An Overview of Antibiotics as Emerging Contaminants: Occurrence in Bivalves as Biomonitoring Organisms.

Antibiotics are used for therapeutic and prophylactic purposes in both human and veterinary medicine and as growth promoting agents in farms and aquaculture. They can accumulate in environmental matrices and in the food chain, causing adverse effects in humans and animals including the development of antibiotic resistance. This review aims to update and discuss the available data on antibiotic residues, using bivalves as biomonitoring organisms. The current research indicates that antibiotics' presence in bivalves has been investigated along European, American and Asian coasts, with the majority of studies reported for the last. Several classes of antibiotics have been detected, with a higher frequency of detection reported for macrolides, sulfonamides and quinolones. The highest concentration was instead reported for tetracyclines in bivalves collected in the North Adriatic Sea. Only oxytetracycline levels detected in this latter site exceeded the maximum residual limit established by the competent authorities. Moreover, the risk that can be derived from bivalve consumption, calculated considering the highest concentrations of antibiotics residues reported in the analyzed studies, is actually negligible. Nevertheless, further supervisions are needed in order to preserve the environment from antibiotic pollution, prevent the development of antimicrobial resistance and reduce the health risk derived from seafood consumption.

Brain renin-angiotensin system modifies the blood pressure response to intracerebroventricular cadmium in rats.

In order to elucidate the involvement of the brain renin-angiotensin system (RAS) in cadmium intracerebroventricular (ICV) hypertension, we evaluated the effects of a pretreatment with different drugs: clonidine, an alpha(2) adrenergic agonist, enalapril and captopril, both ACE inhibitors, and saralasin, a competitive nonselective AT(1) and AT(2) receptor antagonist. We used a rat strain with low levels of kallikrein (LKR) that was more sensitive to ICV cadmium hypertension, compared with normal kallikrein rats (NKRs), the control strain. The interplay between the kallikrein-kinin system and the RAS in the LKR strain caused various hemodynamic alterations, which we believe were the result of elevated RAS activity in these animals. Moreover, we suggest that the defective kallikrein-kinin system in LKR may also cause an alteration in the activation of brain RAS in these animals. The LKR displayed elevated concentrations of plasma AII, hypertrophy of the myocardium, and initial alterations in the renal glomerulotubular system. With the exception of clonidine, all of the other drugs showed greater antihypertensive effects of differing statistical significance in LKR, compared with NKR. Both ACE inhibitors were able to significantly reduce pressor response to cadmium ICV in LKR throughout the experiment, whereas in NKR, they were only able to reduce the hypertensive peak of cadmium. A significant protective effect was also observed in LKR pretreated with saralasin, while no effect was observed in NKR. These findings confirm the presence of brain RAS activation in LKR and its contribution to the central control of pressor response to cadmium ICV.

Gluten exorphin B5 stimulates prolactin secretion through opioid receptors located outside the blood-brain barrier.

Gluten exorphin B5 (GE-B5) is a food-derived opioid peptide identified in digests of wheat gluten. We have recently shown that GE-B5 stimulates prolactin (PRL) secretion in rats; this effect is abolished by preadministration of the opioid receptor antagonist naloxone. However, since the structure of naloxone allows it to cross the blood-brain barrier (BBB) and antagonize opioid effects centrally as well as peripherally, it could not established, on the basis of those data, if GE-B5-induced PRL release is exerted through sites located inside or outside the BBB. In this study, we sought to determine the site of action of GE-B5 on PRL secretion, by pretreating male rats with naloxone methobromide (NMB), an opioid antagonist that does not cross the BBB. Four groups of rats were given the following treatments: 1) intravenous vehicle; 2) intravenous GE-B5 (3 mg kg(-1) body weight); 3) intraperitoneal NMB (5 mg kg(-1) body weight), followed by vehicle; 4) NMB, followed by GE-B5. Blood samples for PRL were taken at intervals for 40 minutes after vehicle or GE-B5 administration. GE-B5 stimulated PRL secretion; the effect was statistically significant at time 20. NMB preadministration completely abolished PRL response. Our experiment indicates that GE-B5 stimulates PRL secretion through opioid receptors located outside the BBB. Since opioid peptides do not exert their effect on PRL secretion directly, but via a reduced dopaminergic tone, our data suggest that GE-B5 can modify brain neurotransmitter release without crossing the BBB.