Endocrine Abstracts

Background: Testosterone acts as a coronary vasodilator, and improves myocardial ischaemia in men with coronary artery disease. The dilatory mechanism of testosterone is independent of the classical androgen receptor and also of the release of endothelial-derived vasodilators. The aim of the present study was to determine whether testosterone has any demonstrable calcium antagonistic action, and if so to determine whether this is via inhibition of voltage-operated calcium channels (VOCCs) or store-operated calcium channels (SOCCs).

Methods: A7r5 aortic smooth muscle cells were grown in culture until confluent. The cells were then re-suspended in physiological buffered saline (PBS), loaded with the calcium sensitive fluorescent probe indo-1-AM (5uM), and incubated for two minutes with either testosterone (1uM), the VOCC blocker verapamil (10uM), the SOCC blocker SK&F96365 (50uM) or an equivalent volume of vehicle. Cells were then exposed to prostaglandin F2alpha (PGF, 10uM) in either calcium containing or calcium free PBS, and the change in cellular fluorescence measured by flow cytometry.

Results. Changes in cellular fluorescence are given as mean (sem) in arbitrary units, and analysed via students unpaired t test. Testosterone (1uM) reduced the change in cellular fluorescence to 10uM PGF, from 9.0 (1.1) to 3.6 (0.6) (P<0.01). The change in cellular fluorescence to 10uM PGF was reduced in calcium free PBS from 15.6 (0.7) to 3.6 (0.3) (P<0.0001), by incubation with SK&F96365 (50uM) from 8.3 (0.7) to 4.7 (0.8) (P<0.01), but was unaffected by incubation with verapamil (10uM); 8.8 (0.9) compared to 7.8 (1.3) (P=0.6).

Conclusion: The increase in intracellular calcium induced by PGF occurs via the release of calcium from intracellular stores, with subsequent extracellular calcium entry via SOCCs. Testosterone acts to inhibit the response to PGF with a similar efficacy as the SOCC blocker SK&F96365. This data therefore supports a calcium antagonistic action for testosterone upon SOCCs.