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PubMed1982

Inhibition of shivering as a cause of metabolic suppression with norepinephrine in warm- and cold-acclimated rats.

The metabolic response of warm-acclimated (25 degrees C for 4 weeks) and cold-acclimated (5 degrees C for 4 weeks) rats to infused norepinephrine (NE) (0.5-4 micrograms/(kg.min)) was measured at an ambient temperature of 13 degrees C, either before or after sinoaortic denervation. In warm-acclimated rats, vigorous shivering consistently occurring at 13 degrees C was greatly inhibited by NE in a dose of 2-4 microgram/(kg.min). After sinoaortic denervation, no such inhibition of shivering was observed. In cold-acclimated rats, NE did not suppress but increased heat production at this temperature, no visible shivering being noticed. Phenylephrine, a alpha-adrenergic stimulant, increased blood pressure and decreased heart rate to the same extent in both groups of rats at this temperature. NE suppressed heat production even in cold-acclimated rats at -5 degrees C, where the animals exhibited shivering. These results indicated that NE infusion inhibits shivering via the sinoaortic baroreceptor reflex, in both warm-acclimated and cold-acclimated rats. The non-occurrence of metabolic suppression in cold-acclimated rats after norepinephrine infusion in the 13 degrees C environment may be due to an absence of shivering which is suppressed at this temperature.

Acclimatization↗

PubMed1986

Heat production of cattle acclimated to cold, thermoneutrality and heat when exposed to thermoneutrality and heat stress.

Four Hereford X Red Angus yearling steers were acclimated to each of the following environments; cold (3 C), thermoneutrality (TNZ; 20 C) and heat (35 C). Intake was equalized for all treatments at 4.9 X kg X head-1 X d-1 (2.9 Mcal metabolizable energy/kg). Heat production, respiration rate and rectal temperature were determined after 3- and (21-h later) 24-h exposures to thermoneutral and heat stress test-temperatures: 25, 30, 32.5, 35, 37.5 and 40 C. Thermoneutral heat production (kcal X kg-.75 X d-1), after 3- and 24-h exposures, was greater (P less than .05) for the cold-acclimated cattle (139.6 +/- 5.0 and 153.0 +/- 5.8) as compared with the TNZ-acclimated cattle (117.7 +/- 5.0 and 121.6 +/- 5.8). Heat production of the heat-acclimated cattle after 3- and 24-h exposures to thermoneutrality was 121.0 +/- 5.1 and 123.5 +/- 3.2 and was not different from the TNZ-acclimated cattle. Heat production of steers acclimated to different temperatures was variable during the 3- and 24-h exposures to test-temperatures ranging from 25 to 40 C. Heat production increased linearly in the TNZ-acclimated cattle (24-h exposure) and in the heat-acclimated cattle (3-h exposure) at the rate of 1.3 and 2.3 kcal X kg-75 X d-1 X C-1 increase in test-temperature, respectively. In the other four comparisons, analysis by regression indicated no significant change in heat production. Rectal temperature and respiration rate increased significantly in either a linear or quadratic manner in all treatment groups exposed to test-temperatures from 25 to 40 C.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗

PubMed1992

Research note: broiler acclimation to heat distress and feed intake effects on body temperature in birds exposed to thermoneutral and high ambient temperatures.

Relationships between ambient temperature, bird acclimation to cycling temperature, heat distress, and feed consumption were evaluated in two experiments. In the first experiment, birds previously acclimated to cycling temperature heat distress (24 to 35 C) for two 24-h cycles were observed to have 24% lower (P less than .01) feed consumption than birds previously housed at 24 C and experiencing their first heat distress exposure. A significant (P less than .01) acclimation history by ambient temperature interaction was detected, with acclimated birds having a higher rectal temperature (42.3 versus 41.2 C) when housed at 24 C and a lower rectal temperature (44.2 versus 44.6 C) when exposed to 35 C than did the unacclimated controls. In the second experiment, feed intake and acclimation effects were separated by precision-feeding birds 0, 5, and 10% of body weight. Rectal temperature in the 24 C and 35 C environments increased linearly (P less than .01) as feeding level increased for both acclimated and unacclimated birds. Similar to the first experiment, an ambient temperature by acclimation history interaction was detected (P less than .01), with acclimated birds exhibiting increased body temperature when housed in thermoneutral environments and lower body temperature when exposed to high ambient temperature distress.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗

PubMed2000

Photosynthetic acclimation to rising atmospheric carbon dioxide concentration.

With rising level of CO2 in the atmosphere plants are expected to be exposed to higher concentration of CO2. Since, CO2 is a substrate limiting photosynthesis particularly in C3 plants in the present atmosphere, the impact of elevated CO2 would depend mainly on how photosynthesis acclimates or adjusts to the long term elevated level of CO2. Photosynthetic acclimation is a change in photosynthetic efficiency of leaves due to long term exposure to elevated CO2. This change in photosynthetic efficiency could be a biochemical adjustment that may improve the overall performance of a plant in a high CO2 environment or it could be due to metabolic compulsions as a result of physiological dysfunction. Acclimation has generally become synonymous with the word response, if long term exposure to elevated CO2 decreases the photosynthesis rate (Pn) at a given CO2 level, it is called negative acclimation, if it stimulates Pn at a given CO2 level, it is called positive acclimation. Photosynthetic acclimation is clearly revealed by comparing Pn of ambient and elevated CO2 grown plants at same level of CO2. Species level differences in acclimation to elevated CO2 have been reported. The physiological basis of differential photosynthetic acclimation to elevated CO2 is discussed in relation to the regulation of photosynthesis and photosynthetic carbon partitioning at cellular level.

Adaptation, Physiological↗

PubMed1976

Acclimation processes by daily exercise stints at temperate conditions followed by short heat exposures.

In order to improve the conventional procedures for heat acclimation by making the process shorter and more efficient, four daily regimens of 30 min of exercise under temperate ambient conditions (22 degrees C) followed by a 30-min walk (5.6 km/hr under hot dry ambient conditions (50 degrees/25 degrees C, Tdb/Twb) were administered to three groups of subjects. The respective exercise part for each group was as follows: 1) 30 min of descent on a laddermill (negative work); 2) 30 min of ascent on a laddermill (positive work), and 3) 15 min of descent followed by 15 min of ascent on the laddermill. The four daily regimens of exercise and heat exposure were followed by four consecutive daily walks of up to 120 min in dry heat. A fourth control group was not subjected to the special acclimation regimen, but underwent the eight daily conventional acclimation procedures. Acclimation was judged by the increase in tolerance time (T) for the walk in the heat and decrease in heart rate (HR) rectal temperature (Tre) and mean skin temperature (Tsk). Partial acclimation was observed after the 4 d of the regimen for the three experimental groups and the 4 d of the conventional procedure on the fourth control group. The final state of acclimation was apparent on the eighth day for all four groups. When the partial acclimation after the 4-d regimen was compared to the final state of acclimation, the following improvements were observed: 90% increase in T; 72% decrease in HR; 56% decrease in Tre, and 45% fall in Tsk. These improvements were similar to those observed after the 4 d of the conventional treatment on the control group as well as to those reported by others.

Acclimatization↗

PubMedDate not supplied

Solute accumulation in heat seedlings during cold acclimation: contribution to increased freezing tolerance.

Accumulation of sugars, amino acids and glycinebetaine in leaf tissues during cold acclimation was simultaneously monitored and compared in three wheat cultivars that have different freezing tolerance. Freezing tolerance was the decreasing order of cv. Norstar (NO) > cv. Chihokukomugi (CH) > or = cv. Haruyutaka (HA). During cold acclimation, there was a significant increase in osmotic concentration in the three cultivars. The increase was largely due to the increase in soluble sugars and the extent of the increase was the greatest in NO and the least in HA. While there was a considerable increase in glucose, fructose and sucrose during the first week of cold acclimation, the increase in raffinose occurred only after the second week. The total sugar content was the order of NO > CH > HA after 4 weeks of cold acclimation. Proline increased in all cultivars after 1 week of cold acclimation but a prolonged cold acclimation resulted in different profiles: no further increase occurred in HA while an additional increase occurred in other two cultivars. In all three cultivars, a noticeable increase of glycinebetaine occurred only after the second week of cold acclimation with the amount being the order of NO > CH > HA. It is concluded that a substantial part of the increase in osmotic concentration during cold acclimation was due to the increase in sugars, but the extent of the contribution of each compatible solute is cultivar-specific and can be associated with the degree of the maximum freezing tolerance attainable.

Acclimatization↗

PubMed1987

The effect of salt acclimation of the water uptake and osmotic permeability of the skin of the toad (Bufo viridis, L.).

1. Water uptake in vivo, and water fluxes across the isolated skin were studied in salt (NaCl) acclimated toads. 2. Water uptake of acclimated toads maintained in the solution of acclimation, decreased with the environmental salinity. 3. The osmotic water permeability (Pos) of the skin increased upon salt (NaCl) acclimation, both in vivo and in vitro. 4. Pos of the skin of toads acclimated to non-permeant solutes such as sucrose (230 mmol/l) or mannitol (400 nmol/l), was greatly reduced. 5. Oxytocin (syntocinon) increased the Pos both in tap water and salt acclimated toads. In high salt (greater than 200 mmol/l NaCl) acclimated toads however, the increased Pos and water flux at larger osmotic gradients, could not be stimulated further by the hormone. 6. The adaptive nature of the selective changes in the permeability properties of the skin under salt acclimation conditions is discussed.

Adaptation, Physiological↗

PubMed1981

Dipsogenesis in cold-acclimated rats.

Water intakes of control rats kept at 25 degrees C and cold-acclimated rats kept at 6 degrees C for at least 4 weeks were compared when both groups were at 25 degrees C. Cold-acclimated rats exhibited an increase in water intake (thermogenic drink) during the first but not the second hour after removal from the cold. Cold-acclimated rats, administered the dipsogenic agents angiotensin I, angiotensin II, isoproterenol or serotonin, had water intakes not significantly different from control rats. Administration (1% of body weight) of several different doses of hypertonic NaCl (0.25 to 1.00M) intraperitoneally increased water intake to the same level in both control and cold-acclimated rats. Water deprivation for 24 h, initiated either 2 or 24 h after removal of cold-acclimated rats from the cold, resulted in water intakes not significantly different between cold-acclimated and control rats. In spite of an initial thermogenic drink on removal of cold-acclimated rats from cold, cold-acclimation does not appear to alter the dipsogenic responsiveness of rats to either extracellular or intracellular dipsogenic stimuli, or to a dipsogenic stimulus (dehydration) involving both.

Acclimatization↗

PubMed1995

Temperature acclimation induces light meromyosin isoforms with different primary structures in carp fast skeletal muscle.

Carp acclimated to 10 degrees C gave 69k, 66k, and 62kDa light meromyosin (LMM) fragments in SDS-PAGE, while fish acclimated to 30 degrees C gave 74k, 69k, 66k, and 62kDa fragments. The microsequence analysis revealed that the 69k and 66kDa components from the 10 degrees C-acclimated carp contained an N-terminal amino acid sequence different from that of 62kDa. The four fragments from the 30 degrees C-acclimated carp showed the same sequence as that of the 69k and 66kDa components from the 10 degrees C-acclimated carp, except that the 2nd amino acid, Ala, of the 10 degrees C-acclimated LMM was replaced by Thr. DNA fragments encoding an N-terminal region of LMM were amplified by PCR or reverse transcriptase-PCR, demonstrating that the two acclimated groups further contained several amino acids substituted.

Acclimatization↗

PubMed1985

Influence of heat stress and acclimation on maximal aerobic power.

Thirteen male volunteers performed cycle ergometer maximal oxygen uptake (VO2max tests) in moderate (21 degrees C, 30% rh) and hot (49 degrees C, 20% rh) environments, before and after a 9-day heat acclimation program. This program resulted in significantly decreased (P less than 0.01) final heart rate (24 bt X min-1) and rectal temperature (0.4 degrees C) from the first to last day of acclimation. The VO2max was lower (P less than 0.01) in the hot environment relative to the moderate environment both before (8%) and after (7%) acclimation with no significant difference (P greater than 0.05) shown for maximal power output (PO max, watts) between environments either before or after acclimation. The VO2max was higher (P less than 0.01) by 4% after acclimation in both environments. Also, PO max was higher (P less than 0.05) after acclimation in both the moderate (4%) and hot (2%) environments. The reduction in VO2max in the hot compared to moderate environment was not related to the difference in core temperature at VO2max between moderate and hot trials, nor was it strongly related with aerobic fitness level. These findings indicate that heat stress, per se, reduced the VO2max. Further, the reduction in VO2max due to heat was not affect be state of heat acclimation, the degree of elevation in core temperature, or level of aerobic fitness.

Acclimatization↗

PubMed1987

Effect of acclimation temperature on the elongation step of protein synthesis in different organs of rainbow trout.

Cytosolic extracts of liver, kidney, spleen, gill, red and white muscle from rainbow trout acclimated to 4 and 17 degrees C, respectively, have been investigated in vitro with respect to their enzymic activity in stimulating the growth of nascent peptide chains (labelled polyphenylalanine) at assay temperatures from 5 to 25 degrees C using polyuracil as messenger RNA. The elongation step of protein synthesis is characterized by a Q10 value of about 2.4 (range 10-25 degrees C) in all organs from both, 4 and 17 degrees C acclimated fish. Except for the red muscle, the organs of cold acclimated trout, however, exhibit significantly higher specific elongation rates (mol phenylalanine polymerized/(g wet weight X h)) at any experimental temperature than those of warm acclimated fish. This increase of the elongation rates varies between the organs and ranges from +29% (liver) to +60% in the gill. The specific acylation rate (mol phenylalanyl-tRNA formed/(g wet weight X h] surpasses the specific elongation rate by a factor of at least 8.5. Moreover, the specific acylation rate per mg protein is independent of acclimation temperature. It is concluded that the increased specific elongation rates in 4 degrees C acclimated trout are not due to altered pool sizes of the precursor phenylalanyl-tRNA, but reflect an effective enhancement of enzymic elongation factor activities. In accordance with data taken from literature, this finding suggests a compensatory enhancement of in vivo protein synthesis to occur in trout during cold acclimation.

Acclimatization↗

PubMed1984

Soman toxication in hypoxia acclimated rats: alterations in brain neuronal RNA and survival.

Effects of prior hypoxia acclimation (14-day at 380 mm Hg) on soman (pinacolyl methylphosphonofluoridate) induced brain neuronal RNA and acetylcholinesterase (AChE) depletion and lethality were monitored in rats following their return to ambient oxygenation. Quantitative cytochemical techniques were used to measure RNA and AChE changes in individual cerebrocortical (Layer III) and striatal (caudate plus putamen) neurons. In ambient Po2 controls, soman eventuated in a moderate diminution of neuronal RNA in both brain regions and severe, dose-dependent suppression of AChE activity. Hypoxia acclimation per se induced RNA alterations as manifested in cortical RNA depletion and increased variability of striatal neuron RNA contents. In hypoxia acclimated rats, the extent of neuronal RNA depletion following soman injection was attenuated in both brain regions, yet there were no discernible differences in saline control AChE levels or in the extent of soman-induced AChE inhibition in ambient control versus hypoxia acclimated treatment groups. Hypoxia acclimated rats, however, were found to be even more susceptible to lethal actions of soman as assessed using 24- and 48-hour survival following a three-point treatment regimen. These data indicate that while compensatory systemic and central metabolic adjustments associated with 14d acclimation to reduced oxygen availability may retard soman-induced neuronal RNA depletion, resistance to lethal or near-lethal soman exposure is not enhanced. It is postulated that hypoxia acclimation is associated with complex adaptive and maladaptive neurophysiological alterations influencing CNS responsiveness to soman toxication, and that detrimental consequences exceed protection afforded by metabolic adaptation.

Acclimatization↗

PubMed2003

Glycoalkaloids and acclimation capacity of hybrids between Solanum tuberosum and the incongruent hardy species Solanum commersonii.

F(1) and backcross hybrids between sexually incompatible species Solanum commersonii and Solanum tuberosum were characterized for glycoalkaloid content and capacity to cold acclimate. Glycoalkaloid (GA) analysis revealed that F(1) triploids and BC(1) pentaploids contained the glycoalkaloids of both parents. In BC(2) (near) tetraploids the situation was different, in that some hybrids produced the GAs of both parents, whereas others contained only the GAs of S. tuberosum. This suggested that the GAs from S. commersonii may be lost rapidly, and that they may have a simple genetic control. The total tuber GA content of BC(1) and BC(2) groups averaged quite acceptable levels (165.9 mg/kg in BC(1) and 192.8 mg/kg in BC(2)), with six genotypes having a GA content <200 mg/kg fresh weight. The F(1) triploid hybrids expressed a capacity to cold acclimate similar to S. commersonii, whereas BC(1) and BC(2) genotypes generally displayed an acclimation capacity higher than the sensitive parent but lower than S. commersonii. However, one BC(1) and two BC(2) genotypes with an acclimation capacity as high as S. commersonii were identified. The polar lipid fatty acid composition in S. commersonii and its hybrid derivatives showed that, following acclimation, there was a significant increase in 18:3. Correlation analysis between the capacity to cold acclimate and the increase in 18:3 was significant, suggesting that the increase in 18:3 can be used as a biochemical marker for the assisted selection of cold-acclimating genotypes in segregating populations.

Acclimatization↗

PubMed2000

Does cold acclimation induce nonshivering thermogenesis in juvenile birds? Experiments with Pekin ducklings and Japanese quail chicks.

The capability to produce heat in cold by nonshivering thermogenesis (NST) was studied in Pekin ducklings and Japanese quail chicks acclimated to cold for 3 weeks using indirect calorimetry (oxygen consumption) and electromyography from breast (M. pectoralis) and leg muscles (quails: M. gastrocnemius; ducklings: M. gastrocnemius, M. iliofibularis). Respiration of muscles in vitro was studied by measuring cytochrome c oxidase activity. In both species, cold acclimation induced clear morphometric and physiological changes, but no clear evidence of nonshivering thermogenesis. This was evident because increased shivering at least in one muscle coincided with increased oxygen consumption. In ducklings, however, amplitudes of shivering EMGs were low (<30 microV) in all muscles studied in both the control and cold-acclimated groups. Ducklings reacted to cold mainly by means of increasing body weight (1796 g in control, 2095 g in cold-acclimated) and circulatory changes. Acclimation did not change oxygen consumption either in vivo or in vitro. In quails, in addition to increased body weight (78.1 g control, 89.9 g cold-acclimated), improved insulation and metabolic adaptation to cold (increased respiration in vivo and in M. pectoralis in vitro) was also utilized. In Japanese quail chicks, 3 weeks of cold acclimation does not seem to induce NST, while in Pekin ducklings the existence of NST could not be totally excluded because of weak overall shivering activity.

Acclimatization↗

PubMed2006

Expression of SK3-type dehydrin in transporting organs is associated with cold acclimation in Solanum species.

The expression of a gene, encoding a dehydrin protein designated as DHN24 was analyzed at the protein level in two groups of Solanum species differing in cold acclimation ability. The DHN24 protein displays consensus amino acid sequences of dehydrins, termed K- and S-segments. The S-segment precedes three K-segments, classifying the protein into SK3-type dehydrins. A group of Solanum species able to cold acclimation constituted by S. sogarandinum and S. tuberosum, cv. Aster, and a second one composed of a S. sogarandinum line, that lost ability to cold acclimation, and of S. tuberosum, cv. Irga, displaying low ability to cold acclimation were studied. Under control conditions, noticeable levels of the DHN24 protein was observed in stems, tubers, and roots of Solanum species. No protein was detected in leaves. During low temperature treatment the DHN24 protein level substantially increased in tubers, in transporting organs and in apical parts, and only a small increase was observed in leaves. The increase in protein abundance was only observed in the plants able to cold acclimate and was found to parallel the acclimation capacity. Upon drought stress, the DHN24 level decreased in stems and in leaves, but increased in apical parts. These results suggest that Dhn24 expression is regulated by organ specific factors in the absence of stress and by factors related to cold acclimation processes during low temperature treatment in collaboration with organ-specific factors. A putative function of the SK3-type dehydrin proteins during plant growth and in the tolerance to low temperature is discussed.

Acclimatization↗

PubMed2006

Role of tannin-binding salivary proteins and tannase-producing bacteria in the acclimation of the Japanese wood mouse to acorn tannins.

We studied the defense mechanisms against the negative effects of tannins in acorns by using the Japanese wood mouse (Apodemus speciosus) and acorns of a Japanese deciduous oak Quercus crispula, which contain 9.9% tannins on a dry weight basis. For the experiment, we allocated 26 wood mice into two groups: acclimated (N = 12) and nonacclimated (N = 14). Mice in the nonacclimated group were fed only acorns for 10 d after 4 wk of receiving a tannin-free diet. In contrast, mice in the acclimated group received ca. 3 g acorns daily in addition to the tannin-free diet for the first 4 wk, then they were fed only acorns for 10 d. Body weight, food intake, and digestibility were monitored. In addition, the amount of salivary proline-rich proteins (PRPs) and abundance of tannase-producing bacteria (TPB) in the feces of mice were measured. Of the 14 mice in the nonacclimated group, 8 died, whereas only 1 of the 12 in the acclimated group died. During the first 5 d of feeding acorns only, mice in the nonacclimated group lost, on average, 17.5% of their body mass, while those in the acclimated group lost only 2.5%. Food intake, dry matter digestibility, and nitrogen digestibility were higher in the acclimated group than in the nonacclimated group. The results indicate that wood mice can mitigate the negative effects of tannins by acclimation. Path analysis revealed that increased secretion of PRPs and abundance of Lactobacillus type of TPB might explain the acclimation to tannins.

Adaptation, Physiological↗

PubMed2007

Photosynthetic acclimation in the context of structural constraints to carbon export from leaves.

The potential role of foliar carbon export features in the acclimation of photosynthetic capacity to differences and changes in light environment was evaluated. These features included apoplastic vs. symplastic phloem loading, density of loading veins, plasmodesmatal frequency in intermediary cells, and the ratio of loading cells to sieve elements. In initial studies, three apoplastic loaders (spinach, pea, Arabidopsis thaliana) exhibited a completely flexible photosynthetic response to changing light conditions, while two symplastic loaders (pumpkin, Verbascum phoeniceum), although able to adjust to different long-term growth conditions, were more limited in their response when transferred from low (LL) to high (HL) light. This suggested that constraints imposed by the completely physical pathway of sugar export might act as a bottleneck in the export of carbon from LL-acclimated leaves of symplastic loaders. While both symplastic loaders exhibited variable loading vein densities (low in LL and high in HL), none of the three apoplastic loaders initially characterized exhibited such differences. However, an additional apoplastic species (tomato) exhibited similar differences in vein density during continuous growth in different light environments. Furthermore, in contrast to the other apoplastic loaders, photosynthetic acclimation in tomato was not complete following a transfer from LL to HL. This suggests that loading vein density and loading cells per sieve element, and thus apparent loading surface capacity, play a major role in the potential for photosynthetic acclimation to changes in light environment. Photosynthetic acclimation and vein density acclimation were also characterized in the slow-growing, sclerophytic evergreen Monstera deliciosa. This evergreen possessed a lower vein density during growth in LL compared to HL and exhibited a more severely limited potential for photosynthetic acclimation to increases in light environment than the rapidly-growing, mesophytic annuals.

Arabidopsis↗

PubMed1992

Effects of temperature acclimation on the expression of hepatic cytochrome P4501A mRNA and protein in the fish Fundulus heteroclitus.

Previous studies showed that hydrocarbon induction of hepatic microsomal monooxygenase activity is attenuated in the teleost fish Fundulus heteroclitus acclimated to low temperature. The basis of that attenuation, and the effects of temperature on monooxygenase activity, were examined by analyzing liver cytochrome P4501A (CYP1A) mRNA, protein, and catalytic activity in control and beta-naphthoflavone (BNF)-treated F. heteroclitus acclimated to 6 or 16 degrees C. There were no temperature-related differences in total P450 content, NADPH-cytochrome c (P450) reductase activity, ethoxyresorufin O-deethylase (EROD) activity, or immunoquantified CYP1A content in hepatic microsomes of untreated fish. Fish acclimated to 16 degrees C and given a single intraperitoneal injection of BNF exhibited a rapid rise and fall in CYP1A mRNA content and an induction of EROD activity and CYP1A protein that was undiminished over 7 days. Similarly treated fish acclimated at 6 degrees C showed an increase in CYP1A mRNA content greater than that in 16 degrees C fish, but with no significant increase in EROD activity or CYP1A content over 7 days. Examined over a longer term, microsomal EROD activity was significantly induced by BNF in fish at both temperatures; activity peaked at 5-7 days in 16 degrees C fish, while in 6 degrees C fish the activity continued to rise slowly over 25 days. However, the greatest activity reached in 6 degrees C fish (0.68 nmol/min/mg) was less than half that seen in the warmer animals (1.46 nmol/min/mg). Immunodetectable CYP1A content showed the same trend as EROD activity, and the turnover number (nmol product formed/min/nmol CYP1A) for EROD activity was about the same in all groups, indicating that concentration of the catalyst alone could account for the different patterns of microsomal activity. CYP1A mRNA content was again induced to a similar degree by BNF in both the 6 and the 16 degrees C fish; the apparent half-life of the mRNA was substantially longer in cold-acclimated than in warm-acclimated BNF-treated fish. Comparing the levels of CYP1A mRNA and protein at the two acclimation temperatures following BNF treatment indicates that translational activity, rather than transcriptional activity, is the sensitive point in the effect of temperature on CYP1A induction in these fish.

Acclimatization↗