Hirano A, Hashimoto H, Nakashima M
Jpn J Pharmacol. 1982 Apr;32(2):221-30. doi: 10.1254/jjp.32.221.
The involvement of alpha- and beta-adrenoceptors in dopamine (DA)-induced positive chronotropic and inotropic effects was investigated in isolated atria from euthyroid and hypothyroid rats. Propranolol at 3 x 10(-7) M remarkably inhibited the positive chronotropic effect of DA in both euthyroid and hypothyroid rats, and 1 x 10(-6) M phentolamine inhibited the effects of DA in the presence of propranolol in hypothyroid rats. Propranolol remarkably inhibited the positive inotropic effect of DA in both euthyroid and hypothyroid rats, while phentolamine was effective only in hypothyroid rats. In atria from reserpinized rats, the pD2-values for DA in both chronotropic and inotropic effects were reduced, but effectiveness of propranolol or phentolamine on DA-induced positive chronotropic and inotropic effects in euthyroid and hypothyroid rats was similar to that in non-reserpinized rats. In hypothyroid rats, DA increased the maximal rate of tension development, which was inhibited by both phentolamine and propranolol. DA shortened the duration of contraction. DA in the presence of phentolamine significantly shortened the duration of contraction but did not in the presence of propranolol. In conclusion the DA-induced positive chronotropic effect is mainly produced by beta-adrenoceptor stimulation in both euthyroid and hypothyroid rats, and also by a alpha-adrenoceptors to some extent in hypothyroid rats. The DA-induced positive inotropic effect is produced by alpha- as well as beta-adrenoceptor stimulation in both groups. However, alpha-adrenoceptors were involved to a greater extent in hypothyroid rats than in euthyroid rats. The stimulation of alpha-adrenoceptors by DA causes an increase in the maximal rate of tension development without a significant change in the duration of contraction, and the stimulation of beta-adrenoceptors by DA causes an increase in the maximal rate of tension development and shortening of the duration of contraction.
研究了α和β肾上腺素能受体在多巴胺（DA）诱导的正常甲状腺和甲状腺功能减退大鼠离体心房正性变时和变力作用中的参与情况。3×10⁻⁷ M的普萘洛尔显著抑制了正常甲状腺和甲状腺功能减退大鼠中DA的正性变时作用，而1×10⁻⁶ M的酚妥拉明在普萘洛尔存在的情况下抑制了甲状腺功能减退大鼠中DA的作用。普萘洛尔显著抑制了正常甲状腺和甲状腺功能减退大鼠中DA的正性变力作用，而酚妥拉明仅在甲状腺功能减退大鼠中有效。在利血平化大鼠的心房中，DA在变时和变力作用方面的pD2值降低，但普萘洛尔或酚妥拉明对正常甲状腺和甲状腺功能减退大鼠中DA诱导的正性变时和变力作用的有效性与未利血平化大鼠相似。在甲状腺功能减退大鼠中，DA增加了张力发展的最大速率，这被酚妥拉明和普萘洛尔均抑制。DA缩短了收缩持续时间。在酚妥拉明存在的情况下，DA显著缩短了收缩持续时间，但在普萘洛尔存在的情况下则没有。总之，DA诱导的正性变时作用在正常甲状腺和甲状腺功能减退大鼠中主要由β肾上腺素能受体刺激产生，在甲状腺功能减退大鼠中也在一定程度上由α肾上腺素能受体产生。DA诱导的正性变力作用在两组中均由α和β肾上腺素能受体刺激产生。然而，α肾上腺素能受体在甲状腺功能减退大鼠中的参与程度比在正常甲状腺大鼠中更大。DA对α肾上腺素能受体的刺激导致张力发展的最大速率增加，而收缩持续时间无显著变化，DA对β肾上腺素能受体的刺激导致张力发展的最大速率增加和收缩持续时间缩短。
