These in vitro tests may prove valuable to screen potential tumor growth promoters.

1 Thioperamide (TP), an imidazole and a highly potent, specific antagonist of the histamine H3 receptor, inhibited the secretion of cortisol from bovine isolated adrenocortical cells (IC50 0.20 gM) and, in the rat (5 mg kg-1) prevented both basal and stress-induced secretion of corticosterone.

No abstract

We have demonstrated specific, high affinity binding of a biologically active Tyr23-monoiodinated derivative of ACTH, [125I][Phe2,Nle4]ACTH 1-24, in rat brain homogenates. Similarly, in metabolically inhibited and noninhibited rat whole brain slices there is a specific "binding-sequestration" process that is dependent on time, protein concentration, and pH. In homogenates, binding curves were best described by a two-site model and provided the following parameters: Kd1 = 0.65 +/- 0.47 nM, Bmax1 = 21 +/- 41 fmol/mg protein; Kd2 = 97 +/- 48 nM, Bmax2 = 3.5 +/- 1.8 pmol/mg protein. In metabolically viable brain slices, concentration-competition curves of [125I][Phe2,Nle4]ACTH 1-24 binding-sequestration can be described by three components (Kd1 = 14 +/- 24 nM, Bmax1 = 50 +/- 95 fmol/mg protein; Kd2 = 2.4 +/- 1.9 microM, Bmax2 = 44 +/- 49 pmol/mg protein; Kd3 = 0.16 +/- 1.0 mM, Bmax3 = 5.3 +/- 54 nmol/mg protein). Metabolic inhibition, by removal of glucose and addition of 100 microM ouabain, abolishes the lowest affinity, highest capacity binding-sequestrian component only (Kd1 = 7.1 +/- 14 nM, Bmax1 = 8.7 +/- 16 fmol/mg protein; Kd2 = 7.4 +/- 4.49 microM, Bmax2 = 37 +/- 27 pmol/mg protein). The two binding-sequestration parameter estimates obtained from metabolically inhibited tissue slices are not significantly different from those of the two higher affinity components obtained with noninhibited tissue. Thus, metabolic inhibition permits demonstration of ACTH receptor binding only, unconfounded by sequestration or internalization of ligand:receptor complexes.(ABSTRACT TRUNCATED AT 250 WORDS)

1 General anaesthetics disrupt normal cell receptivity and responsiveness while sparing vital respiratory processes. Ultimate elucidation of the molecular basis of general anaesthesia presumes the identi®cation of one or more subcellular components with appropriate sensitivity to the entire array of anaesthetics. 2 Previously, we showed the universal cellular enzymes, cytochrome P450 mono-oxygenases, to be sensitive at relevant concentrations to all anaesthetics tested. The potential signi®cance of P450 inhibition by anaesthetics resides in the contribution of this enzyme family, in conjunction with that of cyclooxygenases and lipoxygenases, to the generation from arachidonic acid of lipid second messengers, the eicosanoids. 3 We have shown that P450 enzymes model the site of general anaesthesia in the tadpole with respect to (a) an absolute sensitivity to increasing chain-length series of¯exible, straight chain primary and secondary alcohols and straight chain diols, (b) an absolute sensitivity to increasing molecular weight series of rigid cyclic alkanols and cyclic alkanemethanols, (c) the points of abrupt change and of reversal (cut-o ) in the linear relationship between increasing anaesthetic potency with increasing carbon chain length, and (d) non-di erentiation between secondary alkanol enantiomers. These ®ndings reveal the P450 enzyme family as the most relevant biomolecular counterpart of the site of general anaesthesia, thus far identi®ed.