Wilfried Hanke

The significance of cortisol for osmoregulation in carp (Cyprinus carpio) and tilapia (Sarotherodon mossambicus).

Changes in plasma cortisol and glucose concentration were studied in carp during acclimation from fresh water (FW) to 1.5% salt water and vice versa. There was an increase in cortisol and glucose concentration during acclimation from FW to salt water which lasted for several days. Reacclimation to FW did not cause clear changes in cortisol and glucose levels. One single injection of cortisol (0.2 mg/100 g or 1 mg/100 g) and additional transfer to salt water (1.5% for carp and 2.7% for tilapia) altered the changes caused by acclimation alone of cortisol, glucose, Na+ concentration, and the osmolality in plasma. Gill Na-K-ATPase activity was also influenced. The effects of cortisol on electrolyte concentrations during acclimation and on Na+-K+-ATPase activity differed in both types of fish. Cortisol clearly lowered the increase in plasma Na+ concentration of the stenohaline carp and increased the ATPase activity. The changes in plasma Na+ concentration of the euryhaline tilapia was not clearly altered and the enzyme activity was inhibited. The significance of these cortisol effects is discussed.

The effect of large doses of vitamin C AND magnesium on stress responses in common carp, Cyprinus carpio

1. Plasma magnesium, cortisol, lactate and ascorbic acid were examined in common carp subjected to various dietary treatments and following handling stress. 2. Under conditions of satisfied dietary magnesium and ascorbate requirements, plasma cortisol concentration after stress increased less pronouncedly than in fish fed large doses of ascorbate and/or magnesium. 3. Plasma lactate increased significantly in all groups after stress, although the increase seemed to be more severe (detrimental) in fish on large doses of ascorbate, either as ascorbic acid (AA) or ascorbic monophosphate Mg salt (AP). 4. Large doses of dietary ascorbate, both AA and AP, resulted in a significant increase of total ascorbate concentration in kidney and hepatopancreas of carp in comparison to pre-experimental level. 5. Kidney total ascorbate concentration decreased by 10-23% in all groups but one in which fish fed diet supplemented with AA displayed a significant increase (30%) of tissue ascorbate. The opposite trend was found in hepatopancreas of AA group with 21.5% ascorbate depletion. 6. The present results suggest that plasma cortisol and kidney (steroidogenesis site) and hepatopancreas ascorbate concentration responses to stress may not be related. Our results also do not support the hypothesis of the primary role of the high concentration of ascorbate in the kidney inhibiting steroidogenesis.

Electrolyte changes and volume regulatory processes in the carp (Cyprinus carpio) during osmotic stress

Abstract 1. 1. Stenohaline carps were acclimatized from freshwater to 1.5% salt water and reacclimatized to freshwater. 2. 2. Changes of osmolality and electrolyte content in blood plasma and extracellular and intracellular space, as well as electrolyte content of muscle cells, were measured. 3. 3. The course of hyperregulation could be shown in plasma during the course of acclimatization and the return of the parameters during reacclimatization. 4. 4. The decrease of ICS and the increase of ECS and the shifts of electrolytes after transfer from freshwater to 1.5% saltwater was demonstrated. 5. 5. Acclimatization from 1.5% salt water to freshwater resulted in an increase of ICS and a transitory increase of ECS. 6. 6. The differences during salt water acclimatization between a stenohaline teleost, like carp, and a euryhaline fish, like tilapia, are discussed.

Circadian rhythm of interrenal activity in Xenopus laevis

Young specimens of Xenopus laevis were kept under constant environmental conditions (artifical light from 600 to 1800 hr, feeding between 800 and 900 hr) and the concentrations of aldosterone and corticosterone in the serum were measured every 3 hr. Furthermore, the kidneys containing the interrenals were removed and their corticosteroid release under stimulation by the pars distalis and mammalian ACTH was determined. Under these conditions, the corticosteroid levels in the serum were maximal from 900 to 1200 hr (corticosterone, 7.7 +/- 0.47 ng/ml; aldosterone, 2.8 +/- 0.27 ng/ml) and minimal during the night (corticosterone, 5.2 +/- 0.43 ng/ml; aldosterone, 1.7 +/- 0.18 ng/ml). The basal secretion rate of the interrenals in vitro showed the opposite course (corticosterone, 24 +/- 3 to 72 +/- 8 pg/min/tissue; aldosterone, 46 +/- 5 to 68 +/- 9 pg/min/tissue). Stimulation by the pars distalis and mammalian ACTH clearly increased the secretion rate. After both types of stimulation the original rhythm was lost for aldosterone but still present for corticosterone. The ratio of the amounts of corticosterone/aldosterone was greater than 1.0 in the serum but less than 1.0 in the incubation fluid. It decreased significantly after stimulation in vitro by pars distalis or ACTH.

Atrial natriuretic factor (ANF) binding sites in frog kidney and adrenal

Atrial natriuretic factor (ANF) binding sites were localized and quantified in kidney and adrenal of the frog Rana temporaria by quantitative in vitro autoradiography. [125I]-rat ANF(99-126) binding was present in kidney glomeruli and in the outer layer of interrenal tissue in the adrenal gland. ANF binding exhibited positive cooperativity with a half-maximal binding concentration (EC50) of 102 +/- 16 pM in glomeruli and 93 +/- 19 pM in interrenal tissue (n = 8). The corresponding maximal binding capacities (Bmax) were 1.33 +/- 0.16 and 1.21 +/- 0.36 fmol/mm2. [125I]-Rat ANF(99-126) binding was competitively displaced by unlabeled ANF analogues with an intact disulfide bridge showing a lower affinity than the iodinated ligand. The presence of ANF binding in glomeruli and steroidogenic interrenal cells suggests physiological functions of ANF for the osmomineral regulation in the frog by influencing glomerular filtration rate and adrenal steroid secretion.

Long-term starvation in Xenopus laevis Daudin--II. Effects on several organs.

1. The effect of starvation for 12 months on organo-somatic indices, glycogen, protein and water contents of several organs and the Na+/K+ ratio in muscle was studied in the South African clawed toad Xenopus laevis Daudin. 2. The liver- and ovary-somatic index were reduced by 30 and 70% of the initial value after 12 months. Fat bodies had disappeared after approximately 6 months of starvation. The indices of heart and kidney were not changed. 3. Glycogen concentration of the liver, ovaries and muscle were depleted nearly totally during the first half of the experimental time, whereas glycogen in the kidney seemed to be unaffected. 4. Protein concentration increased in the liver, decreased in the muscle and remained constant in the kidney. 5. Starvation caused an increase of the water concentration of the whole animal and different organs, especially at the end of the experiment. 6. The Na+/K+ ratio of the muscle increased significantly after 6 months of starvation and reached a maximum after 10 months.

Localization of binding sites for atrial natriuretic factor and angiotensin II in the central nervous system of the clawed toad Xenopus laevis

SummaryThe distribution of binding sites for atrial natriuretic factor (ANF) and angiotensin II (A II) was investigated in the central nervous system (CNS) of the clawed toad Xenopus laevis by means of in vitro autoradiography using [125I]-rat ANF(99–126) or [125I] [Val5] A II and [125I]human A II as labeled ligands. The highest densities of specific ANF-binding were detected in the nucleus habenularis, thalamic regions, hypophyseal pars nervosa and nucleus interpeduncularis. Moderate ANF-binding was found in the bulbus olfactorius, pallium, septum, striatum, lateral forebrain bundle, nucleus infundibularis, hypophyseal pars distalis and tectum. The highest levels of specific A II binding sites were observed in the nucleus praeopticus, nucleus habenularis, hypophyseal pars nervosa and pars distalis, whereas the amygdala contained moderate A II binding. The existence of specific binding sites for ANF and A II in the CNS of Xenopus laevis suggests that both peptides act as neurotransmitters or neuromodulators in the amphibian CNS. The co-localization of dense binding sites for both peptides in the nucleus habenularis, hypophyseal pars nervosa and pars distalis supports the view that ANF and A II have opposite regulatory functions in these regions.

The significance of the amino acids during osmotic adjustment in teleost fish—II. Changes in the stenohaline cyprinus carpio

Abstract 1. 1. The concentrations and content of predominant amino acids were determined in muscle and liver during acclimation of carps from FW to 1.5% SW and reacclimation to FW. 2. 2. Glycine and histidine clearly showed increasing concentration and content in muscle during the acclimation period and decreasing values after retransfer. 3. 3. Taurine was the predominant amino acid in muscle and liver. The changes of concentration or content of it during acclimation were not very clear and, therefore, it is suggested that its role for osmoregulation is less important than in euryhaline fish. 4. 4. The concentration of alanine increased in higher external osmolality and decreased during reacclimation in both organs. The contribution to osmotic pressure is not high, especially in muscle tissue. 5. 5. There was a strong increase of glutamate only in the liver when acclimated to 1.5% SW and a decrease after retransfer. This points to the metabolic role of this organ which might be indicated by the concentration of this amino acid.

Electrolyte changes, cell volume regulation and hormonal influences during acclimation of rainbow trout (Salmo gairdnerii) to salt water

Abstract 1. 1. Rainbow trout were acclimated to salt water (1.5, 2.0 or 3.0%, which means 40, 60 or 85% concentrated sea-water) and the electrolyte, glucose and cortisol concentrations of the plasma as well as the extra- and intracellular muscle space, the muscle electrolyte concentrations and the ATPase activity were analysed. 2. 2. Plasma osmolality, Na+, Ca2+ and Mg2+ concentrations of the plasma had a maximum at 24 hr after the start of acclimation when acclimated to 3.0% salt water. Plasma osmolality, Na+ and Mg2+ concentrations were significantly higher during the whole acclimation time when exposed to 3.0% salt water. 3. 3. Variations and regulations of ECS and ICS were clearly demonstrated. The intracellular electrolyte concentrations were also maximal at 24 hr. 4. 4. The plasma glucose level was just slightly elevated, but the cortisol level clearly indicated a stress response at 24 hr. 5. 5. The activity of gill Na-K-ATPase increased during the acclimation time. 6. 6. The regulatory processes in trout during acclimation to salt water are compared with those occurring in tilapia and carp.

Cell volume regulation in juveniles of Xenopus laevis in hypertonic mannitol solution

Abstract o 1. Juvenile Xenopus laevis can be easily adapted to 300 mOsm urea in the external medium, which makes it possible to study cell volume regulatory mechanisms induced by a penetrating external substance (high osmolality and low tonicity). 2. Water loss was caused during the first days of adaptation. 3. Despite urea entrance, urea was not equally distributed, the internal concentration reached only about 1/3 of the external. 4. Increase of plasma osmolality above external level was observed due to an increase of Na + , Cl − and urea concentration. 5. Decrease of Na content and increase of urea content of the cell resulted together with a decrease of intracellular space. 6. Intracellular volume reduction was not regulated during the experimental period which clearly distinguishes this type of adaptation from adaptation to NaCl or impermeable mannitol.