Populations of scavenging seabird species in the North Sea may fluctuate with an artificial food source: the availability of fishery waste. To document this impact, it is necessary to assess the birds' nutritional status during periods with decreased fishing activity. Reference data for this purpose was collected from 22 herring gulls investigated during laboratory fasting. After 6 d of food deprivation and body mass losses exceeding 15%, the first birds entered starvation phase 3. Comparatively, this is a rather weak fasting capacity. Plasma levels of total protein and thyroid hormones decreased and beta-hydroxybutyrate increased with fasting duration. The leucocyte proportions were shifted from lymphocytes to heterophils. After 3 d of refeeding, most of the fasting changes were reversed. Plasma enzyme activities increased and hematocrit, hemoglobin, and erythrocyte numbers decreased in both fasting and control birds, most likely as a result of experimental stress and repeated blood sampling. Glucose, cholesterol, monocytes, basophils, and glycosylated hemoglobin remained fairly constant. Triglycerides, free fatty acids, uric acid, and urea varied significantly, but changes were not as clearly a result of fasting. Therefore, total protein, beta-hydroxybutyrate, triiodothyronine, thyroxine, and lymphocyte and heterophil percentages may be the most reliable indicators of the nutritional status and the condition of free-living herring gulls.

To study the direct effect of mycotoxins belonging to different chemical classes on testicular function, dispersed interstitial cells from testes of adult gerbils were short-term cultured either in the absence or presence of mycotoxins, and testosterone secretion was measured. When interstitial cells were incubated with T-2 toxin (0.0076-38.3 nM) there was a dose-dependent decrease of testosterone production (r = -0.72, ID50 = 0.042 nM). Since neither progesteronenor DHEA-stimulated testosterone production was affected by T-2 toxin, the observed inhibition of basal secretion was apparently due to a decrease of pregnenolone production and/or conversion of pregnenolone to progesterone. Much higher concentrations of zearalenone or of ochratoxin A were necessary to induce a similar inhibition of steroidogenesis (369 microM and 1838 microM, respectively) when compared to T-2 toxin. In contrast, citrinin or cyclopiazonic acid affected testosterone secretion only slightly, values reaching significant levels at doses of 1.74 nM (citrinin) and 149 nM (cyclopiazonic acid). In the presence of kojic acid (2.63-2633 nM) a significant, though not dose-dependent inhibition of testosterone secretion was observed. From these experiments it is concluded that mycotoxins of distinct chemical structure act directly on testicular tissue, presumably by inhibiting early steps of the steroidogenic pathway.

In order to investigate the role of cortisol in the regulation of testicular function, adult male guinea pigs were challenged with ACTH (20 IU), cortisol (8 or 16 mumol), or with ACTH plus dexamethasone (DEX, 2 mumol). The amounts of cortisol, testosterone, progesterone, and androstenedione present in the plasma or secreted by incubated adrenals or testes were determined by radioimmunoassay. The plasma concentrations of LH were determined using a radioimmunoassay for rat LH. ACTH treatment elevated cortisol plasma concentrations to 999% of control values, whereas it reduced testosterone plasma levels to 43% of control values. ACTH treatment did not affect LH plasma levels. A significant negative correlation was found in ACTH-treated animals, when the cortisol and testosterone plasma concentrations in serially taken blood samples (30-240 min after treatment) were compared (rs = -0.90 and rs = -0.99, P < 0.05). In addition to cortisol, ACTH raised progesterone and androstenedione plasma concentrations. If animals were treated with 2 mumol DEX + ACTH, the plasma levels of cortisol and androstenedione but not of progesterone, testosterone or LH were changed. ACTH stimulated the in vitro secretion of cortisol, progesterone and androstenedione by the adrenals but reduced the in vitro release of androstenedione and testosterone by the testes. In summary, treatment of guinea pigs resulted in elevated cortisol and in reduced testosterone plasma concentrations. The mechanism of the cortisol-induced inhibition of testicular function was independent of the LH plasma concentrations. The in vitro experiments indicate that cortisol directly interacts with the Leydig cells, presumably by inhibiting the activity of the testicular 17 alpha-hydroxylase and/or C17,20-lyase. Taking into account the results of comparable investigations in the rat, the inhibition of the testicular 17 alpha-hydroxylase and/or C17,20-lyase takes place if the intracellular cortisol exceeds the capacity of the 11 beta-hydroxysteroid dehydrogenase to inactivate it.

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