acid levels in trophocytes prepared from Periplaneta americana fat body by collagenase treatment was investigated. Following a challenge from either of the hormones the content of palmitic, stearic, oleic, and linoleic acid in the trophopcytes increased. The increase in free fatty acid concentration due to the action of the synthetic hormones was generally in the range of 40–95% for each of the four fatty acids. Crude corpus cardiacum extract containing the native hormone also had a stimulatory effect, which was comparable to that of the synthetic hormones. In the intact insect the injection of synthetic hormone was followed by an increase in the level of the four fatty acids in the hemolymph. HTH-II was more potent in this respect than HTH-I. Free fatty acids in the mycetocytes and urate cells did not respond to either of the synthetic hormones.

The biological requirements of animals change considerably during development from the egg to the (early) adult stage. Some basic physiological requirements (respiration, excretion of metabolic end products, space requisites, aspects of feeding biology) of cultured animals are considered in relation to design (surface area, depth) and maintenance (water refreshment) of shrimp (and fish) culture units. From general relations between respiration and food intake with body weight, the required changes in medium dimensions or animal density can be derived. It follows that water volume of a rearing system should be kept approximately proportional to biomass, surface area, food and water supply and should remain proportional to the metabolic weight (W^b) of the biomass. Depth and water refreshment should be proportional to, respectively, W^1−b and W^b−1 (b ∼ 0.74). The increase of body weight requires a reduction of animal density proportional to the reciprocal of metabolic weight. This can be achieved, for instance, by stepwise increasing the available surface area of the culture enclosure by 10^0.735 (∼5.4) times and depth by 10^0.265 (∼1.8) times at each 10-fold increase in biomass.