Respiratory adaptations to diving in the nile monitor lizard,Varanus niloticus

Summary The objectives of this study included directin vivo measurements of circulating blood gases, pH, heart rate, and blood pressure during voluntary dives of unrestrained Nile monitor lizards. A Radiometer flow-through cuvette was employed for continuous recording of arterial PO₂, PCO₂ and pH. Hematological properties revealed no particular adaptations for diving. Mean values were: hematocrit = 24%; hemoglobin concentration = 7.1 g %; oxygen capacity = 9.3 vol %; red cell dimensions = 22×12 ; red cell count = 0.67 million/l. The respiratory properties of the blood, studiedin vitro andin vivo, show distinct adaptations to habitual diving. Oxygen affinity of blood is low (P₅₀ = 42.4 mm Hg at pH 7.45, 25 °) and the dissociation curve is markedly sigmoid (n = 3.1). These features, coupled with a Bohr factor ( logP ₅₀/pH) of –0.48, ensure increased utilization of oxygen while maintaining relatively high tissue PO₂. Arterial pH decreases during diving from about 7.5 to 7.1 due to combined respiratory and metabolic acidosis. High plasma bicarbonate (30 mM/l at PCO₂ = 25 mm Hg) and a buffering capacity of H C₃ ^–O/ pH = 18.9 mM/l increase the tolerance to this acidosis and prolong diving time. Thein vivo oxygen dissociation curve shows a 90 % depletion of arterial oxygen content during typical dives. Diving elicited a rapidly developing bradycardia with maximum of 85 % reduction in heart rate. The temperature sensitivity of HbO₂ binding was very low (H = –3kcal). This would minimize the HbO₂ affinity increase accompanying the decrease in body temperature likely to occur in lizards going from sun basking to submergence in water.Supported by a grant from the Danish Natural Science Research Council.     

Phenotype modulation in primary cultures of smooth-muscle cells from rat aorta

Early in primary culture, arterial smooth-muscle cells undergo a transition from a contractile to a synthetic phenotype. This process includes the loss of myofilaments and of contractility. At the same time, an extensive rough endoplasmic reticulum and a large Golgi complex are formed, and active synthesis of DNA, RNA and proteins commences. In the present study, chemical and immunocytochemical methods were used to investigate the production of extracellular-matrix proteins in relation to this change in phenotypic properties. The results showed that the phase of rapid cellular proliferation that follows the structural modulation of smooth-muscle cells is associated with high rates of collagen and elastin synthesis, as measured by the incorporation of 3H-proline into 3H-hydroxyproline and 3H-valylproline, respectively. SDS-polyacrylamide gel electrophoresis and fluorography indicated that type-I collagen is the main collagen species synthesized by these cells. Smaller amounts of type-V collagen and (although not definitively identified) type-III collagen were also detected. Indirect immunofluorescence and immunoelectron microscopy demonstrated that smooth-muscle cells surround themselves with an incomplete basement membrane, containing laminin and type-IV collagen, and thin fibrils of type-I collagen. Adjacent to these fibrils, aggregates of amorphous, elastin-like material were also found. Our observations confirm and extend earlier notions of a close similarity between the behaviour of arterial smooth-muscle cells during in vitro cultivation and during the early stages of the formation of atherosclerotic lesions.     

Role of sulfhydryl groups in catalytic activity of purified cholesterol 7α-hydroxylase system from rabbit and rat liver microsomes

Electrophoretically homogeneous preparations of cytochrome P-450 LM₄ from cholestyramine-treated rabbits catalyzed 7α-hydroxylation of cholesterol, 12α-hydroxylation of 5β-cholestane-3α,7α-diol and 25-hydroxylation of 5β-cholestane-3α,7α,12α-triol. Dithiothreitol, a disulfide reducing agent, specifically stimulated the cholesterol 7α-hydroxylase activity severalfold. The 7α-hydroxylase activity was much more sensitive to the sulfhydryl reagents p-chloromercuribenzoate, N-ethylmaleimide and iodoacetamide than the 12α- and 25-hydroxylase activities. Cholesterol 7α-hydroxylase activity, inactivated by these reagents, could be reactivated by treatment with dithiothreitol. Similar results were obtained with purified cytochrome P-450 from rat liver microsomes.The results indicate that sulfhydryl groups are more important for cholesterol 7α-hydroxylation than for other C₂₇-steroid hydroxylations.     

Temperature insensitive O2 in blood of the tree frogChiromantis petersi

Summary Respiratory gas exchange and blood respiratory properties have been studied in the East-African tree frogChiromantis petersi. This frog is unusually xerophilous, occupies dry habitats and prefers body temperatures near 40°C and direct solar exposure. Total O₂ uptake was low at 81 l O₂·g^–1·h^–1±19.0 (SD) at 25°C increasing to 253.5 l O₂·g^–1·h^–1±94.8 (SD) at 40°C giving aQ ₁₀ value of 2.1. Skin O₂ uptake at 25°C was 38.5% of total. The gas exchange ratio was 0.71 for whole body gas exchange, 0.61 for the lungs and 1.02 for the skin at 25°C.Blood O₂ affinity was low with aP ₅₀ of 47.5 mmHg at 25°C and pH 7.65. Then _H-value at 25°C increased from 2.7 aroundP ₅₀ to 5.0 at O₂ saturations exceeding 70–80%. Surprisingly, blood O₂ affinity was nearly insensitive to temperature expressed by a H value of ±1.0 kcal·mole between 25 and 40°C.The adaptive significance of the low O₂ affinity, the increase ofn _H with O₂ saturation and the temperature insensitive O₂-Hb binding is discussed in relation to the high and fluctuating body temperatures ofChiromantis.     

Glycosaminoglycan secretion from perifused monolayer cultures of rabbit ear chondrocytes: Modification of xyloside effect by colchicine and cytochalasin B

Chondrocytes isolated from elastic ear cartilage of young rabbits were grown in monolayer cultures. Secretion into the medium of glycosaminoglycans labeled with ³⁵SO₄ was monitored by continuous perifusion. This experimental system was used to study the influence of colchicine, lumicolchicine, and cytochalasin B on the response to a 2-h β-d-xyloside pulse. In untreated cultures the stimulative effect of the xyloside was seen within 6 min and a new secretory steady state was reached in less than 20 min. Rabbit ear chondrocytes thus respond considerably faster to β-d-xyloside than chick sternum chondrocytes. After xyloside withdrawal glycosaminoglycan production decreased to baseline amounts in about 30 min. Colchicine caused a delayed and protracted response to xyloside. These effects were not mimicked by lumicolchicine. Hence, cytoplasmic microtubules appear to be involved in the secretion of glycosaminoglycans. On the other hand, colchicine had no effect on the size distribution of the labeled macromolecules. These findings suggest that colchicine exerts its action at a stage subsequent to initiation of the synthesis of glycosaminoglycans. Cytochalasin B did not affect the rate of response to xylside exposure or withdrawal.     

Analysis of bromine-oxidised dextran by 13C-n.m.r. spectroscopy

Dextran T 10, elaborated by Leuconostoc mesenteroides NRRL B-512, was oxidised with aqueous bromine at pH 7.0. The resulting oxodextran and its methoximated derivative were analysed by ¹³C-n.m.r. spectroscopy. The total amount of keto groups and their positions were established. Assignments of the ¹³C signals were made by referring to spectra of the corresponding methyl glucosiduloses and an oxodextran having most of the carbonyl groups at position 3 of the glycopyranosyl residues. In accordance with the mechanism for bromine oxidation of mono- and di-saccharides, the glucopyranosyl residues of dextran were oxidised mainly at C-2 and C-4. Over-oxidation resulted in a small proportion of acidic, ring-cleavage products.     

The effect of mate change and new partner's age on reproductive success in the barnacle goose, Branta leucopsis

Mate retention frequencies and correlations between mate changeand reproductive performance were estimated in a populationof barnacle geese, Branta leucopsis, breeding on the islandof Gotland in the Baltic. About 90% of the pairs remained togetherfrom one breeding season to the next. Only 2.4% of the pairsdivorced, most mate changes being consequences of the deathof one partner. Divorces were not forecast by low reproductivesuccess, and seemed to be accidental. In the season before matechange, there was no difference in reproductive performance,measured as clutch size, hatching date, and number of fledgedyoung, between faithful pairs and pairs where one partner wassubsequently changed. However, in the first season with a newpartner, clutch size and number of fledged young decreased onaverage. Hence, because mate change led to a reduction in reproductivesuccess, it was concluded that mate retention is advantageous.Our results suggest that this reduction is more likely due tothe lower average age or breeding experience of new partnersthan to the benefits of breeding experience with one particularpartner. [Behav Ecol 1991 ;2:116–122]     

Testing the monophyly of the New Zealand and Australian endemic family Conoesucidae Ross based on combined molecular and morphological data (Insecta: Trichoptera: Sericostomatoidea)

Conoesucidae (Trichoptera, Insecta) are restricted to SE Australia, Tasmania and New Zealand. The family includes 42 described species in 12 genera, and each genus is endemic to either New Zealand or Australia. Although monophyly has been previously assumed, no morphological characters have been proposed to represent synapomorphies for the group. We collected molecular data from two mitochondrial genes (16S and cytochrome oxidase I), one nuclear gene (elongation factor 1-α) (2237–2277 bp in total), and 12 morphological characters to produce the first phylogeny of the family. We combined the molecular and morphological characters and performed both a maximum parsimony analysis and a Bayesian analysis to test the monophyly of the family, and to hypothesize the phylogeny among its genera. The parsimony analysis revealed a single most parsimonious tree with Conoesucidae being a monophyletic taxon and sistergroup to the Calocidae. The Bayesian inference produced a distribution of trees, the consensus of which is supported with posterior probabilities of 100% for 15 out of 22 possible ingroup clades including the most basal branch of the family, indicating strong support for a monophyletic Conoesucidae. The most parsimonious tree and the tree from the Bayesian analysis were identical except that the ingroup genus Pycnocentria changed position by jumping to a neighbouring clade. Based on the assumption that the ancestral conoesucid species was present on both New Zealand and Australia, a biogeographical analysis using the dispersal-vicariance criteria demonstrated that one or two (depending on which of the two phylogenetic reconstructions were applied) sympatric speciation events took place on New Zealand prior to a single, late dispersal from New Zealand to Australia.