hCG-induced changes in LH/CG receptor mRNA transcript levels in the testis of adult hypophysectomized, ethane dimethyl sulphonate-treated rats.

To elucidate the molecular mechanisms involved in the development of precursor cells into functional Leydig cells, effects of hCG on the expression of the luteinizing hormone (LH)/chorionic gonadotrophin (CG) receptor gene were investigated in the testis of adult hypophysectomized, ethane dimethyl sulphonate (EDS)-treated rats. The alkylating drug EDS specifically destroys Leydig cells in the adult rat testis. In hypophysectomized rats, in the absence of LH, this is not followed by the formation of new Leydig cells, leaving a testis in which Leydig cell precursors are presumed to be the only cell type that possess LH receptors. The absence of Leydig cells was confirmed by determining the gene expression of two key steroidogenic enzymes, 3 beta-hydroxysteroid dehydrogenase/isomerase (3 beta HSD) and P-450 17 alpha-hydroxylase/C17-20 lyase (P-45017 alpha) in these animals. Northern blot analysis revealed that hypophysectomy, followed by EDS treatment decreased the total amount of LH/CG receptor mRNA and drastically changed the pattern of LH/CG receptor mRNA transcripts. In the testis of intact adult rats, the expression of the LH/CG receptor gene results in multiple mRNA transcripts with molecular sizes of approximately 7.0, 4.2, 2.5, 1.8 and 1.2 kb. The most abundant species observed in the testis of adult hypophysectomized, EDS-treated rats was the 1.8 kb mRNA transcript, whereas the levels of the other mRNA transcripts were decreased. To stimulate the development of precursor cells into functional Leydig cells, hypophysectomized, EDS-treated rats were treated with high doses of hCG (100 IU) for different periods of time.(ABSTRACT TRUNCATED AT 250 WORDS)

A field study on stress indices in the sea mussel, Mytilus edulis: application of the "stress approach" in biomonitoring.

Sea mussels, Mytilus edulis, collected from a relatively unpolluted area of the Eastern Scheldt, were transplanted along contaminated sites of the Western Scheldt for 2 1/2 and 5 months. Several established stress indices were determined such as accumulation of pollutants, adenylate energy charge (AEC), and condition index. Following field exposure, mussels were also subjected to an additional lethal or sublethal stress. The data show that environmental exposure alters the mussel's response to stress, viz., aerial exposure and increased temperature, at the organismal (anoxic survival time), biochemical (AEC), and molecular (heat shock protein synthesis) level. The "stress approach" to assessment of environmental contamination appears to be a promising method to disclose early changes in the organism at a stage when conventional parameters (condition index, AEC) remain still unchanged.

Short-term exposure to cadmium modifies phosphorylation of gill proteins in the sea mussel.

1. Sea mussels were exposed to cadmium for short periods of time. The excised gills were incubated with radioactive orthophosphate. The gill proteins were separated by 1- and 2-dimensional gel electrophoresis and the phosphorylation state of the proteins was determined by image analysis of autoradiographs. 2. 1-Dimensional gel electrophoresis revealed that exposure of the animals to cadmium stimulated phosphorylation of the gill proteins in a cadmium concentration-dependent manner. 3. 2-Dimensional gel electrophoresis showed that cadmium differentially affected the phosphorylation of various proteins. Major alterations were observed in the basic, high mol. wt proteins and in the acidic, low mol. wt polypeptides.

Synthesis of stress proteins under normal and heat shock conditions in gill tissue of sea mussels (Mytilus edulis) after chronic exposure to cadmium.

1. Sea mussels were exposed to 16.5 micrograms Cd/1 under semi-field conditions for almost one year. The isolated gills were incubated with 35S-methionine or -cysteine. 2. Chronic exposure to cadmium neither altered the rate of amino acid incorporation nor induced expression of heat shock proteins in the gills. 3. Heat shock imposed after chronic exposure to cadmium resulted in an increased synthesis of heat shock proteins, especially those of high molecular weight. 4. Synthesis of cadmium-binding, low molecular weight proteins was observed at any point of the exposure time. Their cadmium-binding capacity and rate of synthesis, after the initial increase, remained unchanged throughout the exposure.

In vivo and in vitro studies on the pathway of modification of mussel pyruvate kinase.

1. On aerial exposure, pyruvate kinase is inactivated in various organs of M. edulis; the decrease of activity is slower in muscle than in non-muscular tissue. 2. Anoxic in vitro incubation of gills results in a rapid inactivation of pyruvate kinase. No change occurs in an aerated medium. 3. Enzyme inactivation is mimicked in part by oxic incubation in an acidified medium containing 5,5-dimethyloxazolidine-2,4-dione, and by the action of calcium ionophore A23187. 4. Incubation of supernatant of gill homogenate results in a slow inactivation of pyruvate kinase that is inhibited by trifluoperazine or EGTA and stimulated by exogenous calmodulin. 5. Addition of ATP plus cAMP stimulates pyruvate kinase inactivation in supernatant of homogenized muscle but not so in a high molecular weight fraction thereof.