title: Dual effect of adrenaline on noradrenaline release in the pithed rabbit.
abstract: We examined the effects of adrenaline on the noradrenaline release rate and plasma catecholamine levels in the pithed rabbit with electrically stimulated sympathetic outflow (3 Hz). Adrenaline (0.06 micrograms/kg/min) increased the rate of noradrenaline release into the plasma. This increase was prevented by propranolol (0.2 mg/kg + 0.1 mg/kg/h) and probably involves activation of presynaptic beta-adrenoceptors. A higher dose of adrenaline (1.0 micrograms/kg/min) significantly reduced the noradrenaline release rate. The reduction was "reversed" to a facilitatory effect by phenoxybenzamine (4 mg/kg). Propranolol alone slightly inhibited the noradrenaline release rate. After pretreatment with desipramine (1.0 mg/kg + 0.2 mg/kg/h), the inhibitory effect of propranolol on noradrenaline release was more pronounced and blood pressure was also lowered. However, in rabbits pretreated with captopril (1 mg/kg) in addition to desipramine, the sympathoinhibitory effect of propranolol was not observed. These results suggest that adrenaline can activate either presynaptic beta-adrenoceptors to increase noradrenaline release or, in higher doses, presynaptic alpha-adrenoceptors to inhibit noradrenaline release in vivo. The decrease in the noradrenaline release rate produced by propranolol alone may not be due to blockade of facilitatory presynaptic beta-adrenoceptors, but rather to depression of renin secretion. This would decrease angiotensin II formation and hence decrease the presynaptic release-enhancing effect of angiotensin II.
authors.forename: H
authors.initials: H
authors.lastname: Majewski
authors.forename: L
authors.initials: L
authors.lastname: Hedler
authors.forename: C
authors.initials: C
authors.lastname: Schurr
authors.forename: K
authors.initials: K
authors.lastname: Starke
mesh_terms: D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D003655:Decerebrate State; D004837:Epinephrine / Q000494:pharmacology*; D005260:Female; D008297:Male; D009638:Norepinephrine / Q000378:metabolism*; D010643:Phenoxybenzamine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011817:Rabbits; D011943:Receptors, Adrenergic, beta / Q000187:drug effects
chemical_list: D011943:Receptors, Adrenergic, beta; D010643:Phenoxybenzamine; D000804:Angiotensin II; D011433:Propranolol; D009638:Norepinephrine; D004837:Epinephrine