Differential cardiovascular and neuroendocrine effects of epinine and dopamine in conscious pigs before and after adrenoceptor blockade

1 The effects of epinine or dopamine (both 1–10 μg kg−1 min−1) on systemic haemodynamics and plasma concentrations of catecholamines and prolactin were studied in conscious pigs before and after combined non‐selective α‐ and β‐adrenoceptor blockade. 2 The plasma concentrations of the two compounds did not differ from each other over the entire dose‐range. 3 Epinine increased aortic blood flow (AoBF, 24 ± 6%), which was due to an increase in heart rate (HR) for doses less than 10 μg kg−1 min−1. At 10 μg kg−1 min−1, HR decreased slightly (10 ± 3%, as compared to the value obtained at 5 μg kg−1 min−1) and stroke volume increased up to 15% (P < 0.05). Mean arterial pressure (MAP, 99 ± 3 mmHg at baseline) decreased dose‐dependently (14 ± 2%, P < 0.05) up to the infusion rate of 5 μg kg−1 min−1, but increased by 4.0 ± 1.8 mmHg during infusion of 10 μg kg−1 min−1. Systemic vascular resistance (SVR) decreased up to 23 ± 3% for doses less than 10 μg kg−1 min−1, but did not change further during infusion of the highest dose. LVdP/dtmax increased during the two highest infusion rates up to 22 ± 6% (P < 0.05). After the infusion was stopped there was an abrupt increase in HR (18 ± 4%, P < 0.05) and a further decrease in SVR before all parameters returned to baseline. 4 Dopamine caused increases in AoBF (27 ± 3%) similar to epinine, the only difference being that HR continued to increase (32 ± 5%) and MAP (13 ± 3%) and SVR continued to decrease (31 ± 3%) over the entire dose‐range. The increase in LVdP/dtmax at the highest dose (48 ± 4%, P < 0.05) was more pronounced than with epinine. 5 Adrenoceptor blockade inhibited all epinine‐induced changes, but did not affect the dopamine‐induced changes in AoBF, SVR and MAP, but attenuated the increases in HR and LVdP/dtmax. 6 Noradrenaline (NA) and adrenaline (Ad) concentrations did not change during infusion of epinine or dopamine, but NA increased by 50% within 2.5 min after stopping the infusion of epinine. After adrenoceptor blockade NA and Ad concentrations did not change during infusion of dopamine, which contrasted with a decrease of 55 ± 5% (P < 0.05) in NA during infusion of epinine. 7 Prolactin concentrations decreased gradually from 480 ± 40 pg ml−1 to 270 ± 50 pg ml−1 (P < 0.05) during infusion of epinine, but did not change significantly during dopamine infusion. 8 The differential effects of epinine and dopamine on MAP, SVR, plasma NA (before and after adrenoceptor blockade) and prolactin, leads us to conclude th