Showing papers by "Mount Desert Island Biological Laboratory published in 1982"

Ammonia excretion by the gills of two marine teleost fish the importance of NH4+ permeance

Abstract: Varying the concentration of un-ionized ammonia (NH3) in the medium perfusing the gills of the isolated fish head while holding the total ammonia (NH4+ + NH3) concentration constant had no significant effect on gill ammonia excretion. In contrast, alteration in the medium NH4+ concentration at a fixed NH3 concentration produced a significant change in ammonia excretion. Thus, gill ammonia excretion was related to medium NH4+, not NH3, concentration.

Taurine transport by isolated flounder renal tubules.

Abstract: Previous in vivo clearance studies (Schrock et al., '82) have revealed that taurine is secreted by marine fish kidneys. In the present study taurine secretion by the flounder (Pseudopleuronectes americanus) renal tubule was investigated by assaying the transport of 14C-taurine in vitro. Collections from isolated fluid-secreting flounder tubules confirmed the presence of a tubular mechanism for taurine secretion. The flounder renal tubule concentrated taurine in the lumen at a lumen/bath ratio of 25, with the movement across the peritubular membrane identified as the concentrating step of taurine transport. Studies with teased flounder renal tubules identified transport as Na+ and C1- dependent. Taurine transport was inhibited by beta alanine, gamma-aminobutyric acid, and hypotaurine. In a study of the hormonal control of taurine transport, only the adrenal steroid dexamethasone stimulated taurine uptake by the flounder renal tubules. Transport was not affected by the second messengers adenosine 3'5'-cyclic monophosphate, guanosine 3'5'-cyclic monophosphate, adenosine, or Ca++ ionophore (A12384).

Comparison of antifreeze glycopeptides from arctic and antarctic fishes

Abstract: Antifreeze glycopeptides from the Atlantic tomcod Microgadus tomcod), saffron cod (Eleginus gracilis), and Greenland cod (Gadus ogac) were isolated by ion exchange chromatography. Polyacrylamide gel electrophoresis revealed that fewer sizes of antifreeze glycopeptides are present in the serum of M. tomcod and E. gracilis compared to the Antarctic nototheniid (Dissostichus mawsoni), Glycopeptide 6 from M. tomcod and E. gracilis as well as glycopeptide 8 from G. ogac were sequenced and compared with known sequences of similar-sized glycopeptides from Antarctic fishes. It was found that arginine residues in glycopeptide 6 from E. gracilis and M. tomcod occur at positions 15 and 18, that proline periodically replaces alanine (ala) at positions 7, 13, and 19. In contrast, none of the antifreeze glycopeptides from Antarctic fishes contain arginine. Threonine (thr) occupies positions 15 and 18 instead. Glycopeptide 8 from G. ogac was found to have the same sequence as glycopeptide 8 from the polar cod (Boreogadus saida). The results indicate that the repeating sequence (ala-ala-thr) appears to be highly conserved within polar fishes. However, greater variation in antifreeze glycopeptide structure exists within one family of northern cods (Gadidae) than within species belonging to four separate families of Antarctic fishes.

Which components of crude oil are toxic to young seabirds

Abstract: Studies from this laboratory have focused on sublethal physiological effects of small amounts of ingested crude oil in young herring gulls (Larus argentatus). Clearly, the most striking effect of certain oils in gulls is the marked reduction in rates of weight gain found after administration of a single 0.2–1 ml oral dose. For example, dosing with one South Lousiana crude (obtained from the American Petroleum Institute in 1976; SLC-76) reduced weight gain by 40–80%; another SLC, obtained in 1978, had no effect. Gas chromatographic-mass spectrographic analyses of the oils indicated that SLC-1978 lacked certain aromatics. Weathering of SLC-76 over sea water for 36 h did not reduce its ability to inhibit weight gain in gulls. Both findings implicated higher weight aromatics as the active compounds. SLC-76 was split on an alumina column into aliphatic and aromatic fractions; only the aromatic fraction reduced gull rates of weight gain. Using a Prudhoe Bay crude (as toxic to gulls as SLC-76), the aromatic fraction was split into two subfractions on Sephadex LH-20. Analyses showed that one subfraction contained those aromatics with three or less rings and the other contained those with four or more rings. Only the second fraction (high molecular weight aromatics) reduced gull weight gain. These findings clearly show that oil composition is a major determinant of oral toxicity to young seabirds, and that the higher molecular weight aromatics are most effective in reducing gull weight gain.

Relaxin: speculations on its physiological importance in some nonmammalian species

Abstract: The successful completion of pregnancy in many eutherian mammals depends, in part, upon a well-timed softening of the uterine cervix, and in some species, a pre-partum alteration in pubic symphysis morphology. It was the latter change in the late pregnant pocket gopher which led Frederick Hisaw to the discovery of the hormone responsible for these phen0rnena.l Hisaw named the hormone relaxin. Information accumulated since its discovery has confirmed that in some mammals relaxin can initiate cervical softening, induce pubic symphysis relaxation, and inhibit myometrial activity. In addition, relaxin influences the uterine endometrium, the vagina and mammary glands (for a review see Schwabe et ~ 1 . ~ ) . While all activities are inherent in the relaxin molecule, the type and extent of the relaxin responses are species specific. Clearly, the presence of the hormone, as well as the source and site of action, varies greatly in diverse mammalian species. Recent biochzmical analyses have delineated the primary and secondary structures of the relaxin molecule isolated from porcine corpora lutea.? The molecule is composed of two distinct peptides containing 22 and 26 amino acid residues that are covalently linked by two disulfide bridges and exhibit a structure remarkably similar to porcine insulin. Despite the lack of homology in over 50% of the amino acids, relaxin also appears similar to insulin in conformation. With the purification of relaxin and subsequent availability of a specific radioimmunoassay, serum relaxin levels during pregnancy have now been

Bile pigment composition and hepatic UDP-glucuronyl transferase activity in the fetal and adult dogfish shark, Squalus acanthias.

Abstract: 1. 1. Bile pigments from adult and fetal spiny dogfish (Squalus acanthias) were separated and quantitated by high pressure liquid chromatography. 2. 2. In order of relative abundance, bilirubin monoglucuronide, unconjugated bilirubin, bilirubin diglucuronide and bilirubin monoglucoside were present in adult bile and in fetal bile and meconium. 3. 3. All bile pigments were of IXα configuration. 4. 4. Specific hepatic microsomal UDP-glucuronate glucuronosyl transferase activity towards bilirubin and p- nitrophenol were comparable in fetal and adult dogfish.

Amphotericin B and the elasmobranch rectal gland: Implications for the relationship between oxygen consumption and ion transport

Abstract: In slices of the dogfish rectal gland, amphotericin B produced increases in oxygen consumption and ouabain binding similar to those produced by cyclic AMP, except that the increases induced by the latter were inhibited by furosemide whereas those resulting from the addition of amphotericin B were unaffected by the diuretic. Unlike cyclic AMP, however, amphotericin B failed to stimulate secretion by the isolated perfused gland. These results support the suggestion that the increases in ouabain binding and oxygen consumption produced by cyclic AMP result simply from an increased sodium entry into the cells, and as such can be mimicked by amphotericin B, whereas secretion rate itself depends on some additional, cyclic AMP-induced process. The implications of this for determinations of the relationship between rates of oxygen consumption and ion transport are discussed.

The effect of tail skin on the morphology and morphogenesis of limb regenerates in the red-backed salamander, Plethodon cinereus.

Abstract: Tail skin cuffs have been grafted to the upper forelimb of red-backed salamanders in either normal or 180°-rotated dorsoventral orientation. Subsequent amputation through the graft region resulted in arrested regeneration, distally deficient or typical four-digit regenerates. Distribution was not substantially influenced by graft orientation nor were there any supernumerary limbs induced by the axially dislocated tail skin on the limb stumps. Furthermore, regenerates bore no indication of tail-like structures other than large granular skin glands proximally. These data indicate that, unlike limb skin, tail skin is not morphogenetically active in the epimorphic process of limb regeneration. In addition, the species used in this study is a fin-less, round-tailed salamander. It is therefore suggested that the previously reported morphogenetic effects of tail skin on limb regeneration may be related to the presence of tail fins on the species studied.