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·ABSTRACTThe present series of experiments provided evidence that the generally accepted distinction between a-and s-adrenergic receptors is not immutable. In frog hearts and rat atria 3H-phenoxybenzamine (3H-POB ) blocked inotropic responses to catecholamines only at temperatures below l7 0 C and potentiated responses ab ove 23 0 C, and considerably more radioactivity was bound to the myocardium at lower temperatures. The converse was true for l4C-propranolol, and the potency of a-and s-adrenergic agonists was shawn to parallel the effectiveness of the blocking agents. Alkylation of a-adrenergic receptors by POB at l4 0 c prevented the appearance of s-adrenergic receptors when the temperature was subsequently raised ta 24 o C.Phentolamine prevented block by 3H-POB and considerably reduced its binding ta the myocardium at low but not at high temperatures. After exposure ta unlabelled POB in the presence of phentolamine at low temperature and thorough washing, exposure to 3H-POB produced a IIpositive label" of the adrenergic receptors, which was localized in a 20,000 9 (ll mitochondrial ll ) and in a IIsoluble protein" fraction. Pretreatment of rats with 6-hydroxydopamine, but not with reserpine, prevented the appearance of oe-adrenergic receptor charac.teristics in left atria at low temperatures; this indicated that adrenergic innervation, but probably not stores of neurotransmitter, is necessary to allow transformation of the receptors. It is suggested that a-and S-adrenergic receptors may be different allosteric conformations of the same molecule.

Procaine penicillin G was administered by intramuscular (i.m.) injection to groups of healthy 100 kg market pigs at the approved label dose (15,000 IU/kg body weight), once daily for three consecutive days; or an extra-label dose (66,000 IU/kg body weight), once daily for five consecutive days. Penicillin G residue depletion was followed in plasma, tissue and injection sites using a liquid chromatographic method. Groups of pigs were killed 1, 2, 3, 4, 5 and 8 days after the last injection with the label dose. Penicillin G was not detected in liver after 1 day of withdrawal, in muscle and fat after 2 days of withdrawal, in plasma after 4 days of withdrawal, in skin after 5 days of withdrawal, or in kidney and the injection sites after 8 days of withdrawal. Other groups of pigs were killed 1, 2, 3, 5 and 7 days after injection with the extra-label dose. In these pigs penicillin G was not found in liver after 2 days of withdrawal, in fat after 3 days of withdrawal, or in the muscle, skin, plasma and injection sites after 7 days of withdrawal. Penicillin G was found at all times in the kidneys of the groups of pigs that received the high dose. The technique used for neck injections was critical to obtain intramuscular rather than intermuscular injections. The Bureau of Veterinary Drugs, Health Protection Branch, Health Canada calculated that the appropriate withdrawal period for pigs was 8 days for a dose of 15,000 IU procaine penicillin G/kg body weight and 15 days for a dose of 66,000 IU/kg.

The mass spectrometry of an organometallic parasiticide used for treatment of leishmaniasis was studied using primarily fast-atom bombardment with complementary studies conducted using electrospray ionization. The positive-ion mass spectrum of meglumine antimonate contained ions with characteristic antimony isotope ratios (57:43) at mlz 6271629, 5071509, 4061408 and 3141316. There was also evidence of ion clusters containing antimony atoms (Sb,-3), which decompose to the mass 5071509 species under acid pH conditions. For meglumine antimonate, an empirical formula CIJIH,Ol,,N,Sb (molecular weight 507) is proposed with a structure containing four Sb-0 bonds in a symmetrical geometry.Following the return of soldiers from the Gulf war, there was concern about possible infection of leishrnaniasi~,'-~ and new interest in the characterization of various parasiticides. Organometallics containing toxic levels of pentavalent antimony have received extensive use as parasiticides or drugs for treatment of leishmaniasis-infected cattle and human beings. lLS Although the structure of the parasiticide, meglumine antim~natel-~ is not established, it is believed that the drug contains a polar gluconate or gluconate-derived functionality (Fig. 1). The organometallic is thus susceptible to thermal degradation and, upon heating, readily transforms to involatile salts. This has limited its study using gas chromatography/mass spectrometry with electron impact ionization, and hampered the elucidation of mechanistic pathways of the parasiticide. Consequently, little is known about the structure of the intact organometallic, its metabolites and subsequent degradation products.Although conventional analytical methodologies such as atomic absorption and inverse voltametry have been used for study of the drug, these methods are not well suited to the determination of the intact organometallic and metabolites excreted in urine. Reported chemotherapy and clinical trials have therefore relied on the determination of pentavalent antimony metal resulting from samples subjected to acid digestion.IL3In this work, the intact parasiticide, meglumine antimonate was studied, using primarily fast-atom bombardment (FAB) mass spectrometry, with complementary studies employing electrospray ionization, as part of an on-going program to develop mass spectrometric tools for broad spectrum analysis (BSA) of pesticides.'-' BSA is used in the context of optimizing * Author for correspondence the information obtainable from analyses of environmental samples. We report new mass spectral data of relevance to understanding the efficacy of organoantimony parasiticides. EXPERIMENTALStudies were conducted using a VG 70s instrument (Manchester, UK) which was followed by detailed studies using a VG Autospec Q mass spectrometer of EBEQ geometry. For the FAB experiments, suspensions of pharmaceutical grade meglumine antimonate were prepared in glycerol and the target bombarded using argon atoms (6 keV energy). Studies were also conducted using samples acidified with hydro...

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