Effect of the imidazoline-derivative ST-91 on heart rate and blood pressure in healthy man

α-adrenoceptor stimulation attenuates melanoma growth in mice

BACKGROUND AND PURPOSE

Recently, β-adrenoceptor blockade has emerged as a potential strategy to inhibit melanoma growth. However, it remains to be ascertained whether β-adrenoceptor stimulation by circulating catecholamines increases melanoma growth in mice.

EXPERIMENTAL APPROACH

B16F10 melanoma-bearing mice were used to evaluate effects of adrenaline and specific adrenoceptor (AR) ligands on tumor volume. AR expression as well as effects of AR ligands on cell viability, production of mitochondrial reactive oxygen species (mROS) and proliferation activity in B16F10 cells were determined by biochemical analyses.

KEY RESULTS

qPCR analyses revealed that B16F10 cells express both α- (α1B-, α2A- and α2B-AR) and β-ARs (β₂ -AR). We found that treatment with the α- and β-AR agonist adrenaline or with the synthetic catecholamine isoprenaline, that selectively stimulates β-ARs, did not affect melanoma growth. Conversely, adrenaline reduced tumor growth in mice co-treated with propranolol, a β1β2-AR antagonist. Adrenaline had no effect in tumor-bearing β1β2-AR knockout mice, in which β1- and β2-ARs are lacking, but it reduced tumor growth when co-administered with propranolol suggesting that tumor β2-ARs negatively regulate adrenaline antitumor activity. Additionally, we found that α1-AR stimulation with cirazoline yielded a decrease in B16F10 melanoma size. These effects on melanoma growth were paralleled by reduced cell viability and proliferation activity as well as increased mROS production in α1-AR-stimulated B16F10 cells. Decreased viability, proliferation and mitochondrial function in B16F10 cells also occurred after α2-AR stimulation by α2-AR agonist ST-91.

CONCLUSIONS AND IMPLICATIONS

In B16F10 melanoma model, stimulation of α-AR subtypes yields in vivo and in vitro anticancer activity.

Drug-induced piloerection in man: an alpha 1-adrenoceptor agonist effect?

The physiology of piloerection is described and clinical experience is discussed. The objective and subjective evidence for drug-induced piloerection by a number of drugs is given and, where it is known, their pharmacological mechanism is described. The results are considered in relation to the hypothesis that drug-induced piloerection is only produced by drugs with alpha 1-adrenoceptor agonist activity. For those drugs without the latter activity where piloerection is supported only by subjective evidence it is suggested that objective evidence should be sought. The fact that there is no objective evidence that the classical alpha 1-adrenoceptor agonist, phenylephrine, produces piloerection is found surprising and it is suggested that such evidence should be sought. If it is found that phenylephrine does not produce piloerection, then the possibility of the existence of a further alpha-agonist subgroup needs to be considered.

The hypothermic effect of clonidine and other imidazolidines in relation to their ability to enter the central nervous system in mice

Clonidine and several other structurally related imidazolidines were administered intraperitoneally to mice and their capacity to cause hypothermia was used as an indication of their ability to enter the central nervous system. The substances were: clonidine (2-[w,6 dichlorophenylimino] imidazolidine) and its 2, 6-disubstituted derivates: St 91 (2,6-diethyl), St 93 (2-chloro, 6-methyl), St 95 (2,6-dimethyl) and St 1697 (2-ethyl, 6-methyl). All caused dose-dependent reductions in body temperature. Clonidine was most potent and was effective over the range 62.5-500 millimicron/kg i.p. clonidine lowered body temperature by 2.9 0.15oC. Relative potencies (R) were: clonidine (R 1), St 91 (0.41), St 1697 (0.29), St 93 (0.21) and St 95 (0.06). Hypothermia was inhibited by piperoxan injected intracisternally (10 millimicron/kg) but not intraperitoneally (10 and 50 millimicron/kg). Following intracisternal administration, the imidazolidine dose response curves were shifted in a parallel fashion to the left relative to the intraperitoneal administration. It is suggested that these compounds can all cross the blood-brain barrier in mice and interact with central alpha-adrenoceptors to cause hypothermia. These findings are at variance with the abilities of some of these substances to cause sedation and hypotension mediated by interaction with central alpha-adrenoceptors.