Further evidence of interaction between vasodilator β\u3csub\u3e2\u3c/sub\u3e- and vasoconstrictor α\u3csub\u3e2\u3c/sub\u3e-adrenoceptor-mediated responses in maintaining vascular tone in anesthetized rats

The importance of the interaction of α- and β-adrenoceptors in maintaining vascular tone in rats was studied. This interaction after clenbuterol (CLEN) treatment indicates an important contribution of the circulating epinephrine (EPI) levels. In urethane-anesthetized rats, the β2-adrenoceptor antagonist (CI 118.551 was more effective in antagonizing isoproterenol-induced hypotension (mainly β2-mediated) than tachycardia (mainly β1-mediated). Intravenous (i.v.) administration of the α2-adrenoceptor agonist clonidine (CLO) induced an initial pressor response followed by a more prolonged hypotension and bradycardia. The initial hypertensive effect was potentiated by previous acute administration of ICI 118.551 as well as by the nonselective β-adrenoceptor antagonist propranolol, but not by metoprolol, a more selective β1-blocker. Fourteen days of administration of the β2-adrenoceptor agonist CLEN [0.3 mg/kg, subcutaneously (s.c.) twice daily], a treatment that induces desensitization of β2-mediated vasodilation, increased the pressor response induced by CLO, an effect that was not observed in pentobarbital-anesthetized rats. In any case, neither β-blockers nor CLEN treatment affects the hypotension and bradycardia induced by CLO. Mean blood pressure (BP) of CLEN-treated rats was increased under urethane anesthesia but not under pentobarbital anesthesia. Catecholamine levels (principally EPI) were higher in urethane-anesthetized rats. These results provide further evidence of a functional interaction between α2- and β2-adrenoceptor-mediated responses in rat vasculature and suggest that vasodilator β2-adrenoceptors might contribute to the determination of peripheral vascular tone when circulating EPI is substantially elevated

Pressor response induced by clenbuterol treatment in immobilized normotensive rats

Short-term treatment with clenbuterol [0.6 mg/kg-1 subcutaneously (s.c.) daily] produces a pressor effect in stressed rats after a period of immobilization (40 min). The stress applied markedly increases the plasma concentrations of norepinephrine (NE) and epinephrine. After bilateral adrenal demedullation, the increased levels of catecholamines and the hypertensive response obtained after clenbuterol treatment in the stressed animals were reduced to the values of the control rats. Clenbuterol treatment produced desensitization of the β2-adrenoceptor-mediated effect and thus reduced the vasodilator response induced by isoproterenol and increased the vasoconstriction produced by epinephrine but not that caused by NE. This desensitization may be responsible for the hypertensive response after clenbuterol treatment in stressed animals which is attenuated after adrenal demedullation. In conclusion, our results provide evidence that clenbuterol treatment induces pressor effect in normotensive animals under stress

Determination of organochlorine and organophosphate pesticide residues in water from the rivers of Davao City by gas chromatographic-mass spectrometric analysis

Organochlorine and organophosphate pesticides comprise a large group of structural diverse compounds used in the control of agricultural pests. Four major rivers were sampled to evaluate the levels of organochlorine and organophosphate pesticide residues namely: eight (8) sampling stations along Talomo River, four (4) sampling stations along Lipadas River, five (5) sampling stations along Tagluno River, and eight (8) sampling stations in Panigan-Tamugan Rivers. Water samples were extracted by liquid-liquid extraction and analyzed using a gas chromatograph coupled with mass spectrometer detector. A total of ten (10) pesticide residues were identified, and five (5) of the ten are classified banned by the Fertilizers and Pesticides Authority of the Department of Agriculture of the Philippines. The banned pesticides detected in the samples were dieldrin, aldrin, endrin aldehyde, y-chlordane, and B-heptachlorepoxide. The other pesticides identified were penthoate, malathion E50, chlorothalonil, chlorpyrifos, and dichlorodiphenyldichloroethylene (DDE). Concentrations of some detected organochlorine and organophosphate pesticides in water were relatively higher as compared to guideline values set by United States Environmental Protection Agency (US EPA) and by the International Union of Pure and Applied Chemistry (IUPAC) and thus present a threat to various sources of clean water in the locality. Keywords: organochlorine pesticides, organophosphate pesticides, GC-MS, pesticide contaminants, guideline values