Abstract
1. The effect of ouabain on catecholamine (adrenaline and noradrenaline) secretion induced by agents acting on cholinoceptors was studied in perfused cat adrenal glands. Acetylcholine (ACh) (5 x 10(-7) to 10(-3) M), pilocarpine (10(-5) to 10(-3) M) and nicotine (10(-6) to 5 x 10(-5) M) caused dose-dependent increases in catecholamine secretion. Both ACh and nicotine released more noradrenaline than adrenaline and the reverse was the case for pilocarpine. 2. Ouabain (10(-5) M) enhanced catecholamine secretion induced by ACh (10(-5) M), pilocarpine (10(-3) M) and nicotine (3 x 10(-6) M) during perfusion with Locke solution. The ratio of adrenaline to noradrenaline was not affected by ouabain. 3. In the absence of extracellular Ca2+, ACh and pilocarpine, but not nicotine, still caused a small increase in catecholamine secretions, which were enhanced by treatment with ouabain (10(-5) M) plus Ca2+ (2.2 mM) for 25 min. The effect of ouabain was much more significant on noradrenaline secretion than on adrenaline secretion. The enhanced response was blocked by atropine (10(-6) M) but not by hexamethonium (5 x 10(-4) M). 4. Nifedipine (2 x 10(-6) M) inhibited the responses to pilocarpine and nicotine. The treatment with ouabain (10(-5) M) reversed only the response to pilocarpine and resulted in a significant increase in the proportion of noradrenaline released. 5. It is suggested that ouabain enhances evoked catecholamine secretions by facilitating Ca2+ entry through nicotinic receptor-linked Ca2+ channels and by increasing the intracellular Ca2+ pool linked to muscarinic receptors.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.