Omar S A, Hammad D, Varma S
Indian J Physiol Pharmacol. 1979 Jul-Sep;23(3):199-203.
Beta adrenergic agonist isoprenaline (8x10(-6)M) produced a 500% increase in inotropic and 90% increase in the chronotropic responses of isolated rabbit atria at 37 degrees C. On cooling the atria to 23 degrees C, these responses were significantly reduced to 87% and 30% respectively. Similar results were obtained with adrenaline, but isoprenaline was more potent. The positive chronotropic and inotropic responses to isoprenaline were effectively blocked by propranolol and practolol at 37 degrees C whereas at 23 degrees C these beta blockers were unable to block even minor positive responses obtained by isoprenaline at this temperature. On the contrary at 23 degrees C, phenylephrine (alpha adrenergic agonist) produced marked positive chronotropic and inotropic effects indicating enhancement of alpha adrenoceptor activity at lower temperatures. This also suggests that reduced beta receptor activity at lower temperature is not due to a generalised depression of adrenoceptors as a result of hypothermia. Rewarming of atria to 37 degrees C restored the beta adrenoceptor responsiveness to previous level. It appears that ambient temperature is important im maintaining normal beta adrenergic activity of the atria.
β-肾上腺素能激动剂异丙肾上腺素（8×10⁻⁶M）可使37℃下离体兔心房的变力反应增加500%，变时反应增加90%。将心房冷却至23℃时，这些反应分别显著降低至87%和30%。肾上腺素也得到了类似的结果，但异丙肾上腺素的作用更强。在37℃时，普萘洛尔和普拉洛尔可有效阻断异丙肾上腺素引起的正性变时和变力反应，而在23℃时，这些β受体阻滞剂甚至无法阻断异丙肾上腺素在此温度下引起的轻微正性反应。相反，在23℃时，去氧肾上腺素（α-肾上腺素能激动剂）产生明显的正性变时和变力作用，表明在较低温度下α肾上腺素能受体活性增强。这也表明，较低温度下β受体活性降低并非由于低温导致肾上腺素能受体普遍抑制。将心房复温至37℃可使β肾上腺素能受体反应性恢复至先前水平。看来环境温度对于维持心房正常的β肾上腺素能活性很重要。
