Plasma and ovarian thyroxine levels in relation to sexual maturation and gestation in female Sebastes inermis

Plasma T₄ (L-thyroxine) concentrations in the viviparous rockfish Sebastes inermis showed a peak (119·3±27·8 ng ml⁻¹) during the development of embryos. Ovarian T₄ concentrations increased during vitellogenesis and final maturation and decreased during embryogenesis.However, total T₄ content within the ovary increased continuously up to the larval stages. Plasma oestradiol-17β, (E₂) concentrations peaked at the final maturation stage and then recovered to the level seen during the non-reproductive periods. Plasma testosterone (T) concentrations showed a peak (5·33±1·08 ng ml⁻¹) at the embryo stage and high levels were maintained throughout the gestation period. Plasma T₄ concentrations during the embryo stage and ovarian T₄ content during vitellogenesis were much higher than the levels reported in oviparous fishes. These data suggest that in viviparous rockfish, T₄ may be required for sustaining gestation or embryo development within the maternal body. In addition, the high content of total T₄ in the ovary implies that there probably does exist a maternal-embryo relationship during gestation as well as during vitellogenesis.     

Early larval development and metamorphosis in the summer flounder: changes in per cent whole-body water content and effects of altered thyroid status

At the end of premetamorphosis, summer flounder Paralichthys dentatus larvae had 84·1% whole-body water content (WBW), which decreased to the lowest levels (8·5%) at the start of metamorphic climax (MC). During mid- and late MC, %WBW was slightly higher (82·1%) then returned to the lowest levels at the juvenile stage. In fish treated with thyroxine (T₄-Na salt, 100 ng ml⁻¹) beginning at premetamophosis, %WBW never differed from controls of the same age throughout metamorphosis, despite an earlier start of metamorphic climax and transitional settling behaviour. This suggests that thyroid hormones do not mediate the drop in %WBW which accompanies natural metamorphosis. Thiourea (TU, 30 μg ml⁻¹) treatment of fish over the same period induced a developmental stasis in early MC which was accompanied by initially higher %WBW than controls at 33 days post-hatch, followed by a progressive decrease to abnormally low %WBW by 42 and 45 days post-hatch. Since concurrent treatment with TU+T₄ rescued the fish from both the TU-induced developmental stasis and abnormally low %WBW, these findings suggest that thyroid hormones, or thyroid hormone-mediated developmental progression, are necessary for regulating %WBW.     

Seasonal dynamics of invertebrate drift in a Hong Kong stream

Drift samples were taken with paired nets on 19 occasions over a 12-month period in Tai Po Kau Forest Stream (TPKFS), Hong Kong. Mean drift density (±1 S.E.) was 277·9 ± 25·0 individuals 100 m^-3; peaks in density were apparent during autumn and spring. One hundred and two taxa were recovered from the drift, and the total number of taxa drifting was positively related to water temperatures. Over 99% of the aquatic animals collected in drift samples were insects, 10 taxa of which constituted 67·3% of the entire catch. Baetid mayflies dominated the composition of the drift, comprising 40·4% of individuals caught.
Seasonal changes in the drift of individual taxa were evident, reflecting significant relationships between drift densities and water temperature: Simulium T₁ (Diptera). Anisocentropus maculatus (Trichoptera) and Amphinemura chui (Plecoptera) drifted most in winter, whereas Chimarra T₁, Polymorphanisus astictus (Trichoptera), Helodes #1 and cf. Rhantus sp. (Coleoptera) were most numerous in summer. Drifting mayflies showed spring ( Indobaetis sp., Cinygmina T₁, Serratella T₂), autumn ( Baetiella sp., Pseudocloeon T₂), or spring and autumn ( Baetis nr pseudofrequentus ) peaks which were not clearly related to water temperature. In only two cases ( A. maculatus and P. astictus ) was TPKFS drift seasonality associated with life-cycle events. Overall, there was no evidence of community-level trends in the periodicity of stream drift in this seasonal tropical habitat.     

Seasonal changes in thyroidal status in the plaice, Pleuronectes platessa L.

A chemically specific analysis for plasma thyroid hormones has been used to disclose a seasonal bimodality in the concentrations of thyroxine (T₄) and triiodothyronine (T₃) in the plaice; maxima in both hormone levels occur in winter and in summer. The ratio of T₄ concentrations to T₃ varies seasonally being at a minimum in summer. A highly significant correlation of T₄ plasma levels with the landings per unit fishing effort for the same area has been observed.     

Study of the sexual maturity of female bluefin tuna: purification and partial characterization of vitellogenin and its use in an enzyme-linked immunosorbent assay

Plasma steroid levels of female bluefin tuna (BFT) Thunnus thynnus rose from c. 1·5 ng ml⁻¹ during the quiescent period (March) to c. 7 ng ml⁻¹ during the ripening period (May). Testosterone (T) increased further to c. 8 ng ml⁻¹ during the pre-spawning period (June) while 17β-oestradiol (E₂) began to decrease. In the post-spawning period (August) steroid levels decreased to < 1 ng ml⁻¹. Vitellogenin (Vtg) plasma levels seemed to follow changes in E₂, showing an increase from the quiescent period to the ripening period of c. 18 mg ml⁻¹, decreasing slightly before spawning, and then decreasing after spawning. The Vtg content in plasma showed a good correlation both with the plasma levels of E₂ and T and with the percentage of vitellogenic oocytes at different periods of the reproductive cycle. Thus the ELISA could be taken as validated. Immunohistochemical staining of ovaries with anti BFT-Vtg serum demonstrated a high cross-reactivity with yolk proteins allowing the identification of vitellogenic oocytes.     

Changes in thyroid function and gonadotrophin activity during sexual development in ducks Anas sp. (Aves: Anatidae)

Age-related changes in plasma iodohormone concentrations in male and female Aylesbury and Khaki Campbell ducklings were determined between the second week after hatching and sexual maturity.
In both sexes and strains the concentration of total thyroxine (T₄) and the free thyroxine index (FT₄1) were low during the first 6–8 weeks after hatching. A marked increase in the T₄ and FT₄1 occurred when the ducklings were nine weeks old; T₄ progressively increased over the following four weeks and remained high thereafter. The T₄ concentration in both sexes was directly related to age.
Concentrations of total tri-iodothyronine (T₃) were more variable than T₄ but were highest before sexual maturation and inversely age-related. An age-related decline in free tri-iodothyronine index (FT₃1) was observed during the first nine weeks.
The possibility that these maturational changes in thyroid function may reflect changes in gonadal activity was assessed by measuring the concentration of luteinizing hormone (LH) in the same plasma samples. Although plasma LH increased with age, in all cases the increase occurred after changes in the thyroid hormones were observed. Moreover, the maturational pattern of LH was related to sex and strain whereas thyroid function was unaffected by sex or strain.
These results demonstrate reciprocal changes in plasma T₃ and T₄ levels in ducks during sexual development, although the stimuli responsible and physiological significance are uncertain.     

Changes in plasma thyroid hormone levels in pink salmon, Oncorhynchus gorbuscha, during their spawning migration in the Fraser River (Canada)

Plasma thyroid hormone levels were measured in pink salmon, Oncorhynchus gorbuscha , during their spawning migration in the Fraser River, British Columbia. The plasma levels of both l-thyroxine (T₄) and triiodo-l-thyronine (T₃) were significantly higher in males than in females. In both sexes the hormone levels were maintained, or increased somewhat, during the early stages of migration, but fell thereafter. In females the plasma T₄ and T₃ levels of salmon collected on the spawning grounds were at or below detectable levels of the assays. The changes in thyroid hormone levels are correlated with changes in plasma insulin, gonadotropin, gonadal steroid hormones, cortisol and vitellogenin levels measured in the same specimens.     

Endocrine, osmoregulatory, respiratory and haematological parameters in flounder exposed to the water soluble fraction of crude oil

Flounders Pleuronectes flesus with an implanted vascular catheter were exposed to a 50% dilution of the water soluble fraction (WSF) of Omani crude oil (c. 6ppm total aromatic hydrocarbons) and serial blood samples taken to determine their endocrine status (cortisol, catecholamines and thyroid hormones) and the resultant and/or causal physiological (haematological, ionoregulatory and respiratory) disturbances. This resulted in a progressive increase in plasma cortisol concentrations from 3 h onwards (rising from 18 to 51 ng ml⁻¹ after 48-h exposure), and increased plasma glucose concentrations indicating a generalized stress response. Plasma T3 and T4 concentrations of both control and WSF-exposed groups declined progressively over the experimental period; exposure to the WSF of crude oil further depressed plasma T4 concentrations but not plasma T₃ concentrations relative to those of control fish. Plasma osmolality and sodium and chloride concentrations were stable in WSF-exposed fish, however, plasma potassium concentrations were increased significantly at the 24-and 48-h sampling points. The most profound physiological disturbance in WSF-exposed fish was a dramatic decline in blood oxygen content (CvO₂) (from 2–8 to 0–8 ml 100 ml⁻¹ after 48-h exposure), which is likely to be the cause of the increased plasma noradrenaline concentrations from 3 h onwards. Increased noradrenaline is likely in turn to have been responsible for the significant increase in blood haematocrit and blood haemoglobin at the 3-h sampling point, although the dominant effect in the longer-term was a significant decline in both of these haematological parameters.     

Reproductive sensitivity to elevated water temperatures in female Atlantic salmon is heightened at certain stages of vitellogenesis

In order to compare the effects on reproductive performance of short-term or prolonged exposure to elevated temperatures during vitellogenesis, female Atlantic salmon Salmo salar were held at a water temperature of 22° C for periods of 4 or 6 weeks during the austral summer and autumn. Plasma levels of 17β-oestradiol (E₂), testosterone (T) and vitellogenin (Vtg) were monitored and reproductive success was compared to that in groups of fish maintained at 14 or 22° C for 12 weeks from mid-January. Significant endocrine effects were observed within as few as 3 days of the commencement of exposure to 22° C, when plasma levels of E₂ ( c. 0·5 ng ml⁻¹) and Vtg ( c. 1·4 mg ml⁻¹) were approximately half those observed in fish maintained at 14° C ( c. 1·0 ng ml⁻¹ and 2·7 mg ml⁻¹ respectively). The fertility and survival to the eyed stage of ova from fish held at 14° C exceeded 85 and 70% respectively, whereas ova from fish held at 22° C for 6 or 12 weeks exhibited significantly reduced fertility (<70 and <45% respectively) and survival ( c. 40 and 13% respectively). In spite of significant endocrine effects at all stages, a 4 week exposure to 22° C only generated significant reductions in egg fertility (<65%) and survival ( c. 30%) when it occurred between mid-February and mid-March. Together, these data confirm that high temperature spikes can affect reproductive success as strongly as more prolonged exposures, and indicate that there is a critical period of reproductive sensitivity to elevated temperature in late February and early March in this stock of Atlantic salmon.     

Effect of rearing density on thyroid and interrenal gland activity and plasma and hepatic metabolite levels in rainbow trout, Salmo gairdneri Richardson

There were significant inverse correlations between rearing density of rainbow trout, Salmo gairdneri Richardson, and final body weight, plasma L-thyroxine (T₄), trüodo-L-tryronine (T₃), cortisol and protein concentrations, plasma T₄/T₃ ratios and thyroid epithelial cell height. In addition, hepatosomatic indices and plasma free fatty acid concentrations were higher in fish reared at low (134 g 1⁻¹) density compared with groups reared at medium (210g1⁻¹) or high density (299g 1⁻¹), and the post-feeding (3.5-4h) elevation in plasma glucose and triglyceride levels evident in trout maintained at low rearing density was not found in those fish reared at higher densities. There were no significant effects of rearing density on hematocrit, carcass composition, hepatic glycogen and lipid levels and interregnal nucleus size.     

The plant-growth-promoting rhizobacteria Bacillus pumilus and Bacillus licheniformis produce high amounts of physiologically active gibberellins

The plant-growth-promoting rhizobacteria (PGPR), Bacillus pumilus and Bacillus licheniformis, isolated from the rhizosphere of alder ( Alnus glutinosa [L.] Gaertn.) have a strong growth-promoting activity. Bioassay data showed that the dwarf phenotype induced in alder seedlings by paclobutrazol (an inhibitor of gibberellin [GA] biosynthesis) was effectively reversed by applications of extracts from media incubated with both bacteria and also by exogenous GA₃. Full-scan gas chromatography-mass spectrometry analyses on extracts of these media showed the presence of GA₁, GA₃, GA₄and GA₂₀, in addition to the isomers 3- epi -GA₁ and iso -GA₃. Isotope dilution analysis indicated that epi -GA₁ was an artefact. Likewise, iso -GA₃ is also probably an artifact spontaneously formed during extraction and/or analysis. In both culture media, GA₁ was present in higher concentrations (130–150 ng ml⁻¹) than GA₃ (50–60 ng ml⁻¹), GA₄ (8–12 ng ml⁻¹) and GA₂₀ (2–3 ng ml⁻¹). The data indicated that culture of both bacteria accumulate bioactive C19-gibberellins in relative high amounts and that these GAs appear to be physiologically active in the host plant. The evidence suggests that the promotion of stem elongation induced by the PGPR could be mediated by bacterial GAs.     

Seasonal and diurnal rhythms of thyroidal status in the rainbow trout, Salmo gairdneri Richardson

The concentrations of thyroxine (T₄) and triiodothyronine (T₃) in the blood plasma of rainbow trout ( Salmo gairdneri Richardson) at intervals throughout the year have been measured by a chemically specific gas-liquid chromatographic (GLC) method. Mean hormone levels showed a seasonal variation, maximal levels of both hormones occurring in winter and minimal concentrations in mid summer. An apparent secondary maximum in mean T₄ and T₃ concentrations was observed in spring. (T₄)/(T₃) ratios have been found to be highest in winter and lowest in summer. A radioimmunoassay procedure, validated by GLC analyses, revealed the presence of a diurnal rhythm in serum T₄ levels of trout sampled in September and in April.     

Plasma levels of C18-, C19- and C21-steroids in captive and feral female sea bass

Morphometric analysis of the gonads of sea bass Dicentrarchus labrax revealed that captive fish matured 1 month later than feral fish, but levels of gonadal steroids were identical in both groups at the same stage of sexual development. 17β-oestradiol (E₂) (up to 3 ng ml-1) and testosterone (T) (up to 4 ng ml-1) were highest during the gametogenetic period while 17,20β,21-trihydroxy-4-pregnen-3-one (17,20β,21-P) (free and sulphated) were maximal during the spawning period. Free 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) was very low and did not change (c. 0·5 ng ml⁻¹) while 17,20β-P-sulphate increased during the spawning period in both groups (up to 2 ng ml⁻¹). In contrast cortisol levels were higher in captive fish and increased during the spawning period (up to 100 ng ml⁻¹). These results suggest that captivity delays vitellogenesis and spawning in sea bass without affecting the final levels of the gonadal steroids and further indicates a role for cortisol in the latter period. The increased levels during the spawning period suggests a pheromonal role for 17,20β-P-sulphate and 17,20β,21-P-conjugates and the involvement of 17,20β,21-P in final ooccyte maturation.     

Studies on the relationship between osmotic or ionic regulation and thyroid gland activity in two salmonid fishes, Salmo gairdneri Richardson and Oncorhynchus kisutch Walbaum

In freshwater-acclimated rainbow trout a single intraperitoneal injection of ovine TSH significantly elevated plasma thyroxine (T₄) levels within 1 h after the injection. In seawater adapted trout the increase in T₄ after TSH-treatment was not evident until 6 h after the injection. TSH caused a transient fall in plasma Na⁺ and Cl^- between 3 h and 9 h after the injection in seawater-adapted fish and plasma Na⁺ was lowered in freshwater-adapted trout 24 h after the injection. Although there were clear histological changes in the thyroid gland of freshwater-adapted trout after TSH-injection, no such changes were evident in seawater-adapted fish.
Plasma thyroid hormone levels and thyroid histology in freshwater-adapted rainbow trout and coho salmon transferred to sea water, and seawater-adapted trout transferred to fresh water showed no consistent changes compared with controls.
The data are interpreted to indicate that although ambient salinity may have indirect effects on thyroid activity there is no direct involvement in ionic or osmotic regulation in the two species.     

Characterization of the Thyroid Hormone Transport System of Cerebrocortical Rat Neurons in Primary Culture

Abstract: The uptake of 3',3,5-triiodo- l -thyronine (T₃) and l -thyroxine (T₄) by primary cultures derived from rat brain hemispheres was studied under initial velocity conditions, at 25°C. Uptake of both hormones was carrier mediated and obeyed simple Michaelis-Menten kinetics. The K _m of T₃ uptake was very similar to that of T₄, and did not vary significantly from day 1 to 4 in culture (310–400 n M ). The maximal velocity ( V _max) of T₃ uptake nearly doubled between day 1 and 4 of culture (41 ± 3 vs. 70 ± 5 pmol/min/mg of DNA, respectively). The V _max of T₄ uptake did not change (28 ± 8 and 31 ± 4 pmol/min/mg of DNA on days 1 and 4, respectively). The rank order of unlabeled thyroid hormone analogues to compete with labeled T₃ or T₄ uptakes were the same (T₃ > T₄ > 3',5',3-triiodo- l -thyronine > 3',3,5-triiodo- d -thyronine > triiodothyroacetic acid), indicating that the transport system is stereospecific. Unlabeled T₄ was a stronger competitor of labeled T₄ uptake than of labeled T₃ uptake, whereas unlabeled T₃ had the same potency for both processes. These results suggest that T₃ and T₄ are transported either by two distinct carriers or by the same carrier bearing separate binding sites for each hormone. They also indicate that the efficiency of T₃ uptake increases during neuronal maturation.     

Growth and physiological changes during metamorphosis of Senegal sole reared in the laboratory

The metamorphosis of Solea senegalensis was studied in larvae reared at 20° C and fed four different feeding regimes. A, Artemia (4 nauplii ml⁻¹); B, Artemia (2 nauplii ml⁻¹); C, mixed diet (2 nauplii ml⁻¹ and 3 mg ml⁻¹ microencapsulated diet); and D, microencapsulated diet (3·7 mg ml⁻¹). Rotifers were also supplied in all cases during the first days of feeding. These feeding regimes supported different growth rates during the pre-metamorphosis period (regime A, G=0·376 day⁻¹; regime B, G=0·253 day⁻¹; regime C, G=0·254 day⁻¹; regime D, G=0·162 day⁻¹). Larvae started metamorphosis 9 days after hatching (DAH) when fed the regime A, 13 DAH with regime B, 11 DAH with regime C and 15 DAH with regime D. A minimum 5·6–5·9 mm L_T was required under all feeding regimes to initiate the metamorphosis. Eye translocation was completed when the larvae reached 8·6–8·7 mm L_T (regimes A, B and C), but only 7·3 mm L_T with regime D. 4·4–6·2 days were required to complete eye migration under the regimes A, B and C, and 18·3 days under the regime D. This transformation is concomitant with changes in body reserves, and with the pattern of some digestive enzymes.     

Investigations on Myelination In Vitro: Regulation of 2',3'-Cyclic Nucleotide 3'-Phosphohydrolase by Thyroid Hormone in Cultures of Dissociated Brain Cells from Embryonic Mice

Abstract: The direct influence of l -3,3',5-triiodothyronine (T₃) on the development of 2',3'-cyclic nucleotide 3'-phosphohydrolase (EC 3.1.4.37, CNPase) is demonstrated by using an in vitro culture system of dissociated embryonic mouse brain cells. Serum from a thyroidectomized calf, which contained low levels of T₃ (31 ng/100 ml), and thyroxine, T₄ (<1 μg/ml), was used in the culture medium in place of normal calf serum (T₃, 103 ng/100 ml; T₄, 5.7 μg/ml) to render the culture responsive to exogenously added T₃. The lower levels of enzyme activity observed in the presence of such a deficient medium could be restored to normal values by T₃ supplementation. Half-maximal effect was obtained with 2.5 ± 10⁻⁹ m -T₃. Three days of hormone treatment resulted in the maximal stimulation of CNPase. T₄ was less effective in inducing CNPase activity and the inactive analog of the hormone, reverse T₃ (3,3',5'-T₃) was ineffective. The morphological appearance of the cells was characterized by deformed (smaller size and less in number) reaggregates in the cultures, lacking hormone.     

Seasonal differences in routine oxygen consumption rates of the bonnethead shark

Routine oxygen consumption rates of bonnethead sharks, Sphyrna tiburo , increased from 141·3±29·7 mg O₂ kg⁻¹ h⁻¹ during autumn to 218·6±64·2 mg O₂ kg⁻¹ h⁻¹ during spring, and 329·7±38·3 mg O₂ kg⁻¹ h⁻¹ during summer. The rate of routine oxygen consumption increased over the entire seasonal temperature range (20–30° C) at a Q ₁₀=2·34.     

Plasma cortisol and 17β-oestradiol levels in roach exposed to acute and chronic stress

Plasma cortisol levels were measured as an indicator of physiological stress in roach subjected to brief handling, or to a 14-day period of confinement, and in undisturbed control fish, during winter (water temperature 5° C) and summer (16° C), at which time plasma 17 β-oestradiol levels were also determined. Cortisol levels in undisturbed roach were low (mean 8·1 ng ml⁻¹ at 5° C; 1·4 ng ml⁻¹ at 16° C) and both handling and handling+confinement elevated blood cortisol levels significantly to 400 and 140 ng ml⁻¹, respectively (at 5° C) and 700 and 600 ng ml⁻¹, respectively (at 16) C). Blood cortisol levels had almost returned to baseline within 4 h following handling alone but in fish subjected to handling and prolonged confinement cortisol levels remained elevated for up to 168 h. Differences in baseline and poststress levels of cortisol, and in the rate of recovery from acute stress, were observed at the two different temperatures and the possible factors underlying these differences are discussed. Circulating levels of 17 β-oestradiol were reduced significantly within 24 h of exposure to either acute handling or chronic confinement indicating that the reproductive endocrine system in roach is sensitive to disruption by stressors.     

Evidence for Circadian Variations of Thyroid Hormone Concentrations and Type II 5'-Iodothyronine Deiodinase Activity in the Rat Central Nervous System

Abstract: The 24-h patterns of tissue thyroid hormone concentrations and type II 5'- and type III 5-iodothyronine deiodinase (5'D-II and 5D-III, respectively) activities were determined at 4-h intervals in different brain regions of male euthyroid rats entrained to a regular 12-h light/12-h dark cycle (lights on at 6:00 a.m.). Activity of 5'D-II, which catalyzes the intracellular conversion of thyroxine (T₄) to 3,3',5-triiodo- l -thyronine (T₃) in the CNS, and the tissue concentrations of both T₄ and T₃ exhibited significant daily variations in all brain regions examined. Periodic regression analysis revealed significant circadian rhythms with amplitudes ranging from 9 to 23% (for T₃) and from 15 to 40% (for T₄ and 5'D-II) of the daily mean value. 5'D-II activity showed a marked nocturnal increase (1.3–2.1-fold vs. daytime basal value), with a maximum at the end of the dark period and a minimum between noon and 4:00 p.m. 5D-III did not exhibit circadian patterns of variation in any of the brain tissues investigated. Our results disclose circadian rhythms of 5'D-II activity and thyroid hormone concentrations in discrete brain regions of rats entrained to a regular 12:12-h light-dark cycle and reveal that, in the rat CNS, T₃ biosynthesis is activated during the dark phase of the photoperiod. For all parameters under investigation, the patterns of variation observed were in part regionally specific, indicating that different regulatory mechanisms may be involved in generating the observed rhythms.